Description

Computes the geometric center of a geometry, or equivalently, the center of mass of the geometry as a POINT. For [MULTI]POINTs, this is computed as the arithmetic mean of the input coordinates. For [MULTI]LINESTRINGs, this is computed as the weighted length of each line segment. For [MULTI]POLYGONs, "weight" is thought in terms of area. If an empty geometry is supplied, an empty GEOMETRYCOLLECTION is returned. If NULL is supplied, NULL is returned.

The centroid is equal to the centroid of the set of component Geometries of highest dimension (since the lower-dimension geometries contribute zero "weight" to the centroid).

	Computation will be more accurate if performed by the GEOS module (enabled at compile time).

This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.

This method implements the SQL/MM specification. SQL-MM 3: 8.1.4, 9.5.5

Examples

In each of the following illustrations, the blue dot represents the centroid of the source geometry.

Centroid of a MULTIPOINT	Centroid of a LINESTRING
Centroid of a POLYGON	Centroid of a GEOMETRYCOLLECTION

SELECT ST_AsText(ST_Centroid('MULTIPOINT ( -1 0, -1 2, -1 3, -1 4, -1 7, 0 1, 0 3, 1 1, 2 0, 6 0, 7 8, 9 8, 10 6 )'));
				st_astext
------------------------------------------
 POINT(2.30769230769231 3.30769230769231)
(1 row)

See Also

ST_PointOnSurface