Abstract
PostGIS is an extension to the PostgreSQL objectrelational database system which allows GIS (Geographic Information Systems) objects to be stored in the database. PostGIS includes support for GiSTbased RTree spatial indexes, and functions for analysis and processing of GIS objects.
This is the manual for version 1.5.1
Table of Contents
Table of Contents
PostGIS is developed by Refractions Research Inc, as a spatial database technology research project. Refractions is a GIS and database consulting company in Victoria, British Columbia, Canada, specializing in data integration and custom software development. We plan on supporting and developing PostGIS to support a range of important GIS functionality, including full OpenGIS support, advanced topological constructs (coverages, surfaces, networks), desktop user interface tools for viewing and editing GIS data, and webbased access tools.
The PostGIS Project Steering Committee (PSC) coordinates the general direction, release cycles, documentation, and outreach efforts for the PostGIS project. In addition the PSC provides general user support, accepts and approves patches from the general PostGIS community and votes on miscellaneous issues involving PostGIS such as developer commit access, new PSC members or significant API changes.
Coordinates bug fixing and maintenance effort, alignment of PostGIS with PostgreSQL releases, spatial index selectivity and binding, windows production builds, integration of new GEOS functionality, and new function enhancements.
Cofounder of PostGIS project. General bug fixing, geography support, GEOS functionality integration and alignment with GEOS releases.
Documentation, Hudson automated build, advanced user support on PostGIS newsgroup, and postgis maintenance function enhancements.
Documentation, general user support on PostGIS newsgroup, windows production and experimental builds, and smoke testing new functionality or major code changes.
Bug fixes and maintenance and integration of new GEOS functionality. WKT Raster support.
The original developer/Cofounder of PostGIS. Dave wrote the server side objects, index bindings, and many of the server side analytical functions.
Original development of the Shape file loader/dumper. Current PostGIS Project Owner representative.
Ongoing maintenance and development of core functions. Enhanced curve support.
Input output XML (KML,GML)/GeoJSON functions and bug fixes.
WKT Raster overall architecture and programming support
WKT Raster support
General development
Distance function enhancements and additions, Windows testing, and general user support
WKT Raster development
Tiger geocoder development
In alphabetical order: Alex Bodnaru, Alex Mayrhofer, Barbara Phillipot, Ben Jubb, Bernhard Reiter, Bruce Rindahl, Bruno Wolff III, Carl Anderson, Charlie Savage, Dane Springmeyer, David Skea, David Techer, Eduin Carrillo, IIDA Tetsushi, George Silva, Geographic Data BC, Gerald Fenoy, Gino Lucrezi, Guillaume Lelarge, Klaus Foerster, Kris Jurka, Mark Sondheim, Markus Schaber, Michael Fuhr, Nikita Shulga, Norman Vine, Ralph Mason, Steffen Macke, Vincent Picavet
The GEOS geometry operations library, and the algorithmic work of Martin Davis in making it all work, ongoing maintenance and support of Mateusz Loskot, Paul Ramsey and others.
The Proj4 cartographic projection library, and the work of Gerald Evenden and Frank Warmerdam in creating and maintaining it.
The latest software, documentation and news items are available at the PostGIS web site, http://postgis.refractions.net.
More information about the GEOS geometry operations library is available at http://trac.osgeo.org/geos/.
More information about the Proj4 reprojection library is available at http://trac.osgeo.org/proj/.
More information about the PostgreSQL database server is available at the PostgreSQL main site http://www.postgresql.org.
More information about GiST indexing is available at the PostgreSQL GiST development site, http://www.sai.msu.su/~megera/postgres/gist/.
More information about MapServer internet map server is available at http://mapserver.gis.umn.edu.
The "Simple Features for Specification for SQL" is available at the OpenGIS Consortium web site: http://www.opengeospatial.org/.
Table of Contents
This chapter details the steps required to install PostGIS.
tar xvfz postgis1.5.1.tar.gz cd postgis1.5.1 ./configure make make install createdb yourdatabase createlang plpgsql yourdatabase psql d yourdatabase f postgis.sql psql d yourdatabase f postgis_comments.sql psql d yourdatabase f spatial_ref_sys.sql
The rest of this chapter goes into detail each of the above installation steps.
PostGIS has the following requirements for building and usage:
Required
PostgreSQL 8.3 or higher. A complete installation of PostgreSQL (including server headers) is required. PostgreSQL is available from http://www.postgresql.org .
For a full PostgreSQL / PostGIS support matrix and PostGIS/GEOS support matrix refer to http://trac.osgeo.org/postgis/wiki/UsersWikiPostgreSQLPostGIS
GNU C compiler (gcc
). Some other ANSI C compilers
can be used to compile PostGIS, but we find far fewer problems when
compiling with gcc
.
GNU Make (gmake
or make
).
For many systems, GNU make
is the default version
of make. Check the version by invoking make v
.
Other versions of make
may not process the
PostGIS Makefile
properly.
Proj4 reprojection library, version 4.6.0 or greater. The Proj4 library is used to provide coordinate reprojection support within PostGIS. Proj4 is available for download from http://trac.osgeo.org/proj/ .
GEOS geometry library, version 3.1.1 or greater, but GEOS 3.2 is recommended. Without GEOS 3.2, you will be missing some major enhancements with handling of topological exceptions and improvements to ST_Buffer that allow beveling and mitre and much faster buffering. The GEOS library is used to provide geometry tests (ST_Touches(), ST_Contains(), ST_Intersects()) and operations (ST_Buffer(), ST_Union(),ST_Intersection() ST_Difference()) within PostGIS. GEOS is available for download from http://trac.osgeo.org/geos/ .
Optional
Apache Ant (ant
) is required for building any of
the drivers under the java
directory. Ant is
available from
http://ant.apache.org
.
DocBook (xsltproc
) is required for building the
documentation. Docbook is available from
http://www.docbook.org/
.
DBLatex (dblatex
) is required for building the
documentation in PDF format. DBLatex is available from
http://dblatex.sourceforge.net/
.
ImageMagick (convert
) is required to generate the
images used in the documentation. ImageMagick is available from
http://www.imagemagick.org/
.
Retrieve the PostGIS source archive from the downloads website http://postgis.refractions.net/download/postgis1.5.1.tar.gz
wget http://postgis.refractions.net/download/postgis1.5.1.tar.gz tar xvzf postgis1.5.1.tar.gz
This will create a directory called
postgis1.5.1
in the current working
directory.
Alternatively, checkout the source from the svn repository http://svn.osgeo.org/postgis/trunk/ .
svn checkout http://svn.osgeo.org/postgis/trunk/ postgis1.5.1
Change into the newly created
postgis1.5.1
directory to continue
the installation.
Many OS systems now include prebuilt packages for PostgreSQL/PostGIS. In many cases compilation is only necessary if you want the most bleeding edge versions or you are a package maintainer. 
The PostGIS module is an extension to the PostgreSQL backend server. As such, PostGIS 1.5.1 requires full PostgreSQL server headers access in order to compile. It can be built against PostgreSQL versions 8.3 or higher. Earlier versions of PostgreSQL are not supported.
Refer to the PostgreSQL installation guides if you haven't already installed PostgreSQL. http://www.postgresql.org .
For GEOS functionality, when you install PostgresSQL you may need to explicitly link PostgreSQL against the standard C++ library: LDFLAGS=lstdc++ ./configure [YOUR OPTIONS HERE] This is a workaround for bogus C++ exceptions interaction with older development tools. If you experience weird problems (backend unexpectedly closed or similar things) try this trick. This will require recompiling your PostgreSQL from scratch, of course. 
The following steps outline the configuration and compilation of the PostGIS source. They are written for Linux users and will not work on Windows or Mac.
As with most linux installations, the first step is to generate the Makefile that will be used to build the source code. This is done by running the shell script
./configure
With no additional parameters, this command will attempt to automatically locate the required components and libraries needed to build the PostGIS source code on your system. Although this is the most common usage of ./configure, the script accepts several parameters for those who have the required libraries and programs in nonstandard locations.
The following list shows only the most commonly used parameters. For a complete list, use the help or help=short parameters.
This is the location the PostGIS libraries and SQL scripts will be installed to. By default, this location is the same as the detected PostgreSQL installation.
This paramater is currently broken, as the package will only install into the PostgreSQL installation directory. Visit http://trac.osgeo.org/postgis/ticket/160 to track this bug. 
PostgreSQL provides a utility called pg_config to enable extensions like PostGIS to locate the PostgreSQL installation directory. Use this parameter (withpgconfig=/path/to/pg_config) to manually specify a particular PostgreSQL installation that PostGIS will build against.
GEOS, a required geometry library, provides a utility called geosconfig to enable software installations to locate the GEOS installation directory. Use this parameter (withgeosconfig=/path/to/geosconfig) to manually specify a particular GEOS installation that PostGIS will build against.
Proj4 is a reprojection library required by PostGIS. Use this parameter (withprojdir=/path/to/projdir) to manually specify a particular Proj4 installation directory that PostGIS will build against.
Compile the data import GUI (requires GTK+2.0). This will create shp2pgsqlgui graphical interface to shp2pgsql.
If you obtained PostGIS from the SVN repository , the first step is really to run the script ./autogen.sh This script will generate the configure script that in turn is used to customize the intallation of PostGIS. If you instead obtained PostGIS as a tarball, running ./autogen.sh is not necessary as configure has already been generated. 
Once the Makefile has been generated, building PostGIS is as simple as running
make
The last line of the output should be "PostGIS was built
successfully. Ready to install.
"
As of PostGIS v1.4.0, all the functions have comments generated from the documentation. If you wish to install these comments into your spatial databases later, run the command which requires docbook. The postgis_comments.sql is also packaged in the tar.gz distribution in the doc folder so no need to make comments if installing from the tar ball.
make comments
If you wish to test the PostGIS build, run
make check
The above command will run through various checks and regression tests using the generated library against an actual PostgreSQL database.
If you configured PostGIS using nonstandard PostgreSQL, GEOS, or Proj4 locations, you may need to add their library locations to the LD_LIBRARY_PATH environment variable. 
Currently, the make check relies on the

If successful, the output of the test should be similiar to the following:
CUnit  A Unit testing framework for C  Version 2.10 http://cunit.sourceforge.net/ Suite: PostGIS Computational Geometry Suite Test: test_lw_segment_side() ... passed Test: test_lw_segment_intersects() ... passed Test: test_lwline_crossing_short_lines() ... passed Test: test_lwline_crossing_long_lines() ... passed Test: test_lwpoint_set_ordinate() ... passed Test: test_lwpoint_get_ordinate() ... passed Test: test_lwpoint_interpolate() ... passed Test: test_lwline_clip() ... passed Test: test_lwline_clip_big() ... passed Test: test_lwmline_clip() ... passed Test: test_geohash_point() ... passed Test: test_geohash_precision() ... passed Test: test_geohash() ... passed Suite: PostGIS Measures Suite Test: test_mindistance2d_recursive_tolerance() ... passed Run Summary: Type Total Ran Passed Failed suites 2 2 n/a 0 tests 14 14 14 0 asserts 84 84 84 0 Creating spatial db postgis_reg TMPDIR is /tmp/pgis_reg_15328 PostgreSQL 8.3.7 on i686pclinuxgnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.244) Postgis 1.4.0SVN  20090525 20:21:55 GEOS: 3.1.0CAPI1.5.0 PROJ: Rel. 4.6.1, 21 August 2008 Running tests loader/Point.............. ok loader/PointM.............. ok loader/PointZ.............. ok loader/MultiPoint.............. ok loader/MultiPointM.............. ok loader/MultiPointZ.............. ok loader/Arc.............. ok loader/ArcM.............. ok loader/ArcZ.......... ok loader/Polygon.............. ok loader/PolygonM.............. ok loader/PolygonZ.............. ok regress. ok regress_index. ok regress_index_nulls. ok lwgeom_regress. ok regress_lrs. ok removepoint. ok setpoint. ok simplify. ok snaptogrid. ok affine. ok wkt. ok measures. ok long_xact. ok ctors. ok sqlmmserialize. ok sqlmmcircularstring. ok sqlmmcompoundcurve. ok sqlmmcurvepoly. ok sqlmmgeneral. ok sqlmmmulticurve. ok sqlmmmultisurface. ok geojson. ok gml. ok svg. ok kml. ok regress_ogc. ok regress_bdpoly. ok regress_proj. ok regress_ogc_cover. ok regress_ogc_prep. ok Run tests: 42 Failed: 0
To install PostGIS, type
make install
This will copy the PostGIS installation files into their appropriate subdirectory specified by the prefix configuration parameter. In particular:
The loader and dumper binaries are installed in
[prefix]/bin
.
The SQL files, such as postgis.sql
, are
installed in [prefix]/share/contrib
.
The PostGIS libraries are installed in
[prefix]/lib
.
If you previously ran the make comments command to
generate the postgis_comments.sql
file, install the
sql file by running
make commentsinstall

The first step in creating a PostGIS database is to create a simple PostgreSQL database.
createdb [yourdatabase]
Many of the PostGIS functions are written in the PL/pgSQL procedural language. As such, the next step to create a PostGIS database is to enable the PL/pgSQL language in your new database. This is accomplish by the command
createlang plpgsql [yourdatabase]
Now load the PostGIS object and function definitions into your database by
loading the postgis.sql
definitions file (located in
[prefix]/share/contrib
as specified during the
configuration step).
psql d [yourdatabase] f postgis.sql
For a complete set of EPSG coordinate system definition identifiers, you
can also load the spatial_ref_sys.sql
definitions
file and populate the spatial_ref_sys
table. This will
permit you to perform ST_Transform() operations on geometries.
psql d [yourdatabase] f spatial_ref_sys.sql
If you wish to add comments to the PostGIS functions, the final step is to
load the postgis_comments.sql
into your spatial
database. The comments can be viewed by simply typing \dd
[function_name] from a psql terminal window.
psql d [yourdatabase] f postgis_comments.sql
Some packaged distributions of PostGIS (in particular the Win32 installers
for PostGIS >= 1.1.5) load the PostGIS functions into a template
database called template_postgis
. If the
template_postgis
database exists in your PostgreSQL
installation then it is possible for users and/or applications to create
spatiallyenabled databases using a single command. Note that in both
cases, the database user must have been granted the privilege to create
new databases.
From the shell:
# createdb T template_postgis my_spatial_db
From SQL:
postgres=# CREATE DATABASE my_spatial_db TEMPLATE=template_postgis
Upgrading existing spatial databases can be tricky as it requires replacement or introduction of new PostGIS object definitions.
Unfortunately not all definitions can be easily replaced in a live database, so sometimes your best bet is a dump/reload process.
PostGIS provides a SOFT UPGRADE procedure for minor or bugfix releases, and an HARD UPGRADE procedure for major releases.
Before attempting to upgrade postgis, it is always worth to backup your data. If you use the Fc flag to pg_dump you will always be able to restore the dump with an HARD UPGRADE.
After compiling you should find several postgis_upgrade*.sql
files. Install the one
for your version of PostGIS. For example postgis_upgrade_13_to_15.sql
should be used if you are upgrading
from postgis 1.3 to 1.5.
$ psql f postgis_upgrade_13_to_15.sql d your_spatial_database
If a soft upgrade is not possible the script will abort and you will be warned about HARD UPGRADE being required, so do not hesitate to try a soft upgrade first.
If you can't find the $ utils/postgis_proc_upgrade.pl postgis.sql > postgis_upgrade.sql 
By HARD UPGRADE we intend full dump/reload of postgisenabled databases. You need an HARD UPGRADE when postgis objects' internal storage changes or when SOFT UPGRADE is not possible. The Release Notes appendix reports for each version whether you need a dump/reload (HARD UPGRADE) to upgrade.
PostGIS provides an utility script to restore a dump produced with the pg_dump Fc command. It is experimental so redirecting its output to a file will help in case of problems. The procedure is as follow:
Create a "customformat" dump of the database you want to upgrade (let's call it "olddb")
$ pg_dump Fc olddb > olddb.dump
Restore the dump contextually upgrading postgis into a new database. The new database doesn't have to exist. postgis_restore accepts createdb parameters after the dump file name, and that can for instance be used if you are using a nondefault character encoding for your database. Let's call it "newdb", with UNICODE as the character encoding:
$ sh utils/postgis_restore.pl postgis.sql newdb olddb.dump E=UNICODE > restore.log
Check that all restored dump objects really had to be restored from dump and do not conflict with the ones defined in postgis.sql
$ grep ^KEEPING restore.log  less
If upgrading from PostgreSQL < 8.0 to >= 8.0 you might want to drop the attrelid, varattnum and stats columns in the geometry_columns table, which are nomore needed. Keeping them won't hurt. DROPPING THEM WHEN REALLY NEEDED WILL DO HURT !
$ psql newdb c "ALTER TABLE geometry_columns DROP attrelid" $ psql newdb c "ALTER TABLE geometry_columns DROP varattnum" $ psql newdb c "ALTER TABLE geometry_columns DROP stats"
spatial_ref_sys table is restore from the dump, to ensure your custom additions are kept, but the distributed one might contain modification so you should backup your entries, drop the table and source the new one. If you did make additions we assume you know how to backup them before upgrading the table. Replace of it with the new one is done like this:
$ psql newdb newdb=> truncate spatial_ref_sys; TRUNCATE newdb=> \i spatial_ref_sys.sql
There are several things to check when your installation or upgrade doesn't go as you expected.
Check that you you have installed PostgreSQL 8.1 or newer, and that you are compiling against the same version of the PostgreSQL source as the version of PostgreSQL that is running. Mixups can occur when your (Linux) distribution has already installed PostgreSQL, or you have otherwise installed PostgreSQL before and forgotten about it. PostGIS will only work with PostgreSQL 8.1 or newer, and strange, unexpected error messages will result if you use an older version. To check the version of PostgreSQL which is running, connect to the database using psql and run this query:
SELECT version();
If you are running an RPM based distribution, you can check for the existence of preinstalled packages using the rpm command as follows: rpm qa  grep postgresql
Also check that configure has correctly detected the location and version of PostgreSQL, the Proj4 library and the GEOS library.
The output from configure is used to generate the
postgis_config.h
file. Check that the
POSTGIS_PGSQL_VERSION
,
POSTGIS_PROJ_VERSION
and
POSTGIS_GEOS_VERSION
variables have been set
correctly.
The JDBC extensions provide Java objects corresponding to the internal PostGIS types. These objects can be used to write Java clients which query the PostGIS database and draw or do calculations on the GIS data in PostGIS.
Enter the java/jdbc
subdirectory of the PostGIS
distribution.
Run the ant
command. Copy the
postgis.jar
file to wherever you keep your java
libraries.
The JDBC extensions require a PostgreSQL JDBC driver to be present in the current CLASSPATH during the build process. If the PostgreSQL JDBC driver is located elsewhere, you may pass the location of the JDBC driver JAR separately using the D parameter like this:
# ant Dclasspath=/path/to/postgresqljdbc.jar
PostgreSQL JDBC drivers can be downloaded from http://jdbc.postgresql.org .
The data loader and dumper are built and installed automatically as part of the PostGIS build. To build and install them manually:
# cd postgis1.5.1/loader # make # make install
The loader is called shp2pgsql
and converts ESRI
Shape files into SQL suitable for loading in PostGIS/PostgreSQL. The
dumper is called pgsql2shp
and converts PostGIS
tables (or queries) into ESRI Shape files. For more verbose documentation,
see the online help, and the manual pages.
3.1.  What kind of geometric objects can I store?  
You can store point, line, polygon, multipoint, multiline, multipolygon, and geometrycollections. These are specified in the Open GIS Well Known Text Format (with XYZ,XYM,XYZM extensions). There are two data types currently supported. The standard OGC geometry data type which uses a planar coordinate system for measurement and the geography data type which uses a geodetic coordinate system. Only WGS 84 long lat (SRID:4326) is supported by the geography data type.  
3.2.  I'm all confused. Which data store should I use geometry or geography?  
Short Answer: geography is a new data type that supports long range distances measurements. If you use geography  you don't need to learn much about planar coordinate systems. Geography is generally best if all you care about is measuring distances and lengths and you have data from all over the world. Geometry datatype is an older data type that has many functions supporting it and enjoys great support from third party tools. Its best if you are pretty comfortable with spatial reference systems or you are dealing with localized data where all your data fits in a single spatial reference system (SRID), or you need to do a lot of spatial processing. Refer to Section 8.8, “PostGIS Function Support Matrix” to see what is currently supported and what is not. Long Answer: Refer to our more lengthy discussion in the Section 4.2.2, “When to use Geography Data type over Geometry data type” and function type matrix.  
3.3.  I have more intense questions about geography, such as how big of a geographic region can I stuff in a geography column and still get reasonable answers. Are there limitations such as poles, everything in the field must fit in a hemisphere (like SQL Server 2008 has), speed etc?  
Your questions are too deep and complex to be adequately answered in this section. Please refer to our Section 4.2.3, “Geography Advanced FAQ” .  
3.4.  How do I insert a GIS object into the database?  
First, you need to create a table with a column of type "geometry" or "geography" to hold your GIS data. Storing geography type data is a little different than storing geometry. Refer to Section 4.2.1, “Geography Basics” for details on storing geography.
For geometry: Connect to your database with
CREATE TABLE gtest ( ID int4, NAME varchar(20) ); SELECT AddGeometryColumn('', 'gtest','geom',1,'LINESTRING',2); If the geometry column addition fails, you probably have not loaded the PostGIS functions and objects into this database. See the Section 2.4, “Installation”. Then, you can insert a geometry into the table using a SQL insert statement. The GIS object itself is formatted using the OpenGIS Consortium "wellknown text" format: INSERT INTO gtest (ID, NAME, GEOM) VALUES ( 1, 'First Geometry', ST_GeomFromText('LINESTRING(2 3,4 5,6 5,7 8)', 1) ); For more information about other GIS objects, see the object reference. To view your GIS data in the table: SELECT id, name, ST_AsText(geom) AS geom FROM gtest; The return value should look something like this: id  name  geom ++ 1  First Geometry  LINESTRING(2 3,4 5,6 5,7 8) (1 row)  
3.5.  How do I construct a spatial query?  
The same way you construct any other database query, as an SQL combination of return values, functions, and boolean tests. For spatial queries, there are two issues that are important to keep in mind while constructing your query: is there a spatial index you can make use of; and, are you doing expensive calculations on a large number of geometries. In general, you will want to use the "intersects operator" (&&) which tests whether the bounding boxes of features intersect. The reason the && operator is useful is because if a spatial index is available to speed up the test, the && operator will make use of this. This can make queries much much faster. You will also make use of spatial functions, such as Distance(), ST_Intersects(), ST_Contains() and ST_Within(), among others, to narrow down the results of your search. Most spatial queries include both an indexed test and a spatial function test. The index test serves to limit the number of return tuples to only tuples that might meet the condition of interest. The spatial functions are then use to test the condition exactly. SELECT id, the_geom FROM thetable WHERE ST_Contains(the_geom,'POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))');  
3.6.  How do I speed up spatial queries on large tables?  
Fast queries on large tables is the raison d'etre of spatial databases (along with transaction support) so having a good index is important. To build a spatial index on a table with a
CREATE INDEX [indexname] ON [tablename] USING GIST ( [geometrycolumn] ); The "USING GIST" option tells the server to use a GiST (Generalized Search Tree) index.
You should also ensure that the PostgreSQL query planner has enough information about your index to make rational decisions about when to use it. To do this, you have to "gather statistics" on your geometry tables. For PostgreSQL 8.0.x and greater, just run the VACUUM ANALYZE command. For PostgreSQL 7.4.x and below, run the SELECT UPDATE_GEOMETRY_STATS() command.  
3.7.  Why aren't PostgreSQL RTree indexes supported?  
Early versions of PostGIS used the PostgreSQL RTree indexes. However, PostgreSQL RTrees have been completely discarded since version 0.6, and spatial indexing is provided with an RTreeoverGiST scheme. Our tests have shown search speed for native RTree and GiST to be comparable. Native PostgreSQL RTrees have two limitations which make them undesirable for use with GIS features (note that these limitations are due to the current PostgreSQL native RTree implementation, not the RTree concept in general):
 
3.8.  Why should I use the  
If you do not want to use the OpenGIS support functions, you do
not have to. Simply create tables as in older versions, defining your
geometry columns in the CREATE statement. All your geometries will
have SRIDs of 1, and the OpenGIS metadata tables will
not be filled in properly. However, this will
cause most applications based on PostGIS to fail, and it is generally
suggested that you do use MapServer is one application which makes use of the
 
3.9.  What is the best way to find all objects within a radius of another object?  
To use the database most efficiently, it is best to do radius queries which combine the radius test with a bounding box test: the bounding box test uses the spatial index, giving fast access to a subset of data which the radius test is then applied to. The For example, to find all objects with 100 meters of POINT(1000 1000) the following query would work well: SELECT * FROM geotable WHERE ST_DWithin(geocolumn, 'POINT(1000 1000)', 100.0);  
3.10.  How do I perform a coordinate reprojection as part of a query?  
To perform a reprojection, both the source and destination coordinate systems must be defined in the SPATIAL_REF_SYS table, and the geometries being reprojected must already have an SRID set on them. Once that is done, a reprojection is as simple as referring to the desired destination SRID. The below projects a geometry to NAD 83 long lat. The below will only work if the srid of the_geom is not 1 (not undefined spatial ref) SELECT ST_Transform(the_geom,4269) FROM geotable;  
3.11.  I did an ST_AsEWKT and ST_AsText on my rather large geometry and it returned blank field. What gives?  
You are probably using PgAdmin or some other tool that doesn't output large text. If your geometry is big enough, it will appear blank in these tools. Use PSQL if you really need to see it or output it in WKT. To check number of geometries are really blank SELECT count(gid) FROM geotable WHERE the_geom IS NULL;  
3.12.  When I do an ST_Intersects, it says my two geometries don't intersect when I KNOW THEY DO. What gives?  
This generally happens in two common cases. Your geometry is invalid  check ST_IsValid or you are assuming they intersect because ST_AsText truncates the numbers and you have lots of decimals after it is not showing you. 
Table of Contents
The GIS objects supported by PostGIS are a superset of the "Simple Features" defined by the OpenGIS Consortium (OGC). As of version 0.9, PostGIS supports all the objects and functions specified in the OGC "Simple Features for SQL" specification.
PostGIS extends the standard with support for 3DZ,3DM and 4D coordinates.
The OpenGIS specification defines two standard ways of expressing spatial objects: the WellKnown Text (WKT) form and the WellKnown Binary (WKB) form. Both WKT and WKB include information about the type of the object and the coordinates which form the object.
Examples of the text representations (WKT) of the spatial objects of the features are as follows:
POINT(0 0)
LINESTRING(0 0,1 1,1 2)
POLYGON((0 0,4 0,4 4,0 4,0 0),(1 1, 2 1, 2 2, 1 2,1 1))
MULTIPOINT(0 0,1 2)
MULTILINESTRING((0 0,1 1,1 2),(2 3,3 2,5 4))
MULTIPOLYGON(((0 0,4 0,4 4,0 4,0 0),(1 1,2 1,2 2,1 2,1 1)), ((1 1,1 2,2 2,2 1,1 1)))
GEOMETRYCOLLECTION(POINT(2 3),LINESTRING(2 3,3 4))
The OpenGIS specification also requires that the internal storage format of spatial objects include a spatial referencing system identifier (SRID). The SRID is required when creating spatial objects for insertion into the database.
Input/Output of these formats are available using the following interfaces:
bytea WKB = ST_AsBinary(geometry); text WKT = ST_AsText(geometry); geometry = ST_GeomFromWKB(bytea WKB, SRID); geometry = ST_GeometryFromText(text WKT, SRID);
For example, a valid insert statement to create and insert an OGC spatial object would be:
INSERT INTO geotable ( the_geom, the_name ) VALUES ( ST_GeomFromText('POINT(126.4 45.32)', 312), 'A Place');
OGC formats only support 2d geometries, and the associated SRID is *never* embedded in the input/output representations.
PostGIS extended formats are currently superset of OGC one (every valid WKB/WKT is a valid EWKB/EWKT) but this might vary in the future, specifically if OGC comes out with a new format conflicting with our extensions. Thus you SHOULD NOT rely on this feature!
PostGIS EWKB/EWKT add 3dm,3dz,4d coordinates support and embedded SRID information.
Examples of the text representations (EWKT) of the extended spatial objects of the features are as follows:
POINT(0 0 0)  XYZ
SRID=32632;POINT(0 0)  XY with SRID
POINTM(0 0 0)  XYM
POINT(0 0 0 0)  XYZM
SRID=4326;MULTIPOINTM(0 0 0,1 2 1)  XYM with SRID
MULTILINESTRING((0 0 0,1 1 0,1 2 1),(2 3 1,3 2 1,5 4 1))
POLYGON((0 0 0,4 0 0,4 4 0,0 4 0,0 0 0),(1 1 0,2 1 0,2 2 0,1 2 0,1 1 0))
MULTIPOLYGON(((0 0 0,4 0 0,4 4 0,0 4 0,0 0 0),(1 1 0,2 1 0,2 2 0,1 2 0,1 1 0)),((1 1 0,1 2 0,2 2 0,2 1 0,1 1 0)))
GEOMETRYCOLLECTIONM(POINTM(2 3 9), LINESTRINGM(2 3 4, 3 4 5))
Input/Output of these formats are available using the following interfaces:
bytea EWKB = ST_AsEWKB(geometry); text EWKT = ST_AsEWKT(geometry); geometry = ST_GeomFromEWKB(bytea EWKB); geometry = ST_GeomFromEWKT(text EWKT);
For example, a valid insert statement to create and insert a PostGIS spatial object would be:
INSERT INTO geotable ( the_geom, the_name ) VALUES ( ST_GeomFromEWKT('SRID=312;POINTM(126.4 45.32 15)'), 'A Place' )
The "canonical forms" of a PostgreSQL type are the representations you get with a simple query (without any function call) and the one which is guaranteed to be accepted with a simple insert, update or copy. For the postgis 'geometry' type these are:
 Output  binary: EWKB ascii: HEXEWKB (EWKB in hex form)  Input  binary: EWKB ascii: HEXEWKBEWKT
For example this statement reads EWKT and returns HEXEWKB in the process of canonical ascii input/output:
=# SELECT 'SRID=4;POINT(0 0)'::geometry; geometry  01010000200400000000000000000000000000000000000000 (1 row)
The SQL Multimedia Applications Spatial specification extends the simple features for SQL spec by defining a number of circularly interpolated curves.
The SQLMM definitions include 3dm, 3dz and 4d coordinates, but do not allow the embedding of SRID information.
The wellknown text extensions are not yet fully supported. Examples of some simple curved geometries are shown below:
CIRCULARSTRING(0 0, 1 1, 1 0)
CIRCULARSTRING(0 0, 4 0, 4 4, 0 4, 0 0)
The CIRCULARSTRING is the basic curve type, similar to a LINESTRING in the linear world. A single segment required three points, the start and end points (first and third) and any other point on the arc. The exception to this is for a closed circle, where the start and end points are the same. In this case the second point MUST be the center of the arc, ie the opposite side of the circle. To chain arcs together, the last point of the previous arc becomes the first point of the next arc, just like in LINESTRING. This means that a valid circular string must have an odd number of points greated than 1.
COMPOUNDCURVE(CIRCULARSTRING(0 0, 1 1, 1 0),(1 0, 0 1))
A compound curve is a single, continuous curve that has both curved (circular) segments and linear segments. That means that in addition to having wellformed components, the end point of every component (except the last) must be coincident with the start point of the following component.
CURVEPOLYGON(CIRCULARSTRING(0 0, 4 0, 4 4, 0 4, 0 0),(1 1, 3 3, 3 1, 1 1))
Example compound curve in a curve polygon: CURVEPOLYGON(COMPOUNDCURVE(CIRCULARSTRING(0 0,2 0, 2 1, 2 3, 4 3),(4 3, 4 5, 1 4, 0 0)), CIRCULARSTRING(1.7 1, 1.4 0.4, 1.6 0.4, 1.6 0.5, 1.7 1) )
A CURVEPOLYGON is just like a polygon, with an outer ring and zero or more inner rings. The difference is that a ring can take the form of a circular string, linear string or compound string.
As of PostGIS 1.4 PostGIS supports compound curves in a curve polygon.
MULTICURVE((0 0, 5 5),CIRCULARSTRING(4 0, 4 4, 8 4))
The MULTICURVE is a collection of curves, which can include linear strings, circular strings or compound strings.
MULTISURFACE(CURVEPOLYGON(CIRCULARSTRING(0 0, 4 0, 4 4, 0 4, 0 0),(1 1, 3 3, 3 1, 1 1)),((10 10, 14 12, 11 10, 10 10),(11 11, 11.5 11, 11 11.5, 11 11)))
This is a collection of surfaces, which can be (linear) polygons or curve polygons.
PostGIS prior to 1.4 does not support compound curves in a curve polygon, but PostGIS 1.4 and above do support the use of Compound Curves in a Curve Polygon. 
All floating point comparisons within the SQLMM implementation are performed to a specified tolerance, currently 1E8. 
The geography type provides native support for spatial features represented on "geographic" coordinates (sometimes called "geodetic" coordinates, or "lat/lon", or "lon/lat"). Geographic coordinates are spherical coordinates expressed in angular units (degrees).
The basis for the PostGIS geometry type is a plane. The shortest path between two points on the plane is a straight line. That means calculations on geometries (areas, distances, lengths, intersections, etc) can be calculated using cartesian mathematics and straight line vectors.
The basis for the PostGIS geographic type is a sphere. The shortest path between two points on the sphere is a great circle arc. That means that calculations on geographies (areas, distances, lengths, intersections, etc) must be calculated on the sphere, using more complicated mathematics. For more accurate measurements, the calculations must take the actual spheroidal shape of the world into account, and the mathematics becomes very complicated indeed.
Because the underlying mathematics is much more complicated, there are fewer functions defined for the geography type than for the geometry type. Over time, as new algorithms are added, the capabilities of the geography type will expand.
One restriction is that it only supports WGS 84 long lat (SRID:4326). It uses a new data type called geography. I None of the GEOS functions support this new type. As a workaround one can convert back and forth between geometry and geography types.
The new geography type uses the PostgreSQL 8.3+ typmod definition format so that a table with a geography field can be added in a single step. All the standard OGC formats except for curves are supported.
The geography type only supports the simplest of simple features. Standard geometry type data will autocast to geography if it is of SRID 4326. You can also use the EWKT and EWKB conventions to insert data.
POINT: Creating a table with 2d point geometry:
CREATE TABLE testgeog(gid serial PRIMARY KEY, the_geog geography(POINT,4326) );
Creating a table with z coordinate point
CREATE TABLE testgeog(gid serial PRIMARY KEY, the_geog geography(POINTZ,4326) );
LINESTRING
POLYGON
MULTIPOINT
MULTILINESTRING
MULTIPOLYGON
GEOMETRYCOLLECTION
The new geography fields don't get registered in the geometry_columns. They get registered in a new view called geography_columns which is a view against the system catalogs so is always automatically kept up to date without need for an AddGeom... like function.
Now, check the "geography_columns" view and see that your table is listed.
You can create a new table with a GEOGRAPHY column using the CREATE TABLE syntax. Unlike GEOMETRY, there is no need to run a separate AddGeometryColumns() process to register the column in metadata.
CREATE TABLE global_points ( id SERIAL PRIMARY KEY, name VARCHAR(64), location GEOGRAPHY(POINT,4326) );
Note that the location column has type GEOGRAPHY and that geography type supports two optional modifier: a type modifier that restricts the kind of shapes and dimensions allowed in the column; an SRID modifier that restricts the coordinate reference identifier to a particular number.
Allowable values for the type modifier are: POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON. The modifier also supports dimensionality restrictions through suffixes: Z, M and ZM. So, for example a modifier of 'LINESTRINGM' would only allow line strings with three dimensions in, and would treat the third dimension as a measure. Similarly, 'POINTZM' would expect four dimensional data.
The SRID modifier is currently of limited use: only 4326 (WGS84) is allowed as a value. If you do not specify an SRID, the a value 0 (undefined spheroid) will be used, and all calculations will proceed using WGS84 anyways.
In the future, alternate SRIDs will allow calculations on spheroids other than WGS84.
Once you have created your table, you can see it in the GEOGRAPHY_COLUMNS table:
 See the contents of the metadata view SELECT * FROM geography_columns;
You can insert data into the table the same as you would if it was using a GEOMETRY column:
 Add some data into the test table INSERT INTO global_points (name, location) VALUES ('Town', ST_GeographyFromText('SRID=4326;POINT(110 30)') ); INSERT INTO global_points (name, location) VALUES ('Forest', ST_GeographyFromText('SRID=4326;POINT(109 29)') ); INSERT INTO global_points (name, location) VALUES ('London', ST_GeographyFromText('SRID=4326;POINT(0 49)') );
Creating an index works the same as GEOMETRY. PostGIS will note that the column type is GEOGRAPHY and create an appropriate spherebased index instead of the usual planar index used for GEOMETRY.
 Index the test table with a spherical index CREATE INDEX global_points_gix ON global_points USING GIST ( location );
Query and measurement functions use units of meters. So distance parameters should be expressed in meters, and return values should be expected in meters (or square meters for areas).
 Show a distance query and note, London is outside the 1000km tolerance SELECT name FROM global_points WHERE ST_DWithin(location, ST_GeographyFromText('SRID=4326;POINT(110 29)'), 1000000);
You can see the power of GEOGRAPHY in action by calculating the how close a plane flying from Seattle to London (LINESTRING(122.33 47.606, 0.0 51.5)) comes to Reykjavik (POINT(21.96 64.15)).
 Distance calculation using GEOGRAPHY (122.2km) SELECT ST_Distance('LINESTRING(122.33 47.606, 0.0 51.5)'::geography, 'POINT(21.96 64.15)':: geography);
 Distance calculation using GEOMETRY (13.3 "degrees") SELECT ST_Distance('LINESTRING(122.33 47.606, 0.0 51.5)'::geometry, 'POINT(21.96 64.15)':: geometry);
The GEOGRAPHY type calculates the true shortest distance over the sphere between Reykjavik and the great circle flight path between Seattle and London.
Great Circle mapper The GEOMETRY type calculates a meaningless cartesian distance between Reykjavik and the straight line path from Seattle to London plotted on a flat map of the world. The nominal units of the result might be called "degrees", but the result doesn't correspond to any true angular difference between the points, so even calling them "degrees" is inaccurate.
The new GEOGRAPHY type allows you to store data in longitude/latitude coordinates, but at a cost: there are fewer functions defined on GEOGRAPHY than there are on GEOMETRY; those functions that are defined take more CPU time to execute.
The type you choose should be conditioned on the expected working area of the application you are building. Will your data span the globe or a large continental area, or is it local to a state, county or municipality?
Refer to Section 8.8, “PostGIS Function Support Matrix” for compare between what is supported for Geography vs. Geometry. For a brief listing and description of Geography functions, refer to Section 8.3, “PostGIS Geography Support Functions”
The OpenGIS "Simple Features Specification for SQL" defines standard GIS object types, the functions required to manipulate them, and a set of metadata tables. In order to ensure that metadata remain consistent, operations such as creating and removing a spatial column are carried out through special procedures defined by OpenGIS.
There are two OpenGIS metadata tables:
SPATIAL_REF_SYS
and
GEOMETRY_COLUMNS
. The
SPATIAL_REF_SYS
table holds the numeric IDs and textual
descriptions of coordinate systems used in the spatial database.
The spatial_ref_sys table is a PostGIS included and OGC compliant database table that lists over 3000 known spatial reference systems and details needed to transform/reproject between them.
Although the PostGIS spatial_ref_sys table contains over 3000 of the more commonly used spatial reference system definitions that can be handled by the proj library, it does not contain all known to man and you can even define your own custom projection if you are familiar with proj4 constructs. Keep in mind that most spatial reference systems are regional and have no meaning when used outside of the bounds they were intended for.
An excellent resource for finding spatial reference systems not defined in the core set is http://spatialreference.org/
Some of the more commonly used spatial reference systems are: 4326  WGS 84 Long Lat, 4269  NAD 83 Long Lat, 3395  WGS 84 World Mercator, 2163  US National Atlas Equal Area, Spatial reference systems for each NAD 83, WGS 84 UTM zone  UTM zones are one of the most ideal for measurement, but only cover 6degree regions.
Various US state plane spatial reference systems (meter or feet based)  usually one or 2 exists per US state. Most of the meter ones are in the core set, but many of the feet based ones or ESRI created ones you will need to pull from spatialreference.org.
For details on determining which UTM zone to use for your area of interest, check out the utmzone PostGIS plpgsql helper function.
The SPATIAL_REF_SYS
table definition is as
follows:
CREATE TABLE spatial_ref_sys ( srid INTEGER NOT NULL PRIMARY KEY, auth_name VARCHAR(256), auth_srid INTEGER, srtext VARCHAR(2048), proj4text VARCHAR(2048) )
The SPATIAL_REF_SYS
columns are as
follows:
An integer value that uniquely identifies the Spatial Referencing System (SRS) within the database.
The name of the standard or standards body that is being
cited for this reference system. For example, "EPSG" would be a
valid AUTH_NAME
.
The ID of the Spatial Reference System as defined by the
Authority cited in the AUTH_NAME
. In the case
of EPSG, this is where the EPSG projection code would go.
The WellKnown Text representation of the Spatial Reference System. An example of a WKT SRS representation is:
PROJCS["NAD83 / UTM Zone 10N", GEOGCS["NAD83", DATUM["North_American_Datum_1983", SPHEROID["GRS 1980",6378137,298.257222101] ], PRIMEM["Greenwich",0], UNIT["degree",0.0174532925199433] ], PROJECTION["Transverse_Mercator"], PARAMETER["latitude_of_origin",0], PARAMETER["central_meridian",123], PARAMETER["scale_factor",0.9996], PARAMETER["false_easting",500000], PARAMETER["false_northing",0], UNIT["metre",1] ]
For a listing of EPSG projection codes and their corresponding WKT representations, see http://www.opengeospatial.org/. For a discussion of WKT in general, see the OpenGIS "Coordinate Transformation Services Implementation Specification" at http://www.opengeospatial.org/standards. For information on the European Petroleum Survey Group (EPSG) and their database of spatial reference systems, see http://www.epsg.org.
PostGIS uses the Proj4 library to provide coordinate
transformation capabilities. The PROJ4TEXT
column contains the Proj4 coordinate definition string for a
particular SRID. For example:
+proj=utm +zone=10 +ellps=clrk66 +datum=NAD27 +units=m
For more information about, see the Proj4 web site at http://trac.osgeo.org/proj/.
The spatial_ref_sys.sql
file contains both
SRTEXT
and PROJ4TEXT
definitions for all EPSG projections.
The GEOMETRY_COLUMNS
table definition is as
follows:
CREATE TABLE geometry_columns ( f_table_catalog VARRCHAR(256) NOT NULL, f_table_schema VARCHAR(256) NOT NULL, f_table_nam VARCHAR(256) NOT NULL, f_geometry_column VARCHAR(256) NOT NULL, coord_dimension INTEGER NOT NULL, srid INTEGER NOT NULL, type VARCHAR(30) NOT NULL )
The columns are as follows:
The fully qualified name of the feature table containing the
geometry column. Note that the terms "catalog" and "schema" are
Oracleish. There is not PostgreSQL analogue of "catalog" so that
column is left blank  for "schema" the PostgreSQL schema name is
used (public
is the default).
The name of the geometry column in the feature table.
The spatial dimension (2, 3 or 4 dimensional) of the column.
The ID of the spatial reference system used for the
coordinate geometry in this table. It is a foreign key reference
to the SPATIAL_REF_SYS
.
The type of the spatial object. To restrict the spatial column to a single type, use one of: POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, GEOMETRYCOLLECTION or corresponding XYM versions POINTM, LINESTRINGM, POLYGONM, MULTIPOINTM, MULTILINESTRINGM, MULTIPOLYGONM, GEOMETRYCOLLECTIONM. For heterogeneous (mixedtype) collections, you can use "GEOMETRY" as the type.
This attribute is (probably) not part of the OpenGIS specification, but is required for ensuring type homogeneity. 
Creating a table with spatial data is done in two stages:
Create a normal nonspatial table.
For example: CREATE TABLE ROADS_GEOM ( ID int4, NAME varchar(25) )
Add a spatial column to the table using the OpenGIS "AddGeometryColumn" function.
The syntax is:
AddGeometryColumn( <schema_name>, <table_name>, <column_name>, <srid>, <type>, <dimension> )
Or, using current schema:
AddGeometryColumn( <table_name>, <column_name>, <srid>, <type>, <dimension> )
Example1: SELECT AddGeometryColumn('public', 'roads_geom', 'geom', 423, 'LINESTRING', 2)
Example2: SELECT AddGeometryColumn( 'roads_geom', 'geom', 423, 'LINESTRING', 2)
Here is an example of SQL used to create a table and add a spatial column (assuming that an SRID of 128 exists already):
CREATE TABLE parks ( park_id INTEGER, park_name VARCHAR, park_date DATE, park_type VARCHAR ); SELECT AddGeometryColumn('parks', 'park_geom', 128, 'MULTIPOLYGON', 2 );
Here is another example, using the generic "geometry" type and the undefined SRID value of 1:
CREATE TABLE roads ( road_id INTEGER, road_name VARCHAR ); SELECT AddGeometryColumn( 'roads', 'roads_geom', 1, 'GEOMETRY', 3 );
The AddGeometryColumn() approach creates a geometry column and also registers the new column in the geometry_columns table. If your software utilizes geometry_columns, then any geometry columns you need to query by must be registered in this table. Two of the cases where you want a geometry column to be registered in the geometry_columns table, but you can't use AddGeometryColumn, is in the case of SQL Views and bulk inserts. For these cases, you must register the column in the geometry_columns table manually. Below is a simple script to do that.
Lets say you have a view created like this CREATE VIEW public.vwmytablemercator AS SELECT gid, ST_Transform(the_geom,3395) As the_geom, f_name FROM public.mytable; To register this table in AddGeometry columns  do the following INSERT INTO geometry_columns(f_table_catalog, f_table_schema, f_table_name, f_geometry_column, coord_dimension, srid, "type") SELECT '', 'public', 'vwmytablemercator', 'the_geom', ST_CoordDim(the_geom), ST_SRID(the_geom), GeometryType(the_geom) FROM public.vwmytablemercator LIMIT 1;
Lets say you created a derivative table by doing a bulk insert SELECT poi.gid, poi.the_geom, citybounds.city_name INTO myschema.myspecialpois FROM poi INNER JOIN citybounds ON ST_Intersects(citybounds.the_geom, poi.the_geom); Create index on new table CREATE INDEX idx_myschema_myspecialpois_geom_gist ON myschema.myspecialpois USING gist(the_geom); To manually register this new table's geometry column in geometry_columns  we do the same thing as with view INSERT INTO geometry_columns(f_table_catalog, f_table_schema, f_table_name, f_geometry_column, coord_dimension, srid, "type") SELECT '', 'myschema', 'myspecialpois', 'the_geom', ST_CoordDim(the_geom), ST_SRID(the_geom), GeometryType(the_geom) FROM public.myschema.myspecialpois LIMIT 1;
PostGIS is compliant with the Open Geospatial Consortium’s (OGC) OpenGIS Specifications. As such, many PostGIS methods require, or more accurately, assume that geometries that are operated on are both simple and valid. for example, it does not make sense to calculate the area of a polygon that has a hole defined outside of the polygon, or to construct a polygon from a nonsimple boundary line.
According to the OGC Specifications, a simple
geometry is one that has no anomalous geometric points, such as self
intersection or self tangency and primarily refers to 0 or 1dimensional
geometries (i.e. [MULTI]POINT, [MULTI]LINESTRING
).
Geometry validity, on the other hand, primarily refers to 2dimensional
geometries (i.e. [MULTI]POLYGON)
and defines the set
of assertions that characterizes a valid polygon. The description of each
geometric class includes specific conditions that further detail geometric
simplicity and validity.
A POINT
is inheritably simple
as a 0dimensional geometry object.
MULTIPOINT
s are simple if
no two coordinates (POINT
s) are equal (have identical
coordinate values).
A LINESTRING
is simple if
it does not pass through the same POINT
twice (except
for the endpoints, in which case it is referred to as a linear ring and
additionally considered closed).
(a) and
(c) are simple

A MULTILINESTRING
is simple
only if all of its elements are simple and the only intersection between
any two elements occurs at POINT
s that are on the
boundaries of both elements.
(e) and
(f) are simple

By definition, a POLYGON
is always
simple. It is valid if no two
rings in the boundary (made up of an exterior ring and interior rings)
cross. The boundary of a POLYGON
may intersect at a
POINT
but only as a tangent (i.e. not on a line).
A POLYGON
may not have cut lines or spikes and the
interior rings must be contained entirely within the exterior ring.
(h) and
(i) are valid

A MULTIPOLYGON
is valid
if and only if all of its elements are valid and the interiors of no two
elements intersect. The boundaries of any two elements may touch, but
only at a finite number of POINT
s.
(n) and
(o) are not valid

Most of the functions implemented by the GEOS library rely on the assumption that your geometries are valid as specified by the OpenGIS Simple Feature Specification. To check simplicity or validity of geometries you can use the ST_IsSimple() and ST_IsValid()
 Typically, it doesn't make sense to check  for validity on linear features since it will always return TRUE.  But in this example, PostGIS extends the definition of the OGC IsValid  by returning false if a LinearRing (start and end points are the same)  has less than 2 vertices. gisdb=# SELECT ST_IsValid('LINESTRING(0 0, 1 1)'), ST_IsValid('LINESTRING(0 0, 0 0)'); st_isvalid  st_isvalid + t  f
By default, PostGIS does not apply this validity check on geometry input, because testing for validity needs lots of CPU time for complex geometries, especially polygons. If you do not trust your data sources, you can manually enforce such a check to your tables by adding a check constraint:
ALTER TABLE mytable ADD CONSTRAINT geometry_valid_check CHECK (ST_IsValid(the_geom));
If you encounter any strange error messages such as "GEOS Intersection() threw an error!" or "JTS Intersection() threw an error!" when calling PostGIS functions with valid input geometries, you likely found an error in either PostGIS or one of the libraries it uses, and you should contact the PostGIS developers. The same is true if a PostGIS function returns an invalid geometry for valid input.
Strictly compliant OGC geometries cannot have Z or M values. The ST_IsValid() function won't consider higher dimensioned geometries invalid! Invocations of AddGeometryColumn() will add a constraint checking geometry dimensions, so it is enough to specify 2 there. 
It is sometimes the case that the typical spatial predicates (ST_Contains, ST_Crosses, ST_Intersects, ST_Touches, ...) are insufficient in and of themselves to adequately provide that desired spatial filter.
For example, consider a linear
dataset representing a road network. It may be the task of a
GIS analyst to identify all road segments that cross
each other, not at a point, but on a line, perhaps invalidating
some business rule. In this case, ST_Crosses does not
adequately provide the necessary spatial filter since, for
linear features, it returns One twostep solution
might be to first perform the actual intersection
(ST_Intersection) of pairs of road segments that spatially
intersect (ST_Intersects), and then compare the intersection's
ST_GeometryType with ' A more elegant / faster solution may indeed be desirable. 
A second [theoretical] example may be that of a GIS analyst trying to locate all wharfs or docks that intersect a lake's boundary on a line and where only one end of the wharf is up on shore. In other words, where a wharf is within, but not completely within a lake, intersecting the boundary of a lake on a line, and where the wharf's endpoints are both completely within and on the boundary of the lake. The analyst may need to use a combination of spatial predicates to isolate the sought after features:

So enters the Dimensionally Extended 9 Intersection Model, or DE9IM for short.
According to the OpenGIS Simple Features Implementation Specification for SQL, "the basic approach to comparing two geometries is to make pairwise tests of the intersections between the Interiors, Boundaries and Exteriors of the two geometries and to classify the relationship between the two geometries based on the entries in the resulting 'intersection' matrix."
The boundary of a geometry is the set of geometries of
the next lower dimension. For POINT
s, which
have a dimension of 0, the boundary is the empty set. The
boundary of a LINESTRING
are the two
endpoints. For POLYGON
s, the boundary is
the linework that make up the exterior and interior
rings.
The interior of a geometry are those points of a
geometry that are left when the boundary is removed. For
POINT
s, the interior is the
POINT
itself. The interior of a
LINESTRING
are the set of real points
between the endpoints. For POLYGON
s, the
interior is the areal surface inside the polygon.
The exterior of a geometry is the universe, an areal surface, not on the interior or boundary of the geometry.
Given geometry a, where the I(a), B(a), and E(a) are the Interior, Boundary, and Exterior of a, the mathematical representation of the matrix is:
Interior  Boundary  Exterior  

Interior  
Boundary  
Exterior 
Where dim(a) is the dimension of
a as specified by
ST_Dimension but has the domain of
{0,1,2,T,F,*}
0
=> point
1
=> line
2
=> area
T
=>
{0,1,2}
F
=> empty set
*
=> don't care
Visually, for two overlapping polygonal geometries, this looks like:

Read from left to right and from top to bottom, the dimensional matrix is represented, '212101212'.
A relate matrix that would therefore represent our first example of two lines that intersect on a line would be: '1*1***1**'
 Identify road segments that cross on a line SELECT a.id FROM roads a, roads b WHERE a.id != b.id AND a.geom && b.geom AND ST_Relate(a.geom, b.geom, '1*1***1**');
A relate matrix that represents the second example of wharfs partly on the lake's shoreline would be '102101FF2'
 Identify wharfs partly on a lake's shoreline SELECT a.lake_id, b.wharf_id FROM lakes a, wharfs b WHERE a.geom && b.geom AND ST_Relate(a.geom, b.geom, '102101FF2');
For more information or reading, see:
OpenGIS Simple Features Implementation Specification for SQL (version 1.1, section 2.1.13.2)
Dimensionally Extended NineIntersection Model (DE9IM) by Christian Strobl
Encyclopedia of GIS By Hui Xiong
Once you have created a spatial table, you are ready to upload GIS data to the database. Currently, there are two ways to get data into a PostGIS/PostgreSQL database: using formatted SQL statements or using the Shape file loader/dumper.
If you can convert your data to a text representation, then using formatted SQL might be the easiest way to get your data into PostGIS. As with Oracle and other SQL databases, data can be bulk loaded by piping a large text file full of SQL "INSERT" statements into the SQL terminal monitor.
A data upload file (roads.sql
for example)
might look like this:
BEGIN; INSERT INTO roads (road_id, roads_geom, road_name) VALUES (1,ST_GeomFromText('LINESTRING(191232 243118,191108 243242)',1),'Jeff Rd'); INSERT INTO roads (road_id, roads_geom, road_name) VALUES (2,ST_GeomFromText('LINESTRING(189141 244158,189265 244817)',1),'Geordie Rd'); INSERT INTO roads (road_id, roads_geom, road_name) VALUES (3,ST_GeomFromText('LINESTRING(192783 228138,192612 229814)',1),'Paul St'); INSERT INTO roads (road_id, roads_geom, road_name) VALUES (4,ST_GeomFromText('LINESTRING(189412 252431,189631 259122)',1),'Graeme Ave'); INSERT INTO roads (road_id, roads_geom, road_name) VALUES (5,ST_GeomFromText('LINESTRING(190131 224148,190871 228134)',1),'Phil Tce'); INSERT INTO roads (road_id, roads_geom, road_name) VALUES (6,ST_GeomFromText('LINESTRING(198231 263418,198213 268322)',1),'Dave Cres'); COMMIT;
The data file can be piped into PostgreSQL very easily using the "psql" SQL terminal monitor:
psql d [database] f roads.sql
The shp2pgsql
data loader converts ESRI Shape files into SQL suitable for
insertion into a PostGIS/PostgreSQL database either in geometry or geography format. The loader has several operating modes
distinguished by command line flags:
In addition to the shp2pgsql commandline loader, there is an shp2pgsqlgui
graphical interface with most
of the options as the commandline loader, but may be easier to use for oneoff nonscripted loading or if you are new to PostGIS.
It can also be configured as a plugin to PgAdminIII.
Creates a new table and populates it from the shapefile. This is the default mode.
Appends data from the Shape file into the database table. Note that to use this option to load multiple files, the files must have the same attributes and same data types.
Drops the database table before creating a new table with the data in the Shape file.
Only produces the table creation SQL code, without adding any actual data. This can be used if you need to completely separate the table creation and data loading steps.
Display help screen.
Use the PostgreSQL "dump" format for the output data. This can be combined with a, c and d. It is much faster to load than the default "insert" SQL format. Use this for very large data sets.
Creates and populates the geometry tables with the specified SRID.
Keep identifiers' case (column, schema and attributes). Note that attributes in Shapefile are all UPPERCASE.
Coerce all integers to standard 32bit integers, do not create 64bit bigints, even if the DBF header signature appears to warrant it.
Create a GiST index on the geometry column.
Output WKT format, for use with older (0.x) versions of PostGIS. Note that this will introduce coordinate drifts and will drop M values from shapefiles.
Specify encoding of the input data (dbf file). When used, all attributes of the dbf are
converted from the specified encoding to UTF8. The resulting SQL output will contain a
SET CLIENT_ENCODING to UTF8
command, so that the backend will be able to
reconvert from UTF8 to whatever encoding the database is configured to use internally.
NULL geometries handling policy (insert*,skip,abort)
n Only import DBF file. If your data has no corresponding shapefile, it will automatically switch to this mode and load just the dbf. So setting this flag is only needed if you have a full shapefile set, and you only want the attribute data and no geometry.
Use geography type instead of geometry (requires lon/lat data) in WGS84 long lat (SRID=4326)
An example session using the loader to create an input file and uploading it might look like this:
# shp2pgsql c D s 4269 i I shaperoads.shp myschema.roadstable > roads.sql # psql d roadsdb f roads.sql
A conversion and upload can be done all in one step using UNIX pipes:
# shp2pgsql shaperoads.shp myschema.roadstable  psql d roadsdb
Data can be extracted from the database using either SQL or the Shape file loader/dumper. In the section on SQL we will discuss some of the operators available to do comparisons and queries on spatial tables.
The most straightforward means of pulling data out of the database is to use a SQL select query and dump the resulting columns into a parsable text file:
db=# SELECT road_id, ST_AsText(road_geom) AS geom, road_name FROM roads; road_id  geom  road_name ++ 1  LINESTRING(191232 243118,191108 243242)  Jeff Rd 2  LINESTRING(189141 244158,189265 244817)  Geordie Rd 3  LINESTRING(192783 228138,192612 229814)  Paul St 4  LINESTRING(189412 252431,189631 259122)  Graeme Ave 5  LINESTRING(190131 224148,190871 228134)  Phil Tce 6  LINESTRING(198231 263418,198213 268322)  Dave Cres 7  LINESTRING(218421 284121,224123 241231)  Chris Way (6 rows)
However, there will be times when some kind of restriction is necessary to cut down the number of fields returned. In the case of attributebased restrictions, just use the same SQL syntax as normal with a nonspatial table. In the case of spatial restrictions, the following operators are available/useful:
This operator tells whether the bounding box of one geometry intersects the bounding box of another.
This operators tests whether two geometries are geometrically identical. For example, if 'POLYGON((0 0,1 1,1 0,0 0))' is the same as 'POLYGON((0 0,1 1,1 0,0 0))' (it is).
This operator is a little more naive, it only tests whether the bounding boxes of two geometries are the same.
Next, you can use these operators in queries. Note that when specifying geometries and boxes on the SQL command line, you must explicitly turn the string representations into geometries by using the "GeomFromText()" function. So, for example:
SELECT road_id, road_name FROM roads WHERE roads_geom ~= ST_GeomFromText('LINESTRING(191232 243118,191108 243242)',1);
The above query would return the single record from the "ROADS_GEOM" table in which the geometry was equal to that value.
When using the "&&" operator, you can specify either a BOX3D as the comparison feature or a GEOMETRY. When you specify a GEOMETRY, however, its bounding box will be used for the comparison.
SELECT road_id, road_name FROM roads WHERE roads_geom && ST_GeomFromText('POLYGON((...))',1);
The above query will use the bounding box of the polygon for comparison purposes.
The most common spatial query will probably be a "framebased" query, used by client software, like data browsers and web mappers, to grab a "map frame" worth of data for display. Using a "BOX3D" object for the frame, such a query looks like this:
SELECT ST_AsText(roads_geom) AS geom FROM roads WHERE roads_geom && SetSRID('BOX3D(191232 243117,191232 243119)'::box3d,1);
Note the use of the SRID, to specify the projection of the BOX3D. The value 1 is used to indicate no specified SRID.
The pgsql2shp
table dumper connects directly
to the database and converts a table (possibly defined by a query) into
a shape file. The basic syntax is:
pgsql2shp [<options>] <database> [<schema>.]<table>
pgsql2shp [<options>] <database> <query>
The commandline options are:
Write the output to a particular filename.
The database host to connect to.
The port to connect to on the database host.
The password to use when connecting to the database.
The username to use when connecting to the database.
In the case of tables with multiple geometry columns, the geometry column to use when writing the shape file.
Use a binary cursor. This will make the operation faster, but will not work if any NONgeometry attribute in the table lacks a cast to text.
Raw mode. Do not drop the gid
field, or
escape column names.
For backward compatibility: write a 3dimensional shape file when dumping from old (pre1.0.0) postgis databases (the default is to write a 2dimensional shape file in that case). Starting from postgis1.0.0+, dimensions are fully encoded.
Indexes are what make using a spatial database for large data sets possible. Without indexing, any search for a feature would require a "sequential scan" of every record in the database. Indexing speeds up searching by organizing the data into a search tree which can be quickly traversed to find a particular record. PostgreSQL supports three kinds of indexes by default: BTree indexes, RTree indexes, and GiST indexes.
BTrees are used for data which can be sorted along one axis; for example, numbers, letters, dates. GIS data cannot be rationally sorted along one axis (which is greater, (0,0) or (0,1) or (1,0)?) so BTree indexing is of no use for us.
RTrees break up data into rectangles, and subrectangles, and subsub rectangles, etc. RTrees are used by some spatial databases to index GIS data, but the PostgreSQL RTree implementation is not as robust as the GiST implementation.
GiST (Generalized Search Trees) indexes break up data into "things to one side", "things which overlap", "things which are inside" and can be used on a wide range of datatypes, including GIS data. PostGIS uses an RTree index implemented on top of GiST to index GIS data.
GiST stands for "Generalized Search Tree" and is a generic form of indexing. In addition to GIS indexing, GiST is used to speed up searches on all kinds of irregular data structures (integer arrays, spectral data, etc) which are not amenable to normal BTree indexing.
Once a GIS data table exceeds a few thousand rows, you will want to build an index to speed up spatial searches of the data (unless all your searches are based on attributes, in which case you'll want to build a normal index on the attribute fields).
The syntax for building a GiST index on a "geometry" column is as follows:
CREATE INDEX [indexname] ON [tablename] USING GIST ( [geometryfield] );
Building a spatial index is a computationally intensive exercise: on tables of around 1 million rows, on a 300MHz Solaris machine, we have found building a GiST index takes about 1 hour. After building an index, it is important to force PostgreSQL to collect table statistics, which are used to optimize query plans:
VACUUM ANALYZE [table_name] [column_name];  This is only needed for PostgreSQL 7.4 installations and below SELECT UPDATE_GEOMETRY_STATS([table_name], [column_name]);
GiST indexes have two advantages over RTree indexes in PostgreSQL. Firstly, GiST indexes are "null safe", meaning they can index columns which include null values. Secondly, GiST indexes support the concept of "lossiness" which is important when dealing with GIS objects larger than the PostgreSQL 8K page size. Lossiness allows PostgreSQL to store only the "important" part of an object in an index  in the case of GIS objects, just the bounding box. GIS objects larger than 8K will cause RTree indexes to fail in the process of being built.
Ordinarily, indexes invisibly speed up data access: once the index is built, the query planner transparently decides when to use index information to speed up a query plan. Unfortunately, the PostgreSQL query planner does not optimize the use of GiST indexes well, so sometimes searches which should use a spatial index instead default to a sequence scan of the whole table.
If you find your spatial indexes are not being used (or your attribute indexes, for that matter) there are a couple things you can do:
Firstly, make sure statistics are gathered about the number and distributions of values in a table, to provide the query planner with better information to make decisions around index usage. For PostgreSQL 7.4 installations and below this is done by running update_geometry_stats([table_name, column_name]) (compute distribution) and VACUUM ANALYZE [table_name] [column_name] (compute number of values). Starting with PostgreSQL 8.0 running VACUUM ANALYZE will do both operations. You should regularly vacuum your databases anyways  many PostgreSQL DBAs have VACUUM run as an offpeak cron job on a regular basis.
If vacuuming does not work, you can force the planner to use
the index information by using the SET
ENABLE_SEQSCAN=OFF command. You should only use this
command sparingly, and only on spatially indexed queries: generally
speaking, the planner knows better than you do about when to use
normal BTree indexes. Once you have run your query, you should
consider setting ENABLE_SEQSCAN
back on, so that
other queries will utilize the planner as normal.
As of version 0.6, it should not be necessary to force the
planner to use the index with

If you find the planner wrong about the cost of sequential vs index scans try reducing the value of random_page_cost in postgresql.conf or using SET random_page_cost=#. Default value for the parameter is 4, try setting it to 1 or 2. Decrementing the value makes the planner more inclined of using Index scans.
The raison d'etre of spatial database functionality is performing queries inside the database which would ordinarily require desktop GIS functionality. Using PostGIS effectively requires knowing what spatial functions are available, and ensuring that appropriate indexes are in place to provide good performance.
When constructing a query it is important to remember that only
the boundingboxbased operators such as && can take advantage
of the GiST spatial index. Functions such as
distance()
cannot use the index to optimize their
operation. For example, the following query would be quite slow on a
large table:
SELECT the_geom FROM geom_table WHERE ST_Distance(the_geom, ST_GeomFromText('POINT(100000 200000)', 1)) < 100
This query is selecting all the geometries in geom_table which are
within 100 units of the point (100000, 200000). It will be slow because
it is calculating the distance between each point in the table and our
specified point, ie. one ST_Distance()
calculation
for each row in the table. We can avoid this by using the &&
operator to reduce the number of distance calculations required:
SELECT the_geom FROM geom_table WHERE the_geom && 'BOX3D(90900 190900, 100100 200100)'::box3d AND ST_Distance(the_geom, ST_GeomFromText('POINT(100000 200000)', 1)) < 100
This query selects the same geometries, but it does it in a more
efficient way. Assuming there is a GiST index on the_geom, the query
planner will recognize that it can use the index to reduce the number of
rows before calculating the result of the distance()
function. Notice that the BOX3D
geometry which is
used in the && operation is a 200 unit square box centered on
the original point  this is our "query box". The && operator
uses the index to quickly reduce the result set down to only those
geometries which have bounding boxes that overlap the "query box".
Assuming that our query box is much smaller than the extents of the
entire geometry table, this will drastically reduce the number of
distance calculations that need to be done.
Change in Behavior  

As of PostGIS 1.3.0, most of the Geometry Relationship Functions, with the notable exceptions of ST_Disjoint and ST_Relate, include implicit bounding box overlap operators. 
The examples in this section will make use of two tables, a table
of linear roads, and a table of polygonal municipality boundaries. The
table definitions for the bc_roads
table is:
Column  Type  Description ++ gid  integer  Unique ID name  character varying  Road Name the_geom  geometry  Location Geometry (Linestring)
The table definition for the bc_municipality
table is:
Column  Type  Description ++ gid  integer  Unique ID code  integer  Unique ID name  character varying  City / Town Name the_geom  geometry  Location Geometry (Polygon)
Table of Contents
The Minnesota MapServer is an internet webmapping server which conforms to the OpenGIS Web Mapping Server specification.
The MapServer homepage is at http://mapserver.org.
The OpenGIS Web Map Specification is at http://www.opengeospatial.org/standards/wms.
To use PostGIS with MapServer, you will need to know about how to configure MapServer, which is beyond the scope of this documentation. This section will cover specific PostGIS issues and configuration details.
To use PostGIS with MapServer, you will need:
Version 0.6 or newer of PostGIS.
Version 3.5 or newer of MapServer.
MapServer accesses PostGIS/PostgreSQL data like any other
PostgreSQL client  using the libpq
interface. This means that
MapServer can be installed on any machine with network access to the
PostGIS server, and use PostGIS as a source of data. The faster the connection
between the systems, the better.
Compile and install MapServer, with whatever options you desire, including the "withpostgis" configuration option.
In your MapServer map file, add a PostGIS layer. For example:
LAYER CONNECTIONTYPE postgis NAME "widehighways" # Connect to a remote spatial database CONNECTION "user=dbuser dbname=gisdatabase host=bigserver" PROCESSING "CLOSE_CONNECTION=DEFER" # Get the lines from the 'geom' column of the 'roads' table DATA "geom from roads using srid=4326 using unique gid" STATUS ON TYPE LINE # Of the lines in the extents, only render the wide highways FILTER "type = 'highway' and numlanes >= 4" CLASS # Make the superhighways brighter and 2 pixels wide EXPRESSION ([numlanes] >= 6) STYLE COLOR 255 22 22 WIDTH 2 END END CLASS # All the rest are darker and only 1 pixel wide EXPRESSION ([numlanes] < 6) STYLE COLOR 205 92 82 END END END
In the example above, the PostGISspecific directives are as follows:
For PostGIS layers, this is always "postgis".
The database connection is governed by the a 'connection string' which is a standard set of keys and values like this (with the default values in <>):
user=<username> password=<password> dbname=<username> hostname=<server> port=<5432>
An empty connection string is still valid, and any of the key/value pairs can be omitted. At a minimum you will generally supply the database name and username to connect with.
The form of this parameter is "<geocolumn> from <tablename> using srid=<srid> using unique <primary key>" where the column is the spatial column to be rendered to the map, the SRID is SRID used by the column and the primary key is the table primary key (or any other uniquelyvalued column with an index).
You can omit the "using srid" and "using unique" clauses and MapServer will automatically determine the correct values if possible, but at the cost of running a few extra queries on the server for each map draw.
Putting in a CLOSE_CONNECTION=DEFER if you have multiple layers reuses existing connections instead of closing them. This improves speed. Refer to for MapServer PostGIS Performance Tips for a more detailed explanation.
The filter must be a valid SQL string corresponding to the logic normally following the "WHERE" keyword in a SQL query. So, for example, to render only roads with 6 or more lanes, use a filter of "num_lanes >= 6".
In your spatial database, ensure you have spatial (GiST) indexes built for any the layers you will be drawing.
CREATE INDEX [indexname] ON [tablename] USING GIST ( [geometrycolumn] );
If you will be querying your layers using MapServer you will also need to use the "using unique" clause in your DATA statement.
MapServer requires unique identifiers for each spatial record when doing queries, and the PostGIS module of MapServer uses the unique value you specify in order to provide these unique identifiers. Using the table primary key is the best practice.
The USING
pseudoSQL clause is used to add some
information to help mapserver understand the results of more complex
queries. More specifically, when either a view or a subselect is used as
the source table (the thing to the right of "FROM" in a
DATA
definition) it is more difficult for mapserver
to automatically determine a unique identifier for each row and also the
SRID for the table. The USING
clause can provide
mapserver with these two pieces of information as follows:
DATA "the_geom FROM ( SELECT table1.the_geom AS the_geom, table1.oid AS oid, table2.data AS data FROM table1 LEFT JOIN table2 ON table1.id = table2.id ) AS new_table USING UNIQUE gid USING SRID=1"
MapServer requires a unique id for each row in order to
identify the row when doing map queries. Normally it identifies
the primary key from the system tables. However, views and subselects don't
automatically have an known unique column. If you want to use MapServer's
query functionality, you need to ensure your view
or subselect includes a uniquely valued column, and declare it with USING UNIQUE
.
For example, you could explicitly select nee of the table's primary key
values for this purpose, or any other column which is guaranteed
to be unique for the result set.
"Querying a Map" is the action of clicking on a map to ask
for information about the map features in that location. Don't
confuse "map queries" with the SQL query in a

PostGIS needs to know which spatial referencing system is
being used by the geometries in order to return the correct data
back to MapServer. Normally it is possible to find this
information in the "geometry_columns" table in the PostGIS
database, however, this is not possible for tables which are
created on the fly such as subselects and views. So the
USING SRID=
option allows the correct SRID to
be specified in the DATA
definition.
Lets start with a simple example and work our way up. Consider the following MapServer layer definition:
LAYER CONNECTIONTYPE postgis NAME "roads" CONNECTION "user=theuser password=thepass dbname=thedb host=theserver" DATA "the_geom from roads" STATUS ON TYPE LINE CLASS STYLE COLOR 0 0 0 END END END
This layer will display all the road geometries in the roads table as black lines.
Now lets say we want to show only the highways until we get zoomed in to at least a 1:100000 scale  the next two layers will achieve this effect:
LAYER CONNECTIONTYPE postgis CONNECTION "user=theuser password=thepass dbname=thedb host=theserver" PROCESSING "CLOSE_CONNECTION=DEFER" DATA "the_geom from roads" MINSCALE 100000 STATUS ON TYPE LINE FILTER "road_type = 'highway'" CLASS COLOR 0 0 0 END END LAYER CONNECTIONTYPE postgis CONNECTION "user=theuser password=thepass dbname=thedb host=theserver" PROCESSING "CLOSE_CONNECTION=DEFER" DATA "the_geom from roads" MAXSCALE 100000 STATUS ON TYPE LINE CLASSITEM road_type CLASS EXPRESSION "highway" STYLE WIDTH 2 COLOR 255 0 0 END END CLASS STYLE COLOR 0 0 0 END END END
The first layer is used when the scale is greater than 1:100000,
and displays only the roads of type "highway" as black lines. The
FILTER
option causes only roads of type "highway" to
be displayed.
The second layer is used when the scale is less than 1:100000, and will display highways as doublethick red lines, and other roads as regular black lines.
So, we have done a couple of interesting things using only
MapServer functionality, but our DATA
SQL statement
has remained simple. Suppose that the name of the road is stored in
another table (for whatever reason) and we need to do a join to get it
and label our roads.
LAYER CONNECTIONTYPE postgis CONNECTION "user=theuser password=thepass dbname=thedb host=theserver" DATA "the_geom FROM (SELECT roads.oid AS oid, roads.the_geom AS the_geom, road_names.name as name FROM roads LEFT JOIN road_names ON roads.road_name_id = road_names.road_name_id) AS named_roads USING UNIQUE oid USING SRID=1" MAXSCALE 20000 STATUS ON TYPE ANNOTATION LABELITEM name CLASS LABEL ANGLE auto SIZE 8 COLOR 0 192 0 TYPE truetype FONT arial END END END
This annotation layer adds green labels to all the roads when the
scale gets down to 1:20000 or less. It also demonstrates how to use an
SQL join in a DATA
definition.
Java clients can access PostGIS "geometry" objects in the PostgreSQL database either directly as text representations or using the JDBC extension objects bundled with PostGIS. In order to use the extension objects, the "postgis.jar" file must be in your CLASSPATH along with the "postgresql.jar" JDBC driver package.
import java.sql.*; import java.util.*; import java.lang.*; import org.postgis.*; public class JavaGIS { public static void main(String[] args) { java.sql.Connection conn; try { /* * Load the JDBC driver and establish a connection. */ Class.forName("org.postgresql.Driver"); String url = "jdbc:postgresql://localhost:5432/database"; conn = DriverManager.getConnection(url, "postgres", ""); /* * Add the geometry types to the connection. Note that you * must cast the connection to the pgsqlspecific connection * implementation before calling the addDataType() method. */ ((org.postgresql.Connection)conn).addDataType("geometry","org.postgis.PGgeometry") ; ((org.postgresql.Connection)conn).addDataType("box3d","org.postgis.PGbox3d"); /* * Create a statement and execute a select query. */ Statement s = conn.createStatement(); ResultSet r = s.executeQuery("select ST_AsText(geom) as geom,id from geomtable"); while( r.next() ) { /* * Retrieve the geometry as an object then cast it to the geometry type. * Print things out. */ PGgeometry geom = (PGgeometry)r.getObject(1); int id = r.getInt(2); System.out.println("Row " + id + ":"); System.out.println(geom.toString()); } s.close(); conn.close(); } catch( Exception e ) { e.printStackTrace(); } } }
The "PGgeometry" object is a wrapper object which contains a specific topological geometry object (subclasses of the abstract class "Geometry") depending on the type: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon.
PGgeometry geom = (PGgeometry)r.getObject(1); if( geom.getType() = Geometry.POLYGON ) { Polygon pl = (Polygon)geom.getGeometry(); for( int r = 0; r < pl.numRings(); r++) { LinearRing rng = pl.getRing(r); System.out.println("Ring: " + r); for( int p = 0; p < rng.numPoints(); p++ ) { Point pt = rng.getPoint(p); System.out.println("Point: " + p); System.out.println(pt.toString()); } } }
The JavaDoc for the extension objects provides a reference for the various data accessor functions in the geometric objects.
...
Table of Contents
Current PostgreSQL versions (including 8.0) suffer from a query optimizer weakness regarding TOAST tables. TOAST tables are a kind of "extension room" used to store large (in the sense of data size) values that do not fit into normal data pages (like long texts, images or complex geometries with lots of vertices), see http://www.postgresql.org/docs/current/interactive/storagetoast.html for more information).
The problem appears if you happen to have a table with rather large geometries, but not too much rows of them (like a table containing the boundaries of all European countries in high resolution). Then the table itself is small, but it uses lots of TOAST space. In our example case, the table itself had about 80 rows and used only 3 data pages, but the TOAST table used 8225 pages.
Now issue a query where you use the geometry operator && to search for a bounding box that matches only very few of those rows. Now the query optimizer sees that the table has only 3 pages and 80 rows. He estimates that a sequential scan on such a small table is much faster than using an index. And so he decides to ignore the GIST index. Usually, this estimation is correct. But in our case, the && operator has to fetch every geometry from disk to compare the bounding boxes, thus reading all TOAST pages, too.
To see whether your suffer from this bug, use the "EXPLAIN ANALYZE" postgresql command. For more information and the technical details, you can read the thread on the postgres performance mailing list: http://archives.postgresql.org/pgsqlperformance/200502/msg00030.php
The PostgreSQL people are trying to solve this issue by making the query estimation TOASTaware. For now, here are two workarounds:
The first workaround is to force the query planner to use the index. Send "SET enable_seqscan TO off;" to the server before issuing the query. This basically forces the query planner to avoid sequential scans whenever possible. So it uses the GIST index as usual. But this flag has to be set on every connection, and it causes the query planner to make misestimations in other cases, so you should "SET enable_seqscan TO on;" after the query.
The second workaround is to make the sequential scan as fast as the query planner thinks. This can be achieved by creating an additional column that "caches" the bbox, and matching against this. In our example, the commands are like:
SELECT AddGeometryColumn('myschema','mytable','bbox','4326','GEOMETRY','2'); UPDATE mytable SET bbox = ST_Envelope(ST_Force_2d(the_geom));
Now change your query to use the && operator against bbox instead of geom_column, like:
SELECT geom_column FROM mytable WHERE bbox && ST_SetSRID('BOX3D(0 0,1 1)'::box3d,4326);
Of course, if you change or add rows to mytable, you have to keep the bbox "in sync". The most transparent way to do this would be triggers, but you also can modify your application to keep the bbox column current or run the UPDATE query above after every modification.
For tables that are mostly readonly, and where a single index is used for the majority of queries, PostgreSQL offers the CLUSTER command. This command physically reorders all the data rows in the same order as the index criteria, yielding two performance advantages: First, for index range scans, the number of seeks on the data table is drastically reduced. Second, if your working set concentrates to some small intervals on the indices, you have a more efficient caching because the data rows are spread along fewer data pages. (Feel invited to read the CLUSTER command documentation from the PostgreSQL manual at this point.)
However, currently PostgreSQL does not allow clustering on PostGIS GIST indices because GIST indices simply ignores NULL values, you get an error message like:
lwgeom=# CLUSTER my_geom_index ON my_table; ERROR: cannot cluster when index access method does not handle null values HINT: You may be able to work around this by marking column "the_geom" NOT NULL.
As the HINT message tells you, one can work around this deficiency by adding a "not null" constraint to the table:
lwgeom=# ALTER TABLE my_table ALTER COLUMN the_geom SET not null; ALTER TABLE
Of course, this will not work if you in fact need NULL values in your geometry column. Additionally, you must use the above method to add the constraint, using a CHECK constraint like "ALTER TABLE blubb ADD CHECK (geometry is not null);" will not work.
Sometimes, you happen to have 3D or 4D data in your table, but always access it using OpenGIS compliant ST_AsText() or ST_AsBinary() functions that only output 2D geometries. They do this by internally calling the ST_Force_2d() function, which introduces a significant overhead for large geometries. To avoid this overhead, it may be feasible to predrop those additional dimensions once and forever:
UPDATE mytable SET the_geom = ST_Force_2d(the_geom); VACUUM FULL ANALYZE mytable;
Note that if you added your geometry column using AddGeometryColumn() there'll be a constraint on geometry dimension. To bypass it you will need to drop the constraint. Remember to update the entry in the geometry_columns table and recreate the constraint afterwards.
In case of large tables, it may be wise to divide this UPDATE into smaller portions by constraining the UPDATE to a part of the table via a WHERE clause and your primary key or another feasible criteria, and running a simple "VACUUM;" between your UPDATEs. This drastically reduces the need for temporary disk space. Additionally, if you have mixed dimension geometries, restricting the UPDATE by "WHERE dimension(the_geom)>2" skips rewriting of geometries that already are in 2D.
These tips are taken from Kevin Neufeld's presentation "Tips for the PostGIS Power User" at the FOSS4G 2007 conference. Depending on your use of PostGIS (for example, static data and complex analysis vs frequently updated data and lots of users) these changes can provide significant speedups to your queries.
For a more tips (and better formatting), the original presentation is at http://2007.foss4g.org/presentations/view.php?abstract_id=117.
These settings are configured in postgresql.conf:
checkpoint_segment_size (this setting is obsolete in newer versions of PostgreSQL) got replaced with many configurations with names starting with checkpoint and WAL.
# of WAL files = 16MB each; default is 3
Set to at least 10 or 30 for databases with heavy write activity, or more for large database loads. Another article on the topic worth reading Greg Smith: Checkpoint and Background writer
Possibly store the xlog on a separate disk device
Default: off (prior to PostgreSQL 8.4 and for PostgreSQL 8.4+ is set to partition)
This is generally used for table partitioning. If you are running PostgreSQL versions below 8.4, set to "on" to ensure the query planner will optimize as desired. As of PostgreSQL 8.4, the default for this is set to "partition" which is ideal for PostgreSQL 8.4 and above since it will force the planner to only analyze tables for constraint consideration if they are in an inherited hierarchy and not pay the planner penalty otherwise.
Default: ~32MB
Set to about 1/3 to 3/4 of available RAM
work_mem (the memory used for sort operations and complex queries)
Default: 1MB
Adjust up for large dbs, complex queries, lots of RAM
Adjust down for many concurrent users or low RAM.
If you have lots of RAM and few developers:
SET work_mem TO 1200000;
maintenance_work_mem (used for VACUUM, CREATE INDEX, etc.)
Default: 16MB
Generally too low  ties up I/O, locks objects while swapping memory
Recommend 32MB to 256MB on production servers w/lots of RAM, but depends on the # of concurrent users. If you have lots of RAM and few developers:
SET maintainence_work_mem TO 1200000;
Table of Contents
The functions given below are the ones which a user of PostGIS is likely to need. There are other functions which are required support functions to the PostGIS objects which are not of use to a general user.
PostGIS has begun a transition from the existing naming convention to an SQLMMcentric convention. As a result, most of the functions that you know and love have been renamed using the standard spatial type (ST) prefix. Previous functions are still available, though are not listed in this document where updated functions are equivalent. The non ST_ functions not listed in this documentation are deprecated and will be removed in a future release so STOP USING THEM. 
Abstract
This section lists the PostgreSQL data types installed by PostGIS. Note we describe the casting behavior of these which is very important especially when designing your own functions.
A Cast is when one type is coerced into another type. PostgreSQL is unique from most databases in that it allows you to define casting behavior for custom types and the functions used for casting. A cast can be specified as automatic in which case, you do not have to do a CAST(myfoo As otherfootype) or myfoo::otherfootype if you are feeding it to a function that only works with otherfootype and there is an automatic cast in place for it.
The danger of relying on automatic cast behavior is when you have an overloaded function say one that takes a box2d and one that takes a box3d but no geometry. What happens is that both functions are equally good to use with geometry since geometry has an autocast for both  so you end up with an ambiguous function error. To force PostgreSQL to choose, you do a CAST(mygeom As box3d) or mygeom::box3d.
At least as of PostgreSQL 8.3  Everything can be CAST to text (presumably because of the magical unknown type), so no defined CASTS for that need to be present for you to CAST an object to text. 
box2d — A box composed of x min, ymin, xmax, ymax. Often used to return the 2d enclosing box of a geometry.
box3d — A box composed of x min, ymin, zmin, xmax, ymax, zmax. Often used to return the 3d extent of a geometry or collection of geometries.
box3d_extent — A box composed of x min, ymin, zmin, xmax, ymax, zmax. Often used to return the extent of a geometry.
box3d_extent is a data type returned by ST_Extent. In versions prior to PostGIS 1.4, ST_Extent would return a box2d.
geometry — Planar spatial data type.
geometry is a fundamental postgis spatial data type used to represent a feature in the Euclidean coordinate system.
geometry_dump — A spatial datatype with two fields  geom (holding a geometry object) and path[] (a 1d array holding the position of the geometry within the dumped object.)
geometry_dump is a compound data type consisting of a geometry object referenced by the .geom field and path[] a 1dimensional integer array (starting at 1 e.g. path[1] to get first element) array that defines the navigation path within the dumped geometry to find this element. It is used by the ST_Dump* family of functions as an output type to explode a more complex geometry into its constituent parts and location of parts.
TRUE
if STATS usage has been
enabled.geometry_columns
table.geometry_columns
table if they are not there.AddGeometryColumn — Adds a geometry column to an existing table of attributes.
text AddGeometryColumn(
varchar
table_name, varchar
column_name, integer
srid, varchar
type, integer
dimension)
;
text AddGeometryColumn(
varchar
schema_name, varchar
table_name, varchar
column_name, integer
srid, varchar
type, integer
dimension)
;
text AddGeometryColumn(
varchar
catalog_name, varchar
schema_name, varchar
table_name, varchar
column_name, integer
srid, varchar
type, integer
dimension)
;
Adds a geometry column to an existing table of attributes. The
schema_name
is the name of the table schema (unused
for preschema PostgreSQL installations). The srid
must be an integer value reference to an entry in the SPATIAL_REF_SYS
table. The type
must be an uppercase string
corresponding to the geometry type, eg, 'POLYGON' or
'MULTILINESTRING'. An error is thrown if the schemaname doesn't exist
(or not visible in the current search_path) or the specified SRID,
geometry type, or dimension is invalid.
Views and derivatively created spatial tables will need to be registered in geometry_columns manually, since AddGeometryColumn also adds a spatial column which is not needed when you already have a spatial column. Refer to Section 4.3.4, “Manually Registering Geometry Columns in geometry_columns”. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
 Create a new simple PostgreSQL table postgis=# CREATE TABLE my_schema.my_spatial_table (id serial);  Describing the table shows a simple table with a single "id" column. postgis=# \d my_schema.my_spatial_table Table "my_schema.my_spatial_table" Column  Type  Modifiers ++ id  integer  not null default nextval('my_schema.my_spatial_table_id_seq'::regclass)  Add a spatial column to the table postgis=# SELECT AddGeometryColumn ('my_schema','my_spatial_table','the_geom',4326,'POINT',2); Add a curvepolygon SELECT AddGeometryColumn ('my_schema','my_spatial_table','the_geomcp',4326,'CURVEPOLYGON',2);  Describe the table again reveals the addition of a new "the_geom" column. postgis=# \d my_schema.my_spatial_table Column  Type  Modifiers ++ id  integer  not null default nextval('my_schema.my_spatial_table_id_seq'::regclass) the_geom  geometry  the_geomcp  geometry  Check constraints: "enforce_dims_the_geom" CHECK (ndims(the_geom) = 2) "enforce_dims_the_geomcp" CHECK (ndims(the_geomcp) = 2) "enforce_geotype_the_geom" CHECK (geometrytype(the_geom) = 'POINT'::text OR the_geom IS NULL) "enforce_geotype_the_geomcp" CHECK (geometrytype(the_geomcp) = 'CURVEPOLYGON '::text OR the_geomcp IS NULL) "enforce_srid_the_geom" CHECK (srid(the_geom) = 4326) "enforce_srid_the_geomcp" CHECK (srid(the_geomcp) = 4326)
DropGeometryColumn — Removes a geometry column from a spatial table.
text DropGeometryColumn(
varchar
table_name, varchar
column_name)
;
text DropGeometryColumn(
varchar
schema_name, varchar
table_name, varchar
column_name)
;
text DropGeometryColumn(
varchar
catalog_name, varchar
schema_name, varchar
table_name, varchar
column_name)
;
Removes a geometry column from a spatial table. Note that schema_name will need to match the f_table_schema field of the table's row in the geometry_columns table.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
DropGeometryTable — Drops a table and all its references in geometry_columns.
boolean DropGeometryTable(
varchar
table_name)
;
boolean DropGeometryTable(
varchar
schema_name, varchar
table_name)
;
boolean DropGeometryTable(
varchar
catalog_name, varchar
schema_name, varchar
table_name)
;
Drops a table and all its references in geometry_columns. Note: uses current_schema() on schemaaware pgsql installations if schema is not provided.
PostGIS_Full_Version — Reports full postgis version and build configuration infos.
text PostGIS_Full_Version(
)
;
PostGIS_GEOS_Version — Returns the version number of the GEOS library.
text PostGIS_GEOS_Version(
)
;
PostGIS_LibXML_Version — Returns the version number of the libxml2 library.
text PostGIS_LibXML_Version(
)
;
PostGIS_Lib_Build_Date — Returns build date of the PostGIS library.
text PostGIS_Lib_Build_Date(
)
;
PostGIS_Lib_Version — Returns the version number of the PostGIS library.
text PostGIS_Lib_Version(
)
;
PostGIS_PROJ_Version — Returns the version number of the PROJ4 library.
text PostGIS_PROJ_Version(
)
;
Returns the version number of the PROJ4 library, or
NULL
if PROJ4 support is not enabled.
PostGIS_Scripts_Build_Date — Returns build date of the PostGIS scripts.
text PostGIS_Scripts_Build_Date(
)
;
PostGIS_Scripts_Installed — Returns version of the postgis scripts installed in this database.
text PostGIS_Scripts_Installed(
)
;
Returns version of the postgis scripts installed in this database.
If the output of this function doesn't match the output of PostGIS_Scripts_Released you probably missed to properly upgrade an existing database. See the Upgrading section for more info. 
Availability: 0.9.0
PostGIS_Scripts_Released — Returns the version number of the postgis.sql script released with the installed postgis lib.
text PostGIS_Scripts_Released(
)
;
Returns the version number of the postgis.sql script released with the installed postgis lib.
Starting with version 1.1.0 this function returns the same value of PostGIS_Lib_Version. Kept for backward compatibility. 
Availability: 0.9.0
PostGIS_Uses_Stats — Returns TRUE
if STATS usage has been
enabled.
text PostGIS_Uses_Stats(
)
;
PostGIS_Version — Returns PostGIS version number and compiletime options.
text PostGIS_Version(
)
;
Populate_Geometry_Columns — Ensures geometry columns have appropriate spatial constraints
and exist in the geometry_columns
table.
text Populate_Geometry_Columns(
)
;
int Populate_Geometry_Columns(
oid relation_oid)
;
Ensures geometry columns have appropriate spatial constraints and
exist in the geometry_columns
table. In particular,
this means that every geometry column belonging to a table has at least
three constraints:
enforce_dims_the_geom
 ensures every
geometry has the same dimension (see ST_NDims)
enforce_geotype_the_geom
 ensures every
geometry is of the same type (see GeometryType)
enforce_srid_the_geom
 ensures every
geometry is in the same projection (see ST_SRID)
If a table oid
is provided, this function
tries to determine the srid, dimension, and geometry type of all
geometry columns in the table, adding contraints as necessary. If
successful, an appropriate row is inserted into the geometry_columns
table, otherwise, the exception is caught and an error notice is raised
describing the problem.
If the oid
of a view is provided, as with a
table oid, this function tries to determine the srid, dimension, and
type of all the geometries in the view, inserting appropriate entries
into the geometry_columns
table, but nothing is done
to enforce contraints.
The parameterless variant is a simple wrapper for the parameterized
variant that first truncates and repopulates the geometry_columns table
for every spatial table and view in the database, adding spatial
contraints to tables where appropriate. It returns a summary of the
number of geometry columns detected in the database and the number that
were inserted into the geometry_columns
table. The
parameterized version simply returns the number of rows inserted into
the geometry_columns
table.
Availability: 1.4.0
Probe_Geometry_Columns — Scans all tables with PostGIS geometry constraints and adds them to the geometry_columns
table if they are not there.
text Probe_Geometry_Columns(
)
;
Scans all tables with PostGIS geometry constraints and adds them to the geometry_columns
table if they are not there. Also give stats on number of inserts and already present or possibly obsolete.
This will usually only pick up records added by AddGeometryColumn() function. It will not scan views so views will need to be manually added to geometry_columns table. 
UpdateGeometrySRID — Updates the SRID of all features in a geometry column, geometry_columns metadata and srid table constraint
text UpdateGeometrySRID(
varchar
table_name, varchar
column_name, integer
srid)
;
text UpdateGeometrySRID(
varchar
schema_name, varchar
table_name, varchar
column_name, integer
srid)
;
text UpdateGeometrySRID(
varchar
catalog_name, varchar
schema_name, varchar
table_name, varchar
column_name, integer
srid)
;
Updates the SRID of all features in a geometry column, updating constraints and reference in geometry_columns. Note: uses current_schema() on schemaaware pgsql installations if schema is not provided.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
LINESTRING
from WKB with the given SRIDST_BdPolyFromText — Construct a Polygon given an arbitrary collection of closed linestrings as a MultiLineString WellKnown text representation.
geometry ST_BdPolyFromText(
text WKT, integer srid)
;
Construct a Polygon given an arbitrary collection of closed linestrings as a MultiLineString WellKnown text representation.
Throws an error if WKT is not a MULTILINESTRING. Throws an error if output is a MULTIPOLYGON; use ST_BdMPolyFromText in that case, or see ST_BuildArea() for a postgisspecific approach. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
Availability: 1.1.0  requires GEOS >= 2.1.0.
ST_BdMPolyFromText — Construct a MultiPolygon given an arbitrary collection of closed linestrings as a MultiLineString text representation WellKnown text representation.
geometry ST_BdMPolyFromText(
text WKT, integer srid)
;
Construct a Polygon given an arbitrary collection of closed linestrings, polygons, MultiLineStrings as WellKnown text representation.
Throws an error if WKT is not a MULTILINESTRING. Forces MULTIPOLYGON output even when result is really only composed by a single POLYGON; use ST_BdPolyFromText if you're sure a single POLYGON will result from operation, or see ST_BuildArea() for a postgisspecific approach. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
Availability: 1.1.0  requires GEOS >= 2.1.0.
ST_GeogFromText — Return a specified geography value from WellKnown Text representation or extended (WKT).
geography ST_GeogFromText(
text EWKT)
;
ST_GeographyFromText — Return a specified geography value from WellKnown Text representation or extended (WKT).
geography ST_GeographyFromText(
text EWKT)
;
ST_GeogFromWKB — Creates a geography instance from a WellKnown Binary geometry representation (WKB) or extended Well Known Binary (EWKB).
geography ST_GeogFromWKB(
bytea geom)
;
The ST_GeogFromWKB
function, takes a wellknown
binary representation (WKB) of a geometry or PostGIS Extended WKB and creates an instance of the appropriate
geography type. This function plays the role of the Geometry Factory in
SQL.
If SRID is not specified, it defaults to 4326 (WGS 84 long lat).
This method supports Circular Strings and Curves
Although bytea rep contains single \, these need to be escaped when inserting into a table SELECT ST_AsText( ST_GeogFromWKB(E'\\001\\002\\000\\000\\000\\002\\000\\000\\000\\037\\205\\353Q\\270~\\\\\\300\\323Mb\\020X\\231C@\\020X9\\264\\310~\\\\\\300)\\\\\\217\\302\\365\\230C@') ); st_astext  LINESTRING(113.98 39.198,113.981 39.195) (1 row)
ST_GeomCollFromText — Makes a collection Geometry from collection WKT with the given SRID. If SRID is not give, it defaults to 1.
geometry ST_GeomCollFromText(
text WKT, integer srid)
;
geometry ST_GeomCollFromText(
text WKT)
;
Makes a collection Geometry from the WellKnownText (WKT) representation with the given SRID. If SRID is not give, it defaults to 1.
OGC SPEC 3.2.6.2  option SRID is from the conformance suite
Returns null if the WKT is not a GEOMETRYCOLLECTION
If you are absolutely sure all your WKT geometries are collections, don't use this function. It is slower than ST_GeomFromText since it adds an additional validation step. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
This method implements the SQL/MM specification.
ST_GeomFromEWKB — Return a specified ST_Geometry value from Extended WellKnown Binary representation (EWKB).
geometry ST_GeomFromEWKB(
bytea EWKB)
;
Constructs a PostGIS ST_Geometry object from the OGC Extended WellKnown binary (EWKT) representation.
The EWKB format is not an OGC standard, but a PostGIS specific format that includes the spatial reference system (SRID) identifier 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
line string binary rep 0f LINESTRING(71.160281 42.258729,71.160837 42.259113,71.161144 42.25932) in NAD 83 long lat (4269).
NOTE: Even though byte arrays are delimited with \ and may have ', we need to escape both out with \ and ''. So it does not look exactly like its AsEWKB representation. 
SELECT ST_GeomFromEWKB(E'\\001\\002\\000\\000 \\255\\020\\000\\000\\003\\000\\000\\000\\344J= \\013B\\312Q\\300n\\303(\\010\\036!E@''\\277E''K \\312Q\\300\\366{b\\235*!E@\\225\\354.P\\312Q \\300p\\231\\323e1!E@');
ST_GeomFromEWKT — Return a specified ST_Geometry value from Extended WellKnown Text representation (EWKT).
geometry ST_GeomFromEWKT(
text EWKT)
;
Constructs a PostGIS ST_Geometry object from the OGC Extended WellKnown text (EWKT) representation.
The EWKT format is not an OGC standard, but an PostGIS specific format that includes the spatial reference system (SRID) identifier 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_GeomFromEWKT('SRID=4269;LINESTRING(71.160281 42.258729,71.160837 42.259113,71.161144 42.25932)'); SELECT ST_GeomFromEWKT('SRID=4269;MULTILINESTRING((71.160281 42.258729,71.160837 42.259113,71.161144 42.25932))'); SELECT ST_GeomFromEWKT('SRID=4269;POINT(71.064544 42.28787)'); SELECT ST_GeomFromEWKT('SRID=4269;POLYGON((71.1776585052917 42.3902909739571,71.1776820268866 42.3903701743239, 71.1776063012595 42.3903825660754,71.1775826583081 42.3903033653531,71.1776585052917 42.3902909739571))'); SELECT ST_GeomFromEWKT('SRID=4269;MULTIPOLYGON(((71.1031880899493 42.3152774590236, 71.1031627617667 42.3152960829043,71.102923838298 42.3149156848307, 71.1023097974109 42.3151969047397,71.1019285062273 42.3147384934248, 71.102505233663 42.3144722937587,71.10277487471 42.3141658254797, 71.103113945163 42.3142739188902,71.10324876416 42.31402489987, 71.1033002961013 42.3140393340215,71.1033488797549 42.3139495090772, 71.103396240451 42.3138632439557,71.1041521907712 42.3141153348029, 71.1041411411543 42.3141545014533,71.1041287795912 42.3142114839058, 71.1041188134329 42.3142693656241,71.1041112482575 42.3143272556118, 71.1041072845732 42.3143851580048,71.1041057218871 42.3144430686681, 71.1041065602059 42.3145009876017,71.1041097995362 42.3145589148055, 71.1041166403905 42.3146168544148,71.1041258822717 42.3146748022936, 71.1041375307579 42.3147318674446,71.1041492906949 42.3147711126569, 71.1041598612795 42.314808571739,71.1042515013869 42.3151287620809, 71.1041173835118 42.3150739481917,71.1040809891419 42.3151344119048, 71.1040438678912 42.3151191367447,71.1040194562988 42.3151832057859, 71.1038734225584 42.3151140942995,71.1038446938243 42.3151006300338, 71.1038315271889 42.315094347535,71.1037393329282 42.315054824985, 71.1035447555574 42.3152608696313,71.1033436658644 42.3151648370544, 71.1032580383161 42.3152269126061,71.103223066939 42.3152517403219, 71.1031880899493 42.3152774590236)), ((71.1043632495873 42.315113108546,71.1043583974082 42.3151211109857, 71.1043443253471 42.3150676015829,71.1043850704575 42.3150793250568,71.1043632495873 42.315113108546)))'); 3d circular string SELECT ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)');
ST_GeometryFromText — Return a specified ST_Geometry value from WellKnown Text representation (WKT). This is an alias name for ST_GeomFromText
geometry ST_GeometryFromText(
text WKT)
;
geometry ST_GeometryFromText(
text WKT, integer srid)
;
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 5.1.40
ST_GeomFromGML — Takes as input GML representation of geometry and outputs a PostGIS geometry object
geometry ST_GeomFromGML(
text geomgml)
;
Constructs a PostGIS ST_Geometry object from the OGC GML representation.
ST_GeomFromGML works only for GML Geometry fragments. It throws an error if you try to use it on a whole GML document.
OGC GML versions supported:
GML 3.2.1 Namespace
GML 3.1.1 Simple Features profile SF2 (with GML 3.1.0 and 3.0.0 backward compatibility)
GML 2.1.2
OGC GML standards, cf: http://www.opengeospatial.org/standards/gml:
Availability: 1.5
This function supports 3d and will not drop the zindex.
GML allow mixed dimensions (2D and 3D inside the same MultiGeometry for instance). As PostGIS geometries don't, ST_GeomFromGML convert the whole geometry to 2D if a missing Z dimension is found once.
GML support mixed SRS inside the same MultiGeometry. As PostGIS geometries don't, ST_GeomFromGML, in this case, reproject all subgeometries to the SRS root node. If no srsName attribute available for the GML root node, the function throw an error.
ST_GeomFromGML function is not pedantic about an explicit GML namespace. You could avoid to mention it explicitly for common usages. But you need it if you want to use XLink feature inside GML.
ST_GeomFromGML function not support SQL/MM curves geometries. 
SELECT ST_GeomFromGML(' <gml:LineString srsName="EPSG:4269"> <gml:coordinates> 71.16028,42.258729 71.160837,42.259112 71.161143,42.25932 </gml:coordinates> </gml:LineString>');
ST_GeomFromGML(' <gml:LineString xmlns:gml="http://www.opengis.net/gml" xmlns:xlink="http://www.w3.org/1999/xlink" srsName="urn:ogc:def:crs:EPSG::4269"> <gml:pointProperty> <gml:Point gml:id="p1"><gml:pos>42.258729 71.16028</gml:pos></gml:Point> </gml:pointProperty> <gml:pos>42.259112 71.160837</gml:pos> <gml:pointProperty> <gml:Point xlink:type="simple" xlink:href="#p1"/> </gml:pointProperty> </gml:LineString>'););
ST_GeomFromKML — Takes as input KML representation of geometry and outputs a PostGIS geometry object
geometry ST_GeomFromKML(
text geomkml)
;
Constructs a PostGIS ST_Geometry object from the OGC KML representation.
ST_GeomFromKML works only for KML Geometry fragments. It throws an error if you try to use it on a whole KML document.
OGC KML versions supported:
KML 2.2.0 Namespace
OGC KML standards, cf: http://www.opengeospatial.org/standards/kml:
Availability: 1.5
This function supports 3d and will not drop the zindex.
ST_GeomFromKML function not support SQL/MM curves geometries. 
ST_GMLToSQL — Return a specified ST_Geometry value from GML representation. This is an alias name for ST_GeomFromGML
geometry ST_GMLToSQL(
text geomgml)
;
ST_GeomFromText — Return a specified ST_Geometry value from WellKnown Text representation (WKT).
geometry ST_GeomFromText(
text WKT)
;
geometry ST_GeomFromText(
text WKT, integer srid)
;
Constructs a PostGIS ST_Geometry object from the OGC WellKnown text representation.
There are 2 variants of ST_GeomFromText function, the first takes no SRID and returns a geometry with no defined spatial reference system. The second takes a spatial reference id as the second argument and returns an ST_Geometry that includes this srid as part of its metadata. The srid must be defined in the spatial_ref_sys table. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2  option SRID is from the conformance suite.
This method implements the SQL/MM specification. SQLMM 3: 5.1.40
This method supports Circular Strings and Curves
SELECT ST_GeomFromText('LINESTRING(71.160281 42.258729,71.160837 42.259113,71.161144 42.25932)'); SELECT ST_GeomFromText('LINESTRING(71.160281 42.258729,71.160837 42.259113,71.161144 42.25932)',4269); SELECT ST_GeomFromText('MULTILINESTRING((71.160281 42.258729,71.160837 42.259113,71.161144 42.25932))'); SELECT ST_GeomFromText('POINT(71.064544 42.28787)'); SELECT ST_GeomFromText('POLYGON((71.1776585052917 42.3902909739571,71.1776820268866 42.3903701743239, 71.1776063012595 42.3903825660754,71.1775826583081 42.3903033653531,71.1776585052917 42.3902909739571))'); SELECT ST_GeomFromText('MULTIPOLYGON(((71.1031880899493 42.3152774590236, 71.1031627617667 42.3152960829043,71.102923838298 42.3149156848307, 71.1023097974109 42.3151969047397,71.1019285062273 42.3147384934248, 71.102505233663 42.3144722937587,71.10277487471 42.3141658254797, 71.103113945163 42.3142739188902,71.10324876416 42.31402489987, 71.1033002961013 42.3140393340215,71.1033488797549 42.3139495090772, 71.103396240451 42.3138632439557,71.1041521907712 42.3141153348029, 71.1041411411543 42.3141545014533,71.1041287795912 42.3142114839058, 71.1041188134329 42.3142693656241,71.1041112482575 42.3143272556118, 71.1041072845732 42.3143851580048,71.1041057218871 42.3144430686681, 71.1041065602059 42.3145009876017,71.1041097995362 42.3145589148055, 71.1041166403905 42.3146168544148,71.1041258822717 42.3146748022936, 71.1041375307579 42.3147318674446,71.1041492906949 42.3147711126569, 71.1041598612795 42.314808571739,71.1042515013869 42.3151287620809, 71.1041173835118 42.3150739481917,71.1040809891419 42.3151344119048, 71.1040438678912 42.3151191367447,71.1040194562988 42.3151832057859, 71.1038734225584 42.3151140942995,71.1038446938243 42.3151006300338, 71.1038315271889 42.315094347535,71.1037393329282 42.315054824985, 71.1035447555574 42.3152608696313,71.1033436658644 42.3151648370544, 71.1032580383161 42.3152269126061,71.103223066939 42.3152517403219, 71.1031880899493 42.3152774590236)), ((71.1043632495873 42.315113108546,71.1043583974082 42.3151211109857, 71.1043443253471 42.3150676015829,71.1043850704575 42.3150793250568,71.1043632495873 42.315113108546)))',4326); SELECT ST_GeomFromText('CIRCULARSTRING(220268 150415,220227 150505,220227 150406)');
ST_GeomFromWKB — Creates a geometry instance from a WellKnown Binary geometry representation (WKB) and optional SRID.
geometry ST_GeomFromWKB(
bytea geom)
;
geometry ST_GeomFromWKB(
bytea geom, integer srid)
;
The ST_GeomFromWKB
function, takes a wellknown
binary representation of a geometry and a Spatial Reference System ID
(SRID
) and creates an instance of the appropriate
geometry type. This function plays the role of the Geometry Factory in
SQL. This is an alternate name for ST_WKBToSQL.
If SRID is not specified, it defaults to 1 (Unknown).
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.7.2  the optional SRID is from the conformance suite
This method implements the SQL/MM specification. SQLMM 3: 5.1.41
This method supports Circular Strings and Curves
Although bytea rep contains single \, these need to be escaped when inserting into a table SELECT ST_AsEWKT( ST_GeomFromWKB(E'\\001\\002\\000\\000\\000\\002\\000\\000\\000\\037\\205\\353Q\\270~\\\\\\300\\323Mb\\020X\\231C@\\020X9\\264\\310~\\\\\\300)\\\\\\217\\302\\365\\230C@',4326) ); st_asewkt  SRID=4326;LINESTRING(113.98 39.198,113.981 39.195) (1 row) SELECT ST_AsText( ST_GeomFromWKB( ST_AsEWKB('POINT(2 5)'::geometry) ) ); st_astext  POINT(2 5) (1 row)
ST_LineFromMultiPoint — Creates a LineString from a MultiPoint geometry.
geometry ST_LineFromMultiPoint(
geometry aMultiPoint)
;
Creates a LineString from a MultiPoint geometry.
This function supports 3d and will not drop the zindex.
ST_LineFromText — Makes a Geometry from WKT representation with the given SRID. If SRID is not given, it defaults to 1.
geometry ST_LineFromText(
text WKT)
;
geometry ST_LineFromText(
text WKT, integer srid)
;
Makes a Geometry from WKT with the given SRID. If SRID is not give, it defaults to 1. If WKT passed in is not a LINESTRING, then null is returned.
OGC SPEC 3.2.6.2  option SRID is from the conformance suite. 
If you know all your geometries are LINESTRINGS, its more efficient to just use ST_GeomFromText. This just calls ST_GeomFromText and adds additional validation that it returns a linestring. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
This method implements the SQL/MM specification. SQLMM 3: 7.2.8
ST_LineFromWKB — Makes a LINESTRING
from WKB with the given SRID
geometry ST_LineFromWKB(
bytea WKB)
;
geometry ST_LineFromWKB(
bytea WKB, integer srid)
;
The ST_LineFromWKB
function, takes a wellknown binary
representation of geometry and a Spatial Reference System ID (SRID
)
and creates an instance of the appropriate geometry type  in this case, a
LINESTRING
geometry. This function plays the role of the Geometry
Factory in SQL.
If an SRID is not specified, it defaults to 1. NULL
is
returned if the input bytea
does not represent a LINESTRING
.
OGC SPEC 3.2.6.2  option SRID is from the conformance suite. 
If you know all your geometries are 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
This method implements the SQL/MM specification. SQLMM 3: 7.2.9
ST_LinestringFromWKB — Makes a geometry from WKB with the given SRID.
geometry ST_LinestringFromWKB(
bytea WKB)
;
geometry ST_LinestringFromWKB(
bytea WKB, integer srid)
;
The ST_LinestringFromWKB
function, takes a wellknown binary
representation of geometry and a Spatial Reference System ID (SRID
)
and creates an instance of the appropriate geometry type  in this case, a
LINESTRING
geometry. This function plays the role of the Geometry
Factory in SQL.
If an SRID is not specified, it defaults to 1. NULL
is
returned if the input bytea
does not represent a
LINESTRING
geometry. This an alias for ST_LineFromWKB.
OGC SPEC 3.2.6.2  optional SRID is from the conformance suite. 
If you know all your geometries are 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
This method implements the SQL/MM specification. SQLMM 3: 7.2.9
SELECT ST_LineStringFromWKB( ST_AsBinary(ST_GeomFromText('LINESTRING(1 2, 3 4)')) ) AS aline, ST_LinestringFromWKB( ST_AsBinary(ST_GeomFromText('POINT(1 2)')) ) IS NULL AS null_return; aline  null_return  010200000002000000000000000000F ...  t
ST_MakeBox2D — Creates a BOX2D defined by the given point geometries.
box2d ST_MakeBox2D(
geometry pointLowLeft, geometry pointUpRight)
;
Creates a BOX2D defined by the given point geometries. This is useful for doing range queries
Return all features that fall reside or partly reside in a US national atlas coordinate bounding box It is assumed here that the geometries are stored with SRID = 2163 (US National atlas equal area) SELECT feature_id, feature_name, the_geom FROM features WHERE the_geom && ST_SetSRID(ST_MakeBox2D(ST_Point(989502.1875, 528439.5625), ST_Point(987121.375 ,529933.1875)),2163)
ST_MakeBox3D — Creates a BOX3D defined by the given 3d point geometries.
box3d ST_MakeBox3D(
geometry point3DLowLeftBottom, geometry point3DUpRightTop)
;
Creates a BOX3D defined by the given 2 3D point geometries.
This function supports 3d and will not drop the zindex.
ST_MakeLine — Creates a Linestring from point geometries.
geometry ST_MakeLine(
geometry set pointfield)
;
geometry ST_MakeLine(
geometry point1, geometry point2)
;
geometry ST_MakeLine(
geometry[] point_array)
;
ST_MakeLine comes in 3 forms: a spatial aggregate that takes rows of point geometries and returns a line string, a function that takes an array of points, and a regular function that takes two point geometries. You might want to use a subselect to order points before feeding them to the aggregate version of this function.
This function supports 3d and will not drop the zindex.
Availability: 1.4.0  ST_MakeLine(geomarray) was introduced. ST_MakeLine aggregate functions was enhanced to handle more points faster.
This example takes a sequence of GPS points and creates one record for each gps travel where the geometry field is a line string composed of the gps points in the order of the travel.
SELECT gps.gps_track, ST_MakeLine(gps.the_geom) As newgeom FROM (SELECT gps_track,gps_time, the_geom FROM gps_points ORDER BY gps_track, gps_time) As gps GROUP BY gps.gps_track
First example is a simple one off line string composed of 2 points. The second formulates line strings from 2 points a user draws. The third is a oneoff that joins 2 3d points to create a line in 3d space.
SELECT ST_AsText(ST_MakeLine(ST_MakePoint(1,2), ST_MakePoint(3,4))); st_astext  LINESTRING(1 2,3 4) SELECT userpoints.id, ST_MakeLine(startpoint, endpoint) As drawn_line FROM userpoints ; SELECT ST_AsEWKT(ST_MakeLine(ST_MakePoint(1,2,3), ST_MakePoint(3,4,5))); st_asewkt  LINESTRING(1 2 3,3 4 5)
SELECT ST_MakeLine(ARRAY(SELECT ST_Centroid(the_geom) FROM visit_locations ORDER BY visit_time)); Making a 3d line with 3 3d points SELECT ST_AsEWKT(ST_MakeLine(ARRAY[ST_MakePoint(1,2,3), ST_MakePoint(3,4,5), ST_MakePoint(6,6,6)])); st_asewkt  LINESTRING(1 2 3,3 4 5,6 6 6)
ST_MakeEnvelope — Creates a rectangular Polygon formed from the given minimums and maximums. Input values must be in SRS specified by the SRID.
geometry ST_MakeEnvelope(
double precision xmin, double precision ymin, double precision xmax, double precision ymax, integer srid)
;
Creates a rectangular Polygon formed from the minima and maxima. by the given shell. Input values must be in SRS specified by the SRID.
Availability: 1.5
ST_MakePolygon — Creates a Polygon formed by the given shell. Input geometries must be closed LINESTRINGS.
geometry ST_MakePolygon(
geometry linestring)
;
geometry ST_MakePolygon(
geometry outerlinestring, geometry[] interiorlinestrings)
;
Creates a Polygon formed by the given shell. Input geometries must be closed LINESTRINGS. Comes in 2 variants.
Variant 1: takes one closed linestring.
Variant 2: Creates a Polygon formed by the given shell and array of holes. You can construct a geometry array using ST_Accum or the PostgreSQL ARRAY[] and ARRAY() constructs. Input geometries must be closed LINESTRINGS.
This function will not accept a MULTILINESTRING. Use ST_LineMerge or ST_Dump to generate line strings. 
This function supports 3d and will not drop the zindex.
2d line SELECT ST_MakePolygon(ST_GeomFromText('LINESTRING(75.15 29.53,77 29,77.6 29.5, 75.15 29.53)')); If linestring is not closed you can add the start point to close it SELECT ST_MakePolygon(ST_AddPoint(foo.open_line, ST_StartPoint(foo.open_line))) FROM ( SELECT ST_GeomFromText('LINESTRING(75.15 29.53,77 29,77.6 29.5)') As open_line) As foo; 3d closed line SELECT ST_MakePolygon(ST_GeomFromText('LINESTRING(75.15 29.53 1,77 29 1,77.6 29.5 1, 75.15 29.53 1)')); st_asewkt  POLYGON((75.15 29.53 1,77 29 1,77.6 29.5 1,75.15 29.53 1)) measured line  SELECT ST_MakePolygon(ST_GeomFromText('LINESTRINGM(75.15 29.53 1,77 29 1,77.6 29.5 2, 75.15 29.53 2)')); st_asewkt  POLYGONM((75.15 29.53 1,77 29 1,77.6 29.5 2,75.15 29.53 2))
Build a donut with an ant hole
SELECT ST_MakePolygon( ST_ExteriorRing(ST_Buffer(foo.line,10)), ARRAY[ST_Translate(foo.line,1,1), ST_ExteriorRing(ST_Buffer(ST_MakePoint(20,20),1)) ] ) FROM (SELECT ST_ExteriorRing(ST_Buffer(ST_MakePoint(10,10),10,10)) As line ) As foo;
Build province boundaries with holes representing lakes in the province from a set of province polygons/multipolygons and water line strings this is an example of using PostGIS ST_Accum
The use of CASE because feeding a null array into ST_MakePolygon results in NULL 
the use of left join to guarantee we get all provinces back even if they have no lakes 
SELECT p.gid, p.province_name, CASE WHEN ST_Accum(w.the_geom) IS NULL THEN p.the_geom ELSE ST_MakePolygon(ST_LineMerge(ST_Boundary(p.the_geom)), ST_Accum(w.the_geom)) END FROM provinces p LEFT JOIN waterlines w ON (ST_Within(w.the_geom, p.the_geom) AND ST_IsClosed(w.the_geom)) GROUP BY p.gid, p.province_name, p.the_geom; Same example above but utilizing a correlated subquery and PostgreSQL builtin ARRAY() function that converts a row set to an array SELECT p.gid, p.province_name, CASE WHEN EXISTS(SELECT w.the_geom FROM waterlines w WHERE ST_Within(w.the_geom, p.the_geom) AND ST_IsClosed(w.the_geom)) THEN ST_MakePolygon(ST_LineMerge(ST_Boundary(p.the_geom)), ARRAY(SELECT w.the_geom FROM waterlines w WHERE ST_Within(w.the_geom, p.the_geom) AND ST_IsClosed(w.the_geom))) ELSE p.the_geom END As the_geom FROM provinces p;
ST_MakePoint — Creates a 2D,3DZ or 4D point geometry.
geometry ST_MakePoint(
double precision x, double precision y)
;
geometry ST_MakePoint(
double precision x, double precision y, double precision z)
;
geometry ST_MakePoint(
double precision x, double precision y, double precision z, double precision m)
;
Creates a 2D,3DZ or 4D point geometry (geometry with measure).
ST_MakePoint
while not being OGC compliant is
generally faster and more precise than ST_GeomFromText
and ST_PointFromText. It is also easier to use if
you have raw coordinates rather than WKT.
Note x is longitude and y is latitude 
This function supports 3d and will not drop the zindex.
Return point with unknown SRID SELECT ST_MakePoint(71.1043443253471, 42.3150676015829); Return point marked as WGS 84 long lat SELECT ST_SetSRID(ST_MakePoint(71.1043443253471, 42.3150676015829),4326); Return a 3D point (e.g. has altitude) SELECT ST_MakePoint(1, 2,1.5); Get z of point SELECT ST_Z(ST_MakePoint(1, 2,1.5)); result  1.5
ST_MakePointM — Creates a point geometry with an x y and m coordinate.
geometry ST_MakePointM(
float x, float y, float m)
;
Creates a point with x, y and measure coordinates.
Note x is longitude and y is latitude. 
We use ST_AsEWKT in these examples to show the text representation instead of ST_AsText because ST_AsText does not support returning M.
Return EWKT representation of point with unknown SRID SELECT ST_AsEWKT(ST_MakePointM(71.1043443253471, 42.3150676015829, 10)); result st_asewkt  POINTM(71.1043443253471 42.3150676015829 10) Return EWKT representation of point with measure marked as WGS 84 long lat SELECT ST_AsEWKT(ST_SetSRID(ST_MakePointM(71.1043443253471, 42.3150676015829,10),4326)); st_asewkt  SRID=4326;POINTM(71.1043443253471 42.3150676015829 10) Return a 3d point (e.g. has altitude) SELECT ST_MakePoint(1, 2,1.5); Get m of point SELECT ST_M(ST_MakePointM(71.1043443253471, 42.3150676015829,10)); result  10
ST_MLineFromText — Return a specified ST_MultiLineString value from WKT representation.
geometry ST_MLineFromText(
text WKT, integer srid)
;
geometry ST_MLineFromText(
text WKT)
;
Makes a Geometry from WellKnownText (WKT) with the given SRID. If SRID is not give, it defaults to 1.
OGC SPEC 3.2.6.2  option SRID is from the conformance suite
Returns null if the WKT is not a MULTILINESTRING
If you are absolutely sure all your WKT geometries are points, don't use this function. It is slower than ST_GeomFromText since it adds an additional validation step. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
This method implements the SQL/MM specification.SQLMM 3: 9.4.4
ST_MPointFromText — Makes a Geometry from WKT with the given SRID. If SRID is not give, it defaults to 1.
geometry ST_MPointFromText(
text WKT, integer srid)
;
geometry ST_MPointFromText(
text WKT)
;
Makes a Geometry from WKT with the given SRID. If SRID is not give, it defaults to 1.
OGC SPEC 3.2.6.2  option SRID is from the conformance suite
Returns null if the WKT is not a MULTIPOINT
If you are absolutely sure all your WKT geometries are points, don't use this function. It is slower than ST_GeomFromText since it adds an additional validation step. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. 3.2.6.2
This method implements the SQL/MM specification. SQLMM 3: 9.2.4
ST_MPolyFromText — Makes a MultiPolygon Geometry from WKT with the given SRID. If SRID is not give, it defaults to 1.
geometry ST_MPolyFromText(
text WKT, integer srid)
;
geometry ST_MPolyFromText(
text WKT)
;
Makes a MultiPolygon from WKT with the given SRID. If SRID is not give, it defaults to 1.
OGC SPEC 3.2.6.2  option SRID is from the conformance suite
Throws an error if the WKT is not a MULTIPOLYGON
If you are absolutely sure all your WKT geometries are multipolygons, don't use this function. It is slower than ST_GeomFromText since it adds an additional validation step. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
This method implements the SQL/MM specification. SQLMM 3: 9.6.4
SELECT ST_MPolyFromText('MULTIPOLYGON(((0 0 1,20 0 1,20 20 1,0 20 1,0 0 1),(5 5 3,5 7 3,7 7 3,7 5 3,5 5 3)))'); SELECt ST_MPolyFromText('MULTIPOLYGON(((70.916 42.1002,70.9468 42.0946,70.9765 42.0872,70.9754 42.0875,70.9749 42.0879,70.9752 42.0881,70.9754 42.0891,70.9758 42.0894,70.9759 42.0897,70.9759 42.0899,70.9754 42.0902,70.9756 42.0906,70.9753 42.0907,70.9753 42.0917,70.9757 42.0924,70.9755 42.0928,70.9755 42.0942,70.9751 42.0948,70.9755 42.0953,70.9751 42.0958,70.9751 42.0962,70.9759 42.0983,70.9767 42.0987,70.9768 42.0991,70.9771 42.0997,70.9771 42.1003,70.9768 42.1005,70.977 42.1011,70.9766 42.1019,70.9768 42.1026,70.9769 42.1033,70.9775 42.1042,70.9773 42.1043,70.9776 42.1043,70.9778 42.1048,70.9773 42.1058,70.9774 42.1061,70.9779 42.1065,70.9782 42.1078,70.9788 42.1085,70.9798 42.1087,70.9806 42.109,70.9807 42.1093,70.9806 42.1099,70.9809 42.1109,70.9808 42.1112,70.9798 42.1116,70.9792 42.1127,70.979 42.1129,70.9787 42.1134,70.979 42.1139,70.9791 42.1141,70.9987 42.1116,71.0022 42.1273, 70.9408 42.1513,70.9315 42.1165,70.916 42.1002)))',4326);
ST_Point — Returns an ST_Point with the given coordinate values. OGC alias for ST_MakePoint.
geometry ST_Point(
float x_lon, float y_lat)
;
ST_PointFromText — Makes a point Geometry from WKT with the given SRID. If SRID is not given, it defaults to unknown.
geometry ST_PointFromText(
text WKT)
;
geometry ST_PointFromText(
text WKT, integer srid)
;
Constructs a PostGIS ST_Geometry point object from the OGC WellKnown text representation. If SRID is not give, it defaults to unknown (currently 1). If geometry is not a WKT point representation, returns null. If completely invalid WKT, then throws an error.
There are 2 variants of ST_PointFromText function, the first takes no SRID and returns a geometry with no defined spatial reference system. The second takes a spatial reference id as the second argument and returns an ST_Geometry that includes this srid as part of its metadata. The srid must be defined in the spatial_ref_sys table. 
If you are absolutely sure all your WKT geometries are points, don't use this function. It is slower than ST_GeomFromText since it adds an additional validation step. If you are building points from long lat coordinates and care more about performance and accuracy than OGC compliance, use ST_MakePoint or OGC compliant alias ST_Point. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2  option SRID is from the conformance suite.
This method implements the SQL/MM specification. SQLMM 3: 6.1.8
ST_PointFromWKB — Makes a geometry from WKB with the given SRID
geometry ST_GeomFromWKB(
bytea geom)
;
geometry ST_GeomFromWKB(
bytea geom, integer srid)
;
The ST_PointFromWKB
function, takes a wellknown binary
representation of geometry and a Spatial Reference System ID (SRID
)
and creates an instance of the appropriate geometry type  in this case, a
POINT
geometry. This function plays the role of the Geometry
Factory in SQL.
If an SRID is not specified, it defaults to 1. NULL
is
returned if the input bytea
does not represent a
POINT
geometry.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.7.2
This method implements the SQL/MM specification. SQLMM 3: 6.1.9
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
ST_Polygon — Returns a polygon built from the specified linestring and SRID.
geometry ST_Polygon(
geometry aLineString, integer srid)
;
Returns a polygon built from the specified linestring and SRID.
ST_Polygon is similar to first version oST_MakePolygon except it also sets the spatial ref sys (SRID) of the polygon. Will not work with MULTILINESTRINGS so use LineMerge to merge multilines. Also does not create polygons with holes. Use ST_MakePolygon for that. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 8.3.2
This function supports 3d and will not drop the zindex.
a 2d polygon SELECT ST_Polygon(ST_GeomFromText('LINESTRING(75.15 29.53,77 29,77.6 29.5, 75.15 29.53)'), 4326); result POLYGON((75.15 29.53,77 29,77.6 29.5,75.15 29.53)) a 3d polygon SELECT ST_AsEWKT(ST_Polygon(ST_GeomFromEWKT('LINESTRING(75.15 29.53 1,77 29 1,77.6 29.5 1, 75.15 29.53 1)'), 4326)); result  SRID=4326;POLYGON((75.15 29.53 1,77 29 1,77.6 29.5 1,75.15 29.53 1))
ST_PolygonFromText — Makes a Geometry from WKT with the given SRID. If SRID is not give, it defaults to 1.
geometry ST_PolygonFromText(
text WKT)
;
geometry ST_PolygonFromText(
text WKT, integer srid)
;
Makes a Geometry from WKT with the given SRID. If SRID is not give, it defaults to 1. Returns null if WKT is not a polygon.
OGC SPEC 3.2.6.2  option SRID is from the conformance suite
If you are absolutely sure all your WKT geometries are polygons, don't use this function. It is slower than ST_GeomFromText since it adds an additional validation step. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.6.2
This method implements the SQL/MM specification. SQLMM 3: 8.3.6
SELECT ST_PolygonFromText('POLYGON((71.1776585052917 42.3902909739571,71.1776820268866 42.3903701743239, 71.1776063012595 42.3903825660754,71.1775826583081 42.3903033653531,71.1776585052917 42.3902909739571))'); st_polygonfromtext  010300000001000000050000006... SELECT ST_PolygonFromText('POINT(1 2)') IS NULL as point_is_notpoly; point_is_not_poly  t
ST_WKBToSQL — Return a specified ST_Geometry value from WellKnown Binary representation (WKB). This is an alias name for ST_GeomFromWKB that takes no srid
geometry ST_WKBToSQL(
bytea WKB)
;
Return the coordinate dimension of the ST_Geometry value.
LINESTRING
geometry as a POINT
.POLYGON
geometry. Return
NULL if the geometry is not a polygon. Will not work with MULTIPOLYGONTRUE
if the
LINESTRING
's start and end points are coincident.
TRUE
if this
LINESTRING
is both closed and simple.true
if the
ST_Geometry
is well formed.
LINESTRING
geometry as a POINT
.ST_Geometry
.
GeometryType — Returns the type of the geometry as a string. Eg: 'LINESTRING', 'POLYGON', 'MULTIPOINT', etc.
text GeometryType(
geometry geomA)
;
Returns the type of the geometry as a string. Eg: 'LINESTRING', 'POLYGON', 'MULTIPOINT', etc.
OGC SPEC s2.1.1.1  Returns the name of the instantiable subtype of Geometry of which this Geometry instance is a member. The name of the instantiable subtype of Geometry is returned as a string.
This function also indicates if the geometry is measured, by returning a string of the form 'POINTM'. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method supports Circular Strings and Curves
ST_Boundary — Returns the closure of the combinatorial boundary of this Geometry.
geometry ST_Boundary(
geometry geomA)
;
Returns the closure of the combinatorial boundary of this Geometry. The combinatorial boundary is defined as described in section 3.12.3.2 of the OGC SPEC. Because the result of this function is a closure, and hence topologically closed, the resulting boundary can be represented using representational geometry primitives as discussed in the OGC SPEC, section 3.12.2.
Performed by the GEOS module
Do not call with a 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. OGC SPEC s2.1.1.1
This method implements the SQL/MM specification. SQLMM 3: 5.1.14
This function supports 3d and will not drop the zindex.
SELECT ST_AsText(ST_Boundary(ST_GeomFromText('LINESTRING(1 1,0 0, 1 1)'))); st_astext  MULTIPOINT(1 1,1 1) SELECT ST_AsText(ST_Boundary(ST_GeomFromText('POLYGON((1 1,0 0, 1 1, 1 1))'))); st_astext  LINESTRING(1 1,0 0,1 1,1 1) Using a 3d polygon SELECT ST_AsEWKT(ST_Boundary(ST_GeomFromEWKT('POLYGON((1 1 1,0 0 1, 1 1 1, 1 1 1))'))); st_asewkt  LINESTRING(1 1 1,0 0 1,1 1 1,1 1 1) Using a 3d multilinestring SELECT ST_AsEWKT(ST_Boundary(ST_GeomFromEWKT('MULTILINESTRING((1 1 1,0 0 0.5, 1 1 1),(1 1 0.5,0 0 0.5, 1 1 0.5, 1 1 0.5) )'))); st_asewkt  MULTIPOINT(1 1 1,1 1 0.75)
ST_CoordDim —
Return the coordinate dimension of the ST_Geometry value.
integer ST_CoordDim(
geometry geomA)
;
Return the coordinate dimension of the ST_Geometry value.
This is the MM compliant alias name for ST_NDims
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 5.1.3
This method supports Circular Strings and Curves
This function supports 3d and will not drop the zindex.
ST_Dimension — The inherent dimension of this Geometry object, which must be less than or equal to the coordinate dimension.
integer ST_Dimension(
geometry g)
;
The inherent dimension of this Geometry object, which must
be less than or equal to the coordinate dimension. OGC SPEC
s2.1.1.1  returns 0 for POINT
, 1 for LINESTRING
, 2 for POLYGON
, and
the largest dimension of the components of a
GEOMETRYCOLLECTION
.
This method implements the SQL/MM specification. SQLMM 3: 5.1.2
ST_EndPoint — Returns the last point of a LINESTRING
geometry as a POINT
.
boolean ST_EndPoint(
geometry g)
;
Returns the last point of a LINESTRING
geometry
as a POINT
or NULL
if the input
parameter is not a LINESTRING
.
This method implements the SQL/MM specification. SQLMM 3: 7.1.4
This function supports 3d and will not drop the zindex.
postgis=# SELECT ST_AsText(ST_EndPoint('LINESTRING(1 1, 2 2, 3 3)'::geometry)); st_astext  POINT(3 3) (1 row) postgis=# SELECT ST_EndPoint('POINT(1 1)'::geometry) IS NULL AS is_null; is_null  t (1 row) 3d endpoint SELECT ST_AsEWKT(ST_EndPoint('LINESTRING(1 1 2, 1 2 3, 0 0 5)')); st_asewkt  POINT(0 0 5) (1 row)
ST_Envelope — Returns a geometry representing the double precision (float8) bounding box of the supplied geometry.
geometry ST_Envelope(
geometry g1)
;
Returns the float8 minimum bounding box for the supplied geometry, as a geometry.
The polygon is defined by the corner points of the bounding box
((MINX
, MINY
),
(MINX
, MAXY
),
(MAXX
, MAXY
),
(MAXX
, MINY
),
(MINX
, MINY
)). (PostGIS will add a
ZMIN
/ZMAX
coordinate as
well).
Degenerate cases (vertical lines, points) will return a geometry of
lower dimension than POLYGON
, ie.
POINT
or LINESTRING
.
Availability: 1.5.0 behavior changed to output double precision instead of float4
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.1
This method implements the SQL/MM specification. SQLMM 3: 5.1.15
SELECT ST_AsText(ST_Envelope('POINT(1 3)'::geometry)); st_astext  POINT(1 3) (1 row) SELECT ST_AsText(ST_Envelope('LINESTRING(0 0, 1 3)'::geometry)); st_astext  POLYGON((0 0,0 3,1 3,1 0,0 0)) (1 row) SELECT ST_AsText(ST_Envelope('POLYGON((0 0, 0 1, 1.0000001 1, 1.0000001 0, 0 0))'::geometry)); st_astext  POLYGON((0 0,0 1,1.00000011920929 1,1.00000011920929 0,0 0)) (1 row) SELECT ST_AsText(ST_Envelope('POLYGON((0 0, 0 1, 1.0000000001 1, 1.0000000001 0, 0 0))'::geometry)); st_astext  POLYGON((0 0,0 1,1.00000011920929 1,1.00000011920929 0,0 0)) (1 row) SELECT Box3D(geom), Box2D(geom), ST_AsText(ST_Envelope(geom)) As envelopewkt FROM (SELECT 'POLYGON((0 0, 0 1000012333334.34545678, 1.0000001 1, 1.0000001 0, 0 0))'::geometry As geom) As foo;
ST_ExteriorRing — Returns a line string representing the exterior ring of the POLYGON
geometry. Return
NULL if the geometry is not a polygon. Will not work with MULTIPOLYGON
geometry ST_ExteriorRing(
geometry a_polygon)
;
Returns a line string representing the exterior ring of the POLYGON
geometry. Return
NULL if the geometry is not a polygon.
Only works with POLYGON geometry types 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. 2.1.5.1
This method implements the SQL/MM specification. SQLMM 3: 8.2.3, 8.3.3
This function supports 3d and will not drop the zindex.
If you have a table of polygons SELECT gid, ST_ExteriorRing(the_geom) AS ering FROM sometable; If you have a table of MULTIPOLYGONs and want to return a MULTILINESTRING composed of the exterior rings of each polygon SELECT gid, ST_Collect(ST_ExteriorRing(the_geom)) AS erings FROM (SELECT gid, (ST_Dump(the_geom)).geom As the_geom FROM sometable) As foo GROUP BY gid; 3d Example SELECT ST_AsEWKT( ST_ExteriorRing( ST_GeomFromEWKT('POLYGON((0 0 1, 1 1 1, 1 2 1, 1 1 1, 0 0 1))') ) ); st_asewkt  LINESTRING(0 0 1,1 1 1,1 2 1,1 1 1,0 0 1)
ST_GeometryN — Return the 1based Nth geometry if the geometry is a GEOMETRYCOLLECTION, MULTIPOINT, MULTILINESTRING, MULTICURVE or MULTIPOLYGON. Otherwise, return NULL.
geometry ST_GeometryN(
geometry geomA, integer n)
;
Return the 1based Nth geometry if the geometry is a GEOMETRYCOLLECTION, MULTIPOINT, MULTILINESTRING, MULTICURVE or MULTIPOLYGON. Otherwise, return NULL.
Index is 1based as for OGC specs since version 0.8.0. Previous versions implemented this as 0based instead. 
If you want to extract all geometries, of a geometry, ST_Dump is more efficient and will also work for singular geoms. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 9.1.5
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Extracting a subset of points from a 3d multipoint SELECT n, ST_AsEWKT(ST_GeometryN(the_geom, n)) As geomewkt FROM ( VALUES (ST_GeomFromEWKT('MULTIPOINT(1 2 7, 3 4 7, 5 6 7, 8 9 10)') ), ( ST_GeomFromEWKT('MULTICURVE(CIRCULARSTRING(2.5 2.5,4.5 2.5, 3.5 3.5), (10 11, 12 11))') ) )As foo(the_geom) CROSS JOIN generate_series(1,100) n WHERE n <= ST_NumGeometries(the_geom); n  geomewkt + 1  POINT(1 2 7) 2  POINT(3 4 7) 3  POINT(5 6 7) 4  POINT(8 9 10) 1  CIRCULARSTRING(2.5 2.5,4.5 2.5,3.5 3.5) 2  LINESTRING(10 11,12 11) Extracting all geometries (useful when you want to assign an id) SELECT gid, n, ST_GeometryN(the_geom, n) FROM sometable CROSS JOIN generate_series(1,100) n WHERE n <= ST_NumGeometries(the_geom);
ST_GeometryType — Return the geometry type of the ST_Geometry value.
text ST_GeometryType(
geometry g1)
;
Returns the type of the geometry as a string. EG: 'ST_Linestring', 'ST_Polygon','ST_MultiPolygon' etc. This function differs from GeometryType(geometry) in the case of the string and ST in front that is returned, as well as the fact that it will not indicate whether the geometry is measured.
This method implements the SQL/MM specification. SQLMM 3: 5.1.4
ST_InteriorRingN — Return the Nth interior linestring ring of the polygon geometry. Return NULL if the geometry is not a polygon or the given N is out of range.
geometry ST_InteriorRingN(
geometry a_polygon, integer n)
;
Return the Nth interior linestring ring of the polygon geometry. Return NULL if the geometry is not a polygon or the given N is out of range. index starts at 1.
This will not work for MULTIPOLYGONs. Use in conjunction with ST_Dump for MULTIPOLYGONS 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 8.2.6, 8.3.5
This function supports 3d and will not drop the zindex.
ST_IsClosed — Returns TRUE
if the
LINESTRING
's start and end points are coincident.
boolean ST_IsClosed(
geometry g)
;
Returns TRUE
if the LINESTRING
's
start and end points are coincident.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 7.1.5, 9.3.3
SQLMM defines the result of

This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
postgis=# SELECT ST_IsClosed('LINESTRING(0 0, 1 1)'::geometry); st_isclosed  f (1 row) postgis=# SELECT ST_IsClosed('LINESTRING(0 0, 0 1, 1 1, 0 0)'::geometry); st_isclosed  t (1 row) postgis=# SELECT ST_IsClosed('MULTILINESTRING((0 0, 0 1, 1 1, 0 0),(0 0, 1 1))'::geometry); st_isclosed  f (1 row) postgis=# SELECT ST_IsClosed('POINT(0 0)'::geometry); st_isclosed  t (1 row) postgis=# SELECT ST_IsClosed('MULTIPOINT((0 0), (1 1))'::geometry); st_isclosed  t (1 row)
ST_IsEmpty — Returns true if this Geometry is an empty geometry . If true, then this Geometry represents the empty point set  i.e. GEOMETRYCOLLECTION(EMPTY).
boolean ST_IsEmpty(
geometry geomA)
;
Returns true if this Geometry is an empty geometry . If true, then this Geometry represents an empty geometry collection, polygon, point etc.
SQLMM defines the result of ST_IsEmpty(NULL) to be 0, while PostGIS returns NULL. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.1
This method implements the SQL/MM specification. SQLMM 3: 5.1.7
This method supports Circular Strings and Curves
SELECT ST_IsEmpty('GEOMETRYCOLLECTION(EMPTY)'); st_isempty  t (1 row) SELECT ST_IsEmpty(ST_GeomFromText('POLYGON EMPTY')); st_isempty  t (1 row) SELECT ST_IsEmpty(ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))')); st_isempty  f (1 row) SELECT ST_IsEmpty(ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))')) = false; ?column?  t (1 row) SELECT ST_IsEmpty(ST_GeomFromText('CIRCULARSTRING EMPTY')); st_isempty  t (1 row)
ST_IsRing — Returns TRUE
if this
LINESTRING
is both closed and simple.
boolean ST_IsRing(
geometry g)
;
Returns TRUE
if this
LINESTRING
is both ST_IsClosed
(ST_StartPoint(
g
)~=
ST_Endpoint(
) and ST_IsSimple (does not self intersect).g
)
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. 2.1.5.1
This method implements the SQL/MM specification. SQLMM 3: 7.1.6
SQLMM defines the result of

SELECT ST_IsRing(the_geom), ST_IsClosed(the_geom), ST_IsSimple(the_geom) FROM (SELECT 'LINESTRING(0 0, 0 1, 1 1, 1 0, 0 0)'::geometry AS the_geom) AS foo; st_isring  st_isclosed  st_issimple ++ t  t  t (1 row) SELECT ST_IsRing(the_geom), ST_IsClosed(the_geom), ST_IsSimple(the_geom) FROM (SELECT 'LINESTRING(0 0, 0 1, 1 0, 1 1, 0 0)'::geometry AS the_geom) AS foo; st_isring  st_isclosed  st_issimple ++ f  t  f (1 row)
ST_IsSimple — Returns (TRUE) if this Geometry has no anomalous geometric points, such as self intersection or self tangency.
boolean ST_IsSimple(
geometry geomA)
;
Returns true if this Geometry has no anomalous geometric points, such as self intersection or self tangency. For more information on the OGC's definition of geometry simplicity and validity, refer to "Ensuring OpenGIS compliancy of geometries"
SQLMM defines the result of ST_IsSimple(NULL) to be 0, while PostGIS returns NULL. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.1
This method implements the SQL/MM specification. SQLMM 3: 5.1.8
This function supports 3d and will not drop the zindex.
ST_IsValid — Returns true
if the
ST_Geometry
is well formed.
boolean ST_IsValid(
geometry g)
;
Test if an ST_Geometry value is well formed. For geometries that are invalid, the PostgreSQL NOTICE will provide details of why it is not valid. For more information on the OGC's definition of geometry simplicity and validity, refer to "Ensuring OpenGIS compliancy of geometries"
SQLMM defines the result of ST_IsValid(NULL) to be 0, while PostGIS returns NULL. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 5.1.9
ST_IsValidReason — Returns text stating if a geometry is valid or not and if not valid, a reason why.
text ST_IsValidReason(
geometry geomA)
;
Returns text stating if a geometry is valid or not an if not valid, a reason why.
Useful in combination with ST_IsValid to generate a detailed report of invalid geometries and reasons.
Availability: 1.4  requires GEOS >= 3.1.0.
First 3 Rejects from a successful quintuplet experiment SELECT gid, ST_IsValidReason(the_geom) as validity_info FROM (SELECT ST_MakePolygon(ST_ExteriorRing(e.buff), ST_Accum(f.line)) As the_geom, gid FROM (SELECT ST_Buffer(ST_MakePoint(x1*10,y1), z1) As buff, x1*10 + y1*100 + z1*1000 As gid FROM generate_series(4,6) x1 CROSS JOIN generate_series(2,5) y1 CROSS JOIN generate_series(1,8) z1 WHERE x1 > y1*0.5 AND z1 < x1*y1) As e INNER JOIN (SELECT ST_Translate(ST_ExteriorRing(ST_Buffer(ST_MakePoint(x1*10,y1), z1)),y1*1, z1*2) As line FROM generate_series(3,6) x1 CROSS JOIN generate_series(2,5) y1 CROSS JOIN generate_series(1,10) z1 WHERE x1 > y1*0.75 AND z1 < x1*y1) As f ON (ST_Area(e.buff) > 78 AND ST_Contains(e.buff, f.line)) GROUP BY gid, e.buff) As quintuplet_experiment WHERE ST_IsValid(the_geom) = false ORDER BY gid LIMIT 3; gid  validity_info + 5330  Selfintersection [32 5] 5340  Selfintersection [42 5] 5350  Selfintersection [52 5] simple example SELECT ST_IsValidReason('LINESTRING(220227 150406,2220227 150407,222020 150410)'); st_isvalidreason  Valid Geometry
ST_M — Return the M coordinate of the point, or NULL if not available. Input must be a point.
float ST_M(
geometry a_point)
;
Return the M coordinate of the point, or NULL if not available. Input must be a point.
This is not (yet) part of the OGC spec, but is listed here to complete the point coordinate extractor function list. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification.
This function supports 3d and will not drop the zindex.
ST_NDims — Returns coordinate dimension of the geometry as a small int. Values are: 2,3 or 4.
integer ST_NDims(
geometry g1)
;
Returns the coordinate dimension of the geometry. PostGIS supports 2  (x,y) , 3  (x,y,z) or 2D with measure  x,y,m, and 4  3D with measure space x,y,z,m
This function supports 3d and will not drop the zindex.
ST_NPoints — Return the number of points (vertexes) in a geometry.
integer ST_NPoints(
geometry g1)
;
Return the number of points in a geometry. Works for all geometries.
Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
ST_NRings — If the geometry is a polygon or multipolygon returns the number of rings.
integer ST_NRings(
geometry geomA)
;
If the geometry is a polygon or multipolygon returns the number of rings. Unlike NumInteriorRings, it counts the outer rings as well.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
ST_NumGeometries — If geometry is a GEOMETRYCOLLECTION (or MULTI*) return the number of geometries, otherwise return NULL.
integer ST_NumGeometries(
geometry a_multi_or_geomcollection)
;
Returns the number of Geometries. If geometry is a GEOMETRYCOLLECTION (or MULTI*) return the number of geometries, otherwise return NULL.
This method implements the SQL/MM specification. SQLMM 3: 9.1.4
Although ST_NumGeometries will return null when passed a single, you can wrap in ST_Multi to force 1 or more for all geoms SELECT ST_NumGeometries(ST_Multi(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'))); result 1 Geometry Collection Example  multis count as one geom in a collection SELECT ST_NumGeometries(ST_GeomFromEWKT('GEOMETRYCOLLECTION(MULTIPOINT(2 3 , 2 2), LINESTRING(5 5 ,10 10), POLYGON((7 4.2,7.1 5,7.1 4.3,7 4.2)))')); result 3
ST_NumInteriorRings — Return the number of interior rings of the first polygon in the geometry. This will work with both POLYGON and MULTIPOLYGON types but only looks at the first polygon. Return NULL if there is no polygon in the geometry.
integer ST_NumInteriorRings(
geometry a_polygon)
;
Return the number of interior rings of the first polygon in the geometry. This will work with both POLYGON and MULTIPOLYGON types but only looks at the first polygon. Return NULL if there is no polygon in the geometry.
This method implements the SQL/MM specification. SQLMM 3: 8.2.5
If you have a regular polygon SELECT gid, field1, field2, ST_NumInteriorRings(the_geom) AS numholes FROM sometable; If you have multipolygons And you want to know the total number of interior rings in the MULTIPOLYGON SELECT gid, field1, field2, SUM(ST_NumInteriorRings(the_geom)) AS numholes FROM (SELECT gid, field1, field2, (ST_Dump(the_geom)).geom As the_geom FROM sometable) As foo GROUP BY gid, field1,field2;
ST_NumInteriorRing — Return the number of interior rings of the first polygon in the geometry. Synonym to ST_NumInteriorRings.
integer ST_NumInteriorRing(
geometry a_polygon)
;
ST_NumPoints — Return the number of points in an ST_LineString or ST_CircularString value.
integer ST_NumPoints(
geometry g1)
;
Return the number of points in an ST_LineString or ST_CircularString value. Prior to 1.4 only works with Linestrings as the specs state. From 1.4 forward this is an alias for ST_NPoints which returns number of vertexes for not just line strings. Consider using ST_NPoints instead which is multipurpose and works with many geometry types.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 7.2.4
ST_PointN — Return the Nth point in the first linestring or circular linestring in the geometry. Return NULL if there is no linestring in the geometry.
geometry ST_PointN(
geometry a_linestring, integer n)
;
Return the Nth point in the first linestring or circular linestring in the geometry. Return NULL if there is no linestring in the geometry.
Index is 1based as for OGC specs since version 0.8.0. Previous versions implemented this as 0based instead. 
If you want to get the nth point of each line string in a multilinestring, use in conjunction with ST_Dump 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 7.2.5, 7.3.5
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
 Extract all POINTs from a LINESTRING SELECT ST_AsText( ST_PointN( column1, generate_series(1, ST_NPoints(column1)) )) FROM ( VALUES ('LINESTRING(0 0, 1 1, 2 2)'::geometry) ) AS foo; st_astext  POINT(0 0) POINT(1 1) POINT(2 2) (3 rows) Example circular string SELECT ST_AsText(ST_PointN(ST_GeomFromText('CIRCULARSTRING(1 2, 3 2, 1 2)'),2)); st_astext  POINT(3 2)
ST_SRID — Returns the spatial reference identifier for the ST_Geometry as defined in spatial_ref_sys table.
integer ST_SRID(
geometry g1)
;
Returns the spatial reference identifier for the ST_Geometry as defined in Section 4.3.1, “The SPATIAL_REF_SYS Table and Spatial Reference Systems” table.
spatial_ref_sys table is a table that catalogs all spatial reference systems known to PostGIS and is used for transformations from one spatial reference system to another. So verifying you have the right spatial reference system identifier is important if you plan to ever transform your geometries. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.1
This method implements the SQL/MM specification. SQLMM 3: 5.1.5
This method supports Circular Strings and Curves
ST_StartPoint — Returns the first point of a LINESTRING
geometry as a POINT
.
geometry ST_StartPoint(
geometry geomA)
;
Returns the first point of a LINESTRING
geometry
as a POINT
or NULL
if the input
parameter is not a LINESTRING
.
This method implements the SQL/MM specification. SQLMM 3: 7.1.3
This function supports 3d and will not drop the zindex.
SELECT ST_AsText(ST_StartPoint('LINESTRING(0 1, 0 2)'::geometry)); st_astext  POINT(0 1) (1 row) SELECT ST_StartPoint('POINT(0 1)'::geometry) IS NULL AS is_null; is_null  t (1 row) 3d line SELECT ST_AsEWKT(ST_StartPoint('LINESTRING(0 1 1, 0 2 2)'::geometry)); st_asewkt  POINT(0 1 1) (1 row)
ST_Summary — Returns a text summary of the contents of the
ST_Geometry
.
text ST_Summary(
geometry g)
;
Returns a text summary of the contents of the geometry.
This function supports 3d and will not drop the zindex.
SELECT ST_Summary(ST_GeomFromText('LINESTRING(0 0, 1 1)')) As good_line, ST_Summary(ST_GeomFromText('POLYGON((0 0, 1 1, 1 2, 1 1, 0 0))')) As bad_poly results good_line  bad_poly +  Line[B] with 2 points : Polygon[B] with 1 rings : ring 0 has 5 points : 3d polygon SELECT ST_Summary(ST_GeomFromEWKT('LINESTRING(0 0 1, 1 1 1)')) As good_line, ST_Summary(ST_GeomFromEWKT('POLYGON((0 0 1, 1 1 2, 1 2 3, 1 1 1, 0 0 1))')) As poly results good_line  poly +  Line[ZB] with 2 points : Polygon[ZB] with 1 rings : ring 0 has 5 points :
ST_X — Return the X coordinate of the point, or NULL if not available. Input must be a point.
float ST_X(
geometry a_point)
;
Return the X coordinate of the point, or NULL if not available. Input must be a point.
If you want to get the max min x values of any geometry look at ST_XMin, ST_XMax functions. 
This method implements the SQL/MM specification. SQLMM 3: 6.1.3
This function supports 3d and will not drop the zindex.
ST_Y — Return the Y coordinate of the point, or NULL if not available. Input must be a point.
float ST_Y(
geometry a_point)
;
Return the Y coordinate of the point, or NULL if not available. Input must be a point.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 6.1.4
This function supports 3d and will not drop the zindex.
ST_Z — Return the Z coordinate of the point, or NULL if not available. Input must be a point.
float ST_Z(
geometry a_point)
;
ST_Zmflag — Returns ZM (dimension semantic) flag of the geometries as a small int. Values are: 0=2d, 1=3dm, 2=3dz, 3=4d.
smallint ST_Zmflag(
geometry geomA)
;
Returns ZM (dimension semantic) flag of the geometries as a small int. Values are: 0=2d, 1=3dm, 2=3dz, 3=4d.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_Zmflag(ST_GeomFromEWKT('LINESTRING(1 2, 3 4)')); st_zmflag  0 SELECT ST_Zmflag(ST_GeomFromEWKT('LINESTRINGM(1 2 3, 3 4 3)')); st_zmflag  1 SELECT ST_Zmflag(ST_GeomFromEWKT('CIRCULARSTRING(1 2 3, 3 4 3, 5 6 3)')); st_zmflag  2 SELECT ST_Zmflag(ST_GeomFromEWKT('POINT(1 2 3 4)')); st_zmflag  3
ST_AddPoint — Adds a point to a LineString before point <position> (0based index).
geometry ST_AddPoint(
geometry linestring, geometry point)
;
geometry ST_AddPoint(
geometry linestring, geometry point, integer position)
;
Adds a point to a LineString before point <position> (0based index). Third parameter can be omitted or set to 1 for appending.
Availability: 1.1.0
This function supports 3d and will not drop the zindex.
guarantee all linestrings in a table are closed by adding the start point of each linestring to the end of the line string only for those that are not closed UPDATE sometable SET the_geom = ST_AddPoint(the_geom, ST_StartPoint(the_geom)) FROM sometable WHERE ST_IsClosed(the_geom) = false; Adding point to a 3d line SELECT ST_AsEWKT(ST_AddPoint(ST_GeomFromEWKT('LINESTRING(0 0 1, 1 1 1)'), ST_MakePoint(1, 2, 3))); result st_asewkt  LINESTRING(0 0 1,1 1 1,1 2 3)
ST_Affine — Applies a 3d affine transformation to the geometry to do things like translate, rotate, scale in one step.
geometry ST_Affine(
geometry geomA, float a, float b, float c, float d, float e, float f, float g, float h, float i, float xoff, float yoff, float zoff)
;
geometry ST_Affine(
geometry geomA, float a, float b, float d, float e, >
float xoff, float yoff)
;
Applies a 3d affine transformation to the geometry to do things like translate, rotate, scale in one step.
Version 1: The call
ST_Affine(geom, a, b, c, d, e, f, g, h, i, xoff, yoff, zoff)
represents the transformation matrix
/ a b c xoff \  d e f yoff   g h i zoff  \ 0 0 0 1 /
and the vertices are transformed as follows:
x' = a*x + b*y + c*z + xoff y' = d*x + e*y + f*z + yoff z' = g*x + h*y + i*z + zoff
All of the translate / scale functions below are expressed via such an affine transformation.
Version 2: Applies a 2d affine transformation to the geometry. The call
ST_Affine(geom, a, b, d, e, xoff, yoff)
represents the transformation matrix
/ a b 0 xoff \ / a b xoff \  d e 0 yoff  rsp.  d e yoff   0 0 1 0  \ 0 0 1 / \ 0 0 0 1 /
and the vertices are transformed as follows:
x' = a*x + b*y + xoff y' = d*x + e*y + yoff z' = z
This method is a subcase of the 3D method above.
Availability: 1.1.2. Name changed from Affine to ST_Affine in 1.2.2
Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Rotate a 3d line 180 degrees about the z axis. Note this is longhand for doing ST_RotateZ(); SELECT ST_AsEWKT(ST_Affine(the_geom, cos(pi()), sin(pi()), 0, sin(pi()), cos(pi()), 0, 0, 0, 1, 0, 0, 0)) As using_affine, ST_AsEWKT(ST_RotateZ(the_geom, pi())) As using_rotatez FROM (SELECT ST_GeomFromEWKT('LINESTRING(1 2 3, 1 4 3)') As the_geom) As foo; using_affine  using_rotatez + LINESTRING(1 2 3,1 4 3)  LINESTRING(1 2 3,1 4 3) (1 row) Rotate a 3d line 180 degrees in both the x and z axis SELECT ST_AsEWKT(ST_Affine(the_geom, cos(pi()), sin(pi()), 0, sin(pi()), cos(pi()), sin(pi()), 0, sin(pi()), cos(pi()), 0, 0, 0)) FROM (SELECT ST_GeomFromEWKT('LINESTRING(1 2 3, 1 4 3)') As the_geom) As foo; st_asewkt  LINESTRING(1 2 3,1 4 3) (1 row)
ST_Force_2D — Forces the geometries into a "2dimensional mode" so that all output representations will only have the X and Y coordinates.
geometry ST_Force_2D(
geometry geomA)
;
Forces the geometries into a "2dimensional mode" so that all output representations will only have the X and Y coordinates. This is useful for force OGCcompliant output (since OGC only specifies 2D geometries).
This method supports Circular Strings and Curves
SELECT ST_AsEWKT(ST_Force_2D(ST_GeomFromEWKT('CIRCULARSTRING(1 1 2, 2 3 2, 4 5 2, 6 7 2, 5 6 2)'))); st_asewkt  CIRCULARSTRING(1 1,2 3,4 5,6 7,5 6) SELECT ST_AsEWKT(ST_Force_2D('POLYGON((0 0 2,0 5 2,5 0 2,0 0 2),(1 1 2,3 1 2,1 3 2,1 1 2))')); st_asewkt  POLYGON((0 0,0 5,5 0,0 0),(1 1,3 1,1 3,1 1))
ST_Force_3D — Forces the geometries into XYZ mode. This is an alias for ST_Force_3DZ.
geometry ST_Force_3D(
geometry geomA)
;
Forces the geometries into XYZ mode. This is an alias for ST_Force_3DZ. If a geometry has no Z component, then a 0 Z coordinate is tacked on.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Nothing happens to an already 3D geometry SELECT ST_AsEWKT(ST_Force_3D(ST_GeomFromEWKT('CIRCULARSTRING(1 1 2, 2 3 2, 4 5 2, 6 7 2, 5 6 2)'))); st_asewkt  CIRCULARSTRING(1 1 2,2 3 2,4 5 2,6 7 2,5 6 2) SELECT ST_AsEWKT(ST_Force_3D('POLYGON((0 0,0 5,5 0,0 0),(1 1,3 1,1 3,1 1))')); st_asewkt  POLYGON((0 0 0,0 5 0,5 0 0,0 0 0),(1 1 0,3 1 0,1 3 0,1 1 0))
ST_Force_3DZ — Forces the geometries into XYZ mode. This is a synonym for ST_Force_3D.
geometry ST_Force_3DZ(
geometry geomA)
;
Forces the geometries into XYZ mode. This is a synonym for ST_Force_3DZ. If a geometry has no Z component, then a 0 Z coordinate is tacked on.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Nothing happens to an already 3D geometry SELECT ST_AsEWKT(ST_Force_3DZ(ST_GeomFromEWKT('CIRCULARSTRING(1 1 2, 2 3 2, 4 5 2, 6 7 2, 5 6 2)'))); st_asewkt  CIRCULARSTRING(1 1 2,2 3 2,4 5 2,6 7 2,5 6 2) SELECT ST_AsEWKT(ST_Force_3DZ('POLYGON((0 0,0 5,5 0,0 0),(1 1,3 1,1 3,1 1))')); st_asewkt  POLYGON((0 0 0,0 5 0,5 0 0,0 0 0),(1 1 0,3 1 0,1 3 0,1 1 0))
ST_Force_3DM — Forces the geometries into XYM mode.
geometry ST_Force_3DM(
geometry geomA)
;
Forces the geometries into XYM mode. If a geometry has no M component, then a 0 M coordinate is tacked on. If it has a Z component, then Z is removed
This method supports Circular Strings and Curves
Nothing happens to an already 3D geometry SELECT ST_AsEWKT(ST_Force_3DM(ST_GeomFromEWKT('CIRCULARSTRING(1 1 2, 2 3 2, 4 5 2, 6 7 2, 5 6 2)'))); st_asewkt  CIRCULARSTRINGM(1 1 0,2 3 0,4 5 0,6 7 0,5 6 0) SELECT ST_AsEWKT(ST_Force_3DM('POLYGON((0 0 1,0 5 1,5 0 1,0 0 1),(1 1 1,3 1 1,1 3 1,1 1 1))')); st_asewkt  POLYGONM((0 0 0,0 5 0,5 0 0,0 0 0),(1 1 0,3 1 0,1 3 0,1 1 0))
ST_Force_4D — Forces the geometries into XYZM mode.
geometry ST_Force_4D(
geometry geomA)
;
Forces the geometries into XYZM mode. 0 is tacked on for missing Z and M dimensions.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Nothing happens to an already 3D geometry SELECT ST_AsEWKT(ST_Force_4D(ST_GeomFromEWKT('CIRCULARSTRING(1 1 2, 2 3 2, 4 5 2, 6 7 2, 5 6 2)'))); st_asewkt  CIRCULARSTRING(1 1 2 0,2 3 2 0,4 5 2 0,6 7 2 0,5 6 2 0) SELECT ST_AsEWKT(ST_Force_4D('MULTILINESTRINGM((0 0 1,0 5 2,5 0 3,0 0 4),(1 1 1,3 1 1,1 3 1,1 1 1))')); st_asewkt  MULTILINESTRING((0 0 0 1,0 5 0 2,5 0 0 3,0 0 0 4),(1 1 0 1,3 1 0 1,1 3 0 1,1 1 0 1))
ST_Force_Collection — Converts the geometry into a GEOMETRYCOLLECTION.
geometry ST_Force_Collection(
geometry geomA)
;
Converts the geometry into a GEOMETRYCOLLECTION. This is useful for simplifying the WKB representation.
Availability: 1.2.2, prior to 1.3.4 this function will crash with Curves. This is fixed in 1.3.4+
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_AsEWKT(ST_Force_Collection('POLYGON((0 0 1,0 5 1,5 0 1,0 0 1),(1 1 1,3 1 1,1 3 1,1 1 1))')); st_asewkt  GEOMETRYCOLLECTION(POLYGON((0 0 1,0 5 1,5 0 1,0 0 1),(1 1 1,3 1 1,1 3 1,1 1 1))) SELECT ST_AsText(ST_Force_Collection('CIRCULARSTRING(220227 150406,2220227 150407,220227 150406)')); st_astext  GEOMETRYCOLLECTION(CIRCULARSTRING(220227 150406,2220227 150407,220227 150406)) (1 row)
ST_ForceRHR — Forces the orientation of the vertices in a polygon to follow the RightHandRule.
boolean
ST_ForceRHR(
geometry g)
;
Forces the orientation of the vertices in a polygon to follow the RightHandRule. In GIS terminology, this means that the area that is bounded by the polygon is to the right of the boundary. In particular, the exterior ring is orientated in a clockwise direction and the interior rings in a counterclockwise direction.
This function supports 3d and will not drop the zindex.
ST_LineMerge — Returns a (set of) LineString(s) formed by sewing together a MULTILINESTRING.
geometry ST_LineMerge(
geometry amultilinestring)
;
Returns a (set of) LineString(s) formed by sewing together the constituent line work of a MULTILINESTRING.
Only use with MULTILINESTRING/LINESTRINGs. If you feed a polygon or geometry collection into this function, it will return an empty GEOMETRYCOLLECTION 
Availability: 1.1.0
requires GEOS >= 2.1.0 
SELECT ST_AsText(ST_LineMerge( ST_GeomFromText('MULTILINESTRING((29 27,30 29.7,36 31,45 33),(45 33,46 32))') ) ); st_astext  LINESTRING(29 27,30 29.7,36 31,45 33,46 32) (1 row) If can't be merged  original MULTILINESTRING is returned SELECT ST_AsText(ST_LineMerge( ST_GeomFromText('MULTILINESTRING((29 27,30 29.7,36 31,45 33),(45.2 33.2,46 32))') ) ); st_astext  MULTILINESTRING((45.2 33.2,46 32),(29 27,30 29.7,36 31,45 33))
ST_CollectionExtract — Given a GEOMETRYCOLLECTION, returns a MULTI* geometry consisting only of the specified type. Subgeometries that are not the specified type are ignored. If there are no subgeometries of the right type, an EMPTY collection will be returned. Only points, lines and polygons are supported. Type numbers are 1 == POINT, 2 == LINESTRING, 3 == POLYGON.
geometry ST_CollectionExtract(
geometry collection, integer type)
;
Given a GEOMETRYCOLLECTION, returns a MULTI* geometry consisting only of the specified type. Subgeometries that are not the specified type are ignored. If there are no subgeometries of the right type, an EMPTY collection will be returned. Only points, lines and polygons are supported. Type numbers are 1 == POINT, 2 == LINESTRING, 3 == POLYGON.
Availability: 1.5.0
 Constants: 1 == POINT, 2 == LINESTRING, 3 == POLYGON SELECT ST_AsText(ST_CollectionExtract(ST_GeomFromText('GEOMETRYCOLLECTION(GEOMETRYCOLLECTION(POINT(0 0)))'),1)); st_astext  MULTIPOINT(0 0) (1 row) SELECT ST_AsText(ST_CollectionExtract(ST_GeomFromText('GEOMETRYCOLLECTION(GEOMETRYCOLLECTION(LINESTRING(0 0, 1 1)),LINESTRING(2 2, 3 3))'),2)); st_astext  MULTILINESTRING((0 0, 1 1), (2 2, 3 3)) (1 row)
ST_Multi — Returns the geometry as a MULTI* geometry. If the geometry is already a MULTI*, it is returned unchanged.
geometry ST_Multi(
geometry g1)
;
Returns the geometry as a MULTI* geometry. If the geometry is already a MULTI*, it is returned unchanged.
SELECT ST_AsText(ST_Multi(ST_GeomFromText('POLYGON((743238 2967416,743238 2967450, 743265 2967450,743265.625 2967416,743238 2967416))'))); st_astext  MULTIPOLYGON(((743238 2967416,743238 2967450,743265 2967450,743265.625 2967416, 743238 2967416))) (1 row)
ST_RemovePoint — Removes point from a linestring. Offset is 0based.
geometry ST_RemovePoint(
geometry linestring, integer offset)
;
Removes point from a linestring. Useful for turning a closed ring into an open line string
Availability: 1.1.0
This function supports 3d and will not drop the zindex.
ST_Reverse — Returns the geometry with vertex order reversed.
geometry ST_Reverse(
geometry g1)
;
ST_Rotate — This is a synonym for ST_RotateZ
geometry ST_Rotate(
geometry geomA, float rotZRadians)
;
ST_RotateX — Rotate a geometry rotRadians about the X axis.
geometry ST_RotateX(
geometry geomA, float rotRadians)
;
Rotate a geometry geomA  rotRadians about the X axis.

Availability: 1.1.2. Name changed from RotateX to ST_RotateX in 1.2.2
This function supports 3d and will not drop the zindex.
ST_RotateY — Rotate a geometry rotRadians about the Y axis.
geometry ST_RotateY(
geometry geomA, float rotRadians)
;
Rotate a geometry geomA  rotRadians about the y axis.

Availability: 1.1.2. Name changed from RotateY to ST_RotateY in 1.2.2
This function supports 3d and will not drop the zindex.
ST_RotateZ — Rotate a geometry rotRadians about the Z axis.
geometry ST_RotateZ(
geometry geomA, float rotRadians)
;
Rotate a geometry geomA  rotRadians about the Z axis.

Availability: 1.1.2. Name changed from RotateZ to ST_RotateZ in 1.2.2
Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Rotate a line 90 degrees along zaxis SELECT ST_AsEWKT(ST_RotateZ(ST_GeomFromEWKT('LINESTRING(1 2 3, 1 1 1)'), pi()/2)); st_asewkt  LINESTRING(2 1 3,1 1 1) Rotate a curved circle around zaxis SELECT ST_AsEWKT(ST_RotateZ(the_geom, pi()/2)) FROM (SELECT ST_LineToCurve(ST_Buffer(ST_GeomFromText('POINT(234 567)'), 3)) As the_geom) As foo; st_asewkt  CURVEPOLYGON(CIRCULARSTRING(567 237,564.87867965644 236.12132034356,564 234,569.12132034356 231.87867965644,567 237))
ST_Scale — Scales the geometry to a new size by multiplying the ordinates with the parameters. Ie: ST_Scale(geom, Xfactor, Yfactor, Zfactor).
geometry ST_Scale(
geometry geomA, float XFactor, float YFactor, float ZFactor)
;
geometry ST_Scale(
geometry geomA, float XFactor, float YFactor)
;
Scales the geometry to a new size by multiplying the ordinates with the parameters. Ie: ST_Scale(geom, Xfactor, Yfactor, Zfactor).

Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
Availability: 1.1.0.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Version 1: scale X, Y, Z SELECT ST_AsEWKT(ST_Scale(ST_GeomFromEWKT('LINESTRING(1 2 3, 1 1 1)'), 0.5, 0.75, 0.8)); st_asewkt  LINESTRING(0.5 1.5 2.4,0.5 0.75 0.8) Version 2: Scale X Y SELECT ST_AsEWKT(ST_Scale(ST_GeomFromEWKT('LINESTRING(1 2 3, 1 1 1)'), 0.5, 0.75)); st_asewkt  LINESTRING(0.5 1.5 3,0.5 0.75 1)
ST_Segmentize — Return a modified geometry having no segment longer than the given distance. Distance computation is performed in 2d only.
geometry ST_Segmentize(
geometry geomA, float max_length)
;
Returns a modified geometry having no segment longer than the given distance. Distance computation is performed in 2d only.
Availability: 1.2.2
This will only increase segments. It will not lengthen segments shorter than max length 
SELECT ST_AsText(ST_Segmentize( ST_GeomFromText('MULTILINESTRING((29 27,30 29.7,36 31,45 33),(45 33,46 32))') ,5) ); st_astext  MULTILINESTRING((29 27,30 29.7,34.886615700134 30.758766735029,36 31, 40.8809353009198 32.0846522890933,45 33), (45 33,46 32)) (1 row) SELECT ST_AsText(ST_Segmentize(ST_GeomFromText('POLYGON((29 28, 30 40, 29 28))'),10)); st_astext  POLYGON((29 28,29.8304547985374 37.9654575824488,30 40,29.1695452014626 30.0345424175512,29 28)) (1 row)
ST_SetPoint — Replace point N of linestring with given point. Index is 0based.
geometry ST_SetPoint(
geometry linestring, integer zerobasedposition, geometry point)
;
Replace point N of linestring with given point. Index is 0based. This is especially useful in triggers when trying to maintain relationship of joints when one vertex moves.
Availability: 1.1.0
This function supports 3d and will not drop the zindex.
Change first point in line string from 1 3 to 1 1 SELECT ST_AsText(ST_SetPoint('LINESTRING(1 2,1 3)', 0, 'POINT(1 1)')); st_astext  LINESTRING(1 1,1 3) Change last point in a line string (lets play with 3d linestring this time) SELECT ST_AsEWKT(ST_SetPoint(foo.the_geom, ST_NumPoints(foo.the_geom)  1, ST_GeomFromEWKT('POINT(1 1 3)'))) FROM (SELECT ST_GeomFromEWKT('LINESTRING(1 2 3,1 3 4, 5 6 7)') As the_geom) As foo; st_asewkt  LINESTRING(1 2 3,1 3 4,1 1 3)
ST_SetSRID — Sets the SRID on a geometry to a particular integer value.
geometry ST_SetSRID(
geometry
geom, integer
srid)
;
Sets the SRID on a geometry to a particular integer value. Useful in constructing bounding boxes for queries.
This function does not transform the geometry is any way  it simply sets the projection the geometry that it's currently in. Use ST_Transform if you want to transform the geometry into a new projection. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method supports Circular Strings and Curves
ST_SnapToGrid — Snap all points of the input geometry to the grid defined by its origin and cell size. Remove consecutive points falling on the same cell, eventually returning NULL if output points are not enough to define a geometry of the given type. Collapsed geometries in a collection are stripped from it. Useful for reducing precision.
geometry ST_SnapToGrid(
geometry geomA, float originX, float originY, float sizeX, float sizeY)
;
geometry ST_SnapToGrid(
geometry geomA, float sizeX, float sizeY)
;
geometry ST_SnapToGrid(
geometry geomA, float size)
;
geometry ST_SnapToGrid(
geometry geomA, geometry pointOrigin, float sizeX, float sizeY, float sizeZ, float sizeM)
;
Variant 1,2,3: Snap all points of the input geometry to the grid defined by its origin and cell size. Remove consecutive points falling on the same cell, eventually returning NULL if output points are not enough to define a geometry of the given type. Collapsed geometries in a collection are stripped from it.
Variant 4: Introduced 1.1.0  Snap all points of the input geometry to the grid defined by its origin (the second argument, must be a point) and cell sizes. Specify 0 as size for any dimension you don't want to snap to a grid.
The returned geometry might loose its simplicity (see ST_IsSimple). 
Before release 1.1.0 this function always returned a 2d geometry. Starting at 1.1.0 the returned geometry will have same dimensionality as the input one with higher dimension values untouched. Use the version taking a second geometry argument to define all grid dimensions. 
Availability: 1.0.0RC1
Availability: 1.1.0  Z and M support
This function supports 3d and will not drop the zindex.
Snap your geometries to a precision grid of 10^3 UPDATE mytable SET the_geom = ST_SnapToGrid(the_geom, 0.001); SELECT ST_AsText(ST_SnapToGrid( ST_GeomFromText('LINESTRING(1.1115678 2.123, 4.111111 3.2374897, 4.11112 3.23748667)'), 0.001) ); st_astext  LINESTRING(1.112 2.123,4.111 3.237) Snap a 4d geometry SELECT ST_AsEWKT(ST_SnapToGrid( ST_GeomFromEWKT('LINESTRING(1.1115678 2.123 2.3456 1.11111, 4.111111 3.2374897 3.1234 1.1111, 1.11111112 2.123 2.3456 1.1111112)'), ST_GeomFromEWKT('POINT(1.12 2.22 3.2 4.4444)'), 0.1, 0.1, 0.1, 0.01) ); st_asewkt  LINESTRING(1.08 2.12 2.3 1.1144,4.12 3.22 3.1 1.1144,1.08 2.12 2.3 1.1144) With a 4d geometry  the ST_SnapToGrid(geom,size) only touches x and y coords but keeps m and z the same SELECT ST_AsEWKT(ST_SnapToGrid(ST_GeomFromEWKT('LINESTRING(1.1115678 2.123 3 2.3456, 4.111111 3.2374897 3.1234 1.1111)'), 0.01) ); st_asewkt  LINESTRING(1.11 2.12 3 2.3456,4.11 3.24 3.1234 1.1111)
ST_Transform — Returns a new geometry with its coordinates transformed to the SRID referenced by the integer parameter.
geometry ST_Transform(
geometry g1, integer srid)
;
Returns a new geometry with its coordinates transformed to
spatial reference system referenced by the SRID integer parameter. The destination SRID
must exist in the SPATIAL_REF_SYS
table.
ST_Transform is often confused with ST_SetSRID(). ST_Transform actually changes the coordinates of a geometry from one spatial reference system to another, while ST_SetSRID() simply changes the SRID identifier of the geometry
Requires PostGIS be compiled with Proj support. Use PostGIS_Full_Version to confirm you have proj support compiled in. 
If using more than one transformation, it is useful to have a functional index on the commonly used transformations to take advantage of index usage. 
Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 5.1.6
This method supports Circular Strings and Curves
Change Mass state plane US feet geometry to WGS 84 long lat
SELECT ST_AsText(ST_Transform(ST_GeomFromText('POLYGON((743238 2967416,743238 2967450, 743265 2967450,743265.625 2967416,743238 2967416))',2249),4326)) As wgs_geom; wgs_geom  POLYGON((71.1776848522251 42.3902896512902,71.1776843766326 42.3903829478009, 71.1775844305465 42.3903826677917,71.1775825927231 42.3902893647987,71.177684 8522251 42.3902896512902)); (1 row) 3D Circular String example SELECT ST_AsEWKT(ST_Transform(ST_GeomFromEWKT('SRID=2249;CIRCULARSTRING(743238 2967416 1,743238 2967450 2,743265 2967450 3,743265.625 2967416 3,743238 2967416 4)'),4326)); st_asewkt  SRID=4326;CIRCULARSTRING(71.1776848522251 42.3902896512902 1,71.1776843766326 42.3903829478009 2, 71.1775844305465 42.3903826677917 3, 71.1775825927231 42.3902893647987 3,71.1776848522251 42.3902896512902 4)
Example of creating a partial functional index. For tables where you are not sure all the geometries will be filled in, its best to use a partial index that leaves out null geometries which will both conserve space and make your index smaller and more efficient.
CREATE INDEX idx_the_geom_26986_parcels ON parcels USING gist (ST_Transform(the_geom, 26986)) WHERE the_geom IS NOT NULL;
Sometimes coordinate transformation involving a gridshift can fail, for example if PROJ.4 has not been built with gridshift files or the coordinate does not lie within the range for which the grid shift is defined. By default, PostGIS will throw an error if a grid shift file is not present, but this behaviour can be configured on a perSRID basis by altering the proj4text value within the spatial_ref_sys table.
For example, the proj4text parameter +datum=NAD87 is a shorthand form for the following +nadgrids parameter:
+nadgrids=@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat
The @ prefix means no error is reported if the files are not present, but if the end of the list is reached with no file having been appropriate (ie. found and overlapping) then an error is issued.
If, conversely, you wanted to ensure that at least the standard files were present, but that if all files were scanned without a hit a null transformation is applied you could use:
+nadgrids=@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat,null
The null grid shift file is a valid grid shift file covering the whole world and applying no shift. So for a complete example, if you wanted to alter PostGIS so that transformations to SRID 4267 that didn't lie within the correct range did not throw an ERROR, you would use the following:
UPDATE spatial_ref_sys SET proj4text = '+proj=longlat +ellps=clrk66 +nadgrids=@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat,null +no_defs' WHERE srid = 4267;
ST_Translate — Translates the geometry to a new location using the numeric parameters as offsets. Ie: ST_Translate(geom, X, Y) or ST_Translate(geom, X, Y,Z).
geometry ST_Translate(
geometry g1, float deltax, float deltay)
;
geometry ST_Translate(
geometry g1, float deltax, float deltay, float deltaz)
;
Returns a new geometry whose coordinates are translated delta x,delta y,delta z units. Units are based on the units defined in spatial reference (SRID) for this geometry.
Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
Availability: 1.2.2
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Move a point 1 degree longitude
SELECT ST_AsText(ST_Translate(ST_GeomFromText('POINT(71.01 42.37)',4326),1,0)) As wgs_transgeomtxt; wgs_transgeomtxt  POINT(70.01 42.37)
Move a linestring 1 degree longitude and 1/2 degree latitude
SELECT ST_AsText(ST_Translate(ST_GeomFromText('LINESTRING(71.01 42.37,71.11 42.38)',4326),1,0.5)) As wgs_transgeomtxt; wgs_transgeomtxt  LINESTRING(70.01 42.87,70.11 42.88)
Move a 3d point
SELECT ST_AsEWKT(ST_Translate(CAST('POINT(0 0 0)' As geometry), 5, 12,3)); st_asewkt  POINT(5 12 3)
Move a curve and a point
SELECT ST_AsText(ST_Translate(ST_Collect('CURVEPOLYGON(CIRCULARSTRING(4 3,3.12 0.878,1 0,1.121 5.1213,6 7, 8 9,4 3))','POINT(1 3)'),1,2)); st_astext  GEOMETRYCOLLECTION(CURVEPOLYGON(CIRCULARSTRING(5 5,4.12 2.878,2 2,0.121 7.1213,7 9,9 11,5 5)),POINT(2 5))
ST_TransScale — Translates the geometry using the deltaX and deltaY args, then scales it using the XFactor, YFactor args, working in 2D only.
geometry ST_TransScale(
geometry geomA, float deltaX, float deltaY, float XFactor, float YFactor)
;
Translates the geometry using the deltaX and deltaY args, then scales it using the XFactor, YFactor args, working in 2D only.

Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
Availability: 1.1.0.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_AsEWKT(ST_TransScale(ST_GeomFromEWKT('LINESTRING(1 2 3, 1 1 1)'), 0.5, 1, 1, 2)); st_asewkt  LINESTRING(1.5 6 3,1.5 4 1) Buffer a point to get an approximation of a circle, convert to curve and then translate 1,2 and scale it 3,4 SELECT ST_AsText(ST_Transscale(ST_LineToCurve(ST_Buffer('POINT(234 567)', 3)),1,2,3,4)); st_astext  CURVEPOLYGON(CIRCULARSTRING(714 2276,711.363961030679 2267.51471862576,705 2264,698.636038969321 2284.48528137424,714 2276))
ST_AsBinary — Return the WellKnown Binary (WKB) representation of the geometry/geography without SRID meta data.
bytea ST_AsBinary(
geometry g1)
;
bytea ST_AsBinary(
geography g1)
;
bytea ST_AsBinary(
geometry g1, text NDR_or_XDR)
;
Returns the WellKnown Binary representation of the geometry. There are 2 variants of the function. The first variant takes no endian encoding paramater and defaults to little endian. The second variant takes a second argument denoting the encoding  using littleendian ('NDR') or bigendian ('XDR') encoding.
This is useful in binary cursors to pull data out of the database without converting it to a string representation.
The WKB spec does not include the SRID. To get the OGC WKB with SRID format use ST_AsEWKB 
ST_AsBinary is the reverse of ST_GeomFromWKB for geometry. Use ST_GeomFromWKB to convert to a postgis geometry from ST_AsBinary representation. 
Availability: 1.5.0 geography support was introduced.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.1
This method implements the SQL/MM specification. SQLMM 3: 5.1.37
This method supports Circular Strings and Curves
SELECT ST_AsBinary(ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326)); st_asbinary  \001\003\000\000\000\001\000\000\000\005 \000\000\000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000 \000\000\000\360?\000\000\000\000\000\000 \360?\000\000\000\000\000\000\360?\000\000 \000\000\000\000\360?\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000 (1 row)
SELECT ST_AsBinary(ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326), 'XDR'); st_asbinary  \000\000\000\000\003\000\000\000\001\000\000\000\005\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000 \000?\360\000\000\000\000\000\000?\360\000\000\000\000\000\000?\360\000\000 \000\000\000\000?\360\000\000\000\000\000\000\000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000 (1 row)
ST_AsEWKB — Return the WellKnown Binary (WKB) representation of the geometry with SRID meta data.
bytea ST_AsEWKB(
geometry g1)
;
bytea ST_AsEWKB(
geometry g1, text NDR_or_XDR)
;
Returns the WellKnown Binary representation of the geometry with SRID metadata. There are 2 variants of the function. The first variant takes no endian encoding paramater and defaults to little endian. The second variant takes a second argument denoting the encoding  using littleendian ('NDR') or bigendian ('XDR') encoding.
This is useful in binary cursors to pull data out of the database without converting it to a string representation.
The WKB spec does not include the SRID. To get the OGC WKB format use ST_AsBinary 
ST_AsEWKB is the reverse of ST_GeomFromEWKB. Use ST_GeomFromEWKB to convert to a postgis geometry from ST_AsEWKB representation. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_AsEWKB(ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326)); st_asewkb  \001\003\000\000 \346\020\000\000\001\000 \000\000\005\000\000\000\000 \000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000 \000\000\360?\000\000\000\000\000\000\360? \000\000\000\000\000\000\360?\000\000\000\000\000 \000\360?\000\000\000\000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000\000\000\000 (1 row)
SELECT ST_AsEWKB(ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326), 'XDR'); st_asewkb  \000 \000\000\003\000\000\020\346\000\000\000\001\000\000\000\005\000\000\000\000\ 000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000? \360\000\000\000\000\000\000?\360\000\000\000\000\000\000?\360\000\000\000\000 \000\000?\360\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000 \000\000\000\000\000\000\000\000\000\000\000\000\000
ST_AsEWKT — Return the WellKnown Text (WKT) representation of the geometry with SRID meta data.
text ST_AsEWKT(
geometry g1)
;
Returns the WellKnown Text representation of the geometry prefixed with the SRID.
The WKT spec does not include the SRID. To get the OGC WKT format use ST_AsText 
WKT format does not maintain precision so to prevent floating truncation, use ST_AsBinary or ST_AsEWKB format for transport.
ST_AsEWKT is the reverse of ST_GeomFromEWKT. Use ST_GeomFromEWKT to convert to a postgis geometry from ST_AsEWKT representation. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_AsEWKT('0103000020E61000000100000005000000000000 000000000000000000000000000000000000000000000000000000 F03F000000000000F03F000000000000F03F000000000000F03 F000000000000000000000000000000000000000000000000'::geometry); st_asewkt  SRID=4326;POLYGON((0 0,0 1,1 1,1 0,0 0)) (1 row) SELECT ST_AsEWKT('0108000080030000000000000060E30A4100000000785C0241000000000000F03F0000000018 E20A4100000000485F024100000000000000400000000018 E20A4100000000305C02410000000000000840') st_asewkt CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)
ST_AsGeoJSON — Return the geometry as a GeoJSON element.
text ST_AsGeoJSON(
geometry g1)
;
text ST_AsGeoJSON(
geography g1)
;
text ST_AsGeoJSON(
geometry g1, integer max_decimal_digits)
;
text ST_AsGeoJSON(
geography g1, integer max_decimal_digits)
;
text ST_AsGeoJSON(
geometry g1, integer max_decimal_digits, integer options)
;
text ST_AsGeoJSON(
geography g1, integer max_decimal_digits, integer options)
;
text ST_AsGeoJSON(
integer version, geometry g1)
;
text ST_AsGeoJSON(
integer version, geography g1)
;
text ST_AsGeoJSON(
integer version, geometry g1, integer max_decimal_digits)
;
text ST_AsGeoJSON(
integer version, geography g1, integer max_decimal_digits)
;
text ST_AsGeoJSON(
integer version, geometry g1, integer max_decimal_digits, integer options)
;
text ST_AsGeoJSON(
integer version, geography g1, integer max_decimal_digits, integer options)
;
Return the geometry as a Geometry Javascript Object Notation (GeoJSON) element. (Cf GeoJSON specifications 1.0). 2D and 3D Geometries are both supported. GeoJSON only support SFS 1.1 geometry type (no curve support for example).
The version parameter, if specified, must be 1.
The third argument may be used to reduce the maximum number of decimal places used in output (defaults to 15).
The last 'options' argument could be used to add Bbox or Crs in GeoJSON output:
0: means no option (default value)
1: GeoJSON Bbox
2: GeoJSON Short CRS (e.g EPSG:4326)
4: GeoJSON Long CRS (e.g urn:ogc:def:crs:EPSG:4326)
Version 1: ST_AsGeoJSON(geom) / precision=15 version=1 options=0
Version 2: ST_AsGeoJSON(geom, precision) / version=1 options=0
Version 3: ST_AsGeoJSON(geom, precision, options) / version=1
Version 4: ST_AsGeoJSON(version, geom) / precision=15 options=0
Version 5: ST_AsGeoJSON(version, geom, precision) /options=0
Version 6: ST_AsGeoJSON(version, geom, precision,options)
Availability: 1.3.4
Availability: 1.5.0 geography support was introduced.
This function supports 3d and will not drop the zindex.
GeoJSON format is generally more efficient than other formats for use in ajax mapping. One popular javascript client that supports this is Open Layers. Example of its use is OpenLayers GeoJSON Example
SELECT ST_AsGeoJSON(the_geom) from fe_edges limit 1; st_asgeojson  {"type":"MultiLineString","coordinates":[[[89.734634999999997,31.492072000000000], [89.734955999999997,31.492237999999997]]]} (1 row) 3d point SELECT ST_AsGeoJSON('LINESTRING(1 2 3, 4 5 6)'); st_asgeojson  {"type":"LineString","coordinates":[[1,2,3],[4,5,6]]}
ST_AsGML — Return the geometry as a GML version 2 or 3 element.
text ST_AsGML(
geometry g1)
;
text ST_AsGML(
geography g1)
;
text ST_AsGML(
geometry g1, integer precision)
;
text ST_AsGML(
geography g1, integer precision)
;
text ST_AsGML(
integer version, geometry g1)
;
text ST_AsGML(
integer version, geography g1)
;
text ST_AsGML(
integer version, geometry g1, integer precision)
;
text ST_AsGML(
integer version, geography g1, integer precision)
;
text ST_AsGML(
integer version, geometry g1, integer precision, integer options)
;
text ST_AsGML(
integer version, geography g1, integer precision, integer options)
;
Return the geometry as a Geography Markup Language (GML) element. The version parameter, if specified, may be either 2 or 3. If no version parameter is specified then the default is assumed to be 2. The third argument may be used to reduce the maximum number of decimal places used in output (defaults to 15).
GML 2 refer to 2.1.2 version, GML 3 to 3.1.1 version
The last 'options' argument is a bitfield. It could be used to define CRS output type in GML output, and to declare data as lat/lon:
0: GML Short CRS (e.g EPSG:4326), default value
1: GML Long CRS (e.g urn:ogc:def:crs:EPSG:4326)
16: Declare that datas are lat/lon (e.g srid=4326). Default is to assume that data are planars. This option is usefull for GML 3.1.1 output only, related to axis order.
Availability: 1.3.2 Availability: 1.5.0 geography support was introduced. 
This function supports 3d and will not drop the zindex.
SELECT ST_AsGML(ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326)); st_asgml  <gml:Polygon srsName="EPSG:4326"><gml:outerBoundaryIs><gml:LinearRing><gml:coordinates>0,0 0,1 1,1 1,0 0,0</gml:coordinates></gml:LinearRing></gml:outerBoundaryIs></gml:Polygon>
SELECT ST_AsGML(3, ST_GeomFromText('POINT(5.234234233242 6.34534534534)',4326), 5, 17); st_asgml  <gml:Point srsName="urn:ogc:def:crs:EPSG:4326"><gml:pos>6.34535 5.23423</gml:pos></gml:Point>
ST_AsHEXEWKB — Returns a Geometry in HEXEWKB format (as text) using either littleendian (NDR) or bigendian (XDR) encoding.
text ST_AsHEXEWKB(
geometry g1, text NDRorXDR)
;
text ST_AsHEXEWKB(
geometry g1)
;
Returns a Geometry in HEXEWKB format (as text) using either littleendian (NDR) or bigendian (XDR) encoding. If no encoding is specified, then NDR is used.
Availability: 1.2.2 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_AsHEXEWKB(ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326)); which gives same answer as SELECT ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326)::text; st_ashexewkb  0103000020E6100000010000000500 00000000000000000000000000000000 00000000000000000000000000000000F03F 000000000000F03F000000000000F03F000000000000F03 F000000000000000000000000000000000000000000000000
ST_AsKML — Return the geometry as a KML element. Several variants. Default version=2, default precision=15
text ST_AsKML(
geometry g1)
;
text ST_AsKML(
geography g1)
;
text ST_AsKML(
geometry g1, integer precision)
;
text ST_AsKML(
geography g1, integer precision)
;
text ST_AsKML(
integer version, geometry geom1)
;
text ST_AsKML(
integer version, geography geom1)
;
text ST_AsKML(
integer version, geometry geom1, integer precision)
;
text ST_AsKML(
integer version, geography geom1, integer precision)
;
Return the geometry as a Keyhole Markup Language (KML) element. There are several variants of this function. maximum number of decimal places used in output (defaults to 15) and version default to 2.
Version 1: ST_AsKML(geom) / version=2 precision=15
Version 2: ST_AsKML(geom, max_sig_digits) / version=2
Version 3: ST_AsKML(version, geom) / precision=15
Version 4: ST_AsKML(version, geom, precision)
Requires PostGIS be compiled with Proj support. Use PostGIS_Full_Version to confirm you have proj support compiled in. 
Availability: 1.2.2  later variants that include version param came in 1.3.2 
AsKML output will not work with geometries that do not have an SRID 
This function supports 3d and will not drop the zindex.
SELECT ST_AsKML(ST_GeomFromText('POLYGON((0 0,0 1,1 1,1 0,0 0))',4326)); st_askml  <Polygon><outerBoundaryIs><LinearRing><coordinates>0,0 0,1 1,1 1,0 0,0</coordinates></LinearRing></outerBoundaryIs></Polygon> 3d linestring SELECT ST_AsKML('SRID=4326;LINESTRING(1 2 3, 4 5 6)'); <LineString><coordinates>1,2,3 4,5,6</coordinates></LineString>
ST_AsSVG — Returns a Geometry in SVG path data given a geometry or geography object.
text ST_AsSVG(
geometry g1)
;
text ST_AsSVG(
geography g1)
;
text ST_AsSVG(
geometry g1, integer rel)
;
text ST_AsSVG(
geography g1, integer rel)
;
text ST_AsSVG(
geometry g1, integer rel, integer maxdecimaldigits)
;
text ST_AsSVG(
geography g1, integer rel, integer maxdecimaldigits)
;
Return the geometry as Scalar Vector Graphics (SVG) path data. Use 1 as second argument to have the path data implemented in terms of relative moves, the default (or 0) uses absolute moves. Third argument may be used to reduce the maximum number of decimal digits used in output (defaults to 15). Point geometries will be rendered as cx/cy when 'rel' arg is 0, x/y when 'rel' is 1. Multipoint geometries are delimited by commas (","), GeometryCollection geometries are delimited by semicolons (";").
Availability: 1.2.2 . Availability: 1.4.0 Changed in PostGIS 1.4.0 to include L command in absolute path to conform to http://www.w3.org/TR/SVG/paths.html#PathDataBNF 
ST_GeoHash — Return a GeoHash representation (geohash.org) of the geometry.
text ST_GeoHash(
geometry g1)
;
text ST_GeoHash(
geometry g1, integer precision)
;
Return a GeoHash representation (geohash.org) of the geometry. A GeoHash encodes a point into a text form that is sortable and searchable based on prefixing. A shorter GeoHash is a less precise representation of a point. It can also be thought of as a box, that contains the actual point.
The oneparameter variant of ST_GeoHash returns a GeoHash based on the input geometry type. Points return a GeoHash with 20 characters of precision (about enough to hold the full double precision of the input). Other types return a GeoHash with a variable amount of precision, based on the size of the feature. Larger features are represented with less precision, smaller features with more precision. The idea is that the box implied by the GeoHash will always contain the input feature.
The twoparameter variant of ST_GeoHash returns a GeoHash with a requested precision. For nonpoints, the starting point of the calculation is the center of the bounding box of the geometry.
Availability: 1.4.0
ST_GeoHash will not work with geometries that are not in geographic (lon/lat) coordinates. 
This method supports Circular Strings and Curves
ST_AsText — Return the WellKnown Text (WKT) representation of the geometry/geography without SRID metadata.
text ST_AsText(
geometry g1)
;
text ST_AsText(
geography g1)
;
Returns the WellKnown Text representation of the geometry/geography.
The WKT spec does not include the SRID. To get the SRID as part of the data, use the nonstandard PostGIS ST_AsEWKT 
WKT format does not maintain precision so to prevent floating truncation, use ST_AsBinary or ST_AsEWKB format for transport.
ST_AsText is the reverse of ST_GeomFromText. Use ST_GeomFromText to convert to a postgis geometry from ST_AsText representation. 
Availability: 1.5  support for geography was introduced.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.1
This method implements the SQL/MM specification. SQLMM 3: 5.1.25
This method supports Circular Strings and Curves
SELECT ST_AsText('01030000000100000005000000000000000000 000000000000000000000000000000000000000000000000 F03F000000000000F03F000000000000F03F000000000000F03 F000000000000000000000000000000000000000000000000'); st_astext  POLYGON((0 0,0 1,1 1,1 0,0 0)) (1 row)
TRUE
if A's bounding box overlaps B's.TRUE
if A's bounding box overlaps or is to the left of B's.TRUE
if A's bounding box overlaps or is below B's.TRUE
if A' bounding box overlaps or is to the right of B's.TRUE
if A's bounding box is strictly to the left of B's.TRUE
if A's bounding box is strictly below B's.TRUE
if A's bounding box is the same as B's.TRUE
if A's bounding box is strictly to the right of B's.TRUE
if A's bounding box is contained by B's.TRUE
if A's bounding box overlaps or is above B's.TRUE
if A's bounding box is strictly above B's.TRUE
if A's bounding box contains B's.TRUE
if A's bounding box is the same as B's.&& — Returns TRUE
if A's bounding box overlaps B's.
boolean &&(
geometry
A
,
geometry
B
)
;
boolean &&(
geography
A
,
geography
B
)
;
The &&
operator returns TRUE
if the bounding box of geometry A overlaps the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
Availability: 1.5.0 support for geography was introduced.
This method supports Circular Strings and Curves
SELECT tbl1.column1, tbl2.column1, tbl1.column2 && tbl2.column2 AS overlaps FROM ( VALUES (1, 'LINESTRING(0 0, 3 3)'::geometry), (2, 'LINESTRING(0 1, 0 5)'::geometry)) AS tbl1, ( VALUES (3, 'LINESTRING(1 2, 4 6)'::geometry)) AS tbl2; column1  column1  overlaps ++ 1  3  t 2  3  f (2 rows)
&< — Returns TRUE
if A's bounding box overlaps or is to the left of B's.
boolean &<(
geometry
A
,
geometry
B
)
;
The &<
operator returns TRUE
if the bounding box of geometry A
overlaps or is to the left of the bounding box of geometry B, or more accurately, overlaps or is NOT to the right
of the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 &< tbl2.column2 AS overleft FROM ( VALUES (1, 'LINESTRING(1 2, 4 6)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING(0 0, 3 3)'::geometry), (3, 'LINESTRING(0 1, 0 5)'::geometry), (4, 'LINESTRING(6 0, 6 1)'::geometry)) AS tbl2; column1  column1  overleft ++ 1  2  f 1  3  f 1  4  t (3 rows)
&< — Returns TRUE
if A's bounding box overlaps or is below B's.
boolean &<(
geometry
A
,
geometry
B
)
;
The &<
operator returns TRUE
if the bounding box of geometry A
overlaps or is below of the bounding box of geometry B, or more accurately, overlaps or is NOT above the bounding
box of geometry B.
This method supports Circular Strings and Curves
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 &< tbl2.column2 AS overbelow FROM ( VALUES (1, 'LINESTRING(6 0, 6 4)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING(0 0, 3 3)'::geometry), (3, 'LINESTRING(0 1, 0 5)'::geometry), (4, 'LINESTRING(1 2, 4 6)'::geometry)) AS tbl2; column1  column1  overbelow ++ 1  2  f 1  3  t 1  4  t (3 rows)
&> — Returns TRUE
if A' bounding box overlaps or is to the right of B's.
boolean &>(
geometry
A
,
geometry
B
)
;
The &>
operator returns TRUE
if the bounding box of geometry A
overlaps or is to the right of the bounding box of geometry B, or more accurately, overlaps or is NOT to the left
of the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 &> tbl2.column2 AS overright FROM ( VALUES (1, 'LINESTRING(1 2, 4 6)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING(0 0, 3 3)'::geometry), (3, 'LINESTRING(0 1, 0 5)'::geometry), (4, 'LINESTRING(6 0, 6 1)'::geometry)) AS tbl2; column1  column1  overright ++ 1  2  t 1  3  t 1  4  f (3 rows)
<< — Returns TRUE
if A's bounding box is strictly to the left of B's.
boolean <<(
geometry
A
,
geometry
B
)
;
The <<
operator returns TRUE
if the bounding box of geometry A
is strictly to the left of the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 << tbl2.column2 AS left FROM ( VALUES (1, 'LINESTRING (1 2, 1 5)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING (0 0, 4 3)'::geometry), (3, 'LINESTRING (6 0, 6 5)'::geometry), (4, 'LINESTRING (2 2, 5 6)'::geometry)) AS tbl2; column1  column1  left ++ 1  2  f 1  3  t 1  4  t (3 rows)
<< — Returns TRUE
if A's bounding box is strictly below B's.
boolean <<(
geometry
A
,
geometry
B
)
;
The <<
operator returns TRUE
if the bounding box of geometry A
is strictly below the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 << tbl2.column2 AS below FROM ( VALUES (1, 'LINESTRING (0 0, 4 3)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING (1 4, 1 7)'::geometry), (3, 'LINESTRING (6 1, 6 5)'::geometry), (4, 'LINESTRING (2 3, 5 6)'::geometry)) AS tbl2; column1  column1  below ++ 1  2  t 1  3  f 1  4  f (3 rows)
= — Returns TRUE
if A's bounding box is the same as B's.
boolean =(
geometry
A
,
geometry
B
)
;
boolean =(
geography
A
,
geography
B
)
;
The =
operator returns TRUE
if the bounding box of geometry/geography A
is the same as the bounding box of geometry/geography B. PostgreSQL uses the =, <, and > operators defined for geometries to
perform internal orderings and comparison of geometries (ie. in a GROUP BY or ORDER BY clause).
This is cause for a lot of confusion. When you compare geometryA = geometryB it will return true even when the geometries are clearly different IF their bounding boxes are the same. To check for true equality use ST_OrderingEquals or ST_Equals 
This operand will NOT make use of any indexes that may be available on the geometries. 
This method supports Circular Strings and Curves
SELECT 'LINESTRING(0 0, 0 1, 1 0)'::geometry = 'LINESTRING(1 1, 0 0)'::geometry; ?column?  t (1 row) SELECT ST_AsText(column1) FROM ( VALUES ('LINESTRING(0 0, 1 1)'::geometry), ('LINESTRING(1 1, 0 0)'::geometry)) AS foo; st_astext  LINESTRING(0 0,1 1) LINESTRING(1 1,0 0) (2 rows)  Note: the GROUP BY uses the "=" to compare for geometry equivalency. SELECT ST_AsText(column1) FROM ( VALUES ('LINESTRING(0 0, 1 1)'::geometry), ('LINESTRING(1 1, 0 0)'::geometry)) AS foo GROUP BY column1; st_astext  LINESTRING(0 0,1 1) (1 row)
>> — Returns TRUE
if A's bounding box is strictly to the right of B's.
boolean >>(
geometry
A
,
geometry
B
)
;
The >>
operator returns TRUE
if the bounding box of geometry A
is strictly to the right of the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 >> tbl2.column2 AS right FROM ( VALUES (1, 'LINESTRING (2 3, 5 6)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING (1 4, 1 7)'::geometry), (3, 'LINESTRING (6 1, 6 5)'::geometry), (4, 'LINESTRING (0 0, 4 3)'::geometry)) AS tbl2; column1  column1  right ++ 1  2  t 1  3  f 1  4  f (3 rows)
@ — Returns TRUE
if A's bounding box is contained by B's.
boolean ~=(
geometry
A
,
geometry
B
)
;
The @
operator returns TRUE
if the bounding box of geometry A is completely
contained by the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 @ tbl2.column2 AS contained FROM ( VALUES (1, 'LINESTRING (1 1, 3 3)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING (0 0, 4 4)'::geometry), (3, 'LINESTRING (2 2, 4 4)'::geometry), (4, 'LINESTRING (1 1, 3 3)'::geometry)) AS tbl2; column1  column1  contained ++ 1  2  t 1  3  f 1  4  t (3 rows)
&> — Returns TRUE
if A's bounding box overlaps or is above B's.
boolean &>(
geometry
A
,
geometry
B
)
;
The &>
operator returns TRUE
if the bounding box of geometry A
overlaps or is above the bounding box of geometry B, or more accurately, overlaps or is NOT below
the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 &> tbl2.column2 AS overabove FROM ( VALUES (1, 'LINESTRING(6 0, 6 4)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING(0 0, 3 3)'::geometry), (3, 'LINESTRING(0 1, 0 5)'::geometry), (4, 'LINESTRING(1 2, 4 6)'::geometry)) AS tbl2; column1  column1  overabove ++ 1  2  t 1  3  f 1  4  f (3 rows)
>> — Returns TRUE
if A's bounding box is strictly above B's.
boolean >>(
geometry
A
,
geometry
B
)
;
The >>
operator returns TRUE
if the bounding box of geometry A
is strictly to the right of the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 >> tbl2.column2 AS above FROM ( VALUES (1, 'LINESTRING (1 4, 1 7)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING (0 0, 4 2)'::geometry), (3, 'LINESTRING (6 1, 6 5)'::geometry), (4, 'LINESTRING (2 3, 5 6)'::geometry)) AS tbl2; column1  column1  above ++ 1  2  t 1  3  f 1  4  f (3 rows)
~ — Returns TRUE
if A's bounding box contains B's.
boolean ~(
geometry
A
,
geometry
B
)
;
The ~
operator returns TRUE
if the bounding box of geometry A completely
contains the bounding box of geometry B.
This operand will make use of any indexes that may be available on the geometries. 
SELECT tbl1.column1, tbl2.column1, tbl1.column2 ~ tbl2.column2 AS contains FROM ( VALUES (1, 'LINESTRING (0 0, 3 3)'::geometry)) AS tbl1, ( VALUES (2, 'LINESTRING (0 0, 4 4)'::geometry), (3, 'LINESTRING (1 1, 2 2)'::geometry), (4, 'LINESTRING (0 0, 3 3)'::geometry)) AS tbl2; column1  column1  contains ++ 1  2  f 1  3  t 1  4  t (3 rows)
~= — Returns TRUE
if A's bounding box is the same as B's.
boolean ~=(
geometry
A
,
geometry
B
)
;
boolean ~=(
geography
A
,
geography
B
)
;
The ~=
operator returns TRUE
if the bounding box of geometry/geography A
is the same as the bounding box of geometry/geography B.
This operand will make use of any indexes that may be available on the geometries. 
Availability: 1.5.0 changed behavior
This operator has changed behavior in PostGIS 1.5 from testing for actual geometric equality to only checking for bounding box equality. To complicate things it also depends on if you have done a hard or soft upgrade which behavior your database has. To find out which behavior your database has you can run the query below. To check for true equality use ST_OrderingEquals or ST_Equals and to check for bounding box equality =; operator is a safer option. 
TRUE
if the supplied geometries have some, but not all,
interior points in common.ST_Length
POINT
guaranteed to lie on the surface.TRUE
if the geometries have at least one point in common,
but their interiors do not intersect.ST_Area — Returns the area of the surface if it is a polygon or multipolygon. For "geometry" type area is in SRID units. For "geography" area is in square meters.
float ST_Area(
geometry g1)
;
float ST_Area(
geography g1)
;
float ST_Area(
geography g1, boolean use_spheroid)
;
Returns the area of the geometry if it is a polygon or multipolygon. Return the area measurement of an ST_Surface or ST_MultiSurface value. For geometry Area is in the units of the srid. For geography area is in square meters and defaults to measuring about the spheroid of the geography (currently only WGS84). To measure around the faster but less accurate sphere  ST_Area(geog,false).
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 8.1.2, 9.5.3
Return area in square feet for a plot of Massachusetts land and multiply by conversion to get square meters. Note this is in square feet because 2249 is Mass State Plane Feet
SELECT ST_Area(the_geom) As sqft, ST_Area(the_geom)*POWER(0.3048,2) As sqm FROM (SELECT ST_GeomFromText('POLYGON((743238 2967416,743238 2967450, 743265 2967450,743265.625 2967416,743238 2967416))',2249) ) As foo(the_geom); sqft  sqm + 928.625  86.27208552
Return area square feet and transform to Massachusetts state plane meters (26986) to get square meters. Note this is in square feet because 2249 is Mass State Plane Feet and transformed area is in square meters since 26986 is state plane mass meters
SELECT ST_Area(the_geom) As sqft, ST_Area(ST_Transform(the_geom,26986)) As sqm FROM (SELECT ST_GeomFromText('POLYGON((743238 2967416,743238 2967450, 743265 2967450,743265.625 2967416,743238 2967416))',2249) ) As foo(the_geom); sqft  sqm + 928.625  86.2724304199219
Return area square feet and square meters using Geography data type. Note that we transform to our geometry to geography (before you can do that make sure your geometry is in WGS 84 long lat 4326). Geography always measures in meters. This is just for demonstration to compare. Normally your table will be stored in geography data type already.
SELECT ST_Area(the_geog)/POWER(0.3048,2) As sqft_spheroid, ST_Area(the_geog,false)/POWER(0.3048,2) As sqft_sphere, ST_Area(the_geog) As sqm_spheroid FROM (SELECT geography( ST_Transform( ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,743265 2967450,743265.625 2967416,743238 2967416))', 2249 ) ,4326 ) ) ) As foo(the_geog); sqft_spheroid  sqft_sphere  sqm_spheroid ++ 928.684405217197  927.186481558724  86.2776044452694 if your data is in geography already SELECT ST_Area(the_geog)/POWER(0.3048,2) As sqft, ST_Area(the_geog) As sqm FROM somegeogtable;
ST_Azimuth — Returns the angle in radians from the horizontal of the vector defined by pointA and pointB
float ST_Azimuth(
geometry pointA, geometry pointB)
;
Returns the azimuth of the segment defined by the given Point geometries, or NULL if the two points are coincident. Return value is in radians.
The Azimuth is mathematical concept defined as the angle, in this case measured in radian, between a reference plane and a point
Availability: 1.1.0
Azimuth is especially useful in conjunction with ST_Translate for shifting an object along its perpendicular axis. See upgis_lineshift Plpgsqlfunctions PostGIS wiki section for example of this.
ST_Centroid — Returns the geometric center of a geometry.
geometry ST_Centroid(
geometry
g1)
;
Computes the geometric center of a geometry, or equivalently,
the center of mass of the geometry as a POINT
. For
[MULTI
]POINT
s, this is computed
as the arithmetric mean of the input coordinates. For
[MULTI
]LINESTRING
s, this is
computed as the weighted length of each line segment. For
[MULTI
]POLYGON
s, "weight" is
thought in terms of area. If an empty geometry is supplied, an empty
GEOMETRYCOLLECTION
is returned. If
NULL
is supplied, NULL
is
returned.
The centroid is equal to the centroid of the set of component Geometries of highest dimension (since the lowerdimension geometries contribute zero "weight" to the centroid).
Computation will be more accurate if performed by the GEOS module (enabled at compile time). 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 8.1.4, 9.5.5
In each of the following illustrations, the blue dot represents the centroid of the source geometry.
SELECT ST_AsText(ST_Centroid('MULTIPOINT ( 1 0, 1 2, 1 3, 1 4, 1 7, 0 1, 0 3, 1 1, 2 0, 6 0, 7 8, 9 8, 10 6 )')); st_astext  POINT(2.30769230769231 3.30769230769231) (1 row)
ST_ClosestPoint — Returns the 2dimensional point on g1 that is closest to g2. This is the first point of the shortest line.
geometry ST_ClosestPoint(
geometry
g1, geometry
g2)
;
Returns the 2dimensional point on g1 that is closest to g2. This is the first point of the shortest line.
Availability: 1.5.0
SELECT ST_AsText(ST_ClosestPoint(pt,line)) AS cp_pt_line, ST_AsText(ST_ClosestPoint(line,pt)) As cp_line_pt FROM (SELECT 'POINT(100 100)'::geometry As pt, 'LINESTRING (20 80, 98 190, 110 180, 50 75 )'::geometry As line ) As foo; cp_pt_line  cp_line_pt + POINT(100 100)  POINT(73.0769230769231 115.384615384615)

SELECT ST_AsText( ST_ClosestPoint( ST_GeomFromText('POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'), ST_Buffer(ST_GeomFromText('POINT(110 170)'), 20) ) ) As ptwkt; ptwkt  POINT(140.752120669087 125.695053378061)

ST_Contains — Returns true if and only if no points of B lie in the exterior of A, and at least one point of the interior of B lies in the interior of A.
boolean ST_Contains(
geometry
geomA, geometry
geomB)
;
Geometry A contains Geometry B if and only if no points of B lie in the exterior of A, and at least one point of the interior of B lies in the interior of A. An important subtlety of this definition is that A does not contain its boundary, but A does contain itself. Contrast that to ST_ContainsProperly where geometry A does not Contain Properly itself.
Returns TRUE if geometry B is completely inside geometry A. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID. ST_Contains is the inverse of ST_Within. So ST_Contains(A,B) implies ST_Within(B,A) except in the case of invalid geometries where the result is always false regardless or not defined.
Performed by the GEOS module
Do not call with a 
Do not use this function with invalid geometries. You will get unexpected results. 
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_Contains.
NOTE: this is the "allowable" version that returns a boolean, not an integer.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 // s2.1.13.3  same as within(geometry B, geometry A)
This method implements the SQL/MM specification. SQLMM 3: 5.1.31
There are certain subtleties to ST_Contains and ST_Within that are not intuitively obvious. For details check out Subtleties of OGC Covers, Contains, Within
The ST_Contains
predicate returns TRUE
in all the following illustrations.
The ST_Contains
predicate returns FALSE
in all the following illustrations.
 A circle within a circle SELECT ST_Contains(smallc, bigc) As smallcontainsbig, ST_Contains(bigc,smallc) As bigcontainssmall, ST_Contains(bigc, ST_Union(smallc, bigc)) as bigcontainsunion, ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion, ST_Covers(bigc, ST_ExteriorRing(bigc)) As bigcoversexterior, ST_Contains(bigc, ST_ExteriorRing(bigc)) As bigcontainsexterior FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc, ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo;  Result smallcontainsbig  bigcontainssmall  bigcontainsunion  bigisunion  bigcoversexterior  bigcontainsexterior +++++ f  t  t  t  t  f  Example demonstrating difference between contains and contains properly SELECT ST_GeometryType(geomA) As geomtype, ST_Contains(geomA,geomA) AS acontainsa, ST_ContainsProperly(geomA, geomA) AS acontainspropa, ST_Contains(geomA, ST_Boundary(geomA)) As acontainsba, ST_ContainsProperly(geomA, ST_Boundary(geomA)) As acontainspropba FROM (VALUES ( ST_Buffer(ST_Point(1,1), 5,1) ), ( ST_MakeLine(ST_Point(1,1), ST_Point(1,1) ) ), ( ST_Point(1,1) ) ) As foo(geomA); geomtype  acontainsa  acontainspropa  acontainsba  acontainspropba ++++ ST_Polygon  t  f  f  f ST_LineString  t  f  f  f ST_Point  t  t  f  f
ST_ContainsProperly — Returns true if B intersects the interior of A but not the boundary (or exterior). A does not contain properly itself, but does contain itself.
boolean ST_ContainsProperly(
geometry
geomA, geometry
geomB)
;
Returns true if B intersects the interior of A but not the boundary (or exterior).
A does not contain properly itself, but does contain itself.
Every point of the other geometry is a point of this geometry's interior. The DE9IM Intersection Matrix for the two geometries matches [T**FF*FF*] used in ST_Relate
From JTS docs slightly reworded: The advantage to using this predicate over ST_Contains and ST_Intersects is that it can be computed efficiently, with no need to compute topology at individual points. An example use case for this predicate is computing the intersections of a set of geometries with a large polygonal geometry. Since intersection is a fairly slow operation, it can be more efficient to use containsProperly to filter out test geometries which lie wholly inside the area. In these cases the intersection is known a priori to be exactly the original test geometry. 
Availability: 1.4.0  requires GEOS >= 3.1.0.
Do not call with a 
Do not use this function with invalid geometries. You will get unexpected results. 
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_ContainsProperly.
a circle within a circle SELECT ST_ContainsProperly(smallc, bigc) As smallcontainspropbig, ST_ContainsProperly(bigc,smallc) As bigcontainspropsmall, ST_ContainsProperly(bigc, ST_Union(smallc, bigc)) as bigcontainspropunion, ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion, ST_Covers(bigc, ST_ExteriorRing(bigc)) As bigcoversexterior, ST_ContainsProperly(bigc, ST_ExteriorRing(bigc)) As bigcontainsexterior FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc, ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo; Result smallcontainspropbig  bigcontainspropsmall  bigcontainspropunion  bigisunion  bigcoversexterior  bigcontainsexterior +++++ f  t  f  t  t  f example demonstrating difference between contains and contains properly SELECT ST_GeometryType(geomA) As geomtype, ST_Contains(geomA,geomA) AS acontainsa, ST_ContainsProperly(geomA, geomA) AS acontainspropa, ST_Contains(geomA, ST_Boundary(geomA)) As acontainsba, ST_ContainsProperly(geomA, ST_Boundary(geomA)) As acontainspropba FROM (VALUES ( ST_Buffer(ST_Point(1,1), 5,1) ), ( ST_MakeLine(ST_Point(1,1), ST_Point(1,1) ) ), ( ST_Point(1,1) ) ) As foo(geomA); geomtype  acontainsa  acontainspropa  acontainsba  acontainspropba ++++ ST_Polygon  t  f  f  f ST_LineString  t  f  f  f ST_Point  t  t  f  f
ST_Covers — Returns 1 (TRUE) if no point in Geometry B is outside Geometry A
boolean ST_Covers(
geometry
geomA, geometry
geomB)
;
boolean ST_Covers(
geography
geogpolyA, geography
geogpointB)
;
Returns 1 (TRUE) if no point in Geometry/Geography B is outside Geometry/Geography A
Performed by the GEOS module
Do not call with a 
For geography only Polygon covers point is supported. 
Do not use this function with invalid geometries. You will get unexpected results. 
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_Covers.
Availability: 1.2.2  requires GEOS >= 3.0
Availability: 1.5  support for geography was introduced.
NOTE: this is the "allowable" version that returns a boolean, not an integer.
Not an OGC standard, but Oracle has it too.
There are certain subtleties to ST_Contains and ST_Within that are not intuitively obvious. For details check out Subtleties of OGC Covers, Contains, Within
Geometry example
a circle covering a circle SELECT ST_Covers(smallc,smallc) As smallinsmall, ST_Covers(smallc, bigc) As smallcoversbig, ST_Covers(bigc, ST_ExteriorRing(bigc)) As bigcoversexterior, ST_Contains(bigc, ST_ExteriorRing(bigc)) As bigcontainsexterior FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc, ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo; Result smallinsmall  smallcoversbig  bigcoversexterior  bigcontainsexterior +++ t  f  t  f (1 row)
Geeography Example
ST_CoveredBy — Returns 1 (TRUE) if no point in Geometry/Geography A is outside Geometry/Geography B
boolean ST_CoveredBy(
geometry
geomA, geometry
geomB)
;
boolean ST_CoveredBy(
geography
geogA, geography
geogB)
;
Returns 1 (TRUE) if no point in Geometry/Geography A is outside Geometry/Geography B
Performed by the GEOS module
Do not call with a 
Do not use this function with invalid geometries. You will get unexpected results. 
Availability: 1.2.2  requires GEOS >= 3.0
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_CoveredBy.
NOTE: this is the "allowable" version that returns a boolean, not an integer.
Not an OGC standard, but Oracle has it too.
There are certain subtleties to ST_Contains and ST_Within that are not intuitively obvious. For details check out Subtleties of OGC Covers, Contains, Within
a circle coveredby a circle SELECT ST_CoveredBy(smallc,smallc) As smallinsmall, ST_CoveredBy(smallc, bigc) As smallcoveredbybig, ST_CoveredBy(ST_ExteriorRing(bigc), bigc) As exteriorcoveredbybig, ST_Within(ST_ExteriorRing(bigc),bigc) As exeriorwithinbig FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc, ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo; Result smallinsmall  smallcoveredbybig  exteriorcoveredbybig  exeriorwithinbig +++ t  t  t  f (1 row)
ST_Crosses — Returns TRUE
if the supplied geometries have some, but not all,
interior points in common.
boolean ST_Crosses(
geometry g1, geometry g2)
;
ST_Crosses
takes two geometry objects and
returns TRUE
if their intersection "spatially cross", that is, the
geometries have some, but not all interior points in common. The
intersection of the interiors of the geometries must not be the empty
set and must have a dimensionality less than the the maximum dimension
of the two input geometries. Additionally, the intersection of the two
geometries must not equal either of the source geometries. Otherwise, it
returns FALSE
.
In mathematical terms, this is expressed as:
TODO: Insert appropriate MathML markup here or use a gif. Simple HTML markup does not work well in both IE and Firefox.
The DE9IM Intersection Matrix for the two geometries is:
T*T****** (for Point/Line, Point/Area, and Line/Area situations)
T*****T** (for Line/Point, Area/Point, and Area/Line situations)
0******** (for Line/Line situations)
For any other combination of dimensions this predicate returns false.
The OpenGIS Simple Features Specification defines this predicate only for Point/Line, Point/Area, Line/Line, and Line/Area situations. JTS / GEOS extends the definition to apply to Line/Point, Area/Point and Area/Line situations as well. This makes the relation symmetric.
Do not call with a 
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.13.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.29
The following illustrations all return TRUE
.
Consider a situation where a user has two tables: a table of roads and a table of highways.
CREATE TABLE roads ( id serial NOT NULL, the_geom geometry, CONSTRAINT roads_pkey PRIMARY KEY (road_id) );

CREATE TABLE highways ( id serial NOT NULL, the_gem geometry, CONSTRAINT roads_pkey PRIMARY KEY (road_id) );

To determine a list of roads that cross a highway, use a query similiar to:
SELECT roads.id FROM roads, highways WHERE ST_Crosses(roads.the_geom, highways.the_geom);
ST_LineCrossingDirection — Given 2 linestrings, returns a number between 3 and 3 denoting what kind of crossing behavior. 0 is no crossing.
integer ST_LineCrossingDirection(
geometry linestringA, geometry linestringB)
;
Given 2 linestrings, returns a number between 3 and 3 denoting what kind of crossing behavior. 0 is no crossing. This is only supported for LINESTRING
Definition of integer constants is as follows:
0: LINE NO CROSS
1: LINE CROSS LEFT
1: LINE CROSS RIGHT
2: LINE MULTICROSS END LEFT
2: LINE MULTICROSS END RIGHT
3: LINE MULTICROSS END SAME FIRST LEFT
3: LINE MULTICROSS END SAME FIRST RIGHT
Availability: 1.4
SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 , ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1 FROM ( SELECT ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1, ST_GeomFromText('LINESTRING(171 154,20 140,71 74,161 53)') As line2 ) As foo; l1_cross_l2  l2_cross_l1 + 3  3

SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 , ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1 FROM ( SELECT ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1, ST_GeomFromText('LINESTRING (171 154, 20 140, 71 74, 2.99 90.16)') As line2 ) As foo; l1_cross_l2  l2_cross_l1 + 2  2

SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 , ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1 FROM ( SELECT ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1, ST_GeomFromText('LINESTRING (20 140, 71 74, 161 53)') As line2 ) As foo; l1_cross_l2  l2_cross_l1 + 1  1

SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 , ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1 FROM (SELECT ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1, ST_GeomFromText('LINESTRING(2.99 90.16,71 74,20 140,171 154)') As line2 ) As foo; l1_cross_l2  l2_cross_l1 + 2  2

SELECT s1.gid, s2.gid, ST_LineCrossingDirection(s1.the_geom, s2.the_geom) FROM streets s1 CROSS JOIN streets s2 ON (s1.gid != s2.gid AND s1.the_geom && s2.the_geom ) WHERE ST_CrossingDirection(s1.the_geom, s2.the_geom) > 0;
ST_Disjoint — Returns TRUE if the Geometries do not "spatially intersect"  if they do not share any space together.
boolean ST_Disjoint(
geometry
A
,
geometry
B
)
;
Overlaps, Touches, Within all imply geometries are not spatially disjoint. If any of the aforementioned returns true, then the geometries are not spatially disjoint. Disjoint implies false for spatial intersection.
Do not call with a 
Performed by the GEOS module
This function call does not use indexes 
NOTE: this is the "allowable" version that returns a boolean, not an integer. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 //s2.1.13.3  a.Relate(b, 'FF*FF****')
This method implements the SQL/MM specification. SQLMM 3: 5.1.26
ST_Distance — For geometry type Returns the 2dimensional cartesian minimum distance (based on spatial ref) between two geometries in projected units. For geography type defaults to return spheroidal minimum distance between two geographies in meters.
float ST_Distance(
geometry
g1, geometry
g2)
;
float ST_Distance(
geography
gg1, geography
gg2)
;
float ST_Distance(
geography
gg1, geography
gg2, boolean
use_spheroid)
;
For geometry type returns the 2dimensional minimum cartesian distance between two geometries in projected units (spatial ref units). For geography type defaults to return the minimum distance around WGS 84 spheroid between two geographies in meters. Pass in false to return answer in sphere instead of spheroid.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 5.1.23
Availability: 1.5.0 geography support was introduced in 1.5. Speed improvements for planar to better handle large or many vertex geometries
Geometry example  units in planar degrees 4326 is WGS 84 long lat unit=degrees SELECT ST_Distance( ST_GeomFromText('POINT(72.1235 42.3521)',4326), ST_GeomFromText('LINESTRING(72.1260 42.45, 72.123 42.1546)', 4326) ); st_distance  0.00150567726382282  Geometry example  units in meters (SRID: 26986 Massachusetts state plane meters) (most accurate for Massachusetts) SELECT ST_Distance( ST_Transform(ST_GeomFromText('POINT(72.1235 42.3521)',4326),26986), ST_Transform(ST_GeomFromText('LINESTRING(72.1260 42.45, 72.123 42.1546)', 4326),26986) ); st_distance  123.797937878454  Geometry example  units in meters (SRID: 2163 US National Atlas Equal area) (least accurate) SELECT ST_Distance( ST_Transform(ST_GeomFromText('POINT(72.1235 42.3521)',4326),2163), ST_Transform(ST_GeomFromText('LINESTRING(72.1260 42.45, 72.123 42.1546)', 4326),2163) ); st_distance  126.664256056812  Geography example  same but note units in meters  use sphere for slightly faster less accurate SELECT ST_Distance(gg1, gg2) As spheroid_dist, ST_Distance(gg1, gg2, false) As sphere_dist FROM (SELECT ST_GeographyFromText('SRID=4326;POINT(72.1235 42.3521)') As gg1, ST_GeographyFromText('SRID=4326;LINESTRING(72.1260 42.45, 72.123 42.1546)') As gg2 ) As foo ; spheroid_dist  sphere_dist + 123.802076746848  123.475736916397
ST_HausdorffDistance — Returns the Hausdorff distance between two geometries. Basically a measure of how similar or dissimilar 2 geometries are. Units are in the units of the spatial reference system of the geometries.
float ST_HausdorffDistance(
geometry
g1, geometry
g2)
;
float ST_HausdorffDistance(
geometry
g1, geometry
g2, float
densifyFrac)
;
Implements algorithm for computing a distance metric which can be thought of as the "Discrete Hausdorff Distance". This is the Hausdorff distance restricted to discrete points for one of the geometries. Wikipedia article on Hausdorff distance Martin Davis note on how Hausdorff Distance calculation was used to prove correctness of the CascadePolygonUnion approach.
When densifyFrac is specified, this function performs a segment densification before computing the discrete hausdorff distance. The densifyFrac parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equallength subsegments, whose fraction of the total length is closest to the given fraction.
The current implementation supports only vertices as the discrete locations. This could be extended to allow an arbitrary density of points to be used. 
This algorithm is NOT equivalent to the standard Hausdorff distance. However, it computes an approximation that is correct for a large subset of useful cases. One important part of this subset is Linestrings that are roughly parallel to each other, and roughly equal in length. This is a useful metric for line matching. 
Availability: 1.5.0  requires GEOS >= 3.2.0
postgis=# SELECT st_HausdorffDistance( 'LINESTRING (0 0, 2 0)'::geometry, 'MULTIPOINT (0 1, 1 0, 2 1)'::geometry); st_hausdorffdistance  1 (1 row)
postgis=# SELECT st_hausdorffdistance('LINESTRING (130 0, 0 0, 0 150)'::geometry, 'LINESTRING (10 10, 10 150, 130 10)'::geometry, 0.5); st_hausdorffdistance  70 (1 row)
ST_MaxDistance — Returns the 2dimensional largest distance between two geometries in projected units.
float ST_MaxDistance(
geometry g1, geometry g2)
;
Some useful description here.
Returns the 2dimensional maximum distance between two linestrings in projected units. If g1 and g2 is the same geometry the function will return the distance between the two vertices most far from each other in that geometry. 
Availability: 1.5.0
ST_Distance_Sphere — Returns minimum distance in meters between two lon/lat geometries. Uses a spherical earth and radius of 6370986 meters. Faster than ST_Distance_Spheroid, but less accurate. PostGIS versions prior to 1.5 only implemented for points.
float ST_Distance_Sphere(
geometry geomlonlatA, geometry geomlonlatB)
;
Returns minimum distance in meters between two lon/lat points. Uses a spherical earth and radius of 6370986 meters. Faster than ST_Distance_Spheroid, but less accurate. PostGIS Versions prior to 1.5 only implemented for points.
This function currently does not look at the SRID of a geometry and will always assume its in WGS 84 long lat. Prior versions of this function only support points. 
Availability: 1.5  support for other geometry types besides points was introduced. Prior versions only work with points.
SELECT round(CAST(ST_Distance_Sphere(ST_Centroid(the_geom), ST_GeomFromText('POINT(118 38)',4326)) As numeric),2) As dist_meters, round(CAST(ST_Distance(ST_Transform(ST_Centroid(the_geom),32611), ST_Transform(ST_GeomFromText('POINT(118 38)', 4326),32611)) As numeric),2) As dist_utm11_meters, round(CAST(ST_Distance(ST_Centroid(the_geom), ST_GeomFromText('POINT(118 38)', 4326)) As numeric),5) As dist_degrees, round(CAST(ST_Distance(ST_Transform(the_geom,32611), ST_Transform(ST_GeomFromText('POINT(118 38)', 4326),32611)) As numeric),2) As min_dist_line_point_meters FROM (SELECT ST_GeomFromText('LINESTRING(118.584 38.374,118.583 38.5)', 4326) As the_geom) as foo; dist_meters  dist_utm11_meters  dist_degrees  min_dist_line_point_meters +++ 70424.47  70438.00  0.72900  65871.18
ST_Distance_Spheroid — Returns the minimum distance between two lon/lat geometries given a particular spheroid. PostGIS versions prior to 1.5 only support points.
float ST_Distance_Spheroid(
geometry geomlonlatA, geometry geomlonlatB, spheroid measurement_spheroid)
;
Returns minimum distance in meters between two lon/lat geometries given a particular spheroid. See the explanation of spheroids given for ST_Length_Spheroid. PostGIS version prior to 1.5 only support points.
This function currently does not look at the SRID of a geometry and will always assume its in WGS 80 long lat. Prior versions of this function only support points. 
Availability: 1.5  support for other geometry types besides points was introduced. Prior versions only work with points.
SELECT round(CAST( ST_Distance_Spheroid(ST_Centroid(the_geom), ST_GeomFromText('POINT(118 38)',4326), 'SPHEROID["WGS 84",6378137,298.257223563]') As numeric),2) As dist_meters_spheroid, round(CAST(ST_Distance_Sphere(ST_Centroid(the_geom), ST_GeomFromText('POINT(118 38)',4326)) As numeric),2) As dist_meters_sphere, round(CAST(ST_Distance(ST_Transform(ST_Centroid(the_geom),32611), ST_Transform(ST_GeomFromText('POINT(118 38)', 4326),32611)) As numeric),2) As dist_utm11_meters FROM (SELECT ST_GeomFromText('LINESTRING(118.584 38.374,118.583 38.5)', 4326) As the_geom) as foo; dist_meters_spheroid  dist_meters_sphere  dist_utm11_meters ++ 70454.92  70424.47  70438.00
ST_DFullyWithin — Returns true if all of the geometries are within the specified distance of one another
boolean ST_DFullyWithin(
geometry
g1, geometry
g2, double precision
distance)
;
Returns true if the geometries is fully within the specified distance of one another. The distance is specified in units defined by the spatial reference system of the geometries. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID.
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. 
Availability: 1.5.0
postgis=# SELECT ST_DFullyWithin(geom_a, geom_b, 10) as DFullyWithin10, ST_DWithin(geom_a, geom_b, 10) as DWithin10, ST_DFullyWithin(geom_a, geom_b, 20) as DFullyWithin20 from (select ST_GeomFromText('POINT(1 1)') as geom_a,ST_GeomFromText('LINESTRING(1 5, 2 7, 1 9, 14 12)') as geom_b) t1;  DFullyWithin10  DWithin10  DFullyWithin20  +++ f  t  t 
ST_DWithin — Returns true if the geometries are within the specified distance of one another. For geometry units are in those of spatial reference and For geography units are in meters and measurement is defaulted to use_spheroid=true (measure around spheroid), for faster check, use_spheroid=false to measure along sphere.
boolean ST_DWithin(
geometry
g1, geometry
g2, double precision
distance_of_srid)
;
boolean ST_DWithin(
geography
gg1, geography
gg2, double precision
distance_meters)
;
boolean ST_DWithin(
geography
gg1, geography
gg2, double precision
distance_meters, boolean
use_spheroid)
;
Returns true if the geometries are within the specified distance of one another.
For Geometries: The distance is specified in units defined by the spatial reference system of the geometries. For this function to make sense, the source geometries must both be of the same coorindate projection, having the same SRID.
For geography units are in meters and measurement is defaulted to use_spheroid=true (measure around WGS 84 spheroid), for faster check, use_spheroid=false to measure along sphere.
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. 
Prior to 1.3, ST_Expand was commonly used in conjunction with && and ST_Distance to achieve the same effect and in pre1.3.4 this function was basically shorthand for that construct. From 1.3.4, ST_DWithin uses a more shortcircuit distance function which should make it more efficient than prior versions for larger buffer regions. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
Availability: 1.5.0 support for geography was introduced
Find the nearest hospital to each school that is within 3000 units of the school.  We do an ST_DWithin search to utilize indexes to limit our search list  that the nonindexable ST_Distance needs to process If the units of the spatial reference is meters then units would be meters SELECT DISTINCT ON (s.gid) s.gid, s.school_name, s.the_geom, h.hospital_name FROM schools s LEFT JOIN hospitals h ON ST_DWithin(s.the_geom, h.the_geom, 3000) ORDER BY s.gid, ST_Distance(s.the_geom, h.the_geom); The schools with no close hospitals Find all schools with no hospital within 3000 units away from the school. Units is in units of spatial ref (e.g. meters, feet, degrees) SELECT s.gid, s.school_name FROM schools s LEFT JOIN hospitals h ON ST_DWithin(s.the_geom, h.the_geom, 3000) WHERE h.gid IS NULL;
ST_Equals — Returns true if the given geometries represent the same geometry. Directionality is ignored.
boolean ST_Equals(
geometry A, geometry B)
;
Returns TRUE if the given Geometries are "spatially equal". Use this for a 'better' answer than '='. Note by spatially equal we mean ST_Within(A,B) = true and ST_Within(B,A) = true and also mean ordering of points can be different but represent the same geometry structure. To verify the order of points is consistent, use ST_OrderingEquals (it must be noted ST_OrderingEquals is a little more stringent than simply verifying order of points are the same).
This function will return false if either geometry is invalid even if they are binary equal. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2
This method implements the SQL/MM specification. SQLMM 3: 5.1.24
SELECT ST_Equals(ST_GeomFromText('LINESTRING(0 0, 10 10)'), ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10)')); st_equals  t (1 row) SELECT ST_Equals(ST_Reverse(ST_GeomFromText('LINESTRING(0 0, 10 10)')), ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10)')); st_equals  t (1 row)
ST_HasArc — Returns true if a geometry or geometry collection contains a circular string
boolean ST_HasArc(
geometry geomA)
;
Returns true if a geometry or geometry collection contains a circular string
Availability: 1.2.3?
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
ST_Intersects — Returns TRUE if the Geometries/Geography "spatially intersect"  (share any portion of space) and FALSE if they don't (they are Disjoint). For geography  tolerance is 0.00001 meters (so any points that close are considered to intersect)
boolean ST_Intersects(
geometry
geomA
,
geometry
geomB
)
;
boolean ST_Intersects(
geography
geogA
,
geography
geogB
)
;
Overlaps, Touches, Within all imply spatial intersection. If any of the aforementioned returns true, then the geometries also spatially intersect. Disjoint implies false for spatial intersection.
Do not call with a 
Performed by the GEOS module (for geometry), geography is native
Availability: 1.5 support for geography was introduced.
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. 
For geography, this function has a distance tolerance of about 0.00001 meters and uses the sphere rather than spheroid calculation. 
NOTE: this is the "allowable" version that returns a boolean, not an integer. 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 //s2.1.13.3  ST_Intersects(g1, g2 ) > Not (ST_Disjoint(g1, g2 ))
This method implements the SQL/MM specification. SQLMM 3: 5.1.27
SELECT ST_Intersects('POINT(0 0)'::geometry, 'LINESTRING ( 2 0, 0 2 )'::geometry); st_intersects  f (1 row) SELECT ST_Intersects('POINT(0 0)'::geometry, 'LINESTRING ( 0 0, 0 2 )'::geometry); st_intersects  t (1 row)
ST_Length — Returns the 2d length of the geometry if it is a linestring or multilinestring. geometry are in units of spatial reference and geography are in meters (default spheroid)
float ST_Length(
geometry a_2dlinestring)
;
float ST_Length(
geography gg)
;
float ST_Length(
geography gg, boolean use_spheroid)
;
For geometry: Returns the cartesian 2D length of the geometry if it is a linestring, multilinestring, ST_Curve, ST_MultiCurve. 0 is returned for areal geometries. For areal geometries use ST_Perimeter. Geometry: Measurements are in the units of the spatial reference system of the geometry. Geography: Units are in meters and also acts as a Perimeter function for areal geogs.
Currently for geometry this is an alias for ST_Length2D, but this may change to support higher dimensions.
Currently applying this to a MULTI/POLYGON of type geography will give you the perimeter of the POLYGON/MULTIPOLYGON. This is not the case with the geometry implementation. 
For geography measurement defaults spheroid measurement. To use the faster less accurate sphere use ST_Length(gg,false); 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.5.1
This method implements the SQL/MM specification. SQLMM 3: 7.1.2, 9.3.4
Availability: 1.5.0 geography support was introduced in 1.5.
Return length in feet for line string. Note this is in feet because 2249 is Mass State Plane Feet
SELECT ST_Length(ST_GeomFromText('LINESTRING(743238 2967416,743238 2967450,743265 2967450, 743265.625 2967416,743238 2967416)',2249)); st_length  122.630744000095 Transforming WGS 84 linestring to Massachusetts state plane meters SELECT ST_Length( ST_Transform( ST_GeomFromEWKT('SRID=4326;LINESTRING(72.1260 42.45, 72.1240 42.45666, 72.123 42.1546)'), 26986 ) ); st_length  34309.4563576191
Return length of WGS 84 geography line
 default calculation is using a sphere rather than spheroid SELECT ST_Length(the_geog) As length_spheroid, ST_Length(the_geog,false) As length_sphere FROM (SELECT ST_GeographyFromText( 'SRID=4326;LINESTRING(72.1260 42.45, 72.1240 42.45666, 72.123 42.1546)') As the_geog) As foo; length_spheroid  length_sphere + 34310.5703627305  34346.2060960742 (1 row)
ST_Length2D — Returns the 2dimensional length of the geometry if it is a
linestring or multilinestring. This is an alias for ST_Length
float ST_Length2D(
geometry a_2dlinestring)
;
ST_Length3D — Returns the 3dimensional or 2dimensional length of the geometry if it is a linestring or multilinestring.
float ST_Length3D(
geometry a_3dlinestring)
;
Returns the 3dimensional or 2dimensional length of the geometry if it is a linestring or multilinestring. For 2d lines it will just return the 2d length (same as ST_Length and ST_Length2D)
This function supports 3d and will not drop the zindex.
ST_Length_Spheroid — Calculates the 2D or 3D length of a linestring/multilinestring on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection.
float ST_Length_Spheroid(
geometry a_linestring, spheroid a_spheroid)
;
Calculates the length of a geometry on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection. The ellipsoid is a separate database type and can be constructed as follows:
SPHEROID[<NAME>,<SEMIMAJOR
AXIS>,<INVERSE FLATTENING>]
SPHEROID["GRS_1980",6378137,298.257222101]
Will return 0 for anything that is not a MULTILINESTRING or LINESTRING 
This function supports 3d and will not drop the zindex.
SELECT ST_Length_Spheroid( geometry_column, 'SPHEROID["GRS_1980",6378137,298.257222101]' ) FROM geometry_table; SELECT ST_Length_Spheroid( the_geom, sph_m ) As tot_len, ST_Length_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1, ST_Length_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2 FROM (SELECT ST_GeomFromText('MULTILINESTRING((118.584 38.374,118.583 38.5), (71.05957 42.3589 , 71.061 43))') As the_geom, CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m) as foo; tot_len  len_line1  len_line2 ++ 85204.5207562955  13986.8725229309  71217.6482333646 3D SELECT ST_Length_Spheroid( the_geom, sph_m ) As tot_len, ST_Length_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1, ST_Length_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2 FROM (SELECT ST_GeomFromEWKT('MULTILINESTRING((118.584 38.374 20,118.583 38.5 30), (71.05957 42.3589 75, 71.061 43 90))') As the_geom, CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m) as foo; tot_len  len_line1  len_line2 ++ 85204.5259107402  13986.876097711  71217.6498130292
ST_Length2D_Spheroid — Calculates the 2D length of a linestring/multilinestring on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection.
float ST_Length2D_Spheroid(
geometry a_linestring, spheroid a_spheroid)
;
Calculates the 2D length of a geometry on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection. The ellipsoid is a separate database type and can be constructed as follows:
SPHEROID[<NAME>,<SEMIMAJOR
AXIS>,<INVERSE FLATTENING>]
SPHEROID["GRS_1980",6378137,298.257222101]
Will return 0 for anything that is not a MULTILINESTRING or LINESTRING 
This is much like ST_Length_Spheroid and ST_Length3D_Spheroid except it will throw away the Z coordinate in calculations. 
SELECT ST_Length2D_Spheroid( geometry_column, 'SPHEROID["GRS_1980",6378137,298.257222101]' ) FROM geometry_table; SELECT ST_Length2D_Spheroid( the_geom, sph_m ) As tot_len, ST_Length2D_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1, ST_Length2D_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2 FROM (SELECT ST_GeomFromText('MULTILINESTRING((118.584 38.374,118.583 38.5), (71.05957 42.3589 , 71.061 43))') As the_geom, CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m) as foo; tot_len  len_line1  len_line2 ++ 85204.5207562955  13986.8725229309  71217.6482333646 3D Observe same answer SELECT ST_Length2D_Spheroid( the_geom, sph_m ) As tot_len, ST_Length2D_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1, ST_Length2D_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2 FROM (SELECT ST_GeomFromEWKT('MULTILINESTRING((118.584 38.374 20,118.583 38.5 30), (71.05957 42.3589 75, 71.061 43 90))') As the_geom, CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m) as foo; tot_len  len_line1  len_line2 ++ 85204.5207562955  13986.8725229309  71217.6482333646
ST_Length3D_Spheroid — Calculates the length of a geometry on an ellipsoid, taking the elevation into account. This is just an alias for ST_Length_Spheroid.
float ST_Length3D_Spheroid(
geometry a_linestring, spheroid a_spheroid)
;
Calculates the length of a geometry on an ellipsoid, taking the elevation into account. This is just an alias for ST_Length_Spheroid.
Will return 0 for anything that is not a MULTILINESTRING or LINESTRING 
This functionis just an alias for ST_Length_Spheroid. 
This function supports 3d and will not drop the zindex.
ST_LongestLine — Returns the 2dimensional longest line points of two geometries. The function will only return the first longest line if more than one, that the function finds. The line returned will always start in g1 and end in g2. The length of the line this function returns will always be the same as st_maxdistance returns for g1 and g2.
geometry ST_LongestLine(
geometry
g1, geometry
g2)
;
Returns the 2dimensional longest line between the points of two geometries.
Availability: 1.5.0
SELECT ST_AsText( ST_LongestLine('POINT(100 100)'::geometry, 'LINESTRING (20 80, 98 190, 110 180, 50 75 )'::geometry) ) As lline; lline  LINESTRING(100 100,98 190)

SELECT ST_AsText( ST_LongestLine( ST_GeomFromText('POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'), ST_Buffer(ST_GeomFromText('POINT(110 170)'), 20) ) ) As llinewkt; lline  LINESTRING(20 40,121.111404660392 186.629392246051)

SELECT ST_AsText(ST_LongestLine(c.the_geom, c.the_geom)) As llinewkt, ST_MaxDistance(c.the_geom,c.the_geom) As max_dist, ST_Length(ST_LongestLine(c.the_geom, c.the_geom)) As lenll FROM (SELECT ST_BuildArea(ST_Collect(the_geom)) As the_geom FROM (SELECT ST_Translate(ST_SnapToGrid(ST_Buffer(ST_Point(50 ,generate_series(50,190, 50) ),40, 'quad_segs=2'),1), x, 0) As the_geom FROM generate_series(1,100,50) As x) AS foo ) As c; llinewkt  max_dist  lenll ++ LINESTRING(23 22,129 178)  188.605408193933  188.605408193933

ST_OrderingEquals — Returns true if the given geometries represent the same geometry and points are in the same directional order.
boolean ST_OrderingEquals(
geometry A, geometry B)
;
ST_OrderingEquals compares two geometries and t (TRUE) if the geometries are equal and the coordinates are in the same order; otherwise it returns f (FALSE).
This function is implemented as per the ArcSDE SQL specification rather than SQLMM. http://edndoc.esri.com/arcsde/9.1/sql_api/sqlapi3.htm#ST_OrderingEquals 
This method implements the SQL/MM specification. SQLMM 3: 5.1.43
SELECT ST_OrderingEquals(ST_GeomFromText('LINESTRING(0 0, 10 10)'), ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10)')); st_orderingequals  f (1 row) SELECT ST_OrderingEquals(ST_GeomFromText('LINESTRING(0 0, 10 10)'), ST_GeomFromText('LINESTRING(0 0, 0 0, 10 10)')); st_orderingequals  t (1 row) SELECT ST_OrderingEquals(ST_Reverse(ST_GeomFromText('LINESTRING(0 0, 10 10)')), ST_GeomFromText('LINESTRING(0 0, 0 0, 10 10)')); st_orderingequals  f (1 row)
ST_Overlaps — Returns TRUE if the Geometries share space, are of the same dimension, but are not completely contained by each other.
boolean ST_Overlaps(
geometry A, geometry B)
;
Returns TRUE if the Geometries "spatially overlap". By that we mean they intersect, but one does not completely contain another.
Performed by the GEOS module
Do not call with a GeometryCollection as an argument 
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_Overlaps.
NOTE: this is the "allowable" version that returns a boolean, not an integer.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 // s2.1.13.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.32
a point on a line is contained by the line and is of a lower dimension, and therefore does not overlap the line nor crosses SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Crosses(a,b) As a_crosses_b, ST_Intersects(a, b) As a_intersects_b, ST_Contains(b,a) As b_contains_a FROM (SELECT ST_GeomFromText('POINT(1 0.5)') As a, ST_GeomFromText('LINESTRING(1 0, 1 1, 3 5)') As b) As foo a_overlap_b  a_crosses_b  a_intersects_b  b_contains_a +++ f  f  t  t a line that is partly contained by circle, but not fully is defined as intersecting and crossing,  but since of different dimension it does not overlap SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Crosses(a,b) As a_crosses_b, ST_Intersects(a, b) As a_intersects_b, ST_Contains(a,b) As a_contains_b FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 0.5)'), 3) As a, ST_GeomFromText('LINESTRING(1 0, 1 1, 3 5)') As b) As foo; a_overlap_b  a_crosses_b  a_intersects_b  a_contains_b +++ f  t  t  f  a 2dimensional bent hot dog (aka puffered line string) that intersects a circle,  but is not fully contained by the circle is defined as overlapping since they are of the same dimension,  but it does not cross, because the intersection of the 2 is of the same dimension  as the maximum dimension of the 2 SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Crosses(a,b) As a_crosses_b, ST_Intersects(a, b) As a_intersects_b, ST_Contains(b,a) As b_contains_a, ST_Dimension(a) As dim_a, ST_Dimension(b) as dim_b, ST_Dimension(ST_Intersection(a,b)) As dima_intersection_b FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 0.5)'), 3) As a, ST_Buffer(ST_GeomFromText('LINESTRING(1 0, 1 1, 3 5)'),0.5) As b) As foo; a_overlap_b  a_crosses_b  a_intersects_b  b_contains_a  dim_a  dim_b  dima_intersection_b ++++++ t  f  t  f  2  2  2
ST_Perimeter — Return the length measurement of the boundary of an ST_Surface or ST_MultiSurface value. (Polygon, Multipolygon)
float ST_Perimeter(
geometry g1)
;
Returns the 2D perimeter of the geometry if it is a ST_Surface, ST_MultiSurface (Polygon, Multipolygon). 0 is returned for nonareal geometries. For linestrings use ST_Length. Measurements are in the units of the spatial reference system of the geometry.
Currently this is an alias for ST_Perimeter2D, but this may change to support higher dimensions.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.5.1
This method implements the SQL/MM specification. SQLMM 3: 8.1.3, 9.5.4
Return perimeter in feet for polygon and multipolygon. Note this is in feet because 2249 is Mass State Plane Feet
SELECT ST_Perimeter(ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,743265 2967450, 743265.625 2967416,743238 2967416))', 2249)); st_perimeter  122.630744000095 (1 row) SELECT ST_Perimeter(ST_GeomFromText('MULTIPOLYGON(((763104.471273676 2949418.44119003, 763104.477769673 2949418.42538203, 763104.189609677 2949418.22343004,763104.471273676 2949418.44119003)), ((763104.471273676 2949418.44119003,763095.804579742 2949436.33850239, 763086.132105649 2949451.46730207,763078.452329651 2949462.11549407, 763075.354136904 2949466.17407812,763064.362142565 2949477.64291974, 763059.953961626 2949481.28983009,762994.637609571 2949532.04103014, 762990.568508415 2949535.06640477,762986.710889563 2949539.61421415, 763117.237897679 2949709.50493431,763235.236617789 2949617.95619822, 763287.718121842 2949562.20592617,763111.553321674 2949423.91664605, 763104.471273676 2949418.44119003)))', 2249)); st_perimeter  845.227713366825 (1 row)
ST_Perimeter2D — Returns the 2dimensional perimeter of the geometry, if it is a polygon or multipolygon. This is currently an alias for ST_Perimeter.
float ST_Perimeter2D(
geometry geomA)
;
ST_Perimeter3D — Returns the 3dimensional perimeter of the geometry, if it is a polygon or multipolygon.
float ST_Perimeter3D(
geometry geomA)
;
Returns the 3dimensional perimeter of the geometry, if it is a polygon or multipolygon. If the geometry is 2dimensional, then the 2dimensional perimeter is returned.
This function supports 3d and will not drop the zindex.
Perimeter of a slightly elevated polygon in the air in Massachusetts state plane feet
SELECT ST_Perimeter3D(the_geom), ST_Perimeter2d(the_geom), ST_Perimeter(the_geom) FROM (SELECT ST_GeomFromEWKT('SRID=2249;POLYGON((743238 2967416 2,743238 2967450 1, 743265.625 2967416 1,743238 2967416 2))') As the_geom) As foo; st_perimeter3d  st_perimeter2d  st_perimeter ++ 105.465793597674  105.432997272188  105.432997272188
ST_PointOnSurface — Returns a POINT
guaranteed to lie on the surface.
geometry ST_PointOnSurface(
geometry
g1)
;
Returns a POINT
guaranteed to intersect a surface.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s3.2.14.2 // s3.2.18.2
This method implements the SQL/MM specification. SQLMM 3: 8.1.5, 9.5.6. According to the specs, ST_PointOnSurface works for surface geometries (POLYGONs, MULTIPOLYGONS, CURVED POLYGONS). So PostGIS seems to be extending what the spec allows here. Most databases Oracle,DB II, ESRI SDE seem to only support this function for surfaces. SQL Server 2008 like PostGIS supports for all common geometries.
This function supports 3d and will not drop the zindex.
SELECT ST_AsText(ST_PointOnSurface('POINT(0 5)'::geometry)); st_astext  POINT(0 5) (1 row) SELECT ST_AsText(ST_PointOnSurface('LINESTRING(0 5, 0 10)'::geometry)); st_astext  POINT(0 5) (1 row) SELECT ST_AsText(ST_PointOnSurface('POLYGON((0 0, 0 5, 5 5, 5 0, 0 0))'::geometry)); st_astext  POINT(2.5 2.5) (1 row) SELECT ST_AsEWKT(ST_PointOnSurface(ST_GeomFromEWKT('LINESTRING(0 5 1, 0 0 1, 0 10 2)'))); st_asewkt  POINT(0 0 1) (1 row)
ST_Relate — Returns true if this Geometry is spatially related to anotherGeometry, by testing for intersections between the Interior, Boundary and Exterior of the two geometries as specified by the values in the intersectionMatrixPattern. If no intersectionMatrixPattern is passed in, then returns the maximum intersectionMatrixPattern that relates the 2 geometries.
boolean ST_Relate(
geometry geomA, geometry geomB, text intersectionMatrixPattern)
;
text ST_Relate(
geometry geomA, geometry geomB)
;
Version 1: Takes geomA, geomB, intersectionMatrix and Returns 1 (TRUE) if this Geometry is spatially related to anotherGeometry, by testing for intersections between the Interior, Boundary and Exterior of the two geometries as specified by the values in the intersectionMatrixPattern.
This is especially useful for testing compound checks of intersection, crosses, etc in one step.
Do not call with a GeometryCollection as an argument
This is the "allowable" version that returns a boolean, not an integer. This is defined in OGC spec 
This DOES NOT automagically include an index call. The reason for that is some relationships are anti e.g. Disjoint. If you are using a relationship pattern that requires intersection, then include the && index call. 
Version 2: Takes geomA and geomB and returns the DE9IM (dimensionally extended nineintersection matrix)
Do not call with a GeometryCollection as an argument 
not in OGC spec, but implied. see s2.1.13.2
Both Performed by the GEOS module
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 // s2.1.13.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.25
Find all compounds that intersect and not touch a poly (interior intersects) SELECT l.* , b.name As poly_name FROM polys As b INNER JOIN compounds As l ON (p.the_geom && b.the_geom AND ST_Relate(l.the_geom, b.the_geom,'T********')); SELECT ST_Relate(ST_GeometryFromText('POINT(1 2)'), ST_Buffer(ST_GeometryFromText('POINT(1 2)'),2)); st_relate  0FFFFF212 SELECT ST_Relate(ST_GeometryFromText('LINESTRING(1 2, 3 4)'), ST_GeometryFromText('LINESTRING(5 6, 7 8)')); st_relate  FF1FF0102 SELECT ST_Relate(ST_GeometryFromText('POINT(1 2)'), ST_Buffer(ST_GeometryFromText('POINT(1 2)'),2), '0FFFFF212'); st_relate  t SELECT ST_Relate(ST_GeometryFromText('POINT(1 2)'), ST_Buffer(ST_GeometryFromText('POINT(1 2)'),2), '*FF*FF212'); st_relate  t
ST_ShortestLine — Returns the 2dimensional shortest line between two geometries
geometry ST_ShortestLine(
geometry
g1, geometry
g2)
;
Returns the 2dimensional shortest line between two geometries. The function will only return the first shortest line if more than one, that the function finds. If g1 and g2 intersects in just one point the function will return a line with both start and end in that intersectionpoint. If g1 and g2 are intersecting with more than one point the function will return a line with start and end in the same point but it can be any of the intersecting points. The line returned will always start in g1 and end in g2. The length of the line this function returns will always be the same as st_distance returns for g1 and g2.
Availability: 1.5.0
SELECT ST_AsText( ST_ShortestLine('POINT(100 100)'::geometry, 'LINESTRING (20 80, 98 190, 110 180, 50 75 )'::geometry) ) As sline; sline  LINESTRING(100 100,73.0769230769231 115.384615384615)

SELECT ST_AsText( ST_ShortestLine( ST_GeomFromText('POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'), ST_Buffer(ST_GeomFromText('POINT(110 170)'), 20) ) ) As slinewkt; LINESTRING(140.752120669087 125.695053378061,121.111404660392 153.370607753949)

ST_Touches — Returns TRUE
if the geometries have at least one point in common,
but their interiors do not intersect.
boolean ST_Touches(
geometry
g1, geometry
g2)
;
Returns TRUE
if the only points in common between
g1
and g2
lie in the union of the
boundaries of g1
and g2
.
The ST_Touches
relation applies
to all Area/Area, Line/Line, Line/Area, Point/Area and Point/Line pairs of relationships,
but not to the Point/Point pair.
In mathematical terms, this predicate is expressed as:
TODO: Insert appropriate MathML markup here or use a gif. Simple HTML markup does not work well in both IE and Firefox.
The allowable DE9IM Intersection Matrices for the two geometries are:
FT*******
F**T*****
F***T****
Do not call with a 
This function call will automatically include a bounding box
comparison that will make use of any indexes that are available on
the geometries. To avoid using an index, use 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 // s2.1.13.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.28
The ST_Touches
predicate returns TRUE
in all the following illustrations.
SELECT ST_Touches('LINESTRING(0 0, 1 1, 0 2)'::geometry, 'POINT(1 1)'::geometry); st_touches  f (1 row) SELECT ST_Touches('LINESTRING(0 0, 1 1, 0 2)'::geometry, 'POINT(0 2)'::geometry); st_touches  t (1 row)
ST_Within — Returns true if the geometry A is completely inside geometry B
boolean ST_Within(
geometry
A, geometry
B)
;
Returns TRUE if geometry A is completely inside geometry B. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID. It is a given that if ST_Within(A,B) is true and ST_Within(B,A) is true, then the two geometries are considered spatially equal.
Performed by the GEOS module
Do not call with a 
Do not use this function with invalid geometries. You will get unexpected results. 
This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid index use, use the function _ST_Within.
NOTE: this is the "allowable" version that returns a boolean, not an integer.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 // s2.1.13.3  a.Relate(b, 'T*F**F***')
This method implements the SQL/MM specification. SQLMM 3: 5.1.30
a circle within a circle SELECT ST_Within(smallc,smallc) As smallinsmall, ST_Within(smallc, bigc) As smallinbig, ST_Within(bigc,smallc) As biginsmall, ST_Within(ST_Union(smallc, bigc), bigc) as unioninbig, ST_Within(bigc, ST_Union(smallc, bigc)) as biginunion, ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion FROM ( SELECT ST_Buffer(ST_GeomFromText('POINT(50 50)'), 20) As smallc, ST_Buffer(ST_GeomFromText('POINT(50 50)'), 40) As bigc) As foo; Result smallinsmall  smallinbig  biginsmall  unioninbig  biginunion  bigisunion +++++ t  t  f  t  t  t (1 row)
geometry_dump
rows, representing
the exterior and interior rings of a polygon.ST_Buffer — (T) For geometry: Returns a geometry that represents all points whose distance from this Geometry is less than or equal to distance. Calculations are in the Spatial Reference System of this Geometry. For geography: Uses a planar transform wrapper. Introduced in 1.5 support for different end cap and mitre settings to control shape. buffer_style options: quad_segs=#,endcap=roundflatsquare,join=roundmitrebevel,mitre_limit=#.#
geometry ST_Buffer(
geometry g1, float radius_of_buffer)
;
geometry ST_Buffer(
geometry g1, float radius_of_buffer, integer num_seg_quarter_circle)
;
geometry ST_Buffer(
geometry g1, float radius_of_buffer, text buffer_style_parameters)
;
geography ST_Buffer(
geography g1, float radius_of_buffer_in_meters)
;
Returns a geometry/geography that represents all points whose distance from this Geometry/geography is less than or equal to distance.
Geometry: Calculations are in the Spatial Reference System of the geometry. Introduced in 1.5 support for different end cap and mitre settings to control shape.
Geography: For geography this is really a thin wrapper around the geometry implementation. It first determines the best SRID that fits the bounding box of the geography object (favoring UTM, Lambert Azimuthal Equal Area (LAEA) north/south pole, and falling back on mercator in worst case scenario) and then buffers in that planar spatial ref and retransforms back to WGS84 geography. 
For geography this may not behave as expected if object is sufficiently large that it falls between two UTM zones or crosses the dateline
Availability: 1.5  ST_Buffer was enhanced to support different endcaps and join types. These are useful for example to convert road linestrings into polygon roads with flat or square edges instead of rounded edges. Thin wrapper for geography was added.  requires GEOS >= 3.2 to take advantage of advanced geometry functionality.
The optional third parameter (currently only applies to geometry) can either specify number of segments used to approximate a quarter circle (integer case, defaults to 8) or a list of blankseparated key=value pairs (string case) to tweak operations as follows:
Units of radius are measured in units of the spatial reference system.
The inputs can be POINTS, MULTIPOINTS, LINESTRINGS, MULTILINESTRINGS, POLYGONS, MULTIPOLYGONS, and GeometryCollections.
This function ignores the third dimension (z) and will always give a 2d buffer even when presented with a 3dgeometry. 
Performed by the GEOS module.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.17
People often make the mistake of using this function to try to do radius searches. Creating a buffer to to a radius search is slow and pointless. Use ST_DWithin instead. 
SELECT ST_Buffer( ST_GeomFromText('POINT(100 90)'), 50, 'quad_segs=8');

SELECT ST_Buffer( ST_GeomFromText('POINT(100 90)'), 50, 'quad_segs=2');
 
SELECT ST_Buffer( ST_GeomFromText( 'LINESTRING(50 50,150 150,150 50)' ), 10, 'endcap=round join=round');

SELECT ST_Buffer( ST_GeomFromText( 'LINESTRING(50 50,150 150,150 50)' ), 10, 'endcap=square join=round');

SELECT ST_Buffer( ST_GeomFromText( 'LINESTRING(50 50,150 150,150 50)' ), 10, 'endcap=flat join=round');

SELECT ST_Buffer( ST_GeomFromText( 'LINESTRING(50 50,150 150,150 50)' ), 10, 'join=bevel');

SELECT ST_Buffer( ST_GeomFromText( 'LINESTRING(50 50,150 150,150 50)' ), 10, 'join=mitre mitre_limit=5.0');

SELECT ST_Buffer( ST_GeomFromText( 'LINESTRING(50 50,150 150,150 50)' ), 10, 'join=mitre mitre_limit=1.0');

A buffered point approximates a circle  A buffered point forcing approximation of (see diagram)  2 points per circle is poly with 8 sides (see diagram) SELECT ST_NPoints(ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50)) As promisingcircle_pcount, ST_NPoints(ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50, 2)) As lamecircle_pcount; promisingcircle_pcount  lamecircle_pcount + 33  9 A lighter but lamer circle  only 2 points per quarter circle is an octagon Below is a 100 meter octagon  Note coordinates are in NAD 83 long lat which we transform to Mass state plane meter and then buffer to get measurements in meters; SELECT ST_AsText(ST_Buffer( ST_Transform( ST_SetSRID(ST_MakePoint(71.063526, 42.35785),4269), 26986) ,100,2)) As octagon;  POLYGON((236057.59057465 900908.759918696,236028.301252769 900838.049240578,235 957.59057465 900808.759918696,235886.879896532 900838.049240578,235857.59057465 900908.759918696,235886.879896532 900979.470596815,235957.59057465 901008.759918 696,236028.301252769 900979.470596815,236057.59057465 900908.759918696)) Buffer is often also used as a poor man's polygon fixer or a sometimes speedier unioner Sometimes able to fix invalid polygons  using below  using below on anything but a polygon will result in empty geometry  and for geometry collections kill anything in the collection that is not a polygon Poor man's bad poly fixer SELECT ST_IsValid(foo.invalidpoly) as isvalid, ST_IsValid(ST_Buffer(foo.invalidpoly,0.0)) as bufferisvalid, ST_AsText(ST_Buffer(foo.invalidpoly,0.0)) As newpolytextrep FROM (SELECT ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2, 5 6, 1 2))') as invalidpoly) As foo NOTICE: Selfintersection at or near point 1 2 isvalid  bufferisvalid  newpolytextrep ++ f  t  POLYGON((1 2,5 6,3 4,1 2)) Poor man's polygon unioner SELECT ST_AsText(the_geom) as textorig, ST_AsText(ST_Buffer(foo.the_geom,0.0)) As textbuffer FROM (SELECT ST_Collect('POLYGON((1 2, 3 4, 5 6, 1 2))', 'POLYGON((1 2, 2 3, 5 6, 1 2))') As the_geom) as foo; textorig  textbuffer + MULTIPOLYGON(((1 2,3 4,5 6,1 2)),((1 2,2 3,5 6,1 2)))  POLYGON((1 2,5 6,3 4,2 3,1 2))
ST_BuildArea — Creates an areal geometry formed by the constituent linework of given geometry
geometry ST_BuildArea(
geometry A)
;
Creates an areal geometry formed by the constituent linework of given geometry. The return type can be a Polygon or MultiPolygon, depending on input. If the input lineworks do not form polygons NULL is returned. The inputs can be LINESTRINGS, MULTILINESTRINGS, POLYGONS, MULTIPOLYGONS, and GeometryCollections.
This function will assume all inner geometries represent holes
Availability: 1.1.0  requires GEOS >= 2.1.0.
SELECT ST_BuildArea(ST_Collect(smallc,bigc)) FROM (SELECT ST_Buffer( ST_GeomFromText('POINT(100 90)'), 25) As smallc, ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) As bigc) As foo;

SELECT ST_BuildArea(ST_Collect(line,circle)) FROM (SELECT ST_Buffer( ST_MakeLine(ST_MakePoint(10, 10),ST_MakePoint(190, 190)), 5) As line, ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) As circle) As foo; this creates the same gaping hole but using linestrings instead of polygons SELECT ST_BuildArea( ST_Collect(ST_ExteriorRing(line),ST_ExteriorRing(circle)) ) FROM (SELECT ST_Buffer( ST_MakeLine(ST_MakePoint(10, 10),ST_MakePoint(190, 190)) ,5) As line, ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50) As circle) As foo;

ST_Collect — Return a specified ST_Geometry value from a collection of other geometries.
geometry ST_Collect(
geometry set g1field)
;
geometry ST_Collect(
geometry g1, geometry g2)
;
geometry ST_Collect(
geometry[] g1_array)
;
Output type can be a MULTI* or a GEOMETRYCOLLECTION. Comes in 2 variants. Variant 1 collects 2 geometries. Variant 2 is an aggregate function that takes a set of geometries and collects them into a single ST_Geometry.
Aggregate version: This function returns a GEOMETRYCOLLECTION or a MULTI object from a set of geometries. The ST_Collect() function is an "aggregate" function in the terminology of PostgreSQL. That means that it operates on rows of data, in the same way the SUM() and AVG() functions do. For example, "SELECT ST_Collect(GEOM) FROM GEOMTABLE GROUP BY ATTRCOLUMN" will return a separate GEOMETRYCOLLECTION for each distinct value of ATTRCOLUMN.
NonAggregate version: This function returns a geometry being a collection of two input geometries. Output type can be a MULTI* or a GEOMETRYCOLLECTION.
ST_Collect and ST_Union are often interchangeable. ST_Collect is in general orders of magnitude faster than ST_Union because it does not try to dissolve boundaries or validate that a constructed MultiPolgon doesn't have overlapping regions. It merely rolls up single geometries into MULTI and MULTI or mixed geometry types into Geometry Collections. Unfortunately geometry collections are not wellsupported by GIS tools. To prevent ST_Collect from returning a Geometry Collection when collecting MULTI geometries, one can use the below trick that utilizes ST_Dump to expand the MULTIs out to singles and then regroup them. 
Availability: 1.4.0  ST_Collect(geomarray) was introduced. ST_Collect was enhanced to handle more geometries faster.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves This method supports Circular Strings and Curves, but will never return a MULTICURVE or MULTI as one would expect and PostGIS does not currently support those.
Aggregate example
Thread ref: http://postgis.refractions.net/pipermail/postgisusers/2008June/020331.html SELECT stusps, ST_Multi(ST_Collect(f.the_geom)) as singlegeom FROM (SELECT stusps, (ST_Dump(the_geom)).geom As the_geom FROM somestatetable ) As f GROUP BY stusps
NonAggregate example
Thread ref: http://postgis.refractions.net/pipermail/postgisusers/2008June/020331.html SELECT ST_AsText(ST_Collect(ST_GeomFromText('POINT(1 2)'), ST_GeomFromText('POINT(2 3)') )); st_astext  MULTIPOINT(1 2,2 3) Collect 2 d points SELECT ST_AsText(ST_Collect(ST_GeomFromText('POINT(1 2)'), ST_GeomFromText('POINT(1 2)') ) ); st_astext  MULTIPOINT(1 2,1 2) Collect 3d points SELECT ST_AsEWKT(ST_Collect(ST_GeomFromEWKT('POINT(1 2 3)'), ST_GeomFromEWKT('POINT(1 2 4)') ) ); st_asewkt  MULTIPOINT(1 2 3,1 2 4) Example with curves SELECT ST_AsText(ST_Collect(ST_GeomFromText('CIRCULARSTRING(220268 150415,220227 150505,220227 150406)'), ST_GeomFromText('CIRCULARSTRING(220227 150406,2220227 150407,220227 150406)'))); st_astext  GEOMETRYCOLLECTION(CIRCULARSTRING(220268 150415,220227 150505,220227 150406), CIRCULARSTRING(220227 150406,2220227 150407,220227 150406)) New ST_Collect array construct SELECT ST_Collect(ARRAY(SELECT the_geom FROM sometable)); SELECT ST_AsText(ST_Collect(ARRAY[ST_GeomFromText('LINESTRING(1 2, 3 4)'), ST_GeomFromText('LINESTRING(3 4, 4 5)')])) As wktcollect; wkt collect  MULTILINESTRING((1 2,3 4),(3 4,4 5))
ST_ConvexHull — The convex hull of a geometry represents the minimum convex geometry that encloses all geometries within the set.
geometry ST_ConvexHull(
geometry geomA)
;
The convex hull of a geometry represents the minimum convex geometry that encloses all geometries within the set.
One can think of the convex hull as the geometry you get by wrapping an elastic band around a set of geometries. This is different from a concave hull (not currently supported) which is analogous to shrinkwrapping your geometries.
It is usually used with MULTI and Geometry Collections. Although it is not an aggregate  you can use it in conjunction with ST_Collect to get the convex hull of a set of points. ST_ConvexHull(ST_Collect(somepointfield)).
It is often used to determine an affected area based on a set of point observations.
Performed by the GEOS module
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.16
This function supports 3d and will not drop the zindex.
Get estimate of infected area based on point observations SELECT d.disease_type, ST_ConvexHull(ST_Collect(d.the_geom)) As the_geom FROM disease_obs As d GROUP BY d.disease_type;
SELECT ST_AsText(ST_ConvexHull( ST_Collect( ST_GeomFromText('MULTILINESTRING((100 190,10 8),(150 10, 20 30))'), ST_GeomFromText('MULTIPOINT(50 5, 150 30, 50 10, 10 10)') )) ); st_astext POLYGON((50 5,10 8,10 10,100 190,150 30,150 10,50 5))
ST_CurveToLine — Converts a CIRCULARSTRING/CURVEDPOLYGON to a LINESTRING/POLYGON
geometry ST_CurveToLine(
geometry curveGeom)
;
geometry ST_CurveToLine(
geometry curveGeom, integer segments_per_qtr_circle)
;
Converst a CIRCULAR STRING to regular LINESTRING or CURVEPOLYGON to POLYGON. Useful for outputting to devices that can't support CIRCULARSTRING geometry types
Converts a given geometry to a linear geometry. Each curved geometry or segment is converted into a linear approximation using the default value of 32 segments per quarter circle
Availability: 1.2.2?
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQLMM 3: 7.1.7
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_AsText(ST_CurveToLine(ST_GeomFromText('CIRCULARSTRING(220268 150415,220227 150505,220227 150406)'))); Result  LINESTRING(220268 150415,220269.95064912 150416.539364228,220271.823415575 150418.17258804,220273.613787707 150419.895736857, 220275.317452352 150421.704659462,220276.930305234 150423.594998003,220278.448460847 150425.562198489, 220279.868261823 150427.60152176,220281.186287736 150429.708054909,220282.399363347 150431.876723113, 220283.50456625 150434.10230186,220284.499233914 150436.379429536,220285.380970099 150438.702620341,220286.147650624 150441.066277505, 220286.797428488 150443.464706771,220287.328738321 150445.892130112,220287.740300149 150448.342699654, 220288.031122486 150450.810511759,220288.200504713 150453.289621251,220288.248038775 150455.77405574, 220288.173610157 150458.257830005,220287.977398166 150460.734960415,220287.659875492 150463.199479347, 220287.221807076 150465.64544956,220286.664248262 150468.066978495,220285.988542259 150470.458232479,220285.196316903 150472.81345077, 220284.289480732 150475.126959442,220283.270218395 150477.39318505,220282.140985384 150479.606668057, 220280.90450212 150481.762075989,220279.5637474 150483.85421628,220278.12195122 150485.87804878, 220276.582586992 150487.828697901,220274.949363179 150489.701464356,220273.226214362 150491.491836488, 220271.417291757 150493.195501133,220269.526953216 150494.808354014,220267.559752731 150496.326509628, 220265.520429459 150497.746310603,220263.41389631 150499.064336517,220261.245228106 150500.277412127, 220259.019649359 150501.38261503,220256.742521683 150502.377282695,220254.419330878 150503.259018879, 220252.055673714 150504.025699404,220249.657244448 150504.675477269,220247.229821107 150505.206787101, 220244.779251566 150505.61834893,220242.311439461 150505.909171266,220239.832329968 150506.078553494, 220237.347895479 150506.126087555,220234.864121215 150506.051658938,220232.386990804 150505.855446946, 220229.922471872 150505.537924272,220227.47650166 150505.099855856,220225.054972724 150504.542297043, 220222.663718741 150503.86659104,220220.308500449 150503.074365683, 220217.994991777 150502.167529512,220215.72876617 150501.148267175, 220213.515283163 150500.019034164,220211.35987523 150498.7825509, 220209.267734939 150497.441796181,220207.243902439 150496, 220205.293253319 150494.460635772,220203.420486864 150492.82741196,220201.630114732 150491.104263143, 220199.926450087 150489.295340538,220198.313597205 150487.405001997,220196.795441592 150485.437801511, 220195.375640616 150483.39847824,220194.057614703 150481.291945091,220192.844539092 150479.123276887,220191.739336189 150476.89769814, 220190.744668525 150474.620570464,220189.86293234 150472.297379659,220189.096251815 150469.933722495, 220188.446473951 150467.535293229,220187.915164118 150465.107869888,220187.50360229 150462.657300346, 220187.212779953 150460.189488241,220187.043397726 150457.710378749,220186.995863664 150455.22594426, 220187.070292282 150452.742169995,220187.266504273 150450.265039585,220187.584026947 150447.800520653, 220188.022095363 150445.35455044,220188.579654177 150442.933021505,220189.25536018 150440.541767521, 220190.047585536 150438.18654923,220190.954421707 150435.873040558,220191.973684044 150433.60681495, 220193.102917055 150431.393331943,220194.339400319 150429.237924011,220195.680155039 150427.14578372,220197.12195122 150425.12195122, 220198.661315447 150423.171302099,220200.29453926 150421.298535644,220202.017688077 150419.508163512,220203.826610682 150417.804498867, 220205.716949223 150416.191645986,220207.684149708 150414.673490372,220209.72347298 150413.253689397,220211.830006129 150411.935663483, 220213.998674333 150410.722587873,220216.22425308 150409.61738497,220218.501380756 150408.622717305,220220.824571561 150407.740981121, 220223.188228725 150406.974300596,220225.586657991 150406.324522731,220227 150406) 3d example SELECT ST_AsEWKT(ST_CurveToLine(ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)'))); Output  LINESTRING(220268 150415 1,220269.95064912 150416.539364228 1.0181172856673, 220271.823415575 150418.17258804 1.03623457133459,220273.613787707 150419.895736857 1.05435185700189,....AD INFINITUM .... 220225.586657991 150406.324522731 1.32611114201132,220227 150406 3) use only 2 segments to approximate quarter circle SELECT ST_AsText(ST_CurveToLine(ST_GeomFromText('CIRCULARSTRING(220268 150415,220227 150505,220227 150406)'),2)); st_astext  LINESTRING(220268 150415,220287.740300149 150448.342699654,220278.12195122 150485.87804878, 220244.779251566 150505.61834893,220207.243902439 150496,220187.50360229 150462.657300346, 220197.12195122 150425.12195122,220227 150406)
ST_Difference — Returns a geometry that represents that part of geometry A that does not intersect with geometry B.
geometry ST_Difference(
geometry geomA, geometry geomB)
;
Returns a geometry that represents that part of geometry A that does not intersect with geometry B. One can think of this as GeometryA  ST_Intersection(A,B). If A is completely contained in B then an empty geometry collection is returned.
Note  order matters. B  A will always return a portion of B 
Performed by the GEOS module
Do not call with a GeometryCollection as an argument 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.20
This function supports 3d and will not drop the zindex. However it seems to only consider x y when doing the difference and tacks back on the ZIndex


Safe for 2d. This is same geometries as what is shown for st_symdifference SELECT ST_AsText( ST_Difference( ST_GeomFromText('LINESTRING(50 100, 50 200)'), ST_GeomFromText('LINESTRING(50 50, 50 150)') ) ); st_astext  LINESTRING(50 150,50 200)
When used in 3d doesn't quite do the right thing SELECT ST_AsEWKT(ST_Difference(ST_GeomFromEWKT('MULTIPOINT(118.58 38.38 5,118.60 38.329 6,118.614 38.281 7)'), ST_GeomFromEWKT('POINT(118.614 38.281 5)'))); st_asewkt  MULTIPOINT(118.6 38.329 6,118.58 38.38 5)
ST_Dump — Returns a set of geometry_dump (geom,path) rows, that make up a geometry g1.
geometry_dump[]ST_Dump(
geometry g1)
;
This is a setreturning function (SRF). It returns a set of geometry_dump rows, formed by a geometry (geom) and an array of integers (path). When the input geometry is a simple type (POINT,LINESTRING,POLYGON) a single record will be returned with an empty path array and the input geometry as geom. When the input geometry is a collection or multi it will return a record for each of the collection components, and the path will express the position of the component inside the collection.
ST_Dump is useful for expanding geometries. It is the reverse of a GROUP BY in that it creates new rows. For example it can be use to expand MULTIPOLYGONS into POLYGONS.
Availability: PostGIS 1.0.0RC1. Requires PostgreSQL 7.3 or higher.
Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+ 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT sometable.field1, sometable.field1, (ST_Dump(sometable.the_geom)).geom AS the_geom FROM sometable; Break a compound curve into its constituent linestrings and circularstrings SELECT ST_AsEWKT(a.geom), ST_HasArc(a.geom) FROM ( SELECT (ST_Dump(p_geom)).geom AS geom FROM (SELECT ST_GeomFromEWKT('COMPOUNDCURVE(CIRCULARSTRING(0 0, 1 1, 1 0),(1 0, 0 1))') AS p_geom) AS b ) AS a; st_asewkt  st_hasarc + CIRCULARSTRING(0 0,1 1,1 0)  t LINESTRING(1 0,0 1)  f (2 rows)
ST_DumpPoints — Returns a set of geometry_dump (geom,path) rows of all points that make up a geometry.
geometry_dump[]ST_DumpPoints(
geometry geom)
;
This setreturning function (SRF) returns a set of geometry_dump
rows formed
by a geometry (geom
) and an array of integers (path
).
The geom
component of geometry_dump
are
all the POINT
s that make up the supplied geometry
The path
component of geometry_dump
(an integer[]
)
is an index reference enumerating the POINT
s of the supplied geometry.
For example, if a LINESTRING
is supplied, a path of {i}
is
returned where i
is the nth
coordinate in the LINESTRING
.
If a POLYGON
is supplied, a path of {i,j}
is returned where
i
is the outer ring followed by the inner rings and j
enumerates the POINT
s.
Availability: 1.5.0
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT path, ST_AsText(geom) FROM ( SELECT (ST_DumpPoints(g.geom)).* FROM (SELECT 'GEOMETRYCOLLECTION( POINT ( 0 1 ), LINESTRING ( 0 3, 3 4 ), POLYGON (( 2 0, 2 3, 0 2, 2 0 )), POLYGON (( 3 0, 3 3, 6 3, 6 0, 3 0 ), ( 5 1, 4 2, 5 2, 5 1 )), MULTIPOLYGON ( (( 0 5, 0 8, 4 8, 4 5, 0 5 ), ( 1 6, 3 6, 2 7, 1 6 )), (( 5 4, 5 8, 6 7, 5 4 )) ) )'::geometry AS geom ) AS g ) j; path  st_astext + {1,1}  POINT(0 1) {2,1}  POINT(0 3) {2,2}  POINT(3 4) {3,1,1}  POINT(2 0) {3,1,2}  POINT(2 3) {3,1,3}  POINT(0 2) {3,1,4}  POINT(2 0) {4,1,1}  POINT(3 0) {4,1,2}  POINT(3 3) {4,1,3}  POINT(6 3) {4,1,4}  POINT(6 0) {4,1,5}  POINT(3 0) {4,2,1}  POINT(5 1) {4,2,2}  POINT(4 2) {4,2,3}  POINT(5 2) {4,2,4}  POINT(5 1) {5,1,1,1}  POINT(0 5) {5,1,1,2}  POINT(0 8) {5,1,1,3}  POINT(4 8) {5,1,1,4}  POINT(4 5) {5,1,1,5}  POINT(0 5) {5,1,2,1}  POINT(1 6) {5,1,2,2}  POINT(3 6) {5,1,2,3}  POINT(2 7) {5,1,2,4}  POINT(1 6) {5,2,1,1}  POINT(5 4) {5,2,1,2}  POINT(5 8) {5,2,1,3}  POINT(6 7) {5,2,1,4}  POINT(5 4) (29 rows)
ST_DumpRings — Returns a set of geometry_dump
rows, representing
the exterior and interior rings of a polygon.
geometry_dump[] ST_DumpRings(
geometry a_polygon)
;
This is a setreturning function (SRF). It returns a set of
geometry_dump
rows, defined as an integer[]
and a geometry
, aliased "path" and "geom" respectively.
The "path" field holds the polygon ring index containing a single integer: 0 for the shell, >0 for holes.
The "geom" field contains the corresponding ring as a polygon.
Availability: PostGIS 1.1.3. Requires PostgreSQL 7.3 or higher.
This only works for POLYGON geometries. It will not work for MULTIPOLYGONS 
This function supports 3d and will not drop the zindex.
SELECT sometable.field1, sometable.field1, (ST_DumpRings(sometable.the_geom)).geom As the_geom FROM sometableOfpolys; SELECT ST_AsEWKT(geom) As the_geom, path FROM ST_DumpRings( ST_GeomFromEWKT('POLYGON((8149064 5133092 1,8149064 5132986 1,8148996 5132839 1,8148972 5132767 1,8148958 5132508 1,8148941 5132466 1,8148924 5132394 1, 8148903 5132210 1,8148930 5131967 1,8148992 5131978 1,8149237 5132093 1,8149404 5132211 1,8149647 5132310 1,8149757 5132394 1, 8150305 5132788 1,8149064 5133092 1), (8149362 5132394 1,8149446 5132501 1,8149548 5132597 1,8149695 5132675 1,8149362 5132394 1))') ) as foo; path  the_geom  {0}  POLYGON((8149064 5133092 1,8149064 5132986 1,8148996 5132839 1,8148972 5132767 1,8148958 5132508 1,  8148941 5132466 1,8148924 5132394 1,  8148903 5132210 1,8148930 5131967 1,  8148992 5131978 1,8149237 5132093 1,  8149404 5132211 1,8149647 5132310 1,8149757 5132394 1,8150305 5132788 1,8149064 5133092 1)) {1}  POLYGON((8149362 5132394 1,8149446 5132501 1,  8149548 5132597 1,8149695 5132675 1,8149362 5132394 1))
ST_Intersection — (T) Returns a geometry that represents the shared portion of geomA and geomB. The geography implementation does a transform to geometry to do the intersection and then transform back to WGS84.
geometry ST_Intersection(
geometry
geomA
,
geometry
geomB
)
;
geography ST_Intersection(
geography
geogA
,
geography
geogB
)
;
Returns a geometry that represents the point set intersection of the Geometries.
In other words  that portion of geometry A and geometry B that is shared between the two geometries.
If the geometries do not share any space (are disjoint), then an empty geometry collection is returned.
ST_Intersection in conjunction with ST_Intersects is very useful for clipping geometries such as in bounding box, buffer, region queries where you only want to return that portion of a geometry that sits in a country or region of interest.
Geography: For geography this is really a thin wrapper around the geometry implementation. It first determines the best SRID that fits the bounding box of the 2 geography objects (if geography objects are within one half zone UTM but not same UTM will pick one of those) (favoring UTM or Lambert Azimuthal Equal Area (LAEA) north/south pole, and falling back on mercator in worst case scenario) and then intersection in that best fit planar spatial ref and retransforms back to WGS84 geography. 
Do not call with a 
Performed by the GEOS module
Availability: 1.5 support for geography data type was introduced.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.18
SELECT ST_AsText(ST_Intersection('POINT(0 0)'::geometry, 'LINESTRING ( 2 0, 0 2 )'::geometry)); st_astext  GEOMETRYCOLLECTION EMPTY (1 row) SELECT ST_AsText(ST_Intersection('POINT(0 0)'::geometry, 'LINESTRING ( 0 0, 0 2 )'::geometry)); st_astext  POINT(0 0) (1 row) Clip all lines (trails) by country (here we assume country geom are POLYGON or MULTIPOLYGONS)  NOTE: we are only keeping intersections that result in a LINESTRING or MULTILINESTRING because we don't  care about trails that just share a point  the dump is needed to expand a geometry collection into individual single MULT* parts  the below is fairly generic and will work for polys, etc. by just changing the where clause SELECT clipped.gid, clipped.f_name, clipped_geom FROM (SELECT trails.gid, trails.f_name, (ST_Dump(ST_Intersection(country.the_geom, trails.the_geom))).geom As clipped_geom FROM country INNER JOIN trails ON ST_Intersects(country.the_geom, trails.the_geom)) As clipped WHERE ST_Dimension(clipped.clipped_geom) = 1 ; For polys e.g. polygon landmarks, you can also use the sometimes faster hack that buffering anything by 0.0  except a polygon results in an empty geometry collection (so a geometry collection containing polys, lines and points)  buffered by 0.0 would only leave the polygons and dissolve the collection shell SELECT poly.gid, ST_Multi(ST_Buffer( ST_Intersection(country.the_geom, poly.the_geom), 0.0) ) As clipped_geom FROM country INNER JOIN poly ON ST_Intersects(country.the_geom, poly.the_geom) WHERE Not ST_IsEmpty(ST_Buffer(ST_Intersection(country.the_geom, poly.the_geom),0.0));
ST_LineToCurve — Converts a LINESTRING/POLYGON to a CIRCULARSTRING, CURVED POLYGON
geometry ST_LineToCurve(
geometry geomANoncircular)
;
Converts plain LINESTRING/POLYGONS to CIRCULAR STRINGs and Curved Polygons. Note much fewer points are needed to describe the curved equivalent.
Availability: 1.2.2?
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_AsText(ST_LineToCurve(foo.the_geom)) As curvedastext,ST_AsText(foo.the_geom) As non_curvedastext FROM (SELECT ST_Buffer('POINT(1 3)'::geometry, 3) As the_geom) As foo; curvedatext non_curvedastext   CURVEPOLYGON(CIRCULARSTRING(4 3,3.12132034355964 0.878679656440359,  POLYGON((4 3,3.94235584120969 2.41472903395162,3.77163859753386 1.85194970290473 1 0,1.12132034355965 5.12132034355963,4 3))  ,3.49440883690764 1.33328930094119,3.12132034355964 0.878679656440359,  2.66671069905881 0.505591163092366,2.14805029709527 0.228361402466141,  1.58527096604839 0.0576441587903094,1 0,  0.414729033951621 0.0576441587903077,0.148050297095264 0.228361402466137,  0.666710699058802 0.505591163092361,1.12132034355964 0.878679656440353,  1.49440883690763 1.33328930094119,1.77163859753386 1.85194970290472  ETC ,3.94235584120969 3.58527096604839,4 3)) 3D example SELECT ST_AsEWKT(ST_LineToCurve(ST_GeomFromEWKT('LINESTRING(1 2 3, 3 4 8, 5 6 4, 7 8 4, 9 10 4)'))); st_asewkt  CIRCULARSTRING(1 2 3,5 6 4,9 10 4)
ST_MemUnion — Same as ST_Union, only memoryfriendly (uses less memory and more processor time).
geometry ST_MemUnion(
geometry set geomfield)
;
Some useful description here.
Same as ST_Union, only memoryfriendly (uses less memory and more processor time). This aggregate function works by unioning the geometries one at a time to previous result as opposed to ST_Union aggregate which first creates an array and then unions 
This function supports 3d and will not drop the zindex.
ST_MinimumBoundingCircle — Returns the smallest circle polygon that can fully contain a geometry. Default uses 48 segments per quarter circle.
geometry ST_MinimumBoundingCircle(
geometry geomA)
;
geometry ST_MinimumBoundingCircle(
geometry geomA, integer num_segs_per_qt_circ)
;
Returns the smallest circle polygon that can fully contain a geometry.
The circle is approximated by a polygon with a default of 48 segments per quarter circle. This number can be increased with little performance penalty to obtain a more accurate result. 
It is often used with MULTI and Geometry Collections. Although it is not an aggregate  you can use it in conjunction with ST_Collect to get the minimum bounding cirlce of a set of geometries. ST_MinimumBoundingCircle(ST_Collect(somepointfield)).
The ratio of the area of a polygon divided by the area of its Minimum Bounding Circle is often referred to as the Roeck test.
Availability: 1.4.0  requires GEOS
SELECT d.disease_type, ST_MinimumBoundingCircle(ST_Collect(d.the_geom)) As the_geom FROM disease_obs As d GROUP BY d.disease_type;
SELECT ST_AsText(ST_MinimumBoundingCircle( ST_Collect( ST_GeomFromEWKT('LINESTRING(55 75,125 150)'), ST_Point(20, 80)), 8 )) As wktmbc; wktmbc  POLYGON((135.59714732062 115,134.384753327498 102.690357210921,130.79416296937 90.8537670908995,124.963360620072 79.9451031602111,117.116420743937 70.3835792560632,107.554896839789 62.5366393799277,96.6462329091006 56.70583703063,84.8096427890789 53.115246672502,72.5000000000001 51.9028526793802,60.1903572109213 53.1152466725019,48.3537670908996 56.7058370306299,37.4451031602112 62.5366393799276,27.8835792560632 70.383579256063,20.0366393799278 79.9451031602109,14.20583703063 90.8537670908993,10.615246672502 102.690357210921,9.40285267938019 115,10.6152466725019 127.309642789079,14.2058370306299 139.1462329091,20.0366393799275 150.054896839789,27.883579256063 159.616420743937, 37.4451031602108 167.463360620072,48.3537670908992 173.29416296937,60.190357210921 176.884753327498, 72.4999999999998 178.09714732062,84.8096427890786 176.884753327498,96.6462329091003 173.29416296937,107.554896839789 167.463360620072, 117.116420743937 159.616420743937,124.963360620072 150.054896839789,130.79416296937 139.146232909101,134.384753327498 127.309642789079,135.59714732062 115))
ST_Polygonize — Aggregate. Creates a GeometryCollection containing possible polygons formed from the constituent linework of a set of geometries.
geometry ST_Polygonize(
geometry set geomfield)
;
geometry ST_Polygonize(
geometry[] geom_array)
;
Creates a GeometryCollection containing possible polygons formed from the constituent linework of a set of geometries.
Geometry Collections are often difficult to deal with with third party tools, so use ST_Polygonize in conjunction with ST_Dump to dump the polygons out into individual polygons. 
Availability: 1.0.0RC1  requires GEOS >= 2.1.0.
SELECT ST_AsEWKT(ST_Polygonize(the_geom_4269)) As geomtextrep FROM (SELECT the_geom_4269 FROM ma.suffolk_edges ORDER BY tlid LIMIT 45) As foo; geomtextrep  SRID=4269;GEOMETRYCOLLECTION(POLYGON((71.040878 42.285678,71.040943 42.2856,71.04096 42.285752,71.040878 42.285678)), POLYGON((71.17166 42.353675,71.172026 42.354044,71.17239 42.354358,71.171794 42.354971,71.170511 42.354855, 71.17112 42.354238,71.17166 42.353675))) (1 row) Use ST_Dump to dump out the polygonize geoms into individual polygons SELECT ST_AsEWKT((ST_Dump(foofoo.polycoll)).geom) As geomtextrep FROM (SELECT ST_Polygonize(the_geom_4269) As polycoll FROM (SELECT the_geom_4269 FROM ma.suffolk_edges ORDER BY tlid LIMIT 45) As foo) As foofoo; geomtextrep  SRID=4269;POLYGON((71.040878 42.285678,71.040943 42.2856,71.04096 42.285752, 71.040878 42.285678)) SRID=4269;POLYGON((71.17166 42.353675,71.172026 42.354044,71.17239 42.354358 ,71.171794 42.354971,71.170511 42.354855,71.17112 42.354238,71.17166 42.353675)) (2 rows)
ST_Shift_Longitude — Reads every point/vertex in every component of every feature in a geometry, and if the longitude coordinate is <0, adds 360 to it. The result would be a 0360 version of the data to be plotted in a 180 centric map
geometry ST_Shift_Longitude(
geometry geomA)
;
Reads every point/vertex in every component of every feature in a geometry, and if the longitude coordinate is <0, adds 360 to it. The result would be a 0360 version of the data to be plotted in a 180 centric map
This is only useful for data in long lat e.g. 4326 (WGS 84 long lat) 
Pre1.3.4 bug prevented this from working for MULTIPOINT. 1.3.4+ works with MULTIPOINT as well.
This function supports 3d and will not drop the zindex.
3d points SELECT ST_AsEWKT(ST_Shift_Longitude(ST_GeomFromEWKT('SRID=4326;POINT(118.58 38.38 10)'))) As geomA, ST_AsEWKT(ST_Shift_Longitude(ST_GeomFromEWKT('SRID=4326;POINT(241.42 38.38 10)'))) As geomb geomA geomB   SRID=4326;POINT(241.42 38.38 10) SRID=4326;POINT(118.58 38.38 10) regular line string SELECT ST_AsText(ST_Shift_Longitude(ST_GeomFromText('LINESTRING(118.58 38.38, 118.20 38.45)'))) st_astext  LINESTRING(241.42 38.38,241.8 38.45)
ST_Simplify — Returns a "simplified" version of the given geometry using the DouglasPeuker algorithm.
geometry ST_Simplify(
geometry geomA, float tolerance)
;
Returns a "simplified" version of the given geometry using the DouglasPeuker algorithm. Will actually do something only with (multi)lines and (multi)polygons but you can safely call it with any kind of geometry. Since simplification occurs on a objectbyobject basis you can also feed a GeometryCollection to this function.
Note that returned geometry might loose its simplicity (see ST_IsSimple) 
Note topology may not be preserved and may result in invalid geometries. Use (see ST_SimplifyPreserveTopology) to preserve topology. 
Performed by the GEOS module.
Availability: 1.2.2
A circle simplified too much becomes a triangle, medium an octagon,
SELECT ST_Npoints(the_geom) As np_before, ST_NPoints(ST_Simplify(the_geom,0.1)) As np01_notbadcircle, ST_NPoints(ST_Simplify(the_geom,0.5)) As np05_notquitecircle, ST_NPoints(ST_Simplify(the_geom,1)) As np1_octagon, ST_NPoints(ST_Simplify(the_geom,10)) As np10_triangle, (ST_Simplify(the_geom,100) is null) As np100_geometrygoesaway FROM (SELECT ST_Buffer('POINT(1 3)', 10,12) As the_geom) As foo; result np_before  np01_notbadcircle  np05_notquitecircle  np1_octagon  np10_triangle  np100_geometrygoesaway +++++ 49  33  17  9  4  t
ST_SimplifyPreserveTopology — Returns a "simplified" version of the given geometry using the DouglasPeuker algorithm. Will avoid creating derived geometries (polygons in particular) that are invalid.
geometry ST_SimplifyPreserveTopology(
geometry geomA, float tolerance)
;
Returns a "simplified" version of the given geometry using the DouglasPeuker algorithm. Will avoid creating derived geometries (polygons in particular) that are invalid. Will actually do something only with (multi)lines and (multi)polygons but you can safely call it with any kind of geometry. Since simplification occurs on a objectbyobject basis you can also feed a GeometryCollection to this function.
Performed by the GEOS module.
Requires GEOS 3.0.0+ 
Availability: 1.3.3
Same example as Simplify, but we see Preserve Topology prevents oversimplification. The circle can at most become a square.
SELECT ST_Npoints(the_geom) As np_before, ST_NPoints(ST_SimplifyPreserveTopology(the_geom,0.1)) As np01_notbadcircle, ST_NPoints(ST_SimplifyPreserveTopology(the_geom,0.5)) As np05_notquitecircle, ST_NPoints(ST_SimplifyPreserveTopology(the_geom,1)) As np1_octagon, ST_NPoints(ST_SimplifyPreserveTopology(the_geom,10)) As np10_square, ST_NPoints(ST_SimplifyPreserveTopology(the_geom,100)) As np100_stillsquare FROM (SELECT ST_Buffer('POINT(1 3)', 10,12) As the_geom) As foo; result np_before  np01_notbadcircle  np05_notquitecircle  np1_octagon  np10_square  np100_stillsquare +++++ 49  33  17  9  5  5
ST_SymDifference — Returns a geometry that represents the portions of A and B that do not intersect. It is called a symmetric difference because ST_SymDifference(A,B) = ST_SymDifference(B,A).
geometry ST_SymDifference(
geometry geomA, geometry geomB)
;
Returns a geometry that represents the portions of A and B that do not intersect. It is called a symmetric difference because ST_SymDifference(A,B) = ST_SymDifference(B,A). One can think of this as ST_Union(geomA,geomB)  ST_Intersection(A,B).
Performed by the GEOS module
Do not call with a GeometryCollection as an argument 
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3
This method implements the SQL/MM specification. SQLMM 3: 5.1.21
This function supports 3d and will not drop the zindex. However it seems to only consider x y when doing the difference and tacks back on the ZIndex


Safe for 2d  symmetric difference of 2 linestrings SELECT ST_AsText( ST_SymDifference( ST_GeomFromText('LINESTRING(50 100, 50 200)'), ST_GeomFromText('LINESTRING(50 50, 50 150)') ) ); st_astext  MULTILINESTRING((50 150,50 200),(50 50,50 100))
When used in 3d doesn't quite do the right thing SELECT ST_AsEWKT(ST_SymDifference(ST_GeomFromEWKT('LINESTRING(1 2 1, 1 4 2)'), ST_GeomFromEWKT('LINESTRING(1 1 3, 1 3 4)'))) st_astext  MULTILINESTRING((1 3 2.75,1 4 2),(1 1 3,1 2 2.25))
ST_Union — Returns a geometry that represents the point set union of the Geometries.
geometry ST_Union(
geometry set g1field)
;
geometry ST_Union(
geometry g1, geometry g2)
;
geometry ST_Union(
geometry[] g1_array)
;
Output type can be a MULTI* , single geometry, or Geometry Collection. Comes in 2 variants. Variant 1 unions 2 geometries resulting in a new geomety with no intersecting regions. Variant 2 is an aggregate function that takes a set of geometries and unions them into a single ST_Geometry resulting in no intersecting regions.
Aggregate version: This function returns a MULTI geometry or NONMULTI geometry from a set of geometries. The ST_Union() function is an "aggregate" function in the terminology of PostgreSQL. That means that it operates on rows of data, in the same way the SUM() and AVG() functions do.
NonAggregate version: This function returns a geometry being a union of two input geometries. Output type can be a MULTI* ,NONMULTI or GEOMETRYCOLLECTION.
ST_Collect and ST_Union are often interchangeable. ST_Union is in general orders of magnitude slower than ST_Collect because it tries to dissolve boundaries and reorder geometries to ensure that a constructed Multi* doesn't have intersecting regions. 
Performed by the GEOS module.
NOTE: this function was formerly called GeomUnion(), which was renamed from "Union" because UNION is an SQL reserved word.
Availability: 1.4.0  ST_Union was enhanced. ST_Union(geomarray) was introduced and also faster aggregate collection in PostgreSQL. If you are using GEOS 3.1.0+ ST_Union will use the faster Cascaded Union algorithm described in http://blog.cleverelephant.ca/2009/01/mustfasterunionsinpostgis14.html
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3
Aggregate version is not explicitly defined in OGC SPEC. 
This method implements the SQL/MM specification. SQLMM 3: 5.1.19 the zindex (elevation) when polygons are involved.
Aggregate example
SELECT stusps, ST_Multi(ST_Union(f.the_geom)) as singlegeom FROM sometable As f GROUP BY stusps
NonAggregate example
SELECT ST_AsText(ST_Union(ST_GeomFromText('POINT(1 2)'), ST_GeomFromText('POINT(2 3)') ) ) st_astext  MULTIPOINT(2 3,1 2) SELECT ST_AsText(ST_Union(ST_GeomFromText('POINT(1 2)'), ST_GeomFromText('POINT(1 2)') ) ); st_astext  POINT(1 2) 3d example  sort of supports 3d (and with mixed dimensions!) SELECT ST_AsEWKT(st_union(the_geom)) FROM (SELECT ST_GeomFromEWKT('POLYGON((7 4.2,7.1 4.2,7.1 4.3, 7 4.2))') as the_geom UNION ALL SELECT ST_GeomFromEWKT('POINT(5 5 5)') as the_geom UNION ALL SELECT ST_GeomFromEWKT('POINT(2 3 1)') as the_geom UNION ALL SELECT ST_GeomFromEWKT('LINESTRING(5 5 5, 10 10 10)') as the_geom ) as foo; st_asewkt  GEOMETRYCOLLECTION(POINT(2 3 1),LINESTRING(5 5 5,10 10 10),POLYGON((7 4.2 5,7.1 4.2 5,7.1 4.3 5,7 4.2 5))); 3d example not mixing dimensions SELECT ST_AsEWKT(st_union(the_geom)) FROM (SELECT ST_GeomFromEWKT('POLYGON((7 4.2 2,7.1 4.2 3,7.1 4.3 2, 7 4.2 2))') as the_geom UNION ALL SELECT ST_GeomFromEWKT('POINT(5 5 5)') as the_geom UNION ALL SELECT ST_GeomFromEWKT('POINT(2 3 1)') as the_geom UNION ALL SELECT ST_GeomFromEWKT('LINESTRING(5 5 5, 10 10 10)') as the_geom ) as foo; st_asewkt  GEOMETRYCOLLECTION(POINT(2 3 1),LINESTRING(5 5 5,10 10 10),POLYGON((7 4.2 2,7.1 4.2 3,7.1 4.3 2,7 4.2 2))) Examples using new Array construct SELECT ST_Union(ARRAY(SELECT the_geom FROM sometable)); SELECT ST_AsText(ST_Union(ARRAY[ST_GeomFromText('LINESTRING(1 2, 3 4)'), ST_GeomFromText('LINESTRING(3 4, 4 5)')])) As wktunion; wktunion MULTILINESTRING((3 4,4 5),(1 2,3 4))
ST_Line_Interpolate_Point — Returns a point interpolated along a line. Second argument is a float8 between 0 and 1 representing fraction of total length of linestring the point has to be located.
geometry ST_Line_Interpolate_Point(
geometry a_linestring, float a_fraction)
;
Returns a point interpolated along a line. First argument must be a LINESTRING. Second argument is a float8 between 0 and 1 representing fraction of total linestring length the point has to be located.
See ST_Line_Locate_Point for computing the line location nearest to a Point.
Since release 1.1.1 this function also interpolates M and Z values (when present), while prior releases set them to 0.0. 
Availability: 0.8.2, Z and M supported added in 1.1.1
This function supports 3d and will not drop the zindex.
Return point 20% along 2d line SELECT ST_AsEWKT(ST_Line_Interpolate_Point(the_line, 0.20)) FROM (SELECT ST_GeomFromEWKT('LINESTRING(25 50, 100 125, 150 190)') as the_line) As foo; st_asewkt  POINT(51.5974135047432 76.5974135047432)
Return point midway of 3d line SELECT ST_AsEWKT(ST_Line_Interpolate_Point(the_line, 0.5)) FROM (SELECT ST_GeomFromEWKT('LINESTRING(1 2 3, 4 5 6, 6 7 8)') as the_line) As foo; st_asewkt  POINT(3.5 4.5 5.5) find closest point on a line to a point or other geometry SELECT ST_AsText(ST_Line_Interpolate_Point(foo.the_line, ST_Line_Locate_Point(foo.the_line, ST_GeomFromText('POINT(4 3)')))) FROM (SELECT ST_GeomFromText('LINESTRING(1 2, 4 5, 6 7)') As the_line) As foo; st_astext  POINT(3 4)
ST_Line_Locate_Point — Returns a float between 0 and 1 representing the location of the closest point on LineString to the given Point, as a fraction of total 2d line length.
float ST_Line_Locate_Point(
geometry a_linestring, geometry a_point)
;
Returns a float between 0 and 1 representing the location of the closest point on LineString to the given Point, as a fraction of total 2d line length.
You can use the returned location to extract a Point (ST_Line_Interpolate_Point) or a substring (ST_Line_Substring).
This is useful for approximating numbers of addresses
Availability: 1.1.0
Rough approximation of finding the street number of a point along the street Note the whole foo thing is just to generate dummy data that looks like house centroids and street We use ST_DWithin to exclude houses too far away from the street to be considered on the street SELECT ST_AsText(house_loc) As as_text_house_loc, startstreet_num + CAST( (endstreet_num  startstreet_num) * ST_Line_Locate_Point(street_line, house_loc) As integer) As street_num FROM (SELECT ST_GeomFromText('LINESTRING(1 2, 3 4)') As street_line, ST_MakePoint(x*1.01,y*1.03) As house_loc, 10 As startstreet_num, 20 As endstreet_num FROM generate_series(1,3) x CROSS JOIN generate_series(2,4) As y) As foo WHERE ST_DWithin(street_line, house_loc, 0.2); as_text_house_loc  street_num + POINT(1.01 2.06)  10 POINT(2.02 3.09)  15 POINT(3.03 4.12)  20 find closest point on a line to a point or other geometry SELECT ST_AsText(ST_Line_Interpolate_Point(foo.the_line, ST_Line_Locate_Point(foo.the_line, ST_GeomFromText('POINT(4 3)')))) FROM (SELECT ST_GeomFromText('LINESTRING(1 2, 4 5, 6 7)') As the_line) As foo; st_astext  POINT(3 4)
ST_Line_Substring — Return a linestring being a substring of the input one starting and ending at the given fractions of total 2d length. Second and third arguments are float8 values between 0 and 1.
geometry ST_Line_Substring(
geometry a_linestring, float startfraction, float endfraction)
;
Return a linestring being a substring of the input one starting and ending at the given fractions of total 2d length. Second and third arguments are float8 values between 0 and 1. This only works with LINESTRINGs. To use with contiguous MULTILINESTRINGs use in conjunction with ST_LineMerge.
If 'start' and 'end' have the same value this is equivalent to ST_Line_Interpolate_Point.
See ST_Line_Locate_Point for computing the line location nearest to a Point.
Since release 1.1.1 this function also interpolates M and Z values (when present), while prior releases set them to unspecified values. 
Availability: 1.1.0 , Z and M supported added in 1.1.1
This function supports 3d and will not drop the zindex.
Return the approximate 1/3 midrange part of a linestring SELECT ST_AsText(ST_Line_SubString(ST_GeomFromText('LINESTRING(25 50, 100 125, 150 190)'), 0.333, 0.666)); st_astext  LINESTRING(69.2846934853974 94.2846934853974,100 125,111.700356260683 140.210463138888) The below example simulates a while loop in SQL using PostgreSQL generate_series() to cut all linestrings in a table to 100 unit segments  of which no segment is longer than 100 units  units are measured in the SRID units of measurement  It also assumes all geometries are LINESTRING or contiguous MULTILINESTRING and no geometry is longer than 100 units*10000 for better performance you can reduce the 10000 to match max number of segments you expect SELECT field1, field2, ST_Line_Substring(the_geom, 100.00*n/length, CASE WHEN 100.00*(n+1) < length THEN 100.00*(n+1)/length ELSE 1 END) As the_geom FROM (SELECT sometable.field1, sometable.field2, ST_LineMerge(sometable.the_geom) AS the_geom, ST_Length(sometable.the_geom) As length FROM sometable ) AS t CROSS JOIN generate_series(0,10000) AS n WHERE n*100.00/length < 1;
ST_Locate_Along_Measure — Return a derived geometry collection value with elements that match the specified measure. Polygonal elements are not supported.
geometry ST_Locate_Along_Measure(
geometry ageom_with_measure, float a_measure)
;
Return a derived geometry collection value with elements that match the specified measure. Polygonal elements are not supported.
Semantic is specified by: ISO/IEC CD 132493:200x(E)  Text for Continuation CD Editing Meeting
Availability: 1.1.0
Use this function only for geometries with an M component 
This function supports M coordinates.
SELECT ST_AsEWKT(the_geom) FROM (SELECT ST_Locate_Along_Measure( ST_GeomFromEWKT('MULTILINESTRINGM((1 2 3, 3 4 2, 9 4 3), (1 2 3, 5 4 5))'),3) As the_geom) As foo; st_asewkt  GEOMETRYCOLLECTIONM(MULTIPOINT(1 2 3,9 4 3),POINT(1 2 3)) Geometry collections are difficult animals so dump them to make them more digestable SELECT ST_AsEWKT((ST_Dump(the_geom)).geom) FROM (SELECT ST_Locate_Along_Measure( ST_GeomFromEWKT('MULTILINESTRINGM((1 2 3, 3 4 2, 9 4 3), (1 2 3, 5 4 5))'),3) As the_geom) As foo; st_asewkt  POINTM(1 2 3) POINTM(9 4 3) POINTM(1 2 3)
ST_Locate_Between_Measures — Return a derived geometry collection value with elements that match the specified range of measures inclusively. Polygonal elements are not supported.
geometry ST_Locate_Between_Measures(
geometry geomA, float measure_start, float measure_end)
;
Return a derived geometry collection value with elements that match the specified range of measures inclusively. Polygonal elements are not supported.
Semantic is specified by: ISO/IEC CD 132493:200x(E)  Text for Continuation CD Editing Meeting
Availability: 1.1.0
This function supports M coordinates.
SELECT ST_AsEWKT(the_geom) FROM (SELECT ST_Locate_Between_Measures( ST_GeomFromEWKT('MULTILINESTRINGM((1 2 3, 3 4 2, 9 4 3), (1 2 3, 5 4 5))'),1.5, 3) As the_geom) As foo; st_asewkt  GEOMETRYCOLLECTIONM(LINESTRING(1 2 3,3 4 2,9 4 3),POINT(1 2 3)) Geometry collections are difficult animals so dump them to make them more digestable SELECT ST_AsEWKT((ST_Dump(the_geom)).geom) FROM (SELECT ST_Locate_Between_Measures( ST_GeomFromEWKT('MULTILINESTRINGM((1 2 3, 3 4 2, 9 4 3), (1 2 3, 5 4 5))'),1.5, 3) As the_geom) As foo; st_asewkt  LINESTRINGM(1 2 3,3 4 2,9 4 3) POINTM(1 2 3)
ST_LocateBetweenElevations — Return a derived geometry (collection) value with elements that intersect the specified range of elevations inclusively. Only 3D, 4D LINESTRINGS and MULTILINESTRINGS are supported.
geometry ST_LocateBetweenElevations(
geometry geom_mline, float elevation_start, float elevation_end)
;
Return a derived geometry (collection) value with elements that intersect the specified range of elevations inclusively. Only 3D, 3DM LINESTRINGS and MULTILINESTRINGS are supported.
Availability: 1.4.0
This function supports 3d and will not drop the zindex.
SELECT ST_AsEWKT(ST_LocateBetweenElevations( ST_GeomFromEWKT('LINESTRING(1 2 3, 4 5 6)'),2,4)) As ewelev; ewelev  MULTILINESTRING((1 2 3,2 3 4)) SELECT ST_AsEWKT(ST_LocateBetweenElevations( ST_GeomFromEWKT('LINESTRING(1 2 6, 4 5 1, 7 8 9)'),6,9)) As ewelev; ewelev  GEOMETRYCOLLECTION(POINT(1 2 6),LINESTRING(6.1 7.1 6,7 8 9)) Geometry collections are difficult animals so dump them to make them more digestable SELECT ST_AsEWKT((ST_Dump(the_geom)).geom) FROM (SELECT ST_LocateBetweenElevations( ST_GeomFromEWKT('LINESTRING(1 2 6, 4 5 1, 7 8 9)'),6,9) As the_geom) As foo; st_asewkt  POINT(1 2 6) LINESTRING(6.1 7.1 6,7 8 9)
ST_AddMeasure — Return a derived geometry with measure elements linearly interpolated between the start and end points. If the geometry has no measure dimension, one is added. If the geometry has a measure dimension, it is overwritten with new values. Only LINESTRINGS and MULTILINESTRINGS are supported.
geometry ST_AddMeasure(
geometry geom_mline, float measure_start, float measure_end)
;
Return a derived geometry with measure elements linearly interpolated between the start and end points. If the geometry has no measure dimension, one is added. If the geometry has a measure dimension, it is overwritten with new values. Only LINESTRINGS and MULTILINESTRINGS are supported.
Availability: 1.5.0
This function supports 3d and will not drop the zindex.
SELECT ST_AsEWKT(ST_AddMeasure( ST_GeomFromEWKT('LINESTRING(1 0, 2 0, 4 0)'),1,4)) As ewelev; ewelev  LINESTRINGM(1 0 1,2 0 2,4 0 4) SELECT ST_AsEWKT(ST_AddMeasure( ST_GeomFromEWKT('LINESTRING(1 0 4, 2 0 4, 4 0 4)'),10,40)) As ewelev; ewelev  LINESTRING(1 0 4 10,2 0 4 20,4 0 4 40) SELECT ST_AsEWKT(ST_AddMeasure( ST_GeomFromEWKT('LINESTRINGM(1 0 4, 2 0 4, 4 0 4)'),10,40)) As ewelev; ewelev  LINESTRINGM(1 0 10,2 0 20,4 0 40) SELECT ST_AsEWKT(ST_AddMeasure( ST_GeomFromEWKT('MULTILINESTRINGM((1 0 4, 2 0 4, 4 0 4),(1 0 4, 2 0 4, 4 0 4))'),10,70)) As ewelev; ewelev  MULTILINESTRINGM((1 0 10,2 0 20,4 0 40),(1 0 40,2 0 50,4 0 70))
This module and associated pl/pgsql functions have been implemented to provide long locking support required by Web Feature Service specification.
Users must use serializable transaction level otherwise locking mechanism would break. 
AddAuth — Add an authorization token to be used in current transaction.
boolean AddAuth(
text auth_token)
;
Add an authorization token to be used in current transaction.
Creates/adds to a temp table called temp_lock_have_table the current transaction identifier and authorization token key.
Availability: 1.1.3
CheckAuth — Creates trigger on a table to prevent/allow updates and deletes of rows based on authorization token.
integer CheckAuth(
text a_schema_name, text a_table_name, text a_key_column_name)
;
integer CheckAuth(
text a_table_name, text a_key_column_name)
;
Creates trigger on a table to prevent/allow updates and deletes of rows based on authorization token. Identify rows using <rowid_col> column.
If a_schema_name is not passed in, then searches for table in current schema.
If an authorization trigger already exists on this table function errors. If Transaction support is not enabled, function throws an exception. 
Availability: 1.1.3
DisableLongTransactions — Disable long transaction support. This function removes the long transaction support metadata tables, and drops all triggers attached to lockchecked tables.
text DisableLongTransactions(
Disable long transaction support. This function removes the long transaction support metadata tables, and drops all triggers attached to lockchecked tables.
Drops meta table called authorization_table
and a view called authorized_tables
and all triggers called checkauthtrigger
Availability: 1.1.3
EnableLongTransactions — Enable long transaction support. This function creates the required metadata tables, needs to be called once before using the other functions in this section. Calling it twice is harmless.
text EnableLongTransactions(
Enable long transaction support. This function creates the required metadata tables, needs to be called once before using the other functions in this section. Calling it twice is harmless.
Creates a meta table called authorization_table
and a view called authorized_tables
Availability: 1.1.3
LockRow — Set lock/authorization for specific row in table
integer LockRow(
text a_schema_name, text a_table_name, text a_row_key, text an_auth_token, timestamp expire_dt)
;
integer LockRow(
text a_table_name, text a_row_key, text an_auth_token, timestamp expire_dt)
;
integer LockRow(
text a_table_name, text a_row_key, text an_auth_token)
;
Set lock/authorization for specific row in table <authid> is a text value, <expires> is a timestamp defaulting to now()+1hour. Returns 1 if lock has been assigned, 0 otherwise (already locked by other auth)
Availability: 1.1.3
UnlockRows — Remove all locks held by specified authorization id. Returns the number of locks released.
integer UnlockRows(
text auth_token)
;
Remove all locks held by specified authorization id. Returns the number of locks released.
Availability: 1.1.3
ST_Accum — Aggregate. Constructs an array of geometries.
geometry[] ST_Accum(
geometry set geomfield)
;
Aggregate. Constructs an array of geometries.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT (ST_Accum(the_geom)) As all_em, ST_AsText((ST_Accum(the_geom))[1]) As grabone, (ST_Accum(the_geom))[2:4] as grab_rest FROM (SELECT ST_MakePoint(a*CAST(random()*10 As integer), a*CAST(random()*10 As integer), a*CAST(random()*10 As integer)) As the_geom FROM generate_series(1,4) a) As foo; all_emgrabone  grab_rest + {0101000080000000000000144000000000000024400000000000001040: 0101000080000000000 00018400000000000002C400000000000003040: 0101000080000000000000354000000000000038400000000000001840: 010100008000000000000040400000000000003C400000000000003040}  POINT(5 10)  {010100008000000000000018400000000000002C400000000000003040: 0101000080000000000000354000000000000038400000000000001840: 010100008000000000000040400000000000003C400000000000003040} (1 row)
Box2D — Returns a BOX2D representing the maximum extents of the geometry.
box2d Box2D(
geometry geomA)
;
Returns a BOX2D representing the maximum extents of the geometry.
This method supports Circular Strings and Curves
Box3D — Returns a BOX3D representing the maximum extents of the geometry.
box3d Box3D(
geometry geomA)
;
Returns a BOX3D representing the maximum extents of the geometry.
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
ST_Estimated_Extent — Return the 'estimated' extent of the given spatial table. The estimated is taken from the geometry column's statistics. The current schema will be used if not specified.
box2d ST_Estimated_Extent(
text schema_name, text table_name, text geocolumn_name)
;
box2d ST_Estimated_Extent(
text table_name, text geocolumn_name)
;
Return the 'estimated' extent of the given spatial table. The estimated is taken from the geometry column's statistics. The current schema will be used if not specified.
For PostgreSQL>=8.0.0 statistics are gathered by VACUUM ANALYZE and resulting extent will be about 95% of the real one.
For PostgreSQL<8.0.0 statistics are gathered by update_geometry_stats() and resulting extent will be exact.
This method supports Circular Strings and Curves
ST_Expand — Returns bounding box expanded in all directions from the bounding box of the input geometry. Uses doubleprecision
geometry ST_Expand(
geometry g1, float units_to_expand)
;
box2d ST_Expand(
box2d g1, float units_to_expand)
;
box3d ST_Expand(
box3d g1, float units_to_expand)
;
This function returns a bounding box expanded in all directions from the bounding box of the input geometry, by an amount specified in the second argument. Uses doubleprecision. Very useful for distance() queries, or bounding box queries to add an index filter to the query.
There are 3 variants of this. The one that takes a geometry will return a POLYGON geometry representation of the bounding box and is the most commonly used variant.
ST_Expand is similar in concept to ST_Buffer except while buffer expands the geometry in all directions, ST_Expand expands the bounding box an x,y,z unit amount.
Units are in the units of the spatial reference system in use denoted by the SRID
Pre 1.3, ST_Expand was used in conjunction with distance to do indexable queries. Something of the form

Bounding boxes of all geometries are currently 2d even if they are 3dimensional geometries. 
Availability: 1.5.0 behavior changed to output double precision instead of float4 coordinates. 
Examples below use US National Atlas Equal Area (SRID=2163) which is a meter projection 
10 meter expanded box around bbox of a linestring SELECT CAST(ST_Expand(ST_GeomFromText('LINESTRING(2312980 110676,2312923 110701,2312892 110714)', 2163),10) As box2d); st_expand  BOX(2312882 110666,2312990 110724) 10 meter expanded 3d box of a 3d box SELECT ST_Expand(CAST('BOX3D(778783 2951741 1,794875 2970042.61545891 10)' As box3d),10) st_expand  BOX3D(778773 2951731 9,794885 2970052.61545891 20) 10 meter geometry astext rep of a expand box around a point geometry SELECT ST_AsEWKT(ST_Expand(ST_GeomFromEWKT('SRID=2163;POINT(2312980 110676)'),10)); st_asewkt  SRID=2163;POLYGON((2312970 110666,2312970 110686,2312990 110686,2312990 110666,2312970 110666))
ST_Extent — an aggregate function that returns the bounding box that bounds rows of geometries.
box3d_extent ST_Extent(
geometry set geomfield)
;
ST_Extent returns a bounding box that encloses a set of geometries. The ST_Extent function is an "aggregate" function in the terminology of SQL. That means that it operates on lists of data, in the same way the SUM() and AVG() functions do.
Since it returns a bounding box, the spatial Units are in the units of the spatial reference system in use denoted by the SRID
ST_Extent is similar in concept to Oracle Spatial/Locator's SDO_AGGR_MBR
Since ST_Extent returns a bounding box, the SRID metadata is lost. Use ST_SetSRID to force it back into a geometry with SRID meta data. The coordinates are in the units of the spatial ref of the orginal geometries. 
ST_Extent will return boxes with only an x and y component even with (x,y,z) coordinate geometries. To maintain x,y,z use ST_Extent3D instead. 
Availability: 1.4.0 As of 1.4.0 now returns a box3d_extent instead of box2d object. 
Examples below use Massachusetts State Plane ft (SRID=2249) 
SELECT ST_Extent(the_geom) as bextent FROM sometable; st_bextent  BOX(739651.875 2908247.25,794875.8125 2970042.75) Return extent of each category of geometries SELECT ST_Extent(the_geom) as bextent FROM sometable GROUP BY category ORDER BY category; bextent  name + BOX(778783.5625 2951741.25,794875.8125 2970042.75)  A BOX(751315.8125 2919164.75,765202.6875 2935417.25)  B BOX(739651.875 2917394.75,756688.375 2935866)  C Force back into a geometry  and render the extended text representation of that geometry SELECT ST_SetSRID(ST_Extent(the_geom),2249) as bextent FROM sometable; bextent  SRID=2249;POLYGON((739651.875 2908247.25,739651.875 2970042.75,794875.8125 2970042.75, 794875.8125 2908247.25,739651.875 2908247.25))
ST_Extent3D — an aggregate function that returns the box3D bounding box that bounds rows of geometries.
box3d ST_Extent3D(
geometry set geomfield)
;
ST_Extent3D returns a box3d (includes Z coordinate) bounding box that encloses a set of geometries. The ST_Extent3D function is an "aggregate" function in the terminology of SQL. That means that it operates on lists of data, in the same way the SUM() and AVG() functions do.
Since it returns a bounding box, the spatial Units are in the units of the spatial reference system in use denoted by the SRID
Since ST_Extent3D returns a bounding box, the SRID metadata is lost. Use ST_SetSRID to force it back into a geometry with SRID meta data. The coordinates are in the units of the spatial ref of the orginal geometries. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_Extent3D(foo.the_geom) As b3extent FROM (SELECT ST_MakePoint(x,y,z) As the_geom FROM generate_series(1,3) As x CROSS JOIN generate_series(1,2) As y CROSS JOIN generate_series(0,2) As Z) As foo; b3extent  BOX3D(1 1 0,3 2 2) Get the extent of various elevated circular strings SELECT ST_Extent3D(foo.the_geom) As b3extent FROM (SELECT ST_Translate(ST_Force_3DZ(ST_LineToCurve(ST_Buffer(ST_MakePoint(x,y),1))),0,0,z) As the_geom FROM generate_series(1,3) As x CROSS JOIN generate_series(1,2) As y CROSS JOIN generate_series(0,2) As Z) As foo; b3extent  BOX3D(1 0 0,4 2 2)
Find_SRID — The syntax is find_srid(<db/schema>, <table>, <column>) and the function returns the integer SRID of the specified column by searching through the GEOMETRY_COLUMNS table.
integer Find_SRID(
varchar a_schema_name, varchar a_table_name, varchar a_geomfield_name)
;
The syntax is find_srid(<db/schema>, <table>, <column>) and the function returns the integer SRID of the specified column by searching through the GEOMETRY_COLUMNS table. If the geometry column has not been properly added with the AddGeometryColumns() function, this function will not work either.
ST_Mem_Size — Returns the amount of space (in bytes) the geometry takes.
integer ST_Mem_Size(
geometry geomA)
;
Returns the amount of space (in bytes) the geometry takes.
This is a nice compliment to PostgreSQL built in functions pg_size_pretty, pg_relation_size, pg_total_relation_size.
pg_relation_size which gives the byte size of a table may return byte size lower than ST_Mem_Size. This is because pg_relation_size does not add toasted table contribution and large geometries are stored in TOAST tables. pg_total_relation_size  includes, the table, the toasted tables, and the indexes. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
Return how much byte space Boston takes up in our Mass data set SELECT pg_size_pretty(SUM(ST_Mem_Size(the_geom))) as totgeomsum, pg_size_pretty(SUM(CASE WHEN town = 'BOSTON' THEN st_mem_size(the_geom) ELSE 0 END)) As bossum, CAST(SUM(CASE WHEN town = 'BOSTON' THEN st_mem_size(the_geom) ELSE 0 END)*1.00 / SUM(st_mem_size(the_geom))*100 As numeric(10,2)) As perbos FROM towns; totgeomsum bossum perbos    1522 kB 30 kB 1.99 SELECT ST_Mem_Size(ST_GeomFromText('CIRCULARSTRING(220268 150415,220227 150505,220227 150406)'));  73 What percentage of our table is taken up by just the geometry SELECT pg_total_relation_size('public.neighborhoods') As fulltable_size, sum(ST_Mem_Size(the_geom)) As geomsize, sum(ST_Mem_Size(the_geom))*1.00/pg_total_relation_size('public.neighborhoods')*100 As pergeom FROM neighborhoods; fulltable_size geomsize pergeom  262144 96238 36.71188354492187500000
ST_Point_Inside_Circle — Is the point geometry insert circle defined by center_x, center_y , radius
boolean ST_Point_Inside_Circle(
geometry a_point, float center_x, float center_y, float radius)
;
The syntax for this functions is point_inside_circle(<geometry>,<circle_center_x>,<circle_center_y>,<radius>). Returns the true if the geometry is a point and is inside the circle. Returns false otherwise.
This only works for points as the name suggests 
ST_XMax — Returns X maxima of a bounding box 2d or 3d or a geometry.
float ST_XMax(
box3d aGeomorBox2DorBox3D)
;
Returns X maxima of a bounding box 2d or 3d or a geometry.
Although this function is only defined for box3d, it will work for box2d and geometry because of the autocasting behavior defined for geometries and box2d. However you can not feed it a geometry or box2d text represenation, since that will not autocast. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_XMax('BOX3D(1 2 3, 4 5 6)'); st_xmax  4 SELECT ST_XMax(ST_GeomFromText('LINESTRING(1 3 4, 5 6 7)')); st_xmax  5 SELECT ST_XMax(CAST('BOX(3 2, 3 4)' As box2d)); st_xmax  3 Observe THIS DOES NOT WORK because it will try to autocast the string representation to a BOX3D SELECT ST_XMax('LINESTRING(1 3, 5 6)'); ERROR: BOX3D parser  doesnt start with BOX3D( SELECT ST_XMax(ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)')); st_xmax  220288.248780547
ST_XMin — Returns X minima of a bounding box 2d or 3d or a geometry.
float ST_XMin(
box3d aGeomorBox2DorBox3D)
;
Returns X minima of a bounding box 2d or 3d or a geometry.
Although this function is only defined for box3d, it will work for box2d and geometry because of the autocasting behavior defined for geometries and box2d. However you can not feed it a geometry or box2d text represenation, since that will not autocast. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_XMin('BOX3D(1 2 3, 4 5 6)'); st_xmin  1 SELECT ST_XMin(ST_GeomFromText('LINESTRING(1 3 4, 5 6 7)')); st_xmin  1 SELECT ST_XMin(CAST('BOX(3 2, 3 4)' As box2d)); st_xmin  3 Observe THIS DOES NOT WORK because it will try to autocast the string representation to a BOX3D SELECT ST_XMin('LINESTRING(1 3, 5 6)'); ERROR: BOX3D parser  doesnt start with BOX3D( SELECT ST_XMin(ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)')); st_xmin  220186.995121892
ST_YMax — Returns Y maxima of a bounding box 2d or 3d or a geometry.
float ST_YMax(
box3d aGeomorBox2DorBox3D)
;
Returns Y maxima of a bounding box 2d or 3d or a geometry.
Although this function is only defined for box3d, it will work for box2d and geometry because of the autocasting behavior defined for geometries and box2d. However you can not feed it a geometry or box2d text represenation, since that will not autocast. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_YMax('BOX3D(1 2 3, 4 5 6)'); st_ymax  5 SELECT ST_YMax(ST_GeomFromText('LINESTRING(1 3 4, 5 6 7)')); st_ymax  6 SELECT ST_YMax(CAST('BOX(3 2, 3 4)' As box2d)); st_ymax  4 Observe THIS DOES NOT WORK because it will try to autocast the string representation to a BOX3D SELECT ST_YMax('LINESTRING(1 3, 5 6)'); ERROR: BOX3D parser  doesnt start with BOX3D( SELECT ST_YMax(ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)')); st_ymax  150506.126829327
ST_YMin — Returns Y minima of a bounding box 2d or 3d or a geometry.
float ST_YMin(
box3d aGeomorBox2DorBox3D)
;
Returns Y minima of a bounding box 2d or 3d or a geometry.
Although this function is only defined for box3d, it will work for box2d and geometry because of the autocasting behavior defined for geometries and box2d. However you can not feed it a geometry or box2d text represenation, since that will not autocast. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_YMin('BOX3D(1 2 3, 4 5 6)'); st_ymin  2 SELECT ST_YMin(ST_GeomFromText('LINESTRING(1 3 4, 5 6 7)')); st_ymin  3 SELECT ST_YMin(CAST('BOX(3 2, 3 4)' As box2d)); st_ymin  2 Observe THIS DOES NOT WORK because it will try to autocast the string representation to a BOX3D SELECT ST_YMin('LINESTRING(1 3, 5 6)'); ERROR: BOX3D parser  doesnt start with BOX3D( SELECT ST_YMin(ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)')); st_ymin  150406
ST_ZMax — Returns Z minima of a bounding box 2d or 3d or a geometry.
float ST_ZMax(
box3d aGeomorBox2DorBox3D)
;
Returns Z maxima of a bounding box 2d or 3d or a geometry.
Although this function is only defined for box3d, it will work for box2d and geometry because of the autocasting behavior defined for geometries and box2d. However you can not feed it a geometry or box2d text represenation, since that will not autocast. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_ZMax('BOX3D(1 2 3, 4 5 6)'); st_zmax  6 SELECT ST_ZMax(ST_GeomFromEWKT('LINESTRING(1 3 4, 5 6 7)')); st_zmax  7 SELECT ST_ZMax('BOX3D(3 2 1, 3 4 1)' ); st_zmax  1 Observe THIS DOES NOT WORK because it will try to autocast the string representation to a BOX3D SELECT ST_ZMax('LINESTRING(1 3 4, 5 6 7)'); ERROR: BOX3D parser  doesnt start with BOX3D( SELECT ST_ZMax(ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)')); st_zmax  3
ST_ZMin — Returns Z minima of a bounding box 2d or 3d or a geometry.
float ST_ZMin(
box3d aGeomorBox2DorBox3D)
;
Returns Z minima of a bounding box 2d or 3d or a geometry.
Although this function is only defined for box3d, it will work for box2d and geometry because of the autocasting behavior defined for geometries and box2d. However you can not feed it a geometry or box2d text represenation, since that will not autocast. 
This function supports 3d and will not drop the zindex.
This method supports Circular Strings and Curves
SELECT ST_ZMin('BOX3D(1 2 3, 4 5 6)'); st_zmin  3 SELECT ST_ZMin(ST_GeomFromEWKT('LINESTRING(1 3 4, 5 6 7)')); st_zmin  4 SELECT ST_ZMin('BOX3D(3 2 1, 3 4 1)' ); st_zmin  1 Observe THIS DOES NOT WORK because it will try to autocast the string representation to a BOX3D SELECT ST_ZMin('LINESTRING(1 3 4, 5 6 7)'); ERROR: BOX3D parser  doesnt start with BOX3D( SELECT ST_ZMin(ST_GeomFromEWKT('CIRCULARSTRING(220268 150415 1,220227 150505 2,220227 150406 3)')); st_zmin  1
These functions are rarely used functions that should only be used if your data is corrupted in someway. They are used for troubleshooting corruption and also fixing things that should under normal circumstances, never happen.
PostGIS_AddBBox — Add bounding box to the geometry.
geometry PostGIS_AddBBox(
geometry geomA)
;
Add bounding box to the geometry. This would make bounding box based queries faster, but will increase the size of the geometry.
Bounding boxes are automatically added to geometries so in general this is not needed unless the generated bounding box somehow becomes corrupted or you have an old install that is lacking bounding boxes. Then you need to drop the old and readd. 
This method supports Circular Strings and Curves
PostGIS_DropBBox — Drop the bounding box cache from the geometry.
geometry PostGIS_DropBBox(
geometry geomA)
;
Drop the bounding box cache from the geometry. This reduces geometry size, but makes boundingbox based queries slower. It is also used to drop a corrupt bounding box. A taletell sign of a corrupt cached bounding box is when your ST_Intersects and other relation queries leave out geometries that rightfully should return true.
Bounding boxes are automatically added to geometries and improve speed of queries so in general this is not needed unless the generated bounding box somehow becomes corrupted or you have an old install that is lacking bounding boxes. Then you need to drop the old and readd. This kind of corruption has been observed in 8.38.3.6 series whereby cached bboxes were not always recalculated when a geometry changed and upgrading to a newer version without a dump reload will not correct already corrupted boxes. So one can manually correct using below and readd the bbox or do a dump reload. 
This method supports Circular Strings and Curves
This example drops bounding boxes where the cached box is not correct The force to ST_AsBinary before applying Box2D forces a recalculation of the box, and Box2D applied to the table geometry always  returns the cached bounding box. UPDATE sometable SET the_geom = PostGIS_DropBBox(the_geom) WHERE Not (Box2D(ST_AsBinary(the_geom)) = Box2D(the_geom)); UPDATE sometable SET the_geom = PostGIS_AddBBox(the_geom) WHERE Not PostGIS_HasBBOX(the_geom);
PostGIS_HasBBox — Returns TRUE if the bbox of this geometry is cached, FALSE otherwise.
boolean PostGIS_HasBBox(
geometry geomA)
;
Returns TRUE if the bbox of this geometry is cached, FALSE otherwise. Use PostGIS_AddBBox and PostGIS_DropBBox to control caching.
This method supports Circular Strings and Curves
Table of Contents
The functions given below are spatial aggregate functions provided with PostGIS that can be used just like any other sql aggregate function such as sum, average.
The functions given below are PostGIS functions that conform to the SQL/MM 3 standard
SQLMM defines the default SRID of all geometry constructors as 0. PostGIS uses a default SRID of 1. 
The functions and operators given below are PostGIS functions/operators that take as input or return as output a geography data type object.
Functions with a (T) are not native geodetic functions, and use a ST_Transform call to and from geometry to do the operation. As a result, they may not behave as expected when going over dateline, poles, and for large geometries or geometry pairs that cover more than one UTM zone. Basic tranform  (favoring UTM, Lambert Azimuthal (North/South), and falling back on mercator in worst case scenario) 
The functions given below are PostGIS functions that take as input or return as output a set of or single geometry_dump data type object.
The functions given below are PostGIS functions that take as input or return as output the box* family of PostGIS spatial types. The box family of types consists of box2d, box3d, box3d_extent
The functions given below are PostGIS functions that do not throw away the ZIndex.
The functions given below are PostGIS functions that can use CIRCULARSTRING, CURVEDPOLYGON, and other curved geometry types
Below is an alphabetical listing of spatial specific functions in PostGIS and the kinds of spatial types they work with or OGC/SQL compliance they try to conform to.