man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.11 2012/06/20 00:48:54 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 "\-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 \-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), genklemsamp(1), genskyvec(1), mkillum(1),
pkgBSDF(1), rcontrib(1), rtrace(1)
Revision:	1.12
Committed:	Sun Sep 2 15:33:14 2012 UTC (13 years, 2 months ago) by greg
Branch:	MAIN
Changes since 1.11:	+3 -2 lines
Log Message:	Fixes to reciprocity for tensor tree representation
#	User	Rev	Content
1	greg	1.12	.\" RCSid $Id: genBSDF.1,v 1.11 2012/06/20 00:48:54 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	1.6	.B "\-t{3\|4} Nlog2"
15			][
16	greg	1.3	.B "{+\|-}forward"
17			][
18			.B "{+\|-}backward"
19			][
20	greg	1.1	.B "{+\|-}mgf"
21			][
22	greg	1.7	.B "{+\|-}geom unit"
23	greg	1.1	][
24			.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
25			]
26			[
27			.B "geom .."
28			]
29			.SH DESCRIPTION
30			.I GenBSDF
31	greg	1.3	computes a bidirectional scattering distribution function from
32	greg	1.1	a Radiance or MGF scene description given on the input.
33			The program assumes the input is in Radiance format unless the
34			.I \+mgf
35			option is specified.
36			The output conforms to the LBNL Window 6 XML standard for BSDF data,
37			and will include an MGF representation of the input geometry if the
38			.I \+geom
39	greg	1.7	option is given, followed by one of "meter," "foot," "inch,"
40			"centimeter," or "millimeter," depending on the scene units.
41			The default is to include the provided geometry,
42			which is assumed to be in meters.
43			Geometry output can be supressed with the
44			.I \-geom
45			option, which must also be followed by one of the above length units.
46	greg	1.1	.PP
47	greg	1.3	Normally,
48			.I genBSDF
49			computes components needed by a backwards ray-tracing process,
50			.I \+backward.
51			If both forward and backward (front and back) distributions are needed, the
52			.I \+forward
53			option may be given.
54			To turn off backward components, use the
55			.I \-backward
56			option.
57	greg	1.12	Computing both components takes about twice as long as one component, but
58			is recommended when rays will be impinging from either side.
59	greg	1.3	.PP
60	greg	1.1	The geometry must fit a rectangular profile, whose width is along the X-axis,
61			height is in the Y-axis, and depth is in the Z-axis.
62			The positive Z-axis points into the room, and the input geometry should
63			not extend into the room.
64			(I.e., it should not contain any positive Z values, since the putative
65			emitting surface is assumed to lie at Z=0.)\0
66			The entire window system should be modeled, including sills and
67			edge geometry anticipated in the final installation, otherwise
68			accuracy will be impaired.
69			Similarly, materials in the description should be carefully measured.
70			.PP
71			Normally, the input geometry will be positioned according to its actual
72			bounding box, but this may be overridden with the
73			.I \-dim
74			option.
75			Use this in cases where the fenestration system is designed to fit a
76			smaller (or larger) opening or is offset somehow.
77			.PP
78			The variance in the results may be reduced by increasing the number of
79			samples per incident direction using the
80			.I \-c
81			option.
82	greg	1.9	This value defaults to 2000 samples distributed over the incoming plane
83	greg	1.1	for each of the 145 Klems hemisphere directions.
84			.PP
85	greg	1.11	On multi-core machines, processing time may be reduced by the
86	greg	1.1	.I \-n
87			option, which specifies the number of simultaneous
88			processes to run in
89	greg	1.10	.I rcontrib(1).
90	greg	1.4	The
91			.I \-r
92			option may be used to specify a set of quoted arguments to be
93			included on the
94	greg	1.10	.I rcontrib
95	greg	1.4	command line.
96	greg	1.6	.PP
97			The
98			.I \-t4
99			mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
100			suitable for use in the Radiance rendering tools.
101			The parameter given to this option is the log to the base 2 of the
102			sampling resolution in each dimension, and must be an integer.
103			The
104			.I \-c
105			setting should be adjusted so that an appropriate number of samples
106			lands in each region.
107			A
108			.I \-t4
109			parameter of 5 corresponds to 32x32 or 1024 output regions, so a
110			.I \-c
111	greg	1.9	setting of 10240 would provide 10 samples per region on average.
112	greg	1.6	Increasing the resolution to 6 corresponds to 64x64 or 4096
113			regions, so the
114			.I \-c
115			setting would need to be increased by a factor of 4 to provide
116			the same accuracy in each region.
117			.PP
118			The
119			.I \-t3
120			mode is similar to
121			.I \-t4
122			but computes a rank 3 tensor tree rather than rank 4.
123			This provides a much faster computation, but only works
124			in special circumstances.
125			Specifically, do NOT use this option if the system is not in fact isotropic.
126			I.e., only use
127			.I \-t3
128			when you are certain that the system has a high degree of radial symmetry.
129			Again, the parameter to this option sets the maximum resolution as
130			a power of 2 in each dimension, but in this case there is one less
131			dimension being sampled.
132	greg	1.1	.SH EXAMPLE
133			To create a BSDF description including geometry from a set of venetian blinds:
134			.IP "" .2i
135	greg	1.2	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
136	greg	1.1	.br
137	greg	1.4	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
138	greg	1.6	.PP
139			To create a non-uniform, anisotropic BSDF distribution with a maximum
140			resolution of 128x128 from the same description:
141			.IP "" .2i
142			genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
143			.SH NOTES
144			The variable resolution (tensor tree) BSDF representation is not supported
145			by all software and applicatons, and should be used with caution.
146			It provides practical, high-resolution data for use in the
147			Radiance rendering programs, but does not work in the matrix formulation
148			of the daylight coefficient method for example.
149			Also, third party tools generally expect or require a fixed number of sample
150			directions using the Klems directions or similar.
151	greg	1.1	.SH AUTHOR
152			Greg Ward
153			.SH "SEE ALSO"
154	greg	1.7	dctimestep(1), genklemsamp(1), genskyvec(1), mkillum(1),
155	greg	1.10	pkgBSDF(1), rcontrib(1), rtrace(1)