| lightgirl |
2008-09-16 16:27 |
Solution: 7SCI_8`
The plastic material with the rough diffusing surface can be modeled in Apn#o2
TracePro, but as two separate properties (select Define/EditPropertyData). 9@06]EI_
9':$!Eoq
MATERIAL PROPERTY T_WQzEL^
A TracePro Material Property can be created, and the index of refraction of 3[r B:cE/
the material is entered here, as well as an absorption coefficient if it is wah`
known (this would be for absorption losses just from propogating through a Up&q#vqIj
given thickness of a clear polished sample of the material, unrelated to the k s}o9[D3
diffusing surface finish. Entering zero for the absorption coefficient is O]>`B{
propobly a reasonable estimate for a transparent material. ;l'I. j
p* @L1
The Material Property is applied to the Object (Define/Apply Properties). XvdhPOMy
zBbTj IFQ
SURFACE PROPERTY jVz1`\Nje
A TracePro Surface Property can specify 5 possible outcomes for light incident %#,BvQz~
on a surface - Specular Transmission, Specular Reflection, Scattered qJ@?[|2R
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. P7b2I=t
@4i D N
For your property, I expect that Specular Transmission, Specular Reflection, d\v _!7
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). t>xV]W<
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - O 2U/zF:X
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = !Xm : $KH
BRDF(g) = 0, which defines a Lambertian dsitribution. ARE~jzakg
5IMH G%W7
The challenge is to determine the proper ratio of Transmittance vs d,77 L
Reflectance. You can enter a value for BRDF(A) and then use the Solve For hk
I$ow (
feature to solve for BTDF, and the editor will display the resulting <T wq{kt
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and zP9 !f A
to have a ratio that matches the behavior of your surface. If the ratio of T P(` IY +
vs R is dependent on the Incidence Angle, you can use the Add button in the llzl-2` /
property to add Incidence ANgles to the table, and then define the BTDF and KJd;c.
BRDF separately for each incidence angle.
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