| lightgirl |
2008-09-16 16:27 |
Solution: w $2-t
The plastic material with the rough diffusing surface can be modeled in s z}Nal$AC
TracePro, but as two separate properties (select Define/EditPropertyData). p-ry{"XA
& M<431y
MATERIAL PROPERTY 5n Evnnx0
A TracePro Material Property can be created, and the index of refraction of x!G\-2#
the material is entered here, as well as an absorption coefficient if it is dU+1@_
known (this would be for absorption losses just from propogating through a p|W:;(
given thickness of a clear polished sample of the material, unrelated to the Xs t&QKU
diffusing surface finish. Entering zero for the absorption coefficient is 2Q<_l*kk(
propobly a reasonable estimate for a transparent material. J,jl(=G
v^KJU
+
The Material Property is applied to the Object (Define/Apply Properties). ?t<wp3bZ
bv|v9_i
SURFACE PROPERTY _gU [FUBtJ
A TracePro Surface Property can specify 5 possible outcomes for light incident 78 3a Z8
on a surface - Specular Transmission, Specular Reflection, Scattered ~PS%^z xyn
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. ]Y,
7 X
F[ 9IHT6{
For your property, I expect that Specular Transmission, Specular Reflection, viKN:n! Ev
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). 6 ~D:O?2
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - Xr' :/Qjf
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = BhNwC[G?m
BRDF(g) = 0, which defines a Lambertian dsitribution. R[o KhU
t+66kB N
The challenge is to determine the proper ratio of Transmittance vs Qza[~6
Reflectance. You can enter a value for BRDF(A) and then use the Solve For _{T`ka
feature to solve for BTDF, and the editor will display the resulting =(zk-J<nY
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and (A"oMnjWd
to have a ratio that matches the behavior of your surface. If the ratio of T _Z 9I ')
vs R is dependent on the Incidence Angle, you can use the Add button in the EEF}Wf$f
property to add Incidence ANgles to the table, and then define the BTDF and A7ck-9dT/L
BRDF separately for each incidence angle.
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