ST_SymDifference method

Returns the geometry value that represents the point set symmetric difference of two geometries.

Syntax

geometry-expression.ST_SymDifference(geo2)

Parameters

Name	Type	Description
geo2	ST_Geometry	The other geometry value that is to be subtracted from the geometry-expression to find the symmetric difference.

Returns

ST_Geometry Returns the geometry value that represents the point set symmetric difference of two geometries.
The spatial reference system identifier of the result is the same as the spatial reference system of the geometry-expression.

The ST_SymDifference method finds the symmetric difference of two geometries. The symmetric difference consists of all of those points that are in only one of the two geometries. If the two geometry values consist of the same points, the ST_SymDifference method returns an empty geometry.

Note

If the geometry-expression contains circularstrings, then these are interpolated to line strings.

Standards and compatibility

Example

The following example shows the symmetric difference (C) of a square (A) and a circle (B).

SELECT NEW ST_Polygon( 'Polygon( (-1 -0.25, 1 -0.25, 1 2.25, -1 2.25, -1 -0.25) )' ) AS A
    , NEW ST_CurvePolygon( 'CurvePolygon( CircularString( 0 1, 1 2, 2 1, 1 0, 0 1 ) )' )  AS B
    , A.ST_SymDifference( B ) AS C

The following picture shows the result of the symmetric difference as the shaded portion of the picture. The symmetric difference is a multisurface that includes two surfaces: one surface contains all of the points from the square that are not in the circle, and the other surface contains all of the points of the circle that are not in the square.

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