man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.10 2012/06/14 22:42:21 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.
.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:	1.11
Committed:	Wed Jun 20 00:48:54 2012 UTC (12 years, 10 months ago) by greg
Branch:	MAIN
Changes since 1.10:	+2 -3 lines
Log Message:	Fixed reference to -n option
#	Content
1	.\" RCSid $Id: genBSDF.1,v 1.10 2012/06/14 22:42:21 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 'rcontrib opts...'"
13	][
14	.B "\-t{3\|4} Nlog2"
15	][
16	.B "{+\|-}forward"
17	][
18	.B "{+\|-}backward"
19	][
20	.B "{+\|-}mgf"
21	][
22	.B "{+\|-}geom unit"
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, 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	.PP
47	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	Computing both components takes about twice as long as one component.
58	.PP
59	The geometry must fit a rectangular profile, whose width is along the X-axis,
60	height is in the Y-axis, and depth is in the Z-axis.
61	The positive Z-axis points into the room, and the input geometry should
62	not extend into the room.
63	(I.e., it should not contain any positive Z values, since the putative
64	emitting surface is assumed to lie at Z=0.)\0
65	The entire window system should be modeled, including sills and
66	edge geometry anticipated in the final installation, otherwise
67	accuracy will be impaired.
68	Similarly, materials in the description should be carefully measured.
69	.PP
70	Normally, the input geometry will be positioned according to its actual
71	bounding box, but this may be overridden with the
72	.I \-dim
73	option.
74	Use this in cases where the fenestration system is designed to fit a
75	smaller (or larger) opening or is offset somehow.
76	.PP
77	The variance in the results may be reduced by increasing the number of
78	samples per incident direction using the
79	.I \-c
80	option.
81	This value defaults to 2000 samples distributed over the incoming plane
82	for each of the 145 Klems hemisphere directions.
83	.PP
84	On multi-core machines, processing time may be reduced by the
85	.I \-n
86	option, which specifies the number of simultaneous
87	processes to run in
88	.I rcontrib(1).
89	The
90	.I \-r
91	option may be used to specify a set of quoted arguments to be
92	included on the
93	.I rcontrib
94	command line.
95	.PP
96	The
97	.I \-t4
98	mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
99	suitable for use in the Radiance rendering tools.
100	The parameter given to this option is the log to the base 2 of the
101	sampling resolution in each dimension, and must be an integer.
102	The
103	.I \-c
104	setting should be adjusted so that an appropriate number of samples
105	lands in each region.
106	A
107	.I \-t4
108	parameter of 5 corresponds to 32x32 or 1024 output regions, so a
109	.I \-c
110	setting of 10240 would provide 10 samples per region on average.
111	Increasing the resolution to 6 corresponds to 64x64 or 4096
112	regions, so the
113	.I \-c
114	setting would need to be increased by a factor of 4 to provide
115	the same accuracy in each region.
116	.PP
117	The
118	.I \-t3
119	mode is similar to
120	.I \-t4
121	but computes a rank 3 tensor tree rather than rank 4.
122	This provides a much faster computation, but only works
123	in special circumstances.
124	Specifically, do NOT use this option if the system is not in fact isotropic.
125	I.e., only use
126	.I \-t3
127	when you are certain that the system has a high degree of radial symmetry.
128	Again, the parameter to this option sets the maximum resolution as
129	a power of 2 in each dimension, but in this case there is one less
130	dimension being sampled.
131	.SH EXAMPLE
132	To create a BSDF description including geometry from a set of venetian blinds:
133	.IP "" .2i
134	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
135	.br
136	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
137	.PP
138	To create a non-uniform, anisotropic BSDF distribution with a maximum
139	resolution of 128x128 from the same description:
140	.IP "" .2i
141	genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
142	.SH NOTES
143	The variable resolution (tensor tree) BSDF representation is not supported
144	by all software and applicatons, and should be used with caution.
145	It provides practical, high-resolution data for use in the
146	Radiance rendering programs, but does not work in the matrix formulation
147	of the daylight coefficient method for example.
148	Also, third party tools generally expect or require a fixed number of sample
149	directions using the Klems directions or similar.
150	.SH AUTHOR
151	Greg Ward
152	.SH "SEE ALSO"
153	dctimestep(1), genklemsamp(1), genskyvec(1), mkillum(1),
154	pkgBSDF(1), rcontrib(1), rtrace(1)