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PostGIS 1.5.8 Manual225 / 310This function supports 3d and will not drop the z-index.ExamplesSELECT sometable.field1, sometable.field1,(ST_DumpRings(sometable.the_geom)).geom As the_geomFROM sometableOfpolys;SELECT ST_AsEWKT(geom) As the_geom, pathFROM 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 Alsogeometry_dump, Section 8.4, ST_Dump, ST_ExteriorRing, ST_InteriorRingN7.9.10 ST_IntersectionST_Intersection — (T) Returns a geometry that represents the shared portion of geomA and geomB. The geography implementationdoes a transform to geometry to do the intersection and then transform back to WGS84.Synopsisgeometry ST_Intersection( geometry geomA , geometry geomB );geography ST_Intersection( geography geogA , geography geogB );DescriptionReturns a geometry that represents the point set intersection of the Geometries.In other words - that portion of geometry A and geometry B that is shared between the two geometries.If the geometries do not share any space (are disjoint), then an empty geometry collection is returned.ST_Intersection in conjunction with ST_Intersects is very useful for clipping geometries such as in bounding box, buffer, regionqueries where you only want to return that portion of a geometry that sits in a country or region of interest.