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 (14 years ago) by greg
Branch:	MAIN
Changes since 1.5:	+52 -1 lines
Log Message:	Added tensor tree variable-resolution BSDF generation
#	Content
1	.\" RCSid $Id: genBSDF.1,v 1.5 2011/05/06 23:58:09 greg Exp $
2	.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	.B "\-r 'rtcontrib opts...'"
13	][
14	.B "\-t{3\|4} Nlog2"
15	][
16	.B "{+\|-}forward"
17	][
18	.B "{+\|-}backward"
19	][
20	.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	computes a bidirectional scattering distribution function from
32	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	(This is the default, and may be switched off using
41	.I \-geom.)\0
42	.PP
43	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	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	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	.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	.SH EXAMPLE
129	To create a BSDF description including geometry from a set of venetian blinds:
130	.IP "" .2i
131	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
132	.br
133	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
134	.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	.SH AUTHOR
148	Greg Ward
149	.SH "SEE ALSO"
150	dctimestep(1), genklemsamp(1), genskyvec(1), mkillum(1), rtcontrib(1), rtrace(1)