Alain,

First of all, you definitely should win tonight's prize for fastest response
(8 minutes!).

It never would have occurred to me to add the "hollow" keyword; I thought a
disc was supposed to be infinitely thin and that "hollow" wouldn't apply.

But sure enough, once I added "hollow" to the disc definition, the problem
disappeared. Thanks!


"Alain" <aze### [at] qwertygov> wrote in message
news:405f9e9a$1@news.povray.org...
> Scott Gammans nous apporta ses lumieres ainsi en ce 2004/03/22 21:10... :
>
> >I created a model of Saturn using a disc for the rings, but I kept
running
> >into a strange problem that I'm wondering if it's a bug.
> >
> >To depict the gas giant's atmosphere, I added type 4 scattering media to
the
> >planet sphere to give a little pale yellow glow at the edge of the
sphere.
> >But when I placed the camera either above or below the rings **inside**
the
> >outer radius of the rings, the scattering media on the sphere disappeared
on
> >the side of the disc that was the **opposite** of the disc's normal
vector.
> >
> >For instance, if I declared the rings disc like this:
> >
> >#declare Saturn_Rings =  disc {0, y, 4500, 2250 texture {...}}
> >
> >and I placed the camera at <0,-100,2500>, the atmospheric scattering on
the
> >edge of the Saturn sphere would disappear below the plane of the disc. If
I
> >reversed the vector like so:
> >
> >#declare Saturn_Rings =  disc {0, -y, 4500, 2250 texture {...}}
> >
> >and re-ran the render, the scattering edge would reappear below the plane
of
> >the disc, but it would disappear **above** the disc plane.
> >
> >I know I'm not declaring the media on the planet incorrectly, because the
> >problem went away when I substituted a very, very thin cylinder for the
disc
> >to depict the rings (the media on the sphere was visible no matter where
I
> >placed the camera).
> >
> >So, is this a known problem with the disc object and I missed it in the
> >documentation and the bug reports forum, or what? Thanks...
> >
> >
> >
> >
> Did you try to make your disk hollow?
> It looks like the disk is a piece cut out of a plane.
> #declare Saturn_Rings = disc {0, -y, 4500, 2250 texture {...}hollow}
>
> Alain
>
>

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