CGAL users discussion list

["Satyajit Sarangi" <>]

Hi Laurent and Monique,
          I am still having a problem when extracting the infinite cell. When trying to extract the triangles from the infinite cell, I tried both the incident cell approach as well as by iterating through all the cells and then taking into consideration only the infinite cells. Still the result seems to be the same in both the cases. 

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // Loop through all the cells to find the infinite cells
    allCellIterator        celliteratorbegin = p_DelaunayTriangulation->all_cells_begin();
    allCellIterator        celliteratorend = p_DelaunayTriangulation->all_cells_end();
    
    while (celliteratorbegin != celliteratorend)
    {
        // Cells being iterated. All cells. Check whether a cell is infinite or not
        if (p_DelaunayTriangulation->is_infinite(celliteratorbegin))
        {
            // Infinite cell is found. Now 
            cout << "Infinite Cell Found" << endl;
                const int index = celliteratorbegin->index(p_DelaunayTriangulation->infinite_vertex());
                Point3D pa = celliteratorbegin->vertex((index+1)&3)->point();
                Point3D pb = celliteratorbegin->vertex((index+2)&3)->point();
                Point3D pc = celliteratorbegin->vertex((index+3)&3)->point();
               
                // This portion is for my own data structure and can be ignored.
                 // Add the triangle to the Triangle list
                Point p1(pa.x(), pa.y(), pa.z());
                Point p2(pb.x(), pb.y(), pb.z());
                Point p3(pc.x(), pc.y(), pc.z());
                       
                cTriangle *T = new cTriangle(p1, p2, p3); 
                TriangleList.push_back(T);
        }
        ++celliteratorbegin;
    }

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

I don't understand why the triangles somehow point to some interior point of the point cloud. I mean the interior triangles. Essentially it should be the convex hull but thats not what I am getting. I am only including the triangles which are in my "TriangleList" for rendering. Please see the screenshot attached. Laurent, I will definitely try out the convex hull approach but I am trying to see if one of my filtration algorithm works on the delaunay and hence need it. I know its an overkill but right now I have to see both the approaches. 
Thanks and Regards,
Satyajit

On 8/8/07, Laurent Rineau < > wrote:

On Wednesday 08 August 2007 02:09:07 Satyajit Sarangi wrote:
> Hi Laurent,
>             Thanx for the answer. However, the result which I was expecting
> didn't turn out. What I exactly wanted to do was to get the convex hull of
> certain points in 3D by using Delaunay triangulation and then only
> considering the cells which were infinite and extracting the finite
> triangle from the cells. It would be great if you could give me an idea
> about how to go about it.

Monique answered your question. However, the 3D Delaunay triangulation is an
overkill, in my opinion, to address your problem. You should have a look at
the 3D convex hull package, that can compute the polyhedron corresponding to
the convex hull of a set of points.

If you try both methods, please tell us which one is the quickest, on your
data. We, CGAL developers, miss feedback about methods that work for our
users (we usually have only feedback about things that do not work).

(Anyway, please verify that you have the right to use CGAL. If you have not
bought a commercial CGAL license from GeometryFactory, your code need to be
released under an open source license compatible with both LGPL and QPL. If
your lab plans to make non-open source software from CGAL, it should buy CGAL
licenses.)

--
Laurent Rineau
INRIA - Sophia Antipolis
BP 93, 2004 Route des Lucioles
06902 Sophia Antipolis Cedex FRANCE
Tel: +33 4 92 38 78 62
--
You are currently subscribed to cgal-discuss.
To unsubscribe or access the archives, go to
https://lists-sop.inria.fr/wws/info/cgal-discuss

Attachment: Triangulation.bmp
Description: Windows bitmap