| lightgirl |
2008-09-16 16:27 |
Solution: QMy;?,
The plastic material with the rough diffusing surface can be modeled in #T#&qo#
TracePro, but as two separate properties (select Define/EditPropertyData). ~< Gs<c}z
gLl?e8[F
MATERIAL PROPERTY g}ciG!0
A TracePro Material Property can be created, and the index of refraction of q&jZmr
the material is entered here, as well as an absorption coefficient if it is DcSL f4A
known (this would be for absorption losses just from propogating through a K&BlWXT
given thickness of a clear polished sample of the material, unrelated to the ^zs CF0
diffusing surface finish. Entering zero for the absorption coefficient is EVgn^,
propobly a reasonable estimate for a transparent material. "! p#8jR^
?Sn$A S I
The Material Property is applied to the Object (Define/Apply Properties). duXv
[1
6\4oHRJC
SURFACE PROPERTY kzJNdYtdH
A TracePro Surface Property can specify 5 possible outcomes for light incident M`BD]{tN}
on a surface - Specular Transmission, Specular Reflection, Scattered YwoytoXK
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. t
Z\
B xG0vJN |
For your property, I expect that Specular Transmission, Specular Reflection, ;NLL?6~
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). [ueT ]%
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - ~K:#a$!%,
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = =c-j4xna>
BRDF(g) = 0, which defines a Lambertian dsitribution. ?.\ CUVK
4%\L8 :
The challenge is to determine the proper ratio of Transmittance vs 1'c!9
Reflectance. You can enter a value for BRDF(A) and then use the Solve For T6O Ib
feature to solve for BTDF, and the editor will display the resulting [NeOd77y
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and ~;UK/OZ
to have a ratio that matches the behavior of your surface. If the ratio of T {*
>$aI
vs R is dependent on the Incidence Angle, you can use the Add button in the o6xl,T%
property to add Incidence ANgles to the table, and then define the BTDF and hrU.QF8
BRDF separately for each incidence angle.
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