xenial (1) rtcontrib.1.gz

Provided by: radiance_4R1+20120125-1.1_amd64 bug

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), rsensor(1),
       rtrace(1), total(1), vwrays(1), ximage(1)