| lightgirl |
2008-09-16 16:27 |
Solution: @vL0gzE?nB
The plastic material with the rough diffusing surface can be modeled in !hE F.S
TracePro, but as two separate properties (select Define/EditPropertyData). nkz<t
g-H,*^g+
MATERIAL PROPERTY T)tTzgLD}
A TracePro Material Property can be created, and the index of refraction of l3y}nh+ 8
the material is entered here, as well as an absorption coefficient if it is >|0 I\{ C
known (this would be for absorption losses just from propogating through a _Ea1;dJmq
given thickness of a clear polished sample of the material, unrelated to the 3EH@tlTl
diffusing surface finish. Entering zero for the absorption coefficient is w4R~0jXy
propobly a reasonable estimate for a transparent material. fl4 0jo]
V bNN1'a-
The Material Property is applied to the Object (Define/Apply Properties). DH bS=Iih
HG)$ W
SURFACE PROPERTY EWq
< B)
A TracePro Surface Property can specify 5 possible outcomes for light incident :H#D4O8UiH
on a surface - Specular Transmission, Specular Reflection, Scattered 5k?xBk=<
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. N8,g~ ?r^
]AZCf`7/?
For your property, I expect that Specular Transmission, Specular Reflection, LoOw]@>
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). W e*uZ? +
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - fF2] 7:
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = 3lKs>HE0
BRDF(g) = 0, which defines a Lambertian dsitribution. m|;gl|dTB
e;LC\*dG
The challenge is to determine the proper ratio of Transmittance vs v P_mS 4X
Reflectance. You can enter a value for BRDF(A) and then use the Solve For -a l
feature to solve for BTDF, and the editor will display the resulting Q'Uv5p"X
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and crx%;R
to have a ratio that matches the behavior of your surface. If the ratio of T 7mn&w$MS4:
vs R is dependent on the Incidence Angle, you can use the Add button in the ^)'D
eP/
property to add Incidence ANgles to the table, and then define the BTDF and &x4*YM h
BRDF separately for each incidence angle.
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