In article <3d4d152e@news.povray.org>,
 "Gail Shaw" <gai### [at] mwebcoza> wrote:

> I have a scene with a plane, sphere, transparent  hollow box (rgbf 1) 
> and ground fog. If the fog has turbulence then the box is partially 
> visible and casts a shadow. If the fog has no turbulence then the box 
> just casts a shadow. If the fog is removed then box is not visible 
> and casts no shadow (this is what I would expect in all three cases)

The turbulence part is just a side-effect of the way fog is calculated. 
It is a "cheat" that really doesn't simulate the real world very well, 
but is fast to calculate. The turbulence is a 2D effect that depends on 
the beginning location of the ray, not a 3D variation in density which 
would require sampling like media. Not sure what's causing the shadow...

It might be possible to fix this: if the shape is non-refracting and 
totally transmitting (like a media container that shouldn't be visible), 
skip intersections with it and use the next shape out for the fog 
calculations. Wouldn't work if it or that next shape has a partially 
transparent texture or ior, but it would take care of media containers.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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