| lightgirl |
2008-09-16 16:27 |
Solution: .q>4? +
The plastic material with the rough diffusing surface can be modeled in Od> ^yhn
TracePro, but as two separate properties (select Define/EditPropertyData). N'#Lb0`B
""dX4^gtU
MATERIAL PROPERTY ic"n*S Za
A TracePro Material Property can be created, and the index of refraction of 6iozb~!Rr
the material is entered here, as well as an absorption coefficient if it is h%hE$2
known (this would be for absorption losses just from propogating through a lO+<T[
given thickness of a clear polished sample of the material, unrelated to the {GaQV -t
diffusing surface finish. Entering zero for the absorption coefficient is S[TJ{ L(
propobly a reasonable estimate for a transparent material. + UK" .
#&@qmps(T
The Material Property is applied to the Object (Define/Apply Properties). +!(W>4F
) OqQz7'
SURFACE PROPERTY x bG'![OX
A TracePro Surface Property can specify 5 possible outcomes for light incident ~N i#xa
on a surface - Specular Transmission, Specular Reflection, Scattered .>(?c92
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. '.@'^80iQ
"hRY+{m
For your property, I expect that Specular Transmission, Specular Reflection, J.`z;0]op
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). 3wS{@'
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - F4m Q#YlrS
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = MuQBn7F{c
BRDF(g) = 0, which defines a Lambertian dsitribution. iw Hy!Vi-5
CIM 9~:\
The challenge is to determine the proper ratio of Transmittance vs A%VBBvk
Reflectance. You can enter a value for BRDF(A) and then use the Solve For !Q,A# N(
feature to solve for BTDF, and the editor will display the resulting c=YJ:&/5&
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and L"i
B'=
to have a ratio that matches the behavior of your surface. If the ratio of T >.D0McQg
vs R is dependent on the Incidence Angle, you can use the Add button in the X^tVq..0
property to add Incidence ANgles to the table, and then define the BTDF and J,s)Fu\j@
BRDF separately for each incidence angle.
|
|
