| lightgirl |
2008-09-16 16:27 |
Solution: A\z`c
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The plastic material with the rough diffusing surface can be modeled in H}Ucrv:
TracePro, but as two separate properties (select Define/EditPropertyData). )RN<GW'
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MATERIAL PROPERTY @x1 %)1
A TracePro Material Property can be created, and the index of refraction of Qzqc .T
the material is entered here, as well as an absorption coefficient if it is u%u&F^y
known (this would be for absorption losses just from propogating through a 3e% nA8?
given thickness of a clear polished sample of the material, unrelated to the ;I}' }
diffusing surface finish. Entering zero for the absorption coefficient is
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propobly a reasonable estimate for a transparent material. ;HNq>/{
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The Material Property is applied to the Object (Define/Apply Properties). 0*8TS7.3
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SURFACE PROPERTY P(,?#+]-
A TracePro Surface Property can specify 5 possible outcomes for light incident R_ ZK 0ar
on a surface - Specular Transmission, Specular Reflection, Scattered J0Z7 l
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. +D&Pp0xe
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For your property, I expect that Specular Transmission, Specular Reflection, tGjhHp8}c
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). WBr59@V
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - aUc|V{Jp
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = (W[V? !1
BRDF(g) = 0, which defines a Lambertian dsitribution. /mA,F;
Cr C =A=e
The challenge is to determine the proper ratio of Transmittance vs jQ\zG J3
Reflectance. You can enter a value for BRDF(A) and then use the Solve For E{E0Z9t7&
feature to solve for BTDF, and the editor will display the resulting 15U (={
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and nXy>7H[0
to have a ratio that matches the behavior of your surface. If the ratio of T
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4R:
vs R is dependent on the Incidence Angle, you can use the Add button in the JH8}Ru%Z
property to add Incidence ANgles to the table, and then define the BTDF and @-HG`c ct
BRDF separately for each incidence angle.
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