| lightgirl |
2008-09-16 16:27 |
Solution: VD=}GY33=
The plastic material with the rough diffusing surface can be modeled in NO(^P+s
TracePro, but as two separate properties (select Define/EditPropertyData). c!,&]*h"k
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MATERIAL PROPERTY >Yr-aDV
A TracePro Material Property can be created, and the index of refraction of
$ f++n5I
the material is entered here, as well as an absorption coefficient if it is nIRJ5|G(
known (this would be for absorption losses just from propogating through a XUI9)Ne
given thickness of a clear polished sample of the material, unrelated to the N)F&c!anh
diffusing surface finish. Entering zero for the absorption coefficient is 1|]IWX|
propobly a reasonable estimate for a transparent material. *$ U+
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The Material Property is applied to the Object (Define/Apply Properties). ^,P#
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H C %tJ:G
SURFACE PROPERTY D'{NEk@
A TracePro Surface Property can specify 5 possible outcomes for light incident wjJM\BKr`
on a surface - Specular Transmission, Specular Reflection, Scattered 7(ni _|$|
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. |rjHH<
-4rXOmi A
For your property, I expect that Specular Transmission, Specular Reflection, ' 7lHWqN<
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). iD;pXE{2s%
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - .f1
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = R?%J
BRDF(g) = 0, which defines a Lambertian dsitribution. hxCSE$f4
3K8#,TK3
The challenge is to determine the proper ratio of Transmittance vs JbV\eE#KrC
Reflectance. You can enter a value for BRDF(A) and then use the Solve For K-_XdJ\
feature to solve for BTDF, and the editor will display the resulting vb o| q [z
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and W0zRV9"P
to have a ratio that matches the behavior of your surface. If the ratio of T uX.^zg]}%
vs R is dependent on the Incidence Angle, you can use the Add button in the zmA]@'j
property to add Incidence ANgles to the table, and then define the BTDF and {;z{U;j
BRDF separately for each incidence angle.
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