| lightgirl |
2008-09-16 16:27 |
Solution: ZM K"3c9
The plastic material with the rough diffusing surface can be modeled in ?&I gD.
TracePro, but as two separate properties (select Define/EditPropertyData). bZHuE h2w
#+N\u*-S
MATERIAL PROPERTY L>5VnzS I
A TracePro Material Property can be created, and the index of refraction of +0r Mv
the material is entered here, as well as an absorption coefficient if it is VUC
known (this would be for absorption losses just from propogating through a vA2@Db}
given thickness of a clear polished sample of the material, unrelated to the '%_1eaH
diffusing surface finish. Entering zero for the absorption coefficient is a*REx_gLG
propobly a reasonable estimate for a transparent material. kMWu%,s4
8
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The Material Property is applied to the Object (Define/Apply Properties). v_)a=I%o&2
S+py \z%
SURFACE PROPERTY 5L bU'5
A TracePro Surface Property can specify 5 possible outcomes for light incident ?Z0T9e<
on a surface - Specular Transmission, Specular Reflection, Scattered I<e[/#5P\`
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. }YW0?-G.$
i>HipD,TD
For your property, I expect that Specular Transmission, Specular Reflection, !%5ae82~3
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). kq6S`~J^R
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - ;
Xrx>( n
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = 3G9"La,b
BRDF(g) = 0, which defines a Lambertian dsitribution. | :$D[=
e48`cX\E
The challenge is to determine the proper ratio of Transmittance vs nr*~R-,\
Reflectance. You can enter a value for BRDF(A) and then use the Solve For 9r-]@6;
feature to solve for BTDF, and the editor will display the resulting j}u Fp|df<
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and W7>4-gk
to have a ratio that matches the behavior of your surface. If the ratio of T T=35?
vs R is dependent on the Incidence Angle, you can use the Add button in the &sR=N60n
property to add Incidence ANgles to the table, and then define the BTDF and 0@d )DLM?
BRDF separately for each incidence angle.
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