| 869 |
|
.PP |
| 870 |
|
The BSDF material type loads an XML (eXtensible Markup Language) |
| 871 |
|
file describing a bidirectional scattering distribution function. |
| 872 |
– |
|
| 872 |
|
Real arguments to this material may define additional |
| 873 |
|
diffuse components that augment the BSDF data. |
| 874 |
< |
String arguments are used to define thickness for hidden |
| 875 |
< |
objects and the "up" orientation for the material. |
| 874 |
> |
String arguments are used to define thickness for proxied |
| 875 |
> |
surfaces and the "up" orientation for the material. |
| 876 |
|
.DS |
| 877 |
|
mod BSDF id |
| 878 |
|
6+ thick BSDFfile ux uy uz funcfile transform |
| 882 |
|
rbdif gbdif bbdif |
| 883 |
|
rtdif gtdif btdif |
| 884 |
|
.DE |
| 885 |
< |
The first string argument is a "thickness" parameter that is useful |
| 886 |
< |
for hiding detail geometry for transmitting systems, e.g., |
| 887 |
< |
complex fenestration. |
| 888 |
< |
If a view or shadow ray hits a BSDF surface with non-zero specular transmission |
| 890 |
< |
and positive thickness, the ray will pass directly through with no |
| 891 |
< |
reflection or transmission due to the BSDF. |
| 885 |
> |
The first string argument is a "thickness" parameter that may be used |
| 886 |
> |
to hide detail geometry being proxied by an aggregate BSDF material. |
| 887 |
> |
If a view or shadow ray hits a BSDF proxy with non-zero thickness, |
| 888 |
> |
it will pass directly through as if the surface were not there. |
| 889 |
|
Similar to the illum type, this permits direct viewing and |
| 890 |
|
shadow testing of complex geometry. |
| 891 |
< |
In contrast, a scattered ray will use the BSDF transmission, |
| 892 |
< |
offsetting transmitted sample rays by the thickness amount |
| 893 |
< |
to avoid any intervening geometry. |
| 894 |
< |
In this manner, BSDF surfaces may act as simplified stand-ins for detailed |
| 895 |
< |
system geometry, which may still be present and visible in the simulation. |
| 896 |
< |
If the BSDF has back-side reflection data, a parallel surface should be |
| 897 |
< |
specified slightly less than the given thickness away from the front surface |
| 898 |
< |
to enclose the system geometry on both sides. |
| 899 |
< |
A zero thickness implies that the BSDF geomtery is all there is, and |
| 900 |
< |
thickness is ignored if there is no transmitted component, or transmission is |
| 901 |
< |
purely diffuse. |
| 891 |
> |
The BSDF is used when a scattered (indirect) ray hits the surface, |
| 892 |
> |
and any transmitted sample rays will be offset by the thickness amount |
| 893 |
> |
to avoid the hidden geometry and gather samples from the other side. |
| 894 |
> |
In this manner, BSDF surfaces can improve the results for indirect |
| 895 |
> |
scattering from complex systems without sacrificing appearance or |
| 896 |
> |
shadow accuracy. |
| 897 |
> |
If the BSDF has transmission and back-side reflection data, |
| 898 |
> |
a parallel BSDF surface may be |
| 899 |
> |
placed slightly less than the given thickness away from the front surface |
| 900 |
> |
to enclose the complex geometry on both sides. |
| 901 |
> |
The sign of the thickness is important, as it indicates whether the |
| 902 |
> |
proxied geometry is behind the BSDF surface (when thickness is positive) |
| 903 |
> |
or in front (when thickness is negative). |
| 904 |
|
.LP |
| 905 |
|
The second string argument is the name of the BSDF file, which is |
| 906 |
|
found in the usual auxiliary locations. |
| 1551 |
|
in Lausanne, Switzerland. |
| 1552 |
|
.NH 1 |
| 1553 |
|
References |
| 1554 |
+ |
.LP |
| 1555 |
+ |
Ward, G., R. Mistrick, E.S. Lee, A. McNeil, J. Jonsson, |
| 1556 |
+ |
``Simulating the Daylight Performance of Complex Fenestration Systems |
| 1557 |
+ |
Using Bidirectional Scattering Distribution Functions within Radiance,'' |
| 1558 |
+ |
.I "Journal of the Illuminating Engineering Soc. of North America", |
| 1559 |
+ |
April 2011. |
| 1560 |
|
.LP |
| 1561 |
|
Cater, K., A. Chalmers, G. Ward, |
| 1562 |
|
``Detail to Attention: Exploiting Visual Tasks for Selective Rendering,'' |
