Hi Luke, You asked me on the GGL mailing list ( http://bit.ly/hCwdJx ) to verify tests using Boost.Polygon to check Boost.Geometry's behaviour at some points. I cannot reach that point. I ported a test that I already had (recursive polygons) to Boost.Polygon. I'm using the Polygon Set Concept with integer coordinates. Actually all input is in the 90/45 degree range. If I run the program, it often gives me the wrong results, even in the simpler cases. And often it just crashes, in the line 1748 of file polygon_arbitrary_formation.hpp (called from the area function) I extracted two (wrong but not crashing) cases. Source code here: http://bit.ly/fCYRWL Summary of second case: area p: 45000 area q: 55000 area intersection: 0 area union: 60000 The last one, area of union, should be 100000, if the intersection is zero, the union contains everything and its area therefore should sum to 100000 Regards, Barend