[vtkusers] Reading Parallel XML Files Piece by Piece

[Andy Bauer]

Hi Timo,

The pieces that are read on each process are typically specified through
the pipeline from subsequent filters. Something like a writer that can deal
with pieces will request the number of pieces that can be provided to the
writer and based on that the writer would then specify which pieces it
wants. The reader then produces those pieces. See the example at
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Broken/IO/XMLPUnstructuredGridWriter
for an example.

Cheers,
Andy

On Tue, Jan 17, 2017 at 9:31 AM, Timo Oster <timo.oster at ovgu.de> wrote:

> 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
> --
> Timo Oster
>
> Visual Computing Group / Lab. of Fluid Dynamics and Technical Flows
> University of Magdeburg
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