ST_RemovePoints

Signature

GEOMETRY ST_RemovePoints(GEOMETRY geom, POLYGON poly);

Description

Remove all coordinates of geom located within poly. Returns NULL if all coordinates are removed.

Warning

May produce invalid Geometries. Use with caution

Warning

This function does not work on GEOMETRYCOLLECTIONs

Examples

SELECT ST_RemovePoints('MULTIPOINT((5 5), (3 1))',
                      ST_Buffer('POINT(4 2)', 2));
-- Answer: MULTIPOINT((5 5))

In the following two examples, we get the same result whether we use ST_Buffer or a POLYGON:

SELECT ST_RemovePoints('POLYGON((0 1, 5 4, 5 7, 2 6, 0 1))',
                      ST_Buffer('POINT(6 8)', 1.5));
-- Answer: POLYGON((0 1, 5 4, 2 6, 0 1))

SELECT ST_RemovePoints('POLYGON((0 1, 5 4, 5 7, 2 6, 0 1))',
                      'POLYGON((4 8, 6 8, 6 6, 4 6, 4 8))');
-- Answer: POLYGON((0 1, 5 4, 2 6, 0 1))

POLYGON with holes

SELECT ST_RemovePoints('POLYGON((1 1, 1 6, 5 6, 5 1, 1 1),
                               (3 4, 3 5, 4 5, 4 4, 3 4),
                               (2 3, 3 3, 3 2, 2 2, 2 3))',
                       ST_Buffer('POINT(6 7)', 4.5));
-- Answer: POLYGON((1 1, 1 6, 5 1, 1 1), (2 3, 3 3, 3 2, 2 2, 2 3))

A hole is converted to a POLYGON:

SELECT ST_RemovePoints('POLYGON((1 1, 1 6, 5 6, 5 1, 1 1),
                               (3 4, 3 5, 4 5, 4 4, 3 4))',
                    ST_Buffer('POINT(6 7)', 3));
-- Answer: POLYGON((1 1, 1 6, 5 1, 1 1), (3 4, 3 5, 4 4, 3 4))

Here the resulting POLYGON is not valid:

SELECT ST_RemovePoints('POLYGON((1 1, 1 6, 5 6, 5 1, 1 1),
                               (2 2, 2 5, 4 5, 4 2, 2 2))',
                      ST_Buffer('POINT(4 7)', 2));
-- Answer: POLYGON((1 1, 1 6, 5 1, 1 1), (2 2, 2 5, 4 5, 4 2, 2 2))

In the following four examples, we use larger and larger buffers:

SELECT ST_RemovePoints(
            'LINESTRING(0 3, 1 1, 3 3, 5 2, 5 4,
                        6 5, 7 6, 7 7, 6 8)',
            ST_Buffer('POINT(3 4)', 1.01));
-- Answer:   LINESTRING(0 3, 1 1,      5 2, 5 4,
--                      6 5, 7 6, 7 7, 6 8)

SELECT ST_RemovePoints(
            'LINESTRING(0 3, 1 1, 3 3, 5 2, 5 4,
                        6 5, 7 6, 7 7, 6 8)',
            ST_Buffer('POINT(3 4)', 2.01));
-- Answer:   LINESTRING(0 3, 1 1,      5 2,
--                      6 5, 7 6, 7 7, 6 8)

SELECT ST_RemovePoints(
            'LINESTRING(0 3, 1 1, 3 3, 5 2, 5 4,
                        6 5, 7 6, 7 7, 6 8)',
            ST_Buffer('POINT(3 4)', 3.01));
-- Answer:   LINESTRING(0 3, 1 1,
--                      6 5, 7 6, 7 7, 6 8)

Here all points are removed:

SELECT ST_RemovePoints(
            'LINESTRING(0 3, 1 1, 3 3, 5 2, 5 4,
                        6 5, 7 6, 7 7, 6 8)',
            ST_Buffer('POINT(3 4)', 6));
-- Answer: NULL