it seems that there isn't any support for nurbs in povray! is it possible?

thankx leo

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"LEO_BOLOGNA" <l_o### [at] yahooit> wrote:
> it seems that there isn't any support for nurbs in povray! is it possible?

Someone correct me if i'm wrong, but i believe bicubic patches are exactly
that.  They are one of povray primitives and they describe surfaces via
control points which are interpolated by a spline.  Isn't Non-Rational
Uniform B-Splines just that?...

Povray has a long history and many names do not correspond exactly to the
ones popular today.  For instance, people looking for a "Global
Illumination" feature will likely not link Radiosity to it...

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nemesis nous apporta ses lumieres en ce 03/05/2006 12:35:
> "LEO_BOLOGNA" <l_o### [at] yahooit> wrote:
> 
>>it seems that there isn't any support for nurbs in povray! is it possible?
> 
> 
> Someone correct me if i'm wrong, but i believe bicubic patches are exactly
> that.  They are one of povray primitives and they describe surfaces via
> control points which are interpolated by a spline.  Isn't Non-Rational
> Uniform B-Splines just that?...
> 
> Povray has a long history and many names do not correspond exactly to the
> ones popular today.  For instance, people looking for a "Global
> Illumination" feature will likely not link Radiosity to it...
> 
> 
> 
Sory, bicubic patch are not nurbs and don't behave like nurbs. They are more like
arays of bicubic 
splines.

-- 
Alain
-------------------------------------------------
Age is a very high price to pay for maturity.

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Alain wrote:
> nemesis nous apporta ses lumieres en ce 03/05/2006 12:35:
>> "LEO_BOLOGNA" <l_o### [at] yahooit> wrote:
>>
>>> it seems that there isn't any support for nurbs in povray! is it 
>>> possible?
>>
>>
>> Someone correct me if i'm wrong, but i believe bicubic patches are 
>> exactly
>> that.  They are one of povray primitives and they describe surfaces via
>> control points which are interpolated by a spline.  Isn't Non-Rational
>> Uniform B-Splines just that?...
>>
>> Povray has a long history and many names do not correspond exactly to the
>> ones popular today.  For instance, people looking for a "Global
>> Illumination" feature will likely not link Radiosity to it...
>>
>>
>>
> Sory, bicubic patch are not nurbs and don't behave like nurbs. They are 
> more like arays of bicubic splines.
> 

AFAIK, Non-Rational Bicubic B-Splines (NURBS is singular, so would the 
plural be NURBSes?) is the popular name for what used to be popularly 
known as Bezier patches, named for the researcher who first published 
them (although they were previously developed by someone working for the 
Army, who did not permit him to publish his work so I don't remember his 
name).  Mathematically, they're bicubic splines, so this is the name 
that POV-Ray used originally.  NURBS, as a name, is just a little more 
specific (specifying that they are non-rational, and the specific type 
of spline).

Where most people get confused, is that many graphical modelling 
programs create arrays of NURBS, and hide the control points from the 
user, so they don't actually know what's going on under the hood.  The 
POV-Ray syntax (which was never meant to be hand-written, per the 
documentation) requires the declaration of all 16 control points.

...Chambers

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Chambers <ben### [at] pacificwebguycom> wrote:
> AFAIK, Non-Rational Bicubic B-Splines (NURBS is singular, so would the
> plural be NURBSes?)

gee, you just copied-and-pasted my misspelling.  It's Non-Uniform Rational
B-Splines. :P

> Mathematically, they're bicubic splines, so this is the name
> that POV-Ray used originally.  NURBS, as a name, is just a little more
> specific (specifying that they are non-rational, and the specific type
> of spline).

exactly, or so i read in wikipedia:
http://en.wikipedia.org/wiki/Nurbs

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> AFAIK, Non-Rational Bicubic B-Splines (NURBS is singular, so would the
> plural be NURBSes?) is the popular name for what used to be popularly 
> known as Bezier patches, named for the researcher who first published 
> them (although they were previously developed by someone working for
> the Army, who did not permit him to publish his work so I don't
> remember his name).  Mathematically, they're bicubic splines, so this
> is the name that POV-Ray used originally.  NURBS, as a name, is just
> a little more specific (specifying that they are non-rational, and
> the specific type of spline).
NURBS are a *generalisation* of Bezier splines. Non-intuitively,
"non-uniform" doesn't mean "not uniform", it means "not necessarily
uniform". Bezier splines, in contrast, are all uniform.

-- 
"Follow the enemy and try to prevent  the enemy carrying away the guns."
On 25th Oct 1854, Lord Raglan, on a hill, can see one set of guns;  Lord
Lucan, down in the valley,  sees a different, better defended,  set, and
leads the Light Brigade in its fateful charge. http://surreal.istic.org/

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nemesis wrote:
> Chambers <ben### [at] pacificwebguycom> wrote:
>> AFAIK, Non-Rational Bicubic B-Splines (NURBS is singular, so would the
>> plural be NURBSes?)
> 
> gee, you just copied-and-pasted my misspelling.  It's Non-Uniform Rational
> B-Splines. :P

My bad, it was early in the day and this was the first thread I read :)

...Chambers

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"Chambers" <ben### [at] pacificwebguycom> wrote

> AFAIK, Non-Rational Bicubic B-Splines (NURBS is singular, so would the
> plural be NURBSes?) is the popular name for what used to be popularly
> known as Bezier patches, named for the researcher who first published

No. Cubic Bezier splines are a special case of Bezier splines, which are a
special case of B-Splines, which are a special case of NURBS. With NURBS,
you can have

* arbitrary degrees
* arbitrary number of CVs, starting at degree+1
* concept of knots spans ("b-spline" part)
* arbitrary knot spacing ("non-uniform" part)
* arbitrary weights for each CV ("rational" part)

Surfaces are outer/tensor products of curves.

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