PostGIS 1.5.8 Manual - Fedora Project Packages GIT repositories

PostGIS 1.5.8 Manual266 / 310Chapter 8PostGIS Special Functions Index8.1 PostGIS Aggregate FunctionsThe functions given below are spatial aggregate functions provided with PostGIS that can be used just like any other sql aggregatefunction such as sum, average.• ST_Accum - Aggregate. Constructs an array of geometries.• ST_Collect - Return a specified ST_Geometry value from a collection of other geometries.• ST_Extent - an aggregate function that returns the bounding box that bounds rows of geometries.• ST_Extent3D - an aggregate function that returns the box3D bounding box that bounds rows of geometries.• ST_MakeLine - Creates a Linestring from point geometries.• ST_MemUnion - Same as ST_Union, only memory-friendly (uses less memory and more processor time).• ST_Polygonize - Aggregate. Creates a GeometryCollection containing possible polygons formed from the constituent lineworkof a set of geometries.• ST_Union - Returns a geometry that represents the point set union of the Geometries.8.2 PostGIS SQL-MM Compliant FunctionsThe functions given below are PostGIS functions that conform to the SQL/MM 3 standardNoteSQL-MM defines the default SRID of all geometry constructors as 0. PostGIS uses a default SRID of -1.• ST_Area - Returns the area of the surface if it is a polygon or multi-polygon. For "geometry" type area is in SRID units. For"geography" area is in square meters. This method implements the SQL/MM specification. SQL-MM 3: 8.1.2, 9.5.3• ST_AsBinary - Return the Well-Known Binary (WKB) representation of the geometry/geography without SRID meta data.This method implements the SQL/MM specification. SQL-MM 3: 5.1.37• ST_AsText - Return the Well-Known Text (WKT) representation of the geometry/geography without SRID metadata. Thismethod implements the SQL/MM specification. SQL-MM 3: 5.1.25