CGAL users discussion list

[Efi Fogel <>]

If it's 2D, try the 2D Regularized Boolean Set-Operations package (User Manual, Reference Manual).

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On Wed, Aug 20, 2014 at 11:38 AM, areslp <> wrote:

Hi, I have two polygons constructed from the contours of image segmentation
results, the shapes of these polygons are arbitary. I need to perform some
boolean operation on these polygons, for example: I want to know whether a
polygon is inside another polygon or not; a point is inside a polygon or
not, etc. I write some simple code to do these things using Nef Polygon, the
code is shown bellow:

#include <CGAL/Gmpz.h>
#include <CGAL/Filtered_extended_homogeneous.h>
#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Nef_polyhedron_2.h>
typedef CGAL::Gmpz RT;
typedef CGAL::Filtered_extended_homogeneous<RT> Extended_kernel;
typedef CGAL::Nef_polyhedron_2<Extended_kernel> Nef_polyhedron;
typedef Nef_polyhedron::Point Point_2;
typedef Nef_polyhedron::Line Line;

int main() {
  Point_2 p1 ( 0, 0 ), p2 ( 10, 0 ), p3 ( 10, 10 ), p4 ( 0, 10 ), p5 ( 1, 1
), p6 ( 9, 1 ), p7 ( 5, 9 ), p8 ( 20, 0 ), p9 ( 20, 10 );
  // 4 3
  // 1 2
  Point_2 P1[4] = { p1, p2, p3, p4 };
  Point_2 P2[3] = { p5, p6, p7 };

  std::list<std::pair&lt;Point_2 *, Point_2 *> > polylines;
  polylines.push_back ( std::make_pair ( P1, P1 + 1 ) );
  polylines.push_back ( std::make_pair ( P1 + 1, P1 + 2 ) );
  polylines.push_back ( std::make_pair ( P1 + 2, P1 + 3 ) );
  // polylines.push_back(std::make_pair(P1+3,P1));
  Nef_polyhedron N1 ( polylines.begin(), polylines.end(),
Nef_polyhedron::POLYLINES );
  std::cout << N1 << std::endl;

  polylines.clear();
  polylines.push_back ( std::make_pair ( P2, P2 + 1 ) );
  polylines.push_back ( std::make_pair ( P2 + 1, P2 + 2 ) );
  // polylines.push_back(std::make_pair(P2+2,P2));
  Nef_polyhedron N2 ( polylines.begin(), polylines.end(),
Nef_polyhedron::POLYLINES );

  if ( N2 < N1 ) {
    std::cout << "N2<N1&quot; &lt;&lt; std::endl;
  }
  if ( N2 > N1 ) {
    std::cout << "N2>N1" << std::endl;
  }
  Point_2 p ( 5, 5 );
  Point_2 P3[1] = {p};
  Nef_polyhedron Np ( P3, P3 + 1 );
  std::cout << ( Np < N1 ) << std::endl;
  return 0;
}

The result is not as I expected, I think it should be "N2<N1" and "true",
but the output is "false", what's wrong with the code and what's the best
way for doing things like this? Thanks in advance!



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