Extracting boundary points from an unstructured grid

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Extracting boundary points from an unstructured grid

Zoltan Kovacs

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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Re: Extracting boundary points from an unstructured grid

VTK - Users mailing list
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 <[hidden email]> 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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