[vtkusers] [EXTERNAL] Higher order elements in VTU files

David Thompson dcthomp at sandia.gov
Thu Jun 21 17:27:41 EDT 2012


Hi Mikael,

>> NURBS are not implemented.
> Would NURBS be part of the unstructured grids?

Should someone implement NURBS cells, the barrier that keeps a  
vtkUnstructuredGrid from holding them is that  
vtkGenericCell::InstantiateCell enumerates all of the subclasses of  
vtkCell that are supported -- and Kitware is loathe to increase the  
number of cell types here. Because vtkGenericCell(**) is the mechanism  
used by a lot of filters to perform per-cell operations such as  
isocontouring, clipping, and cutting, these operations fail when a  
mesh contains cells of a type it cannot handle.

(**) Note that vtkGenericCell is not related to the vtkGenericDataSet  
described below. Its equivalent in vtkGenericDataSet objects is  
vtkGenericAdaptorCell. The names clash a little because vtkGenericCell  
was around long before the other vtkGenericXXX classes.

>> The VTK_HIGHER_* types are for use with the
>> vtkGenericDataSet mesh format, not vtkUnstructuredGrids. The
>> vtkGenericDataSet mesh was meant to serve as a way for novel PDE
>> discretization techniques to be rendered with VTK -- without VTK  
>> having to
>> understand the interpolation strategy or choose a sampling  
>> strategy. Thus,
>> the class serves as an "adaptor" between visualization code and the  
>> FE
>> solver providing the interpolation functions. Subclasses of
>> vtkGenericAdaptorCell were intended to provide their own linearized
>> approximations for rendering. However, the filters for this mesh  
>> type are
>> not as well tested as those that work with unstructured grids.
>
> So it can't go into VTU-files, but is there any means to store this
> such data in any file format which could be loaded into Paraview?

It is possible to create your own reader and use the vtkGenericDataSet  
filters from ParaView, but this is a lot of work. It is also possible  
to hack vtkGenericCell to include your own cell type, but this is hard  
to maintain. Sorry there is not an easy solution,

	David




More information about the vtkusers mailing list