man/man1/rcontrib.1

.\" RCSid "$Id: rcontrib.1,v 1.25 2025/03/27 01:26:55 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 "\-t secs"
][
.B "\-c count"
][
.B \-fo
|
.B \-r
][
.B "\-e expr"
][
.B "\-f source"
][
.B "\-o ospec"
][
.B "\-p p1=V1,p2=V2"
][
.B "\-b binv"
][
.B "\-bn nbins"
]
{
.B "\-m mod | \-M file"
}
..
[
.B $EVAR
]
[
.B @file
]
[
rtrace options
]
.B octree
.br
.B "rcontrib [ options ] \-defaults"
.br
.B "rcontrib \-features [feat1 ..]"
.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 one, meaning a full record will be produced for
each input ray.
For values greater than one, 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 with
.I \-c
set to zero.
.PP
Output flushing at fixed intervals may be enabled with the
.I \-x
option, which specifies the number of records
(-c accumulations) before each flush.
If the
.I \-y
option is also set, then periodic flushing is disabled and the
output size for an RGB image is the taken from the x and y dimensions.
In lieu of periodic flushing, a flush may be forced as mentioned above
by sending a sample with a zero direction vector, although you
must still send a full record of rays before output occurs.
.PP
If progress reports are desired, the
.I \-t
option specifies a time interval in seconds for reports sent to
standard error.
This requires that the number of input samples is known, meaning a
.I \-y
parameter has been specified.
.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 final integer will be offset incrementally
if the output is a RADIANCE picture and more than one modifier has
the same format specification.)\0
The actual bin number is computed at run time based on ray direction
and surface intersection, as described below.
The number of bins must be specified in advance 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 zero, the bin count is always equal to
the last bin plus one.
The most recent
.I \-p,
.I \-b,
.I \-bn
and
.I \-o
options to the left of each
.I \-m
name are the ones used for that modifier.
Any
.I \-cs
option changing the number of spectral color
samples must appear before the first modifier.
The ordering of other options is unimportant, except for
.I \-x
and
.I \-y
if the
.I \-c
is zero, 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.
Additional parameter values that apply only to this modifier may be specified
with a
.I \-p
option, which contains a list of variable names and assigned values, separated
by commas, colons, or semicolons.
The computed bin value will be
rounded to the nearest whole number.
(Negative bin values will be silently ignored.)\0
For a single bin, you may specify
.I "\-b 0",
which is the default.
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.
Like the other rendering tools,
.I rcontrib
will search the 
.I RAYPATH
library directories for each file given in a
.I \-f
option.
However, a special evaluation context is set for the
.I \-f
and
.I \-e
definitions, so attach a back-quote ('`') to variable and function names
you wish these to apply at the global evaluation level and used by all
materials and modifiers during rendering.
.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.
.PP
.I Rcontrib
supports light source contributions from photon maps generated by
.I mkpmap(1)
with its
.I -apC
option. Enabling photon mapping is described in the
.I rtrace 
man page along with its relevant settings. In photon mapping mode,
.I rcontrib
only supports contributions from light sources, not arbitrary modifiers.
The
.I -b
option is supported along with its associated ray variables, as
discussed above. Ray coefficients are also supported via the
.I \-V-
option. Using fewer photons than there are light sources for the photon
density estimates results in omitted contributions, thus the bandwidth
is clamped accordingly and a warning is issued. 
.SH EXAMPLES
To compute the proportional contributions from sources modified
by "light1" vs. "light2" on a set of irradiance 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 irradiance contributions according to a Tregenza sky:
.IP "" .2i
rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
\-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
.PP
To perform an annual simulation of 365 daily sun positions in photon mapping
mode:
.IP "" .2i
rcontrib \-I+ \-h \-V \-fo \-o c_%s.dat \-M lights \-ap contrib.pm 365
scene.oct < test.dat,
.SH ENVIRONMENT
RAYPATH         path to search for \-f and \-M files
.SH BUGS
We do not currently compute contributions or coefficients properly
in scenes with participating media.
A single warning will be issued if a scattering or absorbing medium
is detected.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
cnt(1), dctimestep(1), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(1), 
pvsum(1), ra_rgbe(1), rcalc(1), rcomb(1), rfluxmtx(1), rmtxop(1), rpict(1),
rsensor(1), rtrace(1), total(1), vwrays(1), ximage(1)

Revision:	1.26
Committed:	Wed Apr 23 15:09:03 2025 UTC (9 days, 17 hours ago) by greg
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.25:	+12 -4 lines
Log Message:	docs: Wording fixes to man pages regarding -e and -f options
#	Content
1	.\" RCSid "$Id: rcontrib.1,v 1.25 2025/03/27 01:26:55 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 "\-t secs"
13	][
14	.B "\-c count"
15	][
16	.B \-fo
17	\|
18	.B \-r
19	][
20	.B "\-e expr"
21	][
22	.B "\-f source"
23	][
24	.B "\-o ospec"
25	][
26	.B "\-p p1=V1,p2=V2"
27	][
28	.B "\-b binv"
29	][
30	.B "\-bn nbins"
31	]
32	{
33	.B "\-m mod \| \-M file"
34	}
35	..
36	[
37	.B $EVAR
38	]
39	[
40	.B @file
41	]
42	[
43	rtrace options
44	]
45	.B octree
46	.br
47	.B "rcontrib [ options ] \-defaults"
48	.br
49	.B "rcontrib \-features [feat1 ..]"
50	.SH DESCRIPTION
51	.I Rcontrib
52	computes ray coefficients
53	for objects whose modifiers are named in one or more
54	.I \-m
55	settings.
56	These modifiers are usually materials associated with
57	light sources or sky domes, and must directly modify some geometric
58	primitives to be considered in the output.
59	A modifier list may also be read from a file using the
60	.I \-M
61	option.
62	The RAYPATH environment variable determines directories to search for
63	this file.
64	(No search takes place if a file name begins with a '.', '/' or '~'
65	character.)\0
66	.PP
67	If the
68	.I \-n
69	option is specified with a value greater than 1, multiple
70	processes will be used to accelerate computation on a shared
71	memory machine.
72	Note that there is no benefit to using more processes
73	than there are local CPUs available to do the work, and the
74	.I rcontrib
75	process itself may use a considerable amount of CPU time.
76	.PP
77	By setting the boolean
78	.I \-V
79	option, you may instruct
80	.I rcontrib
81	to report the contribution from each material rather than the ray
82	coefficient.
83	This is particularly useful for light sources with directional output
84	distributions, whose value would otherwise be lost in the shuffle.
85	With the default
86	.I -V-
87	setting, the output of rcontrib is a coefficient that must be multiplied
88	by the radiance of each material to arrive at a final contribution.
89	This is more convenient for computing daylight coefficeints, or cases
90	where the actual radiance is not desired.
91	Use the
92	.I -V+
93	setting when you wish to simply sum together contributions
94	(with possible adjustment factors) to obtain a final radiance value.
95	Combined with the
96	.I \-i
97	or
98	.I \-I
99	option, irradiance contributions are reported by
100	.I \-V+
101	rather than radiance, and
102	.I \-V-
103	coefficients contain an additonal factor of PI.
104	.PP
105	The
106	.I \-c
107	option tells
108	.I rcontrib
109	how many rays to accumulate for each record.
110	The default value is one, meaning a full record will be produced for
111	each input ray.
112	For values greater than one, contributions will be averaged together
113	over the given number of input rays.
114	If set to zero, only a single record will be produced at the very
115	end, corresponding to the sum of all rays given on the input
116	(rather than the average).
117	This is equivalent to passing all the output records through a program like
118	.I total(1)
119	to sum RGB values together, but is much more efficient.
120	Using this option, it is possible to reverse sampling, sending rays from
121	a parallel source such as the sun to a diffuse surface, for example.
122	Note that output flushing via zero-direction rays is disabled with
123	.I \-c
124	set to zero.
125	.PP
126	Output flushing at fixed intervals may be enabled with the
127	.I \-x
128	option, which specifies the number of records
129	(-c accumulations) before each flush.
130	If the
131	.I \-y
132	option is also set, then periodic flushing is disabled and the
133	output size for an RGB image is the taken from the x and y dimensions.
134	In lieu of periodic flushing, a flush may be forced as mentioned above
135	by sending a sample with a zero direction vector, although you
136	must still send a full record of rays before output occurs.
137	.PP
138	If progress reports are desired, the
139	.I \-t
140	option specifies a time interval in seconds for reports sent to
141	standard error.
142	This requires that the number of input samples is known, meaning a
143	.I \-y
144	parameter has been specified.
145	.PP
146	The output of
147	.I rcontrib
148	has many potential uses.
149	Source contributions can be used as components in linear combination to
150	reproduce any desired variation, e.g., simulating lighting controls or
151	changing sky conditions via daylight coefficients.
152	More generally,
153	.I rcontrib
154	can be used to compute arbitrary input-output relationships in optical
155	systems, such as luminaires, light pipes, and shading devices.
156	.PP
157	.I Rcontrib
158	sends the accumulated rays tallies
159	to one or more destinations according to the given
160	.I \-o
161	specification.
162	If a destination begins with an exclamation mark ('!'), then
163	a pipe is opened to a command and data is sent to its standard input.
164	Otherwise, the destination is treated as a file.
165	An existing file of the same name will not be clobbered, unless the
166	.I \-fo
167	option is given.
168	If instead the
169	.I \-r
170	option is specified, data recovery is attempted on existing files.
171	(If
172	.I "\-c 0"
173	is used together with the
174	.I \-r
175	option, existing files are read in and new ray evaluations are added
176	to the previous results, providing a convenient means for
177	progressive simulation.)\0
178	If an output specification contains a "%s" format, this will be
179	replaced by the modifier name.
180	The
181	.I \-b
182	option may be used to further define
183	a "bin number" within each object if finer resolution is needed, and
184	this will be applied to a "%d" format in the output file
185	specification if present.
186	(The final integer will be offset incrementally
187	if the output is a RADIANCE picture and more than one modifier has
188	the same format specification.)\0
189	The actual bin number is computed at run time based on ray direction
190	and surface intersection, as described below.
191	The number of bins must be specified in advance with the
192	.I \-bn
193	option, and this is critical for output files containing multiple values
194	per record.
195	A variable or constant name may be given for this parameter if
196	it has been defined via a previous
197	.I \-f
198	or
199	.I \-e
200	option.
201	Since bin numbers start from zero, the bin count is always equal to
202	the last bin plus one.
203	The most recent
204	.I \-p,
205	.I \-b,
206	.I \-bn
207	and
208	.I \-o
209	options to the left of each
210	.I \-m
211	name are the ones used for that modifier.
212	Any
213	.I \-cs
214	option changing the number of spectral color
215	samples must appear before the first modifier.
216	The ordering of other options is unimportant, except for
217	.I \-x
218	and
219	.I \-y
220	if the
221	.I \-c
222	is zero, when they control the resolution string
223	produced in the corresponding output.
224	.PP
225	If a
226	.I \-b
227	expression is defined for a particular modifier,
228	the bin number will be evaluated at run time for each
229	ray contribution.
230	Specifically, each ray's world intersection point will be assigned to
231	the variables Px, Py, and Pz, and the normalized ray direction
232	will be assigned to Dx, Dy, and Dz.
233	These parameters may be combined with definitions given in
234	.I \-e
235	arguments and files read using the
236	.I \-f
237	option.
238	Additional parameter values that apply only to this modifier may be specified
239	with a
240	.I \-p
241	option, which contains a list of variable names and assigned values, separated
242	by commas, colons, or semicolons.
243	The computed bin value will be
244	rounded to the nearest whole number.
245	(Negative bin values will be silently ignored.)\0
246	For a single bin, you may specify
247	.I "\-b 0",
248	which is the default.
249	This mechanism allows the user to define precise regions or directions
250	they wish to accumulate, such as the Tregenza sky discretization,
251	which would be otherwise impossible to specify
252	as a set of RADIANCE primitives.
253	The rules and predefined functions available for these expressions are
254	described in the
255	.I rcalc(1)
256	man page.
257	Like the other rendering tools,
258	.I rcontrib
259	will search the
260	.I RAYPATH
261	library directories for each file given in a
262	.I \-f
263	option.
264	However, a special evaluation context is set for the
265	.I \-f
266	and
267	.I \-e
268	definitions, so attach a back-quote ('`') to variable and function names
269	you wish these to apply at the global evaluation level and used by all
270	materials and modifiers during rendering.
271	.PP
272	If no
273	.I \-o
274	specification is given, results are written on the standard output in order
275	of modifier (as given on the command line) then bin number.
276	Concatenated data is also sent to a single destination (i.e., an initial
277	.I \-o
278	specification without formatting strings).
279	If a "%s" format appears but no "%d" in the
280	.I \-o
281	specification, then each modifier will have its own output file, with
282	multiple values per record in the case of a non-zero
283	.I \-b
284	definition.
285	If a "%d" format appears but no "%s", then each bin will get its own
286	output file, with modifiers output in order in each record.
287	For text output, each RGB coefficient triple is separated by a tab,
288	with a newline at the end of each ray record.
289	For binary output formats, there is no such delimiter to mark
290	the end of each record.
291	.PP
292	Input and output format defaults to plain text, where each ray's
293	origin and direction (6 real values) are given on input,
294	and one line is produced per output file per ray.
295	Alternative data representations may be specified by the
296	.I \-f[io]
297	option, which is described in the
298	.I rtrace
299	man page along with the associated
300	.I \-x
301	and
302	.I \-y
303	resolution settings.
304	In particular, the color ('c') output data representation
305	together with positive dimensions for
306	.I \-x
307	and
308	.I \-y
309	will produce an uncompressed RADIANCE picture,
310	suitable for manipulation with
311	.I pcomb(1)
312	and related tools.
313	.PP
314	Options may be given on the command line and/or read from the
315	environment and/or read from a file.
316	A command argument beginning with a dollar sign ('$') is immediately
317	replaced by the contents of the given environment variable.
318	A command argument beginning with an at sign ('@') is immediately
319	replaced by the contents of the given file.
320	.PP
321	.I Rcontrib
322	supports light source contributions from photon maps generated by
323	.I mkpmap(1)
324	with its
325	.I -apC
326	option. Enabling photon mapping is described in the
327	.I rtrace
328	man page along with its relevant settings. In photon mapping mode,
329	.I rcontrib
330	only supports contributions from light sources, not arbitrary modifiers.
331	The
332	.I -b
333	option is supported along with its associated ray variables, as
334	discussed above. Ray coefficients are also supported via the
335	.I \-V-
336	option. Using fewer photons than there are light sources for the photon
337	density estimates results in omitted contributions, thus the bandwidth
338	is clamped accordingly and a warning is issued.
339	.SH EXAMPLES
340	To compute the proportional contributions from sources modified
341	by "light1" vs. "light2" on a set of irradiance values:
342	.IP "" .2i
343	rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
344	.PP
345	To generate a pair of images corresponding to these two lights'
346	contributions:
347	.IP "" .2i
348	vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
349	rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
350	@render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
351	.PP
352	These images may then be recombined using the desired outputs
353	of light1 and light2:
354	.IP "" .2i
355	pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
356	.PP
357	To compute an array of irradiance contributions according to a Tregenza sky:
358	.IP "" .2i
359	rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
360	\-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
361	.PP
362	To perform an annual simulation of 365 daily sun positions in photon mapping
363	mode:
364	.IP "" .2i
365	rcontrib \-I+ \-h \-V \-fo \-o c_%s.dat \-M lights \-ap contrib.pm 365
366	scene.oct < test.dat,
367	.SH ENVIRONMENT
368	RAYPATH path to search for \-f and \-M files
369	.SH BUGS
370	We do not currently compute contributions or coefficients properly
371	in scenes with participating media.
372	A single warning will be issued if a scattering or absorbing medium
373	is detected.
374	.SH AUTHOR
375	Greg Ward
376	.SH "SEE ALSO"
377	cnt(1), dctimestep(1), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(1),
378	pvsum(1), ra_rgbe(1), rcalc(1), rcomb(1), rfluxmtx(1), rmtxop(1), rpict(1),
379	rsensor(1), rtrace(1), total(1), vwrays(1), ximage(1)
380