| lightgirl |
2008-09-16 16:27 |
Solution: (_4;') 9
The plastic material with the rough diffusing surface can be modeled in kNT}dv]<
TracePro, but as two separate properties (select Define/EditPropertyData). `]LSbS
n!6Z]\8~$
MATERIAL PROPERTY hLDA]s
A TracePro Material Property can be created, and the index of refraction of d*oU fiW
the material is entered here, as well as an absorption coefficient if it is g o J|oi
known (this would be for absorption losses just from propogating through a 6l$L~>
given thickness of a clear polished sample of the material, unrelated to the X[2[!)Rk
diffusing surface finish. Entering zero for the absorption coefficient is 7 ~ztwL
propobly a reasonable estimate for a transparent material. Z_gC&7+
?: |-Dq,
The Material Property is applied to the Object (Define/Apply Properties). }n7t h
? <Y+peu
SURFACE PROPERTY ~P h\ Sbp
A TracePro Surface Property can specify 5 possible outcomes for light incident XE3'`D !
on a surface - Specular Transmission, Specular Reflection, Scattered ^ FZ^6*
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. >a1{397Y}
IScRsxFb
For your property, I expect that Specular Transmission, Specular Reflection, 'xv8Gwf"
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). bS
>0DU
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - F`nb21{0y&
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = .)|a2d ~F
BRDF(g) = 0, which defines a Lambertian dsitribution. W23]B x
KOg?FmD
The challenge is to determine the proper ratio of Transmittance vs q> s-Y|
Reflectance. You can enter a value for BRDF(A) and then use the Solve For aZKO Y
feature to solve for BTDF, and the editor will display the resulting b dJ+@r
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and \<vNVz7.D
to have a ratio that matches the behavior of your surface. If the ratio of T ?R-9W+U %f
vs R is dependent on the Incidence Angle, you can use the Add button in the cL8#S>>u.
property to add Incidence ANgles to the table, and then define the BTDF and wh:1PP
BRDF separately for each incidence angle.
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