| lightgirl |
2008-09-16 16:27 |
Solution: i 3(bg,
The plastic material with the rough diffusing surface can be modeled in %o^'(L@z
TracePro, but as two separate properties (select Define/EditPropertyData). 1iF
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W-Hw%bwN/q
MATERIAL PROPERTY xwK<f6H! y
A TracePro Material Property can be created, and the index of refraction of W&+UF'F2
the material is entered here, as well as an absorption coefficient if it is yDy3;*lE
known (this would be for absorption losses just from propogating through a W e9C9)0
given thickness of a clear polished sample of the material, unrelated to the (qB$I\
diffusing surface finish. Entering zero for the absorption coefficient is hnE@+(d=qJ
propobly a reasonable estimate for a transparent material. >@ge[MuS
d@] 0 =Ax
The Material Property is applied to the Object (Define/Apply Properties). 3~Ipcr
B
3n6_yK+D
SURFACE PROPERTY CXA) Zl5#
A TracePro Surface Property can specify 5 possible outcomes for light incident 7 NJ1cQ-}t
on a surface - Specular Transmission, Specular Reflection, Scattered f}XUxIQ-<
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. LZ\}Kgi(!T
#a} fI
For your property, I expect that Specular Transmission, Specular Reflection, . 1?AU 6\
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). M-|4cd]6
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - 'lIT7MK
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = 6aMqU?-
BRDF(g) = 0, which defines a Lambertian dsitribution. M^g" U `
`n5|4yaG~
The challenge is to determine the proper ratio of Transmittance vs &x;v&
Reflectance. You can enter a value for BRDF(A) and then use the Solve For <=jE,6_|
feature to solve for BTDF, and the editor will display the resulting Z;??j+`Eo
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and wU+ofj;
+I
to have a ratio that matches the behavior of your surface. If the ratio of T trgj]|?M
vs R is dependent on the Incidence Angle, you can use the Add button in the OZk(VMuI
property to add Incidence ANgles to the table, and then define the BTDF and `wk#5[Y_
BRDF separately for each incidence angle.
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