| lightgirl |
2008-09-16 16:27 |
Solution: FCg,p2
The plastic material with the rough diffusing surface can be modeled in *QrTZ$\C
TracePro, but as two separate properties (select Define/EditPropertyData). 3c6 <JW
}@x0@sI9
MATERIAL PROPERTY _N<8!(|w
A TracePro Material Property can be created, and the index of refraction of ^f4qs
the material is entered here, as well as an absorption coefficient if it is %cBJ haR{(
known (this would be for absorption losses just from propogating through a wt-)5f'{
given thickness of a clear polished sample of the material, unrelated to the r1,RloyZS
diffusing surface finish. Entering zero for the absorption coefficient is r =s 7be
propobly a reasonable estimate for a transparent material. xNT[ ((
v=|ahsYC
The Material Property is applied to the Object (Define/Apply Properties). e\\ I,
[~$9n_O94
SURFACE PROPERTY 63ht|$G
A TracePro Surface Property can specify 5 possible outcomes for light incident 4O2O0\o:
on a surface - Specular Transmission, Specular Reflection, Scattered n`}vcVL;
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. x H\5T!
S_C+1e
For your property, I expect that Specular Transmission, Specular Reflection, ny{|{ a
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). >i=mw5`D]
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - D (yRI
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = f\1)BZ 'I
BRDF(g) = 0, which defines a Lambertian dsitribution. ao Y "uT+
I:[3x2H
The challenge is to determine the proper ratio of Transmittance vs {]`O $S
Reflectance. You can enter a value for BRDF(A) and then use the Solve For gR%fv
feature to solve for BTDF, and the editor will display the resulting )~rN{W<s`H
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and kAU[lPt*R
to have a ratio that matches the behavior of your surface. If the ratio of T cu.f ]'
vs R is dependent on the Incidence Angle, you can use the Add button in the 4h?[NOA"
property to add Incidence ANgles to the table, and then define the BTDF and i{ xgygp6f
BRDF separately for each incidence angle.
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