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Document: FTS_IO

Purpose: Describes the FITS io routines

Category: FITS

File: fts_io.c

Author: P. Roelfsema

Description: The fts_io routines read or write data from/to FITS tapes
and files.

The following functions are available:

FTSD_GETH Get a FITS header from tape.
FTSI_GETR Get real data from tape.
FTSI_GETI Get integer data from tape.

FTSD_PUTH Put a FITS header on tape.
FTSI_PUTR Put real data on tape.
FTSI_PUTI Put integer data on tape.

FTS_SKIPPIX Skip pixels on a FITS tape.
FTS_SKIPFIL Skips fits file(s).

Each routine is described in more detail in the
appropriate document.

Use:
To read a FITS tape first a tape-device must be opened using MTOPEN
(see MTIODEV.DC2 and references therein). From this device a FITS
read operation is initialised by calling FTSD_GETH. After FTSD_GETH
the calling program has a character array containing the FITS header
records. Using the FTSD_FIND, FTSD_RCHAR, FTSD_RREAL etc. routines
the values of individual FITS keywords can be obtained from this
header. Subsequently a series of calls to FTSI_GETI or FTSI_GETR
(combined with FTS_SKIPPIX calls) can be done to get the FITS data
from the tape into an integer or real array respectively. A read
operation can be stopped before the end of the tape-file by skipping
to the next file with FTS_SKIPFIL.

After an error condition (i.e. a negative return value of one of the
routines) the tape will always be positioned at the beginning of the
next file.

A typical series of FTS calls for a FITS read operation would
look as follows:

MTOPEN( ) - open a tape-device
FTS_SKIPFIL( ) - skip some files

FTSD_GETH( ) - get the header from tape
FTSD_RREAL( ) |
FTSD_RLOG( ) |
. | - decode the header
. |
FTSD_RINT( ) |

FTS_SKIPPIX( ) - skip some pixels

REPEAT - loop to
FTSI_GETR( ) - read data
UNTIL( TID.EQ.0 ) - until all is read in

MTCLOSE( ) - close the tape-device

To write a FITS tape first a FITS header must be generated;
such a header should be a long character type array which can be
filled with FITS record using the FTSD_WCHAR etc. routines.
Subsequently a tape-device must be opened using MTOPEN (see
MTIODEV.DC2 and references therein). The FITS write operation is
initialised by calling FTSD_PUTH which will store the above mentioned
header on tape. After FTSD_PUTH integer or real data can be written
to the device mounted to mtid by calling the routines FTSI_PUTI or
FTSI_PUTR. The writing of data ends when the FTSI_ routine is
told to put 0 (zero) elements on tape, then two tapemarks
(indicating EOF and EOT) will be written to tape.

After an error condition (negative return value) the file that
was being written will be erased. The tape will be positioned
after the previous file on tape.

A typical series of FTS calls for a FITS write operation would
look as follows:

MTOPEN( ) - open a tape-device
REPEAT - skip some files until EOT
UNTIL( FTS_SKIPFIL( ) .EQ. -13 )

FTSD_WREAL( ) |
FTSD_WLOG( ) |
. | - fill the header
. |
FTSD_WINT( ) |
FTSD_PUTH( ) - write the header to tape

REPEAT - loop to
FTSI_PUTR( ) - write data
UNTIL( NPIX.EQ.0 ) - until all is written
FTSI_PUTR( . 0 . ) - write 0 pixels => end of write

MTCLOSE( ) - close the tape-device

Updates:
Jun 27, 1990: PRR, Original document created
Aug 22, 1990: SS, Added write routines.
Sep 12, 1990: SS, Adjustments for new data structure.
Oct 8, 1990: PRR, Major Rewrite.
Nov 12, 1991: MV, Casting of LONG_MIN, because of bug in
gcc compiler.