| lightgirl |
2008-09-16 16:27 |
Solution: ~GJN@ka4%
The plastic material with the rough diffusing surface can be modeled in *1{S*`|cJy
TracePro, but as two separate properties (select Define/EditPropertyData). Q7gY3flg
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MATERIAL PROPERTY 6Pn8f
A TracePro Material Property can be created, and the index of refraction of @
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the material is entered here, as well as an absorption coefficient if it is ,RxYd6
known (this would be for absorption losses just from propogating through a ir16
given thickness of a clear polished sample of the material, unrelated to the Y[Ltrk{
diffusing surface finish. Entering zero for the absorption coefficient is X"q!Y#)
propobly a reasonable estimate for a transparent material. 2+o |A
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The Material Property is applied to the Object (Define/Apply Properties). B*1W`f
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SURFACE PROPERTY B[5r|d'
A TracePro Surface Property can specify 5 possible outcomes for light incident ;AJTytE>%
on a surface - Specular Transmission, Specular Reflection, Scattered %ZP+zh n}
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. rw7_5l
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For your property, I expect that Specular Transmission, Specular Reflection, xJs; v
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). x3p ND
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - ^pnG0( 9
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = !xIm 2+:(
BRDF(g) = 0, which defines a Lambertian dsitribution. Xz 4 x
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The challenge is to determine the proper ratio of Transmittance vs fyWO
Reflectance. You can enter a value for BRDF(A) and then use the Solve For up '
feature to solve for BTDF, and the editor will display the resulting }/P5 >F<H[
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and 8Q{9>^
to have a ratio that matches the behavior of your surface. If the ratio of T <plC_{Y:wu
vs R is dependent on the Incidence Angle, you can use the Add button in the C0*@0~8$9
property to add Incidence ANgles to the table, and then define the BTDF and ]rN5Ao}2
BRDF separately for each incidence angle.
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