[vtkusers] Ghost level in VtkUnstructuredGrid

[Gerard Gorman]

I hope someone will contradict me if I'm wrong here because I don't 
think the documentation is clear on this point.

Ghost levels are used with distributed datasets - e.g. when you have 
partitioned your big unstructured mesh into a number of smaller ones. 
You might have done this if you were running a parallel finite element 
model for example. If you use vtk's distributed file format for 
unstructured meshes then you presumably have a .pvtu file. Ghost levels 
define how much these partitions overlap and this will be defined in the 
.pvtu file. Other terms you hear are "ghost/halo cells/nodes". The 
ambiguity for me lies in the fact that there are two different ways to 
define a mesh partitioning - one can either partition the nodes of the 
mesh or partition the elements of a mesh. When nodes are partitioned 
then one counts the layers of elements that overlap between meshes. When 
elements are partitioned then one counts the layers of nodes that 
overlap. So what exactly level means in vtk depends on how vtk has 
defined partitioning.

Hopefully someone will clarify this for us - if no one does then I'd 
suggest you ask the same question on the paraview mailing list.

Cheers
g

Thinnes wrote:
> Dear vtkUsers,
> 
> Could you explain to me, what is call "Ghost Level" in the 
> vtkUnstructuredGrid?
> I am lacking documentation.
> 
> Thanks for help
> Alexandre
> 
> 
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-- 
----------------------------------------------------------
Gerard Gorman
Applied Modelling and Computation Group
Earth Science and Engineering
Imperial College
Prince Consort Road		Tel. +44 20 7589 5111 ext 59319
London SW7 2BP
U.K.                    o~o         http://www.zmag.org/
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