NAME

     zstretch - map or stretch data lying on a fixed but  irregu-
     lar depth grid to an equally sampled depth grid.

SYNOPSIS

     zstretch [ -Nfile_irreg ] [ -Ofile_reg ] [ -Zfile_zeta  ]  [
     -dzdzeql ] [ -V ] [ -? ]

DESCRIPTION

     zstretch was designed to efficiently resample the output  of
     the  2D  Kirchhoff migration algorithm sammig to a regularly
     (i.e. equally) sampled grid in depth using a 6 point  inter-
     polation algorithm. This routine, when included in the piped
     flow 'prepmig;vsm|vsamp;kray;sammig|zstretch' will result in
     a prestack depth migration equivalent to routine smallmig.

     zstretch gets both its data and its parameters from  command
     line arguments.  These arguments specify the input, outputs,
     and certain floating point values to  override  the  current
     restrictions to trace header integer values.

  Command line arguments
     -N file_irreg
          Enter the input irregularly sampled depth data set file
          name  (output  from  routine  sammig) immediately after
          typing -N unless data are coming  in  from  a  pipe  in
          which  case  the -N option should not be entered.  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 file_reg
          Enter the output regularly (equally) sampled depth data
          set file name after the -O option or, if data are going
          to a pipe, the -O option should not be entered.

     -Z file_zeta
          Enter  the  input  irregular  depth  sample  file  name
          immediately  after typing -Z. The file following the -Z
          option was the output file following the -Z  option  in
          routine  vsamp.  This  input data set requires the full
          path name (see above).

     -dz dz
          Enter the constant depth sample increment at which  the
          input irregular depth data are to be resampled. Default
          is obtained by multiplying the line header word  Dz1000
          *  .001, thus giving a depth model at the same scale as
          the velocity model input to routine vsamp.

     -V   Enter the command line argument '-V' to obtain  verbose
          output.

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

BUGS

     No bugs known at present.

SEE ALSO

     vsm, vsamp, kray, sammig, tstretch

AUTHOR

     K. J. Marfurt (APR)  extracted from S. H. Gray's   algorithm
     smallmig / smigA.

COPYRIGHT

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