WRITEFITS

       Write IDL array and header variables to a disk FITS file.

       A minimal FITS header is created if not supplied.
       WRITEFITS works for all types of FITS files except random groups

       WRITEFITS, filename, data [, header, /APPEND, /COMPRESS, /CHECKSUM]

       FILENAME = String containing the name of the file to be written.
       DATA = Image array to be written to FITS file.    If DATA is
              undefined or a scalar, then only the FITS header (which
              must have NAXIS = 0) will be written to disk

       HEADER = String array containing the header for the FITS file.
                If variable HEADER is not given, the program will generate
                a minimal FITS header.
       HEAP -   A byte array giving the heap area following, e.g. a variable
                length binary table

       /APPEND - If this keyword is set then the supplied header and data
                array are assumed to be an extension and are appended onto
                the end of an existing FITS file.    If the file does not
                exist, then WRITEFITS will create one with a minimal primary
                header (and /EXTEND keyword) and then append the supplied
                extension header and array.     Note that the primary
                header in an existing file must already have an EXTEND
                keyword to indicate the presence of an FITS extension.
       /COMPRESS - If this keyword is set, then the FITS file is written as
                a gzip compressed file.   An extension '.gz' is appended to
                to the file name if it does not already exist.   The /COMPRESS
                option is incompatible with the /APPEND option.
      /Checksum - If set, then the CHECKSUM keywords to monitor data integrity
                 will be included in the FITS header.    For more info, see
                  http://heasarc.gsfc.nasa.gov/docs/heasarc/fits/checksum.html
       NaNvalue - Value in the data array which represents missing pixels.
                This keyword is only used when missing pixels are not
                represented by NaN values in the input array.

       None

       (1) It recommended that BSCALE and BZERO not be used (or set equal
           to 1. and 0) with REAL*4 or REAL*8 data.
       (2) WRITEFITS will remove any group parameters from the FITS header

       Write a randomn 50 x 50 array as a FITS file creating a minimal header.
       IDL> im = randomn(seed, 50, 50)        ;Create array
       IDL> writefits, 'test', im             ;Write to a FITS file "test"

       CHECK_FITS, FITS_ADD_CHECKSUM, MKHDR, MRD_HREAD, SXDELPAR, SXADDPAR,
       SXPAR()

       WRITTEN, Jim Wofford, January, 29 1989
       Added call to IS_IEEE_BIG()  W. Landsman  Apr 96
       Make sure SIMPLE is written in first line of header  W. Landsman Jun 97
       Use SYSTIME() instead of !STIME    W. Landsman  July 97
       Create a default image extension header if needed W. Landsman June 98
       Converted to IDL V5.0   W. Landsman         June 98
       Write unsigned data types W. Landsman       December 1999
       Update for IDL V5.3, add /COMPRESS keyword W. Landsman  February 2000
       Correct BZERO value for unsigned data  W. Landsman   July 2000
       Eliminate duplication of input array if possible W. Landsman April 2001
       Use FILE_SEARCH for V5.5 or later     W. Landsman    April 2002
       Create the file if not already present and /APPEND is set
                                             W. Landsman    September 2002
       Proper call to MRD_HREAD if /APPEND is set  W. Landsman December 2002
       Added /CHECKSUM keyword              W. Landsman     December 2002
       Restored NANvalue keyword, William Thompson,         October 2003
       Write BZERO in beginning of header for unsigned integers WL April 2004
       Added ability to write heap array       WL             October 2004
       Correct checksum if writing heap array   WL           November 2004

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