Computes the convex hull of a Geometry. The convex hull is the smallest convex Geometry that contains all the points in the input Geometry.
Uses the Graham Scan algorithm.
Returns a Geometry that represents the convex hull of the input geometry. The returned geometry contains the minimal number of points needed to represent the convex hull. In particular, no more than two consecutive points will be collinear.
if the convex hull contains 3 or more points, a Polygon ; 2 points, a LineString; 1 point, a Point; 0 points, an empty GeometryCollection.