12.16.7.4 Polygon and MultiPolygon Property Functions

Functions in this section return properties of Polygon or MultiPolygon values.

• Area({poly|mpoly})

  ST_Area() and Area() are synonyms. For more information, see the description of ST_Area().

  Area() is deprecated; expect it to be removed in a future MySQL release. Use ST_Area() instead.

• Centroid({poly|mpoly})

  ST_Centroid() and Centroid() are synonyms. For more information, see the description of ST_Centroid().

  Centroid() is deprecated; expect it to be removed in a future MySQL release. Use ST_Centroid() instead.

• ExteriorRing(poly)

  ST_ExteriorRing() and ExteriorRing() are synonyms. For more information, see the description of ST_ExteriorRing().

  ExteriorRing() is deprecated; expect it to be removed in a future MySQL release. Use ST_ExteriorRing() instead.

• InteriorRingN(poly, N)

  ST_InteriorRingN() and InteriorRingN() are synonyms. For more information, see the description of ST_InteriorRingN().

  InteriorRingN() is deprecated; expect it to be removed in a future MySQL release. Use ST_InteriorRingN() instead.

• NumInteriorRings(poly)

  ST_NumInteriorRings() and NumInteriorRings() are synonyms. For more information, see the description of ST_NumInteriorRings().

  NumInteriorRings() is deprecated; expect it to be removed in a future MySQL release. Use ST_NumInteriorRings() instead.

• ST_Area({poly|mpoly})

  Returns a double-precision number indicating the area of the Polygon or MultiPolygon argument, as measured in its spatial reference system. For arguments of dimension 0 or 1, the result is 0. If the argument is an empty geometry the return value is 0. If the argument is NULL the return value is NULL.

  The result is the sum of the area values of all components for a geometry collection. If a geometry collection is empty, its area is returned as 0.

  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 |
  +----------------------------------+

  ST_Area() and Area() are synonyms.

• ST_Centroid({poly|mpoly})

  Returns the mathematical centroid for the Polygon or MultiPolygon argument as a Point. The result is not guaranteed to be on the MultiPolygon. If the argument is NULL or an empty geometry, the return value is NULL.

  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. If the argument is an empty geometry collection, the return value is NULL.

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

  ST_Centroid() and Centroid() are synonyms.

• ST_ExteriorRing(poly)

  Returns the exterior ring of the Polygon value poly as a LineString. If the argument is NULL or an empty geometry, the return value is NULL.

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

  ST_ExteriorRing() and ExteriorRing() are synonyms.

• ST_InteriorRingN(poly, N)

  Returns the N-th interior ring for the Polygon value poly as a LineString. Rings are numbered beginning with 1. If the argument is NULL or an empty geometry, the return value is NULL.

  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_InteriorRingN() and InteriorRingN() are synonyms.

• ST_NumInteriorRing(poly), ST_NumInteriorRings(poly)

  Returns the number of interior rings in the Polygon value poly. If the argument is NULL or an empty geometry, the return value is NULL.

  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 |
  +---------------------------------------------+

  ST_NumInteriorRing(), ST_NumInteriorRings(), and NumInteriorRings() are synonyms.