[vtkusers] Clipping in parallel to single processor vtk file?

[Mitchell, John A]

vtk-experts: I am looking for guidance and suggestions on handling the following problem.

Question Set-up:
I have a very large multiprocessor simulation where we output to .pvd, .pvtu, .vtu files for each time step.  There are thousands of time steps and the jobs are run on hundreds and even thousands of processors.  The number of files created is in the thousands and post-processing of computed results quickly becomes unmanageable.   Calculations and data is associated with points and we create a vtkUnstructuredGrid and use vtkXMLPUnstructuredGridWriter to write mesh points and results for each time step.  We write both cells ('type=VTK_VERTEX') and points but hang field data off of the points. The challenge is post-processing computed results.

Perhaps one way to handle post-processing is to filter the data down to a very small region of interest during the simulation.  I was thinking of using 'vtkClipVolume' to obtain a set of points within a cubic-like region.  Then I would write this relatively small number of points (and other data) out to '1' vtk file for each time step - ie just one file for each time step.  I want to eliminate the parallel decomposition of the output data at this stage.  This means that I will need to communicate points found within the clipping volume to one processor (say proc=0) , create a vtkUnstructuredGrid, and then write this grid and data to a file for the time step.  After the simulation is done I would have 'one' .vtu file for each time step that contains a relatively few number of points.  I can post-process these files in a straight forward manner.

Question (s):
Does this process make sense?

Is there any existing functionality that can perform this algorithm now?

Will 'vtkClipVolume' keep the data associated with points it finds?

How do I configure 'vtkClipVolume' for positioning a Cartesian like cube (say dx, dy, dz) where dx, dy, and dz are the length of each edge?

Does anyone have any suggestions or specifics on how to handle this case - which vtk filters, how to handle the communications?

Any suggestions/comments are requested.  Thank you.
John Mitchell




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