man/man1/rtrace.1

.\" RCSid "$Id"
.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
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*$3'
.PP
To record the object identifier corresponding to each pixel in an image:
.IP "" .2i
vwrays -fd scene.pic | rtrace -fda `vwrays -d scene.pic` -os scene.oct
.PP
To compute an image with an unusual view mapping:
.IP "" .2i
cnt 640 480 | rcalc -e 'xr:640;yr:480' -f unusual_view.cal | rtrace
-x 640 -y 480 -fac scene.oct > unusual.pic
.SH ENVIRONMENT
RAYPATH         the directories to check for auxiliary files.
.SH FILES
/usr/tmp/rtXXXXXX               common header information for picture sequence
.SH DIAGNOSTICS
If the program terminates from an input related error, the exit status
will be 1.
A system related error results in an exit status of 2.
If the program receives a signal that is caught, it will exit with a status
of 3.
In each case, an error message will be printed to the standard error, or
to the file designated by the
.I \-e
option.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1),
pvalue(1), rpict(1), rview(1), vwrays(1), ximage(1)
Revision:	1.1
Committed:	Tue Mar 11 19:20:21 2003 UTC (21 years, 2 months ago) by greg
Branch:	MAIN
CVS Tags:	rad3R5
Log Message:	Added documentation to repository
#	Content
1	.\" RCSid "$Id"
2	.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	p point of intersection
97	.IP
98	n normal at intersection (perturbed)
99	.IP
100	N normal at intersection (unperturbed)
101	.IP
102	s surface name
103	.IP
104	m modifier name
105	.IP
106	If the letter 't' appears in
107	.I spec,
108	then the fields following will be printed for every ray traced,
109	not just the final result.
110	Spawned rays are indented one tab for each level.
111	.IP
112	Note that there is no space between this option and its argument.
113	.TP
114	.BI -te \ mat
115	Append
116	.I mat
117	to the trace exclude list,
118	so that it will not be reported by the trace option
119	.I (\-ot).
120	Any ray striking an object having
121	.I mat
122	as its modifier will not be reported to the standard output with
123	the rest of the rays being traced.
124	This option has no effect unless the 't' option has been given as
125	part of the output specifier.
126	Any number of excluded materials may be given, but each
127	must appear in a separate option.
128	.TP
129	.BI -ti \ mat
130	Add
131	.I mat
132	to the trace include list,
133	so that it will be considered during the indirect calculation.
134	The program can use either an include list or an exclude
135	list, but not both.
136	.TP
137	.BI -tE \ file
138	Same as
139	.I \-te,
140	except read materials to be excluded from
141	.I file.
142	The RAYPATH environment variable determines which directories are
143	searched for this file.
144	The material names are separated by white space in the file.
145	.TP
146	.BI -tI \ file
147	Same as
148	.I \-ti,
149	except read materials to be included from
150	.I file.
151	.TP
152	.BR \-i
153	Boolean switch to compute irradiance rather than radiance values.
154	This only affects the final result, substituting a Lambertian
155	surface and multiplying the radiance by pi.
156	Glass and other transparent surfaces are ignored during this stage.
157	Light sources still appear with their original radiance values,
158	though the
159	.I \-dv
160	option (below) may be used to override this.
161	This option is especially useful in
162	conjunction with ximage(1) for computing illuminance at scene points.
163	.TP
164	.BR \-I
165	Boolean switch to compute irradiance rather than radiance,
166	with the input origin and direction interpreted instead
167	as measurement point and orientation.
168	.TP
169	.BR \-h
170	Boolean switch for information header on output.
171	.TP
172	.BI -x \ res
173	Set the x resolution to
174	.I res.
175	The output will be flushed after every
176	.I res
177	input rays.
178	A value of zero means that no output flushing will take place.
179	.TP
180	.BI -y \ res
181	Set the y resolution to
182	.I res.
183	The program will exit after
184	.I res
185	scanlines have been processed, where a scanline is the number of rays
186	given by the
187	.I \-x
188	option, or 1 if
189	.I \-x
190	is zero.
191	A value of zero means the program will not halt until the end
192	of file is reached.
193	.IP
194	If both
195	.I \-x
196	and
197	.I \-y
198	options are given, a resolution string is printed at the beginning
199	of the output.
200	This is mostly useful for recovering image dimensions with
201	.I pvalue(1),
202	and for creating valid Radiance picture files using the color output
203	format.
204	(See the
205	.I \-f
206	option, above.)
207	.TP
208	.BI -dj \ frac
209	Set the direct jittering to
210	.I frac.
211	A value of zero samples each source at specific sample points
212	(see the
213	.I \-ds
214	option below), giving a smoother but somewhat less accurate
215	rendering.
216	A positive value causes rays to be distributed over each
217	source sample according to its size, resulting in more accurate
218	penumbras.
219	This option should never be greater than 1, and may even
220	cause problems (such as speckle) when the value is smaller.
221	A warning about aiming failure will issued if
222	.I frac
223	is too large.
224	.TP
225	.BI -ds \ frac
226	Set the direct sampling ratio to
227	.I frac.
228	A light source will be subdivided until
229	the width of each sample area divided by the distance
230	to the illuminated point is below this ratio.
231	This assures accuracy in regions close to large area sources
232	at a slight computational expense.
233	A value of zero turns source subdivision off, sending at most one
234	shadow ray to each light source.
235	.TP
236	.BI -dt \ frac
237	Set the direct threshold to
238	.I frac.
239	Shadow testing will stop when the potential contribution of at least
240	the next and at most all remaining light sources is less than
241	this fraction of the accumulated value.
242	(See the
243	.I \-dc
244	option below.)
245	The remaining light source contributions are approximated
246	statistically.
247	A value of zero means that all light sources will be tested for shadow.
248	.TP
249	.BI \-dc \ frac
250	Set the direct certainty to
251	.I frac.
252	A value of one guarantees that the absolute accuracy of the direct calculation
253	will be equal to or better than that given in the
254	.I \-dt
255	specification.
256	A value of zero only insures that all shadow lines resulting in a contrast
257	change greater than the
258	.I \-dt
259	specification will be calculated.
260	.TP
261	.BI -dr \ N
262	Set the number of relays for secondary sources to
263	.I N.
264	A value of 0 means that secondary sources will be ignored.
265	A value of 1 means that sources will be made into first generation
266	secondary sources; a value of 2 means that first generation
267	secondary sources will also be made into second generation secondary
268	sources, and so on.
269	.TP
270	.BI -dp \ D
271	Set the secondary source presampling density to D.
272	This is the number of samples per steradian
273	that will be used to determine ahead of time whether or not
274	it is worth following shadow rays through all the reflections and/or
275	transmissions associated with a secondary source path.
276	A value of 0 means that the full secondary source path will always
277	be tested for shadows if it is tested at all.
278	.TP
279	.BR \-dv
280	Boolean switch for light source visibility.
281	With this switch off, sources will be black when viewed directly
282	although they will still participate in the direct calculation.
283	This option is mostly for the program
284	.I mkillum(1)
285	to avoid inappropriate counting of light sources, but it
286	may also be desirable in conjunction with the
287	.I \-i
288	option.
289	.TP
290	.BI -sj \ frac
291	Set the specular sampling jitter to
292	.I frac.
293	This is the degree to which the highlights are sampled
294	for rough specular materials.
295	A value of one means that all highlights will be fully sampled
296	using distributed ray tracing.
297	A value of zero means that no jittering will take place, and all
298	reflections will appear sharp even when they should be diffuse.
299	.TP
300	.BI -st \ frac
301	Set the specular sampling threshold to
302	.I frac.
303	This is the minimum fraction of reflection or transmission, under which
304	no specular sampling is performed.
305	A value of zero means that highlights will always be sampled by
306	tracing reflected or transmitted rays.
307	A value of one means that specular sampling is never used.
308	Highlights from light sources will always be correct, but
309	reflections from other surfaces will be approximated using an
310	ambient value.
311	A sampling threshold between zero and one offers a compromise between image
312	accuracy and rendering time.
313	.TP
314	.BR -bv
315	Boolean switch for back face visibility.
316	With this switch off, back faces of opaque objects will be invisible
317	to all rays.
318	This is dangerous unless the model was constructed such that
319	all surface normals on opaque objects face outward.
320	Although turning off back face visibility does not save much
321	computation time under most circumstances, it may be useful as a
322	tool for scene debugging, or for seeing through one-sided walls from
323	the outside.
324	This option has no effect on transparent or translucent materials.
325	.TP
326	.BI -av " red grn blu"
327	Set the ambient value to a radiance of
328	.I "red grn blu".
329	This is the final value used in place of an
330	indirect light calculation.
331	If the number of ambient bounces is one or greater and the ambient
332	value weight is non-zero (see
333	.I -aw
334	and
335	.I -ab
336	below), this value may be modified by the computed indirect values
337	to improve overall accuracy.
338	.TP
339	.BI -aw \ N
340	Set the relative weight of the ambient value given with the
341	.I -av
342	option to
343	.I N.
344	As new indirect irradiances are computed, they will modify the
345	default ambient value in a moving average, with the specified weight
346	assigned to the initial value given on the command and all other
347	weights set to 1.
348	If a value of 0 is given with this option, then the initial ambient
349	value is never modified.
350	This is the safest value for scenes with large differences in
351	indirect contributions, such as when both indoor and outdoor
352	(daylight) areas are visible.
353	.TP
354	.BI -ab \ N
355	Set the number of ambient bounces to
356	.I N.
357	This is the maximum number of diffuse bounces
358	computed by the indirect calculation.
359	A value of zero implies no indirect calculation.
360	.TP
361	.BI -ar \ res
362	Set the ambient resolution to
363	.I res.
364	This number will determine the maximum density of ambient values
365	used in interpolation.
366	Error will start to increase on surfaces spaced closer than
367	the scene size divided by the ambient resolution.
368	The maximum ambient value density is the scene size times the
369	ambient accuracy (see the
370	.I \-aa
371	option below) divided by the ambient resolution.
372	The scene size can be determined using
373	.I getinfo(1)
374	with the
375	.I \-d
376	option on the input octree.
377	.TP
378	.BI -aa \ acc
379	Set the ambient accuracy to
380	.I acc.
381	This value will approximately equal the error
382	from indirect illuminance interpolation.
383	A value of zero implies no interpolation.
384	.TP
385	.BI -ad \ N
386	Set the number of ambient divisions to
387	.I N.
388	The error in the Monte Carlo calculation of indirect
389	illuminance will be inversely proportional to the square
390	root of this number.
391	A value of zero implies no indirect calculation.
392	.TP
393	.BI -as \ N
394	Set the number of ambient super-samples to
395	.I N.
396	Super-samples are applied only to the ambient divisions which
397	show a significant change.
398	.TP
399	.BI -af \ fname
400	Set the ambient file to
401	.I fname.
402	This is where indirect illuminance will be stored and retrieved.
403	Normally, indirect illuminance values are kept in memory and
404	lost when the program finishes or dies.
405	By using a file, different invocations can share illuminance
406	values, saving time in the computation.
407	The ambient file is in a machine-independent binary format
408	which can be examined with
409	.I lookamb(1).
410	.IP
411	The ambient file may also be used as a means of communication and
412	data sharing between simultaneously executing processes.
413	The same file may be used by multiple processes, possibly running on
414	different machines and accessing the file via the network (ie.
415	.I nfs(4)).
416	The network lock manager
417	.I lockd(8)
418	is used to insure that this information is used consistently.
419	.IP
420	If any calculation parameters are changed or the scene
421	is modified, the old ambient file should be removed so that
422	the calculation can start over from scratch.
423	For convenience, the original ambient parameters are listed in the
424	header of the ambient file.
425	.I Getinfo(1)
426	may be used to print out this information.
427	.TP
428	.BI -ae \ mat
429	Append
430	.I mat
431	to the ambient exclude list,
432	so that it will not be considered during the indirect calculation.
433	This is a hack for speeding the indirect computation by
434	ignoring certain objects.
435	Any object having
436	.I mat
437	as its modifier will get the default ambient
438	level rather than a calculated value.
439	Any number of excluded materials may be given, but each
440	must appear in a separate option.
441	.TP
442	.BI -ai \ mat
443	Add
444	.I mat
445	to the ambient include list,
446	so that it will be considered during the indirect calculation.
447	The program can use either an include list or an exclude
448	list, but not both.
449	.TP
450	.BI -aE \ file
451	Same as
452	.I \-ae,
453	except read materials to be excluded from
454	.I file.
455	The RAYPATH environment variable determines which directories are
456	searched for this file.
457	The material names are separated by white space in the file.
458	.TP
459	.BI -aI \ file
460	Same as
461	.I \-ai,
462	except read materials to be included from
463	.I file.
464	.TP
465	.BI -me " rext gext bext"
466	Set the global medium extinction coefficient to the indicated color,
467	in units of 1/distance (distance in world coordinates).
468	Light will be scattered or absorbed over distance according to
469	this value.
470	The ratio of scattering to total scattering plus absorption is set
471	by the albedo parameter, described below.
472	.TP
473	.BI -ma " ralb galb balb"
474	Set the global medium albedo to the given value between 0\00\00
475	and 1\01\01.
476	A zero value means that all light not transmitted by the medium
477	is absorbed.
478	A unitary value means that all light not transmitted by the medium
479	is scattered in some new direction.
480	The isotropy of scattering is determined by the Heyney-Greenstein
481	parameter, described below.
482	.TP
483	.BI \-mg \ gecc
484	Set the medium Heyney-Greenstein eccentricity parameter to
485	.I gecc.
486	This parameter determines how strongly scattering favors the forward
487	direction.
488	A value of 0 indicates perfectly isotropic scattering.
489	As this parameter approaches 1, scattering tends to prefer the
490	forward direction.
491	.TP
492	.BI \-ms \ sampdist
493	Set the medium sampling distance to
494	.I sampdist,
495	in world coordinate units.
496	During source scattering, this will be the average distance between
497	adjacent samples.
498	A value of 0 means that only one sample will be taken per light
499	source within a given scattering volume.
500	.TP
501	.BI -lr \ N
502	Limit reflections to a maximum of
503	.I N.
504	.TP
505	.BI -lw \ frac
506	Limit the weight of each ray to a minimum of
507	.I frac.
508	During ray-tracing, a record is kept of the final contribution
509	a ray would have to the image.
510	If it is less then the specified minimum, the ray is not traced.
511	.TP
512	.BR -ld
513	Boolean switch to limit ray distance.
514	If this option is set, then rays will only be traced as far as the
515	magnitude of each direction vector.
516	Otherwise, vector magnitude is ignored and rays are traced to infinity.
517	.TP
518	.BI -e \ efile
519	Send error messages and progress reports to
520	.I efile
521	instead of the standard error.
522	.TP
523	.BR \-w
524	Boolean switch to suppress warning messages.
525	.TP
526	.BI \-P \ pfile
527	Execute in a persistent mode, using
528	.I pfile
529	as the control file.
530	Persistent execution means that after reaching end-of-file on
531	its input,
532	.I rtrace
533	will fork a child process that will wait for another
534	.I rtrace
535	command with the same
536	.I \-P
537	option to attach to it.
538	(Note that since the rest of the command line options will be those
539	of the original invocation, it is not necessary to give any arguments
540	besides
541	.I \-P
542	for subsequent calls.)
543	Killing the process is achieved with the
544	.I kill(1)
545	command.
546	(The process ID in the first line of
547	.I pfile
548	may be used to identify the waiting
549	.I rtrace
550	process.)
551	This option may be used with the
552	.I \-fr
553	option of
554	.I pinterp(1)
555	to avoid the cost of starting up
556	.I rtrace
557	many times.
558	.TP
559	.BI \-PP \ pfile
560	Execute in continuous-forking persistent mode, using
561	.I pfile
562	as the control file.
563	The difference between this option and the
564	.I \-P
565	option described above is the creation of multiple duplicate
566	processes to handle any number of attaches.
567	This provides a simple and reliable mechanism of memory sharing
568	on most multiprocessing platforms, since the
569	.I fork(2)
570	system call will share memory on a copy-on-write basis.
571	.SH EXAMPLES
572	To compute radiance values for the rays listed in samples.inp:
573	.IP "" .2i
574	rtrace -ov scene.oct < samples.inp > radiance.out
575	.PP
576	To compute illuminance values at locations selected with the 't'
577	command of
578	.I ximage(1):
579	.IP "" .2i
580	ximage scene.pic \| rtrace -h -x 1 -i scene.oct \| rcalc -e '$1=47.4$1+120$2+11.6*$3'
581	.PP
582	To record the object identifier corresponding to each pixel in an image:
583	.IP "" .2i
584	vwrays -fd scene.pic \| rtrace -fda `vwrays -d scene.pic` -os scene.oct
585	.PP
586	To compute an image with an unusual view mapping:
587	.IP "" .2i
588	cnt 640 480 \| rcalc -e 'xr:640;yr:480' -f unusual_view.cal \| rtrace
589	-x 640 -y 480 -fac scene.oct > unusual.pic
590	.SH ENVIRONMENT
591	RAYPATH the directories to check for auxiliary files.
592	.SH FILES
593	/usr/tmp/rtXXXXXX common header information for picture sequence
594	.SH DIAGNOSTICS
595	If the program terminates from an input related error, the exit status
596	will be 1.
597	A system related error results in an exit status of 2.
598	If the program receives a signal that is caught, it will exit with a status
599	of 3.
600	In each case, an error message will be printed to the standard error, or
601	to the file designated by the
602	.I \-e
603	option.
604	.SH AUTHOR
605	Greg Ward
606	.SH "SEE ALSO"
607	getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1),
608	pvalue(1), rpict(1), rview(1), vwrays(1), ximage(1)