boost::geometry::union algorithm returning invalid geometry

Open vschoech opened this issue 8 months ago • 1 comments

My tc::geo::polygon type is actually a multi-polygon, using a polygon type that is based on int, oriented counter-clockwise and open (not closed). I am using boost 1.87.0. Please consider the following example:

tc::geo::polygon<int> polygonA;
boost::geometry::read_wkt("MULTIPOLYGON(((1353 3094,1353 2893,1852 2857,4171 2947,4909 3094,1353 3094)),((4172 2947,5707 3006,5707 3094,4909 3094,4172 2947)),((1353 2838,1353 2384,3228 2758,1852 2857,1353 2838)))", polygonA); // does not throw
boost::geometry::is_valid(polygonA); // returns true

tc::geo::polygon<int> polygonB;
boost::geometry::read_wkt("MULTIPOLYGON(((4171 2947,3228 2758,5707 2581,5707 3006,4171 2947)))", polygonB); // does not throw
boost::geometry::is_valid(polygonB); // returns true

tc::geo::polygon<int> polygonC;
boost::geometry::union_(polygonA, polygonB, polygonC); // does not throw
// polygonC: MULTIPOLYGON(((4909 3094,1353 3094,1353 2893,1852 2857,4171 2947,4909 3094)),((3228 2758,5707 2581,5707 3006,5707 3094,4909 3094,4173 2948,4171 2947,3228 2758)),((1852 2857,1353 2838,1353 2384,3228 2758,1852 2857)))
boost::geometry::is_valid(polygonC); // returns false!

The union of two valid multi-polygons yields an invalid multi-polygon.