| lightgirl |
2008-09-16 16:27 |
Solution: \ZAD Y.ha
The plastic material with the rough diffusing surface can be modeled in iS+"J sz
TracePro, but as two separate properties (select Define/EditPropertyData). Ph""[0n%o
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MATERIAL PROPERTY { DP9^hg
A TracePro Material Property can be created, and the index of refraction of Ga02Z k
the material is entered here, as well as an absorption coefficient if it is -W^{)%4g
known (this would be for absorption losses just from propogating through a =QVk Y7
given thickness of a clear polished sample of the material, unrelated to the fdK E1,;
diffusing surface finish. Entering zero for the absorption coefficient is #T8o+tv
propobly a reasonable estimate for a transparent material. &P9fM-]b
s
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The Material Property is applied to the Object (Define/Apply Properties). +^(_S9CO
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SURFACE PROPERTY m0;j1- t
A TracePro Surface Property can specify 5 possible outcomes for light incident |#o' =whTl
on a surface - Specular Transmission, Specular Reflection, Scattered ! 1I# L!9
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. Ygk_gBRiC
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For your property, I expect that Specular Transmission, Specular Reflection, VnW6$W?g
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). <}[ !k<
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - I[|Y
2i
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = d lfjx
BRDF(g) = 0, which defines a Lambertian dsitribution. B,%6sa~I
p*lP9[7
The challenge is to determine the proper ratio of Transmittance vs 8a 8a:d
Reflectance. You can enter a value for BRDF(A) and then use the Solve For ^yB]_*WJ
feature to solve for BTDF, and the editor will display the resulting !Q|a R
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and ;6PU
to have a ratio that matches the behavior of your surface. If the ratio of T t'eu>a1D
vs R is dependent on the Incidence Angle, you can use the Add button in the w>f.@luO4
property to add Incidence ANgles to the table, and then define the BTDF and ; &J>a8B$
BRDF separately for each incidence angle.
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