| lightgirl |
2008-09-16 16:27 |
Solution: 7kp$C?7K
The plastic material with the rough diffusing surface can be modeled in ECWn/4Aws
TracePro, but as two separate properties (select Define/EditPropertyData). ~8o's`
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MATERIAL PROPERTY TG~:Cmc
A TracePro Material Property can be created, and the index of refraction of "} Of f
the material is entered here, as well as an absorption coefficient if it is eR4%4gW)
known (this would be for absorption losses just from propogating through a _ko16wfg
given thickness of a clear polished sample of the material, unrelated to the dd@qk`Zl&A
diffusing surface finish. Entering zero for the absorption coefficient is 1D sgU6"
propobly a reasonable estimate for a transparent material. G>qzA gA
_pnJ/YE
The Material Property is applied to the Object (Define/Apply Properties). s `B "qw
}Z u>?U
SURFACE PROPERTY |$`)d87,
A TracePro Surface Property can specify 5 possible outcomes for light incident PMe bn$(
on a surface - Specular Transmission, Specular Reflection, Scattered _=Ed>2M)no
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. : " 9F.U
W9D]s~bO;
For your property, I expect that Specular Transmission, Specular Reflection, 6hv4D`d ;o
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). o$8v8="p
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - X>( ?
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = 9
,=7Uh# 7
BRDF(g) = 0, which defines a Lambertian dsitribution. Mhc!v, D$
wu "6Kyu
The challenge is to determine the proper ratio of Transmittance vs wws)**]J8
Reflectance. You can enter a value for BRDF(A) and then use the Solve For !/^i\)j>](
feature to solve for BTDF, and the editor will display the resulting 2>Bx/QF@<
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and HS =qK
to have a ratio that matches the behavior of your surface. If the ratio of T gJ6 C&8tl
vs R is dependent on the Incidence Angle, you can use the Add button in the 6r4o47_t8#
property to add Incidence ANgles to the table, and then define the BTDF and B`3RyM"J @
BRDF separately for each incidence angle.
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