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Revision 1.5 by greg, Fri May 6 23:58:09 2011 UTC vs.
Revision 1.24 by greg, Wed Apr 2 00:55:27 2025 UTC

# Line 9 | Line 9 | genBSDF - generate BSDF description from Radiance or M
9   ][
10   .B "\-n Nproc"
11   ][
12 < .B "\-r 'rtcontrib opts...'"
12 > .B "\-r 'rcontrib opts...'"
13   ][
14 + .B "\-W"
15 + ][
16 + .B "\-s 'x=string;y=string'"
17 + ][
18 + .B "\-t{3|4} Nlog2"
19 + ][
20 + .B "{+|-}C"
21 + ][
22 + .B "{+|-}a"
23 + ][
24   .B "{+|-}forward"
25   ][
26   .B "{+|-}backward"
27   ][
28   .B "{+|-}mgf"
29   ][
30 < .B "{+|-}geom
30 > .B "{+|-}geom unit"
31   ][
32   .B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
33   ]
34   [
35   .B "geom .."
36   ]
37 + .br
38 + or
39 + .br
40 + .B genBSDF
41 + .B "\-recover tempdir"
42   .SH DESCRIPTION
43   .I GenBSDF
44   computes a bidirectional scattering distribution function from
# Line 34 | Line 49 | option is specified.
49   The output conforms to the LBNL Window 6 XML standard for BSDF data,
50   and will include an MGF representation of the input geometry if the
51   .I \+geom
52 < option is given.
53 < (This is the default, and may be switched off using
54 < .I \-geom.)\0
52 > option is given, followed by one of "meter," "foot," "inch,"
53 > "centimeter," or "millimeter," depending on the scene units.
54 > The default is to include the provided geometry,
55 > which is assumed to be in meters.
56 > Geometry output can be supressed with the
57 > .I \-geom
58 > option, which must also be followed by one of the above length units.
59   .PP
60   Normally,
61   .I genBSDF
# Line 48 | Line 67 | option may be given.
67   To turn off backward components, use the
68   .I \-backward
69   option.
70 < Computing both components takes about twice as long as one component.
70 > Computing both components takes about twice as long as one component, but
71 > is recommended when rays will be impinging from either side.
72   .PP
73 + The
74 + .I \+C
75 + option specifies that the output XML should include tristimulus
76 + color information, which is interpreted by the rendering programs.
77 + The default option
78 + .I \-C
79 + reduces all BSDF data to grayscale.
80 + If the input is spectral and a
81 + .I \-cs
82 + parameter of 9 or more is specified as part of the rendering
83 + .I \-r
84 + option list, then full spectral result will be
85 + reduced to an XYZ-equivalent CIE color space in the XML output.
86 + .PP
87 + The
88 + .I \-a
89 + option turns off reciprocity averaging for tensor tree output.
90 + Normally on (+a), this ensures that each tensor-tree hemisphere follows symmetry
91 + implied by Helmholtz reciprocity, and is designed to reduce ray sampling noise.
92 + However, for some systems, reciprocity averaging can actually make the output worse.
93 + .PP
94   The geometry must fit a rectangular profile, whose width is along the X-axis,
95   height is in the Y-axis, and depth is in the Z-axis.
96   The positive Z-axis points into the room, and the input geometry should
# Line 72 | Line 113 | The variance in the results may be reduced by increasi
113   samples per incident direction using the
114   .I \-c
115   option.
116 < This value defaults to 1000 samples distributed over the incoming plane
116 > This value defaults to 2000 samples distributed over the incoming plane
117   for each of the 145 Klems hemisphere directions.
118   .PP
119 < In some cases, the processing time may be reduced by the
119 > On multi-core machines, processing time may be reduced by the
120   .I \-n
121   option, which specifies the number of simultaneous
81 – .I rtrace(1)
122   processes to run in
123 < .I rtcontrib(1).
123 > .I rcontrib(1).
124   The
125   .I \-r
126   option may be used to specify a set of quoted arguments to be
127   included on the
128 < .I rtcontrib
128 > .I rcontrib
129   command line.
130 + .PP
131 + The
132 + .I \-W
133 + option is passed to
134 + .I wrapBSDF(1)
135 + to prepare the XML file for WINDOW6.
136 + Any
137 + .I \-s
138 + parameters are passed to the
139 + .I \-f
140 + option of
141 + .I wrapBSDF,
142 + controlling XML fields such as
143 + the Manufacturer (e.g., -s m=MF) and device Name (e.g, -s n=NM).
144 + .PP
145 + The
146 + .I \-t4
147 + mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
148 + suitable for use in the Radiance rendering tools.
149 + The parameter given to this option is the log to the base 2 of the
150 + sampling resolution in each dimension, and must be an integer.
151 + The
152 + .I \-c
153 + setting should be adjusted so that an appropriate number of samples
154 + lands in each region.
155 + A
156 + .I \-t4
157 + parameter of 5 corresponds to 32x32 or 1024 output regions, so a
158 + .I \-c
159 + setting of 10240 would provide 10 samples per region on average.
160 + Increasing the resolution to 6 corresponds to 64x64 or 4096
161 + regions, so the
162 + .I \-c
163 + setting would need to be increased by a factor of 4 to provide
164 + the same accuracy in each region.
165 + .PP
166 + The
167 + .I \-t3
168 + mode is similar to
169 + .I \-t4
170 + but computes a rank 3 tensor tree rather than rank 4.
171 + This provides a much faster computation, but only works
172 + in special circumstances.
173 + Specifically, do NOT use this option if the system is not in fact isotropic.
174 + I.e., only use
175 + .I \-t3
176 + when you are certain that the system has a high degree of radial symmetry.
177 + Again, the parameter to this option sets the maximum resolution as
178 + a power of 2 in each dimension, but in this case there is one less
179 + dimension being sampled.
180 + .PP
181 + The
182 + .I \-recover
183 + option is available for continuing calculations that were killed by
184 + the system or the user.
185 + Unfortunately, genBSDF puts its temporary files in a directory
186 + that is often cleaned up after reboot, so this may not always work.
187   .SH EXAMPLE
188   To create a BSDF description including geometry from a set of venetian blinds:
189   .IP "" .2i
190   genblinds blind_white blind1 .07 3 1.5 30 40 | xform -rz -90 -rx 90 > blind1.rad
191   .br
192   genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
193 + .PP
194 + To create a non-uniform, anisotropic BSDF distribution with a maximum
195 + resolution of 128x128 from the same description:
196 + .IP "" .2i
197 + genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
198 + .SH NOTES
199 + The variable resolution (tensor tree) BSDF representation is not supported
200 + by all software and applicatons, and should be used with caution.
201 + It provides practical, high-resolution data for use in the
202 + Radiance rendering programs, but does not work in the matrix formulation
203 + of the daylight coefficient method for example.
204 + Also, third party tools generally expect or require a fixed number of sample
205 + directions using the Klems directions or similar.
206   .SH AUTHOR
207   Greg Ward
208   .SH "SEE ALSO"
209 < dctimestep(1), genklemsamp(1), genskyvec(1), mkillum(1), rtcontrib(1), rtrace(1)
209 > dctimestep(1), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
210 > pkgBSDF(1), rcomb(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1) wrapBSDF(1)

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