Appendix A: PostGIS Functions¶

Constructors¶

ST_MakePoint(Longitude, Latitude): Returns a new point. Note the order of the coordinates (longitude then latitude).
ST_GeomFromText(WellKnownText, srid): Returns a new geometry from a standard WKT string and srid.
ST_SetSRID(geometry, srid): Updates the srid on a geometry. Returns the same geometry. This does not alter the coordinates of the geometry, it just updates the srid. This function is useful for conditioning geometries created without an srid.
ST_Expand(geometry, Radius): Returns a new geometry that is an expanded bounding box of the input geometry. This function is useful for creating envelopes for use in indexed searches.

ST_Area(geometry): Returns the area of the geometry in the units of the spatial reference system.
ST_Length(geometry): Returns the length of the geometry in the units of the spatial reference system.
ST_Perimeter(geometry): Returns the perimeter of the geometry in the units of the spatial reference system.
ST_NumPoints(linestring): Returns the number of vertices in a linestring.
ST_NumRings(polygon): Returns the number of rings in a polygon.
ST_NumGeometries(geometry): Returns the number of geometries in a geometry collection.

ST_Distance(geometry, geometry): Returns the distance between two geometries in the units of the spatial reference system.
ST_DWithin(geometry, geometry, radius): Returns true if the geometries are within the radius distance of one another, otherwise false.
ST_Intersects(geometry, geometry): Returns true if the geometries are not disjoint, otherwise false.
ST_Contains(geometry, geometry): Returns true if the first geometry fully contains the second geometry, otherwise false.
ST_Crosses(geometry, geometry): Returns true if a line or polygon boundary crosses another line or polygon boundary, otherwise false.