[Boost-bugs] [Boost C++ Libraries] #10661: difference algorithm returning invalid geometry

Subject: [Boost-bugs] [Boost C++ Libraries] #10661: difference algorithm returning invalid geometry
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-10-15 16:26:52

#10661: difference algorithm returning invalid geometry
-------------------------------------------------+-------------------------
 Reporter:  Volker Schöch <vschoech@…>           |      Owner:
     Type:  Bugs                                 |  barendgehrels
Milestone:  To Be Determined                     |     Status:  new
  Version:  Boost 1.56.0                         |  Component:  geometry
 Keywords:  difference, multi-polygon, polygon,  |   Severity:  Regression
  self-intersection                              |
-------------------------------------------------+-------------------------
 My "_TPolygon" type is actually a '''multi-polygon''', using a polygon
 type that is based on '''int''', oriented '''counter-clockwise''' and
 '''open''' (not closed). Please consider the following example:
 {{{
 _TPolygon<int> polygonA;
 boost::geometry::read_wkt("MULTIPOLYGON(((1701 985,3501 985,3501 2785,1701
 2785,1701 985)))", polygonA); // does not throw
 boost::geometry::is_valid(polygonA); // returns true

 _TPolygon<int> polygonB;
 boost::geometry::read_wkt("MULTIPOLYGON(((1698 1860,1698 1122,2598
 1392,3492 1842,3492 32706,2598 2340,1698 1860)))", polygonB); // does not
 throw
 boost::geometry::is_valid(polygonB); // returns true

 _TPolygon<int> polygonC;
 boost::geometry::difference(polygonA, polygonB, polygonC); // does not
 throw
 // polygonC: MULTIPOLYGON(((1701 1122,1701 985,3501 985,3501 2785,3492
 1857,3492 1842,2598 1392,1701 1122)),((1701 1861,2598 2340,1669 2785,1701
 2785,1701 1861)))
 boost::geometry::is_valid(polygonC); // returns false!

 _TPolygon<int> polygonD;
 boost::geometry::read_wkt("MULTIPOLYGON(((1698 2772,1698 1860,2598
 2340,3492 2412,3492 32743,1698 2772)))", polygonD); // does not throw
 boost::geometry::is_valid(polygonD); // returns true

 _TPolygon<int> polygonE;
 boost::geometry::difference(polygonC, polygonD, polygonE); // throws
 "Boost.Geometry Overlay invalid input exception"!
 }}}

 This '''worked in boost 1.55.0'''. The result for polygonC was slightly
 different in 1.55.0, and there was a reasonable(?) result for polygonE:
 {{{
 polygonC: MULTIPOLYGON(((1701 1122,1701 985,3501 985,3501 2785,3492
 2785,3492 1842,2598 1392,1701 1122)),((1701 1861,2598 2340,2611 2785,1701
 2785,1701 1861)))
 polygonE: MULTIPOLYGON(((3492 2412,3492 1842,2598 1392,1701 1122,1701
 985,3501 985,3501 2785,3492 2785,3492 2412),(1701 1861,2598 2340,1701
 1861)))
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10661>
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