NAME

     azfilt  - pass or reject 3D data based  on  source  receiver
     azimuth

SYNOPSIS

     azfilt [ -Nntap ] [ -Ootap ] [ -asas ] [ -aeae ] [ -bsns ] [
     -D ] [ -P ] [ -V ] [ -? ]

DESCRIPTION

     azfilt passes or rejects input 3D data based on whether  the
     source  -  receiver  azimuth  lies  within  a  start and end
     azimuth defined by the user.  In  the  current  scheme  zero
     degrees  is  along  the positive X direction.  In addition a
     full azimuth histogram is written to the printout file. Mul-
     tiple  pass/reject  cones  can  be  built  by piping filters
     together. Each trace (except dead ones)  must  have  SrPtXC,
     SrPtYC,  RcPtXC, and RcPtYC (source and receiver XYs) filled
     in properly.

     In the XY cartesian system zero  degrees  points  along  the
     positive X axis and angle increases counterclockwise. We use
     the convention that if the source lies ahead of the receiver
     along  positive  X the vector forms an angle of zero degrees
     with the X axis; if the  source  lies  behind  the  receiver
     along  the  X  axis (toward more negative X values) then the
     vector forms an angle of 180 degrees with the X axis.

     azfilt gets both its data and its  parameters  from  command
     line  arguments.  These arguments specify the input, output,
     the start and end azimuths, the azimuth bin size,  and  ver-
     bose printout, if desired.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing -N unless the input is from a pipe in which case
          the -N entry must be omitted.  This input  file  should
          include the complete path name if the file resides in a
          different directory.  Example -N/b/vsp/dummy tells  the
          program to look for file 'dummy' in directory '/b/vsp'.

     -O otap
          Enter the output data  set  name  or  file  immediately
          after typing -O.  This output file is not required when
          piping the output to another process.  The output  data
          set also requires the full path name (see above).

     -as as
          Enter the start azimuth  in  degrees.  In  reject  mode
          traces  with  azimuths  greater  that  or equal to this
          value and less than or equal to the ending azimuth will
          be zeroed and if required, marked as dead. Zero degrees
          is defined to be along the positive  X  axis  and  will
          increase counterclockwise. No default.

     -ae ae
          Enter the end azimuth in degrees. In reject mode traces
          with  azimuths  greater  that  or equal to the starting
          azimuth and less than or equal to  the  ending  azimuth
          will  be  zeroed  and if required, marked as dead. Zero
          degrees is defined to be along the positive X axis  and
          will increase counterclockwise. No default.

     -bs na
          Enter the azimuth bin size in degrees.  This is used to
          compute the number of bins between zero and 360deg used
          to accumulate the azimuth histogram found in the  prin-
          tout file.

     -D   Enter the command line argument '-D' to mark the zeroed
          out  rejected traces as dead (30000 in the StaCor trace
          header word).

     -P   Enter the command line argument  '-V'  to  pass  traces
          between the start and end azimuths.

     -V   Enter the command line argument '-V' to get  additional
          printout.

     -?   Enter the command line  argument  '-?'  to  get  online
          help.   The program terminates after the help screen is
          printed.

EXAMPLES

     Let's reject all azimuths lying within a 20 degree cone cen-
     tered on the X axis (both positive and negative directions):

     azfilt -Nidata -as10 -ae350 -P | \
     azfilt -Oodata -as170 -ae190

     where the first  filter  passes  all  traces  with  azimuths
     between  10 degrees all the way round to 350 degrees, taking
     care of the 20deg cone in the positive direction; the second
     filter  simply rejects the remaining traces within the nega-
     tive X direction cone.

BUGS

     unknown

AUTHOR

     P. R. Gutowski, TRC, x3146, pgutowski@amoco.com

COPYRIGHT

     copyright 2001, Amoco Production Company
               All Rights Reserved
          an affiliate of BP America Inc.