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If any argument isNULL, the return value isNULL.

If any geometry argument is not a syntactically well-formed geometry, anER_GIS_INVALID_DATA error occurs.

If any geometry argument is a syntactically well-formed geometry in an undefined spatial reference system (SRS), anER_SRS_NOT_FOUND error occurs.

If any SRID argument is not within the range of a 32-bit unsigned integer, anER_DATA_OUT_OF_RANGE error occurs.

If any SRID argument refers to an undefined SRS, anER_SRS_NOT_FOUND error occurs.

Otherwise, the return value is non-NULL.

ST_Dimension(g)

Returns the inherent dimension of the geometry valueg. The dimension can be −1, 0, 1, or 2. The meaning of these values is given inSection 13.4.2.2, “Geometry Class”.

ST_Dimension() handles its arguments as described in the introduction to this section.

mysql> SELECT ST_Dimension(ST_GeomFromText('LineString(1 1,2 2)'));+------------------------------------------------------+| ST_Dimension(ST_GeomFromText('LineString(1 1,2 2)')) |+------------------------------------------------------+|                                                    1 |+------------------------------------------------------+

ST_Envelope(g)

Returns the minimum bounding rectangle (MBR) for the geometry valueg. The result is returned as aPolygon value that is defined by the corner points of the bounding box:

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

mysql> SELECT ST_AsText(ST_Envelope(ST_GeomFromText('LineString(1 1,2 2)')));+----------------------------------------------------------------+| ST_AsText(ST_Envelope(ST_GeomFromText('LineString(1 1,2 2)'))) |+----------------------------------------------------------------+| POLYGON((1 1,2 1,2 2,1 2,1 1))                                 |+----------------------------------------------------------------+

If the argument is a point or a vertical or horizontal line segment,ST_Envelope() returns the point or the line segment as its MBR rather than returning an invalid polygon:

mysql> SELECT ST_AsText(ST_Envelope(ST_GeomFromText('LineString(1 1,1 2)')));+----------------------------------------------------------------+| ST_AsText(ST_Envelope(ST_GeomFromText('LineString(1 1,1 2)'))) |+----------------------------------------------------------------+| LINESTRING(1 1,1 2)                                            |+----------------------------------------------------------------+

ST_Envelope() handles its arguments as described in the introduction to this section, with this exception:

ST_GeometryType(g)

Returns a binary string indicating the name of the geometry type of which the geometry instanceg is a member. The name corresponds to one of the instantiableGeometry subclasses.

ST_GeometryType() handles its arguments as described in the introduction to this section.

mysql> SELECT ST_GeometryType(ST_GeomFromText('POINT(1 1)'));+------------------------------------------------+| ST_GeometryType(ST_GeomFromText('POINT(1 1)')) |+------------------------------------------------+| POINT                                          |+------------------------------------------------+

ST_IsEmpty(g)

This function is a placeholder that returns 1 for an empty geometry collection value or 0 otherwise.

The only valid empty geometry is represented in the form of an empty geometry collection value. MySQL does not support GISEMPTY values such asPOINT EMPTY.

ST_IsEmpty() handles its arguments as described in the introduction to this section.

ST_IsSimple(g)

Returns 1 if the geometry valueg is simple according to the ISOSQL/MM Part 3: Spatial standard.ST_IsSimple() returns 0 if the argument is not simple.

The descriptions of the instantiable geometric classes given underSection 13.4.2, “The OpenGIS Geometry Model” include the specific conditions that cause class instances to be classified as not simple.

ST_IsSimple() handles its arguments as described in the introduction to this section, with this exception:

ST_SRID(g [,srid])

With a single argument representing a valid geometry objectg,ST_SRID() returns an integer indicating the ID of the spatial reference system (SRS) associated withg.

With the optional second argument representing a valid SRID value,ST_SRID() returns an object with the same type as its first argument with an SRID value equal to the second argument. This only sets the SRID value of the object; it does not perform any transformation of coordinate values.

ST_SRID() handles its arguments as described in the introduction to this section, with this exception:

ST_SRID(g,target_srid) andST_Transform(g,target_srid) differ as follows:

mysql> SET @g = ST_GeomFromText('LineString(1 1,2 2)', 0);mysql> SELECT ST_SRID(@g);+-------------+| ST_SRID(@g) |+-------------+|           0 |+-------------+mysql> SET @g = ST_SRID(@g, 4326);mysql> SELECT ST_SRID(@g);+-------------+| ST_SRID(@g) |+-------------+|        4326 |+-------------+

It is possible to create a geometry in a particular SRID by passing toST_SRID() the result of one of the MySQL-specific functions for creating spatial values, along with an SRID value. For example:

SET @g1 = ST_SRID(Point(1, 1), 4326);

However, that method creates the geometry in SRID 0, then casts it to SRID 4326 (WGS 84). A preferable alternative is to create the geometry with the correct spatial reference system to begin with. For example:

SET @g1 = ST_PointFromText('POINT(1 1)', 4326);SET @g1 = ST_GeomFromText('POINT(1 1)', 4326);

The two-argument form ofST_SRID() is useful for tasks such as correcting or changing the SRS of geometries that have an incorrect SRID.