[Sidefx-houdini-list] dPds, dPdt troubleshooting...

Dan Seddon dan.seddon at framestore-cfc.com
Thu Aug 31 09:57:47 EDT 2006


hoknamahn at cgtalk.ru wrote:
> > In the case of mantra s and t is the primitive  parameterization - 
> so this can be discontinuous from one face to another in the case of 
> poly/subd's.
>
> I'm trying to figure out when the polygonal geometry behaves as 
> parametric surface and when as polygonal (with discontinuity).
> In some cases the whole piece of polygonal geometry looks like 
> parametric surface (i.e. with nice anisotropy) in other case the whole 
> geometry or the part of geometry looks weird.
The polygonal geometry doesn't have to behave as a parametric surface to 
have continuity ( though it may join large numbers of quad faces 
together in to a grid internally if they can be represented that way) - 
to appear continuous the derivatives just need to match on neighbouring 
faces - you're more than likely seeing this when you have quads arranged 
in a grid like fashion. Try rendering s and t out rather than dPds and 
dPdt on different surfaces and you'll get an idea of what the problem 
involves.



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