NAME

     presort  - compute sort tables

SYNOPSIS

     presort [ -Nntap ] [ -Ootap ] [ -Hw1TrWrd1 ] [ -Hw2TrWrd2  ]
     [ -Hw3TrWrd3 ] [ -Hw4TrWrd4 ] [ -M ] [ -offoff ] [ -grpgrp ]
     [ -R ] [ -X ] [ -K ] [ -V ] [ -? ]

DESCRIPTION

     presort computes the common  source,  common  receiver,  and
     common   depth  sort  table, or alternately, three arbitrary
     primary sorts from user specified trace  header  words  plus
     one  secondary  sort.   The  header  words  are specified by
     mnemonic (see scan documentation for list of header  mnemon-
     ics  and  their  descriptions).   Header  words may still be
     referred to by their old  SIS  1/2  word  position  although
     users are urged to discontinue this practice.

     The sort table has the following entries:

     LINE 1 - -1 (flag)

     LINE 2 -  total  number  traces  to  be  sorted,  number  of
     receiver + source components

     LINE 3 - four pairs (number gathers,  number  traces/gather)
     for  common  receiver, common shot, common depth, and common
     offset

     LINE 4 - first receiver index, receiver index increment

     LINE 5,6,... first 3 numbers are the sorted primary  indices
     (receiver, shot, depth); the next 3 pairs of numbers are the
     corresponding sequential record and trace locations for  the
     primary  indices;  the  next  number is the offset; the next
     pair is the record and trace location of the  common  offset
     sorted index found in the last sort table location.

     presort gets both its data and its parameters  from  command
     line  arguments.  These arguments specify the input, output,
     and verbose printout, if desired.

     Note:  if you sort the input data and at some point  in  the
     preocessing  the  sorted  data are output onto disk you must
     run presort again to create a new table if you plan  to  re-
     sort  these data.  The act of physically sorting changes the
     layout on disk so the old roadmap is no longer valid.   Once
     the  forward  and  backward  presort  tables have been built
     presort does not have to be run again  unless  the  geometry
     again  changes  for some reason on disk (e.g. the ranges are
     limited and the results written to disk)

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing -N.  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 'vsp' stored on the 'b' disk.

     -O otap
          Enter the output data set name or file (i.e. sort table
          name) immediately after typing -O.  The output data set
          also requires the full path name (see above).

     -Hw1 TrWrd1
          Enter the first primary trace header word  mnemonic  to
          sort  on  (one  of  three).  Default = RecInd (receiver
          index).

     -Hw2 TrWrd2
          Enter the second primary header word mnemonic  to  sort
          on  (two  of  three).   Default  = SrcLoc (source index
          (source point x10)).

     -Hw3 TrWrd3
          Enter the third primary header word mnemonic to sort on
          (three of three).  Default = DphInd (depth index).

     -Hw4 TrWrd4
          Enter the secondary trace header word mnemonic to  sort
          on.  Default = DstSgn (signed trace distance).

     -M   Enter the command line argument '-M' to sort on  binned
          trace  distances.   These  are derived from the command
          line arguments below.  Note: this will not  change  the
          actual trace distances on disk

     -off off
          Enter the absolute maximum offset  found  in  the  data
          (ft,m).   If  this is not known try running scan with a
          -S (for summary) on the command line.  This  will  tell
          you the max & min offsets for each record.

     -grp grp
          Enter the group interval (ft,m).  This is used with the
          offset  above  to derive a model spread for binning the
          distances.

     -R   Enter the command line argument '-R' to round the trace
          distances  to the nearest 10 units (ft, m) before sort-
          ing


     -X   Enter the command line argument '-X' to retain original
          record  numbers  in the sort table.  This option should
          be used only if one wishes to eyeball the sort table to
          see  where  the traces will go upon execution of sisort
          and is not intended for normal processing

     -K   Enter the command line argument  '-K'  to  retain  dead
          traces in the sort table.  This takes up more space but
          the table is now an exact roadmap of the data on  disk.
          NOTE:   with  this option the dead traces must have all
          the correct header indices.  If they do not you are  in
          big trouble.

     -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.

COPYRIGHT

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