[Paraview] Strange behaviour with large datasets

Tue Sep 2 13:53:41 EDT 2008

Hi Ken,

"The mesh quality filter will be run multiple times on multiblock data
(once per block), but I assume that is not the case for you as volume
rendering is not available on data with more than one block."

I think this sentence sums up my problem: the unstructured grid does
indeed consist of multiblock data.

Ok thanks so much for your help. I will look for a different approach to
what I am trying to do.

Thanks for your time.

Nat.

Best Regards

Dr. Nathanael Inkson,

Computational Fluid Dynamics Developer,

Digital Flow Solutions,

mob:  +  44 7872010167

web:   wirthresearch.com

________________________________

From: Moreland, Kenneth [mailto:kmorel at sandia.gov] 
Sent: 02 September 2008 18:41
To: Nathanael Inkson
Cc: Simon Hubbard; paraview at paraview.org
Subject: RE: Strange behaviour with large datasets

I am a bit confused.  The initial question sounded like a volume
rendering problem; you could not see the result of the mesh quality
filter very well.  Is the problem you are reporting that the output of
the mesh quality filter is incorrect?  Do the ranges look wrong in the
information tab?  Does the threshold filter not extract cells you expect
to be of poor quality?

Does your modified mesh quality filter behave differently than the one
that comes with ParaView?  The pipeline should not be updating your
filter unless it needs to refresh the calculation.  The mesh quality
filter will be run multiple times on multiblock data (once per block),
but I assume that is not the case for you as volume rendering is not
available on data with more than one block.  The cell count might be off
because you are running in parallel.  Each process will have a partition
of the whole mesh, so the cell count will be smaller unless you are
getting the global multiprocess controller and adding up all the cells.

If the pipeline is inappropriately calling your filter multiple times,
it might be that your filter is calling its own Modified method (usually
indirectly through, for example, a call to one of the Set* macros).  You
can check for that by making sure that the MTime ivar does not change
while invoking RequestData or any other ProcessRequests method.

-Ken

________________________________

From: Nathanael Inkson
[mailto:Nathanael.Inkson at digitalflowsolutions.com] 
Sent: Tuesday, September 02, 2008 11:15 AM
To: Moreland, Kenneth
Cc: simon.hubbard at digitalflowsolutions.com
Subject: RE: Strange behaviour with large datasets

Dear Ken,

    Thanks for your answer but I am not sure that this is the reason as
I have other fields which have large values. If I count the number of
cells in one pass through vtkMeshQuality and output to a file, I find
that the answer is far less than the actual number of cells in the mesh.
I have a gut feeling that because the mesh is so big that the
MeshQuality filter is entered several times as it updates the progress
bar, wouldn't that mean that the newly created quality arrays are
overwritten each time the filter is entered? I'm not too sure about how
the filters actually work.

How is this prevented?

Thanks

Nat.

Best Regards

Dr. Nathanael Inkson,

Computational Fluid Dynamics Developer,

Digital Flow Solutions,

mob:  +  44 7872010167

web:   wirthresearch.com

________________________________

From: Moreland, Kenneth [mailto:kmorel at sandia.gov] 
Sent: 02 September 2008 14:58
To: Nathanael Inkson; paraview at paraview.org
Subject: RE: Strange behaviour with large datasets

If your mesh is typical, then probably most of the cells are of good
quality, and there are a handful of cells of bad quality.  Thus, when
volume rendering most of the cells will be invisible and that handful of
cells will have some opacity.

The probable reason that you can see them in a small mesh and not a
large one is that the cells are spatially much smaller (with respect to
the entire mesh) for the large mesh.  In correct volume rendering, a
material of a constant density will have smaller opacity the thinner it
gets.  Your cells are probably so small that there is not enough
accumulation to actually see them.

You can adjust for the small scale of the cells by adjusting the "Scale"
parameter in the Color Scale Editor dialog box.  That parameter is
actually a unit length specification for the opacity parameters given.
Setting it to about cell length divided by 10 should give you decent
results.  However, an easier and probably more effective approach would
be to bag the volume rendering and use the threshold filter to extract
the cells of interest (in this case, the bad ones).

-Ken

________________________________

From: paraview-bounces at paraview.org
[mailto:paraview-bounces at paraview.org] On Behalf Of Nathanael Inkson
Sent: Tuesday, September 02, 2008 7:31 AM
To: paraview at paraview.org
Subject: [Paraview] Strange behaviour with large datasets

Dear Paraview people,

            I am working with Paraview with very large datasets (around
40Gb). I have written a filter derived from MeshQuality which doesn't
seem to display the returned data arrays correctly. I checked with the
same mesh and the MeshQuality filter. The same thing happens: I put the
output on volume rendering to look at the quality field and the whole
dataset is invisible. I have tried rescaling the range but to know
avail. Is this a known problem?

Any advice? With smaller meshes the problem disappears and the quality
field is visible with volume rendering.

Best Regards

Dr. Nathanael Inkson,

Computational Fluid Dynamics Developer,

Digital Flow Solutions,

mob:  +  44 7872010167

web:   wirthresearch.com

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