[vtkusers] Extracting boundary points from an unstructured grid

[Cory Quammen]

Hi Zoltan,

Would you mind posting your question to https://discourse.vtk.org?
Community support for VTK is transitioning to that forum, so you may be
more likely to get an answer there.

Thanks,
Cory

On Tue, Mar 5, 2019 at 5:52 AM Zoltan Kovacs <Zoltan.Kovacs at esi-group.com>
wrote:

> Dear all,
>
>
>
> I try to extract the boundary nodes of an unstructured grids. Based on the
> example
>
> https://vtk.org/Wiki/VTK/Examples/Cxx/Meshes/BoundaryEdges
>
> I used the following code:
>
>
>
> vtkSmartPointer<vtkUnstructuredGrid> grid =
> vtkSmartPointer<vtkUnstructuredGrid>::New();
>
> vtkSmartPointer<vtkDataSetSurfaceFilter> filter =
> vtkSmartPointer<vtkDataSetSurfaceFilter>::New();
>
> vtkSmartPointer<vtkFeatureEdges> edges =
> vtkSmartPointer<vtkFeatureEdges>::New();
>
>
>
> /* load mesh into grid */
>
> ...
>
>
>
> /* extract the boundary points */
>
>
>
> filter->SetInputData(grid);
>
> filter->Update();
>
> edges->SetInputData(filter->GetOutput());
>
> edges->BoundaryEdgesOn();
>
> edges->FeatureEdgesOff();
>
> edges->NonManifoldEdgesOff();
>
> edges->ManifoldEdgesOff();
>
> edges->Update();
>
>
>
> vtkSmartPointer<vtkPolyData> polyData =  edges->GetOutput();
>
>
>
>
>
> When I print out the number of the points in polydata
> (polydata->GetNumberOfPoints()) I obtain 0, i.e.
>
> polydata is empty. When I comment out the lines
>
>
>
> edges->NonManifoldEdgesOff();
>
> edges->ManifoldEdgesOff()
>
>
>
> then I get some subset of points in polydata extrated from the grid but
> when I visualize these points I see that some boundary points are missing
> and there are some inner nodes in polydata. Thus
>
> polydata does not contain the exact set of the boundary points of the
> grid.
>
> Now I am not sure if this is the correct way to extract the boundary
> points from an unstructured grid
>
> and I would like to ask if there is any. Thank you very much for your help!
>
>
>
> Kind regards,
>
> Zoltan
>
>
>
>
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-- 
Cory Quammen
Staff R&D Engineer
Kitware, Inc.
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