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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