| lightgirl |
2008-09-16 16:27 |
Solution: ]*Tnu98G}
The plastic material with the rough diffusing surface can be modeled in _?IP}} jA:
TracePro, but as two separate properties (select Define/EditPropertyData). C aV>\E)
3 IK +&hk
MATERIAL PROPERTY B&Igm<72x
A TracePro Material Property can be created, and the index of refraction of = Ik G;gg
the material is entered here, as well as an absorption coefficient if it is K#LG7faj
known (this would be for absorption losses just from propogating through a bR*/d-v^
given thickness of a clear polished sample of the material, unrelated to the mI[$c"!BD
diffusing surface finish. Entering zero for the absorption coefficient is H |K}m,g
propobly a reasonable estimate for a transparent material. e#uk+]
Q:+cLl&;hB
The Material Property is applied to the Object (Define/Apply Properties). IR xFcLk
M \f1]L|8d
SURFACE PROPERTY ?[ts<Ltp
A TracePro Surface Property can specify 5 possible outcomes for light incident "++q. y
on a surface - Specular Transmission, Specular Reflection, Scattered =`oQcIkz
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. T P5?%SlJ
pJK}9p =4`
For your property, I expect that Specular Transmission, Specular Reflection, ;Npv 2yAab
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). f4k\hUA
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - M -B -
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = \~YyY'J
BRDF(g) = 0, which defines a Lambertian dsitribution. @fVCGV?'
.L X8ko
The challenge is to determine the proper ratio of Transmittance vs hR] AUH
Reflectance. You can enter a value for BRDF(A) and then use the Solve For 96 &Y
feature to solve for BTDF, and the editor will display the resulting 5>e3srKu
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and fy(i<L
Z
to have a ratio that matches the behavior of your surface. If the ratio of T M]Y72K^
vs R is dependent on the Incidence Angle, you can use the Add button in the =R>%}5
property to add Incidence ANgles to the table, and then define the BTDF and Yp_R +a^
BRDF separately for each incidence angle.
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