| lightgirl |
2008-09-16 16:27 |
Solution: < RGH+4LF
The plastic material with the rough diffusing surface can be modeled in kA:mB;:
TracePro, but as two separate properties (select Define/EditPropertyData). i9 ;
G;Li!H
MATERIAL PROPERTY `H+"7SO
A TracePro Material Property can be created, and the index of refraction of 2Y
vr|] \8
the material is entered here, as well as an absorption coefficient if it is uU H4vUa
known (this would be for absorption losses just from propogating through a ^4dE8Ve"@
given thickness of a clear polished sample of the material, unrelated to the o*cu-j3
diffusing surface finish. Entering zero for the absorption coefficient is ]juPm8e F
propobly a reasonable estimate for a transparent material. n|( l PbD
U"PcNQy
The Material Property is applied to the Object (Define/Apply Properties). !}(B=-
M3(N!xT
SURFACE PROPERTY hyI7X7Hy
A TracePro Surface Property can specify 5 possible outcomes for light incident s g2 ;"E@
on a surface - Specular Transmission, Specular Reflection, Scattered ^q:-ZgM>
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. i?x gV_q;
Npp YUY
For your property, I expect that Specular Transmission, Specular Reflection, xe@1H\ 7:
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). |7qt/z
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - .ZTvOm'mB^
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = =)a24PDG
BRDF(g) = 0, which defines a Lambertian dsitribution. I652Fcj
Q Be6\oq
The challenge is to determine the proper ratio of Transmittance vs N XW *{b
Reflectance. You can enter a value for BRDF(A) and then use the Solve For Ds9)e&yYrb
feature to solve for BTDF, and the editor will display the resulting K d&/9<{>
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and +jm,nM9
to have a ratio that matches the behavior of your surface. If the ratio of T B
`(jTL
vs R is dependent on the Incidence Angle, you can use the Add button in the lSxb:$g
property to add Incidence ANgles to the table, and then define the BTDF and M 5dYcCDE
BRDF separately for each incidence angle.
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