NAME
rtcontrib - compute contribution coefficients in a RADIANCE scene
SYNOPSIS
rtcontrib [ -n nprocs ][ -V ][ -c count ][ -fo | -r ][ -e expr ][ -f
source ][ -o ospec ][ -b binv ][ -bn nbins ] { -m mod | -M file } [
$EVAR ] [ @file ] [ rtrace options ] octree
rtcontrib [ options ] -defaults
DESCRIPTION
Rtcontrib computes ray coefficients for objects whose modifiers are
named in one or more -m settings. These modifiers are usually
materials associated with light sources or sky domes, and must directly
modify some geometric primitives to be considered in the output. A
modifier list may also be read from a file using the -M option. The
RAYPATH environment variable determines directories to search for this
file. (No search takes place if a file name begins with a ’.’, ’/’ or
’~’ character.)
If the -n option is specified with a value greater than 1, multiple
rtrace processes will be used to accelerate computation on a shared
memory machine. Note that there is no benefit to using more processes
than there are local CPUs available to do the work, and the rtcontrib
process itself may use a considerable amount of CPU time.
By setting the boolean -V option, you may instruct rtcontrib to report
the contribution from each material rather than the ray coefficient.
This is particularly useful for light sources with directional output
distributions, whose value would otherwise be lost in the shuffle.
With the default -V- setting, the output of rtcontrib is a coefficient
that must be multiplied by the radiance of each material to arrive at a
final contribution. This is more convenient for computing daylight
coefficeints, or cases where the actual radiance is not desired. Use
the -V+ setting when you wish to simply sum together contributions
(with possible adjustment factors) to obtain a final radiance value.
Combined with the -i or -I option, irradiance contributions are
reported by -V+ rather than radiance, and -V- coefficients contain an
additonal factor of PI.
The -c option tells rtcontrib how many rays to accumulate for each
record. The default value is 1, meaning a full record will be produced
for each input ray. For values greater than 1, contributions will be
averaged together over the given number of input rays. If set to zero,
only a single record will be produced at the very end, corresponding to
the sum of all rays given on the input (rather than the average). This
is equivalent to passing all the output records through a program like
total(1) to sum RGB values together, but is much more efficient. Using
this option, it is possible to reverse sampling, sending rays from a
parallel source such as the sun to a diffuse surface, for example.
Note that output flushing via zero-direction rays is disabled for
accumulated evaluations.
The output of rtcontrib has many potential uses. Source contributions
can be used as components in linear combination to reproduce any
desired variation, e.g., simulating lighting controls or changing sky
conditions via daylight coefficients. More generally, rtcontrib can be
used to compute arbitrary input-output relationships in optical
systems, such as luminaires, light pipes, and shading devices.
Rtcontrib calls rtrace(1) with the -oTW (or -oTV) option to calculate
the daughter ray contributions for each input ray, and the output
tallies are sent to one or more destinations according to the given -o
specification. If a destination begins with an exclamation mark (’!’),
then a pipe is opened to a command and data is sent to its standard
input. Otherwise, the destination is treated as a file. An existing
file of the same name will not be clobbered, unless the -fo option is
given. If instead the -r option is specified, data recovery is
attempted on existing files. (If -c 0 is used together with the -r
option, existing files are read in and new ray evaluations are added to
the previous results, providing a convenient means for progressive
simulation.) If an output specification contains a "%s" format, this
will be replaced by the modifier name. The -b option may be used to
further define a "bin number" within each object if finer resolution is
needed, and this will be applied to a "%d" format in the output file
specification if present. The actual bin number is computed at run
time based on ray direction and surface intersection, as described
below. If the number of bins is known in advance, it should be
specified with the -bn option, and this is critical for output files
containing multiple values per record. A variable or constant name may
be given for this parameter if it has been defined via a previous -f or
-e option. Since bin numbers start from 0, the bin count is always
equal to the last bin plus 1. Set the this value to 0 if the bin count
is unknown (the default). The most recent -b, -bn and -o options to
the left of each -m setting are the ones used for that modifier. The
ordering of other options is unimportant, except for -x and -y if the
-c is 0, when they control the resolution string produced in the
corresponding output.
If a -b expression is defined for a particular modifier, the bin number
will be evaluated at run time for each ray contribution from rtrace.
Specifically, each ray’s world intersection point will be assigned to
the variables Px, Py, and Pz, and the normalized ray direction will be
assigned to Dx, Dy, and Dz. These parameters may be combined with
definitions given in -e arguments and files read using the -f option.
The computed bin value will be rounded to the nearest whole number.
This mechanism allows the user to define precise regions or directions
they wish to accumulate, such as the Tregenza sky discretization, which
would be otherwise impossible to specify as a set of RADIANCE
primitives. The rules and predefined functions available for these
expressions are described in the rcalc(1) man page. Unlike rcalc,
rtcontrib will search the RADIANCE library directories for each file
given in a -f option.
If no -o specification is given, results are written on the standard
output in order of modifier (as given on the command line) then bin
number. Concatenated data is also sent to a single destination (i.e.,
an initial -o specification without formatting strings). If a "%s"
format appears but no "%d" in the -o specification, then each modifier
will have its own output file, with multiple values per record in the
case of a non-zero -b definition. If a "%d" format appears but no
"%s", then each bin will get its own output file, with modifiers output
in order in each record. For text output, each RGB coefficient triple
is separated by a tab, with a newline at the end of each ray record.
For binary output formats, there is no such delimiter to mark the end
of each record.
Input and output format defaults to plain text, where each ray’s origin
and direction (6 real values) are given on input, and one line is
produced per output file per ray. Alternative data representations may
be specified by the -f[io] option, which is described in the rtrace man
page along with the associated -x and -y resolution settings. In
particular, the color (’c’) output data representation together with
positive dimensions for -x and -y will produce an uncompressed RADIANCE
picture, suitable for manipulation with pcomb(1) and related tools.
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.
EXAMPLES
To compute the proportional contributions from sources modified by
"light1" vs. "light2" on a set of illuminance values:
rtcontrib -I+ @render.opt -o c_%s.dat -m light1 -m light2 scene.oct <
test.dat
To generate a pair of images corresponding to these two lights’
contributions:
vwrays -ff -x 1024 -y 1024 -vf best.vf | rtcontrib -ffc ‘vwrays -d -x
1024 -y 1024 -vf best.vf‘ @render.opt -o c_%s.hdr -m light1 -m light2
scene.oct
These images may then be recombined using the desired outputs of light1
and light2:
pcomb -c 100 90 75 c_light1.hdr -c 50 55 57 c_light2.hdr >
combined.hdr
To compute an array of illuminance contributions according to a
Tregenza sky:
rtcontrib -I+ -b tbin -o sky.dat -m skyglow -b 0 -o ground.dat -m
groundglow @render.opt -f tregenza.cal scene.oct < test.dat
ENVIRONMENT
RAYPATH path to search for -f and -M files
AUTHOR
Greg Ward
SEE ALSO
cnt(1), genklemsamp(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1),
rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1)