[vtkusers] ClassifyFirst vs. InterpolateFirst

[Dave Reed]

Can anyone explain the difference between these two compositing
functions for me?

vtkVolumeRayCastCompositeFunction::SetCompositeMethodToInterpolateFirst 
vtkVolumeRayCastCompositeFunction::SetCompositeMethodToClassifyFirst 

And in general, is there somewhere that explains concepts like this? I
have the Prentice Hall VTK book and have looked at the online HTML
documentation. I took a quick glance at the
vtkVolumeRayCastCompositeFunction.cxx file but I couldn't decipher the
differences between:

CastRay_TrilinVertices_Unshaded
CastRay_TrilinSample_UnShaded

>From the looks of the table of contents it does not appear that the
manual Kitware sells will help with this type of information or am I
wrong?

Thanks,
Dave