[vtkusers] Extract boundary from unstructured grid

[Teresa Azevedo]

Hi all.

I have a unstructured grid composed by voxels to visualize a volume  
built in a octree structure (see image attached - it is a hand model,  
cutted in the middle to visualize the size of the voxels, that are  
bigger inside the hand, and go smaller has it approaches the surface).

I would like to do two things:
1 - extract the boundary faces
2 - soften the surface, using for example a marching cubes approach  
(do I need to extract the boundary faces first?)


I already tried vtkContourGrid to generate a isosurface from the  
unstructured grid, but with no success... here is a piece of the code:

(...)
vtkContourGrid* contourGrid = vtkContourGrid::New();
contourGrid->SetInput(octreeUnsGrid); //vtkUnstructuredGrid object
contourGrid->SetValue(0, 0.5); //not sure about these values
contourGrid->Update();

vtkPolyDataMapper *isoMapper = vtkPolyDataMapper::New();
isoMapper->SetInput(contourGrid->GetOutput());
isoMapper->ScalarVisibilityOn();

vtkActor *isoActor = vtkActor::New();
isoActor->SetMapper(isoMapper);
(...)

Can somebody help me, on which functions to use for both cases?

Thank you very much,
Teresa Azevedo
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