man/man1/rtcontrib.1

.\" RCSid "$Id: rtcontrib.1,v 1.16 2007/09/04 17:36:41 greg Exp $"
.TH RTCONTRIB 1 5/25/05 RADIANCE
.SH NAME
rtcontrib - compute contribution coefficients in a RADIANCE scene
.SH SYNOPSIS
.B rtcontrib
[
.B "\-n nprocs"
][
.B \-V
][
.B \-c
][
.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 "rtcontrib [ options ] \-defaults"
.SH DESCRIPTION
.I Rtcontrib
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
By setting the boolean
.I \-V
option, you may instruct
.I rtcontrib
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 rtcontrib 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 output of
.I rtcontrib
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 rtcontrib
can be used to compute arbitrary input-output relationships in optical
systems, such as luminaires, light pipes, and shading devices.
.PP
Setting the
.I \-c
option instructs
.I rtcontrib
to accumulate values rather than reporting one record per ray.
With this option, only a single record will be produced at the very
end, corresponding to the sum of all rays given on the input.
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.
Care must be taken to perform normalization based on the
radiation density and the number of rays sampled.
.PP
.I Rtcontrib
calls
.I rtrace(1)
with the \-oTW (or \-oTV) option to calculate the daughter ray
contributions for each input ray, and the output tallies
are sent 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
is used together with the
.I \-r
option, existing files are read in and new ray evaluations are added
to the previous results, providing a convenient means for
progressive simulation.)\0
If an output specification contains a "%s" format, this will be
replaced by the modifier name.
The
.I \-b
option may be used to further define
a "bin number" within each object if finer resolution is needed, and
this will be applied to a "%d" format in the output file
specification if present.
The actual bin number is computed at run time based on ray direction
and surface intersection, as described below.
If the number of bins is known in advance, it should be specified with the
.I \-bn
option, and this is critical for output files containing multiple values
per record.
Since bin numbers start from 0, the bin count is always equal to
the last bin plus 1.
Set the this value to 0 if the bin count is unknown (the default).
The most recent
.I \-b,
.I \-bn
and
.I \-o
options to the left of each
.I \-m
setting affect only that modifier.
The ordering of other options is unimportant, except for
.I \-x
and
.I \-y
if the
.I \-c
is present, 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 from
.I rtrace.
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 rtcontrib
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
If the
.I \-n
option is specified with a value greater than 1, multiple
.I rtrace
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 rtcontrib
process itself may use a considerable amount of CPU time.
.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
rtcontrib \-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 |
rtcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
@render.opt \-o c_%s.pic \-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.pic \-c 50 55 57 c_light2.pic > combined.pic
.PP
To compute an array of illuminance contributions according to a Tregenza sky:
.IP "" .2i
rtcontrib \-I+ \-b tbin \-o sky.dat \-m skyglow \-b 0 \-o ground.dat \-m groundglow
@render.opt \-f tregenza.cal scene.oct < test.dat
.SH ENVIRONMENT
RAYPATH         path to search for \-f and \-M files
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
cnt(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1)
Revision:	1.17
Committed:	Sat Nov 17 01:13:50 2007 UTC (16 years, 6 months ago) by greg
Branch:	MAIN
Changes since 1.16:	+34 -3 lines
Log Message:	Added -c option to rtcontrib (barely tested, and -r does not work)
#	User	Rev	Content
1	greg	1.17	.\" RCSid "$Id: rtcontrib.1,v 1.16 2007/09/04 17:36:41 greg Exp $"
2	greg	1.3	.TH RTCONTRIB 1 5/25/05 RADIANCE
3	greg	1.1	.SH NAME
4	greg	1.5	rtcontrib - compute contribution coefficients in a RADIANCE scene
5	greg	1.1	.SH SYNOPSIS
6			.B rtcontrib
7			[
8			.B "\-n nprocs"
9			][
10	greg	1.15	.B \-V
11			][
12	greg	1.17	.B \-c
13			][
14	greg	1.14	.B \-fo
15			\|
16	greg	1.8	.B \-r
17			][
18	greg	1.1	.B "\-e expr"
19			][
20			.B "\-f source"
21			][
22	greg	1.7	.B "\-o ospec"
23	greg	1.1	][
24			.B "\-b binv"
25	greg	1.12	][
26			.B "\-bn nbins"
27	greg	1.1	]
28	greg	1.9	{
29			.B "\-m mod \| \-M file"
30			}
31			..
32	greg	1.1	[
33			.B $EVAR
34			]
35			[
36			.B @file
37			]
38			[
39			rtrace options
40			]
41			.B octree
42	greg	1.4	.br
43			.B "rtcontrib [ options ] \-defaults"
44	greg	1.1	.SH DESCRIPTION
45			.I Rtcontrib
46	greg	1.15	computes ray coefficients
47	greg	1.1	for objects whose modifiers are named in one or more
48			.I \-m
49			settings.
50	greg	1.2	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	greg	1.9	A modifier list may also be read from a file using the
54			.I \-M
55			option.
56	greg	1.10	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	greg	1.9	.PP
61	greg	1.15	By setting the boolean
62			.I \-V
63			option, you may instruct
64			.I rtcontrib
65			to report the contribution from each material rather than the ray
66			coefficient.
67			This is particularly useful for light sources with directional output
68			distributions, whose value would otherwise be lost in the shuffle.
69			With the default
70			.I -V-
71			setting, the output of rtcontrib is a coefficient that must be multiplied
72			by the radiance of each material to arrive at a final contribution.
73			This is more convenient for computing daylight coefficeints, or cases
74			where the actual radiance is not desired.
75			Use the
76			.I -V+
77			setting when you wish to simply sum together contributions
78			(with possible adjustment factors) to obtain a final radiance value.
79			Combined with the
80			.I \-i
81			or
82			.I \-I
83			option, irradiance contributions are reported by
84			.I \-V+
85			rather than radiance, and
86			.I \-V-
87			coefficients contain an additonal factor of PI.
88			.PP
89	greg	1.3	The output of
90			.I rtcontrib
91			has many potential uses.
92			Source contributions can be used as components in linear combination to
93	greg	1.1	reproduce any desired variation, e.g., simulating lighting controls or
94			changing sky conditions via daylight coefficients.
95			More generally,
96			.I rtcontrib
97	greg	1.3	can be used to compute arbitrary input-output relationships in optical
98			systems, such as luminaires, light pipes, and shading devices.
99	greg	1.1	.PP
100	greg	1.17	Setting the
101			.I \-c
102			option instructs
103			.I rtcontrib
104			to accumulate values rather than reporting one record per ray.
105			With this option, only a single record will be produced at the very
106			end, corresponding to the sum of all rays given on the input.
107			This is equivalent to passing all the output records through a program like
108			.I total(1)
109			to sum RGB values together, but is much more efficient.
110			Using this option, it is possible to reverse sampling, sending rays from
111			a parallel source such as the sun to a diffuse surface, for example.
112			Care must be taken to perform normalization based on the
113			radiation density and the number of rays sampled.
114			.PP
115	greg	1.2	.I Rtcontrib
116			calls
117			.I rtrace(1)
118	greg	1.16	with the \-oTW (or \-oTV) option to calculate the daughter ray
119	greg	1.5	contributions for each input ray, and the output tallies
120	greg	1.7	are sent to one or more destinations according to the given
121	greg	1.1	.I \-o
122			specification.
123	greg	1.7	If a destination begins with an exclamation mark ('!'), then
124			a pipe is opened to a command and data is sent to its standard input.
125			Otherwise, the destination is treated as a file.
126	greg	1.14	An existing file of the same name will not be clobbered, unless the
127			.I \-fo
128			option is given.
129			If instead the
130	greg	1.8	.I \-r
131	greg	1.14	option is specified, data recovery is attempted on existing files.
132	greg	1.17	(If
133			.I \-c
134			is used together with the
135			.I \-r
136			option, existing files are read in and new ray evaluations are added
137			to the previous results, providing a convenient means for
138			progressive simulation.)\0
139	greg	1.2	If an output specification contains a "%s" format, this will be
140	greg	1.1	replaced by the modifier name.
141			The
142			.I \-b
143			option may be used to further define
144	greg	1.2	a "bin number" within each object if finer resolution is needed, and
145			this will be applied to a "%d" format in the output file
146	greg	1.1	specification if present.
147	greg	1.3	The actual bin number is computed at run time based on ray direction
148			and surface intersection, as described below.
149	greg	1.12	If the number of bins is known in advance, it should be specified with the
150			.I \-bn
151	greg	1.13	option, and this is critical for output files containing multiple values
152			per record.
153			Since bin numbers start from 0, the bin count is always equal to
154			the last bin plus 1.
155			Set the this value to 0 if the bin count is unknown (the default).
156	greg	1.1	The most recent
157	greg	1.12	.I \-b,
158			.I \-bn
159	greg	1.1	and
160			.I \-o
161	greg	1.2	options to the left of each
162	greg	1.1	.I \-m
163	greg	1.2	setting affect only that modifier.
164	greg	1.17	The ordering of other options is unimportant, except for
165			.I \-x
166			and
167			.I \-y
168			if the
169			.I \-c
170			is present, when they control the resolution string
171			produced in the corresponding output.
172	greg	1.1	.PP
173	greg	1.2	If a
174			.I \-b
175			expression is defined for a particular modifier,
176			the bin number will be evaluated at run time for each
177			ray contribution from
178			.I rtrace.
179			Specifically, each ray's world intersection point will be assigned to
180			the variables Px, Py, and Pz, and the normalized ray direction
181			will be assigned to Dx, Dy, and Dz.
182			These parameters may be combined with definitions given in
183			.I \-e
184	greg	1.3	arguments and files read using the
185	greg	1.2	.I \-f
186	greg	1.3	option.
187			The computed bin value will be
188	greg	1.2	rounded to the nearest whole number.
189			This mechanism allows the user to define precise regions or directions
190			they wish to accumulate, such as the Tregenza sky discretization,
191			which would be otherwise impossible to specify
192			as a set of RADIANCE primitives.
193	greg	1.3	The rules and predefined functions available for these expressions are
194			described in the
195			.I rcalc(1)
196			man page.
197	greg	1.6	Unlike
198			.I rcalc,
199			.I rtcontrib
200			will search the RADIANCE library directories for each file given in a
201			.I \-f
202			option.
203	greg	1.1	.PP
204			If no
205			.I \-o
206			specification is given, results are written on the standard output in order
207			of modifier (as given on the command line) then bin number.
208	greg	1.7	Concatenated data is also sent to a single destination (i.e., an initial
209	greg	1.2	.I \-o
210			specification without formatting strings).
211	greg	1.1	If a "%s" format appears but no "%d" in the
212			.I \-o
213			specification, then each modifier will have its own output file, with
214			multiple values per record in the case of a non-zero
215			.I \-b
216			definition.
217			If a "%d" format appears but no "%s", then each bin will get its own
218			output file, with modifiers output in order in each record.
219			For text output, each RGB coefficient triple is separated by a tab,
220			with a newline at the end of each ray record.
221			For binary output formats, there is no such delimiter to mark
222			the end of each record.
223			.PP
224	greg	1.2	Input and output format defaults to plain text, where each ray's
225			origin and direction (6 real values) are given on input,
226			and one line is produced per output file per ray.
227			Alternative data representations may be specified by the
228			.I \-f[io]
229			option, which is described in the
230			.I rtrace
231			man page along with the associated
232			.I \-x
233			and
234			.I \-y
235			resolution settings.
236			In particular, the color ('c') output data representation
237			together with positive dimensions for
238			.I \-x
239			and
240			.I \-y
241			will produce an uncompressed RADIANCE picture,
242			suitable for manipulation with
243			.I pcomb(1)
244			and related tools.
245	greg	1.1	.PP
246			If the
247			.I \-n
248			option is specified with a value greater than 1, multiple
249	greg	1.2	.I rtrace
250	greg	1.1	processes will be used to accelerate computation on a shared
251			memory machine.
252			Note that there is no benefit to using more processes
253	greg	1.2	than there are local CPUs available to do the work, and the
254			.I rtcontrib
255			process itself may use a considerable amount of CPU time.
256	greg	1.1	.PP
257			Options may be given on the command line and/or read from the
258			environment and/or read from a file.
259			A command argument beginning with a dollar sign ('$') is immediately
260			replaced by the contents of the given environment variable.
261			A command argument beginning with an at sign ('@') is immediately
262			replaced by the contents of the given file.
263	greg	1.2	.SH EXAMPLES
264			To compute the proportional contributions from sources modified
265			by "light1" vs. "light2" on a set of illuminance values:
266	greg	1.1	.IP "" .2i
267	greg	1.16	rtcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
268	greg	1.2	.PP
269			To generate a pair of images corresponding to these two lights'
270			contributions:
271	greg	1.1	.IP "" .2i
272	greg	1.16	vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
273			rtcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
274			@render.opt \-o c_%s.pic \-m light1 \-m light2 scene.oct
275	greg	1.2	.PP
276			These images may then be recombined using the desired outputs
277			of light1 and light2:
278	greg	1.1	.IP "" .2i
279	greg	1.16	pcomb \-c 100 90 75 c_light1.pic \-c 50 55 57 c_light2.pic > combined.pic
280	greg	1.1	.PP
281	greg	1.2	To compute an array of illuminance contributions according to a Tregenza sky:
282			.IP "" .2i
283	greg	1.16	rtcontrib \-I+ \-b tbin \-o sky.dat \-m skyglow \-b 0 \-o ground.dat \-m groundglow
284			@render.opt \-f tregenza.cal scene.oct < test.dat
285	greg	1.6	.SH ENVIRONMENT
286	greg	1.16	RAYPATH path to search for \-f and \-M files
287	greg	1.1	.SH AUTHOR
288			Greg Ward
289			.SH "SEE ALSO"
290			cnt(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
291	greg	1.17	rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1)