Returns the convex hull of the input geometry.
That is the smallest convex geometry, which contains the input geometry. The return value will be a simple area geometry with no inner rings.
Parameter 1 - any geometry.
Returns: the convex hull of the input geometry or null if the parameter is not a geometry.
An exception will be thrown if the geometry has less than three vertices.
Note: This function does not currently fully support 3D geometries. Any 3D geometries will be projected down to 2 dimensions.