POV-Ray : Newsgroups : povray.pov4.discussion.general : daylight : Re: daylight Server Time
28 Nov 2023 15:02:57 EST (-0500)
  Re: daylight  
From: MichaelJF
Date: 18 Feb 2013 15:25:00
Message: <web.51228d488f43b627802d06440@news.povray.org>
"Nathalie" <nomail@nomail> wrote:
> Hi,
> I would like to reformulate my question a bit. It is not my intention to make a
> perfect rendering of a church interior. It is rather my intention to render a
> part of a church interior (let's say a niche with a statue) according to three
> daylight calculation methods (ray-tracing, radiosity and photon mapping), with
> the aim of comparing these three methods. I tought POV-ray was the best choice
> to do this, because it makes control over the algorithms possible. Effects to
> improve the rendering (like glow,...) are only interesting insofar as they are
> applicable to the three calculation methods. Is this possible with POV-Ray?
> Because from the previous answers I deducted that only radiosity was possible...
> Please correct me if I'm wrong.
> best regards,
> Nathalie

From the first postings here I had the impression that there is a little bit
misunderstanding between the entrants here. I hope I can clarify the one or
other issue.

Nathalie, you have three items in your list: ray tracing, radiosity and photons.

Ray tracing: The idea is to trace a ray, but backwards. Imagine a usual camera.
It samples the rays that hit the lense and make a photograph of it. Ray tracing
is the other way round. You are looking from the film (or a sensor nowadays)
throught the lens into the world trying to find a way to a light. (That is why
"ray tracing" is sometimes more precisely called "backward ray tracing"). This
works fine, if you hit a light. And this is that what POV always does. So if you
are using POV you can rule out the first item of your list. POV is created to do
ray tracing.

Radiosity: Often the ray from the camera cannot find a light at a direct course.
That is simply because you are in a shadow. The work around here is to snoop
around in some other directions to find a light from this point at an indirect
path. That is not trivial since you have to specify a lot of parameters how this
should be done, but fortunatelly there is the include-file "rad_defs.inc" with
provides a lot of parametrisations under names, one can understand.
"Radiosity_OudoorLQ" e.g., with gives a low quality (LQ) setting for outdoor
scenes. There is a HQ (high quality) setting as well, but first try the LQ since
the HQ renders much longer than the LQ. (LQ may cost some hours, HQ some days -
or weeks).

Photons: If you are looking backwards from the camera to the lights you cannot
see direct effects of the lights like reflections on a wall or reflected and
refracted light by a water glass. Photons are a precalculating step to work
aorund this. You need a lot of experience or a lot of experiments to achieve a
fine result (no include file can be created for this issue).

Ray tracing is the nature of POV, for radiosity I will propose you to work
through the tutorial which came with POV (within the help-files). A fine
reference picture for photons is an entry to the POVComp contest by Tilo Helmig


Source codes are included there.

Best regards,

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