[Boost-bugs] [Boost C++ Libraries] #11676: difference algorithm returning invalid geometry

Subject: [Boost-bugs] [Boost C++ Libraries] #11676: difference algorithm returning invalid geometry
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-09-21 14:59:34

#11676: difference algorithm returning invalid geometry
------------------------------------------------+--------------------------
 Reporter:  anonymous                           |      Owner:
     Type:  Bugs                                |  barendgehrels
Milestone:  To Be Determined                    |     Status:  new
  Version:  Boost 1.59.0                        |  Component:  geometry
 Keywords:  difference, multi-polygon, polygon  |   Severity:  Problem
------------------------------------------------+--------------------------
 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). Please consider the following example:
 {{{
 tc::geo::polygon<int> polygonA;
 boost::geometry::read_wkt("MULTIPOLYGON(((1920 1660,1920 1462,3720
 1462,3720 3262,1920 3262,1920 1959,2218 2189,1920 1660),(3718 1561,3360
 2233,3718 1957,3718 1561),(2818 2653,2218 2189,2818 3253,3360 2233,2818
 2653)))", polygonA); // does not throw
 boost::geometry::is_valid(polygonA); // returns true

 tc::geo::polygon<int> polygonB;
 boost::geometry::read_wkt("MULTIPOLYGON(((1918 2155,1918 1957,2818
 2653,3718 1957,3718 2154,2818 3055,1918 2155)))", polygonB); // does not
 throw
 boost::geometry::is_valid(polygonB); // returns true

 tc::geo::polygon<int> polygonC;
 boost::geometry::difference(polygonA, polygonB, polygonC); // does not
 throw
 // polygonC: MULTIPOLYGON(((2218 2189,1920 1660,1920 1462,3720 1462,3720
 3262,1920 3262,1920 2157,2562 2799,2818 3253,3043 2829,3718 2154,3718
 1957,3718 1561,3360 2233,3718 1957,3360 2234,3360 2233,2818 2653,2218
 2189)))
 boost::geometry::is_valid(polygonC); // returns false!
 }}}
 The difference of two valid multi-polygons yields an invalid multi-
 polygon.

 May be related to Ticket #10661 and Ticket #11674.

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Ticket URL: <https://svn.boost.org/trac/boost/ticket/11676>
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