[Boost-bugs] [Boost C++ Libraries] #10640: boost geometry buffer algorithm and counterclockwise polygons

Subject: [Boost-bugs] [Boost C++ Libraries] #10640: boost geometry buffer algorithm and counterclockwise polygons
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-10-09 16:41:24

#10640: boost geometry buffer algorithm and counterclockwise polygons
------------------------------+---------------------------
 Reporter:  dopamine@…        |      Owner:  barendgehrels
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  geometry
  Version:  Boost 1.56.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+---------------------------
 the buffer algorithm does not seem to work (the result multipolygon is
 always empty) if the input model::polygons are defines as
 counterclockwise.

 test code (adapted from the buffer documentation):


 {{{
 #include <boost/geometry.hpp>
 #include <boost/geometry/geometries/point_xy.hpp>
 #include <boost/geometry/geometries/geometries.hpp>

 int main()
 {
     typedef double coordinate_type;
     typedef boost::geometry::model::d2::point_xy<coordinate_type> point;

     //counterclockwise
     typedef boost::geometry::model::polygon<point,false> polygon;

     const double buffer_distance = 1.0;
     const int points_per_circle = 36;
     boost::geometry::strategy::buffer::distance_symmetric<coordinate_type>
 distance_strategy(buffer_distance);
     boost::geometry::strategy::buffer::join_round
 join_strategy(points_per_circle);
     boost::geometry::strategy::buffer::end_round
 end_strategy(points_per_circle);
     boost::geometry::strategy::buffer::point_circle
 circle_strategy(points_per_circle);
     boost::geometry::strategy::buffer::side_straight side_strategy;

     boost::geometry::model::multi_polygon<polygon> result;
     boost::geometry::model::multi_polygon<polygon> mpol;

     //points reversed to get a positive area()
     boost::geometry::read_wkt("MULTIPOLYGON(((0 1,5 3,2 5,0 1)),((1 1,5
 0,5 2,1 1)))", mpol);

     boost::geometry::buffer(mpol.front(), result,
                 distance_strategy, side_strategy,
                 join_strategy, end_strategy, circle_strategy);

    //always zero
    std::cerr<<"result size = "<<result.size()<<std::endl;

    return 0;
 }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10640>
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