VRML 2.0 and NURBS 
Author Message
 VRML 2.0 and NURBS

Dear vrml 2.0 folks

Can anyone confirm my impression that the VRML 2.0 spec
does *not* include NURBS?  Can't find it in the spec,
or in the index, at any rate.

Thank you   John Sidles



Sat, 06 Mar 1999 03:00:00 GMT  
 VRML 2.0 and NURBS

You are quite correct, VRML 2.0 does not include NURBS.

--

Work: (608) 231-0282  Home: (608) 238-3974
VRML info:   http://www.sdsc.edu/vrml   http://vag.vrml.org/



Sat, 06 Mar 1999 03:00:00 GMT  
 VRML 2.0 and NURBS

VRML 2.0 *does not* include NURBS.  Open Inventor does, however.
http://www.tgs.com.

Robert

: Dear VRML 2.0 folks

: Can anyone confirm my impression that the VRML 2.0 spec
: does *not* include NURBS?  Can't find it in the spec,
: or in the index, at any rate.

: Thank you   John Sidles



Sun, 07 Mar 1999 03:00:00 GMT  
 VRML 2.0 and NURBS

 Can't find it in the spec,

Quote:
>: or in the index, at any rate.

>: Thank you   John Sidles

Ok, I'm ignorant.  What are NURBS?

++++++++++++++++++

Watch this space for new, exciting stuff.



Tue, 09 Mar 1999 03:00:00 GMT  
 VRML 2.0 and NURBS

Quote:

>  Can't find it in the spec,
> >: or in the index, at any rate.

> >: Thank you   John Sidles

> Ok, I'm ignorant.  What are NURBS?

Non Uniform Rational Bezier Splines.  These are the most usable and
powerful implementation of splines.  As seen in programs such as
illustrator and coreldraw, the splines (curves of 'best fit') have
controlling handles at their vertices giving complete control of curve
shape, continuity and vertex position.

If Gavin says there's no NURBS, then there's no NURBS.  But I thought I
read something in the spec suggestion that a door was left open (perhaps
through externprotos) to allow later implementation of NURBS.

As far as I can see (which is only about a foot passed this monitor
here) NURBS are most usefull as a modelling tool, but should be broken
up into a polygon mesh of suitable density before rendertime as they
would pose too much overhead on a realtime rendering engine.  However I
guess they are going to be a more compact way of representing more
complex organic geometry.

--
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         http://www.highway1.com.au/arts/wizards
One crowded hour of glorious life
           Is worth an age without a name.   Mordaunt 1791



Fri, 12 Mar 1999 03:00:00 GMT  
 VRML 2.0 and NURBS

Quote:

> Non Uniform Rational Bezier Splines.  These are the most usable and
> powerful implementation of splines.  As seen in programs such as
> illustrator and coreldraw, the splines (curves of 'best fit') have
> controlling handles at their vertices giving complete control of curve
> shape, continuity and vertex position.

> If Gavin says there's no NURBS, then there's no NURBS.  But I thought I
> read something in the spec suggestion that a door was left open (perhaps
> through externprotos) to allow later implementation of NURBS.

Bezier curves/surfaces are certainly usefull to model "irrational"
surfaces. By just reading the VRML2.0, I think that the extrusion
function will do for most engineering tasks.  For modelling human (or
other) shapes probably Bezier curves/surfaces would have the
theoritical advantage of giving a more compact (less bytes) description
of the model.  
--
Regards / Amitis,
  Robert Lain
---
http://www.bart.nl/~jmlaine/carene      
CARENE50 free hull design CAD with VRML file generation
---


Fri, 12 Mar 1999 03:00:00 GMT  
 VRML 2.0 and NURBS


Quote:

>> Ok, I'm ignorant.  What are NURBS?

> Non Uniform Rational Bezier Splines.

     Nonuniform rational B-splines, actually.  B-splines are more compact
(in terms of amount of data needed to represent the same geometry), more
stable, and easier to work with than Bezier splines.

Quote:
> These are the most usable and powerful implementation of splines.

     Well, since any B-spline can be represented as a Bezier they're not
really more powerful, but they are easier to work with.
     BTW, if VRML ever does incorporate rational B-splines I hope it does it
right, and not the way IGES does it.

============================================================================


                  http://www.connix.com/~dennis/dennis.htm

Disclaimer: "True, I talk of dreams; which are the children of an idle
brain, begot of nothing but vain fantasy; which is as thin of substance as
the air."                      - Romeo & Juliet, Act I Scene iv Verse 96-99



Fri, 12 Mar 1999 03:00:00 GMT  
 VRML 2.0 and NURBS

Quote:

> If Gavin says there's no NURBS, then there's no NURBS.

I am occasionally wrong, but I have a copy of the spec in front of me so
in this case I'm sure they're not part of the 2.0 spec.

Quote:
> But I thought I
> read something in the spec suggestion that a door was left open
> (perhaps through externprotos) to allow later implementation of NURBS.

Well...

You could write a Script that took the parameters for a NURBS surface or
curve and generated an IndexedFaceSet or IndexedLineSet that
approximated it (more precisely, the script will take the NURBS
parameters and send events to an IndexedFaceSet or IndexedLineSet to set
their fields so they approximate the NURB).  It could even define set_
events for the parameters and re-generate when it received events,
allowing animated NURBS.

That wouldn't be too difficult for NURBS curves, would be only a little
more difficult for NURBS surfaces, but is probably impractical for
trimmed NURBS surfaces because the code to implement trimmed NURBS is
infamously complicated.  And from what I've been told (I'm not a NURBS
expert), without trims (holes cut into the surface, usually defined as a
closed NURBS curve) NURBS surfaces aren't very useful.

Once you've written the Scripts, it would be easy to define a PROTO or
EXTERNPROTO for NurbsCurve and NurbsSurface, after which you could
create as many NurbsCurve and NurbsSurface nodes as you like.

--

Work: (608) 231-0282  Home: (608) 238-3974
VRML info:   http://www.sdsc.edu/vrml   http://vag.vrml.org/



Fri, 12 Mar 1999 03:00:00 GMT  
 
 [ 8 post ] 

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