| lightgirl |
2008-09-16 16:27 |
Solution: )NF5,eD
The plastic material with the rough diffusing surface can be modeled in DsJ ikg(J
TracePro, but as two separate properties (select Define/EditPropertyData). ujin+;1
DtEvt+ h
MATERIAL PROPERTY 8NF93tqD6
A TracePro Material Property can be created, and the index of refraction of 0Y >5&
the material is entered here, as well as an absorption coefficient if it is Fal##6B
known (this would be for absorption losses just from propogating through a ,|}}Ml
given thickness of a clear polished sample of the material, unrelated to the xdLMy#U2
diffusing surface finish. Entering zero for the absorption coefficient is W( 4Mvd
propobly a reasonable estimate for a transparent material. % _.kd"
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The Material Property is applied to the Object (Define/Apply Properties). |lDxk[
a^vTBJXo
SURFACE PROPERTY %[cZ, F=
A TracePro Surface Property can specify 5 possible outcomes for light incident {<}9r6k ;f
on a surface - Specular Transmission, Specular Reflection, Scattered "1P[D'HV4|
Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. 42oW]b%P{;
XJZ\ ss
For your property, I expect that Specular Transmission, Specular Reflection, |l-~,eRvi5
and Absorption would all be 0, leaving only Scattered Transmission (BTDF). Qj lQsN!
Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - ApD`i+ Y@
A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = :kMF.9 U:
BRDF(g) = 0, which defines a Lambertian dsitribution. L*6R5i>
=?3b3PZn
The challenge is to determine the proper ratio of Transmittance vs :{LNr!I?I
Reflectance. You can enter a value for BRDF(A) and then use the Solve For ROhhd.
feature to solve for BTDF, and the editor will display the resulting 9 _oAs"w
Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and $xU)t&Df
to have a ratio that matches the behavior of your surface. If the ratio of T Y&u wi :_g
vs R is dependent on the Incidence Angle, you can use the Add button in the |NdWx1
property to add Incidence ANgles to the table, and then define the BTDF and 56?RFnZ&j
BRDF separately for each incidence angle.
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