man/man1/rtrace.1

.\" RCSid "$Id: rtrace.1,v 1.3 2003/12/09 15:59:07 greg Exp $"
.TH RTRACE 1 10/17/97 RADIANCE
.SH NAME
rtrace - trace rays in RADIANCE scene
.SH SYNOPSIS
.B rtrace
[
.B options
]
[
.B $EVAR
]
[
.B @file
]
.B octree
.br
.B "rtrace [ options ] \-defaults"
.SH DESCRIPTION
.I Rtrace
traces rays from the standard input through the RADIANCE scene given by
.I octree
and sends the results to the standard output.
(The octree may be given as the output of a command enclosed in quotes
and preceded by a `!'.)\0
Input for each ray is:

        xorg yorg zorg xdir ydir zdir

If the direction vector is (0,0,0), a bogus record
is printed and the output is flushed if the
.I -x
value is unset or zero.
(See the notes on this option below.)\0
This may be useful for programs that run
.I rtrace
as a separate process.
In the second form, the default values
for the options (modified by those options present)
are printed with a brief explanation.
.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.
Most options are followed by one or more arguments, which must be
separated from the option and each other by white space.
The exceptions to this rule are the boolean options.
Normally, the appearance of a boolean option causes a feature to
be "toggled", that is switched from off to on or on to off
depending on its previous state.
Boolean options may also be set
explicitly by following them immediately with a '+' or '-', meaning
on or off, respectively.
Synonyms for '+' are any of the characters "yYtT1", and synonyms
for '-' are any of the characters "nNfF0".
All other characters will generate an error.
.TP 10n
.BI -f io
Format input according to the character
.I i
and output according to the character
.I o.
.I Rtrace
understands the following input and output formats:  'a' for
ascii, 'f' for single-precision floating point,
and 'd' for double-precision floating point.
In addition to these three choices, the character 'c' may be used
to denote 4-byte floating point (Radiance) color format
for the output of values only
.I (\-ov
option, below).
If the output character is missing, the input format is used.
.IP
Note that there is no space between this option and its argument.
.TP
.BI -o spec
Produce output fields according to
.I spec.
Characters are interpreted as follows:
.IP
o       origin (input)
.IP
d       direction (normalized)
.IP
v       value (radiance)
.IP
w       weight
.IP
l       effective length of ray
.IP
L       first intersection distance
.IP
c       local (u,v) coordinates
.IP
p       point of intersection
.IP
n       normal at intersection (perturbed)
.IP
N       normal at intersection (unperturbed)
.IP
s       surface name
.IP
m       modifier name
.IP
If the letter 't' appears in
.I spec,
then the fields following will be printed for every ray traced,
not just the final result.
Spawned rays are indented one tab for each level.
.IP
Note that there is no space between this option and its argument.
.TP
.BI -te \ mat
Append
.I mat
to the trace exclude list,
so that it will not be reported by the trace option
.I (\-o*t*).
Any ray striking an object having
.I mat
as its modifier will not be reported to the standard output with
the rest of the rays being traced.
This option has no effect unless the 't' option has been given as
part of the output specifier.
Any number of excluded materials may be given, but each
must appear in a separate option.
.TP
.BI -ti \ mat
Add
.I mat
to the trace include list,
so that it will be considered during the indirect calculation.
The program can use either an include list or an exclude
list, but not both.
.TP
.BI -tE \ file
Same as
.I \-te,
except read materials to be excluded from
.I file.
The RAYPATH environment variable determines which directories are
searched for this file.
The material names are separated by white space in the file.
.TP
.BI -tI \ file
Same as
.I \-ti,
except read materials to be included from
.I file.
.TP
.BR \-i
Boolean switch to compute irradiance rather than radiance values.
This only affects the final result, substituting a Lambertian
surface and multiplying the radiance by pi.
Glass and other transparent surfaces are ignored during this stage.
Light sources still appear with their original radiance values,
though the
.I \-dv
option (below) may be used to override this.
This option is especially useful in
conjunction with ximage(1) for computing illuminance at scene points.
.TP
.BR \-I
Boolean switch to compute irradiance rather than radiance,
with the input origin and direction interpreted instead
as measurement point and orientation.
.TP
.BR \-h
Boolean switch for information header on output.
.TP
.BI -x \ res
Set the x resolution to
.I res.
The output will be flushed after every
.I res
input rays.
A value of zero means that no output flushing will take place.
.TP
.BI -y \ res
Set the y resolution to
.I res.
The program will exit after
.I res
scanlines have been processed, where a scanline is the number of rays
given by the
.I \-x
option, or 1 if
.I \-x
is zero.
A value of zero means the program will not halt until the end
of file is reached.
.IP
If both
.I \-x
and
.I \-y
options are given, a resolution string is printed at the beginning
of the output.
This is mostly useful for recovering image dimensions with
.I pvalue(1),
and for creating valid Radiance picture files using the color output
format.
(See the
.I \-f
option, above.)
.TP
.BI -dj \ frac
Set the direct jittering to
.I frac.
A value of zero samples each source at specific sample points
(see the
.I \-ds
option below), giving a smoother but somewhat less accurate
rendering.
A positive value causes rays to be distributed over each
source sample according to its size, resulting in more accurate
penumbras.
This option should never be greater than 1, and may even
cause problems (such as speckle) when the value is smaller.
A warning about aiming failure will issued if
.I frac
is too large.
.TP
.BI -ds \ frac
Set the direct sampling ratio to
.I frac.
A light source will be subdivided until
the width of each sample area divided by the distance
to the illuminated point is below this ratio.
This assures accuracy in regions close to large area sources
at a slight computational expense.
A value of zero turns source subdivision off, sending at most one
shadow ray to each light source.
.TP
.BI -dt \ frac
Set the direct threshold to
.I frac.
Shadow testing will stop when the potential contribution of at least
the next and at most all remaining light sources is less than
this fraction of the accumulated value.
(See the
.I \-dc
option below.)
The remaining light source contributions are approximated
statistically.
A value of zero means that all light sources will be tested for shadow.
.TP
.BI \-dc \ frac
Set the direct certainty to
.I frac.
A value of one guarantees that the absolute accuracy of the direct calculation
will be equal to or better than that given in the
.I \-dt
specification.
A value of zero only insures that all shadow lines resulting in a contrast
change greater than the
.I \-dt
specification will be calculated.
.TP
.BI -dr \ N
Set the number of relays for secondary sources to
.I N.
A value of 0 means that secondary sources will be ignored.
A value of 1 means that sources will be made into first generation
secondary sources; a value of 2 means that first generation
secondary sources will also be made into second generation secondary
sources, and so on.
.TP
.BI -dp \ D
Set the secondary source presampling density to D.
This is the number of samples per steradian 
that will be used to determine ahead of time whether or not
it is worth following shadow rays through all the reflections and/or
transmissions associated with a secondary source path.
A value of 0 means that the full secondary source path will always
be tested for shadows if it is tested at all.
.TP
.BR \-dv
Boolean switch for light source visibility.
With this switch off, sources will be black when viewed directly
although they will still participate in the direct calculation.
This option is mostly for the program
.I mkillum(1)
to avoid inappropriate counting of light sources, but it
may also be desirable in conjunction with the
.I \-i
option.
.TP
.BI -sj \ frac
Set the specular sampling jitter to
.I frac.
This is the degree to which the highlights are sampled
for rough specular materials.
A value of one means that all highlights will be fully sampled
using distributed ray tracing.
A value of zero means that no jittering will take place, and all
reflections will appear sharp even when they should be diffuse.
.TP
.BI -st \ frac
Set the specular sampling threshold to
.I frac.
This is the minimum fraction of reflection or transmission, under which 
no specular sampling is performed.
A value of zero means that highlights will always be sampled by
tracing reflected or transmitted rays.
A value of one means that specular sampling is never used.
Highlights from light sources will always be correct, but
reflections from other surfaces will be approximated using an
ambient value.
A sampling threshold between zero and one offers a compromise between image
accuracy and rendering time.
.TP
.BR -bv
Boolean switch for back face visibility.
With this switch off, back faces of opaque objects will be invisible
to all rays.
This is dangerous unless the model was constructed such that
all surface normals on opaque objects face outward.
Although turning off back face visibility does not save much
computation time under most circumstances, it may be useful as a
tool for scene debugging, or for seeing through one-sided walls from
the outside.
This option has no effect on transparent or translucent materials.
.TP
.BI -av " red grn blu"
Set the ambient value to a radiance of
.I "red grn blu".
This is the final value used in place of an
indirect light calculation.
If the number of ambient bounces is one or greater and the ambient
value weight is non-zero (see
.I -aw
and
.I -ab
below), this value may be modified by the computed indirect values
to improve overall accuracy.
.TP
.BI -aw \ N
Set the relative weight of the ambient value given with the
.I -av
option to
.I N.
As new indirect irradiances are computed, they will modify the
default ambient value in a moving average, with the specified weight
assigned to the initial value given on the command and all other
weights set to 1.
If a value of 0 is given with this option, then the initial ambient
value is never modified.
This is the safest value for scenes with large differences in
indirect contributions, such as when both indoor and outdoor
(daylight) areas are visible.
.TP
.BI -ab \ N
Set the number of ambient bounces to
.I N.
This is the maximum number of diffuse bounces 
computed by the indirect calculation.
A value of zero implies no indirect calculation.
.TP
.BI -ar \ res
Set the ambient resolution to
.I res.
This number will determine the maximum density of ambient values
used in interpolation.
Error will start to increase on surfaces spaced closer than
the scene size divided by the ambient resolution.
The maximum ambient value density is the scene size times the
ambient accuracy (see the
.I \-aa
option below) divided by the ambient resolution.
The scene size can be determined using
.I getinfo(1)
with the
.I \-d
option on the input octree.
.TP
.BI -aa \ acc
Set the ambient accuracy to
.I acc.
This value will approximately equal the error
from indirect illuminance interpolation.
A value of zero implies no interpolation.
.TP
.BI -ad \ N
Set the number of ambient divisions to
.I N.
The error in the Monte Carlo calculation of indirect
illuminance will be inversely proportional to the square
root of this number.
A value of zero implies no indirect calculation.
.TP
.BI -as \ N
Set the number of ambient super-samples to
.I N.
Super-samples are applied only to the ambient divisions which
show a significant change.
.TP
.BI -af \ fname
Set the ambient file to
.I fname.
This is where indirect illuminance will be stored and retrieved.
Normally, indirect illuminance values are kept in memory and
lost when the program finishes or dies.
By using a file, different invocations can share illuminance
values, saving time in the computation.
The ambient file is in a machine-independent binary format
which can be examined with
.I lookamb(1).
.IP
The ambient file may also be used as a means of communication and
data sharing between simultaneously executing processes.
The same file may be used by multiple processes, possibly running on
different machines and accessing the file via the network (ie.
.I nfs(4)).
The network lock manager
.I lockd(8)
is used to insure that this information is used consistently.
.IP
If any calculation parameters are changed or the scene
is modified, the old ambient file should be removed so that
the calculation can start over from scratch.
For convenience, the original ambient parameters are listed in the
header of the ambient file.
.I Getinfo(1)
may be used to print out this information.
.TP
.BI -ae \ mat
Append
.I mat
to the ambient exclude list,
so that it will not be considered during the indirect calculation.
This is a hack for speeding the indirect computation by
ignoring certain objects.
Any object having
.I mat
as its modifier will get the default ambient
level rather than a calculated value.
Any number of excluded materials may be given, but each
must appear in a separate option.
.TP
.BI -ai \ mat
Add
.I mat
to the ambient include list,
so that it will be considered during the indirect calculation.
The program can use either an include list or an exclude
list, but not both.
.TP
.BI -aE \ file
Same as
.I \-ae,
except read materials to be excluded from
.I file.
The RAYPATH environment variable determines which directories are
searched for this file.
The material names are separated by white space in the file.
.TP
.BI -aI \ file
Same as
.I \-ai,
except read materials to be included from
.I file.
.TP
.BI -me " rext gext bext"
Set the global medium extinction coefficient to the indicated color,
in units of 1/distance (distance in world coordinates).
Light will be scattered or absorbed over distance according to
this value.
The ratio of scattering to total scattering plus absorption is set
by the albedo parameter, described below.
.TP
.BI -ma " ralb galb balb"
Set the global medium albedo to the given value between 0\00\00
and 1\01\01.
A zero value means that all light not transmitted by the medium
is absorbed.
A unitary value means that all light not transmitted by the medium
is scattered in some new direction.
The isotropy of scattering is determined by the Heyney-Greenstein
parameter, described below.
.TP
.BI \-mg \ gecc
Set the medium Heyney-Greenstein eccentricity parameter to
.I gecc.
This parameter determines how strongly scattering favors the forward
direction.
A value of 0 indicates perfectly isotropic scattering.
As this parameter approaches 1, scattering tends to prefer the
forward direction.
.TP
.BI \-ms \ sampdist
Set the medium sampling distance to
.I sampdist,
in world coordinate units.
During source scattering, this will be the average distance between
adjacent samples.
A value of 0 means that only one sample will be taken per light
source within a given scattering volume.
.TP
.BI -lr \ N
Limit reflections to a maximum of
.I N.
.TP
.BI -lw \ frac
Limit the weight of each ray to a minimum of
.I frac.
During ray-tracing, a record is kept of the final contribution
a ray would have to the image.
If it is less then the specified minimum, the ray is not traced.
.TP
.BR -ld
Boolean switch to limit ray distance.
If this option is set, then rays will only be traced as far as the
magnitude of each direction vector.
Otherwise, vector magnitude is ignored and rays are traced to infinity.
.TP
.BI -e \ efile
Send error messages and progress reports to
.I efile
instead of the standard error.
.TP
.BR \-w
Boolean switch to suppress warning messages.
.TP
.BI \-P \ pfile
Execute in a persistent mode, using
.I pfile
as the control file.
Persistent execution means that after reaching end-of-file on
its input,
.I rtrace
will fork a child process that will wait for another
.I rtrace
command with the same
.I \-P
option to attach to it.
(Note that since the rest of the command line options will be those
of the original invocation, it is not necessary to give any arguments
besides
.I \-P
for subsequent calls.)
Killing the process is achieved with the
.I kill(1)
command.
(The process ID in the first line of
.I pfile
may be used to identify the waiting
.I rtrace
process.)
This option may be used with the
.I \-fr
option of
.I pinterp(1)
to avoid the cost of starting up
.I rtrace
many times.
.TP
.BI \-PP \ pfile
Execute in continuous-forking persistent mode, using
.I pfile
as the control file.
The difference between this option and the
.I \-P
option described above is the creation of multiple duplicate
processes to handle any number of attaches.
This provides a simple and reliable mechanism of memory sharing
on most multiprocessing platforms, since the
.I fork(2)
system call will share memory on a copy-on-write basis.
.SH EXAMPLES
To compute radiance values for the rays listed in samples.inp:
.IP "" .2i
rtrace -ov scene.oct < samples.inp > radiance.out
.PP
To compute illuminance values at locations selected with the 't'
command of
.I ximage(1):
.IP "" .2i
ximage scene.pic | rtrace -h -x 1 -i scene.oct | rcalc -e '$1=47.4*$1+120*$2+11.6*$3'
.PP
To record the object identifier corresponding to each pixel in an image:
.IP "" .2i
vwrays -fd scene.pic | rtrace -fda `vwrays -d scene.pic` -os scene.oct
.PP
To compute an image with an unusual view mapping:
.IP "" .2i
cnt 640 480 | rcalc -e 'xr:640;yr:480' -f unusual_view.cal | rtrace
-x 640 -y 480 -fac scene.oct > unusual.pic
.SH ENVIRONMENT
RAYPATH         the directories to check for auxiliary files.
.SH FILES
/usr/tmp/rtXXXXXX               common header information for picture sequence
.SH DIAGNOSTICS
If the program terminates from an input related error, the exit status
will be 1.
A system related error results in an exit status of 2.
If the program receives a signal that is caught, it will exit with a status
of 3.
In each case, an error message will be printed to the standard error, or
to the file designated by the
.I \-e
option.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1),
pvalue(1), rpict(1), rvu(1), vwrays(1), ximage(1)
Revision:	1.4
Committed:	Thu Jan 1 19:31:45 2004 UTC (20 years, 4 months ago) by greg
Branch:	MAIN
CVS Tags:	rad3R6, rad3R6P1
Changes since 1.3:	+2 -2 lines
Log Message:	Renamed rview, lam, calc, and neat to rvu, rlam, icalc, and neaten
#	User	Rev	Content
1	greg	1.4	.\" RCSid "$Id: rtrace.1,v 1.3 2003/12/09 15:59:07 greg Exp $"
2	greg	1.1	.TH RTRACE 1 10/17/97 RADIANCE
3			.SH NAME
4			rtrace - trace rays in RADIANCE scene
5			.SH SYNOPSIS
6			.B rtrace
7			[
8			.B options
9			]
10			[
11			.B $EVAR
12			]
13			[
14			.B @file
15			]
16			.B octree
17			.br
18			.B "rtrace [ options ] \-defaults"
19			.SH DESCRIPTION
20			.I Rtrace
21			traces rays from the standard input through the RADIANCE scene given by
22			.I octree
23			and sends the results to the standard output.
24			(The octree may be given as the output of a command enclosed in quotes
25			and preceded by a `!'.)\0
26			Input for each ray is:
27
28			xorg yorg zorg xdir ydir zdir
29
30			If the direction vector is (0,0,0), a bogus record
31			is printed and the output is flushed if the
32			.I -x
33			value is unset or zero.
34			(See the notes on this option below.)\0
35			This may be useful for programs that run
36			.I rtrace
37			as a separate process.
38			In the second form, the default values
39			for the options (modified by those options present)
40			are printed with a brief explanation.
41			.PP
42			Options may be given on the command line and/or read from the
43			environment and/or read from a file.
44			A command argument beginning with a dollar sign ('$') is immediately
45			replaced by the contents of the given environment variable.
46			A command argument beginning with an at sign ('@') is immediately
47			replaced by the contents of the given file.
48			Most options are followed by one or more arguments, which must be
49			separated from the option and each other by white space.
50			The exceptions to this rule are the boolean options.
51			Normally, the appearance of a boolean option causes a feature to
52			be "toggled", that is switched from off to on or on to off
53			depending on its previous state.
54			Boolean options may also be set
55			explicitly by following them immediately with a '+' or '-', meaning
56			on or off, respectively.
57			Synonyms for '+' are any of the characters "yYtT1", and synonyms
58			for '-' are any of the characters "nNfF0".
59			All other characters will generate an error.
60			.TP 10n
61			.BI -f io
62			Format input according to the character
63			.I i
64			and output according to the character
65			.I o.
66			.I Rtrace
67			understands the following input and output formats: 'a' for
68			ascii, 'f' for single-precision floating point,
69			and 'd' for double-precision floating point.
70			In addition to these three choices, the character 'c' may be used
71			to denote 4-byte floating point (Radiance) color format
72			for the output of values only
73			.I (\-ov
74			option, below).
75			If the output character is missing, the input format is used.
76			.IP
77			Note that there is no space between this option and its argument.
78			.TP
79			.BI -o spec
80			Produce output fields according to
81			.I spec.
82			Characters are interpreted as follows:
83			.IP
84			o origin (input)
85			.IP
86			d direction (normalized)
87			.IP
88			v value (radiance)
89			.IP
90			w weight
91			.IP
92			l effective length of ray
93			.IP
94			L first intersection distance
95			.IP
96	greg	1.2	c local (u,v) coordinates
97			.IP
98	greg	1.1	p point of intersection
99			.IP
100			n normal at intersection (perturbed)
101			.IP
102			N normal at intersection (unperturbed)
103			.IP
104			s surface name
105			.IP
106			m modifier name
107			.IP
108			If the letter 't' appears in
109			.I spec,
110			then the fields following will be printed for every ray traced,
111			not just the final result.
112			Spawned rays are indented one tab for each level.
113			.IP
114			Note that there is no space between this option and its argument.
115			.TP
116			.BI -te \ mat
117			Append
118			.I mat
119			to the trace exclude list,
120			so that it will not be reported by the trace option
121			.I (\-ot).
122			Any ray striking an object having
123			.I mat
124			as its modifier will not be reported to the standard output with
125			the rest of the rays being traced.
126			This option has no effect unless the 't' option has been given as
127			part of the output specifier.
128			Any number of excluded materials may be given, but each
129			must appear in a separate option.
130			.TP
131			.BI -ti \ mat
132			Add
133			.I mat
134			to the trace include list,
135			so that it will be considered during the indirect calculation.
136			The program can use either an include list or an exclude
137			list, but not both.
138			.TP
139			.BI -tE \ file
140			Same as
141			.I \-te,
142			except read materials to be excluded from
143			.I file.
144			The RAYPATH environment variable determines which directories are
145			searched for this file.
146			The material names are separated by white space in the file.
147			.TP
148			.BI -tI \ file
149			Same as
150			.I \-ti,
151			except read materials to be included from
152			.I file.
153			.TP
154			.BR \-i
155			Boolean switch to compute irradiance rather than radiance values.
156			This only affects the final result, substituting a Lambertian
157			surface and multiplying the radiance by pi.
158			Glass and other transparent surfaces are ignored during this stage.
159			Light sources still appear with their original radiance values,
160			though the
161			.I \-dv
162			option (below) may be used to override this.
163			This option is especially useful in
164			conjunction with ximage(1) for computing illuminance at scene points.
165			.TP
166			.BR \-I
167			Boolean switch to compute irradiance rather than radiance,
168			with the input origin and direction interpreted instead
169			as measurement point and orientation.
170			.TP
171			.BR \-h
172			Boolean switch for information header on output.
173			.TP
174			.BI -x \ res
175			Set the x resolution to
176			.I res.
177			The output will be flushed after every
178			.I res
179			input rays.
180			A value of zero means that no output flushing will take place.
181			.TP
182			.BI -y \ res
183			Set the y resolution to
184			.I res.
185			The program will exit after
186			.I res
187			scanlines have been processed, where a scanline is the number of rays
188			given by the
189			.I \-x
190			option, or 1 if
191			.I \-x
192			is zero.
193			A value of zero means the program will not halt until the end
194			of file is reached.
195			.IP
196			If both
197			.I \-x
198			and
199			.I \-y
200			options are given, a resolution string is printed at the beginning
201			of the output.
202			This is mostly useful for recovering image dimensions with
203			.I pvalue(1),
204			and for creating valid Radiance picture files using the color output
205			format.
206			(See the
207			.I \-f
208			option, above.)
209			.TP
210			.BI -dj \ frac
211			Set the direct jittering to
212			.I frac.
213			A value of zero samples each source at specific sample points
214			(see the
215			.I \-ds
216			option below), giving a smoother but somewhat less accurate
217			rendering.
218			A positive value causes rays to be distributed over each
219			source sample according to its size, resulting in more accurate
220			penumbras.
221			This option should never be greater than 1, and may even
222			cause problems (such as speckle) when the value is smaller.
223			A warning about aiming failure will issued if
224			.I frac
225			is too large.
226			.TP
227			.BI -ds \ frac
228			Set the direct sampling ratio to
229			.I frac.
230			A light source will be subdivided until
231			the width of each sample area divided by the distance
232			to the illuminated point is below this ratio.
233			This assures accuracy in regions close to large area sources
234			at a slight computational expense.
235			A value of zero turns source subdivision off, sending at most one
236			shadow ray to each light source.
237			.TP
238			.BI -dt \ frac
239			Set the direct threshold to
240			.I frac.
241			Shadow testing will stop when the potential contribution of at least
242			the next and at most all remaining light sources is less than
243			this fraction of the accumulated value.
244			(See the
245			.I \-dc
246			option below.)
247			The remaining light source contributions are approximated
248			statistically.
249			A value of zero means that all light sources will be tested for shadow.
250			.TP
251			.BI \-dc \ frac
252			Set the direct certainty to
253			.I frac.
254			A value of one guarantees that the absolute accuracy of the direct calculation
255			will be equal to or better than that given in the
256			.I \-dt
257			specification.
258			A value of zero only insures that all shadow lines resulting in a contrast
259			change greater than the
260			.I \-dt
261			specification will be calculated.
262			.TP
263			.BI -dr \ N
264			Set the number of relays for secondary sources to
265			.I N.
266			A value of 0 means that secondary sources will be ignored.
267			A value of 1 means that sources will be made into first generation
268			secondary sources; a value of 2 means that first generation
269			secondary sources will also be made into second generation secondary
270			sources, and so on.
271			.TP
272			.BI -dp \ D
273			Set the secondary source presampling density to D.
274			This is the number of samples per steradian
275			that will be used to determine ahead of time whether or not
276			it is worth following shadow rays through all the reflections and/or
277			transmissions associated with a secondary source path.
278			A value of 0 means that the full secondary source path will always
279			be tested for shadows if it is tested at all.
280			.TP
281			.BR \-dv
282			Boolean switch for light source visibility.
283			With this switch off, sources will be black when viewed directly
284			although they will still participate in the direct calculation.
285			This option is mostly for the program
286			.I mkillum(1)
287			to avoid inappropriate counting of light sources, but it
288			may also be desirable in conjunction with the
289			.I \-i
290			option.
291			.TP
292			.BI -sj \ frac
293			Set the specular sampling jitter to
294			.I frac.
295			This is the degree to which the highlights are sampled
296			for rough specular materials.
297			A value of one means that all highlights will be fully sampled
298			using distributed ray tracing.
299			A value of zero means that no jittering will take place, and all
300			reflections will appear sharp even when they should be diffuse.
301			.TP
302			.BI -st \ frac
303			Set the specular sampling threshold to
304			.I frac.
305			This is the minimum fraction of reflection or transmission, under which
306			no specular sampling is performed.
307			A value of zero means that highlights will always be sampled by
308			tracing reflected or transmitted rays.
309			A value of one means that specular sampling is never used.
310			Highlights from light sources will always be correct, but
311			reflections from other surfaces will be approximated using an
312			ambient value.
313			A sampling threshold between zero and one offers a compromise between image
314			accuracy and rendering time.
315			.TP
316			.BR -bv
317			Boolean switch for back face visibility.
318			With this switch off, back faces of opaque objects will be invisible
319			to all rays.
320			This is dangerous unless the model was constructed such that
321			all surface normals on opaque objects face outward.
322			Although turning off back face visibility does not save much
323			computation time under most circumstances, it may be useful as a
324			tool for scene debugging, or for seeing through one-sided walls from
325			the outside.
326			This option has no effect on transparent or translucent materials.
327			.TP
328			.BI -av " red grn blu"
329			Set the ambient value to a radiance of
330			.I "red grn blu".
331			This is the final value used in place of an
332			indirect light calculation.
333			If the number of ambient bounces is one or greater and the ambient
334			value weight is non-zero (see
335			.I -aw
336			and
337			.I -ab
338			below), this value may be modified by the computed indirect values
339			to improve overall accuracy.
340			.TP
341			.BI -aw \ N
342			Set the relative weight of the ambient value given with the
343			.I -av
344			option to
345			.I N.
346			As new indirect irradiances are computed, they will modify the
347			default ambient value in a moving average, with the specified weight
348			assigned to the initial value given on the command and all other
349			weights set to 1.
350			If a value of 0 is given with this option, then the initial ambient
351			value is never modified.
352			This is the safest value for scenes with large differences in
353			indirect contributions, such as when both indoor and outdoor
354			(daylight) areas are visible.
355			.TP
356			.BI -ab \ N
357			Set the number of ambient bounces to
358			.I N.
359			This is the maximum number of diffuse bounces
360			computed by the indirect calculation.
361			A value of zero implies no indirect calculation.
362			.TP
363			.BI -ar \ res
364			Set the ambient resolution to
365			.I res.
366			This number will determine the maximum density of ambient values
367			used in interpolation.
368			Error will start to increase on surfaces spaced closer than
369			the scene size divided by the ambient resolution.
370			The maximum ambient value density is the scene size times the
371			ambient accuracy (see the
372			.I \-aa
373			option below) divided by the ambient resolution.
374			The scene size can be determined using
375			.I getinfo(1)
376			with the
377			.I \-d
378			option on the input octree.
379			.TP
380			.BI -aa \ acc
381			Set the ambient accuracy to
382			.I acc.
383			This value will approximately equal the error
384			from indirect illuminance interpolation.
385			A value of zero implies no interpolation.
386			.TP
387			.BI -ad \ N
388			Set the number of ambient divisions to
389			.I N.
390			The error in the Monte Carlo calculation of indirect
391			illuminance will be inversely proportional to the square
392			root of this number.
393			A value of zero implies no indirect calculation.
394			.TP
395			.BI -as \ N
396			Set the number of ambient super-samples to
397			.I N.
398			Super-samples are applied only to the ambient divisions which
399			show a significant change.
400			.TP
401			.BI -af \ fname
402			Set the ambient file to
403			.I fname.
404			This is where indirect illuminance will be stored and retrieved.
405			Normally, indirect illuminance values are kept in memory and
406			lost when the program finishes or dies.
407			By using a file, different invocations can share illuminance
408			values, saving time in the computation.
409			The ambient file is in a machine-independent binary format
410			which can be examined with
411			.I lookamb(1).
412			.IP
413			The ambient file may also be used as a means of communication and
414			data sharing between simultaneously executing processes.
415			The same file may be used by multiple processes, possibly running on
416			different machines and accessing the file via the network (ie.
417			.I nfs(4)).
418			The network lock manager
419			.I lockd(8)
420			is used to insure that this information is used consistently.
421			.IP
422			If any calculation parameters are changed or the scene
423			is modified, the old ambient file should be removed so that
424			the calculation can start over from scratch.
425			For convenience, the original ambient parameters are listed in the
426			header of the ambient file.
427			.I Getinfo(1)
428			may be used to print out this information.
429			.TP
430			.BI -ae \ mat
431			Append
432			.I mat
433			to the ambient exclude list,
434			so that it will not be considered during the indirect calculation.
435			This is a hack for speeding the indirect computation by
436			ignoring certain objects.
437			Any object having
438			.I mat
439			as its modifier will get the default ambient
440			level rather than a calculated value.
441			Any number of excluded materials may be given, but each
442			must appear in a separate option.
443			.TP
444			.BI -ai \ mat
445			Add
446			.I mat
447			to the ambient include list,
448			so that it will be considered during the indirect calculation.
449			The program can use either an include list or an exclude
450			list, but not both.
451			.TP
452			.BI -aE \ file
453			Same as
454			.I \-ae,
455			except read materials to be excluded from
456			.I file.
457			The RAYPATH environment variable determines which directories are
458			searched for this file.
459			The material names are separated by white space in the file.
460			.TP
461			.BI -aI \ file
462			Same as
463			.I \-ai,
464			except read materials to be included from
465			.I file.
466			.TP
467			.BI -me " rext gext bext"
468			Set the global medium extinction coefficient to the indicated color,
469			in units of 1/distance (distance in world coordinates).
470			Light will be scattered or absorbed over distance according to
471			this value.
472			The ratio of scattering to total scattering plus absorption is set
473			by the albedo parameter, described below.
474			.TP
475			.BI -ma " ralb galb balb"
476			Set the global medium albedo to the given value between 0\00\00
477			and 1\01\01.
478			A zero value means that all light not transmitted by the medium
479			is absorbed.
480			A unitary value means that all light not transmitted by the medium
481			is scattered in some new direction.
482			The isotropy of scattering is determined by the Heyney-Greenstein
483			parameter, described below.
484			.TP
485			.BI \-mg \ gecc
486			Set the medium Heyney-Greenstein eccentricity parameter to
487			.I gecc.
488			This parameter determines how strongly scattering favors the forward
489			direction.
490			A value of 0 indicates perfectly isotropic scattering.
491			As this parameter approaches 1, scattering tends to prefer the
492			forward direction.
493			.TP
494			.BI \-ms \ sampdist
495			Set the medium sampling distance to
496			.I sampdist,
497			in world coordinate units.
498			During source scattering, this will be the average distance between
499			adjacent samples.
500			A value of 0 means that only one sample will be taken per light
501			source within a given scattering volume.
502			.TP
503			.BI -lr \ N
504			Limit reflections to a maximum of
505			.I N.
506			.TP
507			.BI -lw \ frac
508			Limit the weight of each ray to a minimum of
509			.I frac.
510			During ray-tracing, a record is kept of the final contribution
511			a ray would have to the image.
512			If it is less then the specified minimum, the ray is not traced.
513			.TP
514			.BR -ld
515			Boolean switch to limit ray distance.
516			If this option is set, then rays will only be traced as far as the
517			magnitude of each direction vector.
518			Otherwise, vector magnitude is ignored and rays are traced to infinity.
519			.TP
520			.BI -e \ efile
521			Send error messages and progress reports to
522			.I efile
523			instead of the standard error.
524			.TP
525			.BR \-w
526			Boolean switch to suppress warning messages.
527			.TP
528			.BI \-P \ pfile
529			Execute in a persistent mode, using
530			.I pfile
531			as the control file.
532			Persistent execution means that after reaching end-of-file on
533			its input,
534			.I rtrace
535			will fork a child process that will wait for another
536			.I rtrace
537			command with the same
538			.I \-P
539			option to attach to it.
540			(Note that since the rest of the command line options will be those
541			of the original invocation, it is not necessary to give any arguments
542			besides
543			.I \-P
544			for subsequent calls.)
545			Killing the process is achieved with the
546			.I kill(1)
547			command.
548			(The process ID in the first line of
549			.I pfile
550			may be used to identify the waiting
551			.I rtrace
552			process.)
553			This option may be used with the
554			.I \-fr
555			option of
556			.I pinterp(1)
557			to avoid the cost of starting up
558			.I rtrace
559			many times.
560			.TP
561			.BI \-PP \ pfile
562			Execute in continuous-forking persistent mode, using
563			.I pfile
564			as the control file.
565			The difference between this option and the
566			.I \-P
567			option described above is the creation of multiple duplicate
568			processes to handle any number of attaches.
569			This provides a simple and reliable mechanism of memory sharing
570			on most multiprocessing platforms, since the
571			.I fork(2)
572			system call will share memory on a copy-on-write basis.
573			.SH EXAMPLES
574			To compute radiance values for the rays listed in samples.inp:
575			.IP "" .2i
576			rtrace -ov scene.oct < samples.inp > radiance.out
577			.PP
578			To compute illuminance values at locations selected with the 't'
579			command of
580			.I ximage(1):
581			.IP "" .2i
582			ximage scene.pic \| rtrace -h -x 1 -i scene.oct \| rcalc -e '$1=47.4$1+120$2+11.6*$3'
583			.PP
584			To record the object identifier corresponding to each pixel in an image:
585			.IP "" .2i
586			vwrays -fd scene.pic \| rtrace -fda `vwrays -d scene.pic` -os scene.oct
587			.PP
588			To compute an image with an unusual view mapping:
589			.IP "" .2i
590			cnt 640 480 \| rcalc -e 'xr:640;yr:480' -f unusual_view.cal \| rtrace
591			-x 640 -y 480 -fac scene.oct > unusual.pic
592			.SH ENVIRONMENT
593			RAYPATH the directories to check for auxiliary files.
594			.SH FILES
595			/usr/tmp/rtXXXXXX common header information for picture sequence
596			.SH DIAGNOSTICS
597			If the program terminates from an input related error, the exit status
598			will be 1.
599			A system related error results in an exit status of 2.
600			If the program receives a signal that is caught, it will exit with a status
601			of 3.
602			In each case, an error message will be printed to the standard error, or
603			to the file designated by the
604			.I \-e
605			option.
606			.SH AUTHOR
607			Greg Ward
608			.SH "SEE ALSO"
609			getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1),
610	greg	1.4	pvalue(1), rpict(1), rvu(1), vwrays(1), ximage(1)