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       mkillum - compute illum sources for a RADIANCE scene


       mkillum [ -n nprocs ][ rtrace options ] octree [ < file .. ]
       mkillum [ rtrace options ] -defaults


       Mkillum  takes  a prepared RADIANCE scene description and an octree and
       computes light source distributions for each  surface,  replacing  them
       with  secondary  sources  whose  contributions  can  be  computed  more
       efficiently by rpict(1) and rvu(1).  This type of optimization is  most
       useful  for  windows and skylights which represent concentrated sources
       of indirect illumination.  Mkillum is not appropriate  for  very  large
       sources  or  sources  with highly directional distributions.  These are
       best handled respectively by the ambient calculation and the  secondary
       source types in RADIANCE.

       If the -n option is specified with a value greater than 1, multiple ray
       tracing 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.

       Remaining arguments to mkillum are interpreted as rendering options for
       rtrace(1),  to  compute the light distributions for the input surfaces.
       These surfaces can be any combination of polygons, spheres  and  rings.
       Other  surfaces  may  be  included,  but  mkillum  cannot compute their

       By default, mkillum reads from its standard input  and  writes  to  its
       standard  output.   It is possible to specify multiple input files in a
       somewhat unconventional fashion by placing a lesser-than  symbol  (’<’)
       before  the file names.  (Note that this character must be escaped from
       most shells.)   This  is  necessary  so  mkillum  can  tell  where  the
       rendering arguments end and its own input files begin.


       Mkillum  has  a number of parameters that can be changed by comments in
       the input file of the form:

            #@mkillum variable=value option switch{+|-} ..

       String or integer variables are separated  from  their  values  by  the
       equals  sign  (’=’).   Options  appear  by  themselves.   Switches  are
       followed either by a plus sign to turn them on or a minus sign to  turn
       them off.

       Parameters are usually changed many times within the same input file to
       tailor the calculation,  specify  different  labels  and  so  on.   The
       parameters and their meanings are described below.

       o=string  Set  the  output  file  to string.  All subsequent scene data
                 will be sent to this file.  If  this  appears  in  the  first
                 comment  in  the  input, nothing will be sent to the standard
                 output.  Note that  this  is  not  recommended  when  running
                 mkillum  from  rad(1),  which expects the output to be on the
                 standard output.

       m=string  Set the material identifier to string.   This  name  will  be
                 used  not  only as the new surface modifier, but it will also
                 be used to name the distribution pattern and the data  files.
                 The distribution name will be string plus the suffix ".dist".
                 The data file will be named string plus possibly  an  integer
                 plus   a  ".dat"  suffix.   The  integer  is  used  to  avoid
                 accidently writing over an existing file.  If overwriting the
                 file is desired, use the f variable below.

       f=string  Set the data file name to string.  The next data file will be
                 given this name plus a ".dat" suffix.  Subsequent files  will
                 be  named  string plus an integer plus the ".dat" suffix.  An
                 existing file with the same name  will  be  clobbered.   This
                 variable  may  be  unset by leaving off the value.  (See also
                 the m variable above.)

       a         Produce secondary sources for all  of  the  surfaces  in  the
                 input.  This is the default.

       e=string  Produce  secondary  sources  for  all  surfaces  except those
                 modified by string.  Surfaces  modified  by  string  will  be
                 passed to the output unchanged.

       i=string  Only  produce  secondary  sources  for  surfaces  modified by

       n         Do not produce any secondary  sources.   All  input  will  be
                 passed  to  the  output  unaffected, except any void surfaces
                 will be removed.

       b=real    Do not produce a  secondary  source  for  a  surface  if  its
                 average brightness (radiance) is less than the value real.

       c={d|a|n} Use  color  information according to the given character.  If
                 the character is d, then color information will  be  used  in
                 three  separate data files and the distribution will be fully
                 characterized in terms of color.  If the character is a, then
                 only  the average color is computed and the distribution will
                 not contain color information.  If the character is  n,  even
                 the average distribution color will be thrown away, producing
                 secondary sources that are completely uncolored.  This may be
                 desirable from a color-balancing point of view.

       d=integer Set  the  number of direction samples per projected steradian
                 to  integer.   The  number  of  directions  stored   in   the
                 associated  data  file  will  be  approximately  this  number
                 multiplied by pi for polygons  and  rings,  and  by  4pi  for
                 spheres.   If  integer  is  zero,  then  a  diffuse source is
                 assumed and no distribution is created.

       d=string  Set  the  surface   Bidirectional   Scattering   Distribution
                 Function (BSDF) to the given file.  The RADIANCE library path
                 will be searched if the file does not begin with a ’.’ or ’~’
                 character.   This  file  must  contain  an  LBNL Window 6 XML
                 specification of a valid BSDF for the given surface, and  all
                 rays   will   be  interpreted  through  this  function.   The
                 orientation of the BSDF may be controlled with the u setting,
                 described  below.   The  thickness  of  the  surface  may  be
                 controlled with the t  setting.   If  this  variable  has  no
                 setting  or  an  integer is specified, mkillum returns to the
                 default  behavior  of  computing  the   output   distribution

       s=integer Set the number of ray samples per direction to integer.  This
                 variable affects the accuracy of the distribution  value  for
                 each direction as well as the computation time for mkillum.

       l{+|-}    Switch  between  light  sources  and  illum sources.  If this
                 switch is enabled (l+), mkillum will use  the  material  type
                 "light"  to  represent  surfaces.   If disabled (l-), mkillum
                 will use the material type "illum"  with  the  input  surface
                 modifier as its alternate material.  The default is l-.

                 The  given  axis  will be considered "up" for the purposes of
                 interpreting BSDF data specified with the  d  variable.   The
                 BSDF  will be reoriented relative to the surface as necessary
                 to keep the up vector in the  vertical  plane  that  contains
                 this axis and the surface normal, corresponding to an azimuth
                 of 90 degrees.  The default up vector is +Z.

       t=real    Set the surface thickness to real in world coordinates.  This
                 value  is  used for determining where to start rays that need
                 to begin on the opposite side of the surface, specifically to
                 compute  the  incoming  distribution  for a BSDF computation.
                 The default value is 0.


       The following command generates illum’s corresponding  to  geometry  in
       the files "it1.rad" and "it2.rad":

          mkillum  -ab 2 -ad 1024 -av .1 .1 .1 basic.oct "<" it1.rad it2.rad >

       The output file "illums.rad" would then be combined with  the  original
       scene geometry to create a more easily rendered composite.


       RAYPATH        the directories to check for auxiliary files.


       Greg Ward


       Work  on  this program was initiated and sponsored by the LESO group at
       EPFL in Switzerland.


       oconv(1), rad(1), rpict(1), rtrace(1), rvu(1)