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.

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