That works for just fine for concave non self intersecting polys as well - all the signed areas (albeit overlapping) cancel appropriately. (scribble scribble)

That works for just fine for concave non self intersecting polys as well - all the signed areas (albeit overlapping) cancel appropriately. (scribble scribble) ... Edit: and for self intersecting, it gives the area of the poly where winding is odd.