| lightgirl |
2008-09-16 16:27 |
Solution: i/$lO de
The plastic material with the rough diffusing surface can be modeled in O nc! 5L
TracePro, but as two separate properties (select Define/EditPropertyData). |Jq/kmn
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MATERIAL PROPERTY huQ1A0(no
A TracePro Material Property can be created, and the index of refraction of oOD|Fr lY
the material is entered here, as well as an absorption coefficient if it is c\x?k<=
known (this would be for absorption losses just from propogating through a Ny~;" n
given thickness of a clear polished sample of the material, unrelated to the )0%<ZVB
diffusing surface finish. Entering zero for the absorption coefficient is i
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propobly a reasonable estimate for a transparent material. *i n_Z t3
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The Material Property is applied to the Object (Define/Apply Properties). |4'E&(BU-
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SURFACE PROPERTY z^oi15D|{
A TracePro Surface Property can specify 5 possible outcomes for light incident x/Ds`\
on a surface - Specular Transmission, Specular Reflection, Scattered q&N&n%rbm
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. gr2zt&Z4
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For your property, I expect that Specular Transmission, Specular Reflection, $6J5yE
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). RM`8P5i]sF
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - I%(+tJ
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = NKMB,b
BRDF(g) = 0, which defines a Lambertian dsitribution. c '(]n]a%
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The challenge is to determine the proper ratio of Transmittance vs
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Reflectance. You can enter a value for BRDF(A) and then use the Solve For $DQ
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feature to solve for BTDF, and the editor will display the resulting T|}HK]QOX
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and "Fke(?X'
to have a ratio that matches the behavior of your surface. If the ratio of T ~k J#IA
vs R is dependent on the Incidence Angle, you can use the Add button in the :Ert5 7@l
property to add Incidence ANgles to the table, and then define the BTDF and ~pw_*AN
BRDF separately for each incidence angle.
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