[Radiance-general] perfect specular reflection in rtrace

[Antoine Bugeat]

Hello

Thanks again for your help Greg

I still have not been able to solve my problem ...

To summarize my case, I have an environment composed only of surface
"mirror" and a light source "glow" (the sky). I want to get only the
radiation that comes directly from the source without any reflection.
It seems that even with the parameters -ab 1 -dr 0 -lr 0 (-ab 1 because the
sky is modeled with "glow") the radiation coming from the sky produces
reflections in the scene.

I modeled the environment with the material "plastic" and it works
perfectly. I'm almost sure that the problem comes from the material "glow"
combined with materials "mirror" but I want to keep this configuration.

Regards,

Antoine

2017-10-24 20:46 GMT+02:00 Greg Ward <gregoryjward at gmail.com>:

> Hi Antoine,
>
> Glad you got the basic mirror type working.
>
> One thing you should take into consideration for your model is the Fresnel
> factor that affects how light reflects off glazing materials (building
> facades).  The "mirror" type does not change its reflectance with angle,
> but coated and uncoated glazing materials do.  There are exact calculations
> and approximations you can use, which you can apply as a "brightfunc"
> modifier to the "mirror" type.
>
> To answer your question, though, the number of reflections or redirections
> from virtual source materials is controlled by the -dr rendering option.
> Set this to "-dr 0" if you do not wish to include any specular source
> redirections.  You will still get reflections (even multiple reflections)
> of the sky, even if you set -ab 0.  That's because the specular reflections
> don't count in the diffuse interreflection (ambient) calculation.  To fully
> eliminate sky reflections, you'll need to set -lr 0.
>
> Cheers,
> -Greg
>
> *From: *Antoine Bugeat <bugeatantoine at gmail.com>
>
> *Date: *October 24, 2017 10:38:57 AM PDT
>
>
> Hello all,
>
> Thanks again for your quick reply. Now I can model my street walls as a
> perfect specular materials ("mirror" materials) and obtain the results I
> expected.
>
> I come back with an other problem:
>
> The main purpose of my work is to compute the impact of the specular
> reflections in a street canyon.
> So, I would like to separate the light that comes from the reflections of
> the walls (only specular) and the light that comes directly from the sky
> (defined by "glow" material and "skyfunc"). I wanted to do a simulation
> with 0 reflection and an other simulation with 5 (or more) reflections. The
> results obtain with 0 reflection is directly the direct sky component and
> the substraction of 5 reflections - 0 reflections is the "environment" part.
>
> I did the same process with a diffuse environment and it worked well. I
> changed the -ab parameter:
> -ab 1 to have the direct sky component (1 because of "glow" material);
> and -ab 5 to have the entire reflections in the environment.
>
> *But in the specular environment (with "mirror" wall) there is no
> difference between my "0 reflection" case and my "5 reflections" case*
> I tried to change the parameters -ab -dr and -lr and it seems that all the
> reflections is computed whatever the parameters.
> From what I know, -ab is for "diffuse inter-reflections", -dr is for
> "direct reflections", and -lr I don't know...
>
> Obviously, I can replace the "0 reflection specular" case with the "0
> refelction diffuse" case because it should be exactly the same, but I would
> like to understand where this problem comes from.
>
> I do not know if I was clear and precise in my explanation. I am available
> if you have questions.
>
>
> Regards,
>
> Antoine
>
>
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