12.18.5.2. Geometry Property Functions

12.18.5.2.1. 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 Section 12.18.2.2, "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                                    |+------------------------------------------+

IsSimple(g)

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 NULL 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 Section 12.18.2.1, "The Geometry Class Hierarchy".)

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)

This function is a placeholder that returns 0 for any valid geometry value, 1 for any invalid geometry value or NULL.

MySQL does not support GIS EMPTY values such as POINT EMPTY.

12.18.5.2.2. `Point` Functions

A Point consists of X and Y coordinates, which may be obtained using the following functions:

X(p)

Returns the X-coordinate value for the Point object p as a double-precision number.

mysql> SELECT X(POINT(56.7,
                        53.34));+-----------------------+| X(POINT(56.7, 53.34)) |+-----------------------+|                  56.7 |+-----------------------+

Y(p)

Returns the Y-coordinate value for the Point object p as a double-precision number.

mysql> SELECT Y(POINT(56.7,
                        53.34));+-----------------------+| Y(POINT(56.7, 53.34)) |+-----------------------+|                 53.34 |+-----------------------+

12.18.5.2.3. `LineString` Functions

A LineString consists of Point values. You can extract particular points of a LineString, count the number of points that it contains, or obtain its length.

EndPoint(ls)

Returns the Point that is the endpoint of the LineString value ls.

mysql> SET @ls = 'LineString(1 1,2
                        2,3 3)';mysql> SELECT
                        AsText(EndPoint(GeomFromText(@ls)));+-------------------------------------+| AsText(EndPoint(GeomFromText(@ls))) |+-------------------------------------+| POINT(3 3)                          |+-------------------------------------+

GLength(ls)

Returns as a double-precision number the length of the LineString value ls in its associated spatial reference.

mysql> SET @ls = 'LineString(1 1,2
                        2,3 3)';mysql> SELECT
                        GLength(GeomFromText(@ls));+----------------------------+| GLength(GeomFromText(@ls)) |+----------------------------+|            2.8284271247462 |+----------------------------+

GLength() is a nonstandard name. It corresponds to the OpenGIS Length() function.

NumPoints(ls)

Returns the number of Point objects in the LineString value ls.

mysql> SET @ls = 'LineString(1 1,2
                        2,3 3)';mysql> SELECT
                        NumPoints(GeomFromText(@ls));+------------------------------+| NumPoints(GeomFromText(@ls)) |+------------------------------+|                            3 |+------------------------------+

PointN(ls,N)

Returns the N-th Point in the Linestring value ls. Points are numbered beginning with 1.

mysql> SET @ls = 'LineString(1 1,2
                        2,3 3)';mysql> SELECT
                        AsText(PointN(GeomFromText(@ls),2));+-------------------------------------+| AsText(PointN(GeomFromText(@ls),2)) |+-------------------------------------+| POINT(2 2)                          |+-------------------------------------+

StartPoint(ls)

Returns the Point that is the start point of the LineString value ls.

mysql> SET @ls = 'LineString(1 1,2
                        2,3 3)';mysql> SELECT
                        AsText(StartPoint(GeomFromText(@ls)));+---------------------------------------+| AsText(StartPoint(GeomFromText(@ls))) |+---------------------------------------+| POINT(1 1)                            |+---------------------------------------+

The OpenGIS specification also defines the following function, which MySQL does not implement:

IsRing(ls)

Returns 1 if the LineString value ls is closed (that is, its StartPoint() and EndPoint() values are the same) and is simple (does not pass through the same point more than once). Returns 0 if ls is not a ring, and –1 if it is NULL.

12.18.5.2.4. `MultiLineString` Functions

These functions return properties of MultiLineString values.

GLength(mls)

Returns as a double-precision number the length of the MultiLineString value mls. The length of mls is equal to the sum of the lengths of its elements.

mysql> SET @mls = 'MultiLineString((1
                        1,2 2,3 3),(4 4,5 5))';mysql> SELECT
                        GLength(GeomFromText(@mls));+-----------------------------+| GLength(GeomFromText(@mls)) |+-----------------------------+|             4.2426406871193 |+-----------------------------+

GLength() is a nonstandard name. It corresponds to the OpenGIS Length() function.

IsClosed(mls)

Returns 1 if the MultiLineString value mls is closed (that is, the StartPoint() and EndPoint() values are the same for each LineString in mls). Returns 0 if mls is not closed, and –1 if it is NULL.

mysql> SET @mls = 'MultiLineString((1
                        1,2 2,3 3),(4 4,5 5))';mysql> SELECT
                        IsClosed(GeomFromText(@mls));+------------------------------+| IsClosed(GeomFromText(@mls)) |+------------------------------+|                            0 |+------------------------------+

12.18.5.2.5. `Polygon` Functions

These functions return properties of Polygon values.

Area(poly)

Returns as a double-precision number the area of the Polygon value poly, as measured in its spatial reference system.

mysql> SET @poly = 'Polygon((0 0,0
                        3,3 0,0 0),(1 1,1 2,2 1,1 1))';mysql> SELECT
                        Area(GeomFromText(@poly));+---------------------------+| Area(GeomFromText(@poly)) |+---------------------------+|                         4 |+---------------------------+

ExteriorRing(poly)

Returns the exterior ring of the Polygon value poly as a LineString.

mysql> SET @poly =    -> 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1
                        1))';mysql> SELECT
                        AsText(ExteriorRing(GeomFromText(@poly)));+-------------------------------------------+| AsText(ExteriorRing(GeomFromText(@poly))) |+-------------------------------------------+| LINESTRING(0 0,0 3,3 3,3 0,0 0)           |+-------------------------------------------+

InteriorRingN(poly,N)

Returns the N-th interior ring for the Polygon value poly as a LineString. Rings are numbered beginning with 1.

mysql> SET @poly =    -> 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1
                        1))';mysql> SELECT
                        AsText(InteriorRingN(GeomFromText(@poly),1));+----------------------------------------------+| AsText(InteriorRingN(GeomFromText(@poly),1)) |+----------------------------------------------+| LINESTRING(1 1,1 2,2 2,2 1,1 1)              |+----------------------------------------------+

NumInteriorRings(poly)

Returns the number of interior rings in the Polygon value poly.

mysql> SET @poly =    -> 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1
                        1))';mysql> SELECT
                        NumInteriorRings(GeomFromText(@poly));+---------------------------------------+| NumInteriorRings(GeomFromText(@poly)) |+---------------------------------------+|                                     1 |+---------------------------------------+

12.18.5.2.6. `MultiPolygon` Functions

These functions return properties of MultiPolygon values.

Area(mpoly)

Returns as a double-precision number the area of the MultiPolygon value mpoly, as measured in its spatial reference system.

mysql> SET @mpoly =    -> 'MultiPolygon(((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1
                        1)))';mysql> SELECT
                        Area(GeomFromText(@mpoly));+----------------------------+| Area(GeomFromText(@mpoly)) |+----------------------------+|                          8 |+----------------------------+

Centroid(mpoly)

Returns the mathematical centroid for the MultiPolygon value mpoly as a Point. The result is not guaranteed to be on the MultiPolygon.

mysql> SET @poly =    -> GeomFromText('POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7,5
                        5))');mysql> SELECT
                        GeometryType(@poly),AsText(Centroid(@poly));+---------------------+--------------------------------------------+| GeometryType(@poly) | AsText(Centroid(@poly))                    |+---------------------+--------------------------------------------+| POLYGON             | POINT(4.958333333333333 4.958333333333333) |+---------------------+--------------------------------------------+

The OpenGIS specification also defines the following function, which MySQL does not implement:

PointOnSurface(mpoly)

Returns a Point value that is guaranteed to be on the MultiPolygon value mpoly.

12.18.5.2.7. `GeometryCollection` Functions

These functions return properties of GeometryCollection values.

GeometryN(gc,N)

Returns the N-th geometry in the GeometryCollection value gc. Geometries are numbered beginning with 1.

mysql> SET @gc =
                        'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';mysql> SELECT AsText(GeometryN(GeomFromText(@gc),1));+----------------------------------------+| AsText(GeometryN(GeomFromText(@gc),1)) |+----------------------------------------+| POINT(1 1)                             |+----------------------------------------+

NumGeometries(gc)

Returns the number of geometries in the GeometryCollection value gc.

mysql> SET @gc =
                        'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';mysql> SELECT NumGeometries(GeomFromText(@gc));+----------------------------------+| NumGeometries(GeomFromText(@gc)) |+----------------------------------+|                                2 |+----------------------------------+

12.18.5.2. Geometry Property Functions

12.18.5.2.1. General Geometry Functions

12.18.5.2.2. Point Functions

12.18.5.2.3. LineString Functions

12.18.5.2.4. MultiLineString Functions

12.18.5.2.5. Polygon Functions

12.18.5.2.6. MultiPolygon Functions