POV-Ray: Newsgroups: povray.newusers: bezier curves problem

POV-Ray : Newsgroups : povray.newusers : bezier curves problem		Server Time 2 Nov 2024 05:22:05 EDT (-0400)

From: Kurts
Subject: bezier curves problem
Date: 3 Jul 2004 09:04:58
Message: <kurtzlepirate-3ECAB0.15045603072004@news.povray.org>

hi,

i have some trouble with 'bezier' curves. same set of points used in 'prism'
and in 'sphere_sweep' give not the same curve.

#declare courbe = prism {
  bezier_spline
  0, r,
  60,
  p1, p2, p3, ..., p60
  }

#declare spheres = sphere_sweep {
  b_spline,
  60+3,
  p1,r
  p2,r
  p3,r
  ...
  p60, r
  p1, r // for closing the curve
  p2, r
  p3, r
  }

please see image in "povray.binaries.images : bezier curves problem"

what do you think about that ?
where is my mistake ?

@+
louis

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From: Alain
Subject: Re: bezier curves problem
Date: 3 Jul 2004 09:23:41
Message: <40e6b35d$1@news.povray.org>

Kurts nous apporta ses lumieres ainsi en ce 03/07/2004 09:04... :

>hi,
>
>i have some trouble with 'bezier' curves. same set of points used in 'prism'
>and in 'sphere_sweep' give not the same curve.
>
>#declare courbe = prism {
>  bezier_spline
>  0, r,
>  60,
>  p1, p2, p3, ..., p60
>  }
>
>#declare spheres = sphere_sweep {
>  b_spline,
>  60+3,
>  p1,r
>  p2,r
>  p3,r
>  ...
>  p60, r
>  p1, r // for closing the curve
>  p2, r
>  p3, r
>  }
>
>please see image in "povray.binaries.images : bezier curves problem"
>
>what do you think about that ?
>where is my mistake ?
>
>@+
>louis
>  
>
I don't think that the "b" in b_spline stand for bezier, more like 
bicubic... Just a guess as the documentation is not clear for that point.
Bezier need multiple of four points (start, control1, control2, end), 
b_spline can take any number >= 4 like 5, 6, 7...

Alain

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From: Florian Brucker
Subject: Re: bezier curves problem
Date: 15 Jul 2004 08:06:50
Message: <40f6735a$1@news.povray.org>

> i have some trouble with 'bezier' curves. same set of points used in 'prism'
> and in 'sphere_sweep' give not the same curve.

POV got different version of the same spline types internally. You will 
notice that quadratic splines won't behave the same way in lathes and in 
function splines ( spline {} ). Don't know if that's the problem with 
your case but it could be.

HTH,
Florian

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