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.\" RCSid "$Id" |
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.\" RCSid "$Id$" |
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.\" Print using the -ms macro package |
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.DA 2/17/2011 |
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.DA 09/18/2015 |
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.LP |
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.tl """Copyright \(co 2011 Regents, University of California |
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.tl """Copyright \(co 2015 Regents, University of California |
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.sp 2 |
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.TL |
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The |
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.PP |
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The BSDF material type loads an XML (eXtensible Markup Language) |
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file describing a bidirectional scattering distribution function. |
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– |
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Real arguments to this material may define additional |
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diffuse components that augment the BSDF data. |
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String arguments are used to define thickness for hidden |
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objects and the "up" orientation for the material. |
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String arguments are used to define thickness for proxied |
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surfaces and the "up" orientation for the material. |
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.DS |
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mod BSDF id |
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6+ thick BSDFfile ux uy uz funcfile transform |
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rbdif gbdif bbdif |
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rtdif gtdif btdif |
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.DE |
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The first string argument is a "thickness" parameter that is useful |
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for hiding detail geometry for transmitting systems, e.g., |
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complex fenestration. |
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If a view or shadow ray hits a BSDF surface with non-zero specular transmission |
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and positive thickness, the ray will pass directly through with no |
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reflection or transmission due to the BSDF. |
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The first string argument is a "thickness" parameter that may be used |
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to hide detail geometry being proxied by an aggregate BSDF material. |
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If a view or shadow ray hits a BSDF proxy with non-zero thickness, |
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it will pass directly through as if the surface were not there. |
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Similar to the illum type, this permits direct viewing and |
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shadow testing of complex geometry. |
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In contrast, a scattered ray will use the BSDF transmission, |
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offsetting transmitted sample rays by the thickness amount |
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to avoid any intervening geometry. |
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In this manner, BSDF surfaces may act as simplified stand-ins for detailed |
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system geometry, which may still be present and visible in the simulation. |
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If the BSDF has back-side reflection data, a parallel surface should be |
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specified slightly less than the given thickness away from the front surface |
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to enclose the system geometry on both sides. |
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A zero thickness implies that the BSDF geomtery is all there is, and |
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thickness is ignored if there is no transmitted component, or transmission is |
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purely diffuse. |
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The BSDF is used when a scattered (indirect) ray hits the surface, |
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and any transmitted sample rays will be offset by the thickness amount |
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to avoid the hidden geometry and gather samples from the other side. |
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In this manner, BSDF surfaces can improve the results for indirect |
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scattering from complex systems without sacrificing appearance or |
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shadow accuracy. |
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If the BSDF has transmission and back-side reflection data, |
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a parallel BSDF surface may be |
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placed slightly less than the given thickness away from the front surface |
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to enclose the complex geometry on both sides. |
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The sign of the thickness is important, as it indicates whether the |
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proxied geometry is behind the BSDF surface (when thickness is positive) |
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or in front (when thickness is negative). |
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.LP |
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The second string argument is the name of the BSDF file, which is |
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found in the usual auxiliary locations. |
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in Lausanne, Switzerland. |
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.NH 1 |
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References |
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.LP |
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McNeil, A., C.J. Jonsson, D. Appelfeld, G. Ward, E.S. Lee, |
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``A validation of a ray-tracing tool used to generate |
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bi-directional scattering distribution functions for |
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complex fenestration systems,'' |
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.I "Solar Energy", |
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98, 404-14, November 2013. |
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.LP |
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Ward, G., R. Mistrick, E.S. Lee, A. McNeil, J. Jonsson, |
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``Simulating the Daylight Performance of Complex Fenestration Systems |
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Using Bidirectional Scattering Distribution Functions within Radiance,'' |
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.I "Leukos", |
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7(4), |
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April 2011. |
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.LP |
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Cater, K., A. Chalmers, G. Ward, |
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``Detail to Attention: Exploiting Visual Tasks for Selective Rendering,'' |
