Hi!

Is there any technique implemented in POV-Ray (especially in version 3.1) that
makes use of coherence? If so, which kind of coherence (spatial, temporal) is used?

Thanks,

Andre Wesseling

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Andre Wesseling wrote:
> 
> Hi!
> 
> Is there any technique implemented in POV-Ray (especially in version 3.1) that
> makes use of coherence? If so, which kind of coherence (spatial, temporal) is used?
> 

I'm not sure what you mean with coherence, but in case you are talking
about quantum physics related effects ('coherent light'), raytracing in
general does not simulate such effects and photon mapping does not either
(although this could possibly be extended)

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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In article <1103_1011269679@news.povray.org> , Andre Wesseling 
<wes### [at] mathuni-muensterde>  wrote:

> Is there any technique implemented in POV-Ray (especially in version 3.1) that
> makes use of coherence? If so, which kind of coherence (spatial, temporal) is
> used?

Well, POV-Ray uses a ray-model of light and the little I know about the
effects you are asking about suggests they are based on a wave model.

The better question to ask is what physical effects POV-Ray can simulate
because not all physical models are feasible for efficient (or possible)
implementation of a ray-tracer:

So, what particular effect are you looking for?

    Thorsten

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Andre Wesseling <wes### [at] mathuni-muensterde> wrote:
: Is there any technique implemented in POV-Ray (especially in version 3.1) that
: makes use of coherence? If so, which kind of coherence (spatial, temporal) is used?

  Or are you talking about the techniques sometimes used in scanline rendering?
For example temporal coherence in an animation means, IIRC, "render only those
parts of the image which changed with respect to the previous frame".

  POV-Ray doesn't use any of these tricks.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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I meant coherence in the way Warp understood it. So I wanted to know:
- Does POV-Ray use any information of one frame to speed up calculation of
  the next frame while rendering an animation?
- Is a form of ray coherence used to speed up calculation?

My question was not intended towards physical effects based on coherence,
because I know that most ray tracers --including POV-Ray-- are using the particle
model of light, not the wave model. So, this question was about the software
engineering part of POV-Ray =).

Thanks for that fast replies,

Andre Wesseling

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On Thu, 17 Jan 2002 13:21:32 GMT, Andre Wesseling wrote:
> I meant coherence in the way Warp understood it. So I wanted to know:
> - Does POV-Ray use any information of one frame to speed up calculation of
>   the next frame while rendering an animation?

In general, no, but of course you can #write variables calculated in one
frame and #read them for the next frame, if your goal is to avoid doing
complex calculations in each frame or if your calculation is inherently
iterative.  Some include files out there (frex, smokegen) use this technique.

> - Is a form of ray coherence used to speed up calculation?

Some patterns do this.  Uppermost in my mind is the crackle pattern, which 
caches the centers for the most-recently-visited part of its perturbed 
lattice in case the next ray happens to hit the same part of the lattice.
This is much faster than recalculating the centers for each ray.

-- 
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbf 1}hollow interior{media{emission 3-T}}}#end 
Z(-x-x.2x)camera{location z*-10rotate x*90normal{bumps.02scale.05}}

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"Ron Parker" <ron### [at] povrayorg> wrote...
> > - Is a form of ray coherence used to speed up calculation?
>
> Some patterns do this.  Uppermost in my mind is the crackle pattern, which
> caches the centers for the most-recently-visited part of its perturbed
> lattice in case the next ray happens to hit the same part of the lattice.
> This is much faster than recalculating the centers for each ray.

Also, shadow calculations utilize a at least one cache to keep a
recently-used object around for quick intersection tests.

-Nathan

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Light buffers...


news:1103_1011269679@news.povray.org...
> Hi!
>
> Is there any technique implemented in POV-Ray (especially in version 3.1)
that
> makes use of coherence? If so, which kind of coherence (spatial, temporal)
is used?
>
> Thanks,
>
> Andre Wesseling
>
>

Post a reply to this message