- Categories:
ST_CENTROID¶
Returns the Point representing the geometric center of a geospatial object.
Syntax¶
ST_CENTROID( <geography_expression> )
Arguments¶
geography_expression
The argument must be an expression of type GEOGRAPHY.
Returns¶
Returns a GEOGRAPHY object for the Point that represents geometric center of the input object.
Usage Notes¶
Returns NULL if the input is NULL.
If the input object is a GeometryCollection that contains different types of objects (Polygons, LineStrings, and Points), ST_CENTROID uses the type with the highest dimension to determine the geometric center. For example:
If the GeometryCollection contains Polygons, LineStrings, and Points, ST_CENTROID uses the Polygons and ignores the LineStrings and Points in the collection.
If the GeometryCollection contains LineStrings and Points, ST_CENTROID uses the LineStrings and ignores the Points in the collection.
Examples¶
The following example returns the Point that represents the geometric center of a LineString.
SELECT ST_CENTROID( TO_GEOGRAPHY( 'LINESTRING(0 0, 0 -2)' ) ) as center_of_linestring; +----------------------+ | CENTER_OF_LINESTRING | |----------------------| | POINT(0 -1) | +----------------------+
The following example returns the Point that represents the geometric center of a Polygon.
SELECT ST_CENTROID( TO_GEOGRAPHY( 'POLYGON((10 10, 10 20, 20 20, 20 10, 10 10))' ) ) as center_of_polygon; +------------------------+ | CENTER_OF_POLYGON | |------------------------| | POINT(15 15.014819855) | +------------------------+
The following example returns the Point that represents the geometric center of a GeometryCollection. This collection contains a Polygon, LineString, and Point. ST_CENTROID only uses the Polygon (and ignores the LineString and Point) when determining the geometric center.
SELECT ST_CENTROID( TO_GEOGRAPHY( 'GEOMETRYCOLLECTION(POLYGON((10 10, 10 20, 20 20, 20 10, 10 10)), LINESTRING(0 0, 0 -2), POINT(50 -50))' ) ) as center_of_collection_with_polygons; +------------------------------------+ | CENTER_OF_COLLECTION_WITH_POLYGONS | |------------------------------------| | POINT(15 15.014819855) | +------------------------------------+