man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.17 2015/04/02 16:40:31 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 "{+|-}forward"
][
.B "{+|-}backward"
][
.B "{+|-}mgf"
][
.B "{+|-}geom unit"
][
.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
]
[
.B "geom .."
]
.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 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.
.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:	1.18
Committed:	Sun Apr 5 01:32:01 2015 UTC (10 years, 1 month ago) by greg
Branch:	MAIN
CVS Tags:	rad5R0
Changes since 1.17:	+3 -3 lines
Log Message:	Added color rendering to tensor tree and minor fixes to Klems color rendering
#	User	Rev	Content
1	greg	1.18	.\" RCSid $Id: genBSDF.1,v 1.17 2015/04/02 16:40:31 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	1.3	.B "{+\|-}forward"
23			][
24			.B "{+\|-}backward"
25			][
26	greg	1.1	.B "{+\|-}mgf"
27			][
28	greg	1.7	.B "{+\|-}geom unit"
29	greg	1.1	][
30			.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
31			]
32			[
33			.B "geom .."
34			]
35			.SH DESCRIPTION
36			.I GenBSDF
37	greg	1.3	computes a bidirectional scattering distribution function from
38	greg	1.1	a Radiance or MGF scene description given on the input.
39			The program assumes the input is in Radiance format unless the
40			.I \+mgf
41			option is specified.
42			The output conforms to the LBNL Window 6 XML standard for BSDF data,
43			and will include an MGF representation of the input geometry if the
44			.I \+geom
45	greg	1.7	option is given, followed by one of "meter," "foot," "inch,"
46			"centimeter," or "millimeter," depending on the scene units.
47			The default is to include the provided geometry,
48			which is assumed to be in meters.
49			Geometry output can be supressed with the
50			.I \-geom
51			option, which must also be followed by one of the above length units.
52	greg	1.1	.PP
53	greg	1.3	Normally,
54			.I genBSDF
55			computes components needed by a backwards ray-tracing process,
56			.I \+backward.
57			If both forward and backward (front and back) distributions are needed, the
58			.I \+forward
59			option may be given.
60			To turn off backward components, use the
61			.I \-backward
62			option.
63	greg	1.12	Computing both components takes about twice as long as one component, but
64			is recommended when rays will be impinging from either side.
65	greg	1.3	.PP
66	greg	1.17	The
67			.I \+C
68			option specifies that the output XML should include color information,
69			which is interpreted by the rendering programs.
70	greg	1.18	The default option
71			.I \-C
72	greg	1.17	reduces all BSDF data to grayscale.
73			.PP
74	greg	1.1	The geometry must fit a rectangular profile, whose width is along the X-axis,
75			height is in the Y-axis, and depth is in the Z-axis.
76			The positive Z-axis points into the room, and the input geometry should
77			not extend into the room.
78			(I.e., it should not contain any positive Z values, since the putative
79			emitting surface is assumed to lie at Z=0.)\0
80			The entire window system should be modeled, including sills and
81			edge geometry anticipated in the final installation, otherwise
82			accuracy will be impaired.
83			Similarly, materials in the description should be carefully measured.
84			.PP
85			Normally, the input geometry will be positioned according to its actual
86			bounding box, but this may be overridden with the
87			.I \-dim
88			option.
89			Use this in cases where the fenestration system is designed to fit a
90			smaller (or larger) opening or is offset somehow.
91			.PP
92			The variance in the results may be reduced by increasing the number of
93			samples per incident direction using the
94			.I \-c
95			option.
96	greg	1.9	This value defaults to 2000 samples distributed over the incoming plane
97	greg	1.1	for each of the 145 Klems hemisphere directions.
98			.PP
99	greg	1.11	On multi-core machines, processing time may be reduced by the
100	greg	1.1	.I \-n
101			option, which specifies the number of simultaneous
102			processes to run in
103	greg	1.10	.I rcontrib(1).
104	greg	1.4	The
105			.I \-r
106			option may be used to specify a set of quoted arguments to be
107			included on the
108	greg	1.10	.I rcontrib
109	greg	1.4	command line.
110	greg	1.6	.PP
111			The
112	greg	1.14	.I \-W
113	greg	1.15	option is passed to
114			.I wrapBSDF(1)
115			to prepare the XML file for WINDOW6.
116			Any
117			.I \-s
118			parameters are passed to the
119	greg	1.14	.I \-f
120	greg	1.15	option of
121			.I wrapBSDF,
122			controlling XML fields such as
123			the Manufacturer (e.g., -s m=MF) and device Name (e.g, -s n=NM).
124	greg	1.14	.PP
125			The
126	greg	1.6	.I \-t4
127			mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
128			suitable for use in the Radiance rendering tools.
129			The parameter given to this option is the log to the base 2 of the
130			sampling resolution in each dimension, and must be an integer.
131			The
132			.I \-c
133			setting should be adjusted so that an appropriate number of samples
134			lands in each region.
135			A
136			.I \-t4
137			parameter of 5 corresponds to 32x32 or 1024 output regions, so a
138			.I \-c
139	greg	1.9	setting of 10240 would provide 10 samples per region on average.
140	greg	1.6	Increasing the resolution to 6 corresponds to 64x64 or 4096
141			regions, so the
142			.I \-c
143			setting would need to be increased by a factor of 4 to provide
144			the same accuracy in each region.
145			.PP
146			The
147			.I \-t3
148			mode is similar to
149			.I \-t4
150			but computes a rank 3 tensor tree rather than rank 4.
151			This provides a much faster computation, but only works
152			in special circumstances.
153			Specifically, do NOT use this option if the system is not in fact isotropic.
154			I.e., only use
155			.I \-t3
156			when you are certain that the system has a high degree of radial symmetry.
157			Again, the parameter to this option sets the maximum resolution as
158			a power of 2 in each dimension, but in this case there is one less
159			dimension being sampled.
160	greg	1.1	.SH EXAMPLE
161			To create a BSDF description including geometry from a set of venetian blinds:
162			.IP "" .2i
163	greg	1.2	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
164	greg	1.1	.br
165	greg	1.4	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
166	greg	1.6	.PP
167			To create a non-uniform, anisotropic BSDF distribution with a maximum
168			resolution of 128x128 from the same description:
169			.IP "" .2i
170			genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
171			.SH NOTES
172			The variable resolution (tensor tree) BSDF representation is not supported
173			by all software and applicatons, and should be used with caution.
174			It provides practical, high-resolution data for use in the
175			Radiance rendering programs, but does not work in the matrix formulation
176			of the daylight coefficient method for example.
177			Also, third party tools generally expect or require a fixed number of sample
178			directions using the Klems directions or similar.
179	greg	1.1	.SH AUTHOR
180			Greg Ward
181			.SH "SEE ALSO"
182	greg	1.13	dctimestep(1), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
183	greg	1.16	pkgBSDF(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1) wrapBSDF(1)