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Examples

SELECT ST_AsText(ST_PointOnSurface(’POINT(0 5)’::geometry));st_astext

------------POINT(0 5)

(1 row)

SELECT ST_AsText(ST_PointOnSurface(’LINESTRING(0 5, 0 10)’::geometry));st_astext

------------POINT(0 5)

(1 row)

SELECT ST_AsText(ST_PointOnSurface(’POLYGON((0 0, 0 5, 5 5, 5 0, 0 0))’::geometry));st_astext

----------------POINT(2.5 2.5)

(1 row)

SELECT ST_AsEWKT(ST_PointOnSurface(ST_GeomFromEWKT(’LINESTRING(0 5 1, 0 0 1, 0 10 2)’)));st_asewkt

----------------POINT(0 0 1)

(1 row)

See Also

ST_Centroid, ST_Point_Inside_Circle

7.8.35 ST_Relate

Name

ST_Relate – Returns true if this Geometry is spatially related to anotherGeometry, by testing for intersections between theInterior, Boundary and Exterior of the two geometries as specified by the values in the intersectionMatrixPattern. If no intersec-tionMatrixPattern is passed in, then returns the maximum intersectionMatrixPattern that relates the 2 geometries.

Synopsis

boolean ST_Relate(geometry geomA, geometry geomB, text intersectionMatrixPattern);text ST_Relate(geometry geomA, geometry geomB);

Description

Version 1: Takes geomA, geomB, intersectionMatrix and Returns 1 (TRUE) if this Geometry is spatially related to anotherGe-ometry, by testing for intersections between the Interior, Boundary and Exterior of the two geometries as specified by the valuesin the intersectionMatrixPattern.

This is especially useful for testing compound checks of intersection, crosses, etc in one step.

Do not call with a GeometryCollection as an argument

NoteThis is the "allowable" version that returns a boolean, not an integer. This is defined in OGC spec

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NoteThis DOES NOT automagically include an index call. The reason for that is some relationships are anti e.g. Disjoint. Ifyou are using a relationship pattern that requires intersection, then include the && index call.

Version 2: Takes geomA and geomB and returns the DE-9IM (dimensionally extended nine-intersection matrix)

NoteDo not call with a GeometryCollection as an argument

not in OGC spec, but implied. see s2.1.13.2

Both Performed by the GEOS module

This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.2 // s2.1.13.3

This method implements the SQL/MM specification. SQL-MM 3: 5.1.25

Examples

--Find all compounds that intersect and not touch a poly (interior intersects)SELECT l.* , b.name As poly_nameFROM polys As bINNER JOIN compounds As lON (p.the_geom && b.the_geomAND ST_Relate(l.the_geom, b.the_geom,’T********’));

SELECT ST_Relate(ST_GeometryFromText(’POINT(1 2)’), ST_Buffer(ST_GeometryFromText(’POINT(1 ←↩2)’),2));

st_relate-----------0FFFFF212

SELECT ST_Relate(ST_GeometryFromText(’LINESTRING(1 2, 3 4)’), ST_GeometryFromText(’ ←↩LINESTRING(5 6, 7 8)’));

st_relate-----------FF1FF0102

SELECT ST_Relate(ST_GeometryFromText(’POINT(1 2)’), ST_Buffer(ST_GeometryFromText(’POINT(1 ←↩2)’),2), ’0FFFFF212’);

st_relate-----------t

SELECT ST_Relate(ST_GeometryFromText(’POINT(1 2)’), ST_Buffer(ST_GeometryFromText(’POINT(1 ←↩2)’),2), ’*FF*FF212’);

st_relate-----------t