[Paraview] how to write boundary (face) data for 3D tetrahedra (cells) in ASCII VTK file for Paraview visualization? separate value for each face

[Samuel Key]

Victor,

An elementary way is to create a second data set of just the surface 
facets (triangles in your case) with point and/or cell data as you like.

ParaView is quite happy to read in both data sets and with the 
"eye-ball" icon in the pipeline browser you can select either or both to 
view.  The two data sets can also be independently filtered as desired.
One can use the Transformation filter to offset one with respect to the 
other. One can choose separate views in which display the data sets,

All kinds of displays become easy with two displayable graphics objects.

Sam Key

Victor Udoewa wrote:
> March 14, 2009
> 
> 
> Hi, I am not using the VTK software, but I am writing a VTK file to
> visualize with Paraview.
> I have one problem--writing data for the face (boundary) of my 3D
> tetrahedra (cells).
> Does anyone know how to do this for an unstructured grid in vtk? The
> cells are 3D tetrahedra.
> 
> Currently I use CELL_DATA and FIELD type in writing my ASCII file:
> (each tetrahedra gets 4 values for each of the 4 faces)
> 
> CELL_DATA 7927
> FIELD FieldData 1
> Boundary 4 7927 int
> 0 0 0 2 0 0 0 0 0 1 0 2 0 0 1 0 0 0 0 0 0 3 0 3 etc.
> 
> I have no idea if Paraview (or the vtk file format) knows which
> number goes to which face. I'm using the .inp file face numbering system.
> 
> But when I visualize this in Paraview it doesn't seem to work well.
> There are surfaces with boundary values higher than 3. Most of the
> picture is correct, but the tetrahedra (cells) on the corners between
> boundary groups display wrong values.
> 
> 
> I found a similar question on Kitwares mailing list 10 years ago but there
> were no responses I could find.
> 
> http://public.kitware.com/pipermail/vtkusers/1999-November/052114.html
> 
> If you can help it would be greatly appreciated. Thanks.
> 
> 
> Joy,
> Victor Udoewa
> Research Fellow
> CERECAM
> University of Cape Town
> http://www.cerecam.uct.ac.za/
> 
>  
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