man/man1/rcontrib.1

.\" RCSid "$Id: rcontrib.1,v 1.18 2020/09/09 21:28:19 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 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
.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:	1.19
Committed:	Thu Sep 10 17:52:46 2020 UTC (4 years, 8 months ago) by greg
Branch:	MAIN
Changes since 1.18:	+16 -1 lines
Log Message:	doc(rcontrib): Clarified -x and -y settings and interactions with -c, -t
#	Content
1	.\" RCSid "$Id: rcontrib.1,v 1.18 2020/09/09 21:28:19 greg Exp $"
2	.TH RCONTRIB 1 5/25/05 RADIANCE
3	.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 "\-t secs"
13	][
14	.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	.B "\-p p1=V1,p2=V2"
27	][
28	.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	.I Rcontrib
50	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	The default value is one, meaning a full record will be produced for
109	each input ray.
110	For values greater than one, contributions will be averaged together
111	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	Note that output flushing via zero-direction rays is disabled with
121	.I \-c
122	set to zero.
123	.PP
124	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	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	This requires that the number of input samples is known, meaning a
141	.I \-y
142	parameter has been specified.
143	.PP
144	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	.I Rcontrib
156	sends the accumulated rays tallies
157	to one or more destinations according to the given
158	.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	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	The actual bin number is computed at run time based on ray direction
188	and surface intersection, as described below.
189	The number of bins must be specified in advance with the
190	.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	Since bin numbers start from zero, the bin count is always equal to
200	the last bin plus one.
201	The most recent
202	.I \-p,
203	.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	is zero, when they control the resolution string
217	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	ray contribution.
224	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	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	by commas, colons, or semicolons.
237	The computed bin value will be
238	rounded to the nearest whole number.
239	(Negative bin values will be silently ignored.)\0
240	For a single bin, you may specify
241	.I "\-b 0",
242	which is the default.
243	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	Like
252	.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	.PP
307	.I Rcontrib
308	supports light source contributions from photon maps generated by
309	.I mkpmap(1)
310	with its
311	.I -apC
312	option. Enabling photon mapping is described in the
313	.I rtrace
314	man page along with its relevant settings. In photon mapping mode,
315	.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	is clamped accordingly and a warning is issued.
325	.SH EXAMPLES
326	To compute the proportional contributions from sources modified
327	by "light1" vs. "light2" on a set of illuminance values:
328	.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	To compute an array of illuminance contributions according to a Tregenza sky:
344	.IP "" .2i
345	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	.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	.SH ENVIRONMENT
354	RAYPATH path to search for \-f and \-M files
355	.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	.SH AUTHOR
361	Greg Ward
362	.SH "SEE ALSO"
363	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