| lightgirl |
2008-09-16 16:27 |
Solution: V}. uF,>V
The plastic material with the rough diffusing surface can be modeled in X* KQWs.
TracePro, but as two separate properties (select Define/EditPropertyData). w4Qqo(
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MATERIAL PROPERTY @{iws@.
A TracePro Material Property can be created, and the index of refraction of zH0%;
o}
the material is entered here, as well as an absorption coefficient if it is ug'I:#@2
known (this would be for absorption losses just from propogating through a jr bEJ.
given thickness of a clear polished sample of the material, unrelated to the n#uH^@#0
diffusing surface finish. Entering zero for the absorption coefficient is AjKP -[
propobly a reasonable estimate for a transparent material. HgvgO\`]
Wb+ ^Ue
The Material Property is applied to the Object (Define/Apply Properties). l"5$6h
"w9LQ=mW
SURFACE PROPERTY K_{f6c <
A TracePro Surface Property can specify 5 possible outcomes for light incident d rnqX-E;
on a surface - Specular Transmission, Specular Reflection, Scattered X^r5su?
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. / *RDy!m
x #-uf
For your property, I expect that Specular Transmission, Specular Reflection, A[oLV"J6x5
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). #s$b\"4
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - L-hK(W!8pt
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = #+N\u*-S
BRDF(g) = 0, which defines a Lambertian dsitribution. L>5VnzS I
X,: pT\G
The challenge is to determine the proper ratio of Transmittance vs guz{DBlK
Reflectance. You can enter a value for BRDF(A) and then use the Solve For l=8)_z;~D
feature to solve for BTDF, and the editor will display the resulting `zGK$,[%
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and F1J Sf&8
to have a ratio that matches the behavior of your surface. If the ratio of T (# Z2
vs R is dependent on the Incidence Angle, you can use the Add button in the ]W7(}~m
property to add Incidence ANgles to the table, and then define the BTDF and bj\v0NKN4
BRDF separately for each incidence angle.
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