| lightgirl |
2008-09-16 16:27 |
Solution: 2$ze=
/ l
The plastic material with the rough diffusing surface can be modeled in NdD`Hn -
TracePro, but as two separate properties (select Define/EditPropertyData). .E8_Oz
oV|4V:G q
MATERIAL PROPERTY wMg0>
A TracePro Material Property can be created, and the index of refraction of '|8} z4/g
the material is entered here, as well as an absorption coefficient if it is Eu@huN*/
known (this would be for absorption losses just from propogating through a }%{LJ}\Px
given thickness of a clear polished sample of the material, unrelated to the kTu [ y ;
diffusing surface finish. Entering zero for the absorption coefficient is :Ra,Eu
propobly a reasonable estimate for a transparent material. $m-2Hh qZ
2$g6}A`r
The Material Property is applied to the Object (Define/Apply Properties). @a0DT=>d T
aGtf z)
SURFACE PROPERTY dQA'($
A TracePro Surface Property can specify 5 possible outcomes for light incident .ufTQ?Fe
on a surface - Specular Transmission, Specular Reflection, Scattered S ]Mw #O|
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. b((M)Gz
/YMj-S_b~
For your property, I expect that Specular Transmission, Specular Reflection, 'R'*kxf
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). nz=G lO'[
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - LcTt )rs
f
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = `-J%pEIza
BRDF(g) = 0, which defines a Lambertian dsitribution. PIoLywpRn
P"IPcT%Ob%
The challenge is to determine the proper ratio of Transmittance vs 'm FqE n
Reflectance. You can enter a value for BRDF(A) and then use the Solve For -~v2BN/
feature to solve for BTDF, and the editor will display the resulting '}Z~JYa0
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and Tz8PS k1[
to have a ratio that matches the behavior of your surface. If the ratio of T IID-k
vs R is dependent on the Incidence Angle, you can use the Add button in the qzKdQ&vO
property to add Incidence ANgles to the table, and then define the BTDF and xqG[~)~
BRDF separately for each incidence angle.
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