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STDifference (geometry Data Type)

SQL Server 2012

Returns an object that represents the point set from one geometry instance that does not lie within another geometry instance.

Syntax

.STDifference ( other_geometry )

Arguments

other_geometry: Is another geometry instance indicating which points to remove from the instance on which STDifference() is being invoked.

Return Types

SQL Server return type: geometry

CLR return type: SqlGeometry

Remarks

This method always returns null if the spatial reference IDs (SRIDs) of the geometry instances do not match. The result may contain circular arc segments only if the input instances contain circular arc segments.

Examples

A. Computing the difference between two Polygon instances

The following example uses STDifference() to compute the difference between two polygons.

DECLARE @g geometry;
DECLARE @h geometry;
SET @g = geometry::STGeomFromText('POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))', 0);
SET @h = geometry::STGeomFromText('POLYGON((1 1, 3 1, 3 3, 1 3, 1 1))', 0);
SELECT @g.STDifference(@h).ToString();

B. Invoking STDifference() on a CurvePolygon instance

The following example uses STDifference() on a CurvePolygon instance.

DECLARE @g geometry = 'CURVEPOLYGON (CIRCULARSTRING (0 -4, 4 0, 0 4, -4 0, 0 -4))';

DECLARE @h geometry = 'POLYGON ((1 -1, 5 -1, 5 3, 1 3, 1 -1))';

-- Note the different results returned by the two SELECT statements

SELECT @h.STDifference(@g).ToString(), @g.STDifference(@h).ToString();

Other Resources

OGC Methods on Geometry Instances

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