geometry-expression.ST_ConvexHull()

The convex hull of a geometry is the smallest convex geometry that contains all of the points in the geometry.

The convex hull may be visualized by imagining an elastic band stretched to enclose all of the points in the geometry. When released, the elastic band takes the shape of the convex hull.

If the geometry consists of a single point, the point is returned. If all of the points of the geometry lie on a single straight line segment, a linestring is returned. Otherwise, a convex polygon is returned.

The convex hull can serve as an approximation of the original geometry. When testing a spatial relationship, the convex hull can serve as a quick pre-filter because if there is no spatial intersection with the convex hull then there can be no intersection with the original geometry.

• ST_ConvexHullAggr method for type ST_Geometry

The following example shows the convex hull computed from 10 points. The resulting hull is the result Polygon ((1 1, 7 2, 9 3, 6 9, 4 9, 1 5, 1 1)).

SELECT NEW ST_MultiPoint('MultiPoint( (1 1), (2 2), (5 3), (7 2), (9 3), (8 4), (6 6), (6 9), (4 9), (1 5) )').ST_ConvexHull()

The following example returns the single point (0,0). The convex hull of a single point is a point.

SELECT NEW ST_Point(0,0).ST_ConvexHull()

The following example returns the result LineString (0 0, 3 3). The convex hull of a single straight line is a linestring with a single segment.

SELECT NEW ST_LineString('LineString(0 0,1 1,2 2,3 3)').ST_ConvexHull()