ST_CollectionExtract

Signatures

GEOMETRY ST_CollectionExtract(GEOMETRY geom, int dimension);

Description

Given a (multi)geometry, returns a (multi)geometry consisting only of elements of the specified dimension. Dimension numbers are 1 for POINT, 2 for LINESTRING and 3 for POLYGON.

Sub-geometries that are not the specified type are ignored.

If there are no sub-geometries of the right type, an EMPTY geometry will be returned.

Only POINTs, LINEs and POLYGONs are returned.

Examples

SELECT ST_CollectionExtract('POLYGON ((1 3, 1 0, 4 0, 4 2, 5 5, 1 3))', 3) as THE_GEOM;
-- Answer: POLYGON ((1 3, 1 0, 4 0, 4 2, 5 5, 1 3)) 

SELECT ST_CollectionExtract('MULTILINESTRING ((0 0, 4 1), (1 1, 5 5))', 2) as THE_GEOM;
-- Answer: MULTILINESTRING ((0 0, 4 1), (1 1, 5 5))

SELECT ST_CollectionExtract('GEOMETRYCOLLECTION(
                       MULTIPOINT((4 4), (1 1), (1 0), (0 3)),
                       LINESTRING(2 6, 6 2),
                       POLYGON((1 2, 4 2, 4 6, 1 6, 1 2)))', 2) 
                       as THE_GEOM;
-- Answer: LINESTRING (2 6, 6 2)  

SELECT ST_CollectionExtract('POLYGON ((1 3, 1 0, 4 0, 4 2, 5 5, 1 3))', 2) as THE_GEOM;
-- Answer: GEOMETRYCOLLECTION EMPTY

See also