&& overlap.e1 == this.area) {
// completely within other element, no ground area left
return emptyList();
}
TerrainBoundaryWorldObject terrainBoundary =
(TerrainBoundaryWorldObject)otherWO;
SimplePolygonXZ outlinePolygon = terrainBoundary.getOutlinePolygonXZ();
if (outlinePolygon != null) {
subtractPolys.add(outlinePolygon);
allPolys.add(outlinePolygon);