Categories:

Geospatial functions

ST_CENTROID

Returns the Point representing the geometric center of a GEOGRAPHY or GEOMETRY object.

Syntax

ST_CENTROID( <geography_or_geometry_expression> )
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Arguments

geography_or_geometry_expression

The argument must be an expression of type GEOGRAPHY or GEOMETRY.

Returns

Returns a GEOGRAPHY or GEOMETRY 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.

  • For GEOMETRY objects, the returned GEOMETRY object has the same SRID as the input.

Examples

GEOGRAPHY 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) | +----------------------+
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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) | +------------------------+
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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) | +------------------------------------+
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GEOMETRY examples

The following example computes the centroid of a simple rectangular Polygon. Note how the result differs from the result when using ST_CENTROID with a GEOGRAPHY object

SELECT ST_CENTROID(TO_GEOMETRY('POLYGON((10 10, 10 20, 20 20, 20 10, 10 10))'));
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+--------------------------------------------------------------------------+ | ST_CENTROID(TO_GEOMETRY('POLYGON((10 10, 10 20, 20 20, 20 10, 10 10))')) | |--------------------------------------------------------------------------| | POINT(15 15) | +--------------------------------------------------------------------------+
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