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[Bartosz Sawicki <sawickib@xxxxxxxxxxxxx>]

Hi there,

I've found that VTK export in Dolfin has one serious limitation. It 
ignores type of finite element of DiscreteFunction and always 
interpolates function into vertex values.
That is very general solution, which always produce something which can 
be visualized, but in some cases (eg. Lagrange element - 0 order) such 
procedure induces errors.

VTK file format specification allows two types of functions PointData 
and CellData. Paraview also visualize correctly both types. So why do we 
alway transform everything to PointData ?

I've already write some code that enable this feature in Dolfin. 
Unfortunatelly it was not easy, some special hacks was needed. Of course 
I can send path or bundle, but I this can be done better after some 
redesign.

The main problem is that, when I have object of DiscreteFunction I can't 
check what kind of finite element is used inside, or maybe I omit 
something?  So I can't write code which will automatically detect when 
to use PointData, or CellData. At this moment I solve this problem by 
introducing new File::Type (vtkc). When new File object is created user 
has possibility to choose whether it is normal VTK with PointData, or 
VTK with CellData.
What do you think about such solution?

regrd.
BArtosz