| lightgirl |
2008-09-16 16:27 |
Solution: ~-,P1 u!
The plastic material with the rough diffusing surface can be modeled in kO:iA0KUX
TracePro, but as two separate properties (select Define/EditPropertyData). u"K-mr#$[o
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MATERIAL PROPERTY OC z WP,
A TracePro Material Property can be created, and the index of refraction of `x"0
the material is entered here, as well as an absorption coefficient if it is b9[KdVsT6^
known (this would be for absorption losses just from propogating through a GNXQD}L?b?
given thickness of a clear polished sample of the material, unrelated to the M%wj6!5
diffusing surface finish. Entering zero for the absorption coefficient is wSp1ChS k
propobly a reasonable estimate for a transparent material. zh$[UdY6
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The Material Property is applied to the Object (Define/Apply Properties). A/W-'%+`
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SURFACE PROPERTY {m9OgR5U
A TracePro Surface Property can specify 5 possible outcomes for light incident |X9YVZC
on a surface - Specular Transmission, Specular Reflection, Scattered 4WnB{9
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Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. "D7*en
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For your property, I expect that Specular Transmission, Specular Reflection, jNN$/ZWm
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). qoBm!|q
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - E[J7FgU)<S
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = >JFAE5tj&2
BRDF(g) = 0, which defines a Lambertian dsitribution. fbS l$jn.
U S+PI`
The challenge is to determine the proper ratio of Transmittance vs 93%U;0w[Nw
Reflectance. You can enter a value for BRDF(A) and then use the Solve For x`^~| Q
feature to solve for BTDF, and the editor will display the resulting )<
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Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and cpB$b C](
to have a ratio that matches the behavior of your surface. If the ratio of T o}p6qB=;1
vs R is dependent on the Incidence Angle, you can use the Add button in the ;JpU4W2/
property to add Incidence ANgles to the table, and then define the BTDF and 7-+X -Y?
BRDF separately for each incidence angle.
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