[Paraview] mapping scalars onto surface geometry

[Moreland, Kenneth]

Giles,

I think I've figured out your problem. The scalars data you sent me is an unstructured grid with "voxel"-type cells. One of my least favorite features of VTK is that there is a distinction between a box in an unstructured grid (called a hexahedra) and a box in a data set with structured grid (called a voxel). These two cells are essentially the same shape, but the order of the points is different.

The reason why I dislike this feature is that it is technically allowable to put voxel cells in an unstructured grid. However, this fouls up lots of filters that don't check for this corner case. Apparently the probe filter, which is the underlying filter for resample with dataset, is one of the filters broken for voxels. (Unless there is something else about this dataset that I am missing.) I submitted a bug about this (http://www.paraview.org/Bug/view.php?id=15982).

The most expedient way around this problem is to run the tetrahedralize filter on the scalars. That will convert the voxels to tetrahedra correctly, and the probe filter has no problem on that data type. The interpolation will be slightly different but close. Overall a better solution is to save your data as image data rather than convert it to an unstructured grid. The file will be smaller and the interpolation should happen correctly.

-Ken

From: Richardson CFD <garcfd at gmail.com<mailto:garcfd at gmail.com>>
Date: Saturday, February 6, 2016 at 5:54 AM
To: "paraview at paraview.org<mailto:paraview at paraview.org>" <paraview at paraview.org<mailto:paraview at paraview.org>>, Kenneth Moreland <kmorel at sandia.gov<mailto:kmorel at sandia.gov>>
Subject: [EXTERNAL] mapping scalars onto surface geometry

Kenneth,

I have made two files here available for download (sphere.stl and scalars.vtk).

https://drive.google.com/file/d/0B4bNbYR3XwvQVlBZNlVBX0RXSkU/view?usp=sharing

https://drive.google.com/file/d/0B4bNbYR3XwvQTkJxRDhLb0MxZGc/view?usp=sharing

I hope you can give these a try using "Resample with Dataset" to see what the problem is.

Regards Giles.
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