CGAL users discussion list

[Cédric LE MAITRE <>]

Hi Peter,

I try your Visual hull demo. And it works very well.
I just try to export the resulting 3D model into a file. The file is 
then correctly exported with floating precision coordiantes.
But when i want to load this file in a polyhedron with this code:

#include <CGAL/Cartesian.h>
#include <CGAL/Homogeneous.h>
#include <CGAL/Gmpz.h>
#include <CGAL/Quotient.h>
#include <CGAL/Nef_polyhedron_3.h>
#include <CGAL/cartesian_homogeneous_conversion.h>

#include <fstream>

typedef CGAL::Gmpz NT;
typedef    CGAL::Quotient<NT> CNT;
typedef    CGAL::Cartesian<CNT> CKernel;
typedef    CGAL::Homogeneous<NT> Kernel;
typedef CGAL::Cartesian<double>     Kerneld;
typedef    CGAL::Nef_polyhedron_3<Kernel> Nef_polyhedron;
typedef CGAL::Polyhedron_3<Kernel>     Polyhedron;
typedef Polyhedron::HalfedgeDS             HalfedgeDS;

typedef    CKernel::FT    FT;
typedef    CKernel::Point_3 CPoint;
typedef    Kernel::Point_3    Point_3;

#include <CGAL/IO/Polyhedron_iostream.h>
#include <CGAL/IO/Polyhedron_VRML_2_ostream.h>
#include <CGAL/IO/Nef_polyhedron_iostream_3.h>

#include <iostream>

Polyhedron P;
std::ifstream    inf("...");
std::istream*     p_in;
p_in = &inf;
(*p_in) >> P;

This read the file but create a model with integer precision coordinate.

It seems to come from the use of CGAL::Gmpz type for the kernel. I don't 
find how to use this type of kernel, but it works in your demo to 
manipulate float precision.
Please, how do you use float precision with Gmpz ?

Thanks,
Cedric.

Peter Hachenberger a écrit :
> Hi Cedric,
>
> first, a Polyhedron_3 can be converted to a Nef_polyhedron_3, if the
> Polyhedron is 2-manifold. That is not the case in your first example.
> The second example uses the correct approach, but here you you need to
> know is, that it is important how that the polyhedron is consistently
> oriented counterclockwise. The tetrahedra in your example are oriented
> clockwise. So, if you change
>
>         P.make_tetrahedron(p_top, p_center, p1, p2);
>         P.make_tetrahedron(p_top, p_center,p2, p3);
>
> to
>
>         P.make_tetrahedron(p_top, p_center, p2, p1);
>         P.make_tetrahedron(p_top, p_center, p3 p2);
>
> it works. If they are oriented clockwise, they are inside out. Then the 
> union behaves like an intersection and the other way around.
>
> Peter
>
> On Tue, 2006-12-12 at 19:02 +0100, Cédric LE MAITRE wrote:
>   
> > Hi Peter,
> >
> > Sorry. i've seen lot of information in French on CGAL. That's why i
> > used French in my previous mail. 
> > Indeed, what i want to do is to compute a visual hull from 2d polygon
> > contour of silhouettes.
> > I haven't seen the demo that you've already done for visual hull. And
> > this is a good advice. I will have a look on it (after QT
> > installation...)
> >
> > Concerning my problem with polyhedra intersection. i tried to convert
> > my polyhedra to Nef_Polyhedra. 
> > This works well with polyhedra of a simple 3d primitive (cube,
> > tetrahedron). But when i try on more complex polyhedron (like in the
> > next code), my program crashes.
> > i suppose it come of my polyhedron which is an union of tetrahedron
> > which compose my projection cone on the silhouette. So there are some
> > surface inside my polyhedra and maybe this is not compatible with
> > Nef_Polyhedra creation...
> >
> > #include <CGAL/Simple_cartesian.h>
> > #include <CGAL/Polyhedron_3.h>
> > #include <CGAL/IO/Polyhedron_iostream.h>
> > #include <CGAL/IO/Polyhedron_VRML_2_ostream.h> 
> > #include <CGAL/IO/Color.h>
> > #include <iostream>
> >
> >
> > #include <CGAL/Gmpz.h>
> > #include <CGAL/Homogeneous.h>
> > #include <CGAL/Nef_polyhedron_3.h>
> > #include <CGAL/IO/Nef_polyhedron_iostream_3.h>
> >
> > typedef CGAL::Homogeneous<CGAL::Gmpz>  Kernel;
> > typedef CGAL::Polyhedron_3<Kernel>     Polyhedron;
> > typedef Polyhedron::Point_3         Point;
> > typedef CGAL::Nef_polyhedron_3<Kernel> Nef_polyhedron;
> >
> > int main() {
> >         Point p_top(10.0f, 10.0f, 0.0f);
> >         Point p_center(10.0f, 10.0f, -40.0f);
> >         Point p1(20.0f, 5.0f, -40.0f);
> >         Point p2(5.0f, 5.0f, -40.0f);
> >         Point p3(5.0f, 30.0f, -40.0f);
> >         Point p4(15.0f, 30.0f, -40.0f);
> >         Point p5(25.0f, 10.0f, -40.0f);
> >         Polyhedron P;
> >         P.make_tetrahedron(p_top, p_center, p1, p2);
> >         P.make_tetrahedron(p_top, p_center,     p2, p3);
> >         P.make_tetrahedron(p_top, p_center, p3, p4);
> >         P.make_tetrahedron(p_top, p_center, p4, p5);
> >         P.make_tetrahedron(p_top, p_center, p5, p1);
> >
> >         CGAL::VRML_2_ostream out( std::cout);
> >
> >         Nef_polyhedron N1(P);   // it crashes
> >         int t = N1.number_of_vertices ();
> >
> >         Polyhedron P1;
> >         N1.convert_to_Polyhedron(P1);
> >         //std::cout << P;
> >         out << (Polyhedron)P1;
> >
> >    return (1);
> > }
> > So i try with the union of tetrahedra with the Nef_Polyhedron boolean
> > operation. But the union doesn't work. The union resulting polyhedron
> > have 0 vertice...
> >
> > int main() {
> >     Point p_top(10.0f, 10.0f, 0.0f);
> >     Point p_center(10.0f, 10.0f, -40.0f);
> >     Point p1(20.0f, 5.0f, -40.0f);
> >     Point p2(5.0f, 5.0f, -40.0f);
> >     Point p3(5.0f, 30.0f, -40.0f);
> >     Point p4(15.0f, 30.0f, -40.0f);
> >     Point p5(25.0f, 10.0f, -40.0f);
> >
> >     Polyhedron P;
> >     P.make_tetrahedron(p_top, p_center, p1, p2);
> >
> >     Polyhedron P2;
> >     P2.make_tetrahedron(p_top, p_center,    p2, p3);
> >
> >     Nef_polyhedron N1(P);
> >     int t = N1.number_of_vertices (); // returns 4 
> >
> >     Nef_polyhedron N2(P2);
> >     N1 += N2
> >     int t2 = N1.number_of_vertices (); // returns 0
> >
> >    return (1);
> > }
> >
> > Thanks a lot for helping me with my introduction into CGAL.
> >
> > Regards,
> > Cedric LE MAITRE.
> >
> > Peter Hachenberger a écrit : 
> >     
> > > Hi Cedric,
> > >
> > > my French is very bad, but I am in charge of the Nef polyehdra, so I try
> > > to help you. Usually you should write in English to this mailing list.
> > >
> > > First, you can do complex polyhedron intersections with
> > > Nef_polyhedron_3. You can get a Nef_polyhedron from a Polyhedron
> > > by using the constructor Nef_polyhedron_3(Polyhedron_3). It sounds like
> > > you had some problems with that, but my French is not good enough to
> > > understand them. If you can state your problems in English, I will
> > > help you.
> > >
> > > An advice. We already wrote a demo program for the visual hull. You can
> > > find it in demo/Nef_3. Try to compile visual_hull.cpp and run it with
> > > the given example mpi.vsh.
> > >
> > > Best, Peter
> > >
> > > On Tue, 2006-12-12 at 17:40 +0100, Cédric LE MAITRE wrote:
> > >   
> > >       
> > > > Bonjour,
> > > >
> > > > Je suis novice avec la librairie CGAL et j'utilise pour la 1ere fois
> > > > cette mailing-list (je ne connais donc pas les uses et coutumes). 
> > > > En tout cas, j'utiliserais pour cela le Français pour communiquer. Et
> > > > mon message s'adresse à des développeur CGAL.
> > > >
> > > > Je cherche à calculer un polyèdre correspondant l'intersection de 2
> > > > polyèdres 3D. Mes polyèdres sont des cones de vues constitués d'un
> > > > sommet et d'une base constituée de n points (correspondant à n points
> > > > d'un contour sur un plan. L'objectif final étant de reconstruire un
> > > > visual hull à partir de contour 2D de la silhouette d'une forme).
> > > >
> > > > Voici mon code :
> > > >
> > > > #include <CGAL/Simple_cartesian.h>
> > > > #include <CGAL/Polyhedron_3.h>
> > > > #include <CGAL/IO/Polyhedron_iostream.h>
> > > > #include <CGAL/IO/Polyhedron_VRML_2_ostream.h> 
> > > > #include <iostream>
> > > >
> > > >
> > > > #include <CGAL/Gmpz.h>
> > > > #include <CGAL/Homogeneous.h>
> > > > #include <CGAL/Nef_polyhedron_3.h>
> > > > #include <CGAL/IO/Nef_polyhedron_iostream_3.h>
> > > >
> > > > typedef CGAL::Homogeneous<CGAL::Gmpz>  Kernel;
> > > > typedef CGAL::Polyhedron_3<Kernel>     Polyhedron;
> > > > typedef Polyhedron::Point_3         Point;
> > > > typedef CGAL::Nef_polyhedron_3<Kernel> Nef_polyhedron;
> > > >
> > > >
> > > > int main() {
> > > >     Point p_top(10.0f, 10.0f, 0.0f);
> > > >     Point p_center(10.0f, 10.0f, -40.0f);
> > > >     Point p1(20.0f, 5.0f, -40.0f);
> > > >     Point p2(5.0f, 5.0f, -40.0f);
> > > >     Point p3(5.0f, 30.0f, -40.0f);
> > > >     Point p4(15.0f, 30.0f, -40.0f);
> > > >     Point p5(25.0f, 10.0f, -40.0f);
> > > >     Polyhedron P;
> > > >     P.make_tetrahedron(p_top, p_center, p1, p2);
> > > >     P.make_tetrahedron(p_top, p_center,    p2, p3);
> > > >     P.make_tetrahedron(p_top, p_center, p3, p4);
> > > >     P.make_tetrahedron(p_top, p_center, p4, p5);
> > > >     P.make_tetrahedron(p_top, p_center, p5, p1);
> > > >
> > > >
> > > >     Point p2_top(20.0f, 10.0f, -10.0f);
> > > >     Point p2_center(-20.0f, 10.0f, -30.0f);
> > > >     Point p21(-20.0f, 5.0f, 0.0f);
> > > >     Point p22(-20.0f, 5.0f, -25.0f);
> > > >     Point p23(-20.0f, 30.0f, -25.0f);
> > > >     Point p24(-20.0f, 30.0f, -5.0f);
> > > >     Point p25(-20.0f, 10.0f, 5.0f);
> > > >     Polyhedron P2;
> > > >     P2.make_tetrahedron(p2_top, p2_center, p21, p22);
> > > >     P2.make_tetrahedron(p2_top, p2_center, p22, p23);
> > > >     P2.make_tetrahedron(p2_top, p2_center, p23, p24);
> > > >     P2.make_tetrahedron(p2_top, p2_center, p24, p25);
> > > >     P2.make_tetrahedron(p2_top, p2_center, p25, p21);
> > > >
> > > >     CGAL::VRML_2_ostream out( std::cout);
> > > >
> > > >     
> > > >
> > > >     out << (Polyhedron)P;
> > > >     out << (Polyhedron)P2;
> > > >
> > > >
> > > >    return (1);
> > > > }  
> > > >
> > > > J'y crée 2 polyèdre P et P2 (qui possède une zone d'intersection).  
> > > >
> > > > Mon problème est comment calculer le polyèdre d'intersection ?
> > > >
> > > > J'ai essayé de le faire en utilisant la classe Nef_Polyedron et ces
> > > > opération booléenne. Or:
> > > >
> > > >       * il est impossible de créer un Nef_Polyhedron directement à
> > > >         partir d'un Polyhedron tel que P et P2
> > > >         
> > > >               * ex: Nef_polyhedron N1(P); -> plante CGAL
> > > >                 
> > > >       * idem lorsque j'assaie de créer un Nef_Polyhedron en faisant
> > > >         l'union de tetrahedron (sans passer ?
> > > >         
> > > >               * Ex:  Nef_polyhedron N1(P_tetra); // Nb de vertices de
> > > >                 N1 résultat = 4
> > > >                 
> > > >
> > > > Nef_polyhedronN2(P_tetra2);
> > > >
> > > > N1 += N2; // Nb de vertices de N1 résultat = 0 !!
> > > >
> > > >
> > > > Est-il possible de calculer l'intersection de polyèdre complexe avec
> > > > CGAL ?
> > > >
> > > > Merci d'avance à toute les personnes qui prendront le temps de
> > > > répondre à mes questions.
> > > >
> > > > Cédric.
> > > >
> > > >     
> > > >         
> > >
> > >   
> > >       
> >
> >
> > ______________________________________________________________________
> >     
>
>
>
>