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

Tue Jun 28 12:36:25 EDT 2011

Hi Philipp,

A couple of questions:
* Are you using the distributed 3.10.1 binaries or did you compile PV
3.10.1 from source yourself?
* Can you reproduce the behavior with the sample dataset
Data/RectGrid2.vtk (part of both git://vtk.org/VTKData.git and
http://www.paraview.org/files/v3.10/ParaViewData-3.10.1.zip)? That's
also a "Rectilinear Grid". Using the Calculator operation "1 +
coordsX*coordsY" followed by a Contour filter with "Compute Scalars"
checked and 10 auto-chosen values, I got identical results with 1 and 16
cores (using PV 3.10.1 Linux 64-bit binaries and Windows 64-bit
binaries, relying on Auto-MPI ("Settings" - "Use Multi-Core") for the 16
core case)

Karl

Philipp Schlatter wrote, On 28.06.2011 17:50:
> 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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