[Sidefx-houdini-list] my non-rational NURBS surface gets rational when written to disk

jlait at sidefx.com jlait at sidefx.com
Thu Dec 18 13:39:47 EST 2008


On Thu, Dec 18, 2008 at 12:08:30PM -0500, Robert Kelly wrote:
> Thank you, that did the trick!
> 
> As a side note I tried to set the weights on all points to 1 after it was
> made rational, that didn't work. For future reference, is there a way to
> convince a nurbs curve / surface to go back to non-rational?

    The point sop trick usually works.  It doesn't work in this case
becaues the point sop thinks that the weight isn't actually being
changed.  Setting it to a weight of 1.5 and then to 1.0 with two point
sops will kick it out of rational land.
    This isn't the most rational of workflows, I fear.

> 2008/12/18 <jlait at sidefx.com>
> 
> > On Wed, Dec 17, 2008 at 01:47:47PM -0500, Robert Kelly wrote:
> > > my non-rational NURBS surface gets rational when written to disk!?
> > > And is messing up my creep!
> > >
> > > i am making a fairly heavy network and wanted to include some writing and
> > > reading from disk to make it a bit more stable. Only to find that my
> > creep
> > > went funny when I read it from disk. after some head scratching i spotted
> > > that the one from disk becomes  rational when read in, while the geometry
> > > that it is meant to be writing to disk is non-rational.
> > >
> > > So how do I ether have it read and write properly {BUG?} or as a band aid
> > > solution make my now rational nurbs surface back into a non-rational one?
> >
> >     Bandaid solution:
> > Point Sop
> >    New Weights
> >        delete channel, set to 1.
> >    Do this in the Skin SOP before your geometry output to catch the
> > culprit at the source.
> >
> >    What is going wrong is that slight numerical tolerance issues are
> > making the weights non-one.  This causes the geometry to be flagged as
> > rational when read from disk.  When operated in memory, Houdini only
> > checks to see if they are non-one if something happens that should
> > make them non-one.  Since the skin shouldn't result in non-one
> > weights, we don't check, so the NURBs stays flagged as non-rational.
> > --
> >        - Jeff Lait
> >
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-- 
        - Jeff Lait




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