| lightgirl |
2008-09-16 16:27 |
Solution: Q= xXj'W-
The plastic material with the rough diffusing surface can be modeled in JHvev,#4
TracePro, but as two separate properties (select Define/EditPropertyData). ,&WwADZ-s
PC<_1!M]
MATERIAL PROPERTY nWY^?e'S
A TracePro Material Property can be created, and the index of refraction of m 0vW<
the material is entered here, as well as an absorption coefficient if it is CssE8p >"F
known (this would be for absorption losses just from propogating through a *|dK1'Xr
given thickness of a clear polished sample of the material, unrelated to the ix4]^
diffusing surface finish. Entering zero for the absorption coefficient is u"*DI=pwb
propobly a reasonable estimate for a transparent material. Z 9 +f TT
pC>h"Hy
The Material Property is applied to the Object (Define/Apply Properties). 1VlU'qY
ZDbe]9#Xh
SURFACE PROPERTY LrbD%2U$j5
A TracePro Surface Property can specify 5 possible outcomes for light incident _7<{+Zzm
on a surface - Specular Transmission, Specular Reflection, Scattered FZj>N(
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. ~~h#2SX
D4[t^G ; J
For your property, I expect that Specular Transmission, Specular Reflection, >a<1J(c
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). dM^Z,; u
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - DJ:'<"zH7
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = DI{ *E
BRDF(g) = 0, which defines a Lambertian dsitribution. Q'jw=w!|g
t 'Wv? ,
The challenge is to determine the proper ratio of Transmittance vs 3>@VPMi
Reflectance. You can enter a value for BRDF(A) and then use the Solve For ^.!jD+=I
feature to solve for BTDF, and the editor will display the resulting *??lwv Jp
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and WJnGF3G>
to have a ratio that matches the behavior of your surface. If the ratio of T }QE*-GVv]
vs R is dependent on the Incidence Angle, you can use the Add button in the A!B.+p[ G
property to add Incidence ANgles to the table, and then define the BTDF and ` z0q:ME
BRDF separately for each incidence angle.
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