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Revision: 1.23
Committed: Tue Dec 12 16:31:45 2023 UTC (17 months, 3 weeks ago) by greg
Branch: MAIN
Changes since 1.22: +2 -2 lines
Log Message:
chore(rcomb): Renamed rmtxcomb to simpler "rcomb"

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# Content
1 .\" RCSid "$Id: rcontrib.1,v 1.22 2023/12/06 01:27:00 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 .br
49 .B "rcontrib \-features [feat1 ..]"
50 .SH DESCRIPTION
51 .I Rcontrib
52 computes ray coefficients
53 for objects whose modifiers are named in one or more
54 .I \-m
55 settings.
56 These modifiers are usually materials associated with
57 light sources or sky domes, and must directly modify some geometric
58 primitives to be considered in the output.
59 A modifier list may also be read from a file using the
60 .I \-M
61 option.
62 The RAYPATH environment variable determines directories to search for
63 this file.
64 (No search takes place if a file name begins with a '.', '/' or '~'
65 character.)\0
66 .PP
67 If the
68 .I \-n
69 option is specified with a value greater than 1, multiple
70 processes will be used to accelerate computation on a shared
71 memory machine.
72 Note that there is no benefit to using more processes
73 than there are local CPUs available to do the work, and the
74 .I rcontrib
75 process itself may use a considerable amount of CPU time.
76 .PP
77 By setting the boolean
78 .I \-V
79 option, you may instruct
80 .I rcontrib
81 to report the contribution from each material rather than the ray
82 coefficient.
83 This is particularly useful for light sources with directional output
84 distributions, whose value would otherwise be lost in the shuffle.
85 With the default
86 .I -V-
87 setting, the output of rcontrib is a coefficient that must be multiplied
88 by the radiance of each material to arrive at a final contribution.
89 This is more convenient for computing daylight coefficeints, or cases
90 where the actual radiance is not desired.
91 Use the
92 .I -V+
93 setting when you wish to simply sum together contributions
94 (with possible adjustment factors) to obtain a final radiance value.
95 Combined with the
96 .I \-i
97 or
98 .I \-I
99 option, irradiance contributions are reported by
100 .I \-V+
101 rather than radiance, and
102 .I \-V-
103 coefficients contain an additonal factor of PI.
104 .PP
105 The
106 .I \-c
107 option tells
108 .I rcontrib
109 how many rays to accumulate for each record.
110 The default value is one, meaning a full record will be produced for
111 each input ray.
112 For values greater than one, contributions will be averaged together
113 over the given number of input rays.
114 If set to zero, only a single record will be produced at the very
115 end, corresponding to the sum of all rays given on the input
116 (rather than the average).
117 This is equivalent to passing all the output records through a program like
118 .I total(1)
119 to sum RGB values together, but is much more efficient.
120 Using this option, it is possible to reverse sampling, sending rays from
121 a parallel source such as the sun to a diffuse surface, for example.
122 Note that output flushing via zero-direction rays is disabled with
123 .I \-c
124 set to zero.
125 .PP
126 Output flushing at fixed intervals may be enabled with the
127 .I \-x
128 option, which specifies the number of records
129 (-c accumulations) before each flush.
130 If the
131 .I \-y
132 option is also set, then periodic flushing is disabled and the
133 output size for an RGB image is the taken from the x and y dimensions.
134 In lieu of periodic flushing, a flush may be forced as mentioned above
135 by sending a sample with a zero direction vector, although you
136 must still send a full record of rays before output occurs.
137 .PP
138 If progress reports are desired, the
139 .I \-t
140 option specifies a time interval in seconds for reports sent to
141 standard error.
142 This requires that the number of input samples is known, meaning a
143 .I \-y
144 parameter has been specified.
145 .PP
146 The output of
147 .I rcontrib
148 has many potential uses.
149 Source contributions can be used as components in linear combination to
150 reproduce any desired variation, e.g., simulating lighting controls or
151 changing sky conditions via daylight coefficients.
152 More generally,
153 .I rcontrib
154 can be used to compute arbitrary input-output relationships in optical
155 systems, such as luminaires, light pipes, and shading devices.
156 .PP
157 .I Rcontrib
158 sends the accumulated rays tallies
159 to one or more destinations according to the given
160 .I \-o
161 specification.
162 If a destination begins with an exclamation mark ('!'), then
163 a pipe is opened to a command and data is sent to its standard input.
164 Otherwise, the destination is treated as a file.
165 An existing file of the same name will not be clobbered, unless the
166 .I \-fo
167 option is given.
168 If instead the
169 .I \-r
170 option is specified, data recovery is attempted on existing files.
171 (If
172 .I "\-c 0"
173 is used together with the
174 .I \-r
175 option, existing files are read in and new ray evaluations are added
176 to the previous results, providing a convenient means for
177 progressive simulation.)\0
178 If an output specification contains a "%s" format, this will be
179 replaced by the modifier name.
180 The
181 .I \-b
182 option may be used to further define
183 a "bin number" within each object if finer resolution is needed, and
184 this will be applied to a "%d" format in the output file
185 specification if present.
186 (The final integer will be offset incrementally
187 if the output is a RADIANCE picture and more than one modifier has
188 the same format specification.)\0
189 The actual bin number is computed at run time based on ray direction
190 and surface intersection, as described below.
191 The number of bins must be specified in advance with the
192 .I \-bn
193 option, and this is critical for output files containing multiple values
194 per record.
195 A variable or constant name may be given for this parameter if
196 it has been defined via a previous
197 .I \-f
198 or
199 .I \-e
200 option.
201 Since bin numbers start from zero, the bin count is always equal to
202 the last bin plus one.
203 The most recent
204 .I \-p,
205 .I \-b,
206 .I \-bn
207 and
208 .I \-o
209 options to the left of each
210 .I \-m
211 setting are the ones used for that modifier.
212 The ordering of other options is unimportant, except for
213 .I \-x
214 and
215 .I \-y
216 if the
217 .I \-c
218 is zero, when they control the resolution string
219 produced in the corresponding output.
220 .PP
221 If a
222 .I \-b
223 expression is defined for a particular modifier,
224 the bin number will be evaluated at run time for each
225 ray contribution.
226 Specifically, each ray's world intersection point will be assigned to
227 the variables Px, Py, and Pz, and the normalized ray direction
228 will be assigned to Dx, Dy, and Dz.
229 These parameters may be combined with definitions given in
230 .I \-e
231 arguments and files read using the
232 .I \-f
233 option.
234 Additional parameter values that apply only to this modifier may be specified
235 with a
236 .I \-p
237 option, which contains a list of variable names and assigned values, separated
238 by commas, colons, or semicolons.
239 The computed bin value will be
240 rounded to the nearest whole number.
241 (Negative bin values will be silently ignored.)\0
242 For a single bin, you may specify
243 .I "\-b 0",
244 which is the default.
245 This mechanism allows the user to define precise regions or directions
246 they wish to accumulate, such as the Tregenza sky discretization,
247 which would be otherwise impossible to specify
248 as a set of RADIANCE primitives.
249 The rules and predefined functions available for these expressions are
250 described in the
251 .I rcalc(1)
252 man page.
253 Like
254 .I rcalc,
255 .I rcontrib
256 will search the RADIANCE library directories for each file given in a
257 .I \-f
258 option.
259 .PP
260 If no
261 .I \-o
262 specification is given, results are written on the standard output in order
263 of modifier (as given on the command line) then bin number.
264 Concatenated data is also sent to a single destination (i.e., an initial
265 .I \-o
266 specification without formatting strings).
267 If a "%s" format appears but no "%d" in the
268 .I \-o
269 specification, then each modifier will have its own output file, with
270 multiple values per record in the case of a non-zero
271 .I \-b
272 definition.
273 If a "%d" format appears but no "%s", then each bin will get its own
274 output file, with modifiers output in order in each record.
275 For text output, each RGB coefficient triple is separated by a tab,
276 with a newline at the end of each ray record.
277 For binary output formats, there is no such delimiter to mark
278 the end of each record.
279 .PP
280 Input and output format defaults to plain text, where each ray's
281 origin and direction (6 real values) are given on input,
282 and one line is produced per output file per ray.
283 Alternative data representations may be specified by the
284 .I \-f[io]
285 option, which is described in the
286 .I rtrace
287 man page along with the associated
288 .I \-x
289 and
290 .I \-y
291 resolution settings.
292 In particular, the color ('c') output data representation
293 together with positive dimensions for
294 .I \-x
295 and
296 .I \-y
297 will produce an uncompressed RADIANCE picture,
298 suitable for manipulation with
299 .I pcomb(1)
300 and related tools.
301 .PP
302 Options may be given on the command line and/or read from the
303 environment and/or read from a file.
304 A command argument beginning with a dollar sign ('$') is immediately
305 replaced by the contents of the given environment variable.
306 A command argument beginning with an at sign ('@') is immediately
307 replaced by the contents of the given file.
308 .PP
309 .I Rcontrib
310 supports light source contributions from photon maps generated by
311 .I mkpmap(1)
312 with its
313 .I -apC
314 option. Enabling photon mapping is described in the
315 .I rtrace
316 man page along with its relevant settings. In photon mapping mode,
317 .I rcontrib
318 only supports contributions from light sources, not arbitrary modifiers.
319 The
320 .I -b
321 option is supported along with its associated ray variables, as
322 discussed above. Ray coefficients are also supported via the
323 .I \-V-
324 option. Using fewer photons than there are light sources for the photon
325 density estimates results in omitted contributions, thus the bandwidth
326 is clamped accordingly and a warning is issued.
327 .SH EXAMPLES
328 To compute the proportional contributions from sources modified
329 by "light1" vs. "light2" on a set of irradiance values:
330 .IP "" .2i
331 rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
332 .PP
333 To generate a pair of images corresponding to these two lights'
334 contributions:
335 .IP "" .2i
336 vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf |
337 rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
338 @render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
339 .PP
340 These images may then be recombined using the desired outputs
341 of light1 and light2:
342 .IP "" .2i
343 pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
344 .PP
345 To compute an array of irradiance contributions according to a Tregenza sky:
346 .IP "" .2i
347 rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
348 \-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
349 .PP
350 To perform an annual simulation of 365 daily sun positions in photon mapping
351 mode:
352 .IP "" .2i
353 rcontrib \-I+ \-h \-V \-fo \-o c_%s.dat \-M lights \-ap contrib.pm 365
354 scene.oct < test.dat,
355 .SH ENVIRONMENT
356 RAYPATH path to search for \-f and \-M files
357 .SH BUGS
358 We do not currently compute contributions or coefficients properly
359 in scenes with participating media.
360 A single warning will be issued if a scattering or absorbing medium
361 is detected.
362 .SH AUTHOR
363 Greg Ward
364 .SH "SEE ALSO"
365 cnt(1), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(1),
366 ra_rgbe(1), rcalc(1), rcomb(1), rfluxmtx(1), rmtxop(1), rpict(1),
367 rsensor(1), rtrace(1), total(1), vwrays(1), ximage(1)
368