| lightgirl |
2008-09-16 16:27 |
Solution: Q^a&qYK
The plastic material with the rough diffusing surface can be modeled in nd $H
3sf
TracePro, but as two separate properties (select Define/EditPropertyData). ~rgf{oGz
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MATERIAL PROPERTY MB ]#%g&
A TracePro Material Property can be created, and the index of refraction of !dfS|BA]
the material is entered here, as well as an absorption coefficient if it is C6K|:IK{
known (this would be for absorption losses just from propogating through a OLk9A
given thickness of a clear polished sample of the material, unrelated to the & K5C= ]4
diffusing surface finish. Entering zero for the absorption coefficient is 94~"U5oQ:
propobly a reasonable estimate for a transparent material. V*6l6-y~Ih
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The Material Property is applied to the Object (Define/Apply Properties). _7Xd|\Zc
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SURFACE PROPERTY @T<ad7g-2J
A TracePro Surface Property can specify 5 possible outcomes for light incident cJxW;WI!,
on a surface - Specular Transmission, Specular Reflection, Scattered
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Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. >EBZ$ X
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For your property, I expect that Specular Transmission, Specular Reflection, p//T7r s
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). lo cW_/
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - :d;[DYFLxb
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = <\ y!3;
BRDF(g) = 0, which defines a Lambertian dsitribution. ?r{TOj n
> %9^%p^
The challenge is to determine the proper ratio of Transmittance vs H "#)&a7
Reflectance. You can enter a value for BRDF(A) and then use the Solve For n 11LxGwk
feature to solve for BTDF, and the editor will display the resulting \bU`
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and tl DY k
to have a ratio that matches the behavior of your surface. If the ratio of T y\^@p=e
vs R is dependent on the Incidence Angle, you can use the Add button in the >F/XZ C
property to add Incidence ANgles to the table, and then define the BTDF and xU@1!%l@
BRDF separately for each incidence angle.
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