| 9 |
|
][ |
| 10 |
|
.B "\-n Nproc" |
| 11 |
|
][ |
| 12 |
+ |
.B "\-r 'rtcontrib opts...'" |
| 13 |
+ |
][ |
| 14 |
+ |
.B "\-t{3|4} Nlog2" |
| 15 |
+ |
][ |
| 16 |
+ |
.B "{+|-}forward" |
| 17 |
+ |
][ |
| 18 |
+ |
.B "{+|-}backward" |
| 19 |
+ |
][ |
| 20 |
|
.B "{+|-}mgf" |
| 21 |
|
][ |
| 22 |
< |
.B "{+|-}geom |
| 22 |
> |
.B "{+|-}geom unit" |
| 23 |
|
][ |
| 24 |
|
.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax" |
| 25 |
|
] |
| 28 |
|
] |
| 29 |
|
.SH DESCRIPTION |
| 30 |
|
.I GenBSDF |
| 31 |
< |
computes a bidirectional transmittance distribution function from |
| 31 |
> |
computes a bidirectional scattering distribution function from |
| 32 |
|
a Radiance or MGF scene description given on the input. |
| 33 |
|
The program assumes the input is in Radiance format unless the |
| 34 |
|
.I \+mgf |
| 36 |
|
The output conforms to the LBNL Window 6 XML standard for BSDF data, |
| 37 |
|
and will include an MGF representation of the input geometry if the |
| 38 |
|
.I \+geom |
| 39 |
< |
option is given. |
| 40 |
< |
(This is currently the default, and may be switche off using |
| 41 |
< |
.I \-geom.)\0 |
| 39 |
> |
option is given, followed by one of "meter," "foot," "inch," |
| 40 |
> |
"centimeter," or "millimeter," depending on the scene units. |
| 41 |
> |
The default is to include the provided geometry, |
| 42 |
> |
which is assumed to be in meters. |
| 43 |
> |
Geometry output can be supressed with the |
| 44 |
> |
.I \-geom |
| 45 |
> |
option, which must also be followed by one of the above length units. |
| 46 |
|
.PP |
| 47 |
+ |
Normally, |
| 48 |
+ |
.I genBSDF |
| 49 |
+ |
computes components needed by a backwards ray-tracing process, |
| 50 |
+ |
.I \+backward. |
| 51 |
+ |
If both forward and backward (front and back) distributions are needed, the |
| 52 |
+ |
.I \+forward |
| 53 |
+ |
option may be given. |
| 54 |
+ |
To turn off backward components, use the |
| 55 |
+ |
.I \-backward |
| 56 |
+ |
option. |
| 57 |
+ |
Computing both components takes about twice as long as one component. |
| 58 |
+ |
.PP |
| 59 |
|
The geometry must fit a rectangular profile, whose width is along the X-axis, |
| 60 |
|
height is in the Y-axis, and depth is in the Z-axis. |
| 61 |
|
The positive Z-axis points into the room, and the input geometry should |
| 78 |
|
samples per incident direction using the |
| 79 |
|
.I \-c |
| 80 |
|
option. |
| 81 |
< |
This value defaults to 1000 samples distributed over the incoming plane |
| 81 |
> |
This value defaults to 2000 samples distributed over the incoming plane |
| 82 |
|
for each of the 145 Klems hemisphere directions. |
| 83 |
|
.PP |
| 84 |
|
In some cases, the processing time may be reduced by the |
| 87 |
|
.I rtrace(1) |
| 88 |
|
processes to run in |
| 89 |
|
.I rtcontrib(1). |
| 90 |
+ |
The |
| 91 |
+ |
.I \-r |
| 92 |
+ |
option may be used to specify a set of quoted arguments to be |
| 93 |
+ |
included on the |
| 94 |
+ |
.I rtcontrib |
| 95 |
+ |
command line. |
| 96 |
+ |
.PP |
| 97 |
+ |
The |
| 98 |
+ |
.I \-t4 |
| 99 |
+ |
mode computes a non-uniform BSDF represented as a rank 4 tensor tree, |
| 100 |
+ |
suitable for use in the Radiance rendering tools. |
| 101 |
+ |
The parameter given to this option is the log to the base 2 of the |
| 102 |
+ |
sampling resolution in each dimension, and must be an integer. |
| 103 |
+ |
The |
| 104 |
+ |
.I \-c |
| 105 |
+ |
setting should be adjusted so that an appropriate number of samples |
| 106 |
+ |
lands in each region. |
| 107 |
+ |
A |
| 108 |
+ |
.I \-t4 |
| 109 |
+ |
parameter of 5 corresponds to 32x32 or 1024 output regions, so a |
| 110 |
+ |
.I \-c |
| 111 |
+ |
setting of 10240 would provide 10 samples per region on average. |
| 112 |
+ |
Increasing the resolution to 6 corresponds to 64x64 or 4096 |
| 113 |
+ |
regions, so the |
| 114 |
+ |
.I \-c |
| 115 |
+ |
setting would need to be increased by a factor of 4 to provide |
| 116 |
+ |
the same accuracy in each region. |
| 117 |
+ |
.PP |
| 118 |
+ |
The |
| 119 |
+ |
.I \-t3 |
| 120 |
+ |
mode is similar to |
| 121 |
+ |
.I \-t4 |
| 122 |
+ |
but computes a rank 3 tensor tree rather than rank 4. |
| 123 |
+ |
This provides a much faster computation, but only works |
| 124 |
+ |
in special circumstances. |
| 125 |
+ |
Specifically, do NOT use this option if the system is not in fact isotropic. |
| 126 |
+ |
I.e., only use |
| 127 |
+ |
.I \-t3 |
| 128 |
+ |
when you are certain that the system has a high degree of radial symmetry. |
| 129 |
+ |
Again, the parameter to this option sets the maximum resolution as |
| 130 |
+ |
a power of 2 in each dimension, but in this case there is one less |
| 131 |
+ |
dimension being sampled. |
| 132 |
|
.SH EXAMPLE |
| 133 |
|
To create a BSDF description including geometry from a set of venetian blinds: |
| 134 |
|
.IP "" .2i |
| 135 |
|
genblinds blind_white blind1 .07 3 1.5 30 40 | xform -rz -90 -rx 90 > blind1.rad |
| 136 |
|
.br |
| 137 |
< |
genBSDF blind_white.mat glazing.rad blind1.rad > blind1.xml |
| 137 |
> |
genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml |
| 138 |
> |
.PP |
| 139 |
> |
To create a non-uniform, anisotropic BSDF distribution with a maximum |
| 140 |
> |
resolution of 128x128 from the same description: |
| 141 |
> |
.IP "" .2i |
| 142 |
> |
genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml |
| 143 |
|
.SH NOTES |
| 144 |
< |
Currently, |
| 145 |
< |
.I genBSDF |
| 146 |
< |
computes only the forward visible transmitted component, |
| 147 |
< |
though the XML specification provides for front and back |
| 148 |
< |
transmission and reflection as well. |
| 144 |
> |
The variable resolution (tensor tree) BSDF representation is not supported |
| 145 |
> |
by all software and applicatons, and should be used with caution. |
| 146 |
> |
It provides practical, high-resolution data for use in the |
| 147 |
> |
Radiance rendering programs, but does not work in the matrix formulation |
| 148 |
> |
of the daylight coefficient method for example. |
| 149 |
> |
Also, third party tools generally expect or require a fixed number of sample |
| 150 |
> |
directions using the Klems directions or similar. |
| 151 |
|
.SH AUTHOR |
| 152 |
|
Greg Ward |
| 153 |
|
.SH "SEE ALSO" |
| 154 |
< |
dctimestep(1), genklemsamp(1), genskyvec(1), mkillum(1), rtcontrib(1), rtrace(1) |
| 154 |
> |
dctimestep(1), genklemsamp(1), genskyvec(1), mkillum(1), |
| 155 |
> |
pkgBSDF(1), rtcontrib(1), rtrace(1) |
