Hi,
There seems to be a bug in boost::geometry::intersection that we regularly encounter. The result of an intersection is sometimes equal to one of the input polygons, when the result should be empty. For example:
typedef boost::geometry::model::d2::point_xy<double> Point;
typedef boost::geometry::model::polygon<Point> Polygon;
Polygon pg1;
Polygon pg2;
boost::geometry::model::multi_polygon<Polygon> result;
boost::geometry::append(pg1, Point(-6.0, 3.2500000000000013));
boost::geometry::append(pg1, Point(-9.0, 3.2500000000000022));
boost::geometry::append(pg1, Point(-9.0, 6.5));
boost::geometry::append(pg1, Point(-6.0, 6.5));
boost::geometry::append(pg1, Point(-6.0, 3.2500000000000013));
boost::geometry::append(pg2, Point(-3.0, 0.0));
boost::geometry::append(pg2, Point(-6.0, 0.0));
boost::geometry::append(pg2, Point(-6.0, 3.2500000000000013));
boost::geometry::append(pg2, Point(-3.0, 3.2500000000000009));
boost::geometry::append(pg2, Point(-3.0, 0.0));
boost::geometry::intersection(pg1, pg2, result);
After the intersection, result contains a polygon equal to pg1. We're using boost 1.55 and also tried the rescale_to_integer branch, which gives the same results.
The problem seems to be with boost::geometry::within. We've previously had problems with within that we resolved by using a different strategy. Changing the strategy of the within calls in the function update_selection_map in select_rings.hpp makes intersection return the correct result for this case.