POV-Ray : Newsgroups : povray.pov4.discussion.general : NURBS-Surface code in PovRay already exist Server Time
19 May 2022 01:45:53 EDT (-0400)
  NURBS-Surface code in PovRay already exist (Message 1 to 4 of 4)  
From: H  Karsten
Subject: NURBS-Surface code in PovRay already exist
Date: 4 Jan 2010 14:25:00
Message: <web.4b423f647f257aeada6353d60@news.povray.org>
Hi people,

in this post: web.4afb068fe011e9f5da6353d60@news.povray.org I'd suggest to
support NURBS-surfaces is PovRay.

Now I figured out that in MegaPov 0.6 support of NURBS already exist, including
trimming!

Is it possible to use this code from MegaPov 0.6?

You cam find it in the documentary under point 5.5.1. (Rational Bezier), type 2.

"
This patch extends the current bicubic_patch with two new types - one
non-rational (type 2) and one rational (type 3).

It also adds a new object type called bezier_patch with arbitrary u,v order and
trimmed_by option
"

Thanx, Holger


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From: Tor Olav Kristensen
Subject: Re: NURBS-Surface code in PovRay already exist
Date: 4 Jan 2010 15:30:00
Message: <web.4b424f06d18bdb3cd6291f840@news.povray.org>
"H. Karsten" <h-karsten()web.de> wrote:
> Hi people,
>
> in this post: web.4afb068fe011e9f5da6353d60@news.povray.org I'd suggest to
> support NURBS-surfaces is PovRay.
>
> Now I figured out that in MegaPov 0.6 support of NURBS already exist, including
> trimming!

No, I'm afraid that you are wrong Holger.

Bezier curves and rational Bezier curves are both subsets of NURBS curves.

The Bezier code in MegaPOV 0.6a (bezier2.c) seems to implement the de Casteljau
algorithm, which is not very usable for creating B-splines.

To create B-splines (and thereafter NURBS) one would typically use the Cox de
Boor algorithm.

--
Tor Olav
http://subcube.com


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From: Tor Olav Kristensen
Subject: Re: NURBS-Surface code in PovRay already exist
Date: 4 Jan 2010 16:00:00
Message: <web.4b4255b6d18bdb3cd6291f840@news.povray.org>
"Tor Olav Kristensen" <tor### [at] TOBEREMOVEDgmailcom> wrote:
> "H. Karsten" <h-karsten()web.de> wrote:
> > Hi people,
> >
> > in this post: web.4afb068fe011e9f5da6353d60@news.povray.org I'd suggest to
> > support NURBS-surfaces is PovRay.
> >
> > Now I figured out that in MegaPov 0.6 support of NURBS already exist, including
> > trimming!
>
> No, I'm afraid that you are wrong Holger.
>
> Bezier curves and rational Bezier curves are both subsets of NURBS curves.
>
> The Bezier code in MegaPOV 0.6a (bezier2.c) seems to implement the de Casteljau
> algorithm, which is not very usable for creating B-splines.
>
> To create B-splines (and thereafter NURBS) one would typically use the Cox de
> Boor algorithm.

Sorry, I looked into the wrong c-file.

The right one seems to be rbezier.c. But also this file seems to be using the de
Casteljau algorithm, not the Cox de Boor algorithm.

--
Tor Olav
http://subcube.com


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From: H  Karsten
Subject: Re: NURBS-Surface code in PovRay already exist
Date: 4 Jan 2010 17:25:01
Message: <web.4b4269b5d18bdb3cda6353d60@news.povray.org>
> >
> > No, I'm afraid that you are wrong Holger.
> >
> > Bezier curves and rational Bezier curves are both subsets of NURBS curves.
> >
> > The Bezier code in MegaPOV 0.6a (bezier2.c) seems to implement the de Casteljau
> > algorithm, which is not very usable for creating B-splines.
> >
> > To create B-splines (and thereafter NURBS) one would typically use the Cox de
> > Boor algorithm.
>
> Sorry, I looked into the wrong c-file.
>
> The right one seems to be rbezier.c. But also this file seems to be using the de
> Casteljau algorithm, not the Cox de Boor algorithm.
>
> --
> Tor Olav
> http://subcube.com

OK, my fault. It's a great pity, I was so happy to found it - lol :)


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