ST_ConvexHull

Introduction: Returns the smallest convex region containing the input. Geometry hulls are computed in the coordinate plane. Geography hulls are computed on the sphere, with geodesic edges.

Format:

ST_ConvexHull (A: Geometry)

ST_ConvexHull (A: Geography)

Return type: Geometry or Geography, matching the input type

Since: v1.5.0 (Geometry), v1.9.1 (Geography)

For Geography, one unique point produces a Point, collinear points produce a LineString, and all other non-empty inputs produce a spherical Polygon. Empty inputs retain their type and SRID. A hull covering the full sphere is not supported.

Geometry example:

SELECT ST_ConvexHull(ST_GeomFromText('POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'))

Output:

POLYGON ((20 40, 175 150, 125 100, 20 40))

Geography example:

SELECT ST_GeometryType(
    ST_ConvexHull(
        ST_GeogFromWKT(
            'MULTIPOINT ((170 -10), (170 10), (-170 10), (-170 -10))',
            4326
        )
    )
)

Output:

ST_Polygon