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!!)

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

I need this information asap PLEASE.

Thank you

Ammar

Post a reply to this message

"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

Post a reply to this message

where can one find these tests you did?

Nathan Kopp wrote:
> 
> "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

Post a reply to this message

"Nathan Kopp" <Nat### [at] Koppcom> wrote in message
news:39a9d1d7$1@news.povray.org...
>
> 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).

Can you point me to where I might find any examples of what you describe
here?

Thanx..

Post a reply to this message