SEGYREAD - read an SEG-Y tape

segyread > stdout tape=

or

SEG-Y data stream ... | segyread tape=- > stdout

Required parameter:
tape= input tape device or seg-y filename (see notes)

Optional parameters:
buff=1 for buffered device (9-track reel tape drive)
=0 possibly useful for 8mm EXABYTE drives
verbose=0 silent operation
=1 ; echo every 'vblock' traces
vblock=50 echo every 'vblock' traces under verbose option
hfile=header file to store ebcdic block (as ascii)
bfile=binary file to store binary block
over=0 quit if bhed format not equal 1, 2, or 3
= 1 ; override and attempt conversion
format=bh.format if over=1 try to convert assuming format value
conv=1 convert data to native format
= 0 ; assume data is in native format
ns=bh.hns number of samples (use if bhed ns wrong)
trmin=1 first trace to read
trmax=INT_MAX last trace to read
endian=1 set =0 for little-endian machines(PC's,DEC,etc.)
errmax=0 allowable number of consecutive tape IO errors

Notes:
Traditionally tape=/dev/rmt0. However, in the modern world tape device
names are much less uniform. The magic name can often be deduced by
"ls /dev". Likely man pages with the names of the tape devices are:
"mt", "sd" "st". Also try "man -k scsi", " man mt", etc.
Sometimes "mt status" will tell the device name.

For a SEG-Y diskfile use tape=filename.

Remark: a SEG-Y file is not the same as an su file. A SEG-Y file
consists of three parts: an ebcdic header, a binary reel header, and
the traces. The traces are (usually) in 32 bit IBM floating point
format. An SU file consists only of the trace portion written in the
native binary floats.

Formats supported:
1: ibm floating point, 2: ibm fixed point, 4 byte,
3: ibm fixed point, 2 byte

tape=- read from standard input. Caveat, under Solaris, you will
need to use the buff=1 option, as well.

type: sudoc segyread for further information



Note:
If you have a tape with multiple sequences of ebcdic header,
binary header,traces, use the device that
invokes the no-rewind option and issue multiple segyread
commands (making an appropriate shell script if you
want to save all the headers). Consider using >> if
you want a single trace file in the end. Similar
considerations apply for multiple reels of tapes,
but use the standard rewind on end of file.

Note: For buff=1 (default) tape is accessed with 'read', for buff=0
tape is accessed with fread. We suggest that you try buff=1
even with EXABYTE tapes.
Caveat: may be slow on an 8mm streaming (EXABYTE) tapedrive
Warning: segyread or segywrite to 8mm tape is fragile. Allow sufficient
time between successive reads and writes.
Warning: may return the error message "efclose: fclose failed"
intermittently when segyreading/segywriting to 8mm (EXABYTE) tape
even if actual segyread/segywrite is successful. However, this
error message may be returned if your tape drive has a fixed
block size set.
Caution: When reading or writing SEG-Y tapes, the tape
drive should be set to be able to read variable block length
tape files.


Credits:
SEP: Einar Kjartansson
CWP: Jack K. Cohen, Brian Sumner, Chris Liner
: John Stockwell (added 8mm tape stuff)
conv parameter added by:
Tony Kocurko
Department of Earth Sciences
Memorial University of Newfoundland
St. John's, Newfoundland
read from stdin via tape=- added by Tony Kocurko
bhed format = 2,3 conversion by:
Remco Romijn (Applied Geophysics, TU Delft)
J.W. de Bruijn (Applied Geophysics, TU Delft)
--------------------------
Additional Notes:
Brian's subroutine, ibm_to_float, which converts IBM floating
point to IEEE floating point is NOT portable and must be
altered for non-IEEE machines. See the subroutine notes below.

A direct read by dd would suck up the entire tape; hence the
dancing around with buffers and files.