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[Ophir Setter <>]

I checked the manually the also the "intentions" of the code.
The function do_intersect should return true if the two polygons "intersect in their interior".

Ophir

On Wed, Nov 14, 2012 at 9:28 AM, Stefan Schirra <> wrote:

On 14.11.2012 04:11, Graviton wrote:

I think that there is a bug with the method do_intersect.

Test this sample:


/*! \file do_intersect.cpp
  * Determining whether two triangles intersect.
  */

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Boolean_set_operations_2.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2                                   Point_2;
typedef CGAL::Polygon_2<Kernel>                           Polygon_2;

#include "print_utils.h"

int main ()
{
   Polygon_2 P;
   //P.push_back (Point_2 (-1,1));
   //P.push_back (Point_2 (0,-1));
   //P.push_back (Point_2 (1,1));

     P.push_back (Point_2 (13371696.6813195, -23135667.773556));
   P.push_back (Point_2 (13368240.604, -23133412.8));
   P.push_back (Point_2 (13364140.624, -23133192.28));
     P.push_back (Point_2 (13368823.9405681, -23134726.6078103));
   std::cout << "P = "; print_polygon (P);

   Polygon_2 Q;
   //Q.push_back(Point_2 (-1,-1));
   //Q.push_back(Point_2 (1,-1));
   //Q.push_back(Point_2 (0,1));
     Q.push_back(Point_2 (13375139.672, -23136795.756));
   Q.push_back(Point_2 (13371696.6813195, -23135667.773556));
   Q.push_back(Point_2 (13371696.682, -23135667.774));

       Q.push_back(Point_2 (13368823.9405681, -23134726.6078103));
   Q.push_back(Point_2 (13298835.453, -23111797.193));
   Q.push_back(Point_2 (13374018.867, -23140216.837));
   std::cout << "Q = "; print_polygon (Q);

   if ((CGAL::do_intersect (P, Q)))
     std::cout << "The two polygons intersect in their interior." <<
std::endl;
   else
     std::cout << "The two polygons do not intersect." << std::endl;

   return 0;
}


If you notice carefully, the P and Q are not intersecting each other ( two
points of P and Q are the same, and the other two points of P are located on
the RHS of Q).

But from the above program, the CGAL:do_intersect returns a true. It should
return a false.

A quote from the manual:
"do_intersect(obj1, obj2) checks whether obj1 and obj2 intersect. Two objects obj1 and obj2 intersect if there is a point p that is part of both obj1 and obj2..."

So if P and Q have two common points, as you say, true is the correct answer.

best regards

        Stefan

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