"clipka" <nomail@nomail> wrote:
> "Tim Attwood" <tim### [at] anti-spamcomcastnet> wrote:
> > From a scientific point of view POV doesn't even attempt
> > to simulate actual RL scattering. Instead rays pass from
> > the camera through a media without bending or scattering.
>
> That's not quite true.
>
> What you describe is how POV-Ray goes about emissive and absorbing media. Also
> note that there's nothing complicated about simulating such media, as the only
> thing to take into account is the distance travelled, as well as the absorption
> or emission coefficient, respectively (though the coefficients can vary over
> space; numerical integration is used to account for this).
>
> With scattering media, POV-Ray *does* make some attempt to simulate RL
> scattering. It should be noted, however, that only first-order scattering is
> computed, making it a good approximation only for media with low scattering
> coefficients.
>
> The phase function of a medium is approximated by the different scattering
> types; I am not an expert on optics, but I guess the functions provide a fair
> amount of good approximations for RL phase functions, unless you want to
> simulate some sophisticated optical experiment.
>
> Theoretically, it should be no big deal to extend POV-Ray's scattering types
> with a user-specified phase function, but there's currently no interface in the
> SDL for that.

Thanks for the replies, they were really helpful.

Now for Rayleigh the phase function is close to what is found in the literature
multiplied by some normalizing constant (the equation in the literature is
0.75*(1.0 + Sqr(alpha)), POV-Ray uses 0.799372013 instead of 0.75), and for
Henyey-Greenstein it is identical.

However, for Mie scattering, there are angular functions that along with other
functions form the scattering phase matrix which is basically the equivalent of
the phase function. I was unable to find a simple phase equation (as exists in
POV-Ray) to define this process.

As such, it would be helpful to know the source of the phase equations for the
Mie scattering, and if possible (though this is much less important) the reason
for the normalizing constant in Rayleigh. Thanks a lot. Appreciate all your
help.

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