| lightgirl |
2008-09-16 16:27 |
Solution: l \W N
The plastic material with the rough diffusing surface can be modeled in a"D'QqtH
TracePro, but as two separate properties (select Define/EditPropertyData). ?|Ey WAL
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MATERIAL PROPERTY
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A TracePro Material Property can be created, and the index of refraction of oFKTBH:I
the material is entered here, as well as an absorption coefficient if it is gKP=@v%-
known (this would be for absorption losses just from propogating through a "j8`)XXa(
given thickness of a clear polished sample of the material, unrelated to the cAq5vAqmg
diffusing surface finish. Entering zero for the absorption coefficient is 7U !-_)n{
propobly a reasonable estimate for a transparent material. |RL\2j|
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The Material Property is applied to the Object (Define/Apply Properties). ~;}uYJ
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SURFACE PROPERTY M<r]a{Yv
A TracePro Surface Property can specify 5 possible outcomes for light incident j&[u $P*K
on a surface - Specular Transmission, Specular Reflection, Scattered Q^8/"aV\
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. tL M@o|:
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For your property, I expect that Specular Transmission, Specular Reflection, Xp9 ]
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and Absorption would all be 0, leaving only Scattered Transmission (BTDF). C]&/k_k
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - Y+h
?HS
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = *D67&/g.
BRDF(g) = 0, which defines a Lambertian dsitribution. P#} vi$dZ
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The challenge is to determine the proper ratio of Transmittance vs [ldBI3
Reflectance. You can enter a value for BRDF(A) and then use the Solve For =7[}:haB{
feature to solve for BTDF, and the editor will display the resulting J:@yG1VIp
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and ZiPz~G0[^
to have a ratio that matches the behavior of your surface. If the ratio of T kN6 jX
vs R is dependent on the Incidence Angle, you can use the Add button in the = |E8z
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property to add Incidence ANgles to the table, and then define the BTDF and I|wC`VgB
BRDF separately for each incidence angle.
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