Hi Jiajie,
I put some responses inline...
From: "Jiajie Zhu" <[email protected]>
Subject: [Radiance-general] Irradiance map
Date: August 10, 2015 9:31:13 AM PDTHi,
I am trying to calculate an irradiance map on the ground level in front of a concaved building facade for an instant time at a specific location. Here is the problems that I have:
1. If I use the glass type material for the building facade with –i option in rpict, there will be no facade in the final result. I have checked the manual page that I know it is because of the Boolean calculation will ignore the transparent surface in the final result. But I do need the facade to be seen in the final result, how can I solve it.
The -i option is a hack to show the irradiance on surfaces, but glass surfaces appear as transparent to facilitate viewing through windows, etc. The results will still be correct within the limits of the calculation.
2. I found in the result that if I use the glass type material, no matter how low I set the transmissivity values, there will always no ‘hotspot’/convergent irradiance on the ground level. It seems that the program just ignore the reflection process on the glass surface.
Radiance is a conventional light-backwards ray-tracer, so needs special facilities to find caustics. These are the "mirror" type you mention below, and photon-mapping, which is incorporated in the latest HEAD.
3. If I change the facade material to mirror type, I can find an obvious ‘hotspot’ on the ground level as well as the facade in the final result. So I just wonder is it proper to modify the facade material into a mirror type if I am only interested in the exterior irradiance map of a building. Besides, if mirror type material can be used in my situation, how can I set the RGB reflectance values for mirror? For example, if the facade glass has a 40% transmittance, is it equivalent to set RGB values into 0.6 0.6 0.6 for a mirror material?
You need to know the reflectance of your glass, not the transmittance, in order to use the mirror type appropriately. Then, you can give the original glass as the "alternate" type. Most uncoated glass surfaces have a specular reflectance of between 4 and 8% depending on their transparency.
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Many Thanks,
Jiajie