"Ammar Al-Allak" <a.a### [at] ueaacuk> wrote...
> Hi
>
> Fromt what I understand, wave independent scattering is not physically
> accuarate since it doesn't take the wavelength into account, but to be
> honest
> I don't really understand the principal of that. (Some sort of a detailed
> explanation would help!!)

Making it fully wave-dependent would be nearly (if not fully) impossible,
because POV uses the RGB format to store all colors.  This means that the
specturm is discritized into three steps - red, green, and blue.  This
leaves very little information to be used by wavelength-dependent features.

However... scattering can be color-dependent.  Note that I say
color-dependent and not wavelength-dependent... they are different.  Used
properly, you can make color-dependent scattering look a whole lot like
wavelength-dependent scattering.  For example, some work has been done using
scattering type 4 to simulate earth's atmosphere (using scattering type 2
for clouds within the atmosphere).  Using a bluish color for scattering,
with an appropriate density and an extinction of 1.0 generates a nice blue
sky.  And when the light source (sun) is rotated around this virtual earth,
nice pink and red sunsets appear almost magically.  I did some tests a while
back (based on someone else's original code) and it worked very well (though
it was _very_ slow).

> I also need the precise algorithm POV Ray uses for Rayleigh scattering and
> how it could be modified so that it becomes Wave dependent.

The source code can be downloaded from www.povray.org.  That, plus the docs,
should be sufficient for determining the exact algorithm.

-Nathan

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