CGAL users discussion list

["Wesley Smith" <>]

Hi Andreas,
Thanks so much for the help.  Indeed you're right.  I feel retarded.
I had modified the same source but forgot to change one number. I had
this:

// insertion from a vector :
        std::vector<Point> V(3);
        V[0] = Point(0,0,1);

        n = n + T->insert(V.begin(), V.end());

instead of what should've been this:

// insertion from a vector :
        std::vector<Point> V(1);
        V[0] = Point(0,0,1);

        n = n + T->insert(V.begin(), V.end());

Seems the extra vector components added duplicate (0, 0, 0) entries
creating the degenerate cells.  On the bright side I have read the
docs a  number of times now and have a better grasp of the software.

best,
wes


On 9/14/07, Andreas Fabri 
<>
 wrote:
> Wesley Smith wrote:
> > So here's a question.  If I'm iterating over all of the finite cells
> > and the reason I'm getting 4 cells instead of 1 for 4 points in a
> > triangulation_3 is that the convex hull of the triangulation has faces
> > with cells going to the "fictional" infinite point, then shouldn't
> > those cells not be accessible via the finite iterator?
>
> I just modified the example file simple.cpp slighlty,
> and can't reproduce your finding.
>
> Are you sure to iterator over finite_cells and not over finite_faces,
> because for the latter there should be 4.
>
> andreas
>
>
> #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
> #include <CGAL/Triangulation_3.h>
>
> #include <iostream>
> #include <fstream>
> #include <cassert>
> #include <list>
> #include <vector>
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
>
> typedef CGAL::Triangulation_3<K>      Triangulation;
>
> typedef Triangulation::Cell_handle    Cell_handle;
> typedef Triangulation::Vertex_handle  Vertex_handle;
> typedef Triangulation::Locate_type    Locate_type;
> typedef Triangulation::Point          Point;
>
> int main()
> {
>    // construction from a list of points :
>    std::list<Point> L;
>    L.push_front(Point(0,0,0));
>    L.push_front(Point(1,0,0));
>    L.push_front(Point(0,1,0));
>
>    L.push_front(Point(0,0,1));
>    Triangulation T(L.begin(), L.end());
>
>    for(Triangulation::Finite_cells_iterator it = T.finite_cells_begin();
>        it != T.finite_cells_end();
>        ++it){
>      std::cout << "oops" << std::endl;
>    }
>
>    return 0;
> >
> > wes
> >
> > On 9/14/07, Andreas Fabri 
> > <>
> >  wrote:
> >> Wesley Smith wrote:
> >>>> Then you will se that entire R^3 gets triangulated which
> >>>> means that there is one additional tetrahedron per face
> >>>> of the convex hull that has as fourth vertex the, unique,
> >>>> infinite vertex.
> >>> Thanks for pointing this out.  I've been reading through the manual
> >>> and reference manual quite thoroughly but haven't found a way to
> >>> filter these out.  Is there a function such as is_infinite for the
> >>> cells?  I don't see anything like this.  I just need a simple test for
> >>> this.  Any help is greatly appreciated.
> >> ok, so my rtfm doesn't apply here ==:>-
> >>
> >>
> >> As we use derivation, much of the functionality of the Delaunay
> >> triangulation is documented in the base class Triangulation_2
> >>
> >> Go to section "Refines" and click.
> >>
> >> Note that even this class has a further base class.
> >>
> >> Some of the documentation is also in the Vertex and Cell class.
> >>
> >> Also note that there is a user manual which explains things
> >> and gives examples, and the reference manual which is just the
> >> documentation of the API.
> >>
> >> best,
> >>
> >> andreas
> >>
> >>
> >>> thanks,
> >>> wes
> >> --
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