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