Hi!
Sorry it took long to reply because we did spent some time to revise all our material definitions prior to answer this thread. Her we go:
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3ds Max model: explanation of differences between the Radiance material and the 3ds Max A&D Material
Setting the correct diffuse color and specular color in 3ds Max Design:
The values used in the mental ray A&D Materials are different from the values used in the Radiance Materials because they don’t use the same algorithms.
The main difference is that the 3ds max A&D Material handle energy conservation internally, while the Radiance material don’t. Therefore, we need to compensate for this when we input measured data in the 3ds Max A&D Material.
For example:
Assuming a measured material of 77% diffuse reflectance and 4% specular reflectance we would use the following settings:
Radiance Settings:
void plastic InteriorBackWall
0 0
5 0.77 0.77 0.77 0.004 0
3ds Max A&D Material Settings:
#diff_color (color 197.13 197.13 197.13) This represents 0.7730 on a scale of 0 to 1.0
#refl_color (color 255 255 255) This represents 1.0 on a scale of 0 to 1.0
#refl_weight 0.004
#refl_func_low 1.0
#refl_func_high 1.0
First, we consciously chose to disable the Fresnel falloff (BRDF) functionality of the 3ds Max A&D Material by setting the BRDF Curve values to 1.0 at all angles. The reason for this was that we did not have full measurements of the materials and the specular effects are negligible in our case: we are interested into measuring mainly the diffuse illuminance at the sensor points (as the space is generally a diffusely lit space). Defining a Fresnel falloff on our materials would not introduce major differences in the measurements (except for glazing, which is discussed below).
We are left with 3 main parameters: the Specular Color, the Specular Weight and the Diffuse Color. Knowing that the Specular Color is multiplied by the Specular Weight, we leave it at 1.0 1.0 1.0 (White).
Then, we need to do a little bit of maths to figure out the proper balance between the Diffuse Color and the Specular Weight. Since the 3ds Max A&D material performs energy conservation internally, we need to apply the following formulas:
A&D Material Diffuse Color = - ( Measured Diffuse / (Measured Specular -1) )
A&D Material Diffuse Color = -(0.77 / (0.004 – 1))
A&D Material Diffuse Color = 0.773
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Glass vs Thickness:
Glass thickness was ignored. Light rays penetrating in the space are assumed to be attenuated with a Fresnel falloff depending on the incident angle. This attenuation occurs at every surface the light ray hits. The thickness of the glass is ignored and light rays will not be affected by how thick or thin the glass geometry has been defined in the model.
For more information on strategies around modeling glass correctly for lighting simulation, please consult the advanced Daylight Simulation White paper that can be found here:
http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=11360846All the tricks are explained there.
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Errors in the paper:
We did notice some "errors" so we are rerunning the simulations right now to make sure we don't see major differences in the results. However, the errors we spotted are minuscule and are way below the overall errors described in the report. The "official" version of the paper will be published with the corrected data.
Hope this helps clarifying.
![Autodesk Design & Make Report](https://forums.autodesk.com/t5/image/serverpage/image-id/1350519iCB55845EBFC43016/image-size/large?v=v2&px=999" "Autodesk Design & Make Report")