Please, have you seen a good tutorial (or pdf) about the Houdini model UV(W)s used by the Ray SOP, Refine SOP etc.?

How are they calculated? What about deforming objects and their UVs?

For example I would like to use the “hitprimuv” from the RAY SOP (or xyzdist vex function), but I dont have elementary knowledge about the UVs

Also, for example on the Polygon Box, there seems to be no “V” when I try to use Refine SOP.
Please, where should I start to get into the UVs?

I am a newbie so sorry for this confused question.

Here, Tomas Slancik helped me a lot with the UVs, to visualize and understand better:
http://forums.odforce.net/topic/26090-uvw-coordinates-in-the-ray-sop-refine-sop-etc/?do=findComment&comment=151998 [forums.odforce.net]

I hope it doesnt mind, that I did a crosspost after few days.