Introduction to PostGIS

35. Appendix A: PostGIS Functions

35.1. 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.

35.2. Outputs

ST_AsText(geometry)
Returns a geometry in a human-readable text format.
ST_AsGML(geometry)
Returns a geometry in standard OGC GML format.
ST_AsGeoJSON(geometry)
Returns a geometry to a standard GeoJSON format.

35.3. Measurements

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.

35.4. Relationships

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.


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