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> )

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

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

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))'));

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