NAME

       findglare - locate glare sources in a RADIANCE scene

SYNOPSIS

       findglare  [  -v  ][ -ga angles ][ -t threshold ][ -r resolution ][ -c ][ -p picture ][ view options ] [[
       rtrace options ] octree ]

DESCRIPTION

       Findglare locates sources of glare in a specific set of  horizontal  directions  by  computing  luminance
       samples  from  a  RADIANCE  picture and/or octree.  Findglare is intended primarily as a preprocessor for
       glare calculation programs such as glarendx(1), and is usually  accessed  through  the  executive  script
       glare(1).

       If  only  an  octree is given, findglare calls rtrace to compute the samples it needs.  If both an octree
       and a picture are specified, findglare calls rtrace only for samples that are outside the  frame  of  the
       picture.   If  findglare  does  not  have an octree and the picture does not completely cover the area of
       interest, a warning will be issued and everything outside the picture will  be  treated  as  if  it  were
       black.   It  is  preferable to use a picture with a fisheye view and a horizontal and vertical size of at
       least 180 degrees (more horizontally if the -ga option is used -- see below).  Note that the picture file
       must contain correct view specifications, as maintained by rpict(1),  rvu(1),  pfilt(1)  and  pinterp(1).
       Specifically,  findglare  will  not  work  on  pictures  processed by pcompos(1) or pcomb(1).  It is also
       essential to give the proper rtrace options when an octree is  used  so  that  the  calculated  luminance
       values are correct.

       The output of findglare is a list of glare source directions, solid angles and average luminances, plus a
       list of indirect vertical illuminance values as a function of angle.  Angles are measured in degrees from
       the view center, with positive angles to the left and negative angles to the right.

       By  default,  findglare  only computes glare sources and indirect vertical illuminance for the given view
       (taken from the picture if none is specified).  If the view direction is not  horizontal  to  begin  with
       (ie.  perpendicular to the view up vector), findglare will substitute the closest horizontal direction as
       its view center.  The -ga option can be used to specify a set of directions to consider about the  center
       of view.  This specification is given by a starting angle, ending angle, and step angle like so:
            start-end:step
       All  angles  must  be whole degrees within the range 1 to 180.  Multiple angle ranges may be separated by
       commas, and individual angles may be given without the ending and step angles.  Note that findglare  will
       complain if the same angle is given twice either explicitly or implicitly by two ranges.

       Findglare  normally  identifies  glare  sources  as directions that are brighter than 7 times the average
       luminance level.  It is possible to override this determination by giving an explicit luminance threshold
       with the -t option.  It usually works best to use the 'l' command within ximage(1) to  decide  what  this
       value  should  be.   Alternatively,  one  can  use  the 't' command within rvu(1).  The idea is to pick a
       threshold that is well above the average level but smaller than the source areas.

       If the sources in the scene are small, it may be necessary to increase the default sample  resolution  of
       findglare(1)  using  the  -r  option.   The default resolution is 150 vertical samples and a proportional
       number of horizontal samples.  If besides being small,  the  sources  are  not  much  brighter  than  the
       threshold,  the  -c flag should be used to override findglare's default action of absorbing small sources
       it deems to be insignificant.

       The -v flag switches on verbose mode, where findglare reports its progress during the calculation.

EXAMPLE

       To calculate the glare sources in the image "scene.hdr":

         findglare -p scene.hdr > scene.glr

       To compute the Guth visual comfort probability from this result:

         glarendx -t guth_vcp scene.glr

       To compute the glare for a set of angles around the view "good.vp" from the octree "scene.oct"  using  an
       ambient level of .1:

         findglare -vf good.vp -ga 10-60:10 -av .1 .1 .1 scene.oct > scene.glr

AUTHOR

       Greg Ward

ACKNOWLEDGEMENT

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

SEE ALSO

       getinfo(1), glare(1), glarendx(1), pfilt(1), rpict(1), rtrace(1), rvu(1), xglaresrc(1), ximage(1)

RADIANCE                                            11/15/93                                        FINDGLARE(1)