id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
9563,boost::geometry:sym_difference fails when called with two polygons with almost identical points,Johan Doré <jdh@…>,Barend Gehrels,"Dear Boost Contributors,

First of all thanks a lot for all your great work.

I ran into a special case which seems to fail using e.g. boost::geometry:sym_difference.

In the below example I have the two polygons shown in the attached image.
Their points are distributed like on an ellipse. The first polygon 
having 6 points, while the second have 12 points on an ellipse with 
""almost"" identical parameters.

Now using those two polygons causes e.g sym_difference to wrongly returns 0 polygons. 

void Test_SymDifference()
{
  typedef boost::geometry::model::polygon<boost::geometry::model::d2::point_xy<double> > polygon;

  polygon Poly1, Poly2;

  boost::geometry::read_wkt(""POLYGON((16.4030230586813990 21.4147098480789640, 17.3451877762964380 14.8677773110138890, 11.9421647176150360 6.4530674629349205, 5.5969769413186015 4.5852901519210345, 4.6548122237035621 11.1322226889861170, 10.0578352823849610 19.5469325370650790, 16.4030230586813990 21.4147098480789640, 16.4030230586813990 21.4147098480789640))"", Poly1);
  
  boost::geometry::read_wkt(""POLYGON((16.4030230586814020 21.414709848078967, 17.7828326880709360 18.936596729241124, 17.3451877762964410 14.867777311013885, 15.2073549240394820 10.298488470659295, 11.9421647176150340 6.4530674629349125, 8.4245222359685457 4.3618917414181650, 5.5969769413185944 4.5852901519210292, 4.2171673119290620 7.0634032707588670, 4.6548122237035567 11.132222688986115, 6.7926450759605128 15.701511529340699, 10.0578352823849570 19.546932537065082, 13.5754777640314510 21.638108258581831, 16.4030230586814020 21.414709848078967))"", Poly2);

  boost::geometry::model::multi_polygon<polygon> Result;

  sym_difference(Poly1, Poly2, Result);

  _ASSERTE(Result.size() > 0);
}

If it is something I am doing wrong or if I can 
be of additional help please let me know

Best regards

Johan",Bugs,closed,Boost 1.56.0,geometry,Boost 1.55.0,Problem,fixed,,