man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.23 2023/12/12 16:31:45 greg Exp $
.TH GENBSDF 1 9/3/2010 RADIANCE
.SH NAME
genBSDF - generate BSDF description from Radiance or MGF input
.SH SYNOPSIS
.B genBSDF
[
.B "\-c Nsamp"
][
.B "\-n Nproc"
][
.B "\-r 'rcontrib opts...'"
][
.B "\-W"
][
.B "\-s 'x=string;y=string'"
][
.B "\-t{3|4} Nlog2"
][
.B "{+|-}C"
][
.B "{+|-}a"
][
.B "{+|-}forward"
][
.B "{+|-}backward"
][
.B "{+|-}mgf"
][
.B "{+|-}geom unit"
][
.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
]
[
.B "geom .."
]
.br
or
.br
.B genBSDF
.B "\-recover tempdir"
.SH DESCRIPTION
.I GenBSDF
computes a bidirectional scattering distribution function from
a Radiance or MGF scene description given on the input.
The program assumes the input is in Radiance format unless the
.I \+mgf
option is specified.
The output conforms to the LBNL Window 6 XML standard for BSDF data,
and will include an MGF representation of the input geometry if the
.I \+geom
option is given, followed by one of "meter," "foot," "inch,"
"centimeter," or "millimeter," depending on the scene units.
The default is to include the provided geometry,
which is assumed to be in meters.
Geometry output can be supressed with the
.I \-geom
option, which must also be followed by one of the above length units.
.PP
Normally,
.I genBSDF
computes components needed by a backwards ray-tracing process,
.I \+backward.
If both forward and backward (front and back) distributions are needed, the
.I \+forward
option may be given.
To turn off backward components, use the
.I \-backward
option.
Computing both components takes about twice as long as one component, but
is recommended when rays will be impinging from either side.
.PP
The
.I \+C
option specifies that the output XML should include tristimulus
color information, which is interpreted by the rendering programs.
The default option
.I \-C
reduces all BSDF data to grayscale.
If the input is spectral and a
.I \-cs
parameter of 9 or more is specified as part of the rendering
.I \-r
option list, then full spectral result will be 
reduced to an XYZ-equivalent CIE color space in the XML output.
.PP
The
.I \-a
option turns off reciprocity averaging for tensor tree output.
Normally on (+a), this ensures that each tensor-tree hemisphere follows symmetry
implied by Helmholtz reciprocity, and is designed to reduce ray sampling noise.
However, for some systems, reciprocity averaging can actually make the output worse.
.PP
The geometry must fit a rectangular profile, whose width is along the X-axis,
height is in the Y-axis, and depth is in the Z-axis.
The positive Z-axis points into the room, and the input geometry should
not extend into the room.
(I.e., it should not contain any positive Z values, since the putative 
emitting surface is assumed to lie at Z=0.)\0
The entire window system should be modeled, including sills and
edge geometry anticipated in the final installation, otherwise
accuracy will be impaired.
Similarly, materials in the description should be carefully measured.
.PP
Normally, the input geometry will be positioned according to its actual
bounding box, but this may be overridden with the
.I \-dim
option.
Use this in cases where the fenestration system is designed to fit a
smaller (or larger) opening or is offset somehow.
.PP
The variance in the results may be reduced by increasing the number of
samples per incident direction using the
.I \-c
option.
This value defaults to 2000 samples distributed over the incoming plane
for each of the 145 Klems hemisphere directions.
.PP
On multi-core machines, processing time may be reduced by the
.I \-n
option, which specifies the number of simultaneous
processes to run in
.I rcontrib(1).
The
.I \-r
option may be used to specify a set of quoted arguments to be
included on the
.I rcontrib
command line.
.PP
The
.I \-W
option is passed to
.I wrapBSDF(1)
to prepare the XML file for WINDOW6.
Any
.I \-s
parameters are passed to the
.I \-f
option of
.I wrapBSDF,
controlling XML fields such as
the Manufacturer (e.g., -s m=MF) and device Name (e.g, -s n=NM).
.PP
The
.I \-t4
mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
suitable for use in the Radiance rendering tools.
The parameter given to this option is the log to the base 2 of the
sampling resolution in each dimension, and must be an integer.
The
.I \-c
setting should be adjusted so that an appropriate number of samples
lands in each region.
A
.I \-t4
parameter of 5 corresponds to 32x32 or 1024 output regions, so a
.I \-c
setting of 10240 would provide 10 samples per region on average.
Increasing the resolution to 6 corresponds to 64x64 or 4096
regions, so the
.I \-c
setting would need to be increased by a factor of 4 to provide
the same accuracy in each region.
.PP
The
.I \-t3
mode is similar to
.I \-t4
but computes a rank 3 tensor tree rather than rank 4.
This provides a much faster computation, but only works
in special circumstances.
Specifically, do NOT use this option if the system is not in fact isotropic.
I.e., only use
.I \-t3
when you are certain that the system has a high degree of radial symmetry.
Again, the parameter to this option sets the maximum resolution as
a power of 2 in each dimension, but in this case there is one less
dimension being sampled.
.PP
The
.I \-recover
option is available for continuing calculations that were killed by
the system or the user.
Unfortunately, genBSDF puts its temporary files in a directory
that is often cleaned up after reboot, so this may not always work.
.SH EXAMPLE
To create a BSDF description including geometry from a set of venetian blinds:
.IP "" .2i
genblinds blind_white blind1 .07 3 1.5 30 40 | xform -rz -90 -rx 90 > blind1.rad
.br
genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
.PP
To create a non-uniform, anisotropic BSDF distribution with a maximum
resolution of 128x128 from the same description:
.IP "" .2i
genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
.SH NOTES
The variable resolution (tensor tree) BSDF representation is not supported
by all software and applicatons, and should be used with caution.
It provides practical, high-resolution data for use in the
Radiance rendering programs, but does not work in the matrix formulation
of the daylight coefficient method for example.
Also, third party tools generally expect or require a fixed number of sample
directions using the Klems directions or similar.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
dctimestep(1), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
pkgBSDF(1), rcomb(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1) wrapBSDF(1)
Revision:	1.24
Committed:	Wed Apr 2 00:55:27 2025 UTC (4 weeks, 4 days ago) by greg
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.23:	+9 -3 lines
Log Message:	feat(genBSDF): Added support for -r "-cs M" to employ M spectral samples
#	Content
1	.\" RCSid $Id: genBSDF.1,v 1.23 2023/12/12 16:31:45 greg Exp $
2	.TH GENBSDF 1 9/3/2010 RADIANCE
3	.SH NAME
4	genBSDF - generate BSDF description from Radiance or MGF input
5	.SH SYNOPSIS
6	.B genBSDF
7	[
8	.B "\-c Nsamp"
9	][
10	.B "\-n Nproc"
11	][
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 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
45	a Radiance or MGF scene description given on the input.
46	The program assumes the input is in Radiance format unless the
47	.I \+mgf
48	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, 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
62	computes components needed by a backwards ray-tracing process,
63	.I \+backward.
64	If both forward and backward (front and back) distributions are needed, the
65	.I \+forward
66	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, 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
97	not extend into the room.
98	(I.e., it should not contain any positive Z values, since the putative
99	emitting surface is assumed to lie at Z=0.)\0
100	The entire window system should be modeled, including sills and
101	edge geometry anticipated in the final installation, otherwise
102	accuracy will be impaired.
103	Similarly, materials in the description should be carefully measured.
104	.PP
105	Normally, the input geometry will be positioned according to its actual
106	bounding box, but this may be overridden with the
107	.I \-dim
108	option.
109	Use this in cases where the fenestration system is designed to fit a
110	smaller (or larger) opening or is offset somehow.
111	.PP
112	The variance in the results may be reduced by increasing the number of
113	samples per incident direction using the
114	.I \-c
115	option.
116	This value defaults to 2000 samples distributed over the incoming plane
117	for each of the 145 Klems hemisphere directions.
118	.PP
119	On multi-core machines, processing time may be reduced by the
120	.I \-n
121	option, which specifies the number of simultaneous
122	processes to run in
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 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), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
210	pkgBSDF(1), rcomb(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1) wrapBSDF(1)