| lightgirl |
2008-09-16 16:27 |
Solution: X 6 lH|R
The plastic material with the rough diffusing surface can be modeled in T"T;`y@ (
TracePro, but as two separate properties (select Define/EditPropertyData). _Cy:]2o
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MATERIAL PROPERTY 'r} zY-FM`
A TracePro Material Property can be created, and the index of refraction of mmEp' E
the material is entered here, as well as an absorption coefficient if it is * U=]@I}J
known (this would be for absorption losses just from propogating through a pilh@#_h
given thickness of a clear polished sample of the material, unrelated to the H]\Zn%.#
diffusing surface finish. Entering zero for the absorption coefficient is T;\^#1
propobly a reasonable estimate for a transparent material. y/? &pKH^
p<`+sf}A:
The Material Property is applied to the Object (Define/Apply Properties). WlV
z,t'if
B|%tE{F
SURFACE PROPERTY VW@ x=m
A TracePro Surface Property can specify 5 possible outcomes for light incident w %c
on a surface - Specular Transmission, Specular Reflection, Scattered W~ U Lc 9
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. `7+j0kV)
~vgA7E/XV
For your property, I expect that Specular Transmission, Specular Reflection, 4ZC!SgJo
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). m-V02's
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - V5D2\n3A
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = _7kM]" >j
BRDF(g) = 0, which defines a Lambertian dsitribution. +m,!e*g
,>LRa
The challenge is to determine the proper ratio of Transmittance vs Zg:gY"^
Reflectance. You can enter a value for BRDF(A) and then use the Solve For g):]'
feature to solve for BTDF, and the editor will display the resulting d"~(T:=r
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and H] 31l~@]
to have a ratio that matches the behavior of your surface. If the ratio of T U5/qf8) yO
vs R is dependent on the Incidence Angle, you can use the Add button in the
1;| L I?
property to add Incidence ANgles to the table, and then define the BTDF and -DO& _`kn
BRDF separately for each incidence angle.
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