ST_DumpRings

Description

This is a set-returning function (SRF). It returns a set of geometry_dump rows, defined as an integer[] and a geometry , aliased "path" and "geom" respectively. The "path" field holds the polygon ring index containing a single integer: 0 for the shell, >0 for holes. The "geom" field contains the corresponding ring as a polygon.

Availability: PostGIS 1.1.3. Requires PostgreSQL 7.3 or higher.

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

This function supports 3d and will not drop the z-index.

Examples

SELECT sometable.field1, sometable.field1,
	  (ST_DumpRings(sometable.the_geom)).geom As the_geom
FROM sometableOfpolys;

SELECT ST_AsEWKT(geom) As the_geom, path
	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 |                                            the_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 , Section 9.6, “PostGIS Geometry / Geography / Raster Dump Functions” , ST_Dump , ST_ExteriorRing , ST_InteriorRingN