[Boost-bugs] [Boost C++ Libraries] #10835: difference of multilinestring and polygon yields wrong result

Subject: [Boost-bugs] [Boost C++ Libraries] #10835: difference of multilinestring and polygon yields wrong result
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-12-02 12:50:05

#10835: difference of multilinestring and polygon yields wrong result
-------------------------------------------------+-------------------------
 Reporter:  Philipp Müller <pmueller@…>          |      Owner:
     Type:  Bugs                                 |  barendgehrels
Milestone:  To Be Determined                     |     Status:  new
  Version:  Boost 1.57.0                         |  Component:  geometry
 Keywords:  geometry difference                  |   Severity:  Problem
  multi_linestring polygon                       |
-------------------------------------------------+-------------------------
 I am using the following typedefs to simplify reading:

 {{{
 typedef
 boost::geometry::model::point<int,2,boost::geometry::cs::cartesian>
 TPoint;
 typedef boost::geometry::model::linestring<TPoint> TLinestring;
 typedef boost::geometry::model::multi_linestring<TLinestring>
 TMultiLinestring;
 typedef boost::geometry::model::polygon<TPoint, /*ClockWise*/false,
 /*Closed*/false> TPolygon;
 }}}

 I have a multilinestring from which I want to subtract two polygons.
 The multilinestring and polygons are as follows

 {{{
 TMultiLinestring multilinestring;
 boost::geometry::read_wkt("MULTILINESTRING((5239 2113,1020 2986))",
 multilinestring);
 TPolygon polygon1;
 boost::geometry::read_wkt("POLYGON((5233 2113,5200 2205,1020 2205,1020
 2022,5200 2022))", polygon1);
 TPolygon polygon2;
 boost::geometry::read_wkt("POLYGON((5233 2986,5200 3078,1020 3078,1020
 2895,5200 2895))", polygon2);
 }}}

 First, I subtract polygon1 from multilinestring, which works fine:

 {{{
 TMultiLinestring multilinestringOut1;
 boost::geometry::difference(multilinestring, polygon1,
 multilinestringOut1);
 // works as expected: multilinestringOut1 holds MULTILINESTRING((5239
 2113,5233 2114)(4795 2205, 1020 2986))
 }}}

 Now I want to subtract polygon2 from multilinestringOut1 (the intermediate
 result from the previous calculation), which yields a wrong result.


 {{{
 TMultiLinestring multilinestringOut2;
 boost::geometry::difference(multilinestringOut1, polygon2,
 multilinestringOut2);
 // not   as expected: multilinestringOut2 holds MULTILINESTRING((5239
 2113,5233,2114)(4795 2205, 5406 1580))
 }}}

 I would expect multilinestringOut2 to hold

 {{{
 MULTILINESTRING((5239 2113,5233,2114)(4795 2205, 1460 2895))
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10835>
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