Bartosz Sawicki wrote: > 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? >
I don't think that this is the best solution. Ideally, a Function will know what's appropriate. We previously supported cell data (Kristian implemented it) but we removed it because we couldn't determine robustly for a general Function (possibly a mixed element) whether cell or point data was appropriate. This may now be easier now as a lot of changes have been made since we removed support for cell data. Once a Function can determine the appropriate format, formatting the output is pretty straightforward. For now, just project solutions onto a continuous P1 basis. Garth > regrd. > BArtosz > _______________________________________________ > DOLFIN-dev mailing list > [email protected] > http://www.fenics.org/mailman/listinfo/dolfin-dev _______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
