| lightgirl |
2008-09-16 16:27 |
Solution: rhly.f7N=A
The plastic material with the rough diffusing surface can be modeled in e@/' o/
TracePro, but as two separate properties (select Define/EditPropertyData). C}DIm&))
] ;CJ6gM~
MATERIAL PROPERTY '/A X 'U8Y
A TracePro Material Property can be created, and the index of refraction of ~k}O"{
y
the material is entered here, as well as an absorption coefficient if it is ^&$86-PB/
known (this would be for absorption losses just from propogating through a rp2g./2
given thickness of a clear polished sample of the material, unrelated to the \~t!M~H
diffusing surface finish. Entering zero for the absorption coefficient is }U4mXkZF
propobly a reasonable estimate for a transparent material. @2-;,VL 3
1K R4Wq@
The Material Property is applied to the Object (Define/Apply Properties). |WfL'_?$
6s
~!B {Q
SURFACE PROPERTY $xF[j9nM
A TracePro Surface Property can specify 5 possible outcomes for light incident u,N<U t
on a surface - Specular Transmission, Specular Reflection, Scattered 1+Ik\
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. |x>5 T}
wfcR[
For your property, I expect that Specular Transmission, Specular Reflection, wb h=v;
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). Wt=@6 w&
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - 6UL9+9[C
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = ZPz=\^
BRDF(g) = 0, which defines a Lambertian dsitribution. >ffC?5+
-})zRL0!'
The challenge is to determine the proper ratio of Transmittance vs (A=Z ,ed
Reflectance. You can enter a value for BRDF(A) and then use the Solve For D(&WEmm\B
feature to solve for BTDF, and the editor will display the resulting .j=mT[N,I
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and G drVH,j
to have a ratio that matches the behavior of your surface. If the ratio of T b *{U O
vs R is dependent on the Incidence Angle, you can use the Add button in the <U\8&Uv>
property to add Incidence ANgles to the table, and then define the BTDF and ~`B ]G
BRDF separately for each incidence angle.
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