| lightgirl |
2008-09-16 16:27 |
Solution: ws. ?cCTpt
The plastic material with the rough diffusing surface can be modeled in a (P^e)<
TracePro, but as two separate properties (select Define/EditPropertyData). }FHw"
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MATERIAL PROPERTY qjJ{+Rz2
A TracePro Material Property can be created, and the index of refraction of *O!T!J
the material is entered here, as well as an absorption coefficient if it is Ck:#1-t8{
known (this would be for absorption losses just from propogating through a N\c &PS
given thickness of a clear polished sample of the material, unrelated to the 0T 1HQ
diffusing surface finish. Entering zero for the absorption coefficient is IU7$%6<Y
propobly a reasonable estimate for a transparent material. Ii,~HH
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The Material Property is applied to the Object (Define/Apply Properties). |X,$?ZDa p
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SURFACE PROPERTY h=!M6ya p<
A TracePro Surface Property can specify 5 possible outcomes for light incident GJ.kkTMT
on a surface - Specular Transmission, Specular Reflection, Scattered |*Of^IkG0
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. j!6elzg
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For your property, I expect that Specular Transmission, Specular Reflection, '" ^ B&W
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). >0kmRVd
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - @gH(/pFX
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = /A %om|+Gq
BRDF(g) = 0, which defines a Lambertian dsitribution. N[#iT&@T}/
|= tJ|
The challenge is to determine the proper ratio of Transmittance vs '2 w XV;`
Reflectance. You can enter a value for BRDF(A) and then use the Solve For )!'Fa_$ e
feature to solve for BTDF, and the editor will display the resulting ;r g H}r
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and N>Vacc_[
to have a ratio that matches the behavior of your surface. If the ratio of T e$ThSh\+ (
vs R is dependent on the Incidence Angle, you can use the Add button in the $o/0A
property to add Incidence ANgles to the table, and then define the BTDF and R)sp
BRDF separately for each incidence angle.
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