If you have a torus with minor>major, you get a big ugly hole chopped
out of the center. Shouldn't it just be like a torus without a hole,
like a red blood cell sort of thing?

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Larry Fontaine <lfo### [at] isdnet> wrote:
> If you have a torus with minor>major, you get a big ugly hole chopped
> out of the center. Shouldn't it just be like a torus without a hole,
> like a red blood cell sort of thing?
>

It should.

A torus created by a "quartic"-statement renders ok.

Since "torus" uses the same polynomial root solver, the problem
probably lies in the intersection calculation of the bounding volume.

(I had no time to take a peek at the source, but the docs say a cylindrical
ring is used; maybe the author of the code forgot to make provisions for
the case of minor > major.)

Gerald

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I have not tested it, but I would bet that the problem is in the bounding.
  If I remember correctly, a torus is bounded with the difference of a
cylinder and a smaller cylinder. If the minor radius of the torus is greater
than the major radius, the inner cylinder will have a negative radius (instead
of havin a radius 0 as it should).

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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On 17 Oct 1999 06:05:58 -0400, Nieminen Juha
<war### [at] punarastascstutfi> wrote:

>  I have not tested it, but I would bet that the problem is in the bounding.
>  If I remember correctly, a torus is bounded with the difference of a
>cylinder and a smaller cylinder. If the minor radius of the torus is greater
>than the major radius, the inner cylinder will have a negative radius (instead
>of havin a radius 0 as it should).

A torus is bounded by two open cylinders and two capping discs with
holes. If minor > major then the hole of a capping discs would be
greater than its radius. Also, the inner bounding cylinder would
become outer and vice versa, which might pose some "insidedness"
problems.


Peter Popov
ICQ: 15002700

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Larry Fontaine wrote:
> 
> If you have a torus with minor>major, you get a big ugly hole chopped
> out of the center. Shouldn't it just be like a torus without a hole,
> like a red blood cell sort of thing?

I have seen this and as others have suggested, it is a bounding problem.
Simply bound it with sphere{ 0,major+minor }

Cheers, PoD.

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In article <380922BD.C98E15DF@isd.net> , Larry Fontaine <lfo### [at] isdnet>
wrote:

> If you have a torus with minor>major, you get a big ugly hole chopped
> out of the center. Shouldn't it just be like a torus without a hole,
> like a red blood cell sort of thing?

Yes, I can reproduce your problem, here is a sample scene. It should show a
strange dark spot near the center of the torus. (Crossposted to POV-Ray
bugreports.)


#version 3.1;

camera
{
  location  <0.0, 5.5, -0.5>
  direction 1.5*z
  right     4/3*x
  look_at   <0.0, 0.0,  0.0>
}

light_source
{
  <-30, 30, -30>
  color red 1.0  green 1.0  blue 1.0
}

plane { y, -1 pigment {color rgb <0.7,0.5,0.3>}}

torus
{
  0.8,
  1.0
  texture {pigment {radial frequency 8} finish{specular 1}}
}




    Thorsten


____________________________________________________
Thorsten Froehlich
e-mail: mac### [at] povrayorg

I am a member of the POV-Ray Team.
Visit POV-Ray on the web: http://mac.povray.org

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Thorsten Froehlich wrote:
> 
> In article <380922BD.C98E15DF@isd.net> , Larry Fontaine <lfo### [at] isdnet>
> wrote:
> 
> > If you have a torus with minor>major, you get a big ugly hole chopped
> > out of the center. Shouldn't it just be like a torus without a hole,
> > like a red blood cell sort of thing?
> 
> Yes, I can reproduce your problem, here is a sample scene. It should show a
> strange dark spot near the center of the torus. (Crossposted to POV-Ray
> bugreports.)

Is it really a bug when you try to make a torus something other than a torus ?

-- 
Ken Tyler -  1100+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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How is that not a torus? A torus is defined simply as the solid formed by rotating
a circle around a circular path which is perpindicular to the plane of the circle.

Ken wrote:

> Thorsten Froehlich wrote:
> >
> > In article <380922BD.C98E15DF@isd.net> , Larry Fontaine <lfo### [at] isdnet>
> > wrote:
> >
> > > If you have a torus with minor>major, you get a big ugly hole chopped
> > > out of the center. Shouldn't it just be like a torus without a hole,
> > > like a red blood cell sort of thing?
> >
> > Yes, I can reproduce your problem, here is a sample scene. It should show a
> > strange dark spot near the center of the torus. (Crossposted to POV-Ray
> > bugreports.)
>
> Is it really a bug when you try to make a torus something other than a torus ?
>
> --
> Ken Tyler -  1100+ Povray, Graphics, 3D Rendering, and Raytracing Links:
> http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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Larry Fontaine wrote:
> 
> How is that not a torus? A torus is defined simply as the solid formed by rotating
> a circle around a circular path which is perpindicular to the plane of the circle.

Tell me oh bright young one what advantage if any is there in trying
to make the lesser radius larger than the greater radius ?

What do you hope to achieve anyway ?

Why are you bucking the system ?

Where is my other sock ?

Got milk ?

-- 
Ken Tyler -  1100+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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> Got milk ?

Or, as the slogan ran when translated (into Spanish I think): "Are you
lactating?"

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