| lightgirl |
2008-09-16 16:27 |
Solution: t9MCT$U
The plastic material with the rough diffusing surface can be modeled in Sk"hqF.2
TracePro, but as two separate properties (select Define/EditPropertyData). r73W. &
Qd\ ='*:!
MATERIAL PROPERTY )t3`O$J
A TracePro Material Property can be created, and the index of refraction of 6FJ*eWPC
the material is entered here, as well as an absorption coefficient if it is PNd'21N
known (this would be for absorption losses just from propogating through a >itNa.K
given thickness of a clear polished sample of the material, unrelated to the { `Z~T&}~T
diffusing surface finish. Entering zero for the absorption coefficient is -"S94<Y
propobly a reasonable estimate for a transparent material. DA iS|x
TQKcPVlE
The Material Property is applied to the Object (Define/Apply Properties). R2?s
NlF
L1 I1SFG
SURFACE PROPERTY }:YL '$:5!
A TracePro Surface Property can specify 5 possible outcomes for light incident l5=ih9u
on a surface - Specular Transmission, Specular Reflection, Scattered k H<C9z2=
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. ^fe,A=k~1
'_V9FWDZ
For your property, I expect that Specular Transmission, Specular Reflection, ~4Gc~ "
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). TmftEw>u
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - P YWFz
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = Y>/_A%vQU
BRDF(g) = 0, which defines a Lambertian dsitribution. o~e_M-
& zB>
The challenge is to determine the proper ratio of Transmittance vs ]LZ#[xnM7
Reflectance. You can enter a value for BRDF(A) and then use the Solve For G u_\ySV/y
feature to solve for BTDF, and the editor will display the resulting /O.Ql ,6[
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and 9xj }<WM
to have a ratio that matches the behavior of your surface. If the ratio of T 4h_YVG]ur
vs R is dependent on the Incidence Angle, you can use the Add button in the aem gGw<
property to add Incidence ANgles to the table, and then define the BTDF and P
qC#[0Qy
BRDF separately for each incidence angle.
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