man/man1/rcontrib.1

.\" RCSid "$Id: rcontrib.1,v 1.6 2012/11/15 19:41:03 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 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
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.
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.
Set the this value to zero 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 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.
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+ \-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
.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:	1.7
Committed:	Fri Nov 1 15:32:58 2013 UTC (11 years, 6 months ago) by greg
Branch:	MAIN
Changes since 1.6:	+3 -3 lines
Log Message:	Corrected errors in final example mentioned by Lars Grobe
#	User	Rev	Content
1	greg	1.7	.\" RCSid "$Id: rcontrib.1,v 1.6 2012/11/15 19:41:03 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			.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	greg	1.3	.I Rcontrib
46	greg	1.1	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	greg	1.6	The default value is one, meaning a full record will be produced for
105	greg	1.1	each input ray.
106	greg	1.6	For values greater than one, contributions will be averaged together
107	greg	1.1	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	greg	1.6	Note that output flushing via zero-direction rays is disabled with
117			.I \-c
118			set to zero.
119	greg	1.1	.PP
120			The output of
121			.I rcontrib
122			has many potential uses.
123			Source contributions can be used as components in linear combination to
124			reproduce any desired variation, e.g., simulating lighting controls or
125			changing sky conditions via daylight coefficients.
126			More generally,
127			.I rcontrib
128			can be used to compute arbitrary input-output relationships in optical
129			systems, such as luminaires, light pipes, and shading devices.
130			.PP
131	greg	1.3	.I Rcontrib
132	greg	1.4	sends the accumulated rays tallies
133			to one or more destinations according to the given
134	greg	1.1	.I \-o
135			specification.
136			If a destination begins with an exclamation mark ('!'), then
137			a pipe is opened to a command and data is sent to its standard input.
138			Otherwise, the destination is treated as a file.
139			An existing file of the same name will not be clobbered, unless the
140			.I \-fo
141			option is given.
142			If instead the
143			.I \-r
144			option is specified, data recovery is attempted on existing files.
145			(If
146			.I "\-c 0"
147			is used together with the
148			.I \-r
149			option, existing files are read in and new ray evaluations are added
150			to the previous results, providing a convenient means for
151			progressive simulation.)\0
152			If an output specification contains a "%s" format, this will be
153			replaced by the modifier name.
154			The
155			.I \-b
156			option may be used to further define
157			a "bin number" within each object if finer resolution is needed, and
158			this will be applied to a "%d" format in the output file
159			specification if present.
160			The actual bin number is computed at run time based on ray direction
161			and surface intersection, as described below.
162	greg	1.5	The number of bins must be specified in advance with the
163	greg	1.1	.I \-bn
164			option, and this is critical for output files containing multiple values
165			per record.
166			A variable or constant name may be given for this parameter if
167			it has been defined via a previous
168			.I \-f
169			or
170			.I \-e
171			option.
172	greg	1.6	Since bin numbers start from zero, the bin count is always equal to
173			the last bin plus one.
174			Set the this value to zero if the bin count is unknown (the default).
175	greg	1.1	The most recent
176			.I \-b,
177			.I \-bn
178			and
179			.I \-o
180			options to the left of each
181			.I \-m
182			setting are the ones used for that modifier.
183			The ordering of other options is unimportant, except for
184			.I \-x
185			and
186			.I \-y
187			if the
188			.I \-c
189	greg	1.6	is zero, when they control the resolution string
190	greg	1.1	produced in the corresponding output.
191			.PP
192			If a
193			.I \-b
194			expression is defined for a particular modifier,
195			the bin number will be evaluated at run time for each
196	greg	1.4	ray contribution.
197	greg	1.1	Specifically, each ray's world intersection point will be assigned to
198			the variables Px, Py, and Pz, and the normalized ray direction
199			will be assigned to Dx, Dy, and Dz.
200			These parameters may be combined with definitions given in
201			.I \-e
202			arguments and files read using the
203			.I \-f
204			option.
205			The computed bin value will be
206			rounded to the nearest whole number.
207			This mechanism allows the user to define precise regions or directions
208			they wish to accumulate, such as the Tregenza sky discretization,
209			which would be otherwise impossible to specify
210			as a set of RADIANCE primitives.
211			The rules and predefined functions available for these expressions are
212			described in the
213			.I rcalc(1)
214			man page.
215			Unlike
216			.I rcalc,
217			.I rcontrib
218			will search the RADIANCE library directories for each file given in a
219			.I \-f
220			option.
221			.PP
222			If no
223			.I \-o
224			specification is given, results are written on the standard output in order
225			of modifier (as given on the command line) then bin number.
226			Concatenated data is also sent to a single destination (i.e., an initial
227			.I \-o
228			specification without formatting strings).
229			If a "%s" format appears but no "%d" in the
230			.I \-o
231			specification, then each modifier will have its own output file, with
232			multiple values per record in the case of a non-zero
233			.I \-b
234			definition.
235			If a "%d" format appears but no "%s", then each bin will get its own
236			output file, with modifiers output in order in each record.
237			For text output, each RGB coefficient triple is separated by a tab,
238			with a newline at the end of each ray record.
239			For binary output formats, there is no such delimiter to mark
240			the end of each record.
241			.PP
242			Input and output format defaults to plain text, where each ray's
243			origin and direction (6 real values) are given on input,
244			and one line is produced per output file per ray.
245			Alternative data representations may be specified by the
246			.I \-f[io]
247			option, which is described in the
248			.I rtrace
249			man page along with the associated
250			.I \-x
251			and
252			.I \-y
253			resolution settings.
254			In particular, the color ('c') output data representation
255			together with positive dimensions for
256			.I \-x
257			and
258			.I \-y
259			will produce an uncompressed RADIANCE picture,
260			suitable for manipulation with
261			.I pcomb(1)
262			and related tools.
263			.PP
264			Options may be given on the command line and/or read from the
265			environment and/or read from a file.
266			A command argument beginning with a dollar sign ('$') is immediately
267			replaced by the contents of the given environment variable.
268			A command argument beginning with an at sign ('@') is immediately
269			replaced by the contents of the given file.
270			.SH EXAMPLES
271			To compute the proportional contributions from sources modified
272			by "light1" vs. "light2" on a set of illuminance values:
273			.IP "" .2i
274			rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
275			.PP
276			To generate a pair of images corresponding to these two lights'
277			contributions:
278			.IP "" .2i
279			vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
280			rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
281			@render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
282			.PP
283			These images may then be recombined using the desired outputs
284			of light1 and light2:
285			.IP "" .2i
286			pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
287			.PP
288			To compute an array of illuminance contributions according to a Tregenza sky:
289			.IP "" .2i
290	greg	1.7	rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
291			\-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
292	greg	1.1	.SH ENVIRONMENT
293			RAYPATH path to search for \-f and \-M files
294			.SH AUTHOR
295			Greg Ward
296			.SH "SEE ALSO"
297			cnt(1), genklemsamp(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
298			rcalc(1), rpict(1), rsensor(1), rtrace(1), total(1), vwrays(1), ximage(1)