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 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
#	Content
1	.\" RCSid "$Id: rtcontrib.1,v 1.17 2007/11/17 01:13:50 greg Exp $"
2	.TH RTCONTRIB 1 5/25/05 RADIANCE
3	.SH NAME
4	rtcontrib - compute contribution coefficients in a RADIANCE scene
5	.SH SYNOPSIS
6	.B rtcontrib
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 "rtcontrib [ options ] \-defaults"
44	.SH DESCRIPTION
45	.I Rtcontrib
46	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	.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	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	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	The output of
121	.I rtcontrib
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 rtcontrib
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	.I Rtcontrib
132	calls
133	.I rtrace(1)
134	with the \-oTW (or \-oTV) option to calculate the daughter ray
135	contributions for each input ray, and the output tallies
136	are sent to one or more destinations according to the given
137	.I \-o
138	specification.
139	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	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	.I \-r
147	option is specified, data recovery is attempted on existing files.
148	(If
149	.I "\-c 0"
150	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	If an output specification contains a "%s" format, this will be
156	replaced by the modifier name.
157	The
158	.I \-b
159	option may be used to further define
160	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	specification if present.
163	The actual bin number is computed at run time based on ray direction
164	and surface intersection, as described below.
165	If the number of bins is known in advance, it should be specified with the
166	.I \-bn
167	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	The most recent
173	.I \-b,
174	.I \-bn
175	and
176	.I \-o
177	options to the left of each
178	.I \-m
179	setting affect only that modifier.
180	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	.PP
189	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	arguments and files read using the
201	.I \-f
202	option.
203	The computed bin value will be
204	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	The rules and predefined functions available for these expressions are
210	described in the
211	.I rcalc(1)
212	man page.
213	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	.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	Concatenated data is also sent to a single destination (i.e., an initial
225	.I \-o
226	specification without formatting strings).
227	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	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	.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	.SH EXAMPLES
269	To compute the proportional contributions from sources modified
270	by "light1" vs. "light2" on a set of illuminance values:
271	.IP "" .2i
272	rtcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
273	.PP
274	To generate a pair of images corresponding to these two lights'
275	contributions:
276	.IP "" .2i
277	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	.PP
281	These images may then be recombined using the desired outputs
282	of light1 and light2:
283	.IP "" .2i
284	pcomb \-c 100 90 75 c_light1.pic \-c 50 55 57 c_light2.pic > combined.pic
285	.PP
286	To compute an array of illuminance contributions according to a Tregenza sky:
287	.IP "" .2i
288	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	.SH ENVIRONMENT
291	RAYPATH path to search for \-f and \-M files
292	.SH AUTHOR
293	Greg Ward
294	.SH "SEE ALSO"
295	cnt(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
296	rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1)