| lightgirl |
2008-09-16 16:27 |
Solution: VF KFO9
The plastic material with the rough diffusing surface can be modeled in J|([(
TracePro, but as two separate properties (select Define/EditPropertyData).
Az/B/BLB
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=Mdw
MATERIAL PROPERTY b&'Y W*W
A TracePro Material Property can be created, and the index of refraction of TgKSE1
the material is entered here, as well as an absorption coefficient if it is 0D0 uzUD-
known (this would be for absorption losses just from propogating through a szXqJG8|
given thickness of a clear polished sample of the material, unrelated to the j.c{%UYj
diffusing surface finish. Entering zero for the absorption coefficient is @?gRWH;Pq
propobly a reasonable estimate for a transparent material. G[n;%c~`+
1v*N]}`HU
The Material Property is applied to the Object (Define/Apply Properties). i?,\>LTG
h~ O^~"jc
SURFACE PROPERTY WP'.o
A TracePro Surface Property can specify 5 possible outcomes for light incident d+"F(R9
on a surface - Specular Transmission, Specular Reflection, Scattered 5Ha(i [d
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. EA z>`~
yh'*eli
For your property, I expect that Specular Transmission, Specular Reflection, A o@WTs9
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). dJ>tM'G
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - @.,'A[D!K
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = GGU wS
BRDF(g) = 0, which defines a Lambertian dsitribution. %g69kizoWi
V(Cxd.u
The challenge is to determine the proper ratio of Transmittance vs ft~QVe!
Reflectance. You can enter a value for BRDF(A) and then use the Solve For .pH 4[~
feature to solve for BTDF, and the editor will display the resulting e} (8BF
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and 2iC BF-,
to have a ratio that matches the behavior of your surface. If the ratio of T ]ZH6
.@|
vs R is dependent on the Incidence Angle, you can use the Add button in the 5UX- Qqr
property to add Incidence ANgles to the table, and then define the BTDF and uc LDl
BRDF separately for each incidence angle.
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