man/man1/rcontrib.1

.\" RCSid "$Id: rcontrib.1,v 1.3 2012/06/14 22:45:23 greg Exp $"
.TH RCONTRIB 1 5/25/05 RADIANCE
.SH NAME
rcontrib - compute contribution coefficients in a RADIANCE scene
.SH SYNOPSIS
.B rcontrib
[
.B "\-n nprocs"
][
.B \-V
][
.B "\-c count"
][
.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 "rcontrib [ options ] \-defaults"
.SH DESCRIPTION
.I Rcontrib
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
If the
.I \-n
option is specified with a value greater than 1, multiple
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 rcontrib
process itself may use a considerable amount of CPU time.
.PP
By setting the boolean
.I \-V
option, you may instruct
.I rcontrib
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 rcontrib 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
.I \-c
option tells
.I rcontrib
how many rays to accumulate for each record.
The default value is 1, meaning a full record will be produced for
each input ray.
For values greater than 1, contributions will be averaged together
over the given number of input rays.
If set to zero, only a single record will be produced at the very
end, corresponding to the sum of all rays given on the input
(rather than the average).
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.
Note that output flushing via zero-direction rays is disabled
for accumulated evaluations.
.PP
The output of
.I rcontrib
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 rcontrib
can be used to compute arbitrary input-output relationships in optical
systems, such as luminaires, light pipes, and shading devices.
.PP
.I Rcontrib
sends the accumulated rays tallies
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 0"
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.
A variable or constant name may be given for this parameter if
it has been defined via a previous
.I \-f
or
.I \-e
option.
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 are the ones used for that modifier.
The ordering of other options is unimportant, except for
.I \-x
and
.I \-y
if the
.I \-c
is 0, 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.
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 rcontrib
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
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
rcontrib \-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 |
rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
@render.opt \-o c_%s.hdr \-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.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
.PP
To compute an array of illuminance contributions according to a Tregenza sky:
.IP "" .2i
rcontrib \-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), genklemsamp(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
rcalc(1), rpict(1), rsensor(1), rtrace(1), total(1), vwrays(1), ximage(1)
Revision:	1.4
Committed:	Thu Jun 14 22:49:34 2012 UTC (12 years, 11 months ago) by greg
Branch:	MAIN
Changes since 1.3:	+4 -9 lines
Log Message:	Removed inaccurate references to rtrace subprocesses.
#	Content
1	.\" RCSid "$Id: rcontrib.1,v 1.3 2012/06/14 22:45:23 greg Exp $"
2	.TH RCONTRIB 1 5/25/05 RADIANCE
3	.SH NAME
4	rcontrib - compute contribution coefficients in a RADIANCE scene
5	.SH SYNOPSIS
6	.B rcontrib
7	[
8	.B "\-n nprocs"
9	][
10	.B \-V
11	][
12	.B "\-c count"
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 "rcontrib [ options ] \-defaults"
44	.SH DESCRIPTION
45	.I Rcontrib
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	If the
62	.I \-n
63	option is specified with a value greater than 1, multiple
64	processes will be used to accelerate computation on a shared
65	memory machine.
66	Note that there is no benefit to using more processes
67	than there are local CPUs available to do the work, and the
68	.I rcontrib
69	process itself may use a considerable amount of CPU time.
70	.PP
71	By setting the boolean
72	.I \-V
73	option, you may instruct
74	.I rcontrib
75	to report the contribution from each material rather than the ray
76	coefficient.
77	This is particularly useful for light sources with directional output
78	distributions, whose value would otherwise be lost in the shuffle.
79	With the default
80	.I -V-
81	setting, the output of rcontrib is a coefficient that must be multiplied
82	by the radiance of each material to arrive at a final contribution.
83	This is more convenient for computing daylight coefficeints, or cases
84	where the actual radiance is not desired.
85	Use the
86	.I -V+
87	setting when you wish to simply sum together contributions
88	(with possible adjustment factors) to obtain a final radiance value.
89	Combined with the
90	.I \-i
91	or
92	.I \-I
93	option, irradiance contributions are reported by
94	.I \-V+
95	rather than radiance, and
96	.I \-V-
97	coefficients contain an additonal factor of PI.
98	.PP
99	The
100	.I \-c
101	option tells
102	.I rcontrib
103	how many rays to accumulate for each record.
104	The default value is 1, meaning a full record will be produced for
105	each input ray.
106	For values greater than 1, contributions will be averaged together
107	over the given number of input rays.
108	If set to zero, only a single record will be produced at the very
109	end, corresponding to the sum of all rays given on the input
110	(rather than the average).
111	This is equivalent to passing all the output records through a program like
112	.I total(1)
113	to sum RGB values together, but is much more efficient.
114	Using this option, it is possible to reverse sampling, sending rays from
115	a parallel source such as the sun to a diffuse surface, for example.
116	Note that output flushing via zero-direction rays is disabled
117	for accumulated evaluations.
118	.PP
119	The output of
120	.I rcontrib
121	has many potential uses.
122	Source contributions can be used as components in linear combination to
123	reproduce any desired variation, e.g., simulating lighting controls or
124	changing sky conditions via daylight coefficients.
125	More generally,
126	.I rcontrib
127	can be used to compute arbitrary input-output relationships in optical
128	systems, such as luminaires, light pipes, and shading devices.
129	.PP
130	.I Rcontrib
131	sends the accumulated rays tallies
132	to one or more destinations according to the given
133	.I \-o
134	specification.
135	If a destination begins with an exclamation mark ('!'), then
136	a pipe is opened to a command and data is sent to its standard input.
137	Otherwise, the destination is treated as a file.
138	An existing file of the same name will not be clobbered, unless the
139	.I \-fo
140	option is given.
141	If instead the
142	.I \-r
143	option is specified, data recovery is attempted on existing files.
144	(If
145	.I "\-c 0"
146	is used together with the
147	.I \-r
148	option, existing files are read in and new ray evaluations are added
149	to the previous results, providing a convenient means for
150	progressive simulation.)\0
151	If an output specification contains a "%s" format, this will be
152	replaced by the modifier name.
153	The
154	.I \-b
155	option may be used to further define
156	a "bin number" within each object if finer resolution is needed, and
157	this will be applied to a "%d" format in the output file
158	specification if present.
159	The actual bin number is computed at run time based on ray direction
160	and surface intersection, as described below.
161	If the number of bins is known in advance, it should be specified with the
162	.I \-bn
163	option, and this is critical for output files containing multiple values
164	per record.
165	A variable or constant name may be given for this parameter if
166	it has been defined via a previous
167	.I \-f
168	or
169	.I \-e
170	option.
171	Since bin numbers start from 0, the bin count is always equal to
172	the last bin plus 1.
173	Set the this value to 0 if the bin count is unknown (the default).
174	The most recent
175	.I \-b,
176	.I \-bn
177	and
178	.I \-o
179	options to the left of each
180	.I \-m
181	setting are the ones used for that modifier.
182	The ordering of other options is unimportant, except for
183	.I \-x
184	and
185	.I \-y
186	if the
187	.I \-c
188	is 0, when they control the resolution string
189	produced in the corresponding output.
190	.PP
191	If a
192	.I \-b
193	expression is defined for a particular modifier,
194	the bin number will be evaluated at run time for each
195	ray contribution.
196	Specifically, each ray's world intersection point will be assigned to
197	the variables Px, Py, and Pz, and the normalized ray direction
198	will be assigned to Dx, Dy, and Dz.
199	These parameters may be combined with definitions given in
200	.I \-e
201	arguments and files read using the
202	.I \-f
203	option.
204	The computed bin value will be
205	rounded to the nearest whole number.
206	This mechanism allows the user to define precise regions or directions
207	they wish to accumulate, such as the Tregenza sky discretization,
208	which would be otherwise impossible to specify
209	as a set of RADIANCE primitives.
210	The rules and predefined functions available for these expressions are
211	described in the
212	.I rcalc(1)
213	man page.
214	Unlike
215	.I rcalc,
216	.I rcontrib
217	will search the RADIANCE library directories for each file given in a
218	.I \-f
219	option.
220	.PP
221	If no
222	.I \-o
223	specification is given, results are written on the standard output in order
224	of modifier (as given on the command line) then bin number.
225	Concatenated data is also sent to a single destination (i.e., an initial
226	.I \-o
227	specification without formatting strings).
228	If a "%s" format appears but no "%d" in the
229	.I \-o
230	specification, then each modifier will have its own output file, with
231	multiple values per record in the case of a non-zero
232	.I \-b
233	definition.
234	If a "%d" format appears but no "%s", then each bin will get its own
235	output file, with modifiers output in order in each record.
236	For text output, each RGB coefficient triple is separated by a tab,
237	with a newline at the end of each ray record.
238	For binary output formats, there is no such delimiter to mark
239	the end of each record.
240	.PP
241	Input and output format defaults to plain text, where each ray's
242	origin and direction (6 real values) are given on input,
243	and one line is produced per output file per ray.
244	Alternative data representations may be specified by the
245	.I \-f[io]
246	option, which is described in the
247	.I rtrace
248	man page along with the associated
249	.I \-x
250	and
251	.I \-y
252	resolution settings.
253	In particular, the color ('c') output data representation
254	together with positive dimensions for
255	.I \-x
256	and
257	.I \-y
258	will produce an uncompressed RADIANCE picture,
259	suitable for manipulation with
260	.I pcomb(1)
261	and related tools.
262	.PP
263	Options may be given on the command line and/or read from the
264	environment and/or read from a file.
265	A command argument beginning with a dollar sign ('$') is immediately
266	replaced by the contents of the given environment variable.
267	A command argument beginning with an at sign ('@') is immediately
268	replaced by the contents of the given file.
269	.SH EXAMPLES
270	To compute the proportional contributions from sources modified
271	by "light1" vs. "light2" on a set of illuminance values:
272	.IP "" .2i
273	rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
274	.PP
275	To generate a pair of images corresponding to these two lights'
276	contributions:
277	.IP "" .2i
278	vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
279	rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
280	@render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
281	.PP
282	These images may then be recombined using the desired outputs
283	of light1 and light2:
284	.IP "" .2i
285	pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
286	.PP
287	To compute an array of illuminance contributions according to a Tregenza sky:
288	.IP "" .2i
289	rcontrib \-I+ \-b tbin \-o sky.dat \-m skyglow \-b 0 \-o ground.dat \-m groundglow
290	@render.opt \-f tregenza.cal scene.oct < test.dat
291	.SH ENVIRONMENT
292	RAYPATH path to search for \-f and \-M files
293	.SH AUTHOR
294	Greg Ward
295	.SH "SEE ALSO"
296	cnt(1), genklemsamp(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
297	rcalc(1), rpict(1), rsensor(1), rtrace(1), total(1), vwrays(1), ximage(1)