man/man1/rtcontrib.1

.\" RCSid "$Id: rtcontrib.1,v 1.16 2007/09/04 17:36:41 greg Exp $"
.TH RTCONTRIB 1 5/25/05 RADIANCE
.SH NAME
rtcontrib - compute contribution coefficients in a RADIANCE scene
.SH SYNOPSIS
.B rtcontrib
[
.B "\-n nprocs"
][
.B \-V
][
.B \-c
][
.B \-fo
|
.B \-r
][
.B "\-e expr"
][
.B "\-f source"
][
.B "\-o ospec"
][
.B "\-b binv"
][
.B "\-bn nbins"
]
{
.B "\-m mod | \-M file"
}
..
[
.B $EVAR
]
[
.B @file
]
[
rtrace options
]
.B octree
.br
.B "rtcontrib [ options ] \-defaults"
.SH DESCRIPTION
.I Rtcontrib
computes ray coefficients
for objects whose modifiers are named in one or more
.I \-m
settings.
These modifiers are usually materials associated with
light sources or sky domes, and must directly modify some geometric
primitives to be considered in the output.
A modifier list may also be read from a file using the
.I \-M
option.
The RAYPATH environment variable determines directories to search for
this file.
(No search takes place if a file name begins with a '.', '/' or '~'
character.)\0
.PP
By setting the boolean
.I \-V
option, you may instruct
.I rtcontrib
to report the contribution from each material rather than the ray
coefficient.
This is particularly useful for light sources with directional output
distributions, whose value would otherwise be lost in the shuffle.
With the default
.I -V-
setting, the output of rtcontrib is a coefficient that must be multiplied
by the radiance of each material to arrive at a final contribution.
This is more convenient for computing daylight coefficeints, or cases
where the actual radiance is not desired.
Use the
.I -V+
setting when you wish to simply sum together contributions
(with possible adjustment factors) to obtain a final radiance value.
Combined with the
.I \-i
or
.I \-I
option, irradiance contributions are reported by
.I \-V+
rather than radiance, and 
.I \-V-
coefficients contain an additonal factor of PI.
.PP
The output of
.I rtcontrib
has many potential uses.
Source contributions can be used as components in linear combination to
reproduce any desired variation, e.g., simulating lighting controls or
changing sky conditions via daylight coefficients.
More generally,
.I rtcontrib
can be used to compute arbitrary input-output relationships in optical
systems, such as luminaires, light pipes, and shading devices.
.PP
Setting the
.I \-c
option instructs
.I rtcontrib
to accumulate values rather than reporting one record per ray.
With this option, only a single record will be produced at the very
end, corresponding to the sum of all rays given on the input.
This is equivalent to passing all the output records through a program like
.I total(1)
to sum RGB values together, but is much more efficient.
Using this option, it is possible to reverse sampling, sending rays from
a parallel source such as the sun to a diffuse surface, for example.
Care must be taken to perform normalization based on the
radiation density and the number of rays sampled.
.PP
.I Rtcontrib
calls
.I rtrace(1)
with the \-oTW (or \-oTV) option to calculate the daughter ray
contributions for each input ray, and the output tallies
are sent to one or more destinations according to the given
.I \-o
specification.
If a destination begins with an exclamation mark ('!'), then
a pipe is opened to a command and data is sent to its standard input.
Otherwise, the destination is treated as a file.
An existing file of the same name will not be clobbered, unless the
.I \-fo
option is given.
If instead the
.I \-r
option is specified, data recovery is attempted on existing files.
(If 
.I \-c
is used together with the
.I \-r
option, existing files are read in and new ray evaluations are added
to the previous results, providing a convenient means for
progressive simulation.)\0
If an output specification contains a "%s" format, this will be
replaced by the modifier name.
The
.I \-b
option may be used to further define
a "bin number" within each object if finer resolution is needed, and
this will be applied to a "%d" format in the output file
specification if present.
The actual bin number is computed at run time based on ray direction
and surface intersection, as described below.
If the number of bins is known in advance, it should be specified with the
.I \-bn
option, and this is critical for output files containing multiple values
per record.
Since bin numbers start from 0, the bin count is always equal to
the last bin plus 1.
Set the this value to 0 if the bin count is unknown (the default).
The most recent
.I \-b,
.I \-bn
and
.I \-o
options to the left of each
.I \-m
setting affect only that modifier.
The ordering of other options is unimportant, except for
.I \-x
and
.I \-y
if the
.I \-c
is present, when they control the resolution string
produced in the corresponding output.
.PP
If a
.I \-b
expression is defined for a particular modifier,
the bin number will be evaluated at run time for each
ray contribution from
.I rtrace.
Specifically, each ray's world intersection point will be assigned to
the variables Px, Py, and Pz, and the normalized ray direction
will be assigned to Dx, Dy, and Dz.
These parameters may be combined with definitions given in
.I \-e
arguments and files read using the
.I \-f
option.
The computed bin value will be
rounded to the nearest whole number.
This mechanism allows the user to define precise regions or directions
they wish to accumulate, such as the Tregenza sky discretization,
which would be otherwise impossible to specify
as a set of RADIANCE primitives.
The rules and predefined functions available for these expressions are
described in the
.I rcalc(1)
man page.
Unlike
.I rcalc,
.I rtcontrib
will search the RADIANCE library directories for each file given in a
.I \-f
option.
.PP
If no
.I \-o
specification is given, results are written on the standard output in order
of modifier (as given on the command line) then bin number.
Concatenated data is also sent to a single destination (i.e., an initial
.I \-o
specification without formatting strings).
If a "%s" format appears but no "%d" in the
.I \-o
specification, then each modifier will have its own output file, with
multiple values per record in the case of a non-zero
.I \-b
definition.
If a "%d" format appears but no "%s", then each bin will get its own
output file, with modifiers output in order in each record.
For text output, each RGB coefficient triple is separated by a tab,
with a newline at the end of each ray record.
For binary output formats, there is no such delimiter to mark
the end of each record.
.PP
Input and output format defaults to plain text, where each ray's
origin and direction (6 real values) are given on input,
and one line is produced per output file per ray.
Alternative data representations may be specified by the
.I \-f[io]
option, which is described in the
.I rtrace
man page along with the associated
.I \-x
and
.I \-y
resolution settings.
In particular, the color ('c') output data representation
together with positive dimensions for
.I \-x
and
.I \-y
will produce an uncompressed RADIANCE picture,
suitable for manipulation with
.I pcomb(1)
and related tools.
.PP
If the
.I \-n
option is specified with a value greater than 1, multiple
.I rtrace
processes will be used to accelerate computation on a shared
memory machine.
Note that there is no benefit to using more processes
than there are local CPUs available to do the work, and the
.I rtcontrib
process itself may use a considerable amount of CPU time.
.PP
Options may be given on the command line and/or read from the
environment and/or read from a file.
A command argument beginning with a dollar sign ('$') is immediately
replaced by the contents of the given environment variable.
A command argument beginning with an at sign ('@') is immediately
replaced by the contents of the given file.
.SH EXAMPLES
To compute the proportional contributions from sources modified
by "light1" vs. "light2" on a set of illuminance values:
.IP "" .2i
rtcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
.PP
To generate a pair of images corresponding to these two lights'
contributions:
.IP "" .2i
vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf |
rtcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
@render.opt \-o c_%s.pic \-m light1 \-m light2 scene.oct
.PP
These images may then be recombined using the desired outputs
of light1 and light2:
.IP "" .2i
pcomb \-c 100 90 75 c_light1.pic \-c 50 55 57 c_light2.pic > combined.pic
.PP
To compute an array of illuminance contributions according to a Tregenza sky:
.IP "" .2i
rtcontrib \-I+ \-b tbin \-o sky.dat \-m skyglow \-b 0 \-o ground.dat \-m groundglow
@render.opt \-f tregenza.cal scene.oct < test.dat
.SH ENVIRONMENT
RAYPATH         path to search for \-f and \-M files
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
cnt(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1)
Revision:	1.17
Committed:	Sat Nov 17 01:13:50 2007 UTC (17 years, 7 months ago) by greg
Branch:	MAIN
Changes since 1.16:	+34 -3 lines
Log Message:	Added -c option to rtcontrib (barely tested, and -r does not work)
#	Content
1	.\" RCSid "$Id: rtcontrib.1,v 1.16 2007/09/04 17:36:41 greg Exp $"
2	.TH RTCONTRIB 1 5/25/05 RADIANCE
3	.SH NAME
4	rtcontrib - compute contribution coefficients in a RADIANCE scene
5	.SH SYNOPSIS
6	.B rtcontrib
7	[
8	.B "\-n nprocs"
9	][
10	.B \-V
11	][
12	.B \-c
13	][
14	.B \-fo
15	\|
16	.B \-r
17	][
18	.B "\-e expr"
19	][
20	.B "\-f source"
21	][
22	.B "\-o ospec"
23	][
24	.B "\-b binv"
25	][
26	.B "\-bn nbins"
27	]
28	{
29	.B "\-m mod \| \-M file"
30	}
31	..
32	[
33	.B $EVAR
34	]
35	[
36	.B @file
37	]
38	[
39	rtrace options
40	]
41	.B octree
42	.br
43	.B "rtcontrib [ options ] \-defaults"
44	.SH DESCRIPTION
45	.I Rtcontrib
46	computes ray coefficients
47	for objects whose modifiers are named in one or more
48	.I \-m
49	settings.
50	These modifiers are usually materials associated with
51	light sources or sky domes, and must directly modify some geometric
52	primitives to be considered in the output.
53	A modifier list may also be read from a file using the
54	.I \-M
55	option.
56	The RAYPATH environment variable determines directories to search for
57	this file.
58	(No search takes place if a file name begins with a '.', '/' or '~'
59	character.)\0
60	.PP
61	By setting the boolean
62	.I \-V
63	option, you may instruct
64	.I rtcontrib
65	to report the contribution from each material rather than the ray
66	coefficient.
67	This is particularly useful for light sources with directional output
68	distributions, whose value would otherwise be lost in the shuffle.
69	With the default
70	.I -V-
71	setting, the output of rtcontrib is a coefficient that must be multiplied
72	by the radiance of each material to arrive at a final contribution.
73	This is more convenient for computing daylight coefficeints, or cases
74	where the actual radiance is not desired.
75	Use the
76	.I -V+
77	setting when you wish to simply sum together contributions
78	(with possible adjustment factors) to obtain a final radiance value.
79	Combined with the
80	.I \-i
81	or
82	.I \-I
83	option, irradiance contributions are reported by
84	.I \-V+
85	rather than radiance, and
86	.I \-V-
87	coefficients contain an additonal factor of PI.
88	.PP
89	The output of
90	.I rtcontrib
91	has many potential uses.
92	Source contributions can be used as components in linear combination to
93	reproduce any desired variation, e.g., simulating lighting controls or
94	changing sky conditions via daylight coefficients.
95	More generally,
96	.I rtcontrib
97	can be used to compute arbitrary input-output relationships in optical
98	systems, such as luminaires, light pipes, and shading devices.
99	.PP
100	Setting the
101	.I \-c
102	option instructs
103	.I rtcontrib
104	to accumulate values rather than reporting one record per ray.
105	With this option, only a single record will be produced at the very
106	end, corresponding to the sum of all rays given on the input.
107	This is equivalent to passing all the output records through a program like
108	.I total(1)
109	to sum RGB values together, but is much more efficient.
110	Using this option, it is possible to reverse sampling, sending rays from
111	a parallel source such as the sun to a diffuse surface, for example.
112	Care must be taken to perform normalization based on the
113	radiation density and the number of rays sampled.
114	.PP
115	.I Rtcontrib
116	calls
117	.I rtrace(1)
118	with the \-oTW (or \-oTV) option to calculate the daughter ray
119	contributions for each input ray, and the output tallies
120	are sent to one or more destinations according to the given
121	.I \-o
122	specification.
123	If a destination begins with an exclamation mark ('!'), then
124	a pipe is opened to a command and data is sent to its standard input.
125	Otherwise, the destination is treated as a file.
126	An existing file of the same name will not be clobbered, unless the
127	.I \-fo
128	option is given.
129	If instead the
130	.I \-r
131	option is specified, data recovery is attempted on existing files.
132	(If
133	.I \-c
134	is used together with the
135	.I \-r
136	option, existing files are read in and new ray evaluations are added
137	to the previous results, providing a convenient means for
138	progressive simulation.)\0
139	If an output specification contains a "%s" format, this will be
140	replaced by the modifier name.
141	The
142	.I \-b
143	option may be used to further define
144	a "bin number" within each object if finer resolution is needed, and
145	this will be applied to a "%d" format in the output file
146	specification if present.
147	The actual bin number is computed at run time based on ray direction
148	and surface intersection, as described below.
149	If the number of bins is known in advance, it should be specified with the
150	.I \-bn
151	option, and this is critical for output files containing multiple values
152	per record.
153	Since bin numbers start from 0, the bin count is always equal to
154	the last bin plus 1.
155	Set the this value to 0 if the bin count is unknown (the default).
156	The most recent
157	.I \-b,
158	.I \-bn
159	and
160	.I \-o
161	options to the left of each
162	.I \-m
163	setting affect only that modifier.
164	The ordering of other options is unimportant, except for
165	.I \-x
166	and
167	.I \-y
168	if the
169	.I \-c
170	is present, when they control the resolution string
171	produced in the corresponding output.
172	.PP
173	If a
174	.I \-b
175	expression is defined for a particular modifier,
176	the bin number will be evaluated at run time for each
177	ray contribution from
178	.I rtrace.
179	Specifically, each ray's world intersection point will be assigned to
180	the variables Px, Py, and Pz, and the normalized ray direction
181	will be assigned to Dx, Dy, and Dz.
182	These parameters may be combined with definitions given in
183	.I \-e
184	arguments and files read using the
185	.I \-f
186	option.
187	The computed bin value will be
188	rounded to the nearest whole number.
189	This mechanism allows the user to define precise regions or directions
190	they wish to accumulate, such as the Tregenza sky discretization,
191	which would be otherwise impossible to specify
192	as a set of RADIANCE primitives.
193	The rules and predefined functions available for these expressions are
194	described in the
195	.I rcalc(1)
196	man page.
197	Unlike
198	.I rcalc,
199	.I rtcontrib
200	will search the RADIANCE library directories for each file given in a
201	.I \-f
202	option.
203	.PP
204	If no
205	.I \-o
206	specification is given, results are written on the standard output in order
207	of modifier (as given on the command line) then bin number.
208	Concatenated data is also sent to a single destination (i.e., an initial
209	.I \-o
210	specification without formatting strings).
211	If a "%s" format appears but no "%d" in the
212	.I \-o
213	specification, then each modifier will have its own output file, with
214	multiple values per record in the case of a non-zero
215	.I \-b
216	definition.
217	If a "%d" format appears but no "%s", then each bin will get its own
218	output file, with modifiers output in order in each record.
219	For text output, each RGB coefficient triple is separated by a tab,
220	with a newline at the end of each ray record.
221	For binary output formats, there is no such delimiter to mark
222	the end of each record.
223	.PP
224	Input and output format defaults to plain text, where each ray's
225	origin and direction (6 real values) are given on input,
226	and one line is produced per output file per ray.
227	Alternative data representations may be specified by the
228	.I \-f[io]
229	option, which is described in the
230	.I rtrace
231	man page along with the associated
232	.I \-x
233	and
234	.I \-y
235	resolution settings.
236	In particular, the color ('c') output data representation
237	together with positive dimensions for
238	.I \-x
239	and
240	.I \-y
241	will produce an uncompressed RADIANCE picture,
242	suitable for manipulation with
243	.I pcomb(1)
244	and related tools.
245	.PP
246	If the
247	.I \-n
248	option is specified with a value greater than 1, multiple
249	.I rtrace
250	processes will be used to accelerate computation on a shared
251	memory machine.
252	Note that there is no benefit to using more processes
253	than there are local CPUs available to do the work, and the
254	.I rtcontrib
255	process itself may use a considerable amount of CPU time.
256	.PP
257	Options may be given on the command line and/or read from the
258	environment and/or read from a file.
259	A command argument beginning with a dollar sign ('$') is immediately
260	replaced by the contents of the given environment variable.
261	A command argument beginning with an at sign ('@') is immediately
262	replaced by the contents of the given file.
263	.SH EXAMPLES
264	To compute the proportional contributions from sources modified
265	by "light1" vs. "light2" on a set of illuminance values:
266	.IP "" .2i
267	rtcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
268	.PP
269	To generate a pair of images corresponding to these two lights'
270	contributions:
271	.IP "" .2i
272	vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
273	rtcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
274	@render.opt \-o c_%s.pic \-m light1 \-m light2 scene.oct
275	.PP
276	These images may then be recombined using the desired outputs
277	of light1 and light2:
278	.IP "" .2i
279	pcomb \-c 100 90 75 c_light1.pic \-c 50 55 57 c_light2.pic > combined.pic
280	.PP
281	To compute an array of illuminance contributions according to a Tregenza sky:
282	.IP "" .2i
283	rtcontrib \-I+ \-b tbin \-o sky.dat \-m skyglow \-b 0 \-o ground.dat \-m groundglow
284	@render.opt \-f tregenza.cal scene.oct < test.dat
285	.SH ENVIRONMENT
286	RAYPATH path to search for \-f and \-M files
287	.SH AUTHOR
288	Greg Ward
289	.SH "SEE ALSO"
290	cnt(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
291	rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1)