Index of Refraction (IOR)
Thomas Tatum
Does anyone know the IOR of Linoleum?
Thanks,
--
Thomas B Tatum
http://www.cs.clemson.edu/~tatum/tatum.html
Thomas...@eng.clemson.edu
Mark E. Rekai
: Does anyone know the IOR of Linoleum?
Unless there is some sort of clear linoleum that I have never seen or
heard of, there is no IOR for it. A material must transmit (light light
pass though it) light before it can be refracted.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
The probability of anything happening is in inverse ratio to its
desirability.
--John W. Hazard, "Changing Times" 1957
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Thomas Brooks Tatum
>
> Thomas Tatum (tta...@harley.eng.clemson.edu) wrote:
>
> : Does anyone know the IOR of Linoleum?
>
> Unless there is some sort of clear linoleum that I have never seen or
> heard of, there is no IOR for it. A material must transmit (light light
> pass though it) light before it can be refracted.
How about this,
Does anyone know the IOR of a thin layer of floor wax? Or a thin layer of
that transparent plastic that linoleum is processes with?
Thanks,
Thomas
Robert J. MacG. Dawson
>From: tta...@harley.eng.clemson.edu (Thomas Tatum)
>Subject: Index of Refraction (IOR)
>Date: 21 Jan 1995 16:55:50 GMT
>Thanks,
>--
I suspect the short answer is "no". But why the heck are you trying to
render transparent linoleum? IOR is only active on *transmitted* rays - which
there aren't with any linoleum I've ever had the pleasure of walking on :-)
For opaque materials, you don't need it.
This seems to be a widespread hangup. Somebody recently posted an enormous
list of The IOR Of Practically Everything, to 5 decimal places. For
diligence: A. For public-spiritednesss, three cheers and a tiger. But really -
you don't need to go to all that trouble to get realistic raytracing! Almost
everything has an IOR between 1.4 and 2, and the eye doesn't really
distinguish fine gradations. If you use the following rough table you'll be
pretty much safe:
Vacuum: 1 exactly by definition
Air, gases: 1.001: *just* visible if you have a bubble of air in vacuum,
hard-edged and viewed almost tangentially.
'Thin-looking' liquids like gasoline: 1.2-1.3
Water, light plastics: 1.4
Glass, salt, plastic,fluorite, quartz, practically everything: 1.5-1.6
Heavy glasses, precious stones: 1.7-1.8
Cubic zirconia: 2.2
Diamond: 2.5
"Super-diamond" gemstones (mostly imaginary) - what you will!
If you're out by +- .05 at the lower end of the scale, or +- .2 at the upper
end, it really won't be visible. What will be visible in the flashier stones
is the lack of chromatic dispersion, which can't be raytraced effectively
anyhow (though it might be faked with cunningly placed filters inside the stone
or little banks of colored spotlights to cast rainbows on the wall!)
As for refractive indices of rubber, asphalt, linoleum, malachite, ivory,
mud, and other opaque materials: these do turn up in places like the Rubber
Bible, but they are either measured indirectly or, more likely, they are
measured for infrared radiation rather than visible light. They have no
practical value for raytracing. With these materials you won't want any filter
component in your pigment anyhow, so any IOR value you give will be ignored by
the software...
Robert Dawson
Math & CS
Saint Mary's University
Haliufax, NS, Canada
Marty L. Rabens
: end, it really won't be visible. What will be visible in the flashier stones
: is the lack of chromatic dispersion, which can't be raytraced effectively
: anyhow (though it might be faked with cunningly placed filters inside the stone
: or little banks of colored spotlights to cast rainbows on the wall!)
Just out of (admittedly uneducated) curiosity, could the effect of chromatic
dispersion be faked if the raytracer allowed for separate ior's for red, green,
and blue? I'm not talking about producing a scientifically accurate image,
just achieving the effect.
Marty
Marty L. Rabens
: anyhow (though it might be faked with cunningly placed filters inside the stone
: or little banks of colored spotlights to cast rainbows on the wall!)
Just out of (admittedly uneducated) curiosity, could the effect of chromatic
dispersion be faked if the raytracer allowed for separate ior's for red, green,
and blue? I'm not refering to a scientifically accurate image, here, just the
effect.
Marty
Llew Mason
: Thomas Brooks Tatum <tta...@hubcap.clemson.edu> wrote:
: >max...@oasis.ot.com (Mark E. Rekai) wrote:
: >>
: >> Thomas Tatum (tta...@harley.eng.clemson.edu) wrote:
: >>
: >> : Does anyone know the IOR of Linoleum?
: >>
: >> Unless there is some sort of clear linoleum that I have never seen or
: >> heard of, there is no IOR for it. A material must transmit (light light
: >> pass though it) light before it can be refracted.
Hmm.. last time I heard, copper wasn't too see-through either, but it
certainly has an index of refraction. Index of refraction is the ratio
of the speed of electro-magnetic waves in a vacuum to the speed of
electro-magnetic waves in the material.
(as an aside, electro-magnetic waves don't pass through copper too
well, since it is a conducter... but that is besides the point.)
Just because _visible_ light has problems passing through it, doesn't
have anything to do with it.
In fact, most advanced shading models (include Cook-Torrance) utilise
the IOR of the material for specular reflection calculations.
cya
Llew Mason
Albert Goodman
You might find a useable value for some equivalent material (perhaps gelatin?) in
Sven-Erik Andersen's extensive IOR_PLUS.INC file. It can be found via WWW at
http://www.oslonett.no/home/svenerik/ior_plus.html
He also posts the latest version regularly in this group, if I rememebr correctly.
******************************************************************************
* Albert Goodman e-mail: agoo...@deakin.edu.au *
* School of Computing and Mathematics *
* Deakin University _--_|\ *
* Clayton / \ *
* Victoria \_.--.*/ *
* AUSTRALIA 3168 v *
******************************************************************************