Returns the boundary for a line or area object.
Tests whether a line and an area have the boundary left relationship. That is, the area is on the left of the line, and the line is contained in the boundary of the area.
Parameter 1 - a line geometry.
Parameter 2 - an area geometry.
Returns: a Boolean value, true if the boundary left relationship holds and false otherwise. If parameter 1 is not a line or parameter 2 is not an area, the result is false. Returns null if either parameter is not a geometry.
Note: This function does not fully support 3D geometries. Any 3D geometries will be projected down to 2 dimensions.