NAME
rtrace - trace rays in RADIANCE scene
SYNOPSIS
rtrace [ options ] [ $EVAR ] [ @file ] octree
rtrace [ options ] -defaults
DESCRIPTION
Rtrace traces rays from the standard input through the RADIANCE scene
given by octree and sends the results to the standard output. (The
octree may be given as the output of a command enclosed in quotes and
preceded by a ‘!’.) Input for each ray is:
xorg yorg zorg xdir ydir zdir
If the direction vector is (0,0,0), a bogus record is printed and the
output is flushed if the -x value is unset or zero. (See the notes on
this option below.) This may be useful for programs that run rtrace as
a separate process. In the second form, the default values for the
options (modified by those options present) are printed with a brief
explanation.
Options may be given on the command line and/or read from the
environment and/or read from a file. A command argument beginning with
a dollar sign (’$’) 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.
-fio Format input according to the character i and output
according to the character o. 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 (-ov
option, below). If the output character is missing, the
input format is used.
Note that there is no space between this option and its
argument.
-ospec Produce output fields according to spec. Characters are
interpreted as follows:
o origin (input)
d direction (normalized)
v value (radiance)
V contribution (radiance)
w weight
W color coefficient
l effective length of ray
L first intersection distance
c local (u,v) coordinates
p point of intersection
n normal at intersection (perturbed)
N normal at intersection (unperturbed)
s surface name
m modifier name
M material name
~ tilde (end of trace marker)
If the letter ’t’ appears in spec, then the fields following
will be printed for every ray traced, not just the final
result. If the capital letter ’T’ is given instead of ’t’,
then all rays will be reported, including shadow testing rays
to light sources. Spawned rays are indented one tab for each
level. The tilde marker (’~’) is a handy way of
differentiating the final ray value from daughter values in a
traced ray tree, and usually appears right before the ’t’ or
’T’ output flags. E.g., -ov~TmW will emit a tilde followed
by a tab at the end of each trace, which can be easily
distinguished even in binary output.
Note that there is no space between this option and its
argument.
-te mod Append mod to the trace exclude list, so that it will not be
reported by the trace option (-o*t*). Any ray striking an
object having 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 either the ’t’ or ’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.
-ti mod Add mod to the trace include list, so that it will be
reported by the trace option. The program can use either an
include list or an exclude list, but not both.
-tE file Same as -te, except read modifiers to be excluded from file.
The RAYPATH environment variable determines which directories
are searched for this file. The modifier names are separated
by white space in the file.
-tI file Same as -ti, except read modifiers to be included from file.
-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 -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.
-u Boolean switch to control uncorrelated random sampling. When
"off", a low-discrepancy sequence is used, which reduces
variance but can result in a brushed appearance in specular
highlights. When "on", pure Monte Carlo sampling is used in
all calculations.
-I Boolean switch to compute irradiance rather than radiance,
with the input origin and direction interpreted instead as
measurement point and orientation.
-h Boolean switch for information header on output.
-x res Set the x resolution to res. The output will be flushed
after every res input rays. A value of zero means that no
output flushing will take place.
-y res Set the y resolution to res. The program will exit after res
scanlines have been processed, where a scanline is the number
of rays given by the -x option, or 1 if -x is zero. A value
of zero means the program will not halt until the end of file
is reached.
If both -x and -y options are given, a resolution string is
printed at the beginning of the output. This is mostly
useful for recovering image dimensions with pvalue(1), and
for creating valid Radiance picture files using the color
output format. (See the -f option, above.)
-n nproc Execute in parallel on nproc local processes. This option is
incompatible with the -P and -PP, options. Multiple
processes also do not work properly with ray tree output
using any of the -o*t* options. There is no benefit from
specifying more processes than there are cores available on
the system or the -x setting, which forces a wait at each
flush.
-dj frac Set the direct jittering to frac. A value of zero samples
each source at specific sample points (see the -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 frac is too large.
-ds frac Set the direct sampling ratio to 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.
-dt frac Set the direct threshold to 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 -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.
-dc frac Set the direct certainty to 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 -dt specification.
A value of zero only insures that all shadow lines resulting
in a contrast change greater than the -dt specification will
be calculated.
-dr N Set the number of relays for secondary sources to 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.
-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.
-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 mkillum(1) to avoid
inappropriate counting of light sources, but it may also be
desirable in conjunction with the -i option.
-sj frac Set the specular sampling jitter to 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.
-st frac Set the specular sampling threshold to 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.
-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.
-av red grn blu
Set the ambient value to a radiance of 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 -aw and
-ab below), this value may be modified by the computed
indirect values to improve overall accuracy.
-aw N Set the relative weight of the ambient value given with the
-av option to 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.
-ab N Set the number of ambient bounces to N. This is the maximum
number of diffuse bounces computed by the indirect
calculation. A value of zero implies no indirect
calculation.
-ar res Set the ambient resolution to 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 -aa option below)
divided by the ambient resolution. The scene size can be
determined using getinfo(1) with the -d option on the input
octree.
-aa acc Set the ambient accuracy to acc. This value will
approximately equal the error from indirect illuminance
interpolation. A value of zero implies no interpolation.
-ad N Set the number of ambient divisions to 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.
-as N Set the number of ambient super-samples to N. Super-samples
are applied only to the ambient divisions which show a
significant change.
-af fname Set the ambient file to 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 lookamb(1).
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. nfs(4)). The network lock manager lockd(8) is
used to insure that this information is used consistently.
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. Getinfo(1) may be used to print out this
information.
-ae mod Append 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 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.
-ai mod Add 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.
-aE file Same as -ae, except read modifiers to be excluded from file.
The RAYPATH environment variable determines which directories
are searched for this file. The modifier names are separated
by white space in the file.
-aI file Same as -ai, except read modifiers to be included from file.
-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.
-ma ralb galb balb
Set the global medium albedo to the given value between 0 0 0
and 1 1 1. 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.
-mg gecc Set the medium Heyney-Greenstein eccentricity parameter to
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.
-ms sampdist
Set the medium sampling distance to 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.
-lr N Limit reflections to a maximum of N, if N is a positive
integer. If N is zero or negative, then Russian roulette is
used for ray termination, and the -lw setting (below) must be
positive. If N is a negative integer, then this sets the
upper limit of reflections past which Russian roulette will
be used. In scenes with dielectrics and total internal
reflection, a setting of 0 (no limit) may cause a stack
overflow.
-lw frac Limit the weight of each ray to a minimum of frac. During
ray-tracing, a record is kept of the estimated contribution
(weight) a ray would have in the image. If this weight is
less than the specified minimum and the -lr setting (above)
is positive, the ray is not traced. Otherwise, Russian
roulette is used to continue rays with a probability equal to
the ray weight divided by the given frac.
-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.
-e efile Send error messages and progress reports to efile instead of
the standard error.
-w Boolean switch to suppress warning messages.
-P pfile Execute in a persistent mode, using pfile as the control
file. Persistent execution means that after reaching end-of-
file on its input, rtrace will fork a child process that will
wait for another rtrace command with the same -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 -P for subsequent
calls.) Killing the process is achieved with the kill(1)
command. (The process ID in the first line of pfile may be
used to identify the waiting rtrace process.) This option
may be used with the -fr option of pinterp(1) to avoid the
cost of starting up rtrace many times.
-PP pfile Execute in continuous-forking persistent mode, using pfile as
the control file. The difference between this option and the
-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 fork(2) system call
will share memory on a copy-on-write basis.
EXAMPLES
To compute radiance values for the rays listed in samples.inp:
rtrace -ov scene.oct < samples.inp > radiance.out
To compute illuminance values at locations selected with the ’t’
command of ximage(1):
ximage scene.hdr | rtrace -h -x 1 -i scene.oct | rcalc -e
’$1=47.4*$1+120*$2+11.6*$3’
To record the object identifier corresponding to each pixel in an
image:
vwrays -fd scene.hdr | rtrace -fda ‘vwrays -d scene.hdr‘ -os
scene.oct
To compute an image with an unusual view mapping:
cnt 480 640 | rcalc -e ’xr:640;yr:480’ -f unusual_view.cal | rtrace
-x 640 -y 480 -fac scene.oct > unusual.hdr
ENVIRONMENT
RAYPATH the directories to check for auxiliary files.
FILES
/tmp/rtXXXXXX common header information for picture sequence
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 -e option.
AUTHOR
Greg Ward
SEE ALSO
getinfo(1), lookamb(1), oconv(1), pfilt(1), pinterp(1), pvalue(1),
rpict(1), rtcontrib(1), rvu(1), vwrays(1), ximage(1)