This question applies to 3.5...

So, what exactly the "Fresnel reflectivity function?" What sort of
calculations are going on with this? And it seems to create variable
reflection... is this more accurate than normally specifying two reflection
values? I'm just wondering what this keyword is really *doing*...

- Slime
[ http://www.slimeland.com/ ]
[ http://www.slimeland.com/images/ ]

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Fresnel reflection is a realistic type of variable reflection.  The fresnel
reflection model uses the ior of the material to calculate the reflection of
light which, AFAIK, is how the physics of light works. I'm sure others have
more in-depth explainations for you.  I use pretty much exclusively fresnel
reflection now , mostly because it is more realistic and it save me from
figuring out what I think is realistic.

-tgq


"Slime" <noo### [at] hotmailcom> wrote in message
news:3bec5708$1@news.povray.org...
> This question applies to 3.5...
>
> So, what exactly the "Fresnel reflectivity function?" What sort of
> calculations are going on with this? And it seems to create variable
> reflection... is this more accurate than normally specifying two
reflection
> values? I'm just wondering what this keyword is really *doing*...
>
> - Slime
> [ http://www.slimeland.com/ ]
> [ http://www.slimeland.com/images/ ]
>
>

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Slime wrote:
> 
> This question applies to 3.5...
> 
> So, what exactly the "Fresnel reflectivity function?" What sort of
> calculations are going on with this? And it seems to create variable
> reflection... is this more accurate than normally specifying two reflection
> values? I'm just wondering what this keyword is really *doing*...
> 

Have a look at:

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/freseq.html
http://dustbunny.physics.indiana.edu/~dzierba/P360n/KPAD/Exps/Fresnel/fresnelnote.pdf

Normal variable reflection has a linear transit between min and max
according to the cosine of the angle, if you use a higher falloff value
you can get pretty much similar results, but note that the fresnel model
depends on the ior of the material.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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Probably I'm wrong, but shouldn't a *fresnel material* have its diffuse
value dependant on that angle too?

--
Jonathan.

"Christoph Hormann" <chr### [at] gmxde> ha scritto nel messaggio
news:3BECE593.4083C4F5@gmx.de...
>
>
> Slime wrote:
> >
> > This question applies to 3.5...
> >
> > So, what exactly the "Fresnel reflectivity function?" What sort of
> > calculations are going on with this? And it seems to create variable
> > reflection... is this more accurate than normally specifying two
reflection
> > values? I'm just wondering what this keyword is really *doing*...
> >
>
> Have a look at:
>
> http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/freseq.html
>
http://dustbunny.physics.indiana.edu/~dzierba/P360n/KPAD/Exps/Fresnel/fresne
lnote.pdf
>
> Normal variable reflection has a linear transit between min and max
> according to the cosine of the angle, if you use a higher falloff value
> you can get pretty much similar results, but note that the fresnel model
> depends on the ior of the material.
>
> Christoph
>
> --
> Christoph Hormann <chr### [at] gmxde>
> IsoWood include, radiosity tutorial, TransSkin and other
> things on: http://www.schunter.etc.tu-bs.de/~chris/

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JRG wrote:
> 
> Probably I'm wrong, but shouldn't a *fresnel material* have its diffuse
> value dependant on that angle too?
> 

What angle? Angle of light or angle of view.  

In fact it's the definition of diffuse reflection that the appearance is
independent of the viewing angle.  Of course there are rarely perfectly
diffuse materials.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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