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Appendix A: PostGIS Functions
Constructors
- :command:`ST_MakePoint(Longitude, Latitude)`
Returns a new point. Note the order of the coordinates (longitude then latitude).
- :command:`ST_GeomFromText(WellKnownText, srid)`
Returns a new geometry from a standard WKT string and srid.
- :command:`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.
- :command:`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.
Outputs
- :command:`ST_AsText(geometry)`
Returns a geometry in a human-readable text format.
- :command:`ST_AsGML(geometry)`
Returns a geometry in standard OGC :term:`GML` format.
- :command:`ST_AsGeoJSON(geometry)`
Returns a geometry to a standard GeoJSON format.
Measurements
- :command:`ST_Area(geometry)`
Returns the area of the geometry in the units of the spatial reference system.
- :command:`ST_Length(geometry)`
Returns the length of the geometry in the units of the spatial reference system.
- :command:`ST_Perimeter(geometry)`
Returns the perimeter of the geometry in the units of the spatial reference system.
- :command:`ST_NumPoints(linestring)`
Returns the number of vertices in a linestring.
- :command:`ST_NumRings(polygon)`
Returns the number of rings in a polygon.
- :command:`ST_NumGeometries(geometry)`
Returns the number of geometries in a geometry collection.
Relationships
- :command:`ST_Distance(geometry, geometry)`
Returns the distance between two geometries in the units of the spatial reference system.
- :command:`ST_DWithin(geometry, geometry, radius)`
Returns true if the geometries are within the radius distance of one another, otherwise false.
- :command:`ST_Intersects(geometry, geometry)`
Returns true if the geometries are not disjoint, otherwise false.
- :command:`ST_Contains(geometry, geometry)`
Returns true if the first geometry fully contains the second geometry, otherwise false.
- :command:`ST_Crosses(geometry, geometry)`
Returns true if a line or polygon boundary crosses another line or polygon boundary, otherwise false.