PostGIS 1.5.8 Manual - Fedora Project Packages GIT repositories

PostGIS 1.5.8 Manual236 / 310Performed by the GEOS module.NOTE: this function was formerly called GeomUnion(), which was renamed from "Union" because UNION is an SQL reservedword.Availability: 1.4.0 - ST_Union was enhanced. ST_Union(geomarray) was introduced and also faster aggregate collection in PostgreSQL.If you are using GEOS 3.1.0+ ST_Union will use the faster Cascaded Union algorithm described in http://blog.cleverelephant.ca/2009/01/must-faster-unions-in-postgis-14.htmlThis method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s2.1.1.3NoteAggregate version is not explicitly defined in OGC SPEC.This method implements the SQL/MM specification. SQL-MM 3: 5.1.19 the z-index (elevation) when polygons areinvolved.ExamplesAggregate exampleSELECT stusps,ST_Multi(ST_Union(f.the_geom)) as singlegeomFROM sometable As fGROUP BY stuspsNon-Aggregate exampleSELECT ST_AsText(ST_Union(ST_GeomFromText(’POINT(1 2)’),ST_GeomFromText(’POINT(-2 3)’) ) )st_astext----------MULTIPOINT(-2 3,1 2)SELECT ST_AsText(ST_Union(ST_GeomFromText(’POINT(1 2)’),ST_GeomFromText(’POINT(1 2)’) ) );st_astext----------POINT(1 2)--3d example - sort of supports 3d (and with mixed dimensions!)SELECT ST_AsEWKT(st_union(the_geom))FROM(SELECT ST_GeomFromEWKT(’POLYGON((-7 4.2,-7.1 4.2,-7.1 4.3,-7 4.2))’) as the_geomUNION ALLSELECT ST_GeomFromEWKT(’POINT(5 5 5)’) as the_geomUNION ALLSELECT ST_GeomFromEWKT(’POINT(-2 3 1)’) as the_geomUNION ALLSELECT ST_GeomFromEWKT(’LINESTRING(5 5 5, 10 10 10)’) as the_geom ) as foo;st_asewkt---------