On Sun, 15 Nov 1998 23:25:26 +0200, Basil S. Lewis, MD. 
	<lew### [at] txtechnionacil> wrote:
>I am now learning optics in school, and would like to point out the
>following optic errors in POV-Ray. I don't know how realistic pov is
>supposed to get, but I hope that one day these errors will be fixed.

I think "errors" is a bit too strong of a word to describe some
fundamental flaws in the raytracing model.  These are not bugs,
btw, so this discussion should be in .general (note followups)

>1) When I use media/atmospheric light effects, I don't see the light
>curving when it goes through lens. It keeps going the way it did.

The reason this happens is that raytracing traces a ray from the eye 
back to the light.  Since light can travel by many routes, it's impossible
for a raytracer to determine all of the possible routes by which light
could have arrived at the point for which it is determining the illumination.

There is a simulation of refractive caustics built in to POV, but it's 
likely not accurate enough to do optics experiments with.  There are 
statistical methods for doing this sort of thing relatively efficiently
as well, but so far none of them are available for POV.

>2) When I make a wall split to two by a small hole along its height, and
>point a light on to it, and then put a board behind, the light just
>projects a staight line (as we would expect) but does not show the wave
>property effects of light. This effect should produce dark areas across
>the board.

POV also doesn't accurately simulate some other properties of light.  For 
example: variable IOR by frequency (chromatic aberration), fluorescence, 
phosphorescence, and polarization. Nor can it simulate materials with 
spatially varying IOR. There are just some things we shouldn't expect 
from a program whose main purpose is, after all, creating pretty pictures.

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Are we talking refraction here, ie splitting light into its componat colors?

I tried this a whil ago, and failed to achive results, can this be
simulated? - without texture maps which kinda defeat the object?

also will this be implamented in a future version of POV (not like right
now, but at somepoint down the road?)

Rick

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On Wed, 18 Nov 1998 00:40:30 -0000, Rick <kit### [at] dialpipexcom> wrote:
>Are we talking refraction here, ie splitting light into its componat colors?
>
>I tried this a whil ago, and failed to achive results, can this be
>simulated? - without texture maps which kinda defeat the object?

It can be simulated, but only on direct viewing through the prism or 
other transparent object.  In other words, you won't be able to do
the album cover from "Dark Side of the Moon".

There's a fairly good treatise on modifying POV 3.02 to do dispersion
effects at http://www.newcolor.com/darenw/dswpov/disp.html , though I
wouldn't recommend trying it unless you're relatively familiar with 
the guts of POV.  There's also an include file somewhere that simulates
dispersion, also for version 3.0x, but I don't have a URL for that 
handy.

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>You need to specify "ior" to see such effects.


I don't think it's that simple. In POV, beams of light will
not be bended by refraction as far as I know.
Point two: the wave-effect (interference) cannot be realised
in a standard way. You'll have to simulate this effect,
since POV doesn't use wavelengths for the different colors
of light... in fact, it doesn't 'think' of light beams as
being waves, but as straight lines.

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Here's the address to my links page with spectrar.inc there, if that's what is 
mentioned below:

  http://members.aol.com/inversez/index.html

There's an example picture near the bottom, click on that.
Daren Wilson was the reference for making it. He already had a working script 
which produced a good example of the spectral dispersion effect. I added more 
colors to blend and used proxy real-world wavelengths for the spectral 
characteristics (none of this is science, by the way, in the sense that 
POV-Ray is not pure physics-based in the department of light to begin with 
from what I understand, rather the product of realism is probable if enough 
additions were to be used to sort out the rough draft of the ray-tracer). I 
tried for reflection color dispersion too and only got an intolerably slow 
render, no reflection changes visible.
This does NOT work in POV-Ray 3.1*, even with semi-colons ;)

Message <3652cabc.0@news.povray.org>, Ron Parker typed...
>
>On Wed, 18 Nov 1998 00:40:30 -0000, Rick <kit### [at] dialpipexcom> wrote:
>>Are we talking refraction here, ie splitting light into its componat colors?
>>
>>I tried this a whil ago, and failed to achive results, can this be
>>simulated? - without texture maps which kinda defeat the object?
>
>It can be simulated, but only on direct viewing through the prism or 
>other transparent object.  In other words, you won't be able to do
>the album cover from "Dark Side of the Moon".
>
>There's a fairly good treatise on modifying POV 3.02 to do dispersion
>effects at http://www.newcolor.com/darenw/dswpov/disp.html , though I
>wouldn't recommend trying it unless you're relatively familiar with 
>the guts of POV.  There's also an include file somewhere that simulates
>dispersion, also for version 3.0x, but I don't have a URL for that 
>handy.

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/POVring.html
=Bob

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Well, there's a new patch up at patch station for just this problem.  Its
called dswpov.  Check it out

Http://www.twysted.net/patchstation/

KillFile

"Basil S. Lewis, MD." wrote:

> noa### [at] writemecom
>
> I am now learning optics in school, and would like to point out the
> following optic errors in POV-Ray. I don't know how realistic pov is
> supposed to get, but I hope that one day these errors will be fixed.
>
> 1) When I use media/atmospheric light effects, I don't see the light
> curving when it goes through lens. It keeps going the way it did.
> Morever, if I point a beam into lens and watch where the beam falls on
> the other side, I see that the light kept going as if it wasn't
> affected. Only if I point the camera at the lens do I see the object
> behind the lens in the right way.
>
> 2) When I make a wall split to two by a small hole along its height, and
> point a light on to it, and then put a board behind, the light just
> projects a staight line (as we would expect) but does not show the wave
> property effects of light. This effect should produce dark areas across
> the board.
>
> I love POV, like all of us, and would love to see it beat nature ;)
>
>  - Noam Lewis
> noa### [at] writemecom

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In article <36504c4d.0@news.povray.org>, par### [at] my-dejanewscom wrote:

> There are just some things we shouldn't expect 
> from a program whose main purpose is, after all, creating pretty pictures.

I tried to use POV-ray to make a scene for an optics exam question, and
noticed the same thing: shadows are not influenced by the index of
refraction. I understand your explanation why this would be very difficult
to program, but it would be nice to include a remark on this in the
documentation.
-- 
Pie### [at] itnhhse        http://www.hh.se/staff/piku/

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On Sun, 10 Jan 1999 16:18:16 +0100, Pie### [at] itnhhse (Pieter
Kuiper) wrote:

>I tried to use POV-ray to make a scene for an optics exam question, and
>noticed the same thing: shadows are not influenced by the index of
>refraction. I understand your explanation why this would be very difficult
>to program, but it would be nice to include a remark on this in the
>documentation.

You mean like the documentation in the "faked caustics" section of the
manual?

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That was a way of putting it..

"Ronald L. Parker" wrote:
> 
> On Sun, 10 Jan 1999 16:18:16 +0100, Pie### [at] itnhhse (Pieter
> Kuiper) wrote:
> 
> >I tried to use POV-ray to make a scene for an optics exam question, and
> >noticed the same thing: shadows are not influenced by the index of
> >refraction. I understand your explanation why this would be very difficult
> >to program, but it would be nice to include a remark on this in the
> >documentation.
> 
> You mean like the documentation in the "faked caustics" section of the
> manual?

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Those who care about real caustics should check out my recent post in
povray.binaries.images.  The images there were made with a (very pre-alpha)
unofficial version of POV-Ray.  By the end of this spring semester I should
have a good solid version available (probably beta versions before that). I'm
doing this as a directed study for my undergraduate degree in CS.

-Nathan

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