Am 08.11.2018 um 17:02 schrieb Shuffle:

> What I actually try to achieve is to model a planet with a dense atmosphere.
> Like Venus or, in my case, Saturn's moon Titan. The camera will approach the
> body and dive into the atmosphere, revealing the terrain only at lower
> altitudes.
> You can get a pretty good idea of what I'm trying to achieve by following this
> link: https://www.youtube.com/watch?v=9L471ct7YDo&t=55s

I've only found time now to completely read your original post.

I can guarantee you that in order to achieve what you're shooting for 
you /will/ have to cheat.

POV-Ray provides two mechanisms to deal with scattering material:

- The older mechanism, "media", only creates realistic results for cases 
where the mean free distance (the average distance a light ray travels 
before being scattered or absorbed) is larger than the distance between 
camera and object. (*)

- The newer mechanism, "subsurface light transport", only creates 
realistic results for cases where the mean free distance is 
significantly smaller than the dimensions involved. (Besides, it 
requires the material to have a clear-cut surface.)

In a camera dive into the atmosphere of a densely clouded planet down to 
the surface, you are transitioning from the regime where the mean free 
distance is comparatively small to the regime where it is comparatively 
large.


The easiest solution is probably to create two entirely separate 
animation sequences: One that takes you from orbit into dense atmosphere 
(with the planet invisible), and another one that takes you from dense 
atmosphere down to the surface (with the sky invisible).

The trick then will be to match the colour of the first animation's last 
frame to the second animation's first frame - or simply do a slow fade 
between the two animations.


(*) The problem is not so much that you can't use scattering media to 
obscure objects inside it - you can, all you have to do is crank up the 
density / colour high enough. The true problem is the scattering effect, 
which will go bonkers at such high settings, even if you mess with the 
extinction setting and/or add extra absorbing media.

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