| lightgirl |
2008-09-16 16:27 |
Solution: sW8dPw
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The plastic material with the rough diffusing surface can be modeled in Q=yg8CQ
TracePro, but as two separate properties (select Define/EditPropertyData). uFga~&#g
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MATERIAL PROPERTY he hFEy x
A TracePro Material Property can be created, and the index of refraction of 18:%~>.!
the material is entered here, as well as an absorption coefficient if it is lU8Hd|@-
known (this would be for absorption losses just from propogating through a +m,yA mEEd
given thickness of a clear polished sample of the material, unrelated to the .(2ik5A%9
diffusing surface finish. Entering zero for the absorption coefficient is ;i +#fQO7Q
propobly a reasonable estimate for a transparent material. x'R`.
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The Material Property is applied to the Object (Define/Apply Properties). R@rBEW&
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SURFACE PROPERTY E8&TO~"a]e
A TracePro Surface Property can specify 5 possible outcomes for light incident q'MZ R'<@
on a surface - Specular Transmission, Specular Reflection, Scattered \1Em`nvOX
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. b>JDH1)
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For your property, I expect that Specular Transmission, Specular Reflection, [}] Q?*_
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). BIL Lq8)
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - ;sFF+^~L
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = P7/X| M z
BRDF(g) = 0, which defines a Lambertian dsitribution. xKp4*[}m
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The challenge is to determine the proper ratio of Transmittance vs jRV/A!4
Reflectance. You can enter a value for BRDF(A) and then use the Solve For )53y
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feature to solve for BTDF, and the editor will display the resulting >[*qf9$
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and 4+ Z]3oIRE
to have a ratio that matches the behavior of your surface. If the ratio of T (Ep\Z 6*
vs R is dependent on the Incidence Angle, you can use the Add button in the /&94 e C
property to add Incidence ANgles to the table, and then define the BTDF and 6) Lk-D
BRDF separately for each incidence angle.
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