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      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

Calling Sequence

      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

Optional Input

      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

Optional Input Keyword

      /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
                By default, checksum keywords will updated if they are already
                in the FITS header.
      NaNvalue - Value in the data array which represents missing pixels.
This keyword should only used when missing pixels are not
represented by NaN values in the input array.




      (1) It recommended that BSCALE and BZERO not be used (or set equal
          to 1. and 0) except with integer data
      (2) WRITEFITS will remove any group parameters from the FITS header
      (3) As of Feb 2008, WRITEFITS no longer requires the primary header of a
          FITS file with extension contain the EXTEND keyword, consistent with
          Section of the FITS 3.0 standard. A warning is still
          given. See http://fits.gsfc.nasa.gov/fits_standard.html


      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"

Procedures Used


Modification History

      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
      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
      Assume since V5.5, no VMS support, use file_search() WL September 2006
      Set nbytes variable to LONG64 for very large files WL May 2007
      Update CHECKSUM keywords if already present WL Oct 2007
      EXTEND keyword no longer required in FITS files with extensions WL Feb 2008
      Bug fix when filename ends with '.gz' and COMPRESS is used,
            the output file must be compressed S. Koposov June 2008
      Introduce V6.0 notation W.L. Nov. 2010
      Set /APPEND if XTENSION specifies a table W.L. July 2012

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