| lightgirl |
2008-09-16 16:27 |
Solution: xUU p ?]9y
The plastic material with the rough diffusing surface can be modeled in hb{(r@[WHv
TracePro, but as two separate properties (select Define/EditPropertyData). 9"e!0Q4 0
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MATERIAL PROPERTY `N 0E;=g
A TracePro Material Property can be created, and the index of refraction of Q2o:wXvj
the material is entered here, as well as an absorption coefficient if it is B(5g&+{Lq~
known (this would be for absorption losses just from propogating through a X"]ZV]7(]s
given thickness of a clear polished sample of the material, unrelated to the - p }]r
diffusing surface finish. Entering zero for the absorption coefficient is @{G(. S
propobly a reasonable estimate for a transparent material. 53c6 dl
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The Material Property is applied to the Object (Define/Apply Properties). L [^e< I
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SURFACE PROPERTY Wi l +"[Ge
A TracePro Surface Property can specify 5 possible outcomes for light incident n9%r jS$
on a surface - Specular Transmission, Specular Reflection, Scattered %k~=iDk@
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. 3
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For your property, I expect that Specular Transmission, Specular Reflection, AMr 9rB d
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). GU xhCoxb
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - K(?7E6\vO
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = C^a~)r.h
BRDF(g) = 0, which defines a Lambertian dsitribution. Kt-@a%O0
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The challenge is to determine the proper ratio of Transmittance vs 9"rATgN1
Reflectance. You can enter a value for BRDF(A) and then use the Solve For ?$ ?Ni)Z
feature to solve for BTDF, and the editor will display the resulting 3 f 3?%9
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and Ez )Go6Q
to have a ratio that matches the behavior of your surface. If the ratio of T g!8-yri
vs R is dependent on the Incidence Angle, you can use the Add button in the :JlJB
property to add Incidence ANgles to the table, and then define the BTDF and $I'ES#8P6
BRDF separately for each incidence angle.
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