[Paraview] Strange behaviour with large datasets

Tue Sep 2 13:41:22 EDT 2008

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,

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mob:  +  44 7872010167
web:   wirthresearch.com<http://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,

 [cid:image001.jpg at 01C90CF0.D2911E60]
[cid:image002.jpg at 01C90CF0.D2911E60]
mob:  +  44 7872010167
web:   wirthresearch.com

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