man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.14 2015/02/20 18:26:08 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 "\-s '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
option is passed to
.I wrapBSDF(1)
to prepare the XML file for WINDOW6.
Any
.I \-s
parameters are passed to the
.I \-f
option of
.I wrapBSDF,
controlling XML fields such as
the Manufacturer (e.g., -s m=MF) and device Name (e.g, -s 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:	1.15
Committed:	Fri Mar 27 00:08:49 2015 UTC (10 years, 1 month ago) by greg
Branch:	MAIN
Changes since 1.14:	+12 -7 lines
Log Message:	Fixed overloaded -f option, renaming to -s
#	Content
1	.\" RCSid $Id: genBSDF.1,v 1.14 2015/02/20 18:26:08 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 "\-W"
15	][
16	.B "\-s 'x=string;y=string'"
17	][
18	.B "\-t{3\|4} Nlog2"
19	][
20	.B "{+\|-}forward"
21	][
22	.B "{+\|-}backward"
23	][
24	.B "{+\|-}mgf"
25	][
26	.B "{+\|-}geom unit"
27	][
28	.B "\-dim Xmin Xmax Ymin Ymax Zmin Zmax"
29	]
30	[
31	.B "geom .."
32	]
33	.SH DESCRIPTION
34	.I GenBSDF
35	computes a bidirectional scattering distribution function from
36	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	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	.PP
51	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	Computing both components takes about twice as long as one component, but
62	is recommended when rays will be impinging from either side.
63	.PP
64	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	This value defaults to 2000 samples distributed over the incoming plane
87	for each of the 145 Klems hemisphere directions.
88	.PP
89	On multi-core machines, processing time may be reduced by the
90	.I \-n
91	option, which specifies the number of simultaneous
92	processes to run in
93	.I rcontrib(1).
94	The
95	.I \-r
96	option may be used to specify a set of quoted arguments to be
97	included on the
98	.I rcontrib
99	command line.
100	.PP
101	The
102	.I \-W
103	option is passed to
104	.I wrapBSDF(1)
105	to prepare the XML file for WINDOW6.
106	Any
107	.I \-s
108	parameters are passed to the
109	.I \-f
110	option of
111	.I wrapBSDF,
112	controlling XML fields such as
113	the Manufacturer (e.g., -s m=MF) and device Name (e.g, -s n=NM).
114	.PP
115	The
116	.I \-t4
117	mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
118	suitable for use in the Radiance rendering tools.
119	The parameter given to this option is the log to the base 2 of the
120	sampling resolution in each dimension, and must be an integer.
121	The
122	.I \-c
123	setting should be adjusted so that an appropriate number of samples
124	lands in each region.
125	A
126	.I \-t4
127	parameter of 5 corresponds to 32x32 or 1024 output regions, so a
128	.I \-c
129	setting of 10240 would provide 10 samples per region on average.
130	Increasing the resolution to 6 corresponds to 64x64 or 4096
131	regions, so the
132	.I \-c
133	setting would need to be increased by a factor of 4 to provide
134	the same accuracy in each region.
135	.PP
136	The
137	.I \-t3
138	mode is similar to
139	.I \-t4
140	but computes a rank 3 tensor tree rather than rank 4.
141	This provides a much faster computation, but only works
142	in special circumstances.
143	Specifically, do NOT use this option if the system is not in fact isotropic.
144	I.e., only use
145	.I \-t3
146	when you are certain that the system has a high degree of radial symmetry.
147	Again, the parameter to this option sets the maximum resolution as
148	a power of 2 in each dimension, but in this case there is one less
149	dimension being sampled.
150	.SH EXAMPLE
151	To create a BSDF description including geometry from a set of venetian blinds:
152	.IP "" .2i
153	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
154	.br
155	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
156	.PP
157	To create a non-uniform, anisotropic BSDF distribution with a maximum
158	resolution of 128x128 from the same description:
159	.IP "" .2i
160	genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
161	.SH NOTES
162	The variable resolution (tensor tree) BSDF representation is not supported
163	by all software and applicatons, and should be used with caution.
164	It provides practical, high-resolution data for use in the
165	Radiance rendering programs, but does not work in the matrix formulation
166	of the daylight coefficient method for example.
167	Also, third party tools generally expect or require a fixed number of sample
168	directions using the Klems directions or similar.
169	.SH AUTHOR
170	Greg Ward
171	.SH "SEE ALSO"
172	dctimestep(1), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
173	pkgBSDF(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1)