| lightgirl |
2008-09-16 16:27 |
Solution: T@Bu Fr`]<
The plastic material with the rough diffusing surface can be modeled in E< ILZpP
TracePro, but as two separate properties (select Define/EditPropertyData). $ >8O2p7W
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MATERIAL PROPERTY "Xg~1)%
A TracePro Material Property can be created, and the index of refraction of XU`ly3 !
the material is entered here, as well as an absorption coefficient if it is {wDq*va
known (this would be for absorption losses just from propogating through a *@ {
given thickness of a clear polished sample of the material, unrelated to the qeW.~B!B
diffusing surface finish. Entering zero for the absorption coefficient is y6dQ4Whv&
propobly a reasonable estimate for a transparent material. rB|1<jR
=@nE :uto]
The Material Property is applied to the Object (Define/Apply Properties). v 8YF+N
6HguZ_jC
SURFACE PROPERTY v.&c1hK Hb
A TracePro Surface Property can specify 5 possible outcomes for light incident
Y(
on a surface - Specular Transmission, Specular Reflection, Scattered :GN++\ 1pw
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. MK- +[K
xnC:?d
For your property, I expect that Specular Transmission, Specular Reflection, e ^<' H
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). NQGa=kXeJ
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - YQ@2p ?4 m
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = ~ulcLvm:i
BRDF(g) = 0, which defines a Lambertian dsitribution. TI}a$I *
x k
The challenge is to determine the proper ratio of Transmittance vs Gshy$'_e
Reflectance. You can enter a value for BRDF(A) and then use the Solve For (wFoI}s
feature to solve for BTDF, and the editor will display the resulting \11+~
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and i)] f0F
to have a ratio that matches the behavior of your surface. If the ratio of T ]H aX.Z<
vs R is dependent on the Incidence Angle, you can use the Add button in the g[R4/]K^$
property to add Incidence ANgles to the table, and then define the BTDF and (j~T7og
BRDF separately for each incidence angle.
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