man/man1/genBSDF.1

.\" RCSid $Id: genBSDF.1,v 1.13 2013/01/20 02:07:16 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 "\-f '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
and
.I \-f
options are passed to
.I wrapBSDF(1),
and prepare the output for WINDOW6 and make addition settings, such as
the Manufacturer (e.g., -f m=MF) and device Name (e.g, -f 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:	1.14
Committed:	Fri Feb 20 18:26:08 2015 UTC (10 years, 2 months ago) by greg
Branch:	MAIN
Changes since 1.13:	+15 -2 lines
Log Message:	Created wrapBSDF tool and major overhaul of genBSDF to use it with rfluxmtx
#	Content
1	.\" RCSid $Id: genBSDF.1,v 1.13 2013/01/20 02:07:16 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 "\-f '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	and
104	.I \-f
105	options are passed to
106	.I wrapBSDF(1),
107	and prepare the output for WINDOW6 and make addition settings, such as
108	the Manufacturer (e.g., -f m=MF) and device Name (e.g, -f n=NM).
109	.PP
110	The
111	.I \-t4
112	mode computes a non-uniform BSDF represented as a rank 4 tensor tree,
113	suitable for use in the Radiance rendering tools.
114	The parameter given to this option is the log to the base 2 of the
115	sampling resolution in each dimension, and must be an integer.
116	The
117	.I \-c
118	setting should be adjusted so that an appropriate number of samples
119	lands in each region.
120	A
121	.I \-t4
122	parameter of 5 corresponds to 32x32 or 1024 output regions, so a
123	.I \-c
124	setting of 10240 would provide 10 samples per region on average.
125	Increasing the resolution to 6 corresponds to 64x64 or 4096
126	regions, so the
127	.I \-c
128	setting would need to be increased by a factor of 4 to provide
129	the same accuracy in each region.
130	.PP
131	The
132	.I \-t3
133	mode is similar to
134	.I \-t4
135	but computes a rank 3 tensor tree rather than rank 4.
136	This provides a much faster computation, but only works
137	in special circumstances.
138	Specifically, do NOT use this option if the system is not in fact isotropic.
139	I.e., only use
140	.I \-t3
141	when you are certain that the system has a high degree of radial symmetry.
142	Again, the parameter to this option sets the maximum resolution as
143	a power of 2 in each dimension, but in this case there is one less
144	dimension being sampled.
145	.SH EXAMPLE
146	To create a BSDF description including geometry from a set of venetian blinds:
147	.IP "" .2i
148	genblinds blind_white blind1 .07 3 1.5 30 40 \| xform -rz -90 -rx 90 > blind1.rad
149	.br
150	genBSDF -r @rtc.opt blind_white.mat glazing.rad blind1.rad > blind1.xml
151	.PP
152	To create a non-uniform, anisotropic BSDF distribution with a maximum
153	resolution of 128x128 from the same description:
154	.IP "" .2i
155	genBSDF -r @rtc.opt -t4 7 -c 160000 blind_white.mat glazing.rad blind1.rad > blind12.xml
156	.SH NOTES
157	The variable resolution (tensor tree) BSDF representation is not supported
158	by all software and applicatons, and should be used with caution.
159	It provides practical, high-resolution data for use in the
160	Radiance rendering programs, but does not work in the matrix formulation
161	of the daylight coefficient method for example.
162	Also, third party tools generally expect or require a fixed number of sample
163	directions using the Klems directions or similar.
164	.SH AUTHOR
165	Greg Ward
166	.SH "SEE ALSO"
167	dctimestep(1), gendaymtx(1), genklemsamp(1), genskyvec(1), mkillum(1),
168	pkgBSDF(1), rcontrib(1), rfluxmtx(1), rmtxop(1), rtrace(1)