This is the picture

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Attachments:
Download 'bugreport_1.png' (22 KB)

Preview of image 'bugreport_1.png'

And here is the scene file:

http://news.povray.org/povray.binaries.scene-files/thread/%3Cweb.551e94cd7c9493f713709ea20%40news.povray.org%3E/

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I made two animations about this.
https://www.youtube.com/watch?v=PKpVpUucw3g

The second is the same camera setting, but just this object:
torus{
-0.01247, 0.02357
rotate <-90,0,0>
pigment{rgb<0.34,0.38,0.12>}
}


https://www.youtube.com/watch?v=8Pj7F41Tfyo

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On 04/03/2015 09:16 AM, And wrote:
> This is the picture

I've found tori to be artifact-prone whenever the major radius is less 
than the minor radius.  With negative major R, I've gotten bounding 
artifacts.  With zero major R, the entire object is one big coincident 
surface artifact.  With major R less than half minor r, I get artifacts 
with CSG merge, although I have found a workaround for my particular 
situation.  I suspect that this last artifact can show up with r > R > 
r/2, but I haven't tried to come up with such a scenario.

These problems are probably due to the way the polynomial object works. 
  (The torus primitive is nothing more than a garden variety polynomial, 
with some optimized bounding.)

Have you tried the sturm keyword?  (I'm really sleepy now, and haven't 
yet looked at your code.)

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Cousin Ricky <ric### [at] yahoocom> wrote:
> On 04/03/2015 09:16 AM, And wrote:
> > This is the picture
>
> I've found tori to be artifact-prone whenever the major radius is less
> than the minor radius.  With negative major R, I've gotten bounding
> artifacts.  With zero major R, the entire object is one big coincident
> surface artifact.  With major R less than half minor r, I get artifacts
> with CSG merge, although I have found a workaround for my particular
> situation.  I suspect that this last artifact can show up with r > R >
> r/2, but I haven't tried to come up with such a scenario.
>
> These problems are probably due to the way the polynomial object works.
>   (The torus primitive is nothing more than a garden variety polynomial,
> with some optimized bounding.)
>
> Have you tried the sturm keyword?  (I'm really sleepy now, and haven't
> yet looked at your code.)

Ok, thank you. I will test it tomorrow.

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intersection{
    torus{
    0.01247, 0.02357
    rotate <-90,0,0>
    inverse
    }
    sphere{
    <0,0,0>,0.02
    }
pigment{rgb<0.34,0.38,0.12>}
}

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Attachments:
Download 'poly torus_1.png' (24 KB)

Preview of image 'poly torus_1.png'

#macro Poly_Torus(_major_r, _minor_r)
#local R = _major_r;
#local r = _minor_r;

#local poly_obj =
polynomial{
4,
xyz(4,0,0):1,
xyz(0,4,0):1,
xyz(0,0,4):1,
xyz(2,2,0):2,
xyz(0,2,2):2,
xyz(2,0,2):2,
xyz(2,0,0):-2*R*R - 2*r*r,
xyz(0,2,0):-2*R*R - 2*r*r,
xyz(0,0,2):2*R*R - 2*r*r,
xyz(0,0,0):pow(R*R - r*r,2),
}
poly_obj
#end




intersection{
    sphere{
    <0,0,0>,0.02
    }
    object{
    Poly_Torus(0.01247, 0.02357)
    inverse
    }
pigment{rgb<0.34,0.38,0.12>}
}

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Attachments:
Download 'poly torus_2.png' (26 KB)

Preview of image 'poly torus_2.png'

On 07/04/2015 17:28, And wrote:
> intersection{
>      sphere{
>      <0,0,0>,0.02
>      }
>      object{
>      Poly_Torus(0.01247, 0.02357)
>      inverse
>      }
> pigment{rgb<0.34,0.38,0.12>}
> }

I liked the shape and decided to animate it rotating.
http://youtu.be/frVgXyupZX8

I am not too sure about the shading. It is as if the normals flipped 
from one half to the other.
The material is a spiral1 pigment with a colour map.

To straighten the spiral I changed your code to:

intersection {
	torus {
		0.012470,0.023570
		sturm
		texture{ Spiral_Texture }
		rotate    <-90.0,0.0,0.0>
		}

	sphere {
		0.0, 0.020000
		}

	scale     <200.0,200.0,200.0>

		}


I'm not sure why putting the texture on the torus straightens it out.

-- 

Regards
     Stephen

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Stephen <mca### [at] aolcom> wrote:
> On 07/04/2015 17:28, And wrote:
> > intersection{
> >      sphere{
> >      <0,0,0>,0.02
> >      }
> >      object{
> >      Poly_Torus(0.01247, 0.02357)
> >      inverse
> >      }
> > pigment{rgb<0.34,0.38,0.12>}
> > }
>
> I liked the shape and decided to animate it rotating.
> http://youtu.be/frVgXyupZX8
>
> I am not too sure about the shading. It is as if the normals flipped
> from one half to the other.
> The material is a spiral1 pigment with a colour map.
>
> To straighten the spiral I changed your code to:
>
> intersection {
>  torus {
>   0.012470,0.023570
>   sturm
              here lack of inverse
>   texture{ Spiral_Texture }
>   rotate    <-90.0,0.0,0.0>
>   }
>
>  sphere {
>   0.0, 0.020000
>   }
>
>  scale     <200.0,200.0,200.0>
>
>   }
>
>
> I'm not sure why putting the texture on the torus straightens it out.
>
> --
>
> Regards
>      Stephen


.. this is what I rendered.

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Attachments:
Download 'torus test2 1.png' (168 KB)

Preview of image 'torus test2 1.png'

And the polynomial version:

It is still there, but not so visible.

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Attachments:
Download 'torus test2 1 poly.png' (182 KB)

Preview of image 'torus test2 1 poly.png'