# Geometry Processing Functions

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=round|flat|square,join=round|mitre|bevel,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

### Description

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 blank-separated key=value pairs (string case) to tweak operations as follows:

- 'quad_segs=#' : number of segments used to approximate a quarter circle (defaults to 8).
- 'endcap=round|flat|square' : endcap style (defaults to "round", needs GEOS-3.2 or higher for a different value). 'butt' is also accepted as a synonym for 'flat'.
- 'join=round|mitre|bevel' : join style (defaults to "round", needs GEOS-3.2 or higher for a different value). 'miter' is also accepted as a synonym for 'mitre'.
- 'mitre_limit=#.#' : mitre ratio limit (only affects mitred join style). 'miter_limit' is also accepted as a synonym for 'mitre_limit'.

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 2-d buffer even when presented with a 3d-geometry.

Performed by the GEOS module.

&sfs_compliant; s2.1.1.3

&sqlmm_compliant; SQL-MM 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 instead.

### Examples

quad_segs=8 (default)
    SELECT ST_Buffer(
     ST_GeomFromText('POINT(100 90)'),
     50, 'quad_segs=8');
| quad_segs=2 (lame)
    SELECT ST_Buffer(
     ST_GeomFromText('POINT(100 90)'),
     50, 'quad_segs=2');
endcap=round join=round (default)
    SELECT ST_Buffer(
     ST_GeomFromText(
      'LINESTRING(50 50,150 150,150 50)'
     ), 10, 'endcap=round join=round');
| endcap=square
    SELECT ST_Buffer(
     ST_GeomFromText(
      'LINESTRING(50 50,150 150,150 50)'
     ), 10, 'endcap=square join=round');
| endcap=flat
    SELECT ST_Buffer(
     ST_GeomFromText(
      'LINESTRING(50 50,150 150,150 50)'
     ), 10, 'endcap=flat join=round');
join=bevel
    SELECT ST_Buffer(
     ST_GeomFromText(
      'LINESTRING(50 50,150 150,150 50)'
     ), 10, 'join=bevel');
| join=mitre mitre_limit=5.0 (default mitre limit)
    SELECT ST_Buffer(
     ST_GeomFromText(
      'LINESTRING(50 50,150 150,150 50)'
     ), 10, 'join=mitre mitre_limit=5.0');
| join=mitre mitre_limit=1
    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:  Self-intersection 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))

### See Also

, , , ,

ST_BuildArea Creates an areal geometry formed by the constituent linework of given geometry
geometry `ST_BuildArea` geometry A

### Description

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.

### Examples

This will create a donut
    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;
This will create a gaping hole inside the circle with prongs sticking out
    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;

### See Also

, wrappers to this function with standard OGC interface

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

### Description

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.

Non-Aggregate 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 well-supported by GIS tools. To prevent ST_Collect from returning a Geometry Collection when collecting MULTI geometries, one can use the below trick that utilizes 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.

&Z_support;

&curve_support; 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.

### Examples

Aggregate example

    Thread ref: http://postgis.refractions.net/pipermail/postgis-users/2008-June/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

Non-Aggregate example

    Thread ref: http://postgis.refractions.net/pipermail/postgis-users/2008-June/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))

### See Also

,

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

### Description

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 shrink-wrapping 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

&sfs_compliant; s2.1.1.3

&sqlmm_compliant; SQL-MM 3: 5.1.16

&Z_support;

### Examples

    --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;

Convex Hull of a MultiLinestring and a MultiPoint seen together with the MultiLinestring and MultiPoint

    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))

### See Also

,

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

### Description

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?

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 7.1.7

&Z_support;

&curve_support;

### Examples

    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)

### See Also

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

### Description

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

&sfs_compliant; s2.1.1.3

&sqlmm_compliant; SQL-MM 3: 5.1.20

&Z_support; However it seems to only consider x y when doing the difference and tacks back on the Z-Index

### Examples

The original linestrings shown together. | The difference of the two linestrings

    --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)

### See Also

ST_Dump Returns a set of geometry_dump (geom,path) rows, that make up a geometry g1.
geometry_dump[]`ST_Dump` geometry g1

### Description

This is a set-returning 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+

&Z_support;

&curve_support;

### Examples

    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)

### See Also

, , , ,

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

### Description

This set-returning 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

&Z_support;

&curve_support;

### Examples

    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)

### See Also

, , ,

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

### Description

This is a set-returning 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

&Z_support;

### Examples

    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))

### See Also

, , , ,

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

### Description

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 `GEOMETRYCOLLECTION` as an argument

Performed by the GEOS module

Availability: 1.5 support for geography data type was introduced.

&sfs_compliant; s2.1.1.3

&sqlmm_compliant; SQL-MM 3: 5.1.18

### Examples

    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));

### See Also

, , , , ,

ST_LineToCurve Converts a LINESTRING/POLYGON to a CIRCULARSTRING, CURVED POLYGON
geometry `ST_LineToCurve` geometry geomANoncircular

### Description

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?

&Z_support;

&curve_support;

### Examples

    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)

### See Also

ST_MemUnion Same as ST_Union, only memory-friendly (uses less memory and more processor time).
geometry `ST_MemUnion` geometry set geomfield

### Description

Some useful description here.

Same as ST_Union, only memory-friendly (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

&Z_support;

### Examples

    See ST_Union

### See Also

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

### Description

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

### Examples

    SELECT d.disease_type,
    	ST_MinimumBoundingCircle(ST_Collect(d.the_geom)) As the_geom
    	FROM disease_obs As d
    	GROUP BY d.disease_type;

Minimum bounding circle of a point and linestring. Using 8 segs to approximate a quarter circle

    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))

### See Also

,

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

### Description

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 to dump the polygons out into individual polygons.

Availability: 1.0.0RC1 - requires GEOS >= 2.1.0.

### Examples: Polygonizing single linestrings

    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)

### See Also

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 0-360 version of the data to be plotted in a 180 centric map
geometry `ST_Shift_Longitude` geometry geomA

### Description

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 0-360 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)

Pre-1.3.4 bug prevented this from working for MULTIPOINT. 1.3.4+ works with MULTIPOINT as well.

&Z_support;

### Examples

    --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)

### See Also

, ,

ST_Simplify Returns a "simplified" version of the given geometry using the Douglas-Peucker algorithm.
geometry `ST_Simplify` geometry geomA float tolerance

### Description

Returns a "simplified" version of the given geometry using the Douglas-Peucker 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 object-by-object basis you can also feed a GeometryCollection to this function.

Note that returned geometry might loose its simplicity (see )

Note topology may not be preserved and may result in invalid geometries. Use (see ) to preserve topology.

Performed by the GEOS module.

Availability: 1.2.2

### Examples

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

### See Also

,

ST_SimplifyPreserveTopology Returns a "simplified" version of the given geometry using the Douglas-Peucker algorithm. Will avoid creating derived geometries (polygons in particular) that are invalid.
geometry `ST_SimplifyPreserveTopology` geometry geomA float tolerance

### Description

Returns a "simplified" version of the given geometry using the Douglas-Peucker 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 object-by-object basis you can also feed a GeometryCollection to this function.

Performed by the GEOS module.

Requires GEOS 3.0.0+

Availability: 1.3.3

### Examples

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

### See Also

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

### Description

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

&sfs_compliant; s2.1.1.3

&sqlmm_compliant; SQL-MM 3: 5.1.21

&Z_support; However it seems to only consider x y when doing the difference and tacks back on the Z-Index

### Examples

The original linestrings shown together | The symmetric difference of the two linestrings

    --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))

### See Also

, ,

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

### Description

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 NON-MULTI 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.

Non-Aggregate version: This function returns a geometry being a union of two input geometries. Output type can be a MULTI* ,NON-MULTI 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/must-faster-unions-in-postgis-14.html

&sfs_compliant; s2.1.1.3

Aggregate version is not explicitly defined in OGC SPEC.

&sqlmm_compliant; SQL-MM 3: 5.1.19 the z-index (elevation) when polygons are involved.

### Examples

Aggregate example

    SELECT stusps,
    	   ST_Multi(ST_Union(f.the_geom)) as singlegeom
    	 FROM sometable As f
    GROUP BY stusps

Non-Aggregate 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))

### See Also