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Hi all,

This should be a very easy question.

When I check if the points (0.14, 0.22), (0.15, 0.21) and (0.19,0.17) are 
collinear, using CGAL::collinear, it returns “CGAL_LEFT”, which is false, 
because those points are in fact collinear.

However, if I do the same with the points (14, 22), (15, 21) and (19, 17) I 
get the correct answer: “CGAL_COLLINEAR”.

My code is:


#include "bso_rational_nt.h"

#include <CGAL/Cartesian.h>
#include <CGAL/predicates_on_points_2.h>

//#include <CGAL/Exact_predicates_exact_constructions_kernel.h>

#include<stdio.h>

//typedef CGAL::Exact_predicates_exact_constructions_kernel  Kernel;
//typedef Kernel::Point_2 Point;

typedef CGAL::Cartesian<Number_type> K;
typedef CGAL::Point_2<K> Point;


int main()
{
 
  //line y=-x+36
  switch (CGAL::orientation(Point(14,22),Point(15,21),Point(19,17))){
          case CGAL::LEFT_TURN:
                  std::cout << "Left"  << std::endl;
                  break;
          case CGAL::RIGHT_TURN:
                  std::cout << "Right"  << std::endl;
                  break;
          case CGAL::COLLINEAR:
                  std::cout << "Collinear"  << std::endl;
                  break;
  };

  //line y=-x+0.36
  switch 
(CGAL::orientation(Point(0.14,0.22),Point(0.15,0.21),Point(0.19,0.17))){
          case CGAL::LEFT_TURN:
                  std::cout << "Left"  << std::endl;
                  break;
          case CGAL::RIGHT_TURN:
                  std::cout << "Right"  << std::endl;
                  break;
          case CGAL::COLLINEAR:
                  std::cout << "Collinear"  << std::endl;
                  break;
  };

}


(The <bso_rational_nt.h> is the file that is in the folder "C:\Program 
Files\CGAL-3.2.1\examples\Boolean_set_operations_2".)

I already tried to use the CGAL::Exact_predicates_exact_constructions_kernel 
(as you can check above), but the problem remains.

This problem, in fact, happens with other points, however this is a simple 
example.

Anyone have any ideia of what is wrong??

I am using CGAL 3.2.1 and Microsoft Visual Studio 2005. 

I really don’t know what is happening. Anyone can help me?

Thanks,
 Mafalda