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Le 04/08/2015 18:11, LanuHum a écrit :
> clipka <ano### [at] anonymousorg> wrote:
>> Am 03.08.2015 um 19:33 schrieb LanuHum:
>>> Hi! I don't understand how sor is created? The form doesn't
>>> correspond to a green curve. Not the curve, but control points 
>>> rotates. Or it not NURBS?
>>> 
>>> nurbs, cubic, bubic. quadric, madric. What is that? Oh, My
>>> God! Why very much? There is bezier - clear and operated. :)
>> 
>> SOR is the surface of revolution of a piecewise defined
>> 3rd-order (cubic) polynomial function (defined by a set of points
>> on the curve) rotated about the x axis (and the resulting shape
>> subsequently rotated so that its axis of rotational symmetry is
>> mapped onto the y axis of 3D space); no splines involved.
>> 
>> To generate the surface of revolution of proper splines, there's
>> the "lathe" keyword, which supports linear, quadratic and cubic
>> splines (the latter with various different parameterizations
>> based on the control points, including bezier splines).
>> 
>> POV-Ray doesn't support NURBS (non-uniform rational B-splines).
> 
> Thanks! There is no support of nurbs, there is no support of bezier
> (an exception of lathe and prism). Refusal of nurbs and bezier is a
> concept?

there is bicubic_patch.

http://povray.org/documentation/view/3.6.1/64/
http://wiki.povray.org/content/Reference:Bicubic_Patch
http://www.povray.org/documentation/view/3.6.1/290/

It's a Bezier patch.

> Badly. It strongly limits possibilities of data transmission from
> the Blender to Povray.

Most nurbs rendering transforms them in mesh anyway. (I recommend
mesh2 format for them).

It's not a concept (to refuse nurbs), it's just that solving the
intersection of a ray with a nurbs is not something that can be easily
solved mathematically (I would say: at once, without iterations or
approximation).

Now, if you can solve it (a nurbs, a ray, return the list of
intersection points) (as well as "a nurbs, a 3D point, return a
boolean for the point being inside the volume delimited by the nurbs),
without generating a mesh under the cover, it can be considered for
addition.

But beware, even bicubic_patch has a cheating method (type 1), as
solving pure (type 0) bezier is slow. (but memory effective)

> I can't give animation, I can't give the arrays built along curves 
> Interestingly, what 3D - editors have no nurbs and bezier, but have
> cubic and quadratic? I such didn't see. If I wrote the
> AutodeskMaya2Povray exporter, I would meet the same problems? :(
> 
> 

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