man/man1/rtrace.1

.\" RCSid "$Id: rtrace.1,v 1.5 2005/02/16 05:40:07 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
M       material 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 \ mod
Append
.I mod
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 mod
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 modifiers may be given, but each
must appear in a separate option.
.TP
.BI -ti \ mod
Add
.I mod
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 modifiers to be excluded from
.I file.
The RAYPATH environment variable determines which directories are
searched for this file.
The modifier names are separated by white space in the file.
.TP
.BI -tI \ file
Same as
.I \-ti,
except read modifiers 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 \ mod
Append
.I mod
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 mod
as its modifier will get the default ambient
level rather than a calculated value.
Any number of excluded modifiers may be given, but each
must appear in a separate option.
.TP
.BI -ai \ mod
Add
.I mod
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 modifiers to be excluded from
.I file.
The RAYPATH environment variable determines which directories are
searched for this file.
The modifier names are separated by white space in the file.
.TP
.BI -aI \ file
Same as
.I \-ai,
except read modifiers 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*$3'
.PP
To record the object identifier corresponding to each pixel in an image:
.IP "" .2i
vwrays -fd scene.pic | rtrace -fda `vwrays -d scene.pic` -os scene.oct
.PP
To compute an image with an unusual view mapping:
.IP "" .2i
cnt 640 480 | rcalc -e 'xr:640;yr:480' -f unusual_view.cal | rtrace
-x 640 -y 480 -fac scene.oct > unusual.pic
.SH ENVIRONMENT
RAYPATH         the directories to check for auxiliary files.
.SH FILES
/tmp/rtXXXXXX           common header information for picture sequence
.SH DIAGNOSTICS
If the program terminates from an input related error, the exit status
will be 1.
A system related error results in an exit status of 2.
If the program receives a signal that is caught, it will exit with a status
of 3.
In each case, an error message will be printed to the standard error, or
to the file designated by the
.I \-e
option.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1),
pvalue(1), rpict(1), rvu(1), vwrays(1), ximage(1)
Revision:	1.6
Committed:	Thu Apr 14 18:04:12 2005 UTC (19 years, 1 month ago) by greg
Branch:	MAIN
Changes since 1.5:	+21 -19 lines
Log Message:	Added -oM option to rtrace to output material
#	Content
1	.\" RCSid "$Id: rtrace.1,v 1.5 2005/02/16 05:40:07 greg Exp $"
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	c local (u,v) coordinates
97	.IP
98	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	M material name
109	.IP
110	If the letter 't' appears in
111	.I spec,
112	then the fields following will be printed for every ray traced,
113	not just the final result.
114	Spawned rays are indented one tab for each level.
115	.IP
116	Note that there is no space between this option and its argument.
117	.TP
118	.BI -te \ mod
119	Append
120	.I mod
121	to the trace exclude list,
122	so that it will not be reported by the trace option
123	.I (\-ot).
124	Any ray striking an object having
125	.I mod
126	as its modifier will not be reported to the standard output with
127	the rest of the rays being traced.
128	This option has no effect unless the 't' option has been given as
129	part of the output specifier.
130	Any number of excluded modifiers may be given, but each
131	must appear in a separate option.
132	.TP
133	.BI -ti \ mod
134	Add
135	.I mod
136	to the trace include list,
137	so that it will be considered during the indirect calculation.
138	The program can use either an include list or an exclude
139	list, but not both.
140	.TP
141	.BI -tE \ file
142	Same as
143	.I \-te,
144	except read modifiers to be excluded from
145	.I file.
146	The RAYPATH environment variable determines which directories are
147	searched for this file.
148	The modifier names are separated by white space in the file.
149	.TP
150	.BI -tI \ file
151	Same as
152	.I \-ti,
153	except read modifiers to be included from
154	.I file.
155	.TP
156	.BR \-i
157	Boolean switch to compute irradiance rather than radiance values.
158	This only affects the final result, substituting a Lambertian
159	surface and multiplying the radiance by pi.
160	Glass and other transparent surfaces are ignored during this stage.
161	Light sources still appear with their original radiance values,
162	though the
163	.I \-dv
164	option (below) may be used to override this.
165	This option is especially useful in
166	conjunction with ximage(1) for computing illuminance at scene points.
167	.TP
168	.BR \-I
169	Boolean switch to compute irradiance rather than radiance,
170	with the input origin and direction interpreted instead
171	as measurement point and orientation.
172	.TP
173	.BR \-h
174	Boolean switch for information header on output.
175	.TP
176	.BI -x \ res
177	Set the x resolution to
178	.I res.
179	The output will be flushed after every
180	.I res
181	input rays.
182	A value of zero means that no output flushing will take place.
183	.TP
184	.BI -y \ res
185	Set the y resolution to
186	.I res.
187	The program will exit after
188	.I res
189	scanlines have been processed, where a scanline is the number of rays
190	given by the
191	.I \-x
192	option, or 1 if
193	.I \-x
194	is zero.
195	A value of zero means the program will not halt until the end
196	of file is reached.
197	.IP
198	If both
199	.I \-x
200	and
201	.I \-y
202	options are given, a resolution string is printed at the beginning
203	of the output.
204	This is mostly useful for recovering image dimensions with
205	.I pvalue(1),
206	and for creating valid Radiance picture files using the color output
207	format.
208	(See the
209	.I \-f
210	option, above.)
211	.TP
212	.BI -dj \ frac
213	Set the direct jittering to
214	.I frac.
215	A value of zero samples each source at specific sample points
216	(see the
217	.I \-ds
218	option below), giving a smoother but somewhat less accurate
219	rendering.
220	A positive value causes rays to be distributed over each
221	source sample according to its size, resulting in more accurate
222	penumbras.
223	This option should never be greater than 1, and may even
224	cause problems (such as speckle) when the value is smaller.
225	A warning about aiming failure will issued if
226	.I frac
227	is too large.
228	.TP
229	.BI -ds \ frac
230	Set the direct sampling ratio to
231	.I frac.
232	A light source will be subdivided until
233	the width of each sample area divided by the distance
234	to the illuminated point is below this ratio.
235	This assures accuracy in regions close to large area sources
236	at a slight computational expense.
237	A value of zero turns source subdivision off, sending at most one
238	shadow ray to each light source.
239	.TP
240	.BI -dt \ frac
241	Set the direct threshold to
242	.I frac.
243	Shadow testing will stop when the potential contribution of at least
244	the next and at most all remaining light sources is less than
245	this fraction of the accumulated value.
246	(See the
247	.I \-dc
248	option below.)
249	The remaining light source contributions are approximated
250	statistically.
251	A value of zero means that all light sources will be tested for shadow.
252	.TP
253	.BI \-dc \ frac
254	Set the direct certainty to
255	.I frac.
256	A value of one guarantees that the absolute accuracy of the direct calculation
257	will be equal to or better than that given in the
258	.I \-dt
259	specification.
260	A value of zero only insures that all shadow lines resulting in a contrast
261	change greater than the
262	.I \-dt
263	specification will be calculated.
264	.TP
265	.BI -dr \ N
266	Set the number of relays for secondary sources to
267	.I N.
268	A value of 0 means that secondary sources will be ignored.
269	A value of 1 means that sources will be made into first generation
270	secondary sources; a value of 2 means that first generation
271	secondary sources will also be made into second generation secondary
272	sources, and so on.
273	.TP
274	.BI -dp \ D
275	Set the secondary source presampling density to D.
276	This is the number of samples per steradian
277	that will be used to determine ahead of time whether or not
278	it is worth following shadow rays through all the reflections and/or
279	transmissions associated with a secondary source path.
280	A value of 0 means that the full secondary source path will always
281	be tested for shadows if it is tested at all.
282	.TP
283	.BR \-dv
284	Boolean switch for light source visibility.
285	With this switch off, sources will be black when viewed directly
286	although they will still participate in the direct calculation.
287	This option is mostly for the program
288	.I mkillum(1)
289	to avoid inappropriate counting of light sources, but it
290	may also be desirable in conjunction with the
291	.I \-i
292	option.
293	.TP
294	.BI -sj \ frac
295	Set the specular sampling jitter to
296	.I frac.
297	This is the degree to which the highlights are sampled
298	for rough specular materials.
299	A value of one means that all highlights will be fully sampled
300	using distributed ray tracing.
301	A value of zero means that no jittering will take place, and all
302	reflections will appear sharp even when they should be diffuse.
303	.TP
304	.BI -st \ frac
305	Set the specular sampling threshold to
306	.I frac.
307	This is the minimum fraction of reflection or transmission, under which
308	no specular sampling is performed.
309	A value of zero means that highlights will always be sampled by
310	tracing reflected or transmitted rays.
311	A value of one means that specular sampling is never used.
312	Highlights from light sources will always be correct, but
313	reflections from other surfaces will be approximated using an
314	ambient value.
315	A sampling threshold between zero and one offers a compromise between image
316	accuracy and rendering time.
317	.TP
318	.BR -bv
319	Boolean switch for back face visibility.
320	With this switch off, back faces of opaque objects will be invisible
321	to all rays.
322	This is dangerous unless the model was constructed such that
323	all surface normals on opaque objects face outward.
324	Although turning off back face visibility does not save much
325	computation time under most circumstances, it may be useful as a
326	tool for scene debugging, or for seeing through one-sided walls from
327	the outside.
328	This option has no effect on transparent or translucent materials.
329	.TP
330	.BI -av " red grn blu"
331	Set the ambient value to a radiance of
332	.I "red grn blu".
333	This is the final value used in place of an
334	indirect light calculation.
335	If the number of ambient bounces is one or greater and the ambient
336	value weight is non-zero (see
337	.I -aw
338	and
339	.I -ab
340	below), this value may be modified by the computed indirect values
341	to improve overall accuracy.
342	.TP
343	.BI -aw \ N
344	Set the relative weight of the ambient value given with the
345	.I -av
346	option to
347	.I N.
348	As new indirect irradiances are computed, they will modify the
349	default ambient value in a moving average, with the specified weight
350	assigned to the initial value given on the command and all other
351	weights set to 1.
352	If a value of 0 is given with this option, then the initial ambient
353	value is never modified.
354	This is the safest value for scenes with large differences in
355	indirect contributions, such as when both indoor and outdoor
356	(daylight) areas are visible.
357	.TP
358	.BI -ab \ N
359	Set the number of ambient bounces to
360	.I N.
361	This is the maximum number of diffuse bounces
362	computed by the indirect calculation.
363	A value of zero implies no indirect calculation.
364	.TP
365	.BI -ar \ res
366	Set the ambient resolution to
367	.I res.
368	This number will determine the maximum density of ambient values
369	used in interpolation.
370	Error will start to increase on surfaces spaced closer than
371	the scene size divided by the ambient resolution.
372	The maximum ambient value density is the scene size times the
373	ambient accuracy (see the
374	.I \-aa
375	option below) divided by the ambient resolution.
376	The scene size can be determined using
377	.I getinfo(1)
378	with the
379	.I \-d
380	option on the input octree.
381	.TP
382	.BI -aa \ acc
383	Set the ambient accuracy to
384	.I acc.
385	This value will approximately equal the error
386	from indirect illuminance interpolation.
387	A value of zero implies no interpolation.
388	.TP
389	.BI -ad \ N
390	Set the number of ambient divisions to
391	.I N.
392	The error in the Monte Carlo calculation of indirect
393	illuminance will be inversely proportional to the square
394	root of this number.
395	A value of zero implies no indirect calculation.
396	.TP
397	.BI -as \ N
398	Set the number of ambient super-samples to
399	.I N.
400	Super-samples are applied only to the ambient divisions which
401	show a significant change.
402	.TP
403	.BI -af \ fname
404	Set the ambient file to
405	.I fname.
406	This is where indirect illuminance will be stored and retrieved.
407	Normally, indirect illuminance values are kept in memory and
408	lost when the program finishes or dies.
409	By using a file, different invocations can share illuminance
410	values, saving time in the computation.
411	The ambient file is in a machine-independent binary format
412	which can be examined with
413	.I lookamb(1).
414	.IP
415	The ambient file may also be used as a means of communication and
416	data sharing between simultaneously executing processes.
417	The same file may be used by multiple processes, possibly running on
418	different machines and accessing the file via the network (ie.
419	.I nfs(4)).
420	The network lock manager
421	.I lockd(8)
422	is used to insure that this information is used consistently.
423	.IP
424	If any calculation parameters are changed or the scene
425	is modified, the old ambient file should be removed so that
426	the calculation can start over from scratch.
427	For convenience, the original ambient parameters are listed in the
428	header of the ambient file.
429	.I Getinfo(1)
430	may be used to print out this information.
431	.TP
432	.BI -ae \ mod
433	Append
434	.I mod
435	to the ambient exclude list,
436	so that it will not be considered during the indirect calculation.
437	This is a hack for speeding the indirect computation by
438	ignoring certain objects.
439	Any object having
440	.I mod
441	as its modifier will get the default ambient
442	level rather than a calculated value.
443	Any number of excluded modifiers may be given, but each
444	must appear in a separate option.
445	.TP
446	.BI -ai \ mod
447	Add
448	.I mod
449	to the ambient include list,
450	so that it will be considered during the indirect calculation.
451	The program can use either an include list or an exclude
452	list, but not both.
453	.TP
454	.BI -aE \ file
455	Same as
456	.I \-ae,
457	except read modifiers to be excluded from
458	.I file.
459	The RAYPATH environment variable determines which directories are
460	searched for this file.
461	The modifier names are separated by white space in the file.
462	.TP
463	.BI -aI \ file
464	Same as
465	.I \-ai,
466	except read modifiers to be included from
467	.I file.
468	.TP
469	.BI -me " rext gext bext"
470	Set the global medium extinction coefficient to the indicated color,
471	in units of 1/distance (distance in world coordinates).
472	Light will be scattered or absorbed over distance according to
473	this value.
474	The ratio of scattering to total scattering plus absorption is set
475	by the albedo parameter, described below.
476	.TP
477	.BI -ma " ralb galb balb"
478	Set the global medium albedo to the given value between 0\00\00
479	and 1\01\01.
480	A zero value means that all light not transmitted by the medium
481	is absorbed.
482	A unitary value means that all light not transmitted by the medium
483	is scattered in some new direction.
484	The isotropy of scattering is determined by the Heyney-Greenstein
485	parameter, described below.
486	.TP
487	.BI \-mg \ gecc
488	Set the medium Heyney-Greenstein eccentricity parameter to
489	.I gecc.
490	This parameter determines how strongly scattering favors the forward
491	direction.
492	A value of 0 indicates perfectly isotropic scattering.
493	As this parameter approaches 1, scattering tends to prefer the
494	forward direction.
495	.TP
496	.BI \-ms \ sampdist
497	Set the medium sampling distance to
498	.I sampdist,
499	in world coordinate units.
500	During source scattering, this will be the average distance between
501	adjacent samples.
502	A value of 0 means that only one sample will be taken per light
503	source within a given scattering volume.
504	.TP
505	.BI -lr \ N
506	Limit reflections to a maximum of
507	.I N.
508	.TP
509	.BI -lw \ frac
510	Limit the weight of each ray to a minimum of
511	.I frac.
512	During ray-tracing, a record is kept of the final contribution
513	a ray would have to the image.
514	If it is less then the specified minimum, the ray is not traced.
515	.TP
516	.BR -ld
517	Boolean switch to limit ray distance.
518	If this option is set, then rays will only be traced as far as the
519	magnitude of each direction vector.
520	Otherwise, vector magnitude is ignored and rays are traced to infinity.
521	.TP
522	.BI -e \ efile
523	Send error messages and progress reports to
524	.I efile
525	instead of the standard error.
526	.TP
527	.BR \-w
528	Boolean switch to suppress warning messages.
529	.TP
530	.BI \-P \ pfile
531	Execute in a persistent mode, using
532	.I pfile
533	as the control file.
534	Persistent execution means that after reaching end-of-file on
535	its input,
536	.I rtrace
537	will fork a child process that will wait for another
538	.I rtrace
539	command with the same
540	.I \-P
541	option to attach to it.
542	(Note that since the rest of the command line options will be those
543	of the original invocation, it is not necessary to give any arguments
544	besides
545	.I \-P
546	for subsequent calls.)
547	Killing the process is achieved with the
548	.I kill(1)
549	command.
550	(The process ID in the first line of
551	.I pfile
552	may be used to identify the waiting
553	.I rtrace
554	process.)
555	This option may be used with the
556	.I \-fr
557	option of
558	.I pinterp(1)
559	to avoid the cost of starting up
560	.I rtrace
561	many times.
562	.TP
563	.BI \-PP \ pfile
564	Execute in continuous-forking persistent mode, using
565	.I pfile
566	as the control file.
567	The difference between this option and the
568	.I \-P
569	option described above is the creation of multiple duplicate
570	processes to handle any number of attaches.
571	This provides a simple and reliable mechanism of memory sharing
572	on most multiprocessing platforms, since the
573	.I fork(2)
574	system call will share memory on a copy-on-write basis.
575	.SH EXAMPLES
576	To compute radiance values for the rays listed in samples.inp:
577	.IP "" .2i
578	rtrace -ov scene.oct < samples.inp > radiance.out
579	.PP
580	To compute illuminance values at locations selected with the 't'
581	command of
582	.I ximage(1):
583	.IP "" .2i
584	ximage scene.pic \| rtrace -h -x 1 -i scene.oct \| rcalc -e '$1=47.4$1+120$2+11.6*$3'
585	.PP
586	To record the object identifier corresponding to each pixel in an image:
587	.IP "" .2i
588	vwrays -fd scene.pic \| rtrace -fda `vwrays -d scene.pic` -os scene.oct
589	.PP
590	To compute an image with an unusual view mapping:
591	.IP "" .2i
592	cnt 640 480 \| rcalc -e 'xr:640;yr:480' -f unusual_view.cal \| rtrace
593	-x 640 -y 480 -fac scene.oct > unusual.pic
594	.SH ENVIRONMENT
595	RAYPATH the directories to check for auxiliary files.
596	.SH FILES
597	/tmp/rtXXXXXX common header information for picture sequence
598	.SH DIAGNOSTICS
599	If the program terminates from an input related error, the exit status
600	will be 1.
601	A system related error results in an exit status of 2.
602	If the program receives a signal that is caught, it will exit with a status
603	of 3.
604	In each case, an error message will be printed to the standard error, or
605	to the file designated by the
606	.I \-e
607	option.
608	.SH AUTHOR
609	Greg Ward
610	.SH "SEE ALSO"
611	getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1),
612	pvalue(1), rpict(1), rvu(1), vwrays(1), ximage(1)