UV(W) coordinates (in the Ray SOP, Refine SOP etc.)

[ikoon]

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

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.
And what about deforming objects and their UVs?

I am a newbie so sorry for this confused question. Please, where should I start to get into the UVs?

Edited May 23, 2016 by ikoon
to define it better

[acey195]

The UVs these things use intrinsic face UVs (as opposed to a normal texture UV map)

But I second this, if someone knows on a lower level how they are precisely calculated, I would be interested in that as well. (I do know how you can use them with a primuv function for instance) but not really how they are calculated (especially in the case of nGons)

Edited May 23, 2016 by acey195

[ikoon]

I have tried to visualize those intristic UVs with a Visualize SOP or with scene visualizers, but I did not succeed :-/

Could anybody please create a setup, that visualizes those UVs? Then we could experiment and understand it better, how those UVs behave?

[anim]

here is simple example of visualizing primuvs for polygons and from that is quite obvious how they are calculated (they slightly differ for tri, quad, n-gons)

for curves and NURBS primitives they logically match the u and v directions

vis_primuv.hip

Edited June 4, 2016 by anim

[ikoon]

Thank you very much Tomas! Moc děkuji

Now I will experiment with the Attribute Interpolate node and with the primuv VEX function.