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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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