| lightgirl |
2008-09-16 16:27 |
Solution: N q
%@ (K
The plastic material with the rough diffusing surface can be modeled in J5 PXmL
TracePro, but as two separate properties (select Define/EditPropertyData). Dl hb'*@
O}\$E {-
MATERIAL PROPERTY b#cXn4< 3D
A TracePro Material Property can be created, and the index of refraction of & xOEp
the material is entered here, as well as an absorption coefficient if it is H SEfpbh
known (this would be for absorption losses just from propogating through a :/'2@M
given thickness of a clear polished sample of the material, unrelated to the 9')
diffusing surface finish. Entering zero for the absorption coefficient is o!6gl]U'y9
propobly a reasonable estimate for a transparent material. 3}{ od$3G
Cw "Y=`
The Material Property is applied to the Object (Define/Apply Properties). 7,U^v}$
j8kax/*[
SURFACE PROPERTY NU>={ 9!
A TracePro Surface Property can specify 5 possible outcomes for light incident ``bIqY
on a surface - Specular Transmission, Specular Reflection, Scattered e\%emp->
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. kd^ C Z;O
P+00wbx0
For your property, I expect that Specular Transmission, Specular Reflection, ab4(?-'-
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). K~Lh'6
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - FTvFtdY
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) =
meQ>mW
BRDF(g) = 0, which defines a Lambertian dsitribution. B[k {u#Kp
8$</HNu,
The challenge is to determine the proper ratio of Transmittance vs z /zUb``
Reflectance. You can enter a value for BRDF(A) and then use the Solve For rMkoE7 n
feature to solve for BTDF, and the editor will display the resulting Bu4J8eLx
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and 8z\v|-%Z
to have a ratio that matches the behavior of your surface. If the ratio of T yxq+<A4,a
vs R is dependent on the Incidence Angle, you can use the Add button in the 9AQMB1D*v4
property to add Incidence ANgles to the table, and then define the BTDF and /7Z5_q_
BRDF separately for each incidence angle.
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