| lightgirl |
2008-09-16 16:27 |
Solution: Jqt|' G3
The plastic material with the rough diffusing surface can be modeled in hXn@vK6
TracePro, but as two separate properties (select Define/EditPropertyData). 2|8$@*-\
:HN\A4=kc(
MATERIAL PROPERTY gAy"W$F
A TracePro Material Property can be created, and the index of refraction of -$y/ *'
the material is entered here, as well as an absorption coefficient if it is
: DBJ2n
known (this would be for absorption losses just from propogating through a sRGIHT#
given thickness of a clear polished sample of the material, unrelated to the Vdf~ rV
diffusing surface finish. Entering zero for the absorption coefficient is [\pp K C
propobly a reasonable estimate for a transparent material. I%ZSh]On
B+=Xb;p8
The Material Property is applied to the Object (Define/Apply Properties). ]B-3Lh
A4VV y~sd
SURFACE PROPERTY M4}zRr([.5
A TracePro Surface Property can specify 5 possible outcomes for light incident xO'xZ%cUI
on a surface - Specular Transmission, Specular Reflection, Scattered 6b=7{nLF
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. Ns `:=
%@[ ~s,6 <
For your property, I expect that Specular Transmission, Specular Reflection, 0Y ld!L
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). dw< b}2
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - WL N;LT
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = DUu~s,A
BRDF(g) = 0, which defines a Lambertian dsitribution. ] Y6y ]u
mF] 8
The challenge is to determine the proper ratio of Transmittance vs u=!n9W~"
Reflectance. You can enter a value for BRDF(A) and then use the Solve For Vb8{OD3PK
feature to solve for BTDF, and the editor will display the resulting qu0dWgK
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and uF\f>E)/N%
to have a ratio that matches the behavior of your surface. If the ratio of T H- Or
vs R is dependent on the Incidence Angle, you can use the Add button in the ndB* ^nT
property to add Incidence ANgles to the table, and then define the BTDF and +K*_=gHF.
BRDF separately for each incidence angle.
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