| lightgirl |
2008-09-16 16:27 |
Solution: qb$_xIQpDL
The plastic material with the rough diffusing surface can be modeled in %yhI;M^
TracePro, but as two separate properties (select Define/EditPropertyData). 2fP~;\AP
w`Xg%*]}
MATERIAL PROPERTY v>:=w|.HC
A TracePro Material Property can be created, and the index of refraction of j J-d/"(
the material is entered here, as well as an absorption coefficient if it is SJ[AiHR
known (this would be for absorption losses just from propogating through a @#CF".fuN>
given thickness of a clear polished sample of the material, unrelated to the T0?uC/7H
diffusing surface finish. Entering zero for the absorption coefficient is oek #^:pF
propobly a reasonable estimate for a transparent material. kYtHX ~@
\bRy(Z)
The Material Property is applied to the Object (Define/Apply Properties). X#7}c5 ^Y
3FY_A(+
SURFACE PROPERTY Z fqQ {_
A TracePro Surface Property can specify 5 possible outcomes for light incident c.-cpFk^L&
on a surface - Specular Transmission, Specular Reflection, Scattered oB}K[3uB:t
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. i P,v=pS6
4JSZ0: O
For your property, I expect that Specular Transmission, Specular Reflection, c
_p[yS
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). 6d};|#}
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - w Oj88J)
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = uDI}R]8~
BRDF(g) = 0, which defines a Lambertian dsitribution. O sB?1;:
7 y>(H<^>
The challenge is to determine the proper ratio of Transmittance vs gE1|lY$NL
Reflectance. You can enter a value for BRDF(A) and then use the Solve For &|NZ8:*+#
feature to solve for BTDF, and the editor will display the resulting 1V0sl 0i4
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and q
/:T1a7!
to have a ratio that matches the behavior of your surface. If the ratio of T ]p\u$VY9
vs R is dependent on the Incidence Angle, you can use the Add button in the )5'rw<:="
property to add Incidence ANgles to the table, and then define the BTDF and hw|t8 ShW
BRDF separately for each incidence angle.
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