"Kirk Andrews" <kir### [at] tektonartcom> wrote:
> So I'm continuing on my acquaintance with media.  I have this scene where I have
> a large sphere with sparse media which acts as atmosphere.  Then, I add an oval
> which contains much denser media in order to make a cloud (which is within the
> large sphere, of course).  I'm happy with the results of either media when used
> independently, but in this picture you can clearly see the outline of the oval...

Like others here, I've been grappling with this conundrum for a long time. Based
on *lots* of tests and experiments, I've come to some conclusions:

1) When there are two media objects, one inside the other (like your cloud oval
inside your atmosphere), the larger enclosing sphere's media samples value
completely overrides the smaller sphere's (and, I believe, its method and
intervals as well.) You can test this by giving your cloud media samples 1000,
and your atmosphere samples 1.  It will render lightning fast--and look
terrible! Reverse the order, and BOTH spheres' media take on samples 1000. Or
more generally, both spheres' medias seem to be treated as one, samples-wise.
This has caused me grief in the past, when I actually *wanted* the smaller
sphere to have a smaller samples count, just for the look.  But it can't be
done, unfortunately. As others have mentioned, the best (and only?) way of
eliminating or minimizing the small sphere's "visibility" is to keep pumping up
the samples count--in the larger enclosing sphere's media.

2)  When using two or more medias in a single interior statement (in a single
sphere, of course), there is a similar limitation.  Consider this:

interior{
     media #1{ pattern, samples, density, etc....}
     media #2 {pattern, samples, density, etc....}
        }

In this case, media #2's samples completely override those in media #1. I.e.,
the final media samples override the one(s) before it. But on the upside, there
is no 2nd sphere shape "outline" to have to worry about.  And the two medias can
be translated within the sphere relative to each other, to a degree. With
appropriate color_maps for each media's density, and some media translations,
you might be able to get both your cloud(s) and atmophere this way, in one
sphere. Certainly not as easy as using two spheres, though!

Ken W.

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