id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
10108	boost::geometry::intersection fails for triangle-triangle intersection	Raffael Casagrande <raffael@…>	Barend Gehrels	"A small test case which involves two triangles that intersect each other in a very tiny patch. boost::geometry::intersection returns one of the triangles instead of the correct (tiny) intersection triangle.

Note that boost 1.55 returned an empty intersection in this case which seems more appropriate (although there is in a fact a small, tiny intersection triangle)

I've attached a picture that depicts the situation to this report.


{{{
#include<cmath>
#include<fstream>

#include<boost/geometry.hpp>
#include<boost/geometry/geometries/ring.hpp>
#include<boost/geometry/io/svg/svg_mapper.hpp>
#include<boost/geometry/geometries/point_xy.hpp>


namespace bg = boost::geometry;

int main() {
  typedef bg::model::d2::point_xy<double> point_t;
  typedef bg::model::ring<point_t, false, true> ring_t;

  ring_t ring0;
  bg::append(ring0, point_t(-0.85012528418186883439,0.66468648958045217778));
  bg::append(ring0, point_t(-1.0190633474909247536, 0.58375169123203618504));
  bg::append(ring0, point_t(-0.81735787096893253167, 0.85208889314502478385));
  bg::append(ring0, ring0[0]);

  ring_t ring1;
  bg::append(ring1, point_t(-1.0898104946524889147, 1.0651111163194444398));
  bg::append(ring1, point_t(-1.0543813205484939832, 0.82438792455048248708));
  bg::append(ring1, point_t(-0.81735787088719669136, 0.8520888930811181261));
  bg::append(ring1, ring1[0]);

  bg::correct(ring0);
  bg::correct(ring1);

  std::vector<ring_t> result;
  bg::intersection(ring0, ring1, result);
  std::cout << result.size() << std::endl;


  // Output in SVG:
  std::ofstream stream(""debug.svg"");
  bg::svg_mapper<point_t> mapper(stream, 400,400);
  mapper.add(ring0);
  mapper.add(ring1);
  mapper.map(ring0, ""fill-opacity:0.5;fill:rgb(153,204,0)"");
  mapper.map(ring1, ""fill-opacity:0.3;fill:rgb(51,51,153)"");
  if(result.size()==1) {
    mapper.map(result[0], ""fill:none;stroke:rgb(0,0,0);stroke-width:1"");
  }
}
}}}"	Bugs	closed	To Be Determined	geometry	Boost 1.56.0	Problem	fixed	intersection, triangle, robustness