man/man1/rtcontrib.1

.\" RCSid "$Id: rtcontrib.1,v 1.17 2007/11/17 01:13:50 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 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 "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
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
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
.I \-c
option tells
.I rtcontrib
how many rays to accumulate for each record.
The default value is 1, meaning a full record will be produced for
each input ray.
For values greater than 1, 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
for accumulated evaluations.
.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
.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 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.
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
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:	1.18
Committed:	Fri Apr 18 18:06:29 2008 UTC (16 years, 1 month ago) by greg
Branch:	MAIN
CVS Tags:	rad3R9
Changes since 1.17:	+34 -29 lines
Log Message:	Modified rtcontrib -c option to accumulate a specified number of rays
#	User	Rev	Content
1	greg	1.18	.\" RCSid "$Id: rtcontrib.1,v 1.17 2007/11/17 01:13:50 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	1.18	.B "\-c count"
13	greg	1.17	][
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	1.18	If the
62			.I \-n
63			option is specified with a value greater than 1, multiple
64			.I rtrace
65			processes will be used to accelerate computation on a shared
66			memory machine.
67			Note that there is no benefit to using more processes
68			than there are local CPUs available to do the work, and the
69			.I rtcontrib
70			process itself may use a considerable amount of CPU time.
71			.PP
72	greg	1.15	By setting the boolean
73			.I \-V
74			option, you may instruct
75			.I rtcontrib
76			to report the contribution from each material rather than the ray
77			coefficient.
78			This is particularly useful for light sources with directional output
79			distributions, whose value would otherwise be lost in the shuffle.
80			With the default
81			.I -V-
82			setting, the output of rtcontrib is a coefficient that must be multiplied
83			by the radiance of each material to arrive at a final contribution.
84			This is more convenient for computing daylight coefficeints, or cases
85			where the actual radiance is not desired.
86			Use the
87			.I -V+
88			setting when you wish to simply sum together contributions
89			(with possible adjustment factors) to obtain a final radiance value.
90			Combined with the
91			.I \-i
92			or
93			.I \-I
94			option, irradiance contributions are reported by
95			.I \-V+
96			rather than radiance, and
97			.I \-V-
98			coefficients contain an additonal factor of PI.
99			.PP
100	greg	1.18	The
101			.I \-c
102			option tells
103			.I rtcontrib
104			how many rays to accumulate for each record.
105			The default value is 1, meaning a full record will be produced for
106			each input ray.
107			For values greater than 1, contributions will be averaged together
108			over the given number of input rays.
109			If set to zero, only a single record will be produced at the very
110			end, corresponding to the sum of all rays given on the input
111			(rather than the average).
112			This is equivalent to passing all the output records through a program like
113			.I total(1)
114			to sum RGB values together, but is much more efficient.
115			Using this option, it is possible to reverse sampling, sending rays from
116			a parallel source such as the sun to a diffuse surface, for example.
117			Note that output flushing via zero-direction rays is disabled
118			for accumulated evaluations.
119			.PP
120	greg	1.3	The output of
121			.I rtcontrib
122			has many potential uses.
123			Source contributions can be used as components in linear combination to
124	greg	1.1	reproduce any desired variation, e.g., simulating lighting controls or
125			changing sky conditions via daylight coefficients.
126			More generally,
127			.I rtcontrib
128	greg	1.3	can be used to compute arbitrary input-output relationships in optical
129			systems, such as luminaires, light pipes, and shading devices.
130	greg	1.1	.PP
131	greg	1.2	.I Rtcontrib
132			calls
133			.I rtrace(1)
134	greg	1.16	with the \-oTW (or \-oTV) option to calculate the daughter ray
135	greg	1.5	contributions for each input ray, and the output tallies
136	greg	1.7	are sent to one or more destinations according to the given
137	greg	1.1	.I \-o
138			specification.
139	greg	1.7	If a destination begins with an exclamation mark ('!'), then
140			a pipe is opened to a command and data is sent to its standard input.
141			Otherwise, the destination is treated as a file.
142	greg	1.14	An existing file of the same name will not be clobbered, unless the
143			.I \-fo
144			option is given.
145			If instead the
146	greg	1.8	.I \-r
147	greg	1.14	option is specified, data recovery is attempted on existing files.
148	greg	1.17	(If
149	greg	1.18	.I "\-c 0"
150	greg	1.17	is used together with the
151			.I \-r
152			option, existing files are read in and new ray evaluations are added
153			to the previous results, providing a convenient means for
154			progressive simulation.)\0
155	greg	1.2	If an output specification contains a "%s" format, this will be
156	greg	1.1	replaced by the modifier name.
157			The
158			.I \-b
159			option may be used to further define
160	greg	1.2	a "bin number" within each object if finer resolution is needed, and
161			this will be applied to a "%d" format in the output file
162	greg	1.1	specification if present.
163	greg	1.3	The actual bin number is computed at run time based on ray direction
164			and surface intersection, as described below.
165	greg	1.12	If the number of bins is known in advance, it should be specified with the
166			.I \-bn
167	greg	1.13	option, and this is critical for output files containing multiple values
168			per record.
169			Since bin numbers start from 0, the bin count is always equal to
170			the last bin plus 1.
171			Set the this value to 0 if the bin count is unknown (the default).
172	greg	1.1	The most recent
173	greg	1.12	.I \-b,
174			.I \-bn
175	greg	1.1	and
176			.I \-o
177	greg	1.2	options to the left of each
178	greg	1.1	.I \-m
179	greg	1.2	setting affect only that modifier.
180	greg	1.17	The ordering of other options is unimportant, except for
181			.I \-x
182			and
183			.I \-y
184			if the
185			.I \-c
186			is present, when they control the resolution string
187			produced in the corresponding output.
188	greg	1.1	.PP
189	greg	1.2	If a
190			.I \-b
191			expression is defined for a particular modifier,
192			the bin number will be evaluated at run time for each
193			ray contribution from
194			.I rtrace.
195			Specifically, each ray's world intersection point will be assigned to
196			the variables Px, Py, and Pz, and the normalized ray direction
197			will be assigned to Dx, Dy, and Dz.
198			These parameters may be combined with definitions given in
199			.I \-e
200	greg	1.3	arguments and files read using the
201	greg	1.2	.I \-f
202	greg	1.3	option.
203			The computed bin value will be
204	greg	1.2	rounded to the nearest whole number.
205			This mechanism allows the user to define precise regions or directions
206			they wish to accumulate, such as the Tregenza sky discretization,
207			which would be otherwise impossible to specify
208			as a set of RADIANCE primitives.
209	greg	1.3	The rules and predefined functions available for these expressions are
210			described in the
211			.I rcalc(1)
212			man page.
213	greg	1.6	Unlike
214			.I rcalc,
215			.I rtcontrib
216			will search the RADIANCE library directories for each file given in a
217			.I \-f
218			option.
219	greg	1.1	.PP
220			If no
221			.I \-o
222			specification is given, results are written on the standard output in order
223			of modifier (as given on the command line) then bin number.
224	greg	1.7	Concatenated data is also sent to a single destination (i.e., an initial
225	greg	1.2	.I \-o
226			specification without formatting strings).
227	greg	1.1	If a "%s" format appears but no "%d" in the
228			.I \-o
229			specification, then each modifier will have its own output file, with
230			multiple values per record in the case of a non-zero
231			.I \-b
232			definition.
233			If a "%d" format appears but no "%s", then each bin will get its own
234			output file, with modifiers output in order in each record.
235			For text output, each RGB coefficient triple is separated by a tab,
236			with a newline at the end of each ray record.
237			For binary output formats, there is no such delimiter to mark
238			the end of each record.
239			.PP
240	greg	1.2	Input and output format defaults to plain text, where each ray's
241			origin and direction (6 real values) are given on input,
242			and one line is produced per output file per ray.
243			Alternative data representations may be specified by the
244			.I \-f[io]
245			option, which is described in the
246			.I rtrace
247			man page along with the associated
248			.I \-x
249			and
250			.I \-y
251			resolution settings.
252			In particular, the color ('c') output data representation
253			together with positive dimensions for
254			.I \-x
255			and
256			.I \-y
257			will produce an uncompressed RADIANCE picture,
258			suitable for manipulation with
259			.I pcomb(1)
260			and related tools.
261	greg	1.1	.PP
262			Options may be given on the command line and/or read from the
263			environment and/or read from a file.
264			A command argument beginning with a dollar sign ('$') is immediately
265			replaced by the contents of the given environment variable.
266			A command argument beginning with an at sign ('@') is immediately
267			replaced by the contents of the given file.
268	greg	1.2	.SH EXAMPLES
269			To compute the proportional contributions from sources modified
270			by "light1" vs. "light2" on a set of illuminance values:
271	greg	1.1	.IP "" .2i
272	greg	1.16	rtcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
273	greg	1.2	.PP
274			To generate a pair of images corresponding to these two lights'
275			contributions:
276	greg	1.1	.IP "" .2i
277	greg	1.16	vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
278			rtcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
279			@render.opt \-o c_%s.pic \-m light1 \-m light2 scene.oct
280	greg	1.2	.PP
281			These images may then be recombined using the desired outputs
282			of light1 and light2:
283	greg	1.1	.IP "" .2i
284	greg	1.16	pcomb \-c 100 90 75 c_light1.pic \-c 50 55 57 c_light2.pic > combined.pic
285	greg	1.1	.PP
286	greg	1.2	To compute an array of illuminance contributions according to a Tregenza sky:
287			.IP "" .2i
288	greg	1.16	rtcontrib \-I+ \-b tbin \-o sky.dat \-m skyglow \-b 0 \-o ground.dat \-m groundglow
289			@render.opt \-f tregenza.cal scene.oct < test.dat
290	greg	1.6	.SH ENVIRONMENT
291	greg	1.16	RAYPATH path to search for \-f and \-M files
292	greg	1.1	.SH AUTHOR
293			Greg Ward
294			.SH "SEE ALSO"
295			cnt(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
296	greg	1.17	rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1)