| 11 |
|
][ |
| 12 |
|
.B "\-r 'rtcontrib opts...'" |
| 13 |
|
][ |
| 14 |
+ |
.B "\-t{3|4} Nlog2" |
| 15 |
+ |
][ |
| 16 |
|
.B "{+|-}forward" |
| 17 |
|
][ |
| 18 |
|
.B "{+|-}backward" |
| 89 |
|
included on the |
| 90 |
|
.I rtcontrib |
| 91 |
|
command line. |
| 92 |
+ |
.PP |
| 93 |
+ |
The |
| 94 |
+ |
.I \-t4 |
| 95 |
+ |
mode computes a non-uniform BSDF represented as a rank 4 tensor tree, |
| 96 |
+ |
suitable for use in the Radiance rendering tools. |
| 97 |
+ |
The parameter given to this option is the log to the base 2 of the |
| 98 |
+ |
sampling resolution in each dimension, and must be an integer. |
| 99 |
+ |
The |
| 100 |
+ |
.I \-c |
| 101 |
+ |
setting should be adjusted so that an appropriate number of samples |
| 102 |
+ |
lands in each region. |
| 103 |
+ |
A |
| 104 |
+ |
.I \-t4 |
| 105 |
+ |
parameter of 5 corresponds to 32x32 or 1024 output regions, so a |
| 106 |
+ |
.I \-c |
| 107 |
+ |
setting of 102400 would provide 100 samples per region on average. |
| 108 |
+ |
Increasing the resolution to 6 corresponds to 64x64 or 4096 |
| 109 |
+ |
regions, so the |
| 110 |
+ |
.I \-c |
| 111 |
+ |
setting would need to be increased by a factor of 4 to provide |
| 112 |
+ |
the same accuracy in each region. |
| 113 |
+ |
.PP |
| 114 |
+ |
The |
| 115 |
+ |
.I \-t3 |
| 116 |
+ |
mode is similar to |
| 117 |
+ |
.I \-t4 |
| 118 |
+ |
but computes a rank 3 tensor tree rather than rank 4. |
| 119 |
+ |
This provides a much faster computation, but only works |
| 120 |
+ |
in special circumstances. |
| 121 |
+ |
Specifically, do NOT use this option if the system is not in fact isotropic. |
| 122 |
+ |
I.e., only use |
| 123 |
+ |
.I \-t3 |
| 124 |
+ |
when you are certain that the system has a high degree of radial symmetry. |
| 125 |
+ |
Again, the parameter to this option sets the maximum resolution as |
| 126 |
+ |
a power of 2 in each dimension, but in this case there is one less |
| 127 |
+ |
dimension being sampled. |
| 128 |
|
.SH EXAMPLE |
| 129 |
|
To create a BSDF description including geometry from a set of venetian blinds: |
| 130 |
|
.IP "" .2i |
| 131 |
|
genblinds blind_white blind1 .07 3 1.5 30 40 | xform -rz -90 -rx 90 > blind1.rad |
| 132 |
|
.br |
| 133 |
|
genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml |
| 134 |
+ |
.PP |
| 135 |
+ |
To create a non-uniform, anisotropic BSDF distribution with a maximum |
| 136 |
+ |
resolution of 128x128 from the same description: |
| 137 |
+ |
.IP "" .2i |
| 138 |
+ |
genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml |
| 139 |
+ |
.SH NOTES |
| 140 |
+ |
The variable resolution (tensor tree) BSDF representation is not supported |
| 141 |
+ |
by all software and applicatons, and should be used with caution. |
| 142 |
+ |
It provides practical, high-resolution data for use in the |
| 143 |
+ |
Radiance rendering programs, but does not work in the matrix formulation |
| 144 |
+ |
of the daylight coefficient method for example. |
| 145 |
+ |
Also, third party tools generally expect or require a fixed number of sample |
| 146 |
+ |
directions using the Klems directions or similar. |
| 147 |
|
.SH AUTHOR |
| 148 |
|
Greg Ward |
| 149 |
|
.SH "SEE ALSO" |
