| lightgirl |
2008-09-16 16:27 |
Solution: K"r*M.P>
The plastic material with the rough diffusing surface can be modeled in E2m8UBS
TracePro, but as two separate properties (select Define/EditPropertyData). )a-Du$kd
m}X`> aD/
MATERIAL PROPERTY m@^ 1 JlH
A TracePro Material Property can be created, and the index of refraction of qTqwPWW*
the material is entered here, as well as an absorption coefficient if it is L31HG H2l
known (this would be for absorption losses just from propogating through a t2l S
~l)
given thickness of a clear polished sample of the material, unrelated to the NgY =&W,
diffusing surface finish. Entering zero for the absorption coefficient is 7(5
4/
propobly a reasonable estimate for a transparent material. g[ 3)P+
q#s,- u u
The Material Property is applied to the Object (Define/Apply Properties). ) BwjZMJ.N
)gMG #>up@
SURFACE PROPERTY !1 ED~3 /X
A TracePro Surface Property can specify 5 possible outcomes for light incident 7R`mf
on a surface - Specular Transmission, Specular Reflection, Scattered PbmDNKEh{
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. sJDas,7>
<"_d ]?,
For your property, I expect that Specular Transmission, Specular Reflection, } q$ WvY/
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). \ioH\9
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - c` o7d)_Ke
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = !7kG!)40
BRDF(g) = 0, which defines a Lambertian dsitribution. `5C,N!d8X
s{$(* _
The challenge is to determine the proper ratio of Transmittance vs uB]b}"+l
Reflectance. You can enter a value for BRDF(A) and then use the Solve For D}mjN=Y
feature to solve for BTDF, and the editor will display the resulting 6*3.SGUY
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and #H :7@
to have a ratio that matches the behavior of your surface. If the ratio of T F~P%AjAx'
vs R is dependent on the Incidence Angle, you can use the Add button in the * cgI.+
property to add Incidence ANgles to the table, and then define the BTDF and lqm1!5dt
BRDF separately for each incidence angle.
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