| lightgirl |
2008-09-16 16:27 |
Solution: 8090+ ( U
The plastic material with the rough diffusing surface can be modeled in 9R-2\D]
TracePro, but as two separate properties (select Define/EditPropertyData). v/v PU
Ui1s ]R
MATERIAL PROPERTY y5^OD63s
A TracePro Material Property can be created, and the index of refraction of y
La E]
the material is entered here, as well as an absorption coefficient if it is /&c zaAR-
known (this would be for absorption losses just from propogating through a &(p5z4Df
given thickness of a clear polished sample of the material, unrelated to the k PA g *
diffusing surface finish. Entering zero for the absorption coefficient is 4OAR ["f
propobly a reasonable estimate for a transparent material. XW2ZQMos1
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The Material Property is applied to the Object (Define/Apply Properties). ) 3 f\H
f4f)9n
SURFACE PROPERTY NP4u/C<
A TracePro Surface Property can specify 5 possible outcomes for light incident ![I|hB
on a surface - Specular Transmission, Specular Reflection, Scattered J5<1 6}*
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. &U([Wd?E2
rmWs o b
For your property, I expect that Specular Transmission, Specular Reflection, ])?h ~
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). MIiB NNURX
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - 1IT(5Mleb
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = DH i@ ujr
BRDF(g) = 0, which defines a Lambertian dsitribution. G-:7,9
23'{{@30
The challenge is to determine the proper ratio of Transmittance vs
$Tt.r
Reflectance. You can enter a value for BRDF(A) and then use the Solve For im)r4={
9
feature to solve for BTDF, and the editor will display the resulting B"5x s
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and Oc.8d<
to have a ratio that matches the behavior of your surface. If the ratio of T s%~Nx3,
vs R is dependent on the Incidence Angle, you can use the Add button in the c& h8Qk3
property to add Incidence ANgles to the table, and then define the BTDF and 4?
rEO(SZ
BRDF separately for each incidence angle.
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