[vtkusers] Colormap unstructured grid by vector magnitude

[Peter Schmitt]

Hi,
I have data stored as an unstructured grid.  Each point has a vector
associated with it.  I want to color each point in my grid according
to vector magnitude.

vtkMapper has lots of options for colormaps, but it only seems to look
at scalar data.  Is it possible to have vtk determine the magnitude of
the vectors on the fly & color accordingly?

If I were working with Glyphs, it would be easy to do colormaps with
SetColorModeToColorByVector... I was hoping there would be something
similar for the vtkMapper class.

Thanks! 
Pete