| lightgirl |
2008-09-16 16:27 |
Solution: 4Ij-Ilg)%
The plastic material with the rough diffusing surface can be modeled in K; FW
TracePro, but as two separate properties (select Define/EditPropertyData). \b}~2oX
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MATERIAL PROPERTY u6:pV.p
A TracePro Material Property can be created, and the index of refraction of 79zJ\ B_
the material is entered here, as well as an absorption coefficient if it is K}[>T(0E
known (this would be for absorption losses just from propogating through a pIW I
given thickness of a clear polished sample of the material, unrelated to the UDf9FnG}L
diffusing surface finish. Entering zero for the absorption coefficient is iE0ab,OF
propobly a reasonable estimate for a transparent material. BiE08,nj
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The Material Property is applied to the Object (Define/Apply Properties). c41: !u^
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SURFACE PROPERTY -#-p1^v}
A TracePro Surface Property can specify 5 possible outcomes for light incident s?WCnT
on a surface - Specular Transmission, Specular Reflection, Scattered DaNW~rd{
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. $]aBe
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For your property, I expect that Specular Transmission, Specular Reflection, 9Qj2W
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). P`U<7xF~
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - ryO$6L
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = "S~_[/q
BRDF(g) = 0, which defines a Lambertian dsitribution. HEK-L)S.
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The challenge is to determine the proper ratio of Transmittance vs dsK&U\ej}
Reflectance. You can enter a value for BRDF(A) and then use the Solve For ^GN8V-X4y
feature to solve for BTDF, and the editor will display the resulting 0f ER*.F
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and ') +0nPV
to have a ratio that matches the behavior of your surface. If the ratio of T '%v#v 3'
vs R is dependent on the Incidence Angle, you can use the Add button in the ,]R8(bD)
property to add Incidence ANgles to the table, and then define the BTDF and HOt>}x
BRDF separately for each incidence angle.
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