(mysql.info) general-geometry-property-functions

(mysql.info) geometry-property-functions
(mysql.info) point-property-functions
 
 16.5.2.1 General Geometry Functions
 ...................................
 
 The functions listed in this section do not restrict their argument and
 accept a geometry value of any type.
 
    * `Dimension(G)'
 
      Returns the inherent dimension of the geometry value G. The result
      can be -1, 0, 1, or 2. The meaning of these values is given in
       gis-class-geometry.
 
           mysql> SELECT Dimension(GeomFromText('LineString(1 1,2 2)'));
           +------------------------------------------------+
           | Dimension(GeomFromText('LineString(1 1,2 2)')) |
           +------------------------------------------------+
           |                                              1 |
           +------------------------------------------------+
 
    * `Envelope(G)'
 
      Returns the Minimum Bounding Rectangle (MBR) for the geometry
      value G. The result is returned as a `Polygon' value.
 
      The polygon is defined by the corner points of the bounding box:
 
           POLYGON((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY))
 
           mysql> SELECT AsText(Envelope(GeomFromText('LineString(1 1,2 2)')));
           +-------------------------------------------------------+
           | AsText(Envelope(GeomFromText('LineString(1 1,2 2)'))) |
           +-------------------------------------------------------+
           | POLYGON((1 1,2 1,2 2,1 2,1 1))                        |
           +-------------------------------------------------------+
 
    * `GeometryType(G)'
 
      Returns as a string the name of the geometry type of which the
      geometry instance G is a member. The name corresponds to one of
      the instantiable `Geometry' subclasses.
 
           mysql> SELECT GeometryType(GeomFromText('POINT(1 1)'));
           +------------------------------------------+
           | GeometryType(GeomFromText('POINT(1 1)')) |
           +------------------------------------------+
           | POINT                                    |
           +------------------------------------------+
 
    * `SRID(G)'
 
      Returns an integer indicating the Spatial Reference System ID for
      the geometry value G.
 
      In MySQL, the SRID value is just an integer associated with the
      geometry value. All calculations are done assuming Euclidean
      (planar) geometry.
 
           mysql> SELECT SRID(GeomFromText('LineString(1 1,2 2)',101));
           +-----------------------------------------------+
           | SRID(GeomFromText('LineString(1 1,2 2)',101)) |
           +-----------------------------------------------+
           |                                           101 |
           +-----------------------------------------------+
 
 The OpenGIS specification also defines the following functions, which
 MySQL does not implement:
 
    * `Boundary(G)'
 
      Returns a geometry that is the closure of the combinatorial
      boundary of the geometry value G.
 
    * `IsEmpty(G)'
 
      Returns 1 if the geometry value G is the empty geometry, 0 if it
      is not empty, and -1 if the argument is `NULL'. If the geometry is
      empty, it represents the empty point set.
 
    * `IsSimple(G)'
 
      Currently, this function is a placeholder and should not be used.
      If implemented, its behavior will be as described in the next
      paragraph.
 
      Returns 1 if the geometry value G has no anomalous geometric
      points, such as self-intersection or self-tangency.  `IsSimple()'
      returns 0 if the argument is not simple, and -1 if it is `NULL'.
 
      The description of each instantiable geometric class given earlier
      in the chapter includes the specific conditions that cause an
      instance of that class to be classified as not simple. (See 
      gis-geometry-class-hierarchy.)
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