lightgirl |
2008-09-16 16:27 |
Solution: A\z`c
e! The plastic material with the rough diffusing surface can be modeled in H}Ucrv: TracePro, but as two separate properties (select Define/EditPropertyData). )RN<GW' KOey8tB)1 MATERIAL PROPERTY @x1%)1 A TracePro Material Property can be created, and the index of refraction of Qzqc .T the material is entered here, as well as an absorption coefficient if it is u%u&F^y known (this would be for absorption losses just from propogating through a 3e% nA8? given thickness of a clear polished sample of the material, unrelated to the ;I}'} diffusing surface finish. Entering zero for the absorption coefficient is
_X4!xbP propobly a reasonable estimate for a transparent material. ;HNq>/{ \'Ssn(s The Material Property is applied to the Object (Define/Apply Properties). 0*8TS7.3 Ipe n SURFACE PROPERTY P(,?#+]- A TracePro Surface Property can specify 5 possible outcomes for light incident R_ ZK 0ar on a surface - Specular Transmission, Specular Reflection, Scattered J0Z7l Transmission (BTDF). Scattered Reflection (BRDF), and Absorption. +D&Pp0xe aI3CNeav For your property, I expect that Specular Transmission, Specular Reflection, tGjhHp8}c and Absorption would all be 0, leaving only Scattered Transmission (BTDF). WBr59@V Scattered Reflection (BRDF). BTDF and BRDF are controlled by 3 coefficients - aUc|V{Jp A, B, and g. For an initial estimate, I would suggest entering BTDF(g) = (W[V?!1 BRDF(g) = 0, which defines a Lambertian dsitribution. /mA,F;
Cr C=A=e The challenge is to determine the proper ratio of Transmittance vs jQ\zG J3 Reflectance. You can enter a value for BRDF(A) and then use the Solve For E{E0Z9t7& feature to solve for BTDF, and the editor will display the resulting 15U (={ Integrated BTDF and Integrated BRDF values. You want these to sum to 1, and nXy>7H[0 to have a ratio that matches the behavior of your surface. If the ratio of T
8|6
4R: vs R is dependent on the Incidence Angle, you can use the Add button in the JH8}Ru%Z property to add Incidence ANgles to the table, and then define the BTDF and @-HG`c ct BRDF separately for each incidence angle.
|
|