PROCESS OUTPUT  (WRITES TO MAGNETIC TAPE)

Parameters, alphabetically:
device    fon       nfskip    posaft    ofmt      ontrcs
ounit     ounit2    rewind    trace0

Document Date: July 2004

PROCESS OUTPUT writes seismic data to magnetic tape in SEG-Y or modified
SEG-Y format.  The SEG-Y format has an EBCDIC tape header and a binary
tape header at the beginning of every tape.  Every trace is the
concatenation of a trace header and the data trace.  See the SIOSEIS
SEG-Y documentation for more information about the SEG-Y format.

Output record (shot or rp) numbers should be monotonically increasing
by 1 since process input expects them this way.

Output tape changes are handled by process output through operator
intervention when the physical end-of-tape is detected.  The operator
must specify the new tape unit number to the program via file out, when
the new tape is mounted and ready.  The file 'out' must be in the
directory that the job is running in.  The file can be created with any
standard editor, for example vi or ex on an Unix based system.

The output tape is positioned after the terminal file mark at the 
conclusion of each SIOSEIS job.

Only one process output may be performed in the job.

THE PARAMETER DICTIONARY
--- --------- ----------

DEVICE - The UNIX device name to use rather than /dev/nrst.  OUNIT is
         ignored when DEVICE is given, but may be specified by the
         user.  USE A NO-REWIND DEVICE so that Unix does not rewind
         the tape when an end-of-tape is written.  USE A BSD DEVICE
         so that SIOSEIS controls tape positioning on multiple file
         tapes.  Any valid positive unit number may be used in file
         OUT for tape changes.  Use "ls /dev/rmt" for a list of
         available tape drives for each computer.
         e.g.  Solaris 5.8 says:
         /dev/rmt/[][]
         Where density can be  l,  m,  h,  u/c  (low,  medium,  high,
         ultra/compressed, respectively), the BSD behavior  option is
         b, and the no rewind  option is n.
         Preset = none  e.g.  device  /dev/rmt/0cbn

OUNIT  - OBSOLETE, but still functional.  Parameter DEVICE is preferred.
         Output tape drive unit number.  BSD Unix (e.g. Sun) tape
         assignment is /dev/nrstOUNIT.   e.g. ounit 0 is /dev/nrst0.
         (Note in HP-UX the device is /dev/rmt/OUNITm.)
         Preset = 0.    e.g. ounit 2

FON    - First output number.
         Preset = 0.    e.g.  fon 41
       <0,  when used in conjunction with posaft<0, FON is set to 1
            greater than the last record on tape.
       =0,  The output record numbers are the same as the input (or
            calculated in process geom).
       >0,  The output record numbers will start with fon and will
            increase by 1 on subsequent output records.

POSAFT - Output tape position indicator.  Positioning is done prior to
         writing the first output trace, but after parameters REWIND
         and NFSKIP are done.  Not valid when DEVICE is used since
         POSAFT requires the use of a backspace, which device can not
         do.  Position after last record is not available on SUN
         computers since they do not permit skipping backwards overfile-
         marks (as they used to).  HP and SGI permit this.
         Preset = 0.
        <0, The tape will be positioned after the last trace on the tape.
        =0, The tape will not be positioned.
        >0, The tape will be positioned after the shot (rp) with number
         POSAFT.

INFREQUENTLY USED PARAMETERS
------------ ---- ----------

OFMT   - The output format.  Specifies the type of segy format to write.
         ******   Note:  *****
         Host floating point (ofmt 5) is not a standard SEG-Y format and
         must not be used when transfering data between computers with
         different floating point word representations.
         Preset = 5     e.g. ofmt 2    
       = 0, same format as the input tape.
       = 1, IBM 360 floating point.
       = 2, Integer*4.  (32 Bit integer)
       = 3, integer*2 (not recommended).
       = 4, Not available.
       = 5, IEEE Floating Point (SEG-Y Rev. 1 standard)

ONTRCS - The number of traces per output record.  Output shot numbers
         are normally incremented after ONTRCS have been written.  Rp
         numbers are incremented after an end-of-gather flag is
         detected.  Post stack rp numbers are incremented on each rp.
         Works only when fon<>0.
         Preset=same as input

NFSKIP - The number of files to skip before writing the first output.
         The file skip is done after parameter REWIND and before
         parameter POSAFT.  Both SEG-Y "tape" headers are written.
         While this is a violation of the SEG-Y standard, it is
         extremely useful when writing DATs or Exabyte tapes.  The
         number of files skipped is from the current tape position when
         parameter REWIND is 0, and is from the beginning of tape if
         REWIND is set to 1.
         Preset = 0

REWIND - A YES/NO switch indicating whether the output tape should be
         rewound prior to any tape functions are performed, including
         parameters NFSKIP and POSAFT.
       = YES, rewind.
       = NO, NO rewind.
         Preset = yes,      e.g.  rewind no    # don't rewind

TRACE0 - A YES/NO switch indicating whether the SEG-D external header
         should be written to tape as a trace numbered 0 and SEG-Y
         trace id (short word 15) 28.
         Preset = NO    e.g.    trace0 yes   # a trace 0 will be written

OUNIT2 - A second tape drive unit number so that two tapes can be created
         simultaneously.  Parameter DEVICE is not honored with OUNIT2.
         POSAFT is NOT honored either.  Output tape changes will NOT
         work on OUNIT2
         Preset = 0.    e.g. ounit 2  ounit2 3


Written and copyrighted by:
Paul Henkart, Scripps Institution of Oceanography, La Jolla, CA, Jan.1980
ALL RIGHTS RESERVED