STDifference (geography Data Type)

Applies to: yesSQL Server (all supported versions) YesAzure SQL Database

Returns an object that represents the point set from one geography instance that lies outside another geography instance.

Syntax

  
.STDifference ( other_geography )  

Note

To view Transact-SQL syntax for SQL Server 2014 and earlier, see Previous versions documentation.

Arguments

other_geography
Is another geography instance indicating which points to remove from the instance on which STDifference() is being invoked.

Return Types

SQL Server return type: geography

CLR return type: SqlGeography

Exceptions

This method throws an ArgumentException if the instance contains an antipodal edge.

Remarks

This method always returns null if the spatial reference identifiers (SRIDs) of the geography instances do not match.

In SQL Server, the set of possible results returned on the server has been extended to FullGlobe instances. SQL Server supports spatial instances that are larger than a hemisphere. The result may contain circular arc segments only if the input instances contain circular arc segments. This method is not precise.

Examples

A. Computing the difference between two geography instances

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

DECLARE @g geography;  
DECLARE @h geography;  
SET @g = geography::STGeomFromText('POLYGON((-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))', 4326);  
SET @h = geography::STGeomFromText('LINESTRING(-122.360 47.656, -122.343 47.656)', 4326);  
SELECT @g.STDifference(@h).ToString();  

B. Using a FullGlobe with STDifference()

The following example uses FullGlobe instance. The first result is an empty GeometryCollection and the second result is a Polygon instance. STDifference() returns an empty GeometryCollection when a FullGlobe instance is the parameter. Every point in an invoking geography instance is contained in a FullGlobe instance.

 DECLARE @g geography = 'POLYGON((-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))';  
 DECLARE @h geography = 'FULLGLOBE';  
 SELECT @g.STDifference(@h).ToString(),  
 @h.STDifference(@g).ToString();

See Also

OGC Methods on Geography Instances