man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.20 2017/05/31 17:25:21 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 color information,
which is interpreted by the rendering programs.
The default option
.I \-C
reduces all BSDF data to grayscale.
.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), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1) wrapBSDF(1)
Revision:	1.21
Committed:	Sun Dec 12 20:17:02 2021 UTC (3 years, 4 months ago) by greg
Branch:	MAIN
CVS Tags:	rad5R4
Changes since 1.20:	+4 -3 lines
Log Message:	docs: clarified explanation of -a option
#	User	Rev	Content
1	greg	1.21	.\" RCSid $Id: genBSDF.1,v 1.20 2017/05/31 17:25:21 greg Exp $
2	greg	1.1	.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	greg	1.10	.B "\-r 'rcontrib opts...'"
13	greg	1.4	][
14	greg	1.14	.B "\-W"
15			][
16	greg	1.15	.B "\-s 'x=string;y=string'"
17	greg	1.14	][
18	greg	1.6	.B "\-t{3\|4} Nlog2"
19			][
20	greg	1.17	.B "{+\|-}C"
21			][
22	greg	1.20	.B "{+\|-}a"
23			][
24	greg	1.3	.B "{+\|-}forward"
25			][
26			.B "{+\|-}backward"
27			][
28	greg	1.1	.B "{+\|-}mgf"
29			][
30	greg	1.7	.B "{+\|-}geom unit"
31	greg	1.1	][
32			.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
33			]
34			[
35			.B "geom .."
36			]
37	greg	1.19	.br
38			or
39			.br
40			.B genBSDF
41			.B "\-recover tempdir"
42	greg	1.1	.SH DESCRIPTION
43			.I GenBSDF
44	greg	1.3	computes a bidirectional scattering distribution function from
45	greg	1.1	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	greg	1.7	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	greg	1.1	.PP
60	greg	1.3	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	greg	1.12	Computing both components takes about twice as long as one component, but
71			is recommended when rays will be impinging from either side.
72	greg	1.3	.PP
73	greg	1.17	The
74			.I \+C
75			option specifies that the output XML should include color information,
76			which is interpreted by the rendering programs.
77	greg	1.18	The default option
78			.I \-C
79	greg	1.17	reduces all BSDF data to grayscale.
80			.PP
81	greg	1.20	The
82			.I \-a
83			option turns off reciprocity averaging for tensor tree output.
84	greg	1.21	Normally on (+a), this ensures that each tensor-tree hemisphere follows symmetry
85			implied by Helmholtz reciprocity, and is designed to reduce ray sampling noise.
86			However, for some systems, reciprocity averaging can actually make the output worse.
87	greg	1.20	.PP
88	greg	1.1	The geometry must fit a rectangular profile, whose width is along the X-axis,
89			height is in the Y-axis, and depth is in the Z-axis.
90			The positive Z-axis points into the room, and the input geometry should
91			not extend into the room.
92			(I.e., it should not contain any positive Z values, since the putative
93			emitting surface is assumed to lie at Z=0.)\0
94			The entire window system should be modeled, including sills and
95			edge geometry anticipated in the final installation, otherwise
96			accuracy will be impaired.
97			Similarly, materials in the description should be carefully measured.
98			.PP
99			Normally, the input geometry will be positioned according to its actual
100			bounding box, but this may be overridden with the
101			.I \-dim
102			option.
103			Use this in cases where the fenestration system is designed to fit a
104			smaller (or larger) opening or is offset somehow.
105			.PP
106			The variance in the results may be reduced by increasing the number of
107			samples per incident direction using the
108			.I \-c
109			option.
110	greg	1.9	This value defaults to 2000 samples distributed over the incoming plane
111	greg	1.1	for each of the 145 Klems hemisphere directions.
112			.PP
113	greg	1.11	On multi-core machines, processing time may be reduced by the
114	greg	1.1	.I \-n
115			option, which specifies the number of simultaneous
116			processes to run in
117	greg	1.10	.I rcontrib(1).
118	greg	1.4	The
119			.I \-r
120			option may be used to specify a set of quoted arguments to be
121			included on the
122	greg	1.10	.I rcontrib
123	greg	1.4	command line.
124	greg	1.6	.PP
125			The
126	greg	1.14	.I \-W
127	greg	1.15	option is passed to
128			.I wrapBSDF(1)
129			to prepare the XML file for WINDOW6.
130			Any
131			.I \-s
132			parameters are passed to the
133	greg	1.14	.I \-f
134	greg	1.15	option of
135			.I wrapBSDF,
136			controlling XML fields such as
137			the Manufacturer (e.g., -s m=MF) and device Name (e.g, -s n=NM).
138	greg	1.14	.PP
139			The
140	greg	1.6	.I \-t4
141			mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
142			suitable for use in the Radiance rendering tools.
143			The parameter given to this option is the log to the base 2 of the
144			sampling resolution in each dimension, and must be an integer.
145			The
146			.I \-c
147			setting should be adjusted so that an appropriate number of samples
148			lands in each region.
149			A
150			.I \-t4
151			parameter of 5 corresponds to 32x32 or 1024 output regions, so a
152			.I \-c
153	greg	1.9	setting of 10240 would provide 10 samples per region on average.
154	greg	1.6	Increasing the resolution to 6 corresponds to 64x64 or 4096
155			regions, so the
156			.I \-c
157			setting would need to be increased by a factor of 4 to provide
158			the same accuracy in each region.
159			.PP
160			The
161			.I \-t3
162			mode is similar to
163			.I \-t4
164			but computes a rank 3 tensor tree rather than rank 4.
165			This provides a much faster computation, but only works
166			in special circumstances.
167			Specifically, do NOT use this option if the system is not in fact isotropic.
168			I.e., only use
169			.I \-t3
170			when you are certain that the system has a high degree of radial symmetry.
171			Again, the parameter to this option sets the maximum resolution as
172			a power of 2 in each dimension, but in this case there is one less
173			dimension being sampled.
174	greg	1.19	.PP
175			The
176			.I \-recover
177			option is available for continuing calculations that were killed by
178			the system or the user.
179			Unfortunately, genBSDF puts its temporary files in a directory
180			that is often cleaned up after reboot, so this may not always work.
181	greg	1.1	.SH EXAMPLE
182			To create a BSDF description including geometry from a set of venetian blinds:
183			.IP "" .2i
184	greg	1.2	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
185	greg	1.1	.br
186	greg	1.4	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
187	greg	1.6	.PP
188			To create a non-uniform, anisotropic BSDF distribution with a maximum
189			resolution of 128x128 from the same description:
190			.IP "" .2i
191			genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
192			.SH NOTES
193			The variable resolution (tensor tree) BSDF representation is not supported
194			by all software and applicatons, and should be used with caution.
195			It provides practical, high-resolution data for use in the
196			Radiance rendering programs, but does not work in the matrix formulation
197			of the daylight coefficient method for example.
198			Also, third party tools generally expect or require a fixed number of sample
199			directions using the Klems directions or similar.
200	greg	1.1	.SH AUTHOR
201			Greg Ward
202			.SH "SEE ALSO"
203	greg	1.13	dctimestep(1), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
204	greg	1.16	pkgBSDF(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1) wrapBSDF(1)