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STConvexHull (geography Data Type)

Returns an object that represents the convex hull of a geography instance.

Applies to: SQL Server (SQL Server 2008 through current version), Azure SQL Database.

.STConvexHull ( )

SQL Server return type: geography

CLR return type: SqlGeography

Returns a FullGlobe object for geography instance which has an envelope angle larger than 90 degrees.

Returns an empty geography collection for an empty geography instance.

Returns null for an uninitialized geography instance.

A. Using STConvexHull() on an uninitialized geography instance

The following example uses STConvexHull() on an uninitialized geography instance.

DECLARE @g geography;

SELECT @g.STConvexHull();

B. Using STConvexHull on an empty geography instance

The following example uses STConvexHull() on an empty Polygon instance.

DECLARE @g geography = 'POLYGON EMPTY';

SELECT @g.STConvexHull().ToString();

C. Finding the convex hull of a non-convex Polygon instance

The following example uses STConvexHull() to find the convex hull of a non-convex Polygon instance.

DECLARE @g geography;
SET @g = geography::Parse('POLYGON((-120.533 46.566, -118.283 46.1, -122.3 47.45, -120.533 46.566))');
SELECT @g.STConvexHull().ToString();

D. Finding the convex hull on a geography instance with an envelope angle larger than 90 degrees

The following example uses STConvexHull() on a geography instance with an envelope angle larger than 90 degrees.

DECLARE @g geography = 'POLYGON((20.533 46.566, -18.283 46.1, -22.3 47.45, 20.533 46.566))';

SELECT @g.STConvexHull().ToString();

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