Description

Returns a geometry representing the portions of geometries A and B that do not intersect. This is equivalent to ST_Union(A,B) - ST_Intersection(A,B). It is called a symmetric difference because ST_SymDifference(A,B) = ST_SymDifference(B,A).

If the optional gridSize parameter is given (GEOS-3.9.0 or higher required), all result vertices are guaranteed to fall on a snap-rounded grid of the specified size. Note that operations performed on a grid may contain small artifacts produced during grid alignment, see ST_ReducePrecision.

Performed by the GEOS module

Enhanced: 3.1.0 accept a gridSize parameter.

Requires GEOS >= 3.9.0 to use the gridSize parameter

This method implements the OGC Simple Features Implementation Specification for SQL 1.1. s2.1.1.3

This method implements the SQL/MM specification. SQL-MM 3: 5.1.21

This function supports 3d and will not drop the z-index. However, the result is computed using XY only. The result Z values are copied, averaged or interpolated.

Examples

This example shows a 2D-safe symmetric difference of two LineStrings.

SELECT ST_SymDifference('LINESTRING(50 100,50 200)',
        'LINESTRING(50 50,50 150)'
    );

MULTILINESTRING((50 150,50 200),(50 50,50 100))

01050000000200000001020000000200000000000000000049400000000000C06240000000000000494000000000000069400102000000020000000000000000004940000000000000494000000000000049400000000000005940

Figure

In 3D, this example does not produce the expected result.

SELECT ST_SymDifference('LINESTRING(1 2 1,1 4 2)',
    'LINESTRING(1 1 3,1 3 4)');

MULTILINESTRING((1 3 4,1 4 2),(1 1 3,1 2 1))

010500008002000000010200008002000000000000000000F03F00000000000008400000000000001040000000000000F03F00000000000010400000000000000040010200008002000000000000000000F03F000000000000F03F0000000000000840000000000000F03F0000000000000040000000000000F03F

Figure

See Also

ST_Difference, ST_Intersection, ST_Union, ST_ReducePrecision