I have begun on my first POV-RAY rendering and seem to be at an impasse
An element I wish to use involved concentrating some spotlights on a highly
reflective sphere. The spotlights more than illuminate the sphere, but the
light does not bounce off of the sphere. Checking the documentation, I
happened upon this very sad passage:


"POV-Ray and most other ray-tracers can only simulate directly light which
comes directly from actual light sources. Light coming from other objects
such as mirrors via specular reflection (such as shining a flashlight onto a
mirror for example) cannot be simulated."


Does this mean no Disco Mirror Balls? No bouncing lasers off mirrors? No
scattering light of broken mirror shards?

Have I missed something very simple, or is the sad truth that light really
can't be reflected off of reflective surfaces?

Thanks,
-Dave

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Whine, moan, complain. Yes it is true. Be glad it is so
for your images would take not minutes or hours but
days and months to calculate all of the additional reflected
rays in a scene. It's kinda sad as you point out but most
people are happy with the current system and the time
is saves in the process.

Ken Tyler

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Then what's Radiosity?

Ken wrote:

> Whine, moan, complain. Yes it is true. Be glad it is so
> for your images would take not minutes or hours but
> days and months to calculate all of the additional reflected
> rays in a scene. It's kinda sad as you point out but most
> people are happy with the current system and the time
> is saves in the process.
>
> Ken Tyler

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It is a different process completely and will not achieve
the properties the original poster was talking about.

(The same yet different ?)

Ken Tyler

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Well, it will do some of what the original poster would want, I would
think.  At least you get some light bouncing around with radiosity.

Interesting dillema though.  Am I the only one that when walking into a
well-lighted room starts thinking about all those rays bouncing around?
I think if everyone thought about it that question wouldn't be asked
quite so often.

-Mike

Ken wrote:

> It is a different process completely and will not achieve
> the properties the original poster was talking about.
>
> (The same yet different ?)
>
> Ken Tyler

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Dave Mann <dcm### [at] i-americanet> wrote:
: Does this mean no Disco Mirror Balls? No bouncing lasers off mirrors? No
: scattering light of broken mirror shards?

: Have I missed something very simple, or is the sad truth that light really
: can't be reflected off of reflective surfaces?

  You should read some documentation about raytracing, what you can do with
it and what you can't. Raytracing is not a perfect technique to model the
real world. I don't know if there is any.
  For example, with raytracing it's extremely difficult, if not impossible
to model area lights (area lights in povray are not true area lights as you
can read from the docs), reflective and refractive caustics, etc.
  You should think about how raytracing works and try to understand why
it's almost impossible to model caustics with it.
  There are other techniques to model area lights and caustics, for example
radiosity and photon mapping, but I don't know if they are very appliable
to a raytracing engine (ok, radiosity is, but I don't know about the
photon mapping).

-- 
main(i){char*_="BdsyFBThhHFBThhHFRz]NFTITQF|DJIFHQhhF";while(i=
*_++)for(;i>1;printf("%s",i-70?i&1?"[]":" ":(i=0,"\n")),i/=2);} /*- Warp. -*/

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It is not _almost_ impossible to create caustics with the standard
raytracing model - it's just impossible.
Both (true) radiosity and photon mapping should be applicable to a
raytracing engine. I am not sure if they can be applied to POV without
fundamental changes; I believe both would require some kind of surface
meshing.
POV's radiosity is not "true" radiosity - it uses a raytracing approach
to simulate radiosity effects and does no energy balancing of the scene.
I would love to have true caustics in POV, even if my scenes would take
days to render. They fundamentally increase the realism of many scenes
(and they look cool).

Margus

Nieminen Mika wrote:
 
>   You should read some documentation about raytracing, what you can do with
> it and what you can't. Raytracing is not a perfect technique to model the
> real world. I don't know if there is any.
>   For example, with raytracing it's extremely difficult, if not impossible
> to model area lights (area lights in povray are not true area lights as you
> can read from the docs), reflective and refractive caustics, etc.
>   You should think about how raytracing works and try to understand why
> it's almost impossible to model caustics with it.
>   There are other techniques to model area lights and caustics, for example
> radiosity and photon mapping, but I don't know if they are very appliable
> to a raytracing engine (ok, radiosity is, but I don't know about the
> photon mapping).
> 
> --
> main(i){char*_="BdsyFBThhHFBThhHFRz]NFTITQF|DJIFHQhhF";while(i=
> *_++)for(;i>1;printf("%s",i-70?i&1?"[]":" ":(i=0,"\n")),i/=2);} /*- Warp. -*/

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Margus Ramst wrote:

> POV's radiosity is not "true" radiosity - it uses a raytracing approach
> to simulate radiosity effects and does no energy balancing of the scene.

Not to mention that radiosity is a diffused reflection and
does not have incident angle reflection characteristics.

Ken Tyler

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Mike <Ama### [at] aolcom> wrote:
: Interesting dillema though.  Am I the only one that when walking into a
: well-lighted room starts thinking about all those rays bouncing around?

  Actually they are not rays, but waves.
  This may start a physics flame war, but a photon is not a particle but
a electromagnetic wave quantum (is that the right term? I have studied
physics only in finnish... :) ).
  Instead of thinking about the light as rays, think about it as if you
had a swimming pool full of water. When you make waves on the water,
the waves will bounce from the walls of the pool. At least I think about
it that way :)

-- 
main(i){char*_="BdsyFBThhHFBThhHFRz]NFTITQF|DJIFHQhhF";while(i=
*_++)for(;i>1;printf("%s",i-70?i&1?"[]":" ":(i=0,"\n")),i/=2);} /*- Warp. -*/

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I'd like to thank everyone who participated in this thread. Its been very
illuminating (but not reflective).

In less than 48 hours I've learn more about POV-Ray and its capabilities,
limitations, and functions because of the many web sites devoted to it and
these newsgroups. I've seen some astounding things and hope to contribute
something of value soon.

And yes... when I look around at the world now I am beginning to break
things down into its ray traced elements.

I'll have more questions I am sure. Thanks for answering this one!


-Dave

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