RDFITS-Read file in AAO de facto 'Disk FITS' format

Description:

RDFITS reads a disk file containing data in a 'Disk FITS' format and creates a Figaro data file from it. RDFITS was originally intended to handle the AAO 'de facto disk FITS' format, but the addition of the SWAP keyword and code to determine the disk format in use has made it rather more general. Note that RDFITS with SWAP set to NO can read files written in the 'JT disk FITS' format handled by RJT.

Parameters:

FILE

The name of a disk file containing an image in 'Disk FITS' format - i.e. 2880 byte records looking exactly the same as the records in a FITS tape.

IMAGE

The name of the resulting Figaro image. Note that this will contain the image data itself and the 'FITS' header information in a .FITS structure. The conventions used by the header information - e.g. is RA in hours, minutes and seconds or in fractional minutes? - may not be those used by normal Figaro routines, so be wary of just copying them into any standard observation structure.

SWAP

FITS data is by definition stored on tape in IBM byte order which is the reverse of internal storage on a VAX. SWAP = YES for de facto 'disk FITS' files such as that from AAO and written by the Figaro function WDFITS. Some other 'disk FITS' formats such as JT's may require SWAP=NO.

FLOAT

The default setting for FLOAT is YES, and this causes FITS to generate an output data structure with a main data array whose type will be FLOAT. This is the recommended way to create the file. If the data was originally written with BITPIX=16, then disk space can be saved by setting FLOAT=NO. FLOAT=NO will be overidden if the FITS header specifies BSCALE and BZERO values other than 1.0 and 0.0 respectively, although the special case of FLOAT=NO combined with BSCALE=1.0 BZERO=32768.0, BITPIX=16 is trapped and produces a main data array of unsigned 16bit integers (some FITS writers, notably WDFITS, use this as an efficient way of writing 16bit unsigned integer data).

See also:

FIGARO: WDFITS, FITSKEYS.
KAPPA: FITSDIN, FITSIN, FITSHEAD, FITSIMP, FITSLIST.

Source comments:

 R D F I T S

 Figaro routine to read file in a 'Disk FITS' format,
 creating a Figaro data structure file that contains all
 the information from the disk file (although not necessarily in
 an ideal form, since the program cannot guess at the meaning
 of all the various FITS keywords).  For more details, see the
 listing for FIG_FITIN.

 Command parameters -

 FILE       (Character) The name of the 'Disk Fits' file.

 IMAGE      (Character) The name of the Figaro output file.

 Command keywords -

 SWAP       Swap bytes.  This should be set to YES if the data
            have been stored in the proper FITS format (IBM-style)
            and the program is running on a non-IBM byte order
            machine such as a VAX.  On a VAX, you should use:
            SWAP=YES for AAO de facto 'disk FITS'.
            SWAP=NO for WJT 'disk FITS'.

 FLOAT      Convert the data to floating point numbers. This is
            normally what will be required, although note that only
            single precision is supported.  If FLOAT=NO is specified,
            FITS will still convert to floating point if the data have
            scaling and offset factors that are not 1.0 and 0.0
            respectively.  The case where FLOAT=NO, BITPIX=16,
            BSCALE=1.0, BZERO=32768 is treated as a special case and
            will generate an array of unsigned 16 bit integers.
            FLOAT=NO is usually only useful in this special case and
            in the case where BSCALE=1.0, BZERO=0.0, BITPIX=16, where
            it will create a smaller data file with no loss of precision.

 User Variables used -   None

 Note:  Most of the various 'disk FITS' formats differ only in
        whether or not they swap bytes, and in the details of the
        way the disk data is organised in records.  For example,
        a VAX VMS file may have a 'FIXED', 'VARIABLE', or 'SEGMENTED'
        format, whereas UNIX files are generally simpler.  Also on
        a machine that has a record-based file structure (like a VAX)
        the record lengths may or may not be the 2880 bytes that would
        match a FITS tape. This program determines the disk format
        (fixed, variable,segmented) and record length for itself, and
        uses the SWAP keyword to indicate whether the data bytes are to
        be treated as swapped or not.  It should therefore be able to
        handle most of the available 'disk FITS' formats.

                                         KS / AAO 17th June 1986