"Bruno Cabasson" <bru### [at] cabassoncom> wrote:
> "And" <49341109@ntnu.edu.tw> wrote:
> > "Bruno Cabasson" <bru### [at] cabassoncom> wrote:
> > >
> > > Besides, real atmosphere is a very complex thing, not easy to model, and
> > > real clouds are also quite complex and there are many kinds of them, each one
having a specific behaviour with li
gh
> t.
> >
> >
> > In fact, for a fully automatic volumn(cloud) renderer, it is not so different
> > between different kind of cloud. The main difference of them is the height, and
> > the shape(density map), and the average density(because a dense cloud needs more
> > multiple scattering)
> >
> > ice droplets and liquid water droplets have different phase function when
> > scatters light. but for a dense media(if light from sun light source collide
> > many times in the cloud) the difference of the final appearance is small.
> > And because water droplets almost never absorb light, represent the albedo of
> > cloud almost 1.0( between visible wavelength range), so it is seldom eliminated
> > in cloud, a light beam can collide hundred of times in a heavy cloud. You can
> > see this:
> >
http://news.povray.org/povray.binaries.utilities/message/%3Cweb.5bec15ae87bb2a51c8edf6b30%40news.povray.org%3E/#%3C
we
> b.
> > 5bec15ae87bb2a51c8edf6b30%40news.povray.org%3E
> >
> > This is the power(sp-radiance) at different level scattering output quantity.
> > Maybe you can say the most of it still concentrated at first level. But this is
> > an image contains a white cloud on the center, and the blue sky the other. It is
> >  the average sp-radiance on the whole image. If look at the cloud separately,
> > the multiple scattering part is the dominate.
> >
> > And I attach a comparison. The image contains three images I rendered one year
> > ago but should be the same (or similar) condition. They are 1 level, 3 level,
> > and 27 level scattering renders.
> > (up to down.)
> >
> >
> >
> >
> >
> >
> > "Bruno Cabasson" <bru### [at] cabassoncom> wrote:
> >

> > > the rest is the same values, except the sun power and the parmeters for the fog
> > > media. Colors are obtained automatically thanks to media, mainly the atmosphere
> > > with rayleigh scattering.
> > >
> > > Regards
> >
> > When I watch this I guess you use scattering "extinction" not 1, because if you
> > use correct extinction 1 and lacks of multiple scattering, your clouds
> > is impossible so white. finally you use 0.25. When I use POV-Ray rendering
> > cloud, I always find I need use filled lights or additional emission.
>
> Well... The fact is that I used exinction 0.25 for the cloud media for the
> renders I posted in this thread. But a value of 1 is supposed to the the only
> one realistic. I'll play with this, but I think it will not be dramatic.
>
> AKAIK, POV-Ray allows you to define several media within the same container
> (they add together), and several density functions for each of them (they
> multiply together). Therefore, you can complexify and enrich the model that way,
> at the expense of render time (and carbon footprint). I'll also play with this.
>
> interior
> {
>     // Media #1
>     media
>     {
>         <media1 parameters>
>         density
>         {
>             <media1/density1 function>
>         }
>         density
>         {
>             <media1/density2 function>
>         }
>
>         .../...
>
>         // Densities are multipled together for the current media
>     }
>
>     // Media # 2
>     media
>     {
>         <media2 parameters>
>         density
>         {
>             <media2/density1 function>
>         }
>         density
>         {
>             <media2/density2 function>
>         }
>
>         .../...
>
>         // Densities are multipled together for the current media
>     }
>
>     // More media
>
>     .../...
>
>     // Media contributions are added together
>
> }
>
> B.


Thanks. But I don't understand <media2/density1 function> mean.., the /
represent division?

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