[Paraview] FW: FW: Coloured isosurfaces when running MPI

Tue Jun 28 11:50:10 EDT 2011

Dear all,
Unfortunately, I am still struggling with running MPI and producing coloured
isosurfaces. A screenshot exemplifying the problem can be found at
http://www.mech.kth.se/~pschlatt/files/Screenshot.png; note that the colour
scheme based on the x-coordinate is just to show the problem, but in reality
I am using some scalar data coming from file.

Anyway, I wanted to ask you whether any of you has had similar problems,
i.e. colouring isosurfaces when running MPI. It seems to me that the data
field used to colour the surfaces is only created on one MPI rank and then
used by all other ranks, instead of computed for each rank independently
based on the local data. Can anyone confirm that behaviour?

This problem makes it at the moment impossible for me to visualise a certain
very large data set as I need to use MPI to distribute the data due to
memory limitation.

Thanks a lot for any help! 

Philipp

-----Original Message-----
From: Philipp Schlatter [mailto:pschlatt at mech.kth.se] 
Sent: den 20 juni 2011 22:55
To: 'Utkarsh Ayachit'
Cc: paraview at paraview.org
Subject: RE: [Paraview] FW: Coloured isosurfaces when running MPI

Dear Utkarsh,
Thanks a lot for your answer. The type of my data is "Rectilinear Grid"
(turbulence data on a regular grid). The test case that I use to reproduce
the data leads to a size of the contours (from the statistics inspector)
230316 cells, and a memory of 15 MB. I have turned off all the remote render
thresholds etc. and the problem persists. Thus it is likely that it is the
contour filter that causes the miscolouring. 

I have just reroduced the problem using the latest version 3.10.1 (Linux
32-bit); and I generated a screenshot on
http://www.mech.kth.se/~pschlatt/files/Screenshot.png.

The test is simple; I read in a rectilinear grid with a few velocity
components. Then I compute a new scalar field, essentially being the
x-corrdinate. Then I plot an isocontour, and colour it with the result of
the calculator. I would expect a continuous colour going from blue to red
spread over the whole x extent, however - according to the number of
processors used (in that case 16) - I get a repetitive pattern. By some more
experimenting it becomes clear that for some reason the colouring is done
based on the scalar value on the first processor only.

Running on 1 processor everything is fine.

I am of course happy to provide the respective data files, if this could
help.

Thanks for any help! 
Best regards,
Philipp

-----Original Message-----
From: Utkarsh Ayachit [mailto:utkarsh.ayachit at kitware.com]
Sent: den 20 juni 2011 16:59
To: Philipp Schlatter
Cc: paraview at paraview.org
Subject: Re: [Paraview] FW: Coloured isosurfaces when running MPI

That's very peculiar. What datatype are you contouring? (With the reader
selected in the pipeline browser, go to the information tab, what does the
"Type" field say?) Also after generating the iso-surface, open the
statistics inspector (View | Statistics Inspector). What is the size of the
geometry generated from  the contour filter. If that's not too large, you
try doing local-rendering (go to Edit | Settings, on the Server page,
uncheck Remote Render Threshold). Does that help? This will help diagnose if
the issue is with rendering or with the data generated by the contour filter
itself.

Utkarsh

On Sun, Jun 19, 2011 at 11:25 AM, Philipp Schlatter <pschlatt at mech.kth.se>
wrote:
> Dear forum,
>
> I am using Paraview to visualise a large dataset coming from a direct 
> simulation of turbulence (size of the original data of order 10-100GB).
> Naturally, I am running in parallel on a cluster (using the mesa), 
> which also works very well.
>
> However, there is one issue: I want to visualise isosurfaces of a 
> quantity, and colour them using another scalar quantity. When running 
> serial, everything is fine. When using multiple processors with MPI 
> leading to the data being distributed, the rendering of the isosurfaces is
still ok.
> However, the colouring seems to be based on the scalar field of the 
> first data segment (i.e. the first processor) only. This then leads to 
> very visible boundaries between the processors as the colours are 
> clearly not correct (see example on 
> http://www.mech.kth.se/~pschlatt/files/resampled.jpg). Again, running 
> on a single processor everything is correct, and running on different 
> numbers of processors will shift the edges.
>
> This issue could be confirmed in all version up to 3.10.
>
> Due to this, I am required to run in serial, which is very painful 
> both due to memory requirements and very long rendering times (up to
> 15 minutes for a single frame). Thus, if there would be a simple fix, I'd
be very interested.
>
> Thanks a lot in advance for any hint.
> Best regards,
> Philipp Schlatter
> KTH Mechanics, Stockholm, Sweden
>
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