"And" <49341109@ntnu.edu.tw> wrote:
> "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?

Oh, sorry, it was not a division. I ment density1 for media1. I should have said
media1_density1, media1_density2, and so forth.

B.

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