[Boost-bugs] [Boost C++ Libraries] #9563: boost::geometry:sym_difference fails when called with two polygons with almost identical points

Subject: [Boost-bugs] [Boost C++ Libraries] #9563: boost::geometry:sym_difference fails when called with two polygons with almost identical points
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-01-12 13:30:38

#9563: boost::geometry:sym_difference fails when called with two polygons with
almost identical points
--------------------------------+---------------------------
 Reporter:  Johan Doré <jdh@…>  |      Owner:  barendgehrels
     Type:  Bugs                |     Status:  new
Milestone:  To Be Determined    |  Component:  geometry
  Version:  Boost 1.55.0        |   Severity:  Problem
 Keywords:                      |
--------------------------------+---------------------------
 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

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9563>
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