[vtkusers] How to explicitely get the different regions with ConnectivityFilter?

[C P]

Hi Nicolas,

I had a similar problem: I want to extract all connected components of a
surface mesh and copy each one to a separate vtkPolyData object. Here is
what I did. Maybe this could help you.

    cc_filter = vtk.vtkPolyDataConnectivityFilter()
    cc_filter.SetInputData(mesh)
    cc_filter.SetExtractionModeToSpecifiedRegions()

    components = list()
    idx = 0

    while True:
      cc_filter.AddSpecifiedRegion(idx)
      cc_filter.Update()

      component = vtk.vtkPolyData()
      component.DeepCopy(cc_filter.GetOutput())
      # Make sure we got something
      if component.GetNumberOfCells() <= 0:
        break

      components.append(component)
      cc_filter.DeleteSpecifiedRegion(idx)
      idx += 1

    return components

Best regards,
CP


On Fri, Feb 17, 2017 at 2:38 PM, Nicolas Cedilnik <nicolas.cedilnik at inria.fr
> wrote:

> Hello,
>
> I have an unstructured grid with several point data arrays and would like
> to extract the connected regions and their associated data into separate
> files.
>
> I can do that with paraview but I'm struggling to get it done using python
> vtk bindings.
>
> So far I've managed to extract the cells corresponding to the the largest
> region:
>
> rd = vtk.vtkGenericDataObjectReader()
> rd.SetFileName(my_input_vtk_file)
> rd.Update()
> ug = rd.GetOutput()
> f = vtk.vtkConnectivityFilter()
> f.SetInputData(ug)
> f.SetExtractionModeToLargestRegion()
> f.Update()
> out = f.GetOutput()
>
> ug.GetNumberOfCells() # 28396, the original number of cells
> out.GetNumberOfCells() # 27740, less cells, looks good
>
> from which I can work something out, but I have two problems with this
> approach:
> - I'd like to know the indices of the other connected regions
> - the `ug` input only has 1 point data array, I believe this is a known
> limitation
>
> I've found a SetExtractionModeToAllRegions method but I don't understand
> how to deal with it:
> f.SetExtractionModeToAllRegions()
> b = f.GetOutput()
> b.GetNumberOfCells() # 28396, same as input
> b.GetCellData().GetNumberOfArrays() # 0, I would have expected an array
> where the cells where labeled by region number...
>
> All in all, I have two questions:
> - How do I use the filter to get the cells labeled by region?
> - (less important) Is it possible to read different point data arrays with
> vtk python bindings?
>
> Thanks in advance for your help and advices on how to use vtk properly
>
> --
> Nicolas
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