[vtkusers] quadratic (or higher-order) elements on linear triangles

[David Thompson]

Hi Nico,

> ... using point_data, I can easily store continuous piecewise-linear
> functions on a (triangular) mesh.
> Is there a default way to store higher-order elements, i.e.,
> continuous, piecewise-quadratic function on a (triangular mesh?

Not in vtkUnstructuredGrid; all of VTK's higher order elements are isoparametric (i.e., they use the same basis functions for geometric and attribute interpolation). So, you must create additional points (linearly interpolated along edges) and additional connectivity entries for the higher order cells. Only then will the vtkPointData have the correct number of entries for storing quadratic attributes.

The vtkGenericDataSet class allows for non-isoparametric elements, but the filters for it are not widely used and tested; nor is it a simple task to subclass the dataset and implement your own cells with a custom interpolant.

	David