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*$3'
.PP
To record the object identifier corresponding to each pixel in an image:
.IP "" .2i
vwrays -fd scene.pic | rtrace -fda `vwrays -d scene.pic` -os scene.oct
.PP
To compute an image with an unusual view mapping:
.IP "" .2i
cnt 640 480 | rcalc -e 'xr:640;yr:480' -f unusual_view.cal | rtrace
-x 640 -y 480 -fac scene.oct > unusual.pic
.SH ENVIRONMENT
RAYPATH         the directories to check for auxiliary files.
.SH FILES
/usr/tmp/rtXXXXXX               common header information for picture sequence
.SH DIAGNOSTICS
If the program terminates from an input related error, the exit status
will be 1.
A system related error results in an exit status of 2.
If the program receives a signal that is caught, it will exit with a status
of 3.
In each case, an error message will be printed to the standard error, or
to the file designated by the
.I \-e
option.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1),
pvalue(1), rpict(1), rvu(1), vwrays(1), ximage(1)
Revision:	1.4
Committed:	Thu Jan 1 19:31:45 2004 UTC (20 years, 4 months ago) by greg
Branch:	MAIN
CVS Tags:	rad3R6, rad3R6P1
Changes since 1.3:	+2 -2 lines
Log Message:	Renamed rview, lam, calc, and neat to rvu, rlam, icalc, and neaten
#	Content
1	.\" RCSid "$Id: rtrace.1,v 1.3 2003/12/09 15:59:07 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	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	pvalue(1), rpict(1), rvu(1), vwrays(1), ximage(1)