I am using boost geometry in 1.47 and am pretty happy with it. However, I am having a problem performing an intersection that I can't figure out how to solve. When I difference two geometries, I am sometimes left with a result that uses reverse winding to subtract a piece of the result rather than providing a "clean" polygon with winding in one direction only. I've posted an image here that demonstrates this: http://oi42.tinypic.com/2elfp0o.jpg I get the feeling that if I were to use the right models this might somehow be fixed? If not is there an algorithm that can clean up the result? Here is the code I am using: typedef boost::geometry::model::d2::point_xy<double> BoostPoint; typedef boost::geometry::model::polygon<BoostPoint> BoostPolygon; typedef boost::geometry::model::ring<BoostPoint> BoostRing; BoostRing facePolygon; BoostRing otherFacePolygon; std::vector<BoostPolygon> faceDifferenceResult; .... boost::geometry::difference(facePolygon, otherFacePolygon, faceDifferenceResult); Any ideas are much appreciated, thanks a lot, Dan