NAME

     stretch  - do forward/inverse generalized  stretch/squeezing
     of seismic traces

SYNOPSIS

     stretch [ -Nntap ] [ -Ootap ] [ -tminntmin ] [ -ssfact  ]  [
     -exppwr ] [ -fifunc ] [ -R ] [ -V ] [ -? ]

DESCRIPTION

     stretch does a  time  axis  generalized  stretch/squeeze  of
     seismic  traces.  The internal workings involve cubic spline
     interpolation for speed and accuracy to minimize   amplitude
     distortion present in the output data at the higher frequen-
     cies.

     Currently   5   functions    are    supported:    (1)    log
     stretch/squeeze,  (2)  power  function  stretch/squeeze, (3)
     linear stretch/squeeze, (4) sin(t) stretch/squeeze, and  (5)
     cos(t) stretch/squeeze.

     stretch gets both its data and its parameters  from  command
     line  arguments.  These arguments specify the input, output,
     functions type and  parameters,  forward/inverse  flag,  and
     verbose 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).

     -tmin ntmin
          Enter the minimum time of interest  (ms).   This  value
          must  be  nonzero  to  avoid taking the log of zero and
          must be large enough to avoid the output number of sam-
          ples  becoming  enormous.  Data less than this value is
          zeroed.  (default = 0.10 * input trace length)

     -s sfact
          Enter the stretch factor of the time axis  for  options
          2,  3,  and  4  below, e.g. -s2 for option2 implies the
          data are linearly  stretched  to  double  the  original
          length.  default = 1.0

     -exp pwr
          Enter the exponent by which  to  power  the  time  axis
          (i.e. t ** pwr).  A value less than 1.0 results in out-
          put stretched in time; a value greater then 1.0 results
          in output squeezed in time.  default = 1.0

     -f ifunc
          Enter the function type (default = 0):

          ifunc = 0  log stretch/squeeze

          ifunc = 1  power (t ** pwr) stretch/squeeze

          ifunc = 2  linear stretch/squeeze

          ifunc = 3  sin (sfact * t) stretch/squeeze

                     default sfact = 1.0

          ifunc = 4  cos (sfact * t) stretch/squeeze

                     default sfact = 1.0

     -R   Enter the command line argument  '-R'  to  inverse  log
          stretch  (eg  undo  a  previous  forward  log stretch).
          Note:  to properly do the  inverse  the  -tmin  and  -s
          entries  must  be  the same as for the forward stretch,
          or, better let the default value be used for both  for-
          ward & reverse.

     -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.

BUGS

     The sample interval is in micro seconds  which  the  inverse
     stretch  understands.   Other  programs may not be so under-
     standing however.  Also in the case of the first  3  options
     beware  of  the  number  of  output samples generated (check
     using scan on a test case), and increase the -tmin entry  if
     necessary.  If the maximum allowable number of samples/trace
     on a system has been reached a message will be placed in the
     printout  file  and the trace will be truncated.  This might
     cause data to be lost off the end of the trace after  recon-
     struction (-R).

SEE ALSO

     dmofast, dmofx

AUTHOR

     Paul Gutowski, APR

COPYRIGHT

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