MySQL Reference Manual for version 4.0.18.

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17.5.2.1 General Geometry Functions

The functions listed in this ssection do not restrict their argument and accept a geometry value of any type.

GeometryType(g)
Returns as a string the name of the geometry type of which the geometry instance g is a member. The name will correspond to one of the instantiable Geometry subclasses.

 
mysql> SELECT GeometryType(GeomFromText('POINT(1 1)'));
+------------------------------------------+
| GeometryType(GeomFromText('POINT(1 1)')) |
+------------------------------------------+
| POINT                                    |
+------------------------------------------+

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 17.2.2 Class Geometry.)

 
mysql> SELECT Dimension(GeomFromText('LineString(1 1,2 2)'));
+------------------------------------------------+
| Dimension(GeomFromText('LineString(1 1,2 2)')) |
+------------------------------------------------+
|                                              1 |
+------------------------------------------------+

SRID(g)
Returns an integer indicating the Spatial Reference System ID for the geometry value g.

 
mysql> SELECT SRID(GeomFromText('LineString(1 1,2 2)',101));
+-----------------------------------------------+
| SRID(GeomFromText('LineString(1 1,2 2)',101)) |
+-----------------------------------------------+
|                                           101 |
+-----------------------------------------------+

Envelope(g)
Returns the Minimum Bounding Rectangle (MBR) for the geometry value g. The result is returned as a polygon value.

 
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))                        |
+-------------------------------------------------------+

The polygon is defined by the corner points of the bounding box:

 
POLYGON((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY))

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.


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