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Comparing ray/doc/man/man1/rtcontrib.1 (file contents):
Revision 1.17 by greg, Sat Nov 17 01:13:50 2007 UTC vs.
Revision 1.18 by greg, Fri Apr 18 18:06:29 2008 UTC

# Line 9 | Line 9 | rtcontrib - compute contribution coefficients in a RAD
9   ][
10   .B \-V
11   ][
12 < .B \-c
12 > .B "\-c count"
13   ][
14   .B \-fo
15   |
# Line 58 | Line 58 | 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
# Line 86 | Line 97 | 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.
# Line 97 | Line 128 | More generally,
128   can be used to compute arbitrary input-output relationships in optical
129   systems, such as luminaires, light pipes, and shading devices.
130   .PP
100 – 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
131   .I Rtcontrib
132   calls
133   .I rtrace(1)
# Line 130 | Line 146 | If instead the
146   .I \-r
147   option is specified, data recovery is attempted on existing files.
148   (If
149 < .I \-c
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
# Line 242 | Line 258 | will produce an uncompressed RADIANCE picture,
258   suitable for manipulation with
259   .I pcomb(1)
260   and related tools.
245 – .PP
246 – If the
247 – .I \-n
248 – option is specified with a value greater than 1, multiple
249 – .I rtrace
250 – 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 – 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.
261   .PP
262   Options may be given on the command line and/or read from the
263   environment and/or read from a file.

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