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Hello everyone,
I'm working on a real time approach to GI and
I was looking for an engine able to provide the ground
truth for my experiments.
Essentially I have the following setting:
A "hollow" object filled with an homogeneous media
and containing one or more solid objects.
I want a rendering accounting for:
* single and multiple scattering
* reflection / diffraction
I've browsed for existing engines and POV Ray seems the only
one that should be able to do it (by photon mapping).
So my question is simply: did I get something wrong of do you foresee
problem to do it with povray?
Thanks in advance,
Fabio
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fabio schrieb:
> Hello everyone,
> I'm working on a real time approach to GI and
> I was looking for an engine able to provide the ground
> truth for my experiments.
> Essentially I have the following setting:
>
> A "hollow" object filled with an homogeneous media
> and containing one or more solid objects.
>
> I want a rendering accounting for:
> * single and multiple scattering
> * reflection / diffraction
>
> I've browsed for existing engines and POV Ray seems the only
> one that should be able to do it (by photon mapping).
>
> So my question is simply: did I get something wrong of do you foresee
> problem to do it with povray?
That depends on what exactly you intend to do.
If you're looking for some rendering engine speedy enough to use as a
basis for "real time" rendering (whatever your definition of that may
actually be), then POV-Ray may not be what you want.
If you're looking for a reference rendering engine to compare the output
of some self-made software with, then POV-Ray may not be ideally suited
either, as its roots are artwork, not physically realistic simulations,
and even though it has grown quite good at simulating realistic
/effects/, the relationship between POV-Ray's parameterization and the
underlying physical parameters are often somewhat obscure.
McPOV, a patch to POV-Ray (actually a patch to MegaPOV, which in turn is
a patched POV-Ray derivative), might be a better choice for such a
purpose, as its monte-carlo based unbiased approach circumvents the most
"unphysical" stuff in POV-Ray.
Another issue is the "multiple scattering"; I guess you're not talking
about diffuse interreflection between objects here, but rather about
media interaction, and I am sorry to say that POV-Ray only supports
single scattering there, and this is even true for McPOV.
Depending on what type of media you're actually trying to simulate,
POV-Ray 3.7.0's experimental subsurface scattering may be closest to
what you want; it uses a mathematical approximation to compute both
single and multiple scattering in highly-scattering media, based on the
work by Jensen et al.
Post a reply to this message
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> Hello everyone,
> I'm working on a real time approach to GI and
> I was looking for an engine able to provide the ground
> truth for my experiments.
> Essentially I have the following setting:
>
> A "hollow" object filled with an homogeneous media
> and containing one or more solid objects.
>
> I want a rendering accounting for:
> * single and multiple scattering
> * reflection / diffraction
>
> I've browsed for existing engines and POV Ray seems the only
> one that should be able to do it (by photon mapping).
>
> So my question is simply: did I get something wrong of do you foresee
> problem to do it with povray?
>
> Thanks in advance,
> Fabio
>
>
Single scattering: easily done using scattering media. Assume the
scattering particles are small to very small compared to ther individual
dimention and spacing. Can be computationaly heavy.
Multiple scattering, assuming a large number of scattering events: Use
the current 3.7 beta and subsurface light transport (SSLT).
Computationaly heavy.
Intermediate case where there are few, but more than one scattering
events: NOT supported at the present time. Maybe never.
Reflections and difracions: supported. Relatively light on computation.
You can add dispersion simulation. Can be computationaly heavy depending
on the smoothness desired.
Diffuse interreflections: effectively simulated using the radiosity
feature. Can take into acount the scattered light from a media. CAN'T
illuminate that media from the diffused light from an object.
Computationaly heavy.
Imaging the path of reflected light from a reflective surface, or the
refracted light through a transparent object : done using photons.
Photons can illuminate a media.
All those are modelisations. Exact emulation of the real effects is not
guaranteed, but is most of the time close enough.
Hard to do: diffuse reflection and difraction. No direct support. Can be
done using averaged normal perturbation. Will cause render time to soar.
Each tracing ray hiting those get multiplied at each such surface.
If you want to use all those features, "real time" rendering becomes
undoable. Even with the more powerfull computer available now, and in
the close future.
If you want a reference, you are on the right track.
Alain
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clipka <ano### [at] anonymous org> wrote:
> fabio schrieb:
> > Hello everyone,
> > I'm working on a real time approach to GI and
> > I was looking for an engine able to provide the ground
> > truth for my experiments.
> > Essentially I have the following setting:
> >
> > A "hollow" object filled with an homogeneous media
> > and containing one or more solid objects.
> >
> > I want a rendering accounting for:
> > * single and multiple scattering
> > * reflection / diffraction
> >
> > I've browsed for existing engines and POV Ray seems the only
> > one that should be able to do it (by photon mapping).
> >
> > So my question is simply: did I get something wrong of do you foresee
> > problem to do it with povray?
>
> That depends on what exactly you intend to do.
>
> If you're looking for some rendering engine speedy enough to use as a
> basis for "real time" rendering (whatever your definition of that may
> actually be), then POV-Ray may not be what you want.
>
> If you're looking for a reference rendering engine to compare the output
> of some self-made software with, then POV-Ray may not be ideally suited
> either, as its roots are artwork, not physically realistic simulations,
> and even though it has grown quite good at simulating realistic
> /effects/, the relationship between POV-Ray's parameterization and the
> underlying physical parameters are often somewhat obscure.
>
> McPOV, a patch to POV-Ray (actually a patch to MegaPOV, which in turn is
> a patched POV-Ray derivative), might be a better choice for such a
> purpose, as its monte-carlo based unbiased approach circumvents the most
> "unphysical" stuff in POV-Ray.
Thanks for the informative reply. Yes, I'm looking for a physically based
rendering engine to compare the results of a approximation technique of mine.
So the time needed for rendering is not an issue for me, I can wait.
I would also need diffuse inter-reflection but media interaction is dominant,
so it would also be useful just that.
From your answers (I also thank Alain for the reply) it seems I should look
for some alternative (I'll check McPOV out before).
One last thing. Do you have any advise for a physically based rendering engine
that I could use ?
Thanks again,
Fabio
>
>
> Another issue is the "multiple scattering"; I guess you're not talking
> about diffuse interreflection between objects here, but rather about
> media interaction, and I am sorry to say that POV-Ray only supports
> single scattering there, and this is even true for McPOV.
>
> Depending on what type of media you're actually trying to simulate,
> POV-Ray 3.7.0's experimental subsurface scattering may be closest to
> what you want; it uses a mathematical approximation to compute both
> single and multiple scattering in highly-scattering media, based on the
> work by Jensen et al.
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fabio schrieb:
> One last thing. Do you have any advise for a physically based rendering engine
> that I could use ?
No, unfortunately I personally don't.
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"fabio" <nomail@nomail> wrote:
> One last thing. Do you have any advise for a physically based rendering engine
> that I could use ?
Check out Maxwell Render at http://www.maxwellrender.com
I haven't tried it but it looks like an amazing (and expensive) physically based
renderer. I read a press release last week that their new v2.0 was just
released. You can download a demo version that renders up to 800x600 px and
should give you a good basis for comparison (according to them "unrivaled").
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