ST_ForcePolygonCW

Signature

GEOMETRY ST_ForcePolygonCW(GEOMETRY geom);

Description

Forces (MULTI)POLYGON’s to have:

a clockwise orientation for their exterior ring,
and a counter-clockwise orientation for their interior rings.

Non-polygonal geometries are returned unchanged.

Examples

With `POLYGON`

SELECT ST_ForcePolygonCW('POLYGON((1 2, 5 2, 5 6, 1 6, 1 2))');

-- Answer: POLYGON ((1 2, 1 6, 5 6, 5 2, 1 2))

With `MULTIPOLYGON`

SELECT ST_ForcePolygonCW('MULTIPOLYGON(((1 2, 5 2, 5 6, 1 6, 1 2)), 
                                       ((6 4, 7 4, 7 7, 6 7, 6 4)))');

-- Answer: MULTIPOLYGON (((1 2, 1 6, 5 6, 5 2, 1 2)), 
--                      ((6 4, 6 7, 7 7, 7 4, 6 4)))

With interior ring

SELECT ST_ForcePolygonCW('POLYGON((1 2, 5 2, 5 6, 1 6, 1 2),
                                  (2 3, 3 3, 3 5, 2 5, 2 3))');

-- Answer: POLYGON ((1 2, 1 6, 5 6, 5 2, 1 2), 
--                  (2 3, 3 3, 3 5, 2 5, 2 3))

See also