MySQL 9.3 Reference Manual Including MySQL NDB Cluster 9.3
Functions in this section return properties of
Polygon or MultiPolygon
values.
Unless otherwise specified, functions in this section handle their geometry arguments as follows:
If any argument is NULL or any geometry
argument is an empty geometry, the return value is
NULL.
If any geometry argument is not a syntactically well-formed
geometry, an
ER_GIS_INVALID_DATA error
occurs.
If any geometry argument is a syntactically well-formed
geometry in an undefined spatial reference system (SRS), an
ER_SRS_NOT_FOUND error
occurs.
For functions that take multiple geometry arguments, if
those arguments are not in the same SRS, an
ER_GIS_DIFFERENT_SRIDS error
occurs.
Otherwise, the return value is non-NULL.
These functions are available for obtaining polygon properties:
Returns a double-precision number indicating the area of the
Polygon or
MultiPolygon argument, as measured in its
spatial reference system.
ST_Area() handles its
arguments as described in the introduction to this section,
with these exceptions:
If the geometry is geometrically invalid, either the result is an undefined area (that is, it can be any number), or an error occurs.
If the geometry is valid but is not a
Polygon or
MultiPolygon object, an
ER_UNEXPECTED_GEOMETRY_TYPE
error occurs.
If the geometry is a valid Polygon in
a Cartesian SRS, the result is the Cartesian area of the
polygon.
If the geometry is a valid
MultiPolygon in a Cartesian SRS, the
result is the sum of the Cartesian area of the polygons.
If the geometry is a valid Polygon in
a geographic SRS, the result is the geodetic area of the
polygon in that SRS, in square meters.
If the geometry is a valid
MultiPolygon in a geographic SRS, the
result is the sum of geodetic area of the polygons in
that SRS, in square meters.
If an area computation results in
+inf, an
ER_DATA_OUT_OF_RANGE
error occurs.
If the geometry has a geographic SRS with a longitude or latitude that is out of range, an error occurs:
If a longitude value is not in the range
(−180, 180], an
ER_GEOMETRY_PARAM_LONGITUDE_OUT_OF_RANGE
error occurs.
If a latitude value is not in the range [−90,
90], an
ER_GEOMETRY_PARAM_LATITUDE_OUT_OF_RANGE
error occurs.
Ranges shown are in degrees. The exact range limits deviate slightly due to floating-point arithmetic.
mysql>SET @poly ='Polygon((0 0,0 3,3 0,0 0),(1 1,1 2,2 1,1 1))';mysql>SELECT ST_Area(ST_GeomFromText(@poly));+---------------------------------+ | ST_Area(ST_GeomFromText(@poly)) | +---------------------------------+ | 4 | +---------------------------------+ 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 ST_Area(ST_GeomFromText(@mpoly));+----------------------------------+ | ST_Area(ST_GeomFromText(@mpoly)) | +----------------------------------+ | 8 | +----------------------------------+
Returns the mathematical centroid for the
Polygon or
MultiPolygon argument as a
Point. The result is not guaranteed to be
on the MultiPolygon.
This function processes geometry collections by computing
the centroid point for components of highest dimension in
the collection. Such components are extracted and made into
a single MultiPolygon,
MultiLineString, or
MultiPoint for centroid computation.
ST_Centroid() handles its
arguments as described in the introduction to this section,
with these exceptions:
The return value is NULL for the
additional condition that the argument is an empty
geometry collection.
If the geometry has an SRID value for a geographic
spatial reference system (SRS), an
ER_NOT_IMPLEMENTED_FOR_GEOGRAPHIC_SRS
error occurs.
mysql>SET @poly =ST_GeomFromText('POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7,5 5))');mysql>SELECT ST_GeometryType(@poly),ST_AsText(ST_Centroid(@poly));+------------------------+--------------------------------------------+ | ST_GeometryType(@poly) | ST_AsText(ST_Centroid(@poly)) | +------------------------+--------------------------------------------+ | POLYGON | POINT(4.958333333333333 4.958333333333333) | +------------------------+--------------------------------------------+
Returns the exterior ring of the Polygon
value poly as a
LineString.
ST_ExteriorRing() handles its
arguments as described in the introduction to this section.
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 ST_AsText(ST_ExteriorRing(ST_GeomFromText(@poly)));+----------------------------------------------------+ | ST_AsText(ST_ExteriorRing(ST_GeomFromText(@poly))) | +----------------------------------------------------+ | LINESTRING(0 0,0 3,3 3,3 0,0 0) | +----------------------------------------------------+
Returns the N-th interior ring
for the Polygon value
poly as a
LineString. Rings are numbered beginning
with 1.
ST_InteriorRingN() handles
its arguments as described in the introduction to this
section.
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 ST_AsText(ST_InteriorRingN(ST_GeomFromText(@poly),1));+-------------------------------------------------------+ | ST_AsText(ST_InteriorRingN(ST_GeomFromText(@poly),1)) | +-------------------------------------------------------+ | LINESTRING(1 1,1 2,2 2,2 1,1 1) | +-------------------------------------------------------+
ST_NumInteriorRing(,
poly)ST_NumInteriorRings(
poly)
Returns the number of interior rings in the
Polygon value
poly.
ST_NumInteriorRing()
and ST_NuminteriorRings()
handle their arguments as described in the introduction to
this section.
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 ST_NumInteriorRings(ST_GeomFromText(@poly));+---------------------------------------------+ | ST_NumInteriorRings(ST_GeomFromText(@poly)) | +---------------------------------------------+ | 1 | +---------------------------------------------+