id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
11576,boost::geometry::intersection wrong results,alex-x@…,Barend Gehrels,"Here is a code of intersection of two 2d triangles.
boost::geometry::intersection (inside get_poly_intersection_area_S_2d function) gives empty result.
It was ok in boost 1.55.0 version.

{{{
// boost_geom.cpp : Defines the entry point for the console application.
//

#include ""stdafx.h""
#include <time.h>
#include <deque>

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/foreach.hpp>


bool	get_poly_intersection_area_S_2d(	const double *poly_x_1, const int poly_n_1, 
											const double *poly_x_2, const int poly_n_2, double *S)
{
	// intersects two 2d polygons using boost::geometry library
	// polygons are in 3d format [(x0, y0, 0.0) (x1, y1, 0.0) .... (xn, yn, 0.0) ]
	// S is resulting area of intersection
	// returns true if intersection exists (area > DBL_EPSILON) and false otherwise

	typedef boost::geometry::model::d2::point_xy<double> bg_point;
	typedef boost::geometry::model::polygon< bg_point, false, false > bg_polygon;

	*S = 0.0;

	bg_polygon bg_poly_1, bg_poly_2;

	// init boost 2d polygons by our double 3D polygons
	for(int i=0; i<poly_n_1; i++)
		bg_poly_1.outer().push_back(bg_point(poly_x_1[i*3], poly_x_1[i*3+1]));

	for(int i=0; i<poly_n_2; i++)
		bg_poly_2.outer().push_back(bg_point(poly_x_2[i*3], poly_x_2[i*3+1]));

	// correct polygons
	boost::geometry::correct(bg_poly_1);
	boost::geometry::correct(bg_poly_2);

	// call intersection
	std::deque<bg_polygon> output;
	bool res = boost::geometry::intersection(bg_poly_1, bg_poly_2, output);

	if(!res)
		return false;

	// for each polygon of intersection we add area
	BOOST_FOREACH(bg_polygon const& p, output)
	{
		double s = boost::geometry::area(p);
		*S += s;
	}

	// no intersection
	if(fabs(*S) <= DBL_EPSILON)
		return false;

	// intersection > DBL_EPSILON
	return true;
}


int _tmain(int argc, _TCHAR* argv[])
{
	/*double p1[3 * 3] = {0.00000000000000000,
			-0.00000000000000000,
			0.00000000000000000,
			0.0025482760575599476,
			0.00000000000000000,
			0.00000000000000000,
			0.00053468140165232941,
			0.0010376086029810613,
			0.00000000000000000};

	double p2[4 * 3] = {0.0030662413355881501,
			0.0010051691098038377,
			0.00000000000000000,	
			0.0019811507896907981,	
			-0.0011005695262458440,	
			0.00000000000000000,	
			-3.2443866216813556e-005,
			-6.2960923264770714e-005,
			0.00000000000000000,	
			0.0010526466796805442,
			0.0020427777127849226,
			0.00000000000000000};*/

	double p1[3 * 3]={
			-0.00000000000000000	,
			0.00000000000000000	,
			0.00000000000000000	,
			0.0030892383152813277,
			0.00000000000000000	,
			0.00000000000000000	,
			0.0017033357506405240,
			0.0015364430953530355,
			0.00000000000000000

	};

	double p2[3 * 3] = {
			0.0023117731015916947,
			0.00082400923980274917,
			0.00000000000000000,
			0.00079878052059454633,
			0.00072051609032968962,
			0.00000000000000000,
			0.0016845031281539609,
			0.0015194556912103366,
			0.00000000000000000
	};


	
	double s = 0;
	get_poly_intersection_area_S_2d(p1, 3, p2, 3, &s);

	return 0;
}
}}}
",Bugs,reopened,Boost 1.61.0,geometry,Boost 1.61.0,Problem,,intersection,