ST_Centroid

Introduction: Returns the spherical centroid of a geography as a Geography point, computed on the sphere using S2:

• Polygon / MultiPolygon — area-weighted centroid via S2Polygon.getCentroid().
• LineString / MultiLineString — length-weighted centroid via S2Polyline.getCentroid().
• Point / MultiPoint — mean of the unit vectors.
• GeographyCollection — recursive weighted sum across the children.

The result is the unit-length centroid on the sphere. Unlike a planar (lon/lat) centroid, it is correct for antimeridian-crossing and high-latitude geographies. As with JTS for non-convex shapes, the centroid may lie outside the input geometry. Returns NULL when the centroid is undefined (empty geometry, or antipodal points whose unit vectors cancel).

Format:

ST_Centroid (A: Geography)

Return type: Geography

Since: v1.9.1

SQL Example

SELECT ST_AsEWKT(ST_Centroid(ST_GeogFromWKT('POLYGON ((0 0, 2 0, 2 2, 0 2, 0 0))')));

Output (small O(d²/R²) spherical correction vs the planar (1 1)):

POINT (1 1)

For an antimeridian-crossing polygon, the spherical centroid stays on the antimeridian instead of jumping to the opposite side of the planet, which a planar centroid would do:

SELECT ST_AsEWKT(ST_Centroid(ST_GeogFromWKT('POLYGON ((170 -1, -170 -1, -170 1, 170 1, 170 -1))')));
-- result: POINT near (180, 0) (or (-180, 0)), NOT (0, 0)