man/man1/rcontrib.1

.\" RCSid "$Id: rcontrib.1,v 1.19 2020/09/10 17:52:46 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"
.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), rfluxmtx(1), rmtxop(1), rpict(1), rsensor(1), 
rtrace(1), total(1), vwrays(1), ximage(1)

Revision:	1.20
Committed:	Wed Oct 19 18:23:14 2022 UTC (2 years, 7 months ago) by greg
Branch:	MAIN
Changes since 1.19:	+3 -3 lines
Log Message:	docs: made use of "virtual" and "secondary" sources more consistent
#	User	Rev	Content
1	greg	1.20	.\" RCSid "$Id: rcontrib.1,v 1.19 2020/09/10 17:52:46 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			.SH DESCRIPTION
49	greg	1.3	.I Rcontrib
50	greg	1.1	computes ray coefficients
51			for objects whose modifiers are named in one or more
52			.I \-m
53			settings.
54			These modifiers are usually materials associated with
55			light sources or sky domes, and must directly modify some geometric
56			primitives to be considered in the output.
57			A modifier list may also be read from a file using the
58			.I \-M
59			option.
60			The RAYPATH environment variable determines directories to search for
61			this file.
62			(No search takes place if a file name begins with a '.', '/' or '~'
63			character.)\0
64			.PP
65			If the
66			.I \-n
67			option is specified with a value greater than 1, multiple
68			processes will be used to accelerate computation on a shared
69			memory machine.
70			Note that there is no benefit to using more processes
71			than there are local CPUs available to do the work, and the
72			.I rcontrib
73			process itself may use a considerable amount of CPU time.
74			.PP
75			By setting the boolean
76			.I \-V
77			option, you may instruct
78			.I rcontrib
79			to report the contribution from each material rather than the ray
80			coefficient.
81			This is particularly useful for light sources with directional output
82			distributions, whose value would otherwise be lost in the shuffle.
83			With the default
84			.I -V-
85			setting, the output of rcontrib is a coefficient that must be multiplied
86			by the radiance of each material to arrive at a final contribution.
87			This is more convenient for computing daylight coefficeints, or cases
88			where the actual radiance is not desired.
89			Use the
90			.I -V+
91			setting when you wish to simply sum together contributions
92			(with possible adjustment factors) to obtain a final radiance value.
93			Combined with the
94			.I \-i
95			or
96			.I \-I
97			option, irradiance contributions are reported by
98			.I \-V+
99			rather than radiance, and
100			.I \-V-
101			coefficients contain an additonal factor of PI.
102			.PP
103			The
104			.I \-c
105			option tells
106			.I rcontrib
107			how many rays to accumulate for each record.
108	greg	1.6	The default value is one, meaning a full record will be produced for
109	greg	1.1	each input ray.
110	greg	1.6	For values greater than one, contributions will be averaged together
111	greg	1.1	over the given number of input rays.
112			If set to zero, only a single record will be produced at the very
113			end, corresponding to the sum of all rays given on the input
114			(rather than the average).
115			This is equivalent to passing all the output records through a program like
116			.I total(1)
117			to sum RGB values together, but is much more efficient.
118			Using this option, it is possible to reverse sampling, sending rays from
119			a parallel source such as the sun to a diffuse surface, for example.
120	greg	1.6	Note that output flushing via zero-direction rays is disabled with
121			.I \-c
122			set to zero.
123	greg	1.1	.PP
124	greg	1.19	Output flushing at fixed intervals may be enabled with the
125			.I \-x
126			option, which specifies the number of records
127			(-c accumulations) before each flush.
128			If the
129			.I \-y
130			option is also set, then periodic flushing is disabled and the
131			output size for an RGB image is the taken from the x and y dimensions.
132			In lieu of periodic flushing, a flush may be forced as mentioned above
133			by sending a sample with a zero direction vector, although you
134			must still send a full record of rays before output occurs.
135			.PP
136	greg	1.18	If progress reports are desired, the
137			.I \-t
138			option specifies a time interval in seconds for reports sent to
139			standard error.
140	greg	1.19	This requires that the number of input samples is known, meaning a
141			.I \-y
142			parameter has been specified.
143	greg	1.18	.PP
144	greg	1.1	The output of
145			.I rcontrib
146			has many potential uses.
147			Source contributions can be used as components in linear combination to
148			reproduce any desired variation, e.g., simulating lighting controls or
149			changing sky conditions via daylight coefficients.
150			More generally,
151			.I rcontrib
152			can be used to compute arbitrary input-output relationships in optical
153			systems, such as luminaires, light pipes, and shading devices.
154			.PP
155	greg	1.3	.I Rcontrib
156	greg	1.4	sends the accumulated rays tallies
157			to one or more destinations according to the given
158	greg	1.1	.I \-o
159			specification.
160			If a destination begins with an exclamation mark ('!'), then
161			a pipe is opened to a command and data is sent to its standard input.
162			Otherwise, the destination is treated as a file.
163			An existing file of the same name will not be clobbered, unless the
164			.I \-fo
165			option is given.
166			If instead the
167			.I \-r
168			option is specified, data recovery is attempted on existing files.
169			(If
170			.I "\-c 0"
171			is used together with the
172			.I \-r
173			option, existing files are read in and new ray evaluations are added
174			to the previous results, providing a convenient means for
175			progressive simulation.)\0
176			If an output specification contains a "%s" format, this will be
177			replaced by the modifier name.
178			The
179			.I \-b
180			option may be used to further define
181			a "bin number" within each object if finer resolution is needed, and
182			this will be applied to a "%d" format in the output file
183	greg	1.13	specification if present.
184			(The final integer will be offset incrementally
185			if the output is a RADIANCE picture and more than one modifier has
186			the same format specification.)\0
187	greg	1.1	The actual bin number is computed at run time based on ray direction
188			and surface intersection, as described below.
189	greg	1.5	The number of bins must be specified in advance with the
190	greg	1.1	.I \-bn
191			option, and this is critical for output files containing multiple values
192			per record.
193			A variable or constant name may be given for this parameter if
194			it has been defined via a previous
195			.I \-f
196			or
197			.I \-e
198			option.
199	greg	1.6	Since bin numbers start from zero, the bin count is always equal to
200			the last bin plus one.
201	greg	1.1	The most recent
202	greg	1.10	.I \-p,
203	greg	1.1	.I \-b,
204			.I \-bn
205			and
206			.I \-o
207			options to the left of each
208			.I \-m
209			setting are the ones used for that modifier.
210			The ordering of other options is unimportant, except for
211			.I \-x
212			and
213			.I \-y
214			if the
215			.I \-c
216	greg	1.6	is zero, when they control the resolution string
217	greg	1.1	produced in the corresponding output.
218			.PP
219			If a
220			.I \-b
221			expression is defined for a particular modifier,
222			the bin number will be evaluated at run time for each
223	greg	1.4	ray contribution.
224	greg	1.1	Specifically, each ray's world intersection point will be assigned to
225			the variables Px, Py, and Pz, and the normalized ray direction
226			will be assigned to Dx, Dy, and Dz.
227			These parameters may be combined with definitions given in
228			.I \-e
229			arguments and files read using the
230			.I \-f
231			option.
232	greg	1.10	Additional parameter values that apply only to this modifier may be specified
233			with a
234			.I \-p
235			option, which contains a list of variable names and assigned values, separated
236	greg	1.17	by commas, colons, or semicolons.
237	greg	1.1	The computed bin value will be
238			rounded to the nearest whole number.
239	greg	1.9	(Negative bin values will be silently ignored.)\0
240	greg	1.8	For a single bin, you may specify
241			.I "\-b 0",
242			which is the default.
243	greg	1.1	This mechanism allows the user to define precise regions or directions
244			they wish to accumulate, such as the Tregenza sky discretization,
245			which would be otherwise impossible to specify
246			as a set of RADIANCE primitives.
247			The rules and predefined functions available for these expressions are
248			described in the
249			.I rcalc(1)
250			man page.
251	greg	1.8	Like
252	greg	1.1	.I rcalc,
253			.I rcontrib
254			will search the RADIANCE library directories for each file given in a
255			.I \-f
256			option.
257			.PP
258			If no
259			.I \-o
260			specification is given, results are written on the standard output in order
261			of modifier (as given on the command line) then bin number.
262			Concatenated data is also sent to a single destination (i.e., an initial
263			.I \-o
264			specification without formatting strings).
265			If a "%s" format appears but no "%d" in the
266			.I \-o
267			specification, then each modifier will have its own output file, with
268			multiple values per record in the case of a non-zero
269			.I \-b
270			definition.
271			If a "%d" format appears but no "%s", then each bin will get its own
272			output file, with modifiers output in order in each record.
273			For text output, each RGB coefficient triple is separated by a tab,
274			with a newline at the end of each ray record.
275			For binary output formats, there is no such delimiter to mark
276			the end of each record.
277			.PP
278			Input and output format defaults to plain text, where each ray's
279			origin and direction (6 real values) are given on input,
280			and one line is produced per output file per ray.
281			Alternative data representations may be specified by the
282			.I \-f[io]
283			option, which is described in the
284			.I rtrace
285			man page along with the associated
286			.I \-x
287			and
288			.I \-y
289			resolution settings.
290			In particular, the color ('c') output data representation
291			together with positive dimensions for
292			.I \-x
293			and
294			.I \-y
295			will produce an uncompressed RADIANCE picture,
296			suitable for manipulation with
297			.I pcomb(1)
298			and related tools.
299			.PP
300			Options may be given on the command line and/or read from the
301			environment and/or read from a file.
302			A command argument beginning with a dollar sign ('$') is immediately
303			replaced by the contents of the given environment variable.
304			A command argument beginning with an at sign ('@') is immediately
305			replaced by the contents of the given file.
306	greg	1.12	.PP
307			.I Rcontrib
308	rschregle	1.14	supports light source contributions from photon maps generated by
309	greg	1.12	.I mkpmap(1)
310			with its
311			.I -apC
312	rschregle	1.15	option. Enabling photon mapping is described in the
313			.I rtrace
314			man page along with its relevant settings. In photon mapping mode,
315	greg	1.12	.I rcontrib
316			only supports contributions from light sources, not arbitrary modifiers.
317			The
318			.I -b
319			option is supported along with its associated ray variables, as
320			discussed above. Ray coefficients are also supported via the
321			.I \-V-
322			option. Using fewer photons than there are light sources for the photon
323			density estimates results in omitted contributions, thus the bandwidth
324	rschregle	1.15	is clamped accordingly and a warning is issued.
325	greg	1.1	.SH EXAMPLES
326			To compute the proportional contributions from sources modified
327	greg	1.20	by "light1" vs. "light2" on a set of irradiance values:
328	greg	1.1	.IP "" .2i
329			rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
330			.PP
331			To generate a pair of images corresponding to these two lights'
332			contributions:
333			.IP "" .2i
334			vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
335			rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
336			@render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
337			.PP
338			These images may then be recombined using the desired outputs
339			of light1 and light2:
340			.IP "" .2i
341			pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
342			.PP
343	greg	1.20	To compute an array of irradiance contributions according to a Tregenza sky:
344	greg	1.1	.IP "" .2i
345	greg	1.7	rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
346			\-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
347	greg	1.12	.PP
348			To perform an annual simulation of 365 daily sun positions in photon mapping
349			mode:
350			.IP "" .2i
351			rcontrib \-I+ \-h \-V \-fo \-o c_%s.dat \-M lights \-ap contrib.pm 365
352			scene.oct < test.dat,
353	greg	1.1	.SH ENVIRONMENT
354			RAYPATH path to search for \-f and \-M files
355	greg	1.16	.SH BUGS
356			We do not currently compute contributions or coefficients properly
357			in scenes with participating media.
358			A single warning will be issued if a scattering or absorbing medium
359			is detected.
360	greg	1.1	.SH AUTHOR
361			Greg Ward
362			.SH "SEE ALSO"
363	greg	1.12	cnt(1), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(1),
364			ra_rgbe(1), rcalc(1), rfluxmtx(1), rmtxop(1), rpict(1), rsensor(1),
365			rtrace(1), total(1), vwrays(1), ximage(1)
366