man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.13 2013/01/20 02:07:16 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 "\-f 'x=string;y=string'"
][
.B "\-t{3|4} Nlog2"
][
.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 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
and
.I \-f
options are passed to
.I wrapBSDF(1),
and prepare the output for WINDOW6 and make addition settings, such as
the Manufacturer (e.g., -f m=MF) and device Name (e.g, -f 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)
Revision:	1.14
Committed:	Fri Feb 20 18:26:08 2015 UTC (10 years, 2 months ago) by greg
Branch:	MAIN
Changes since 1.13:	+15 -2 lines
Log Message:	Created wrapBSDF tool and major overhaul of genBSDF to use it with rfluxmtx
#	User	Rev	Content
1	greg	1.14	.\" RCSid $Id: genBSDF.1,v 1.13 2013/01/20 02:07:16 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			.B "\-f 'x=string;y=string'"
17			][
18	greg	1.6	.B "\-t{3\|4} Nlog2"
19			][
20	greg	1.3	.B "{+\|-}forward"
21			][
22			.B "{+\|-}backward"
23			][
24	greg	1.1	.B "{+\|-}mgf"
25			][
26	greg	1.7	.B "{+\|-}geom unit"
27	greg	1.1	][
28			.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
29			]
30			[
31			.B "geom .."
32			]
33			.SH DESCRIPTION
34			.I GenBSDF
35	greg	1.3	computes a bidirectional scattering distribution function from
36	greg	1.1	a Radiance or MGF scene description given on the input.
37			The program assumes the input is in Radiance format unless the
38			.I \+mgf
39			option is specified.
40			The output conforms to the LBNL Window 6 XML standard for BSDF data,
41			and will include an MGF representation of the input geometry if the
42			.I \+geom
43	greg	1.7	option is given, followed by one of "meter," "foot," "inch,"
44			"centimeter," or "millimeter," depending on the scene units.
45			The default is to include the provided geometry,
46			which is assumed to be in meters.
47			Geometry output can be supressed with the
48			.I \-geom
49			option, which must also be followed by one of the above length units.
50	greg	1.1	.PP
51	greg	1.3	Normally,
52			.I genBSDF
53			computes components needed by a backwards ray-tracing process,
54			.I \+backward.
55			If both forward and backward (front and back) distributions are needed, the
56			.I \+forward
57			option may be given.
58			To turn off backward components, use the
59			.I \-backward
60			option.
61	greg	1.12	Computing both components takes about twice as long as one component, but
62			is recommended when rays will be impinging from either side.
63	greg	1.3	.PP
64	greg	1.1	The geometry must fit a rectangular profile, whose width is along the X-axis,
65			height is in the Y-axis, and depth is in the Z-axis.
66			The positive Z-axis points into the room, and the input geometry should
67			not extend into the room.
68			(I.e., it should not contain any positive Z values, since the putative
69			emitting surface is assumed to lie at Z=0.)\0
70			The entire window system should be modeled, including sills and
71			edge geometry anticipated in the final installation, otherwise
72			accuracy will be impaired.
73			Similarly, materials in the description should be carefully measured.
74			.PP
75			Normally, the input geometry will be positioned according to its actual
76			bounding box, but this may be overridden with the
77			.I \-dim
78			option.
79			Use this in cases where the fenestration system is designed to fit a
80			smaller (or larger) opening or is offset somehow.
81			.PP
82			The variance in the results may be reduced by increasing the number of
83			samples per incident direction using the
84			.I \-c
85			option.
86	greg	1.9	This value defaults to 2000 samples distributed over the incoming plane
87	greg	1.1	for each of the 145 Klems hemisphere directions.
88			.PP
89	greg	1.11	On multi-core machines, processing time may be reduced by the
90	greg	1.1	.I \-n
91			option, which specifies the number of simultaneous
92			processes to run in
93	greg	1.10	.I rcontrib(1).
94	greg	1.4	The
95			.I \-r
96			option may be used to specify a set of quoted arguments to be
97			included on the
98	greg	1.10	.I rcontrib
99	greg	1.4	command line.
100	greg	1.6	.PP
101			The
102	greg	1.14	.I \-W
103			and
104			.I \-f
105			options are passed to
106			.I wrapBSDF(1),
107			and prepare the output for WINDOW6 and make addition settings, such as
108			the Manufacturer (e.g., -f m=MF) and device Name (e.g, -f n=NM).
109			.PP
110			The
111	greg	1.6	.I \-t4
112			mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
113			suitable for use in the Radiance rendering tools.
114			The parameter given to this option is the log to the base 2 of the
115			sampling resolution in each dimension, and must be an integer.
116			The
117			.I \-c
118			setting should be adjusted so that an appropriate number of samples
119			lands in each region.
120			A
121			.I \-t4
122			parameter of 5 corresponds to 32x32 or 1024 output regions, so a
123			.I \-c
124	greg	1.9	setting of 10240 would provide 10 samples per region on average.
125	greg	1.6	Increasing the resolution to 6 corresponds to 64x64 or 4096
126			regions, so the
127			.I \-c
128			setting would need to be increased by a factor of 4 to provide
129			the same accuracy in each region.
130			.PP
131			The
132			.I \-t3
133			mode is similar to
134			.I \-t4
135			but computes a rank 3 tensor tree rather than rank 4.
136			This provides a much faster computation, but only works
137			in special circumstances.
138			Specifically, do NOT use this option if the system is not in fact isotropic.
139			I.e., only use
140			.I \-t3
141			when you are certain that the system has a high degree of radial symmetry.
142			Again, the parameter to this option sets the maximum resolution as
143			a power of 2 in each dimension, but in this case there is one less
144			dimension being sampled.
145	greg	1.1	.SH EXAMPLE
146			To create a BSDF description including geometry from a set of venetian blinds:
147			.IP "" .2i
148	greg	1.2	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
149	greg	1.1	.br
150	greg	1.4	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
151	greg	1.6	.PP
152			To create a non-uniform, anisotropic BSDF distribution with a maximum
153			resolution of 128x128 from the same description:
154			.IP "" .2i
155			genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
156			.SH NOTES
157			The variable resolution (tensor tree) BSDF representation is not supported
158			by all software and applicatons, and should be used with caution.
159			It provides practical, high-resolution data for use in the
160			Radiance rendering programs, but does not work in the matrix formulation
161			of the daylight coefficient method for example.
162			Also, third party tools generally expect or require a fixed number of sample
163			directions using the Klems directions or similar.
164	greg	1.1	.SH AUTHOR
165			Greg Ward
166			.SH "SEE ALSO"
167	greg	1.13	dctimestep(1), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
168	greg	1.14	pkgBSDF(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1)