CGAL users discussion list

["J.L.M." <>]

When I perform the Minkowski sum of two Nef_polyhedra_3 when one of them 
is a boundary, the result is nothing. Should this work as expected? I 
expect the resultant shape to be the equivalent of translating the one 
polyhedra by every coordinate in the boundary of the other polyhedra.

Specifically, I have a tetrahedron, and the boundary of a cube. The 
tetrahedron is much smaller than the cube, so I expect the Minkowski sum 
to have a cavity in the center. Instead, I get nothing. Below is a very 
simple example. When I use N0 I get something, when I use N0_boundary, I 
get nothing.

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Nef_polyhedron_3.h>
#include <CGAL/IO/Nef_polyhedron_iostream_3.h>
#include <CGAL/minkowski_sum_3.h>
#include <CGAL/IO/Qt_widget_Nef_3.h>
#include <CGAL/aff_transformation_tags.h>
#include <CGAL/Polyhedron_3.h>
#include <CGAL/IO/Polyhedron_iostream.h>
#include <fstream>
#include <iostream>
#include <qapplication.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef CGAL::Nef_polyhedron_3<Kernel> Nef_polyhedron_3;
typedef CGAL::Aff_transformation_3<Kernel> Aff_transformation;
typedef CGAL::Polyhedron_3<Kernel> Polyhedron;
typedef Kernel::Point_3 Point_3;

int main(int argc, char* argv[])
{
  Nef_polyhedron_3 N0;
  std::ifstream in("cube.nef3");
  in >> N0;
  Aff_transformation scale(10, 0, 0, 0, 10, 0, 0, 0, 10, 2);
  N0.transform(scale);
  Point_3 p( 1.0, 0.0, 0.0);
  Point_3 q( 0.0, 1.0, 0.0);
  Point_3 r( 0.0, 0.0, 1.0);
  Point_3 s( 0.0, 0.0, 0.0);
  Polyhedron P;
  P.make_tetrahedron(p, q, r, s);
  if(P.is_closed())
  {
    Nef_polyhedron_3 N1(P);
    Nef_polyhedron_3 N0_boundary=N0.boundary();
    Nef_polyhedron_3 U10=CGAL::minkowski_sum_3(N1, N0_boundary);
    std::cout << U10;
    QApplication a(argc, argv);
    CGAL::Qt_widget_Nef_3<Nef_polyhedron_3>* w=new 
CGAL::Qt_widget_Nef_3<Nef_polyhedron_3>(U10);
    a.setMainWidget(w);
    w->show();
    return a.exec();
  }
  return 0;
}