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 , "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 binary 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 MariaDB 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 , "The Geometry Class Hierarchy".)

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