[vtk-developers] Number of neighbours for each cell

[Will Schroeder]

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>
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]
> Gesendet: Freitag, 22. Juli 2016 14:09
> An: Lodron, Gerald
> Cc: VTK Developer (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>
> 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
> general fax: +43-316-876-1751
> web: http://www.joanneum.at/digital
> e-mail: 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
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> will.schroeder at kitware.com
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> (518) 881-4902
>



-- 
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
http://www.kitware.com
(518) 881-4902
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