[vtk-developers] Number of neighbours for each cell

[Lodron, Gerald]

Cool

For my first test that implementation below worked and i found out that this kind of algorithm does not help me on my problem, arg

Can I send you an image/screenshot of the “geometric” stuff I want to filter? May you as an expert has a better idea for solving my problem. Short text description (but is really hard to explain):

I have a mesh of a surface, scanned with a 3d scanner (triangles, vtkPolydata as explained). On the border of that mesh I have single “noisy” (or fringy) structures which I want to filter. These noise structures are minimal connected to the main mesh, so I can not use connected component filter (which I also used apriory to remove noise in the air).

Von: Will Schroeder [mailto:will.schroeder at kitware.com]
Gesendet: Freitag, 22. Juli 2016 14:37
An: Lodron, Gerald
Cc: VTK Developer (vtk-developers at vtk.org)
Betreff: Re: [vtk-developers] Number of neighbours for each cell

Yes this is a great start. Since I am on a performance kick, I would probably use (under the hood) vtkStaticCellLocator which builds the links between points and cells much faster (threaded using vtkSMPTools and a parallel sort).  The actual "counting" of the neighbors could then be sped up using vtkSMPTools as well. It's probably overkill, but I'd like VTK to knock off the socks of anyone using it, and also to support our HPC friends who have this humbling habit of dumping really big data on top of VTK :-)

Best,
W

On Fri, Jul 22, 2016 at 8:25 AM, Lodron, Gerald <Gerald.Lodron at joanneum.at<mailto:Gerald.Lodron at joanneum.at>> wrote:
In my case the definition would be an edge, but yes it would be useful to define that as parameter….

I already found a maybe not beautiful algorithm for vertices, not edges, may you want to reuse it as initial code:

       vtkSmartPointer<vtkUnsignedIntArray> neighbours = vtkSmartPointer<vtkUnsignedIntArray>::New();
        neighbours ->SetName("NumberOfNeighbours");
        neighbours ->SetNumberOfValues(numberOfCells);

        vtkSmartPointer<vtkIdList> cellPointIds = vtkSmartPointer<vtkIdList>::New();

        vtkSmartPointer<vtkIdList> ptids = vtkSmartPointer<vtkIdList>::New();
        vtkSmartPointer<vtkIdList> cellids = vtkSmartPointer<vtkIdList>::New();

        for (vtkIdType cellId = 0; cellId < numberOfCells; ++cellId)
        {
            input->GetCellPoints(cellId, ptids);
            /*
            does not work
            input ->GetCellNeighbors(cellId, oPtIds, oCellIds);
            neighbours ->SetValue(cellId, static_cast<unsigned int>(oCellIds->GetNumberOfIds()));*/
            std::set<vtkIdType> id_set;

            for (vtkIdType ptid = 0; ptid < ptids ->GetNumberOfIds();ptid++)
            {
                poInput1->GetPointCells(ptids ->GetId(ptid), cellids);
                for (vtkIdType cid = 0; cid < cellids ->GetNumberOfIds();cid++)
                {
                    vtkIdType id = cellids ->GetId(cid);
                    if (id != cellId)
                    {
                        id_set.insert(cellids->GetId(cid));
                    }
                }
            }
            neighbours ->SetValue(cellId, static_cast<unsigned int>( id_set.size()));
        }
        output->GetCellData()->AddArray(neighbours);

Von: Will Schroeder [mailto:will.schroeder at kitware.com<mailto:will.schroeder at kitware.com>]
Gesendet: Freitag, 22. Juli 2016 14:09
An: Lodron, Gerald
Cc: VTK Developer (vtk-developers at vtk.org<mailto:vtk-developers at vtk.org>)
Betreff: Re: [vtk-developers] Number of neighbours for each cell

I don't know of such a filter but it would be easy to put together. Certainly it would be another useful tool in the topological analysis toolbox.

Question: what is your definition of a neighbor? Connected at a vertex or along an edge? I suppose if we were to write such a filter the definition of a neighbor would be an optional parameter. I also suggest that this be a general filter so the same analysis could be applied to unstructured grids, etc. or to polygonal meshes with other than triangle cells.

Best,
W

On Fri, Jul 22, 2016 at 6:51 AM, Lodron, Gerald <Gerald.Lodron at joanneum.at<mailto:Gerald.Lodron at joanneum.at>> wrote:


Hi

I have a mesh (vtkPolyData with all triangles) where i want to visualize the number of neighbouring cells/triangles for each cell/triangle. (I later may want to threshold/filter it with that number to remove “noisy” triangles on border with low number of neighbours)

Is there a filter for that available?

Best regards

------------------------------------------------------------------------------------
Gerald Lodron

Researcher of Machine Vision Applications Group
DIGITAL - Institute for Information and Communication Technologies

JOANNEUM RESEARCH Forschungsgesellschaft mbH
Steyrergasse 17, 8010 Graz, AUSTRIA

phone:   +43-316-876-1751<tel:%2B43-316-876-1751>
general fax: +43-316-876-1751<tel:%2B43-316-876-1751>
web: http://www.joanneum.at/digital
e-mail: gerald.lodron at joanneum.at<mailto:gerald.lodron at joanneum.at>




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--
William J. Schroeder, PhD
Kitware, Inc. - Building the World's Technical Computing Software
28 Corporate Drive
Clifton Park, NY 12065
will.schroeder at kitware.com<mailto:will.schroeder at kitware.com>
http://www.kitware.com
(518) 881-4902
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