Allow Volume module to work with cell data about mayavi HOT 2 OPEN

I don't know how much has changed in VTK in the recent past but when I wrote the volume module, it was the case that almost all the filters and algorithms worked only on point data. Volume rendering especially so. As a result I must have defaulted to point data. This should perhaps be re-investigated when someone has the time but unfortunately, I will not be able to get to this in a while.

from mayavi.

My understanding is that the volume module displays the cells specified in the VTK file, shaded with some colour and opacity. It seems natural then, to want this colour to correspond to the cell data for that cell. If point data is used, it is not clear to me which cell that point data is associated with. Is it an average of the point data for all the vertices for instance? Would this not be simpler algorithmically than using point data?

But using a celltopointdata filter seems to generate usable results, so perhaps this is not critical...

from mayavi.