man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.5 2011/05/06 23:58:09 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 'rtcontrib opts...'"
][
.B "\-t{3|4} Nlog2"
][
.B "{+|-}forward"
][
.B "{+|-}backward"
][
.B "{+|-}mgf"
][
.B "{+|-}geom
][
.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.
(This is the default, and may be switched off using
.I \-geom.)\0
.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.
.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 1000 samples distributed over the incoming plane
for each of the 145 Klems hemisphere directions.
.PP
In some cases, the processing time may be reduced by the
.I \-n
option, which specifies the number of simultaneous
.I rtrace(1)
processes to run in
.I rtcontrib(1).
The
.I \-r
option may be used to specify a set of quoted arguments to be
included on the
.I rtcontrib
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 102400 would provide 100 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), rtcontrib(1), rtrace(1)
Revision:	1.6
Committed:	Fri Jun 3 19:41:14 2011 UTC (13 years, 11 months ago) by greg
Branch:	MAIN
Changes since 1.5:	+52 -1 lines
Log Message:	Added tensor tree variable-resolution BSDF generation
#	User	Rev	Content
1	greg	1.6	.\" RCSid $Id: genBSDF.1,v 1.5 2011/05/06 23:58:09 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	1.4	.B "\-r 'rtcontrib opts...'"
13			][
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			.B "{+\|-}geom
23			][
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			option is given.
40	greg	1.3	(This is the default, and may be switched off using
41	greg	1.1	.I \-geom.)\0
42			.PP
43	greg	1.3	Normally,
44			.I genBSDF
45			computes components needed by a backwards ray-tracing process,
46			.I \+backward.
47			If both forward and backward (front and back) distributions are needed, the
48			.I \+forward
49			option may be given.
50			To turn off backward components, use the
51			.I \-backward
52			option.
53			Computing both components takes about twice as long as one component.
54			.PP
55	greg	1.1	The geometry must fit a rectangular profile, whose width is along the X-axis,
56			height is in the Y-axis, and depth is in the Z-axis.
57			The positive Z-axis points into the room, and the input geometry should
58			not extend into the room.
59			(I.e., it should not contain any positive Z values, since the putative
60			emitting surface is assumed to lie at Z=0.)\0
61			The entire window system should be modeled, including sills and
62			edge geometry anticipated in the final installation, otherwise
63			accuracy will be impaired.
64			Similarly, materials in the description should be carefully measured.
65			.PP
66			Normally, the input geometry will be positioned according to its actual
67			bounding box, but this may be overridden with the
68			.I \-dim
69			option.
70			Use this in cases where the fenestration system is designed to fit a
71			smaller (or larger) opening or is offset somehow.
72			.PP
73			The variance in the results may be reduced by increasing the number of
74			samples per incident direction using the
75			.I \-c
76			option.
77			This value defaults to 1000 samples distributed over the incoming plane
78			for each of the 145 Klems hemisphere directions.
79			.PP
80			In some cases, the processing time may be reduced by the
81			.I \-n
82			option, which specifies the number of simultaneous
83			.I rtrace(1)
84			processes to run in
85			.I rtcontrib(1).
86	greg	1.4	The
87			.I \-r
88			option may be used to specify a set of quoted arguments to be
89			included on the
90			.I rtcontrib
91			command line.
92	greg	1.6	.PP
93			The
94			.I \-t4
95			mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
96			suitable for use in the Radiance rendering tools.
97			The parameter given to this option is the log to the base 2 of the
98			sampling resolution in each dimension, and must be an integer.
99			The
100			.I \-c
101			setting should be adjusted so that an appropriate number of samples
102			lands in each region.
103			A
104			.I \-t4
105			parameter of 5 corresponds to 32x32 or 1024 output regions, so a
106			.I \-c
107			setting of 102400 would provide 100 samples per region on average.
108			Increasing the resolution to 6 corresponds to 64x64 or 4096
109			regions, so the
110			.I \-c
111			setting would need to be increased by a factor of 4 to provide
112			the same accuracy in each region.
113			.PP
114			The
115			.I \-t3
116			mode is similar to
117			.I \-t4
118			but computes a rank 3 tensor tree rather than rank 4.
119			This provides a much faster computation, but only works
120			in special circumstances.
121			Specifically, do NOT use this option if the system is not in fact isotropic.
122			I.e., only use
123			.I \-t3
124			when you are certain that the system has a high degree of radial symmetry.
125			Again, the parameter to this option sets the maximum resolution as
126			a power of 2 in each dimension, but in this case there is one less
127			dimension being sampled.
128	greg	1.1	.SH EXAMPLE
129			To create a BSDF description including geometry from a set of venetian blinds:
130			.IP "" .2i
131	greg	1.2	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
132	greg	1.1	.br
133	greg	1.4	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
134	greg	1.6	.PP
135			To create a non-uniform, anisotropic BSDF distribution with a maximum
136			resolution of 128x128 from the same description:
137			.IP "" .2i
138			genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
139			.SH NOTES
140			The variable resolution (tensor tree) BSDF representation is not supported
141			by all software and applicatons, and should be used with caution.
142			It provides practical, high-resolution data for use in the
143			Radiance rendering programs, but does not work in the matrix formulation
144			of the daylight coefficient method for example.
145			Also, third party tools generally expect or require a fixed number of sample
146			directions using the Klems directions or similar.
147	greg	1.1	.SH AUTHOR
148			Greg Ward
149			.SH "SEE ALSO"
150			dctimestep(1), genklemsamp(1), genskyvec(1), mkillum(1), rtcontrib(1), rtrace(1)