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NAME

       vwrays - compute rays for a given picture or view

SYNOPSIS

       vwrays [ -i -u -f{a|f|d} | -d ] { view opts ..  | picture [zbuf] }

DESCRIPTION

       Vwrays  takes  a  picture  or  view  specification and computes the ray
       origin and direction corresponding to each pixel in  the  image.   This
       information   may   then  be  passed  to  rtrace(1)  to  perform  other
       calculations.  If a given pixel has no corresponding ray (because it is
       outside  the  legal  view  boundaries),  then  six zero values are sent
       instead.

       The -i option may be used to specify desired  pixel  positions  on  the
       standard  input rather than generating all the pixels for a given view.
       If the -u option is also given, output will be unbuffered.

       The -f option may be used to set the record format to  something  other
       than  the default ASCII.  Using raw float or double records for example
       can reduce the  time  requirements  of  transferring  and  interpreting
       information in rtrace.

       View  options  may  be  any  combination  of  standard  view parameters
       described in the rpict(1) manual page, including input from a view file
       with  the  -vf option.  Additionally, the target X and Y dimensions may
       be specified with -x and -y options, and the pixel aspect ratio may  be
       given  with  -pa.   The  default  dimensions  are 512x512, with a pixel
       aspect ratio of 1.0.  Just as in rpict, the X or the Y  dimension  will
       be reduced if necessary to best match the specified pixel aspect ratio,
       unless this ratio is set to zero.  The -pj option may be used to jitter
       samples.  The default value of 0 turns off ray jittering.

       If  the  -d option is given, then vwrays just prints the computed image
       dimensions, which are based on the view aspect  and  the  pixel  aspect
       ratio  just  described.  The -ld switch will also be printed, with -ld+
       if the view file has an aft clipping plane, and -ld-  otherwise.   This
       is useful for passing options to the rtrace command line.  (See below.)

       If  the  view  contains  an  aft  clipping plane (-va option), then the
       magnitudes of the ray directions will equal the  maximum  distance  for
       each pixel, which will be interpreted correctly by rtrace with the -ld+
       option.  Note that this option should not be given unless there  is  an
       aft  clipping plane, since the ray direction vectors will be normalized
       otherwise, which would produce a uniform clipping distance of 1.

       If a picture is given on the command line rather than  a  set  of  view
       options,  then the view and image dimensions are taken from the picture
       file, and the reported ray origins and directions will match the center
       of each pixel in the picture (plus optional jitter).

       If  a  depth  buffer  file  is  given as well, then vwrays computes the
       intersection point of each pixel ray (equal to the ray origin plus  the
       depth  times  the  ray  direction), and reports this instead of the ray
       origin.  The  reported  ray  direction  will  also  be  reversed.   The
       interpretation  of  this data is an image of origins and directions for
       light rays leaving the scene surfaces to strike each pixel.

EXAMPLES

       To  compute  the  ray  intersection  points  and  returned   directions
       corresponding to a picture and its depth buffer:

         vwrays scene_v2.hdr scene_v2.zbf > scene_v2.pts

       To determine what the dimensions of a given view would be:

         vwrays -d -vf myview.vf -x 2048 -y 2048

       To generate a RADIANCE picture using rtrace instead of rpict:

         vwrays  -ff  -vf  view1.vf  -x  1024  -y 1024 | rtrace `vwrays -d -vf
         view1.vf -x 1024 -y 1024` -ffc scene.oct > view1.hdr

AUTHOR

       Greg Ward Larson

ACKNOWLEDGMENT

       This work was supported by Silicon Graphics, Inc.

BUGS

       Although vwrays can reproduce  any  pixel  ordering  (i.e.,  any  image
       orientation)  when  given  a  rendered  picture,  it  will only produce
       standard scanline-ordered rays when given a set of view parameters.

SEE ALSO

       rcalc(1), rpict(1), rtcontrib(1), rtrace(1)



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