geometry-expression.ST_Difference(geo2)

The ST_Difference method finds the spatial difference of two geometries. A point is included in the result if it is present in the geometry-expression but not present in geo2.

Unlike other spatial set operations (ST_Union, ST_Intersection, ST_SymDifference), the ST_Difference method is not symmetric: the method can give a different answer for A.ST_Difference( B ) and B.ST_Difference( A ).

• ST_Intersection method for type ST_Geometry
• ST_SymDifference method for type ST_Geometry
• ST_Union method for type ST_Geometry

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

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_Difference( B ) AS C
    , B.ST_Difference( A ) AS D

The following picture shows the difference C=A-B and D=B-A as the shaded portion of the picture. Each difference is a single surface that contains all of the points that are in the geometry on the left side of the difference and not in the geometry on the right side.