man/man1/rcontrib.1

.\" RCSid "$Id: rcontrib.1,v 1.22 2023/12/06 01:27:00 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
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 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
.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.
.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), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(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:	1.23
Committed:	Tue Dec 12 16:31:45 2023 UTC (17 months, 1 week ago) by greg
Branch:	MAIN
Changes since 1.22:	+2 -2 lines
Log Message:	chore(rcomb): Renamed rmtxcomb to simpler "rcomb"
#	User	Rev	Content
1	greg	1.23	.\" RCSid "$Id: rcontrib.1,v 1.22 2023/12/06 01:27:00 greg Exp $"
2	greg	1.2	.TH RCONTRIB 1 5/25/05 RADIANCE
3	greg	1.1	.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	greg	1.18	.B "\-t secs"
13			][
14	greg	1.1	.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	greg	1.10	.B "\-p p1=V1,p2=V2"
27			][
28	greg	1.1	.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	greg	1.21	.br
49			.B "rcontrib \-features [feat1 ..]"
50	greg	1.1	.SH DESCRIPTION
51	greg	1.3	.I Rcontrib
52	greg	1.1	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	greg	1.6	The default value is one, meaning a full record will be produced for
111	greg	1.1	each input ray.
112	greg	1.6	For values greater than one, contributions will be averaged together
113	greg	1.1	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	greg	1.6	Note that output flushing via zero-direction rays is disabled with
123			.I \-c
124			set to zero.
125	greg	1.1	.PP
126	greg	1.19	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	greg	1.18	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	greg	1.19	This requires that the number of input samples is known, meaning a
143			.I \-y
144			parameter has been specified.
145	greg	1.18	.PP
146	greg	1.1	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	greg	1.3	.I Rcontrib
158	greg	1.4	sends the accumulated rays tallies
159			to one or more destinations according to the given
160	greg	1.1	.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	greg	1.13	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	greg	1.1	The actual bin number is computed at run time based on ray direction
190			and surface intersection, as described below.
191	greg	1.5	The number of bins must be specified in advance with the
192	greg	1.1	.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	greg	1.6	Since bin numbers start from zero, the bin count is always equal to
202			the last bin plus one.
203	greg	1.1	The most recent
204	greg	1.10	.I \-p,
205	greg	1.1	.I \-b,
206			.I \-bn
207			and
208			.I \-o
209			options to the left of each
210			.I \-m
211			setting are the ones used for that modifier.
212			The ordering of other options is unimportant, except for
213			.I \-x
214			and
215			.I \-y
216			if the
217			.I \-c
218	greg	1.6	is zero, when they control the resolution string
219	greg	1.1	produced in the corresponding output.
220			.PP
221			If a
222			.I \-b
223			expression is defined for a particular modifier,
224			the bin number will be evaluated at run time for each
225	greg	1.4	ray contribution.
226	greg	1.1	Specifically, each ray's world intersection point will be assigned to
227			the variables Px, Py, and Pz, and the normalized ray direction
228			will be assigned to Dx, Dy, and Dz.
229			These parameters may be combined with definitions given in
230			.I \-e
231			arguments and files read using the
232			.I \-f
233			option.
234	greg	1.10	Additional parameter values that apply only to this modifier may be specified
235			with a
236			.I \-p
237			option, which contains a list of variable names and assigned values, separated
238	greg	1.17	by commas, colons, or semicolons.
239	greg	1.1	The computed bin value will be
240			rounded to the nearest whole number.
241	greg	1.9	(Negative bin values will be silently ignored.)\0
242	greg	1.8	For a single bin, you may specify
243			.I "\-b 0",
244			which is the default.
245	greg	1.1	This mechanism allows the user to define precise regions or directions
246			they wish to accumulate, such as the Tregenza sky discretization,
247			which would be otherwise impossible to specify
248			as a set of RADIANCE primitives.
249			The rules and predefined functions available for these expressions are
250			described in the
251			.I rcalc(1)
252			man page.
253	greg	1.8	Like
254	greg	1.1	.I rcalc,
255			.I rcontrib
256			will search the RADIANCE library directories for each file given in a
257			.I \-f
258			option.
259			.PP
260			If no
261			.I \-o
262			specification is given, results are written on the standard output in order
263			of modifier (as given on the command line) then bin number.
264			Concatenated data is also sent to a single destination (i.e., an initial
265			.I \-o
266			specification without formatting strings).
267			If a "%s" format appears but no "%d" in the
268			.I \-o
269			specification, then each modifier will have its own output file, with
270			multiple values per record in the case of a non-zero
271			.I \-b
272			definition.
273			If a "%d" format appears but no "%s", then each bin will get its own
274			output file, with modifiers output in order in each record.
275			For text output, each RGB coefficient triple is separated by a tab,
276			with a newline at the end of each ray record.
277			For binary output formats, there is no such delimiter to mark
278			the end of each record.
279			.PP
280			Input and output format defaults to plain text, where each ray's
281			origin and direction (6 real values) are given on input,
282			and one line is produced per output file per ray.
283			Alternative data representations may be specified by the
284			.I \-f[io]
285			option, which is described in the
286			.I rtrace
287			man page along with the associated
288			.I \-x
289			and
290			.I \-y
291			resolution settings.
292			In particular, the color ('c') output data representation
293			together with positive dimensions for
294			.I \-x
295			and
296			.I \-y
297			will produce an uncompressed RADIANCE picture,
298			suitable for manipulation with
299			.I pcomb(1)
300			and related tools.
301			.PP
302			Options may be given on the command line and/or read from the
303			environment and/or read from a file.
304			A command argument beginning with a dollar sign ('$') is immediately
305			replaced by the contents of the given environment variable.
306			A command argument beginning with an at sign ('@') is immediately
307			replaced by the contents of the given file.
308	greg	1.12	.PP
309			.I Rcontrib
310	rschregle	1.14	supports light source contributions from photon maps generated by
311	greg	1.12	.I mkpmap(1)
312			with its
313			.I -apC
314	rschregle	1.15	option. Enabling photon mapping is described in the
315			.I rtrace
316			man page along with its relevant settings. In photon mapping mode,
317	greg	1.12	.I rcontrib
318			only supports contributions from light sources, not arbitrary modifiers.
319			The
320			.I -b
321			option is supported along with its associated ray variables, as
322			discussed above. Ray coefficients are also supported via the
323			.I \-V-
324			option. Using fewer photons than there are light sources for the photon
325			density estimates results in omitted contributions, thus the bandwidth
326	rschregle	1.15	is clamped accordingly and a warning is issued.
327	greg	1.1	.SH EXAMPLES
328			To compute the proportional contributions from sources modified
329	greg	1.20	by "light1" vs. "light2" on a set of irradiance values:
330	greg	1.1	.IP "" .2i
331			rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
332			.PP
333			To generate a pair of images corresponding to these two lights'
334			contributions:
335			.IP "" .2i
336			vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
337			rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
338			@render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
339			.PP
340			These images may then be recombined using the desired outputs
341			of light1 and light2:
342			.IP "" .2i
343			pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
344			.PP
345	greg	1.20	To compute an array of irradiance contributions according to a Tregenza sky:
346	greg	1.1	.IP "" .2i
347	greg	1.7	rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
348			\-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
349	greg	1.12	.PP
350			To perform an annual simulation of 365 daily sun positions in photon mapping
351			mode:
352			.IP "" .2i
353			rcontrib \-I+ \-h \-V \-fo \-o c_%s.dat \-M lights \-ap contrib.pm 365
354			scene.oct < test.dat,
355	greg	1.1	.SH ENVIRONMENT
356			RAYPATH path to search for \-f and \-M files
357	greg	1.16	.SH BUGS
358			We do not currently compute contributions or coefficients properly
359			in scenes with participating media.
360			A single warning will be issued if a scattering or absorbing medium
361			is detected.
362	greg	1.1	.SH AUTHOR
363			Greg Ward
364			.SH "SEE ALSO"
365	greg	1.12	cnt(1), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(1),
366	greg	1.23	ra_rgbe(1), rcalc(1), rcomb(1), rfluxmtx(1), rmtxop(1), rpict(1),
367	greg	1.22	rsensor(1), rtrace(1), total(1), vwrays(1), ximage(1)
368	greg	1.12