[vtkusers] Reading Parallel XML Files Piece by Piece

Timo Oster timo.oster at ovgu.de
Tue Jan 17 09:31:18 EST 2017

Hi VTK users,

I am converting my (parallel) program to output (PolyData) files in
parallel VTK XML format. I do this to improve efficiency and because the
data can become too large to be contained in a single process' memory
all at once.

I have been successful in writing the parallel files, but now I also
need to be able to read them back in. Because of the size of the data,
just reading it into one giant data set all at once is not feasible.
What I would need to do is read the data piece by piece, and distribute
it to the parallel processes. The given class vtkXMLPPolyDataReader does
not seem to offer a way of doing that, or I don't understand it from
just reading the documentation and browsing the source code a little. It
offers a GetNumberOfPieces() function, but no public function that
explicitly reads only a single piece. The GetOutput() function has an
overload that takes an index, but the non-overloaded version just calls
GetOutput(0), so it seems implausible that this is the piece index.

What would be the best way to read a parallel VTK XML file piece by
piece? Is there something I'm missing in the reader class? Is there a
simple way of getting the piece file names from the summary file to read
them separately? Please advise.

Best Regards,

Timo Oster

Visual Computing Group / Lab. of Fluid Dynamics and Technical Flows
University of Magdeburg
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