Name

ST_SymDifference — Returns a geometry that represents the portions of A and B that do not intersect. It is called a symmetric difference because ST_SymDifference(A,B) = ST_SymDifference(B,A).

Synopsis

`geometry ST_SymDifference(`geometry geomA, geometry geomB`)`;

Description

Returns a geometry that represents the portions of A and B that do not intersect. It is called a symmetric difference because ST_SymDifference(A,B) = ST_SymDifference(B,A). One can think of this as ST_Union(geomA,geomB) - ST_Intersection(A,B).

Performed by the GEOS module Do not call with a GeometryCollection as an argument This method implements the OpenGIS 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 it seems to only consider x y when doing the difference and tacks back on the Z-Index

Examples The original linestrings shown together The symmetric difference of the two linestrings
```--Safe for 2d - symmetric difference of 2 linestrings
SELECT ST_AsText(
ST_SymDifference(
ST_GeomFromText('LINESTRING(50 100, 50 200)'),
ST_GeomFromText('LINESTRING(50 50, 50 150)')
)
);

st_astext
---------
MULTILINESTRING((50 150,50 200),(50 50,50 100))
```
```
--When used in 3d doesn't quite do the right thing
SELECT ST_AsEWKT(ST_SymDifference(ST_GeomFromEWKT('LINESTRING(1 2 1, 1 4 2)'),
ST_GeomFromEWKT('LINESTRING(1 1 3, 1 3 4)')))

st_astext
------------
MULTILINESTRING((1 3 2.75,1 4 2),(1 1 3,1 2 2.25))
```