| lightgirl |
2008-09-16 16:27 |
Solution: 9T`$ gAI
The plastic material with the rough diffusing surface can be modeled in DrAp&A|WV|
TracePro, but as two separate properties (select Define/EditPropertyData). VFm G \
4b\R@Knu
MATERIAL PROPERTY .<#oLM^
A TracePro Material Property can be created, and the index of refraction of UweXz.x7
the material is entered here, as well as an absorption coefficient if it is 41-u*$
known (this would be for absorption losses just from propogating through a jXa;ov PK
given thickness of a clear polished sample of the material, unrelated to the xIOYwVC
diffusing surface finish. Entering zero for the absorption coefficient is q m J#cmN
propobly a reasonable estimate for a transparent material. sBN"eHg
p$5uS=:4`8
The Material Property is applied to the Object (Define/Apply Properties). 49 ('pq?D
s5`CV$bz
SURFACE PROPERTY t@#+vs@
A TracePro Surface Property can specify 5 possible outcomes for light incident Sw1z^`
on a surface - Specular Transmission, Specular Reflection, Scattered !?AgAsSmc
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. h>w(Th\H
wwvS05=[T
For your property, I expect that Specular Transmission, Specular Reflection, 71S~*"O0f
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). B=?m_4\$m
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - D^_] x51>
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = cDkq@H:
BRDF(g) = 0, which defines a Lambertian dsitribution. !^[i"F:G
I{/}pr>
The challenge is to determine the proper ratio of Transmittance vs M%yeI{m
Reflectance. You can enter a value for BRDF(A) and then use the Solve For Q1Jw7R #?l
feature to solve for BTDF, and the editor will display the resulting '' P u
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and VnjhEEM!
to have a ratio that matches the behavior of your surface. If the ratio of T jDO"?@+
vs R is dependent on the Incidence Angle, you can use the Add button in the (h8RthQt
property to add Incidence ANgles to the table, and then define the BTDF and M]5)u=}S-
BRDF separately for each incidence angle.
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