2011/2/22, Roy Stogner <royst...@ices.utexas.edu>:
>
>>> Does VTK have native support for higher-order data? If so, adding
>>> that to our VTKIO output would be fantastic.
>>
>> Yes, VTK does, but it's not implemented in VTKIO. I attached a patch
>> that does it. :-)
>
> Does it, but how well? It looks like the higher order coefficients
> are getting added to the file, fine, but I don't see how they're
> supposed to end up being accurately visualized. How is a VTK reader
> going to know whether a given higher order DoF index is the
> coefficient of a quadratic interpolatory function in a Lagrange basis,
> a quartic bubble function in a hierarchic basis, or a normal flux
> function in a cubic macroelement Clough-Tocher basis?
Oh, that's what you mean by "native support". Well, in that case VTK
doesn't. It only allows multiple components per node/element
("tuples"), but does not specify what these components stand for. A
VTK reader will therefore not be able to visualize the shape
functions/solution properly, without the user telling the software how
to interpret the data. Specifying interpolation types is just not part
of the VTK file format.
I suppose it's a matter of opinion/objective. Do the libMesh
developers/users want their solution output either
a) complete, including higher order terms, in a way that complies with
the VTK file format, but not necessarily perfectly visualizable in,
say, Paraview without further ado in all cases
or
b) incomplete, i.e. only first order terms, not using the full
capability of the VTK file format, but with a higher chance that VTK
readers will be able to deal with at least this first order component
properly
?
Case a) is implemented with my patch, case b) is the current way of
implementation. There is a third possibility, which is a compromise:
In the case of higher order variables, one could write each component
separately as scalar variables, perhaps with a suffix in the name
denoting the component. This way, all information is written, while
Paraview will still be able to recognize the first order solution as
scalars and display it as it does currently.
Roman
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