| lightgirl |
2008-09-16 16:27 |
Solution: fXI :Y8T
The plastic material with the rough diffusing surface can be modeled in HK\~Qnq
TracePro, but as two separate properties (select Define/EditPropertyData). o<IAeH {+
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MATERIAL PROPERTY fb8%~3i >
A TracePro Material Property can be created, and the index of refraction of akw,P$i
the material is entered here, as well as an absorption coefficient if it is 1I@8A>2^OX
known (this would be for absorption losses just from propogating through a }_=eT]
given thickness of a clear polished sample of the material, unrelated to the ;%tF5 8&
diffusing surface finish. Entering zero for the absorption coefficient is T91moRv
propobly a reasonable estimate for a transparent material. lj+u@Z<xA
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The Material Property is applied to the Object (Define/Apply Properties). ] Q]W5WDe:
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SURFACE PROPERTY =X.LA%Sf=u
A TracePro Surface Property can specify 5 possible outcomes for light incident AJ#Nenmj
on a surface - Specular Transmission, Specular Reflection, Scattered wtje(z5IL
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. @(r /dZc
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For your property, I expect that Specular Transmission, Specular Reflection, .bBdQpF-
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). @gY)8xMbA
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - lHgs;> U$
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = 45hF`b>%,
BRDF(g) = 0, which defines a Lambertian dsitribution. %HrAzM.QBF
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The challenge is to determine the proper ratio of Transmittance vs n ; {76Q
Reflectance. You can enter a value for BRDF(A) and then use the Solve For w$Jv B5O
feature to solve for BTDF, and the editor will display the resulting N('&jHF
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and >EY3/Go>
to have a ratio that matches the behavior of your surface. If the ratio of T ;b-XWK=
vs R is dependent on the Incidence Angle, you can use the Add button in the J:V?EE,\-
property to add Incidence ANgles to the table, and then define the BTDF and cnTaJ/o
BRDF separately for each incidence angle.
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