# Geometry Accessors

GeometryType

Returns the type of a geometry as text.

    			text GeometryType
    			geometry  geomA

### Description

Returns the type of the geometry as a string. Eg: 'LINESTRING', 'POLYGON', 'MULTIPOINT', etc.

OGC SPEC s2.1.1.1 - Returns the name of the instantiable subtype of Geometry of which this Geometry instance is a member. The name of the instantiable subtype of Geometry is returned as a string.

This function also indicates if the geometry is measured, by returning a string of the form 'POINTM'.

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

&sfs_compliant;

&curve_support;

&Z_support;

&P_support;

&T_support;

### Examples

    SELECT GeometryType(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'));
     geometrytype
    --------------
     LINESTRING

    SELECT ST_GeometryType(ST_GeomFromEWKT('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)) )'));
    			--result
    			POLYHEDRALSURFACE

    SELECT GeometryType(geom) as result
      FROM
        (SELECT
           ST_GeomFromEWKT('TIN (((
                    0 0 0,
                    0 0 1,
                    0 1 0,
                    0 0 0
                )), ((
                    0 0 0,
                    0 1 0,
                    1 1 0,
                    0 0 0
                ))
                )')  AS geom
        ) AS g;
     result
    --------
     TIN

### See Also

ST_GeometryType

ST_Boundary

Returns the boundary of a geometry.

    			geometry ST_Boundary

    			geometry  geomA

### Description

Returns the closure of the combinatorial boundary of this Geometry. The combinatorial boundary is defined as described in section 3.12.3.2 of the OGC SPEC. Because the result of this function is a closure, and hence topologically closed, the resulting boundary can be represented using representational geometry primitives as discussed in the OGC SPEC, section 3.12.2.

Performed by the GEOS module

Prior to 2.0.0, this function throws an exception if used with `GEOMETRYCOLLECTION`. From 2.0.0 up it will return NULL instead (unsupported input).

&sfs_compliant; OGC SPEC s2.1.1.1

&sqlmm_compliant; SQL-MM 3: 5.1.14

&Z_support;

Enhanced: 2.1.0 support for Triangle was introduced

Changed: 3.2.0 support for TIN, does not use geos, does not linearize curves

### Examples

Linestring with boundary points overlaid
    SELECT ST_Boundary(geom)
    FROM (SELECT 'LINESTRING(100 150,50 60, 70 80, 160 170)'::geometry As geom) As f;
    -- ST_AsText output
    MULTIPOINT((100 150),(160 170))
| polygon holes with boundary multilinestring
    SELECT ST_Boundary(geom)
    FROM (SELECT
    'POLYGON (( 10 130, 50 190, 110 190, 140 150, 150 80, 100 10, 20 40, 10 130 ),
    	( 70 40, 100 50, 120 80, 80 110, 50 90, 70 40 ))'::geometry As geom) As f;
    -- ST_AsText output
    MULTILINESTRING((10 130,50 190,110 190,140 150,150 80,100 10,20 40,10 130),
    	(70 40,100 50,120 80,80 110,50 90,70 40))

    SELECT ST_AsText(ST_Boundary(ST_GeomFromText('LINESTRING(1 1,0 0, -1 1)')));
    st_astext
    -----------
    MULTIPOINT((1 1),(-1 1))

    SELECT ST_AsText(ST_Boundary(ST_GeomFromText('POLYGON((1 1,0 0, -1 1, 1 1))')));
    st_astext
    ----------
    LINESTRING(1 1,0 0,-1 1,1 1)

    --Using a 3d polygon
    SELECT ST_AsEWKT(ST_Boundary(ST_GeomFromEWKT('POLYGON((1 1 1,0 0 1, -1 1 1, 1 1 1))')));

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

    --Using a 3d multilinestring
    SELECT ST_AsEWKT(ST_Boundary(ST_GeomFromEWKT('MULTILINESTRING((1 1 1,0 0 0.5, -1 1 1),(1 1 0.5,0 0 0.5, -1 1 0.5, 1 1 0.5) )')));

    st_asewkt
    ----------
    MULTIPOINT((-1 1 1),(1 1 0.75))

### See Also

ST_AsText, ST_ExteriorRing, ST_MakePolygon

ST_BoundingDiagonal

Returns the diagonal of a geometry's bounding box.

    				geometry ST_BoundingDiagonal

    				geometry  geom
    				boolean  fits=false

### Description

Returns the diagonal of the supplied geometry's bounding box as a LineString. The diagonal is a 2-point LineString with the minimum values of each dimension in its start point and the maximum values in its end point. If the input geometry is empty, the diagonal line is a LINESTRING EMPTY.

The optional `fits` parameter specifies if the best fit is needed. If false, the diagonal of a somewhat larger bounding box can be accepted (which is faster to compute for geometries with many vertices). In either case, the bounding box of the returned diagonal line always covers the input geometry.

The returned geometry retains the SRID and dimensionality (Z and M presence) of the input geometry.

In degenerate cases (i.e. a single vertex in input) the returned linestring will be formally invalid (no interior). The result is still topologically valid.

Availability: 2.2.0

&Z_support;

&M_support;

### Examples

    -- Get the minimum X in a buffer around a point
    SELECT ST_X(ST_StartPoint(ST_BoundingDiagonal(
      ST_Buffer(ST_Point(0,0),10)
    )));
     st_x
    ------
      -10

### See Also

ST_StartPoint, ST_EndPoint, ST_X, ST_Y, ST_Z, ST_M, ST_Envelope

ST_CoordDim

Return the coordinate dimension of a geometry.

    			integer ST_CoordDim
    			geometry  geomA

### Description

Return the coordinate dimension of the ST_Geometry value.

This is the MM compliant alias name for ST_NDims

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 5.1.3

&curve_support;

&Z_support;

&P_support;

&T_support;

### Examples

    SELECT ST_CoordDim('CIRCULARSTRING(1 2 3, 1 3 4, 5 6 7, 8 9 10, 11 12 13)');
    			---result--
    				3

    				SELECT ST_CoordDim(ST_Point(1,2));
    			--result--
    				2

### See Also

ST_NDims

ST_Dimension

Returns the topological dimension of a geometry.

    			integer ST_Dimension

    			geometry  g

### Description

Return the topological dimension of this Geometry object, which must be less than or equal to the coordinate dimension. OGC SPEC s2.1.1.1 - returns 0 for `POINT`, 1 for `LINESTRING`, 2 for `POLYGON`, and the largest dimension of the components of a `GEOMETRYCOLLECTION`. If the dimension is unknown (e.g. for an empty `GEOMETRYCOLLECTION`) 0 is returned.

&sqlmm_compliant; SQL-MM 3: 5.1.2

Enhanced: 2.0.0 support for Polyhedral surfaces and TINs was introduced. No longer throws an exception if given empty geometry.

Prior to 2.0.0, this function throws an exception if used with empty geometry.

&P_support;

&T_support;

### Examples

    SELECT ST_Dimension('GEOMETRYCOLLECTION(LINESTRING(1 1,0 0),POINT(0 0))');
    ST_Dimension
    -----------
    1

### See Also

ST_NDims

ST_Dump

Returns a set of `geometry_dump` rows for the components of a geometry.

    			geometry_dump[] ST_Dump
    			geometry  g1

### Description

A set-returning function (SRF) that extracts the components of a geometry. It returns a set of geometry_dump rows, each containing a geometry (`geom` field) and an array of integers (`path` field).

For an atomic geometry type (POINT,LINESTRING,POLYGON) a single record is returned with an empty `path` array and the input geometry as `geom`. For a collection or multi-geometry a record is returned for each of the collection components, and the `path` denotes the position of the component inside the collection.

ST_Dump is useful for expanding geometries. It is the inverse of a ST_Collect / GROUP BY, in that it creates new rows. For example it can be use to expand MULTIPOLYGONS into POLYGONS.

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

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+

&curve_support;

&P_support;

&T_support;

&Z_support;

### Standard Examples

    SELECT sometable.field1, sometable.field1,
          (ST_Dump(sometable.geom)).geom AS 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)

### Polyhedral Surfaces, TIN and Triangle Examples

    -- Polyhedral surface example
    -- Break a Polyhedral surface into its faces
    SELECT (a.p_geom).path[1] As path, ST_AsEWKT((a.p_geom).geom) As geom_ewkt
      FROM (SELECT ST_Dump(ST_GeomFromEWKT('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))
    )') ) AS p_geom )  AS a;

     path |                geom_ewkt
    ------+------------------------------------------
        1 | POLYGON((0 0 0,0 0 1,0 1 1,0 1 0,0 0 0))
        2 | POLYGON((0 0 0,0 1 0,1 1 0,1 0 0,0 0 0))
        3 | POLYGON((0 0 0,1 0 0,1 0 1,0 0 1,0 0 0))
        4 | POLYGON((1 1 0,1 1 1,1 0 1,1 0 0,1 1 0))
        5 | POLYGON((0 1 0,0 1 1,1 1 1,1 1 0,0 1 0))
        6 | POLYGON((0 0 1,1 0 1,1 1 1,0 1 1,0 0 1))

    -- TIN --
    SELECT (g.gdump).path, ST_AsEWKT((g.gdump).geom) as wkt
      FROM
        (SELECT
           ST_Dump( ST_GeomFromEWKT('TIN (((
                    0 0 0,
                    0 0 1,
                    0 1 0,
                    0 0 0
                )), ((
                    0 0 0,
                    0 1 0,
                    1 1 0,
                    0 0 0
                ))
                )') ) AS gdump
        ) AS g;
    -- result --
     path |                 wkt
    ------+-------------------------------------
     {1}  | TRIANGLE((0 0 0,0 0 1,0 1 0,0 0 0))
     {2}  | TRIANGLE((0 0 0,0 1 0,1 1 0,0 0 0))

### See Also

geometry_dump, PostGIS_Geometry_DumpFunctions, ST_Collect, ST_GeometryN

ST_DumpPoints

Returns a set of `geometry_dump` rows for the coordinates in a geometry.

    				geometry_dump[] ST_DumpPoints
    				geometry  geom

### Description

A set-returning function (SRF) that extracts the coordinates (vertices) of a geometry. It returns a set of geometry_dump rows, each containing a geometry (`geom` field) and an array of integers (`path` field).

- the `geom` field `POINT`s represent the coordinates of the supplied geometry.

- the `path` field (an `integer[]`) is an index enumerating the coordinate positions in the elements of the supplied geometry. The indices are 1-based. For example, for a `LINESTRING` the paths are `{i}` where `i` is the `nth` coordinate in the `LINESTRING`. For a `POLYGON` the paths are `{i,j}` where `i` is the ring number (1 is outer; inner rings follow) and `j` is the coordinate position in the ring.

To obtain a single geometry containing the coordinates use ST_Points.

Enhanced: 2.1.0 Faster speed. Reimplemented as native-C.

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

Availability: 1.5.0

&curve_support;

&P_support;

&T_support;

&Z_support;

### Classic Explode a Table of LineStrings into nodes

    SELECT edge_id, (dp).path[1] As index, ST_AsText((dp).geom) As wktnode
    FROM (SELECT 1 As edge_id
    	, ST_DumpPoints(ST_GeomFromText('LINESTRING(1 2, 3 4, 10 10)')) AS dp
         UNION ALL
         SELECT 2 As edge_id
    	, ST_DumpPoints(ST_GeomFromText('LINESTRING(3 5, 5 6, 9 10)')) AS dp
       ) As foo;
     edge_id | index |    wktnode
    ---------+-------+--------------
           1 |     1 | POINT(1 2)
           1 |     2 | POINT(3 4)
           1 |     3 | POINT(10 10)
           2 |     1 | POINT(3 5)
           2 |     2 | POINT(5 6)
           2 |     3 | POINT(9 10)

### Standard Geometry 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)

### Polyhedral Surfaces, TIN and Triangle Examples

    -- Polyhedral surface cube --
    SELECT (g.gdump).path, ST_AsEWKT((g.gdump).geom) as wkt
      FROM
        (SELECT
           ST_DumpPoints(ST_GeomFromEWKT('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)) )') ) AS gdump
        ) AS g;
    -- result --
      path   |     wkt
    ---------+--------------
     {1,1,1} | POINT(0 0 0)
     {1,1,2} | POINT(0 0 1)
     {1,1,3} | POINT(0 1 1)
     {1,1,4} | POINT(0 1 0)
     {1,1,5} | POINT(0 0 0)
     {2,1,1} | POINT(0 0 0)
     {2,1,2} | POINT(0 1 0)
     {2,1,3} | POINT(1 1 0)
     {2,1,4} | POINT(1 0 0)
     {2,1,5} | POINT(0 0 0)
     {3,1,1} | POINT(0 0 0)
     {3,1,2} | POINT(1 0 0)
     {3,1,3} | POINT(1 0 1)
     {3,1,4} | POINT(0 0 1)
     {3,1,5} | POINT(0 0 0)
     {4,1,1} | POINT(1 1 0)
     {4,1,2} | POINT(1 1 1)
     {4,1,3} | POINT(1 0 1)
     {4,1,4} | POINT(1 0 0)
     {4,1,5} | POINT(1 1 0)
     {5,1,1} | POINT(0 1 0)
     {5,1,2} | POINT(0 1 1)
     {5,1,3} | POINT(1 1 1)
     {5,1,4} | POINT(1 1 0)
     {5,1,5} | POINT(0 1 0)
     {6,1,1} | POINT(0 0 1)
     {6,1,2} | POINT(1 0 1)
     {6,1,3} | POINT(1 1 1)
     {6,1,4} | POINT(0 1 1)
     {6,1,5} | POINT(0 0 1)
    (30 rows)

    -- Triangle --
    SELECT (g.gdump).path, ST_AsText((g.gdump).geom) as wkt
      FROM
        (SELECT
           ST_DumpPoints( ST_GeomFromEWKT('TRIANGLE ((
                    0 0,
                    0 9,
                    9 0,
                    0 0
                ))') ) AS gdump
        ) AS g;
    -- result --
     path |    wkt
    ------+------------
     {1}  | POINT(0 0)
     {2}  | POINT(0 9)
     {3}  | POINT(9 0)
     {4}  | POINT(0 0)

    -- TIN --
    SELECT (g.gdump).path, ST_AsEWKT((g.gdump).geom) as wkt
      FROM
        (SELECT
           ST_DumpPoints( ST_GeomFromEWKT('TIN (((
                    0 0 0,
                    0 0 1,
                    0 1 0,
                    0 0 0
                )), ((
                    0 0 0,
                    0 1 0,
                    1 1 0,
                    0 0 0
                ))
                )') ) AS gdump
        ) AS g;
    -- result --
      path   |     wkt
    ---------+--------------
     {1,1,1} | POINT(0 0 0)
     {1,1,2} | POINT(0 0 1)
     {1,1,3} | POINT(0 1 0)
     {1,1,4} | POINT(0 0 0)
     {2,1,1} | POINT(0 0 0)
     {2,1,2} | POINT(0 1 0)
     {2,1,3} | POINT(1 1 0)
     {2,1,4} | POINT(0 0 0)
    (8 rows)

### See Also

geometry_dump, PostGIS_Geometry_DumpFunctions, ST_Dump, ST_DumpRings, ST_Points

ST_DumpSegments

Returns a set of `geometry_dump` rows for the segments in a geometry.

    				geometry_dump[] ST_DumpSegments
    				geometry  geom

### Description

A set-returning function (SRF) that extracts the segments of a geometry. It returns a set of geometry_dump rows, each containing a geometry (`geom` field) and an array of integers (`path` field).

- the `geom` field `LINESTRING`s represent the segments of the supplied geometry.

- the `path` field (an `integer[]`) is an index enumerating the segment start point positions in the elements of the supplied geometry. The indices are 1-based. For example, for a `LINESTRING` the paths are `{i}` where `i` is the `nth` segment start point in the `LINESTRING`. For a `POLYGON` the paths are `{i,j}` where `i` is the ring number (1 is outer; inner rings follow) and `j` is the segment start point position in the ring.

Availability: 3.2.0

&T_support;

&Z_support;

### Standard Geometry Examples

    SELECT path, ST_AsText(geom)
    FROM (
        SELECT (ST_DumpSegments(g.geom)).*
        FROM (SELECT 'GEOMETRYCOLLECTION(
        LINESTRING(1 1, 3 3, 4 4),
        POLYGON((5 5, 6 6, 7 7, 5 5))
    )'::geometry AS geom
            ) AS g
    ) j;

      path   │      st_astext
    ---------------------------------
     {1,1}   │ LINESTRING(1 1,3 3)
     {1,2}   │ LINESTRING(3 3,4 4)
     {2,1,1} │ LINESTRING(5 5,6 6)
     {2,1,2} │ LINESTRING(6 6,7 7)
     {2,1,3} │ LINESTRING(7 7,5 5)
    (5 rows)

### TIN and Triangle Examples

    -- Triangle --
    SELECT path, ST_AsText(geom)
    FROM (
        SELECT (ST_DumpSegments(g.geom)).*
        FROM (SELECT 'TRIANGLE((
            0 0,
            0 9,
            9 0,
            0 0
        ))'::geometry AS geom
            ) AS g
    ) j;

     path  │      st_astext
     ---------------------------------
     {1,1} │ LINESTRING(0 0,0 9)
     {1,2} │ LINESTRING(0 9,9 0)
     {1,3} │ LINESTRING(9 0,0 0)
    (3 rows)

    -- TIN --
    SELECT path, ST_AsEWKT(geom)
    FROM (
        SELECT (ST_DumpSegments(g.geom)).*
        FROM (SELECT 'TIN(((
            0 0 0,
            0 0 1,
            0 1 0,
            0 0 0
        )), ((
            0 0 0,
            0 1 0,
            1 1 0,
            0 0 0
        ))
        )'::geometry AS geom
            ) AS g
    ) j;

      path   │        st_asewkt
      ---------------------------------
     {1,1,1} │ LINESTRING(0 0 0,0 0 1)
     {1,1,2} │ LINESTRING(0 0 1,0 1 0)
     {1,1,3} │ LINESTRING(0 1 0,0 0 0)
     {2,1,1} │ LINESTRING(0 0 0,0 1 0)
     {2,1,2} │ LINESTRING(0 1 0,1 1 0)
     {2,1,3} │ LINESTRING(1 1 0,0 0 0)
    (6 rows)

### See Also

geometry_dump, PostGIS_Geometry_DumpFunctions, ST_Dump, ST_DumpRings

ST_DumpRings

Returns a set of `geometry_dump` rows for the exterior and interior rings of a Polygon.

    			geometry_dump[] ST_DumpRings
    			geometry  a_polygon

### Description

A set-returning function (SRF) that extracts the rings of a polygon. It returns a set of geometry_dump rows, each containing a geometry (`geom` field) and an array of integers (`path` field).

The `geom` field contains each ring as a POLYGON. The `path` field is an integer array of length 1 containing the polygon ring index. The exterior ring (shell) has index 0. The interior rings (holes) have indices of 1 and higher.

This only works for POLYGON geometries. It does not work for MULTIPOLYGONS

Availability: PostGIS 1.1.3. Requires PostgreSQL 7.3 or higher.

&Z_support;

### Examples

General form of query.

    SELECT polyTable.field1, polyTable.field1,
    	  (ST_DumpRings(polyTable.geom)).geom As geom
    FROM polyTable;

A polygon with a single hole.

    SELECT path, ST_AsEWKT(geom) As geom
    	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 |                                            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

geometry_dump, PostGIS_Geometry_DumpFunctions, ST_Dump, ST_ExteriorRing, ST_InteriorRingN

ST_EndPoint

Returns the last point of a LineString or CircularLineString.

    			geometry ST_EndPoint

    			geometry  g

### Description

Returns the last point of a `LINESTRING` or `CIRCULARLINESTRING` geometry as a `POINT`. Returns `NULL` if the input is not a `LINESTRING` or `CIRCULARLINESTRING`.

&sqlmm_compliant; SQL-MM 3: 7.1.4

&Z_support;

&curve_support;

Changed: 2.0.0 no longer works with single geometry MultiLineStrings. In older versions of PostGIS a single-line MultiLineString would work with this function and return the end point. In 2.0.0 it returns NULL like any other MultiLineString. The old behavior was an undocumented feature, but people who assumed they had their data stored as LINESTRING may experience these returning NULL in 2.0.0.

### Examples

End point of a LineString

    postgis=# SELECT ST_AsText(ST_EndPoint('LINESTRING(1 1, 2 2, 3 3)'::geometry));
     st_astext
    ------------
     POINT(3 3)

End point of a non-LineString is NULL

    SELECT ST_EndPoint('POINT(1 1)'::geometry) IS NULL AS is_null;
      is_null
    ----------
     t

End point of a 3D LineString

    --3d endpoint
    SELECT ST_AsEWKT(ST_EndPoint('LINESTRING(1 1 2, 1 2 3, 0 0 5)'));
      st_asewkt
    --------------
     POINT(0 0 5)

End point of a CircularString

    SELECT ST_AsText(ST_EndPoint('CIRCULARSTRING(5 2,-3 1.999999, -2 1, -4 2, 6 3)'::geometry));
     st_astext
    ------------
     POINT(6 3)

### See Also

ST_PointN, ST_StartPoint

ST_Envelope

Returns a geometry representing the bounding box of a geometry.

    				geometry ST_Envelope

    				geometry  g1

### Description

Returns the double-precision (float8) minimum bounding box for the supplied geometry, as a geometry. The polygon is defined by the corner points of the bounding box ((`MINX`, `MINY`), (`MINX`, `MAXY`), (`MAXX`, `MAXY`), (`MAXX`, `MINY`), (`MINX`, `MINY`)). (PostGIS will add a `ZMIN`/`ZMAX` coordinate as well).

Degenerate cases (vertical lines, points) will return a geometry of lower dimension than `POLYGON`, ie. `POINT` or `LINESTRING`.

Availability: 1.5.0 behavior changed to output double precision instead of float4

&sfs_compliant; s2.1.1.1

&sqlmm_compliant; SQL-MM 3: 5.1.15

### Examples

    SELECT ST_AsText(ST_Envelope('POINT(1 3)'::geometry));
     st_astext
    ------------
     POINT(1 3)
    (1 row)

    SELECT ST_AsText(ST_Envelope('LINESTRING(0 0, 1 3)'::geometry));
    		   st_astext
    --------------------------------
     POLYGON((0 0,0 3,1 3,1 0,0 0))
    (1 row)

    SELECT ST_AsText(ST_Envelope('POLYGON((0 0, 0 1, 1.0000001 1, 1.0000001 0, 0 0))'::geometry));
    						  st_astext
    --------------------------------------------------------------
     POLYGON((0 0,0 1,1.00000011920929 1,1.00000011920929 0,0 0))
    (1 row)
    SELECT ST_AsText(ST_Envelope('POLYGON((0 0, 0 1, 1.0000000001 1, 1.0000000001 0, 0 0))'::geometry));
    						  st_astext
    --------------------------------------------------------------
     POLYGON((0 0,0 1,1.00000011920929 1,1.00000011920929 0,0 0))
    (1 row)

    SELECT Box3D(geom), Box2D(geom), ST_AsText(ST_Envelope(geom)) As envelopewkt
    	FROM (SELECT 'POLYGON((0 0, 0 1000012333334.34545678, 1.0000001 1, 1.0000001 0, 0 0))'::geometry As geom) As foo;

Envelope of a point and linestring.

    SELECT ST_AsText(ST_Envelope(
    		ST_Collect(
    			ST_GeomFromText('LINESTRING(55 75,125 150)'),
    				ST_Point(20, 80))
    				)) As wktenv;
    wktenv
    -----------
    POLYGON((20 75,20 150,125 150,125 75,20 75))

### See Also

Box2D, Box3D, ST_OrientedEnvelope

ST_ExteriorRing

Returns a LineString representing the exterior ring of a Polygon.

    			geometry ST_ExteriorRing

    			geometry  a_polygon

### Description

Returns a LINESTRING representing the exterior ring (shell) of a POLYGON. Returns NULL if the geometry is not a polygon.

This function does not support MULTIPOLYGONs. For MULTIPOLYGONs use in conjunction with ST_GeometryN or ST_Dump

&sfs_compliant; 2.1.5.1

&sqlmm_compliant; SQL-MM 3: 8.2.3, 8.3.3

&Z_support;

### Examples

    --If you have a table of polygons
    SELECT gid, ST_ExteriorRing(geom) AS ering
    FROM sometable;

    --If you have a table of MULTIPOLYGONs
    --and want to return a MULTILINESTRING composed of the exterior rings of each polygon
    SELECT gid, ST_Collect(ST_ExteriorRing(geom)) AS erings
    	FROM (SELECT gid, (ST_Dump(geom)).geom As geom
    			FROM sometable) As foo
    GROUP BY gid;

    --3d Example
    SELECT ST_AsEWKT(
    	ST_ExteriorRing(
    	ST_GeomFromEWKT('POLYGON((0 0 1, 1 1 1, 1 2 1, 1 1 1, 0 0 1))')
    	)
    );

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

### See Also

ST_InteriorRingN, ST_Boundary, ST_NumInteriorRings

ST_GeometryN

Return an element of a geometry collection.

    			geometry ST_GeometryN
    			geometry  geomA
    			integer  n

### Description

Return the 1-based Nth element geometry of an input geometry which is a GEOMETRYCOLLECTION, MULTIPOINT, MULTILINESTRING, MULTICURVE, MULTI)POLYGON, or POLYHEDRALSURFACE. Otherwise, returns NULL.

Index is 1-based as for OGC specs since version 0.8.0. Previous versions implemented this as 0-based instead.

To extract all elements of a geometry, ST_Dump is more efficient and works for atomic geometries.

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

Changed: 2.0.0 Prior versions would return NULL for singular geometries. This was changed to return the geometry for ST_GeometryN(..,1) case.

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 9.1.5

&Z_support;

&curve_support;

&P_support;

&T_support;

### Standard Examples

    --Extracting a subset of points from a 3d multipoint
    SELECT n, ST_AsEWKT(ST_GeometryN(geom, n)) As geomewkt
    FROM (
    VALUES (ST_GeomFromEWKT('MULTIPOINT((1 2 7), (3 4 7), (5 6 7), (8 9 10))') ),
    ( ST_GeomFromEWKT('MULTICURVE(CIRCULARSTRING(2.5 2.5,4.5 2.5, 3.5 3.5), (10 11, 12 11))') )
    	)As foo(geom)
    	CROSS JOIN generate_series(1,100) n
    WHERE n <= ST_NumGeometries(geom);

     n |               geomewkt
    ---+-----------------------------------------
     1 | POINT(1 2 7)
     2 | POINT(3 4 7)
     3 | POINT(5 6 7)
     4 | POINT(8 9 10)
     1 | CIRCULARSTRING(2.5 2.5,4.5 2.5,3.5 3.5)
     2 | LINESTRING(10 11,12 11)

    --Extracting all geometries (useful when you want to assign an id)
    SELECT gid, n, ST_GeometryN(geom, n)
    FROM sometable CROSS JOIN generate_series(1,100) n
    WHERE n <= ST_NumGeometries(geom);

### Polyhedral Surfaces, TIN and Triangle Examples

    -- Polyhedral surface example
    -- Break a Polyhedral surface into its faces
    SELECT ST_AsEWKT(ST_GeometryN(p_geom,3)) As geom_ewkt
      FROM (SELECT ST_GeomFromEWKT('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))
    )')  AS p_geom )  AS a;

                    geom_ewkt
    ------------------------------------------
     POLYGON((0 0 0,1 0 0,1 0 1,0 0 1,0 0 0))

    -- TIN --
    SELECT ST_AsEWKT(ST_GeometryN(geom,2)) as wkt
      FROM
        (SELECT
           ST_GeomFromEWKT('TIN (((
                    0 0 0,
                    0 0 1,
                    0 1 0,
                    0 0 0
                )), ((
                    0 0 0,
                    0 1 0,
                    1 1 0,
                    0 0 0
                ))
                )')  AS geom
        ) AS g;
    -- result --
                     wkt
    -------------------------------------
     TRIANGLE((0 0 0,0 1 0,1 1 0,0 0 0))

### See Also

ST_Dump, ST_NumGeometries

ST_GeometryType

Returns the SQL-MM type of a geometry as text.

    			text ST_GeometryType
    			geometry  g1

### Description

Returns the type of the geometry as a string. EG: 'ST_LineString', 'ST_Polygon','ST_MultiPolygon' etc. This function differs from GeometryType(geometry) in the case of the string and ST in front that is returned, as well as the fact that it will not indicate whether the geometry is measured.

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

&sqlmm_compliant; SQL-MM 3: 5.1.4

&Z_support;

&P_support;

### Examples

    SELECT ST_GeometryType(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'));
    			--result
    			ST_LineString

    SELECT ST_GeometryType(ST_GeomFromEWKT('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)) )'));
    			--result
    			ST_PolyhedralSurface

    SELECT ST_GeometryType(ST_GeomFromEWKT('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)) )'));
    			--result
    			ST_PolyhedralSurface

    SELECT ST_GeometryType(geom) as result
      FROM
        (SELECT
           ST_GeomFromEWKT('TIN (((
                    0 0 0,
                    0 0 1,
                    0 1 0,
                    0 0 0
                )), ((
                    0 0 0,
                    0 1 0,
                    1 1 0,
                    0 0 0
                ))
                )')  AS geom
        ) AS g;
     result
    --------
     ST_Tin

### See Also

GeometryType

ST_HasArc

Tests if a geometry contains a circular arc

    			boolean ST_HasArc
    			geometry  geomA

### Description

Returns true if a geometry or geometry collection contains a circular string

Availability: 1.2.3?

&Z_support;

&curve_support;

### Examples

    SELECT ST_HasArc(ST_Collect('LINESTRING(1 2, 3 4, 5 6)', 'CIRCULARSTRING(1 1, 2 3, 4 5, 6 7, 5 6)'));
    		st_hasarc
    		--------
    		t

### See Also

ST_CurveToLine, ST_LineToCurve

ST_InteriorRingN

Returns the Nth interior ring (hole) of a Polygon.

    			geometry ST_InteriorRingN
    			geometry  a_polygon
    			integer  n

### Description

Returns the Nth interior ring (hole) of a POLYGON geometry as a LINESTRING. The index starts at 1. Returns NULL if the geometry is not a polygon or the index is out of range.

This function does not support MULTIPOLYGONs. For MULTIPOLYGONs use in conjunction with ST_GeometryN or ST_Dump

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 8.2.6, 8.3.5

&Z_support;

### Examples

    SELECT ST_AsText(ST_InteriorRingN(geom, 1)) As geom
    FROM (SELECT ST_BuildArea(
    		ST_Collect(ST_Buffer(ST_Point(1,2), 20,3),
    			ST_Buffer(ST_Point(1, 2), 10,3))) As geom
    		)  as foo;

### See Also

ST_ExteriorRing, ST_BuildArea, ST_Collect, ST_Dump, ST_NumInteriorRing, ST_NumInteriorRings

ST_IsClosed

Tests if a LineStrings's start and end points are coincident. For a PolyhedralSurface tests if it is closed (volumetric).

    			boolean ST_IsClosed

    			geometry  g

### Description

Returns `TRUE` if the `LINESTRING`'s start and end points are coincident. For Polyhedral Surfaces, reports if the surface is areal (open) or volumetric (closed).

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 7.1.5, 9.3.3

SQL-MM defines the result of `ST_IsClosed(`NULL`)` to be 0, while PostGIS returns `NULL`.

&Z_support;

&curve_support;

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

&P_support;

### Line String and Point Examples

    postgis=# SELECT ST_IsClosed('LINESTRING(0 0, 1 1)'::geometry);
     st_isclosed
    -------------
     f
    (1 row)

    postgis=# SELECT ST_IsClosed('LINESTRING(0 0, 0 1, 1 1, 0 0)'::geometry);
     st_isclosed
    -------------
     t
    (1 row)

    postgis=# SELECT ST_IsClosed('MULTILINESTRING((0 0, 0 1, 1 1, 0 0),(0 0, 1 1))'::geometry);
     st_isclosed
    -------------
     f
    (1 row)

    postgis=# SELECT ST_IsClosed('POINT(0 0)'::geometry);
     st_isclosed
    -------------
     t
    (1 row)

    postgis=# SELECT ST_IsClosed('MULTIPOINT((0 0), (1 1))'::geometry);
     st_isclosed
    -------------
     t
    (1 row)

### Polyhedral Surface Examples

    		-- A cube --
    		SELECT ST_IsClosed(ST_GeomFromEWKT('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_isclosed
    -------------
     t

     -- Same as cube but missing a side --
     SELECT ST_IsClosed(ST_GeomFromEWKT('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)) )'));

     st_isclosed
    -------------
     f

### See Also

ST_IsRing

ST_IsCollection

Tests if a geometry is a geometry collection type.

    			boolean ST_IsCollection
    			geometry  g

### Description

Returns `TRUE` if the geometry type of the argument a geometry collection type. Collection types are the following:

- GEOMETRYCOLLECTION

- MULTI{POINT,POLYGON,LINESTRING,CURVE,SURFACE}

- COMPOUNDCURVE

This function analyzes the type of the geometry. This means that it will return `TRUE` on collections that are empty or that contain a single element.

&Z_support;

&curve_support;

### Examples

    postgis=# SELECT ST_IsCollection('LINESTRING(0 0, 1 1)'::geometry);
     st_iscollection
    -------------
     f
    (1 row)

    postgis=# SELECT ST_IsCollection('MULTIPOINT EMPTY'::geometry);
     st_iscollection
    -------------
     t
    (1 row)

    postgis=# SELECT ST_IsCollection('MULTIPOINT((0 0))'::geometry);
     st_iscollection
    -------------
     t
    (1 row)

    postgis=# SELECT ST_IsCollection('MULTIPOINT((0 0), (42 42))'::geometry);
     st_iscollection
    -------------
     t
    (1 row)

    postgis=# SELECT ST_IsCollection('GEOMETRYCOLLECTION(POINT(0 0))'::geometry);
     st_iscollection
    -------------
     t
    (1 row)

### See Also

ST_NumGeometries

ST_IsEmpty

Tests if a geometry is empty.

    			boolean ST_IsEmpty
    			geometry  geomA

### Description

Returns true if this Geometry is an empty geometry. If true, then this Geometry represents an empty geometry collection, polygon, point etc.

SQL-MM defines the result of ST_IsEmpty(NULL) to be 0, while PostGIS returns NULL.

&sfs_compliant; s2.1.1.1

&sqlmm_compliant; SQL-MM 3: 5.1.7

&curve_support;

Changed: 2.0.0 In prior versions of PostGIS ST_GeomFromText('GEOMETRYCOLLECTION(EMPTY)') was allowed. This is now illegal in PostGIS 2.0.0 to better conform with SQL/MM standards

### Examples

    SELECT ST_IsEmpty(ST_GeomFromText('GEOMETRYCOLLECTION EMPTY'));
     st_isempty
    ------------
     t
    (1 row)

     SELECT ST_IsEmpty(ST_GeomFromText('POLYGON EMPTY'));
     st_isempty
    ------------
     t
    (1 row)

    SELECT ST_IsEmpty(ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))'));

     st_isempty
    ------------
     f
    (1 row)

     SELECT ST_IsEmpty(ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))')) = false;
     ?column?
    ----------
     t
    (1 row)

     SELECT ST_IsEmpty(ST_GeomFromText('CIRCULARSTRING EMPTY'));
      st_isempty
    ------------
     t
    (1 row)

ST_IsPolygonCCW

Tests if Polygons have exterior rings oriented counter-clockwise and interior rings oriented clockwise.

    						boolean
    						ST_IsPolygonCCW

    						geometry
    						geom

### Description

Returns true if all polygonal components of the input geometry use a counter-clockwise orientation for their exterior ring, and a clockwise direction for all interior rings.

Returns true if the geometry has no polygonal components.

Closed linestrings are not considered polygonal components, so you would still get a true return by passing a single closed linestring no matter its orientation.

If a polygonal geometry does not use reversed orientation for interior rings (i.e., if one or more interior rings are oriented in the same direction as an exterior ring) then both ST_IsPolygonCW and ST_IsPolygonCCW will return false.

Availability: 2.4.0

&Z_support;

&M_support;

### See Also

ST_ForcePolygonCW, ST_ForcePolygonCCW, ST_IsPolygonCW

ST_IsPolygonCW

Tests if Polygons have exterior rings oriented clockwise and interior rings oriented counter-clockwise.

    						boolean
    						ST_IsPolygonCW

    						geometry
    						geom

### Description

Returns true if all polygonal components of the input geometry use a clockwise orientation for their exterior ring, and a counter-clockwise direction for all interior rings.

Returns true if the geometry has no polygonal components.

Closed linestrings are not considered polygonal components, so you would still get a true return by passing a single closed linestring no matter its orientation.

If a polygonal geometry does not use reversed orientation for interior rings (i.e., if one or more interior rings are oriented in the same direction as an exterior ring) then both ST_IsPolygonCW and ST_IsPolygonCCW will return false.

Availability: 2.4.0

&Z_support;

&M_support;

### See Also

ST_ForcePolygonCW, ST_ForcePolygonCCW, ST_IsPolygonCW

ST_IsRing

Tests if a LineString is closed and simple.

    		  boolean ST_IsRing

    		  geometry  g

### Description

Returns `TRUE` if this `LINESTRING` is both ST_IsClosed (`ST_StartPoint(`g`)` `~=` `ST_Endpoint(`g`)`) and ST_IsSimple (does not self intersect).

&sfs_compliant; 2.1.5.1

&sqlmm_compliant; SQL-MM 3: 7.1.6

SQL-MM defines the result of `ST_IsRing(`NULL`)` to be 0, while PostGIS returns `NULL`.

### Examples

    SELECT ST_IsRing(geom), ST_IsClosed(geom), ST_IsSimple(geom)
    FROM (SELECT 'LINESTRING(0 0, 0 1, 1 1, 1 0, 0 0)'::geometry AS geom) AS foo;
     st_isring | st_isclosed | st_issimple
    -----------+-------------+-------------
     t         | t           | t
    (1 row)

    SELECT ST_IsRing(geom), ST_IsClosed(geom), ST_IsSimple(geom)
    FROM (SELECT 'LINESTRING(0 0, 0 1, 1 0, 1 1, 0 0)'::geometry AS geom) AS foo;
     st_isring | st_isclosed | st_issimple
    -----------+-------------+-------------
     f         | t           | f
    (1 row)

### See Also

ST_IsClosed, ST_IsSimple, ST_StartPoint, ST_EndPoint

ST_IsSimple

Tests if a geometry has no points of self-intersection or self-tangency.

    			boolean ST_IsSimple
    			geometry  geomA

### Description

Returns true if this Geometry has no anomalous geometric points, such as self-intersection or self-tangency. For more information on the OGC's definition of geometry simplicity and validity, refer to "Ensuring OpenGIS compliancy of geometries"

SQL-MM defines the result of ST_IsSimple(NULL) to be 0, while PostGIS returns NULL.

&sfs_compliant; s2.1.1.1

&sqlmm_compliant; SQL-MM 3: 5.1.8

&Z_support;

### Examples

     SELECT ST_IsSimple(ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))'));
     st_issimple
    -------------
     t
    (1 row)

     SELECT ST_IsSimple(ST_GeomFromText('LINESTRING(1 1,2 2,2 3.5,1 3,1 2,2 1)'));
     st_issimple
    -------------
     f
    (1 row)

### See Also

ST_IsValid

ST_M

Returns the M coordinate of a Point.

    			float ST_M
    			geometry  a_point

### Description

Return the M coordinate of a Point, or NULL if not available. Input must be a Point.

This is not (yet) part of the OGC spec, but is listed here to complete the point coordinate extractor function list.

&sfs_compliant;

&sqlmm_compliant;

&Z_support;

### Examples

    SELECT ST_M(ST_GeomFromEWKT('POINT(1 2 3 4)'));
     st_m
    ------
    	4
    (1 row)

### See Also

ST_GeomFromEWKT, ST_X, ST_Y, ST_Z

ST_MemSize

Returns the amount of memory space a geometry takes.

    			integer ST_MemSize
    			geometry  geomA

### Description

Returns the amount of memory space (in bytes) the geometry takes.

This complements the PostgreSQL built-in database object functions pg_column_size, pg_size_pretty, pg_relation_size, pg_total_relation_size.

pg_relation_size which gives the byte size of a table may return byte size lower than ST_MemSize. This is because pg_relation_size does not add toasted table contribution and large geometries are stored in TOAST tables.

pg_total_relation_size - includes, the table, the toasted tables, and the indexes.

pg_column_size returns how much space a geometry would take in a column considering compression, so may be lower than ST_MemSize

&Z_support;

&curve_support;

&P_support;

&T_support;

Changed: 2.2.0 name changed to ST_MemSize to follow naming convention.

### Examples

    --Return how much byte space Boston takes up  in our Mass data set
    SELECT pg_size_pretty(SUM(ST_MemSize(geom))) as totgeomsum,
    pg_size_pretty(SUM(CASE WHEN town = 'BOSTON' THEN ST_MemSize(geom) ELSE 0 END)) As bossum,
    CAST(SUM(CASE WHEN town = 'BOSTON' THEN ST_MemSize(geom) ELSE 0 END)*1.00 /
    		SUM(ST_MemSize(geom))*100 As numeric(10,2)) As perbos
    FROM towns;

    totgeomsum	bossum	perbos
    ----------	------	------
    1522 kB		30 kB	1.99

    SELECT ST_MemSize(ST_GeomFromText('CIRCULARSTRING(220268 150415,220227 150505,220227 150406)'));

    ---
    73

    --What percentage of our table is taken up by just the geometry
    SELECT pg_total_relation_size('public.neighborhoods') As fulltable_size, sum(ST_MemSize(geom)) As geomsize,
    sum(ST_MemSize(geom))*1.00/pg_total_relation_size('public.neighborhoods')*100 As pergeom
    FROM neighborhoods;
    fulltable_size geomsize  pergeom
    ------------------------------------------------
    262144         96238	 36.71188354492187500000

ST_NDims

Returns the coordinate dimension of a geometry.

    			integer ST_NDims
    			geometry  g1

### Description

Returns the coordinate dimension of the geometry. PostGIS supports 2 - (x,y) , 3 - (x,y,z) or 2D with measure - x,y,m, and 4 - 3D with measure space x,y,z,m

&Z_support;

### Examples

    SELECT ST_NDims(ST_GeomFromText('POINT(1 1)')) As d2point,
    	ST_NDims(ST_GeomFromEWKT('POINT(1 1 2)')) As d3point,
    	ST_NDims(ST_GeomFromEWKT('POINTM(1 1 0.5)')) As d2pointm;

    	 d2point | d3point | d2pointm
    ---------+---------+----------
    	   2 |       3 |        3

### See Also

ST_CoordDim, ST_Dimension, ST_GeomFromEWKT

ST_NPoints

Returns the number of points (vertices) in a geometry.

    			integer ST_NPoints
    			geometry  g1

### Description

Return the number of points in a geometry. Works for all geometries.

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

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;

&P_support;

### Examples

    SELECT ST_NPoints(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'));
    --result
    4

    --Polygon in 3D space
    SELECT ST_NPoints(ST_GeomFromEWKT('LINESTRING(77.29 29.07 1,77.42 29.26 0,77.27 29.31 -1,77.29 29.07 3)'))
    --result
    4

### See Also

ST_NumPoints

ST_NRings

Returns the number of rings in a polygonal geometry.

    			integer ST_NRings
    			geometry  geomA

### Description

If the geometry is a polygon or multi-polygon returns the number of rings. Unlike NumInteriorRings, it counts the outer rings as well.

&Z_support;

&curve_support;

### Examples

    SELECT ST_NRings(geom) As Nrings, ST_NumInteriorRings(geom) As ninterrings
    					FROM (SELECT ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))') As geom) As foo;
    	 nrings | ninterrings
    --------+-------------
    	  1 |           0
    (1 row)

### See Also

ST_NumInteriorRings

ST_NumGeometries

Returns the number of elements in a geometry collection.

    			integer ST_NumGeometries
    			geometry  geom

### Description

Returns the number of Geometries. If geometry is a GEOMETRYCOLLECTION (or MULTI*) return the number of geometries, for single geometries will return 1, otherwise return NULL.

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

Changed: 2.0.0 In prior versions this would return NULL if the geometry was not a collection/MULTI type. 2.0.0+ now returns 1 for single geometries e.g POLYGON, LINESTRING, POINT.

&sqlmm_compliant; SQL-MM 3: 9.1.4

&Z_support;

&P_support;

&T_support;

### Examples

    --Prior versions would have returned NULL for this -- in 2.0.0 this returns 1
    SELECT ST_NumGeometries(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'));
    --result
    1

    --Geometry Collection Example - multis count as one geom in a collection
    SELECT ST_NumGeometries(ST_GeomFromEWKT('GEOMETRYCOLLECTION(MULTIPOINT((-2 3),(-2 2)),
    LINESTRING(5 5 ,10 10),
    POLYGON((-7 4.2,-7.1 5,-7.1 4.3,-7 4.2)))'));
    --result
    3

### See Also

ST_GeometryN, ST_Multi

ST_NumInteriorRings

Returns the number of interior rings (holes) of a Polygon.

    			integer ST_NumInteriorRings
    			geometry  a_polygon

### Description

Return the number of interior rings of a polygon geometry. Return NULL if the geometry is not a polygon.

&sqlmm_compliant; SQL-MM 3: 8.2.5

Changed: 2.0.0 - in prior versions it would allow passing a MULTIPOLYGON, returning the number of interior rings of first POLYGON.

### Examples

    --If you have a regular polygon
    SELECT gid, field1, field2, ST_NumInteriorRings(geom) AS numholes
    FROM sometable;

    --If you have multipolygons
    --And you want to know the total number of interior rings in the MULTIPOLYGON
    SELECT gid, field1, field2, SUM(ST_NumInteriorRings(geom)) AS numholes
    FROM (SELECT gid, field1, field2, (ST_Dump(geom)).geom As geom
    	FROM sometable) As foo
    GROUP BY gid, field1,field2;

### See Also

ST_NumInteriorRing, ST_InteriorRingN

ST_NumInteriorRing

Returns the number of interior rings (holes) of a Polygon. Aias for ST_NumInteriorRings

    			integer ST_NumInteriorRing
    			geometry  a_polygon

### See Also

ST_NumInteriorRings, ST_InteriorRingN

ST_NumPatches

Return the number of faces on a Polyhedral Surface. Will return null for non-polyhedral geometries.

    			integer ST_NumPatches
    			geometry  g1

### Description

Return the number of faces on a Polyhedral Surface. Will return null for non-polyhedral geometries. This is an alias for ST_NumGeometries to support MM naming. Faster to use ST_NumGeometries if you don't care about MM convention.

Availability: 2.0.0

&Z_support;

&sfs_compliant;

&sqlmm_compliant; SQL-MM ISO/IEC 13249-3

&P_support;

### Examples

    SELECT ST_NumPatches(ST_GeomFromEWKT('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)) )'));
    		--result
    		6

### See Also

ST_GeomFromEWKT, ST_NumGeometries

ST_NumPoints

Returns the number of points in a LineString or CircularString.

    			integer ST_NumPoints
    			geometry  g1

### Description

Return the number of points in an ST_LineString or ST_CircularString value. Prior to 1.4 only works with linestrings as the specs state. From 1.4 forward this is an alias for ST_NPoints which returns number of vertexes for not just linestrings. Consider using ST_NPoints instead which is multi-purpose and works with many geometry types.

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 7.2.4

### Examples

    SELECT ST_NumPoints(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'));
    		--result
    		4

### See Also

ST_NPoints

ST_PatchN

Returns the Nth geometry (face) of a PolyhedralSurface.

    			geometry ST_PatchN
    			geometry  geomA
    			integer  n

### Description

Returns the 1-based Nth geometry (face) if the geometry is a POLYHEDRALSURFACE or POLYHEDRALSURFACEM. Otherwise, returns NULL. This returns the same answer as ST_GeometryN for PolyhedralSurfaces. Using ST_GeometryN is faster.

Index is 1-based.

If you want to extract all elements of a geometry ST_Dump is more efficient.

Availability: 2.0.0

&sqlmm_compliant; SQL-MM ISO/IEC 13249-3

&Z_support;

&P_support;

### Examples

    --Extract the 2nd face of the polyhedral surface
    SELECT ST_AsEWKT(ST_PatchN(geom, 2)) As geomewkt
    FROM (
    VALUES (ST_GeomFromEWKT('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)) )')) ) As foo(geom);

                  geomewkt
    ---+-----------------------------------------
     POLYGON((0 0 0,0 1 0,1 1 0,1 0 0,0 0 0))

### See Also

ST_AsEWKT, ST_GeomFromEWKT, ST_Dump, ST_GeometryN, ST_NumGeometries

ST_PointN

Returns the Nth point in the first LineString or circular LineString in a geometry.

    			geometry ST_PointN
    			geometry  a_linestring
    			integer  n

### Description

Return the Nth point in a single linestring or circular linestring in the geometry. Negative values are counted backwards from the end of the LineString, so that -1 is the last point. Returns NULL if there is no linestring in the geometry.

Index is 1-based as for OGC specs since version 0.8.0. Backward indexing (negative index) is not in OGC Previous versions implemented this as 0-based instead.

If you want to get the Nth point of each LineString in a MultiLineString, use in conjunction with ST_Dump

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 7.2.5, 7.3.5

&Z_support;

&curve_support;

Changed: 2.0.0 no longer works with single geometry multilinestrings. In older versions of PostGIS -- a single line multilinestring would work happily with this function and return the start point. In 2.0.0 it just returns NULL like any other multilinestring.

Changed: 2.3.0 : negative indexing available (-1 is last point)

### Examples

    -- Extract all POINTs from a LINESTRING
    SELECT ST_AsText(
       ST_PointN(
    	  column1,
    	  generate_series(1, ST_NPoints(column1))
       ))
    FROM ( VALUES ('LINESTRING(0 0, 1 1, 2 2)'::geometry) ) AS foo;

     st_astext
    ------------
     POINT(0 0)
     POINT(1 1)
     POINT(2 2)
    (3 rows)

    --Example circular string
    SELECT ST_AsText(ST_PointN(ST_GeomFromText('CIRCULARSTRING(1 2, 3 2, 1 2)'), 2));

     st_astext
    ------------
     POINT(3 2)
    (1 row)

    SELECT ST_AsText(f)
    FROM ST_GeomFromText('LINESTRING(0 0 0, 1 1 1, 2 2 2)') AS g
      ,ST_PointN(g, -2) AS f; -- 1 based index

        st_astext
    -----------------
     POINT Z (1 1 1)
    (1 row)

### See Also

ST_NPoints

ST_Points

Returns a MultiPoint containing the coordinates of a geometry.

    					geometry ST_Points

    						geometry
    						geom

### Description

Returns a MultiPoint containing all the coordinates of a geometry. Duplicate points are preserved, including the start and end points of ring geometries. (If desired, duplicate points can be removed by calling ST_RemoveRepeatedPoints on the result).

To obtain information about the position of each coordinate in the parent geometry use ST_DumpPoints.

M and Z coordinates are preserved if present.

&curve_support;

&Z_support;

Availability: 2.3.0

### Examples

    SELECT ST_AsText(ST_Points('POLYGON Z ((30 10 4,10 30 5,40 40 6, 30 10))'));

    --result
    MULTIPOINT Z ((30 10 4),(10 30 5),(40 40 6),(30 10 4))

### See Also

ST_RemoveRepeatedPoints, ST_DumpPoints

ST_StartPoint

Returns the first point of a LineString.

    		  geometry ST_StartPoint

    		  geometry  geomA

### Description

Returns the first point of a `LINESTRING` or `CIRCULARLINESTRING` geometry as a `POINT`. Returns `NULL` if the input is not a `LINESTRING` or `CIRCULARLINESTRING`.

&sqlmm_compliant; SQL-MM 3: 7.1.3

&Z_support;

&curve_support;

Enhanced: 3.2.0 returns a point for all geometries. Prior behavior returns NULLs if input was not a LineString.

Changed: 2.0.0 no longer works with single geometry MultiLineStrings. In older versions of PostGIS a single-line MultiLineString would work happily with this function and return the start point. In 2.0.0 it just returns NULL like any other MultiLineString. The old behavior was an undocumented feature, but people who assumed they had their data stored as LINESTRING may experience these returning NULL in 2.0.0.

### Examples

Start point of a LineString

    SELECT ST_AsText(ST_StartPoint('LINESTRING(0 1, 0 2)'::geometry));
     st_astext
    ------------
     POINT(0 1)

Start point of a non-LineString is NULL

    SELECT ST_StartPoint('POINT(0 1)'::geometry) IS NULL AS is_null;
      is_null
    ----------
     t

Start point of a 3D LineString

    SELECT ST_AsEWKT(ST_StartPoint('LINESTRING(0 1 1, 0 2 2)'::geometry));
     st_asewkt
    ------------
     POINT(0 1 1)

Start point of a CircularString

    SELECT ST_AsText(ST_StartPoint('CIRCULARSTRING(5 2,-3 1.999999, -2 1, -4 2, 6 3)'::geometry));
     st_astext
    ------------
     POINT(5 2)

### See Also

ST_EndPoint, ST_PointN

ST_Summary

Returns a text summary of the contents of a geometry.

    			text ST_Summary
    			geometry  g

    			text ST_Summary
    			geography  g

### Description

Returns a text summary of the contents of the geometry.

Flags shown square brackets after the geometry type have the following meaning:

- M: has M coordinate

- Z: has Z coordinate

- B: has a cached bounding box

- G: is geodetic (geography)

- S: has spatial reference system

&curve_support;

&P_support;

&T_support;

Availability: 1.2.2

Enhanced: 2.0.0 added support for geography

Enhanced: 2.1.0 S flag to denote if has a known spatial reference system

Enhanced: 2.2.0 Added support for TIN and Curves

### Examples

    =# SELECT ST_Summary(ST_GeomFromText('LINESTRING(0 0, 1 1)')) as geom,
            ST_Summary(ST_GeogFromText('POLYGON((0 0, 1 1, 1 2, 1 1, 0 0))')) geog;
                geom             |          geog
    -----------------------------+--------------------------
     LineString[B] with 2 points | Polygon[BGS] with 1 rings
                                 | ring 0 has 5 points
                                 :
    (1 row)

    =# SELECT ST_Summary(ST_GeogFromText('LINESTRING(0 0 1, 1 1 1)')) As geog_line,
            ST_Summary(ST_GeomFromText('SRID=4326;POLYGON((0 0 1, 1 1 2, 1 2 3, 1 1 1, 0 0 1))')) As geom_poly;
    ;
               geog_line             |        geom_poly
    -------------------------------- +--------------------------
     LineString[ZBGS] with 2 points | Polygon[ZBS] with 1 rings
                                    :    ring 0 has 5 points
                                    :
    (1 row)

### See Also

PostGIS_DropBBox, PostGIS_AddBBox, ST_Force_3DM, ST_Force_3DZ, ST_Force2D, geography

ST_IsValid, ST_IsValid, ST_IsValidReason, ST_IsValidDetail

ST_X

Returns the X coordinate of a Point.

    			float ST_X
    			geometry  a_point

### Description

Return the X coordinate of the point, or NULL if not available. Input must be a point.

To get the minimum and maximum X value of geometry coordinates use the functions ST_XMin and ST_XMax.

&sqlmm_compliant; SQL-MM 3: 6.1.3

&Z_support;

### Examples

    SELECT ST_X(ST_GeomFromEWKT('POINT(1 2 3 4)'));
     st_x
    ------
    	1
    (1 row)

    SELECT ST_Y(ST_Centroid(ST_GeomFromEWKT('LINESTRING(1 2 3 4, 1 1 1 1)')));
     st_y
    ------
      1.5
    (1 row)

### See Also

ST_Centroid, ST_GeomFromEWKT, ST_M, ST_XMax, ST_XMin, ST_Y, ST_Z

ST_Y

Returns the Y coordinate of a Point.

    			float ST_Y
    			geometry  a_point

### Description

Return the Y coordinate of the point, or NULL if not available. Input must be a point.

To get the minimum and maximum Y value of geometry coordinates use the functions ST_YMin and ST_YMax.

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 6.1.4

&Z_support;

### Examples

    SELECT ST_Y(ST_GeomFromEWKT('POINT(1 2 3 4)'));
     st_y
    ------
    	2
    (1 row)

    SELECT ST_Y(ST_Centroid(ST_GeomFromEWKT('LINESTRING(1 2 3 4, 1 1 1 1)')));
     st_y
    ------
      1.5
    (1 row)

### See Also

ST_Centroid, ST_GeomFromEWKT, ST_M, ST_X, ST_YMax, ST_YMin, ST_Z

ST_Z

Returns the Z coordinate of a Point.

    			float ST_Z
    			geometry  a_point

### Description

Return the Z coordinate of the point, or NULL if not available. Input must be a point.

To get the minimum and maximum Z value of geometry coordinates use the functions ST_ZMin and ST_ZMax.

&sqlmm_compliant;

&Z_support;

### Examples

    SELECT ST_Z(ST_GeomFromEWKT('POINT(1 2 3 4)'));
     st_z
    ------
    	3
    (1 row)

### See Also

ST_GeomFromEWKT, ST_M, ST_X, ST_Y, ST_ZMax, ST_ZMin

ST_Zmflag

Returns a code indicating the ZM coordinate dimension of a geometry.

    			smallint ST_Zmflag
    			geometry  geomA

### Description

Returns a code indicating the ZM coordinate dimension of a geometry.

Values are: 0 = 2D, 1 = 3D-M, 2 = 3D-Z, 3 = 4D.

&Z_support;

&curve_support;

### Examples

    SELECT ST_Zmflag(ST_GeomFromEWKT('LINESTRING(1 2, 3 4)'));
     st_zmflag
    -----------
    		 0

    SELECT ST_Zmflag(ST_GeomFromEWKT('LINESTRINGM(1 2 3, 3 4 3)'));
     st_zmflag
    -----------
    		 1

    SELECT ST_Zmflag(ST_GeomFromEWKT('CIRCULARSTRING(1 2 3, 3 4 3, 5 6 3)'));
     st_zmflag
    -----------
    		 2
    SELECT ST_Zmflag(ST_GeomFromEWKT('POINT(1 2 3 4)'));
     st_zmflag
    -----------
    		 3

### See Also

ST_CoordDim, ST_NDims, ST_Dimension