These functions create modified geometries by changing type, structure or vertices.

# Geometry Editors

ST_AddPoint

Add a point to a LineString.

    				geometry ST_AddPoint
    				geometry linestring
    				geometry point

    				geometry ST_AddPoint
    				geometry linestring
    				geometry point
    				integer position = -1

### Description

Adds a point to a LineString before the index `position` (using a 0-based index). If the `position` parameter is omitted or is -1 the point is appended to the end of the LineString.

Availability: 1.1.0

&Z_support;

### Examples

Add a point to the end of a 3D line

    SELECT ST_AsEWKT(ST_AddPoint('LINESTRING(0 0 1, 1 1 1)', ST_MakePoint(1, 2, 3)));

        st_asewkt
        ----------
        LINESTRING(0 0 1,1 1 1,1 2 3)

Guarantee all lines in a table are closed by adding the start point of each line to the end of the line only for those that are not closed.

    UPDATE sometable
    SET geom = ST_AddPoint(geom, ST_StartPoint(geom))
    FROM sometable
    WHERE ST_IsClosed(geom) = false;

### See Also

ST_RemovePoint, ST_SetPoint

ST_CollectionExtract

Given a geometry collection, returns a multi-geometry containing only elements of a specified type.

    				geometry ST_CollectionExtract
    				geometry  collection

                    geometry ST_CollectionExtract
                    geometry  collection
                    integer  type

### Description

Given a geometry collection, returns a homogeneous multi-geometry.

If the `type` is not specified, returns a multi-geometry containing only geometries of the highest dimension. So polygons are preferred over lines, which are preferred over points.

If the `type` is specified, returns a multi-geometry containing only that type. If there are no sub-geometries of the right type, an EMPTY geometry is returned. Only points, lines and polygons are supported. The type numbers are:

- 1 == POINT

- 2 == LINESTRING

- 3 == POLYGON

For atomic geometry inputs, the geometry is retured unchanged if the input type matches the requested type. Otherwise, the result is an EMPTY geometry of the specified type. If required, these can be converted to multi-geometries using ST_Multi.

MultiPolygon results are not checked for validity. If the polygon components are adjacent or overlapping the result will be invalid. (For example, this can occur when applying this function to an ST_Split result.) This situation can be checked with ST_IsValid and repaired with ST_MakeValid.

Availability: 1.5.0

Prior to 1.5.3 this function returned atomic inputs unchanged, no matter type. In 1.5.3 non-matching single geometries returned a NULL result. In 2.0.0 non-matching single geometries return an EMPTY result of the requested type.

### Examples

Extract highest-dimension type:

    SELECT ST_AsText(ST_CollectionExtract(
            'GEOMETRYCOLLECTION( POINT(0 0), LINESTRING(1 1, 2 2) )'));
        st_astext
        ---------------
        MULTILINESTRING((1 1, 2 2))

Extract points (type 1 == POINT):

    SELECT ST_AsText(ST_CollectionExtract(
            'GEOMETRYCOLLECTION(GEOMETRYCOLLECTION(POINT(0 0)))',
            1 ));
        st_astext
        ---------------
        MULTIPOINT(0 0)

Extract lines (type 2 == LINESTRING):

    SELECT ST_AsText(ST_CollectionExtract(
            'GEOMETRYCOLLECTION(GEOMETRYCOLLECTION(LINESTRING(0 0, 1 1)),LINESTRING(2 2, 3 3))',
            2 ));
        st_astext
        ---------------
        MULTILINESTRING((0 0, 1 1), (2 2, 3 3))

### See Also

ST_CollectionHomogenize, ST_Multi, ST_IsValid, ST_MakeValid

ST_CollectionHomogenize

Returns the simplest representation of a geometry collection.

                    geometry ST_CollectionHomogenize
                    geometry  collection

### Description

Given a geometry collection, returns the "simplest" representation of the contents.

- Homogeneous (uniform) collections are returned as the appropriate multi-geometry.

- Heterogeneous (mixed) collections are flattened into a single GeometryCollection.

- Collections containing a single atomic element are returned as that element.

- Atomic geometries are returned unchanged. If required, these can be converted to a multi-geometry using ST_Multi.

This function does not ensure that the result is valid. In particular, a collection containing adjacent or overlapping Polygons will create an invalid MultiPolygon. This situation can be checked with ST_IsValid and repaired with ST_MakeValid.

Availability: 2.0.0

### Examples

Single-element collection converted to an atomic geometry

      SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0))'));

    	st_astext
    	------------
    	POINT(0 0)

Nested single-element collection converted to an atomic geometry:

    SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(MULTIPOINT((0 0)))'));

    	st_astext
    	------------
    	POINT(0 0)

Collection converted to a multi-geometry:

    SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0),POINT(1 1))'));

    	st_astext
    	---------------------
    	MULTIPOINT(0 0,1 1)

Nested heterogeneous collection flattened to a GeometryCollection:

    SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION(POINT(0 0), GEOMETRYCOLLECTION( LINESTRING(1 1, 2 2)))'));

    	st_astext
    	---------------------
    	GEOMETRYCOLLECTION(POINT(0 0),LINESTRING(1 1,2 2))

Collection of Polygons converted to an (invalid) MultiPolygon:

    SELECT ST_AsText(ST_CollectionHomogenize('GEOMETRYCOLLECTION (POLYGON ((10 50, 50 50, 50 10, 10 10, 10 50)), POLYGON ((90 50, 90 10, 50 10, 50 50, 90 50)))'));

    	st_astext
    	---------------------
    	MULTIPOLYGON(((10 50,50 50,50 10,10 10,10 50)),((90 50,90 10,50 10,50 50,90 50)))

### See Also

ST_CollectionExtract, ST_Multi, ST_IsValid, ST_MakeValid

ST_CurveToLine

Converts a geometry containing curves to a linear geometry.

                geometry ST_CurveToLine
                geometry curveGeom
                float tolerance
                integer tolerance_type
                integer flags

### Description

Converts a CIRCULAR STRING to regular LINESTRING or CURVEPOLYGON to POLYGON or MULTISURFACE to MULTIPOLYGON. 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 given `tolerance` and options (32 segments per quadrant and no options by default).

The 'tolerance_type' argument determines interpretation of the `tolerance` argument. It can take the following values:

- 0 (default): Tolerance is max segments per quadrant.

- 1: Tolerance is max-deviation of line from curve, in source units.

- 2: Tolerance is max-angle, in radians, between generating radii.

The 'flags' argument is a bitfield. 0 by default. Supported bits are:

- 1: Symmetric (orientation idependent) output.

- 2: Retain angle, avoids reducing angles (segment lengths) when producing symmetric output. Has no effect when Symmetric flag is off.

Availability: 1.3.0

Enhanced: 2.4.0 added support for max-deviation and max-angle tolerance, and for symmetric output.

Enhanced: 3.0.0 implemented a minimum number of segments per linearized arc to prevent topological collapse.

&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)

    -- Ensure approximated line is no further than 20 units away from
    -- original curve, and make the result direction-neutral
    SELECT ST_AsText(ST_CurveToLine(
     'CIRCULARSTRING(0 0,100 -100,200 0)'::geometry,
        20, -- Tolerance
        1, -- Above is max distance between curve and line
        1  -- Symmetric flag
    ));
    st_astext
    -------------------------------------------------------------------------------------------
     LINESTRING(0 0,50 -86.6025403784438,150 -86.6025403784439,200 -1.1331077795296e-13,200 0)

### See Also

ST_LineToCurve

ST_Scroll

Change start point of a closed LineString.

                geometry ST_Scroll
                geometry linestring
                geometry point

### Description

Changes the start/end point of a closed LineString to the given vertex `point`.

Availability: 3.2.0

&Z_support;

&M_support;

### Examples

Make e closed line start at its 3rd vertex

    SELECT ST_AsEWKT(ST_Scroll('SRID=4326;LINESTRING(0 0 0 1, 10 0 2 0, 5 5 4 2,0 0 0 1)', 'POINT(5 5 4 2)'));

    st_asewkt
    ----------
    SRID=4326;LINESTRING(5 5 4 2,0 0 0 1,10 0 2 0,5 5 4 2)

### See Also

ST_Normalize

ST_FlipCoordinates

Returns a version of a geometry with X and Y axis flipped.

                geometry ST_FlipCoordinates
                geometry geom

### Description

Returns a version of the given geometry with X and Y axis flipped. Useful for fixing geometries which contain coordinates expressed as latitude/longitude (Y,X).

Availability: 2.0.0

&curve_support;

&Z_support;

&M_support;

&P_support;

&T_support;

### Example

    SELECT ST_AsEWKT(ST_FlipCoordinates(GeomFromEWKT('POINT(1 2)')));
     st_asewkt
    ------------
    POINT(2 1)

### See Also

ST_SwapOrdinates

ST_Force2D

Force the geometries into a "2-dimensional mode".

    			geometry ST_Force2D
    			geometry  geomA

### Description

Forces the geometries into a "2-dimensional mode" so that all output representations will only have the X and Y coordinates. This is useful for force OGC-compliant output (since OGC only specifies 2-D geometries).

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

Changed: 2.1.0. Up to 2.0.x this was called ST_Force_2D.

&curve_support;

&P_support;

&Z_support;

### Examples

    SELECT ST_AsEWKT(ST_Force2D(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_Force2D('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))

### See Also

ST_Force_3D

ST_Force3D

Force the geometries into XYZ mode. This is an alias for ST_Force3DZ.

    			geometry ST_Force3D
    			geometry  geomA
    			float  Zvalue = 0.0

### Description

Forces the geometries into XYZ mode. This is an alias for ST_Force3DZ. If a geometry has no Z component, then a `Zvalue` Z coordinate is tacked on.

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

Changed: 2.1.0. Up to 2.0.x this was called ST_Force_3D.

Changed: 3.1.0. Added support for supplying a non-zero Z value.

&P_support;

&curve_support;

&Z_support;

### Examples

    		--Nothing happens to an already 3D geometry
    		SELECT ST_AsEWKT(ST_Force3D(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_Force3D('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))

### See Also

ST_AsEWKT, ST_Force2D, ST_Force_3DM, ST_Force_3DZ

ST_Force3DZ

Force the geometries into XYZ mode.

    			geometry ST_Force3DZ
    			geometry  geomA
    			float  Zvalue = 0.0

### Description

Forces the geometries into XYZ mode. If a geometry has no Z component, then a `Zvalue` Z coordinate is tacked on.

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

Changed: 2.1.0. Up to 2.0.x this was called ST_Force_3DZ.

Changed: 3.1.0. Added support for supplying a non-zero Z value.

&P_support;

&Z_support;

&curve_support;

### Examples

    --Nothing happens to an already 3D geometry
    SELECT ST_AsEWKT(ST_Force3DZ(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_Force3DZ('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))

### See Also

ST_AsEWKT, ST_Force2D, ST_Force_3DM, ST_Force_3D

ST_Force3DM

Force the geometries into XYM mode.

    			geometry ST_Force3DM
    			geometry  geomA
    			float  Mvalue = 0.0

### Description

Forces the geometries into XYM mode. If a geometry has no M component, then a `Mvalue` M coordinate is tacked on. If it has a Z component, then Z is removed

Changed: 2.1.0. Up to 2.0.x this was called ST_Force_3DM.

Changed: 3.1.0. Added support for supplying a non-zero M value.

&curve_support;

### Examples

    --Nothing happens to an already 3D geometry
    SELECT ST_AsEWKT(ST_Force3DM(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_Force3DM('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))

### See Also

ST_AsEWKT, ST_Force2D, ST_Force_3DM, ST_Force_3D, ST_GeomFromEWKT

ST_Force4D

Force the geometries into XYZM mode.

    			geometry ST_Force4D
    			geometry  geomA
    			float  Zvalue = 0.0
    			float  Mvalue = 0.0

### Description

Forces the geometries into XYZM mode. `Zvalue` and `Mvalue` is tacked on for missing Z and M dimensions, respectively.

Changed: 2.1.0. Up to 2.0.x this was called ST_Force_4D.

Changed: 3.1.0. Added support for supplying non-zero Z and M values.

&Z_support;

&curve_support;

### Examples

    --Nothing happens to an already 3D geometry
    SELECT ST_AsEWKT(ST_Force4D(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_Force4D('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))

### See Also

ST_AsEWKT, ST_Force2D, ST_Force_3DM, ST_Force_3D

ST_ForcePolygonCCW

Orients all exterior rings counter-clockwise and all interior rings clockwise.

    						geometry
    						ST_ForcePolygonCCW

    						geometry
    						geom

### Description

Forces (Multi)Polygons to use a counter-clockwise orientation for their exterior ring, and a clockwise orientation for their interior rings. Non-polygonal geometries are returned unchanged.

Availability: 2.4.0

&Z_support;

&M_support;

### See Also

ST_ForcePolygonCW, ST_IsPolygonCCW, ST_IsPolygonCW

ST_ForceCollection

Convert the geometry into a GEOMETRYCOLLECTION.

    			geometry ST_ForceCollection
    			geometry  geomA

### Description

Converts the geometry into a GEOMETRYCOLLECTION. This is useful for simplifying the WKB representation.

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

Availability: 1.2.2, prior to 1.3.4 this function will crash with Curves. This is fixed in 1.3.4+

Changed: 2.1.0. Up to 2.0.x this was called ST_Force_Collection.

&P_support;

&Z_support;

&curve_support;

### Examples

    SELECT  ST_AsEWKT(ST_ForceCollection('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_ForceCollection('CIRCULARSTRING(220227 150406,2220227 150407,220227 150406)'));
    								   st_astext
    --------------------------------------------------------------------------------
     GEOMETRYCOLLECTION(CIRCULARSTRING(220227 150406,2220227 150407,220227 150406))
    (1 row)

    -- POLYHEDRAL example --
    SELECT ST_AsEWKT(ST_ForceCollection('POLYHEDRALSURFACE(((0 0 0,0 0 1,0 1 1,0 1 0,0 0 0)),
     ((0 0 0,0 1 0,1 1 0,1 0 0,0 0 0)),
     ((0 0 0,1 0 0,1 0 1,0 0 1,0 0 0)),
     ((1 1 0,1 1 1,1 0 1,1 0 0,1 1 0)),
     ((0 1 0,0 1 1,1 1 1,1 1 0,0 1 0)),
     ((0 0 1,1 0 1,1 1 1,0 1 1,0 0 1)))'))

    								   st_asewkt
    ----------------------------------------------------------------------------------
    GEOMETRYCOLLECTION(
      POLYGON((0 0 0,0 0 1,0 1 1,0 1 0,0 0 0)),
      POLYGON((0 0 0,0 1 0,1 1 0,1 0 0,0 0 0)),
      POLYGON((0 0 0,1 0 0,1 0 1,0 0 1,0 0 0)),
      POLYGON((1 1 0,1 1 1,1 0 1,1 0 0,1 1 0)),
      POLYGON((0 1 0,0 1 1,1 1 1,1 1 0,0 1 0)),
      POLYGON((0 0 1,1 0 1,1 1 1,0 1 1,0 0 1))
    )

### See Also

ST_AsEWKT, ST_Force2D, ST_Force_3DM, ST_Force_3D, ST_GeomFromEWKT

ST_ForcePolygonCW

Orients all exterior rings clockwise and all interior rings counter-clockwise.

    						geometry
    						ST_ForcePolygonCW

    						geometry
    						geom

### Description

Forces (Multi)Polygons to use a clockwise orientation for their exterior ring, and a counter-clockwise orientation for their interior rings. Non-polygonal geometries are returned unchanged.

Availability: 2.4.0

&Z_support;

&M_support;

### See Also

ST_ForcePolygonCCW, ST_IsPolygonCCW, ST_IsPolygonCW

ST_ForceSFS

Force the geometries to use SFS 1.1 geometry types only.

    			geometry ST_ForceSFS
    			geometry  geomA

    			geometry ST_ForceSFS
    			geometry  geomA
    			text  version

### Description

&P_support;

&T_support;

&curve_support;

&Z_support;

ST_ForceRHR

Force the orientation of the vertices in a polygon to follow the Right-Hand-Rule.

    					geometry
    						ST_ForceRHR
    						geometry g

### Description

Forces the orientation of the vertices in a polygon to follow a Right-Hand-Rule, in which 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 counter-clockwise direction. This function is a synonym for ST_ForcePolygonCW

The above definition of the Right-Hand-Rule conflicts with definitions used in other contexts. To avoid confusion, it is recommended to use ST_ForcePolygonCW.

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

&Z_support;

&P_support;

### Examples

    SELECT ST_AsEWKT(
      ST_ForceRHR(
    	'POLYGON((0 0 2, 5 0 2, 0 5 2, 0 0 2),(1 1 2, 1 3 2, 3 1 2, 1 1 2))'
      )
    );
    						  st_asewkt
    --------------------------------------------------------------
     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))
    (1 row)

### See Also

ST_ForcePolygonCCW, ST_ForcePolygonCW, ST_IsPolygonCCW, ST_IsPolygonCW, ST_BuildArea, ST_Polygonize, ST_Reverse

ST_ForceCurve

Upcast a geometry into its curved type, if applicable.

    					geometry
    						ST_ForceCurve
    						geometry g

### Description

Turns a geometry into its curved representation, if applicable: lines become compoundcurves, multilines become multicurves polygons become curvepolygons multipolygons become multisurfaces. If the geometry input is already a curved representation returns back same as input.

Availability: 2.2.0

&Z_support;

&curve_support;

### Examples

    SELECT ST_AsText(
      ST_ForceCurve(
    	'POLYGON((0 0 2, 5 0 2, 0 5 2, 0 0 2),(1 1 2, 1 3 2, 3 1 2, 1 1 2))'::geometry
      )
    );
                                  st_astext
    ----------------------------------------------------------------------
     CURVEPOLYGON Z ((0 0 2,5 0 2,0 5 2,0 0 2),(1 1 2,1 3 2,3 1 2,1 1 2))
    (1 row)

### See Also

ST_LineToCurve

ST_LineToCurve

Converts a linear geometry to a curved geometry.

                geometry ST_LineToCurve
                geometry  geomANoncircular

### Description

Converts plain LINESTRING/POLYGON to CIRCULAR STRINGs and Curved Polygons. Note much fewer points are needed to describe the curved equivalent.

If the input LINESTRING/POLYGON is not curved enough to clearly represent a curve, the function will return the same input geometry.

Availability: 1.3.0

&Z_support;

&curve_support;

### Examples

     -- 2D Example
    SELECT ST_AsText(ST_LineToCurve(foo.geom)) As curvedastext,ST_AsText(foo.geom) As non_curvedastext
        FROM (SELECT ST_Buffer('POINT(1 3)'::geometry, 3) As 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_AsText(ST_LineToCurve(geom)) As curved, ST_AsText(geom) AS not_curved
    FROM (SELECT ST_Translate(ST_Force3D(ST_Boundary(ST_Buffer(ST_Point(1,3), 2,2))),0,0,3) AS geom) AS foo;

                            curved                        |               not_curved
    ------------------------------------------------------+---------------------------------------------------------------------
     CIRCULARSTRING Z (3 3 3,-1 2.99999999999999 3,3 3 3) | LINESTRING Z (3 3 3,2.4142135623731 1.58578643762691 3,1 1 3,
                                                          | -0.414213562373092 1.5857864376269 3,-1 2.99999999999999 3,
                                                          | -0.414213562373101 4.41421356237309 3,
                                                          | 0.999999999999991 5 3,2.41421356237309 4.4142135623731 3,3 3 3)
    (1 row)

### See Also

ST_CurveToLine

ST_Multi

Return the geometry as a MULTI* geometry.

    				geometry ST_Multi
    				geometry  geom

### Description

Returns the geometry as a MULTI* geometry collection. If the geometry is already a collection, it is returned unchanged.

### Examples

    SELECT ST_AsText(ST_Multi('POLYGON ((10 30, 30 30, 30 10, 10 10, 10 30))'));
                        st_astext
        -------------------------------------------------
        MULTIPOLYGON(((10 30,30 30,30 10,10 10,10 30)))

### See Also

ST_AsText

ST_Normalize

Return the geometry in its canonical form.

    				geometry ST_Normalize
    				geometry  geom

### Description

Returns the geometry in its normalized/canonical form. May reorder vertices in polygon rings, rings in a polygon, elements in a multi-geometry complex.

Mostly only useful for testing purposes (comparing expected and obtained results).

Availability: 2.3.0

### Examples

    SELECT ST_AsText(ST_Normalize(ST_GeomFromText(
      'GEOMETRYCOLLECTION(
        POINT(2 3),
        MULTILINESTRING((0 0, 1 1),(2 2, 3 3)),
        POLYGON(
          (0 10,0 0,10 0,10 10,0 10),
          (4 2,2 2,2 4,4 4,4 2),
          (6 8,8 8,8 6,6 6,6 8)
        )
      )'
    )));
                                                                         st_astext
    ----------------------------------------------------------------------------------------------------------------------------------------------------
     GEOMETRYCOLLECTION(POLYGON((0 0,0 10,10 10,10 0,0 0),(6 6,8 6,8 8,6 8,6 6),(2 2,4 2,4 4,2 4,2 2)),MULTILINESTRING((2 2,3 3),(0 0,1 1)),POINT(2 3))
    (1 row)

### See Also

ST_Equals,

ST_QuantizeCoordinates

Sets least significant bits of coordinates to zero

    						geometry
    						ST_QuantizeCoordinates

    						geometry
    						g

    						int
    						prec_x

    						int
    						prec_y

    						int
    						prec_z

    						int
    						prec_m

### Description

`ST_QuantizeCoordinates` determines the number of bits (`N`) required to represent a coordinate value with a specified number of digits after the decimal point, and then sets all but the `N` most significant bits to zero. The resulting coordinate value will still round to the original value, but will have improved compressiblity. This can result in a significant disk usage reduction provided that the geometry column is using a compressible storage type. The function allows specification of a different number of digits after the decimal point in each dimension; unspecified dimensions are assumed to have the precision of the `x` dimension. Negative digits are interpreted to refer digits to the left of the decimal point, (i.e., `prec_x=-2` will preserve coordinate values to the nearest 100.

The coordinates produced by `ST_QuantizeCoordinates` are independent of the geometry that contains those coordinates and the relative position of those coordinates within the geometry. As a result, existing topological relationships between geometries are unaffected by use of this function. The function may produce invalid geometry when it is called with a number of digits lower than the intrinsic precision of the geometry.

Availability: 2.5.0

### Technical Background

PostGIS stores all coordinate values as double-precision floating point integers, which can reliably represent 15 significant digits. However, PostGIS may be used to manage data that intrinsically has fewer than 15 significant digits. An example is TIGER data, which is provided as geographic coordinates with six digits of precision after the decimal point (thus requiring only nine significant digits of longitude and eight significant digits of latitude.)

When 15 significant digits are available, there are many possible representations of a number with 9 significant digits. A double precision floating point number uses 52 explicit bits to represent the significand (mantissa) of the coordinate. Only 30 bits are needed to represent a mantissa with 9 significant digits, leaving 22 insignificant bits; we can set their value to anything we like and still end up with a number that rounds to our input value. For example, the value 100.123456 can be represented by the floating point numbers closest to 100.123456000000, 100.123456000001, and 100.123456432199. All are equally valid, in that `ST_AsText(geom, 6)` will return the same result with any of these inputs. As we can set these bits to any value, `ST_QuantizeCoordinates` sets the 22 insignificant bits to zero. For a long coordinate sequence this creates a pattern of blocks of consecutive zeros that is compressed by PostgreSQL more effeciently.

Only the on-disk size of the geometry is potentially affected by `ST_QuantizeCoordinates`. ST_MemSize, which reports the in-memory usage of the geometry, will return the the same value regardless of the disk space used by a geometry.

### Examples

    SELECT ST_AsText(ST_QuantizeCoordinates('POINT (100.123456 0)'::geometry, 4));
    st_astext
    -------------------------
    POINT(100.123455047607 0)

    WITH test AS (SELECT 'POINT (123.456789123456 123.456789123456)'::geometry AS geom)
    SELECT
      digits,
      encode(ST_QuantizeCoordinates(geom, digits), 'hex'),
      ST_AsText(ST_QuantizeCoordinates(geom, digits))
    FROM test, generate_series(15, -15, -1) AS digits;

    digits  |                   encode                   |                st_astext
    --------+--------------------------------------------+------------------------------------------
    15      | 01010000005f9a72083cdd5e405f9a72083cdd5e40 | POINT(123.456789123456 123.456789123456)
    14      | 01010000005f9a72083cdd5e405f9a72083cdd5e40 | POINT(123.456789123456 123.456789123456)
    13      | 01010000005f9a72083cdd5e405f9a72083cdd5e40 | POINT(123.456789123456 123.456789123456)
    12      | 01010000005c9a72083cdd5e405c9a72083cdd5e40 | POINT(123.456789123456 123.456789123456)
    11      | 0101000000409a72083cdd5e40409a72083cdd5e40 | POINT(123.456789123456 123.456789123456)
    10      | 0101000000009a72083cdd5e40009a72083cdd5e40 | POINT(123.456789123455 123.456789123455)
    9       | 0101000000009072083cdd5e40009072083cdd5e40 | POINT(123.456789123418 123.456789123418)
    8       | 0101000000008072083cdd5e40008072083cdd5e40 | POINT(123.45678912336 123.45678912336)
    7       | 0101000000000070083cdd5e40000070083cdd5e40 | POINT(123.456789121032 123.456789121032)
    6       | 0101000000000040083cdd5e40000040083cdd5e40 | POINT(123.456789076328 123.456789076328)
    5       | 0101000000000000083cdd5e40000000083cdd5e40 | POINT(123.456789016724 123.456789016724)
    4       | 0101000000000000003cdd5e40000000003cdd5e40 | POINT(123.456787109375 123.456787109375)
    3       | 0101000000000000003cdd5e40000000003cdd5e40 | POINT(123.456787109375 123.456787109375)
    2       | 01010000000000000038dd5e400000000038dd5e40 | POINT(123.45654296875 123.45654296875)
    1       | 01010000000000000000dd5e400000000000dd5e40 | POINT(123.453125 123.453125)
    0       | 01010000000000000000dc5e400000000000dc5e40 | POINT(123.4375 123.4375)
    -1      | 01010000000000000000c05e400000000000c05e40 | POINT(123 123)
    -2      | 01010000000000000000005e400000000000005e40 | POINT(120 120)
    -3      | 010100000000000000000058400000000000005840 | POINT(96 96)
    -4      | 010100000000000000000058400000000000005840 | POINT(96 96)
    -5      | 010100000000000000000058400000000000005840 | POINT(96 96)
    -6      | 010100000000000000000058400000000000005840 | POINT(96 96)
    -7      | 010100000000000000000058400000000000005840 | POINT(96 96)
    -8      | 010100000000000000000058400000000000005840 | POINT(96 96)
    -9      | 010100000000000000000058400000000000005840 | POINT(96 96)
    -10     | 010100000000000000000058400000000000005840 | POINT(96 96)
    -11     | 010100000000000000000058400000000000005840 | POINT(96 96)
    -12     | 010100000000000000000058400000000000005840 | POINT(96 96)
    -13     | 010100000000000000000058400000000000005840 | POINT(96 96)
    -14     | 010100000000000000000058400000000000005840 | POINT(96 96)
    -15     | 010100000000000000000058400000000000005840 | POINT(96 96)

### See Also

ST_SnapToGrid

ST_RemovePoint

Remove a point from a linestring.

    			geometry ST_RemovePoint
    			geometry linestring
    			integer offset

### Description

Removes a point from a LineString, given its index (0-based). Useful for turning a closed line (ring) into an open linestring.

Enhanced: 3.2.0

Availability: 1.1.0

&Z_support;

### Examples

Guarantees no lines are closed by removing the end point of closed lines (rings). Assumes geom is of type LINESTRING

    UPDATE sometable
    	SET geom = ST_RemovePoint(geom, ST_NPoints(geom) - 1)
    	FROM sometable
    	WHERE ST_IsClosed(geom);

### See Also

ST_AddPoint, ST_NPoints, ST_NumPoints

ST_RemoveRepeatedPoints

Returns a version of the given geometry with duplicated points removed.

                geometry ST_RemoveRepeatedPoints
                geometry geom
                float8 tolerance

### Description

Returns a version of the given geometry with duplicated points removed. Will actually do something only with (multi)lines, (multi)polygons and multipoints 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.

If the tolerance parameter is provided, vertices within the tolerance of one another will be considered the "same" for the purposes of removal.

Enhanced: 3.2.0

Availability: 2.2.0

&P_support;

&Z_support;

### See Also

ST_Simplify

ST_Reverse

Return the geometry with vertex order reversed.

    			geometry ST_Reverse
    			geometry  g1

### Description

Can be used on any geometry and reverses the order of the vertexes.

Enhanced: 2.4.0 support for curves was introduced.

&Z_support;

&P_support;

### Examples

    SELECT ST_AsText(geom) as line, ST_AsText(ST_Reverse(geom)) As reverseline
    FROM
    (SELECT ST_MakeLine(ST_Point(1,2),
    		ST_Point(1,10)) As geom) as foo;
    --result
    		line         |     reverseline
    ---------------------+----------------------
    LINESTRING(1 2,1 10) | LINESTRING(1 10,1 2)

ST_Segmentize

Return a modified geometry/geography having no segment longer than the given distance.

    				geometry ST_Segmentize
    				geometry  geom
    				float  max_segment_length

    				geography ST_Segmentize
    				geography  geog
    				float  max_segment_length

### Description

Returns a modified geometry having no segment longer than the given `max_segment_length`. Distance computation is performed in 2d only. For geometry, length units are in units of spatial reference. For geography, units are in meters.

Availability: 1.2.2

Enhanced: 3.0.0 Segmentize geometry now uses equal length segments

Enhanced: 2.3.0 Segmentize geography now uses equal length segments

Enhanced: 2.1.0 support for geography was introduced.

Changed: 2.1.0 As a result of the introduction of geography support: The construct `SELECT ST_Segmentize('LINESTRING(1 2, 3 4)',0.5);` will result in ambiguous function error. You need to have properly typed object e.g. a geometry/geography column, use ST_GeomFromText, ST_GeogFromText or `SELECT ST_Segmentize('LINESTRING(1 2, 3 4)'::geometry,0.5);`

This will only increase segments. It will not lengthen segments shorter than max length

### Examples

    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)

### See Also

ST_LineSubstring

ST_SetPoint

Replace point of a linestring with a given point.

    				geometry ST_SetPoint
    				geometry linestring
    				integer zerobasedposition
    				geometry point

### Description

Replace point N of linestring with given point. Index is 0-based.Negative index are counted backwards, so that -1 is last point. This is especially useful in triggers when trying to maintain relationship of joints when one vertex moves.

Availability: 1.1.0

Updated 2.3.0 : negative indexing

&Z_support;

### Examples

    --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.geom, ST_NumPoints(foo.geom) - 1, ST_GeomFromEWKT('POINT(-1 1 3)')))
    FROM (SELECT ST_GeomFromEWKT('LINESTRING(-1 2 3,-1 3 4, 5 6 7)') As geom) As foo;
    	   st_asewkt
    -----------------------
    LINESTRING(-1 2 3,-1 3 4,-1 1 3)

    SELECT ST_AsText(ST_SetPoint(g, -3, p))
    FROM ST_GEomFromText('LINESTRING(0 0, 1 1, 2 2, 3 3, 4 4)') AS g
    	, ST_PointN(g,1) as p;
    	   st_astext
    -----------------------
    LINESTRING(0 0,1 1,0 0,3 3,4 4)

### See Also

ST_AddPoint, ST_NPoints, ST_NumPoints, ST_PointN, ST_RemovePoint

ST_ShiftLongitude

Shifts the longitude coordinates of a geometry between -180..180 and 0..360.

                geometry ST_ShiftLongitude
                geometry  geom

### Description

Reads every point/vertex in a geometry, and shifts its longitude coordinate from -180..0 to 180..360 and vice versa if between these ranges. This function is symmetrical so the result is a 0..360 representation of a -180..180 data and a -180..180 representation of a 0..360 data.

This is only useful for data with coordinates in longitude/latitude; e.g. SRID 4326 (WGS 84 geographic)

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

&Z_support;

Enhanced: 2.0.0 support for Polyhedral surfaces and TIN was introduced.

NOTE: this function was renamed from "ST_Shift_Longitude" in 2.2.0

&P_support;

&T_support;

### Examples

    --single point forward transformation
    SELECT ST_AsText(ST_ShiftLongitude('SRID=4326;POINT(270 0)'::geometry))

    st_astext
    ----------
    POINT(-90 0)

    --single point reverse transformation
    SELECT ST_AsText(ST_ShiftLongitude('SRID=4326;POINT(-90 0)'::geometry))

    st_astext
    ----------
    POINT(270 0)

    --for linestrings the functions affects only to the sufficient coordinates
    SELECT ST_AsText(ST_ShiftLongitude('SRID=4326;LINESTRING(174 12, 182 13)'::geometry))

    st_astext
    ----------
    LINESTRING(174 12,-178 13)

### See Also

ST_WrapX

ST_WrapX

Wrap a geometry around an X value.

                geometry ST_WrapX
                geometry  geom
                float8  wrap
                float8  move

### Description

This function splits the input geometries and then moves every resulting component falling on the right (for negative 'move') or on the left (for positive 'move') of given 'wrap' line in the direction specified by the 'move' parameter, finally re-unioning the pieces together.

This is useful to "recenter" long-lat input to have features of interest not spawned from one side to the other.

Availability: 2.3.0 requires GEOS

&Z_support;

### Examples

    -- Move all components of the given geometries whose bounding box
    -- falls completely on the left of x=0 to +360
    select ST_WrapX(geom, 0, 360);

    -- Move all components of the given geometries whose bounding box
    -- falls completely on the left of x=-30 to +360
    select ST_WrapX(geom, -30, 360);

### See Also

ST_Shift_Longitude

ST_SnapToGrid

Snap all points of the input geometry to a regular grid.

    			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

### Description

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. Useful for reducing precision.

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 lose 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

&Z_support;

### Examples

    --Snap your geometries to a precision grid of 10^-3
    UPDATE mytable
       SET geom = ST_SnapToGrid(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)

### See Also

ST_Snap, ST_AsEWKT, ST_AsText, ST_GeomFromText, ST_GeomFromEWKT, ST_Simplify

ST_Snap

Snap segments and vertices of input geometry to vertices of a reference geometry.

    			geometry ST_Snap
    			geometry  input
    			geometry  reference
    			float  tolerance

### Description

Snaps the vertices and segments of a geometry to another Geometry's vertices. A snap distance tolerance is used to control where snapping is performed. The result geometry is the input geometry with the vertices snapped. If no snapping occurs then the input geometry is returned unchanged.

Snapping one geometry to another can improve robustness for overlay operations by eliminating nearly-coincident edges (which cause problems during noding and intersection calculation).

Too much snapping can result in invalid topology being created, so the number and location of snapped vertices is decided using heuristics to determine when it is safe to snap. This can result in some potential snaps being omitted, however.

The returned geometry might lose its simplicity (see ST_IsSimple) and validity (see ST_IsValid).

Performed by the GEOS module.

Availability: 2.0.0

### Examples

A multipolygon shown with a linestring (before any snapping)
A multipolygon snapped to linestring to tolerance: 1.01 of distance. The new multipolygon is shown with reference linestring
    SELECT ST_AsText(ST_Snap(poly,line, ST_Distance(poly,line)*1.01)) AS polysnapped
    FROM (SELECT
       ST_GeomFromText('MULTIPOLYGON(
         ((26 125, 26 200, 126 200, 126 125, 26 125 ),
          ( 51 150, 101 150, 76 175, 51 150 )),
          (( 151 100, 151 200, 176 175, 151 100 )))') As poly,
           ST_GeomFromText('LINESTRING (5 107, 54 84, 101 100)') As line
    	) As foo;

                                 polysnapped
    ---------------------------------------------------------------------
     MULTIPOLYGON(((26 125,26 200,126 200,126 125,101 100,26 125),
     (51 150,101 150,76 175,51 150)),((151 100,151 200,176 175,151 100)))
| A multipolygon snapped to linestring to tolerance: 1.25 of distance. The new multipolygon is shown with reference linestring
    SELECT ST_AsText(
        ST_Snap(poly,line, ST_Distance(poly,line)*1.25)
      ) AS polysnapped
    FROM (SELECT
      ST_GeomFromText('MULTIPOLYGON(
        (( 26 125, 26 200, 126 200, 126 125, 26 125 ),
          ( 51 150, 101 150, 76 175, 51 150 )),
          (( 151 100, 151 200, 176 175, 151 100 )))') As poly,
           ST_GeomFromText('LINESTRING (5 107, 54 84, 101 100)') As line
    	) As foo;

                                 polysnapped
    ---------------------------------------------------------------------
    MULTIPOLYGON(((5 107,26 200,126 200,126 125,101 100,54 84,5 107),
    (51 150,101 150,76 175,51 150)),((151 100,151 200,176 175,151 100)))
The linestring snapped to the original multipolygon at tolerance 1.01 of distance. The new linestring is shown with reference multipolygon
    SELECT ST_AsText(
       ST_Snap(line, poly, ST_Distance(poly,line)*1.01)
      ) AS linesnapped
    FROM (SELECT
      ST_GeomFromText('MULTIPOLYGON(
         ((26 125, 26 200, 126 200, 126 125, 26 125),
          (51 150, 101 150, 76 175, 51 150 )),
          ((151 100, 151 200, 176 175, 151 100)))') As poly,
           ST_GeomFromText('LINESTRING (5 107, 54 84, 101 100)') As line
    	) As foo;

                  linesnapped
    ----------------------------------------
     LINESTRING(5 107,26 125,54 84,101 100)
| The linestring snapped to the original multipolygon at tolerance 1.25 of distance. The new linestring is shown with reference multipolygon
    SELECT ST_AsText(
     ST_Snap(line, poly, ST_Distance(poly,line)*1.25)
      ) AS linesnapped
    FROM (SELECT
      ST_GeomFromText('MULTIPOLYGON(
         (( 26 125, 26 200, 126 200, 126 125, 26 125 ),
          (51 150, 101 150, 76 175, 51 150 )),
          ((151 100, 151 200, 176 175, 151 100 )))') As poly,
           ST_GeomFromText('LINESTRING (5 107, 54 84, 101 100)') As line
    	) As foo;
                  linesnapped
    ---------------------------------------
    LINESTRING(26 125,54 84,101 100)

### See Also

ST_SnapToGrid

ST_SwapOrdinates

Returns a version of the given geometry with given ordinate values swapped.

    			geometry ST_SwapOrdinates
    			geometry geom
    			cstring ords

### Description

Returns a version of the given geometry with given ordinates swapped.

The `ords` parameter is a 2-characters string naming the ordinates to swap. Valid names are: x,y,z and m.

Availability: 2.2.0

&curve_support;

&Z_support;

&M_support;

&P_support;

&T_support;

### Example

    -- Scale M value by 2
    SELECT ST_AsText(
      ST_SwapOrdinates(
        ST_Scale(
          ST_SwapOrdinates(g,'xm'),
          2, 1
        ),
      'xm')
    ) FROM ( SELECT 'POINT ZM (0 0 0 2)'::geometry g ) foo;
         st_astext
    --------------------
     POINT ZM (0 0 0 4)

### See Also

ST_FlipCoordinates