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      Open a Space Telescope formatted (STSDAS) header file.


      Saves the parameters required subsequent SX routines in
      the common block Stcommn. Optionally save the header in
      the string array Header, and the history in the string array
      History. Open the data file associated with this
      header on the same unit.

Calling Sequence

      SXOPEN, Unit, Fname [, Header [,History] [,Access]]


      Unit = IDL unit used for IO. Must be from 1 to 9.
      Fname = File name of header file. Default extension
              is .hhh for header files and .hhd for data
              files. If an extension is supplied it must have the
              form .xxh where xx are any alphanumeric characters. The
              data file must have extension .xxd
              No version number is allowed. Most recent versions
              of the files are used.

Optional Input Parameter

      Access = 'R' to open for read, 'W' to open for write.


      Stcommn = Common block containing ST parameter blocks.
              (Long arrays.)

Optional Output Parameters

      Header = 80 char by N string array containing the
              names, values and comments from the FITS header.
              Use the function SXPAR to obtain individual
              parameter values.
      History = String array containing the value of the
              history parameter.

Common Blocks

      STCOMMN - Contains RESULT(20,10) where RESULT(i,LUN) =
      0 - 121147 for consistency check, 1 - Unit for consistency,
      2 - bitpix, 3 - naxis, 4 - groups (0 or 1), 5 - pcount,
      6 - gcount, 7 - psize, 8 - data type as idl type code,
      9 - bytes / record, 10 to 10+N-1 - dimension N,
      17 = record length of file in bytes.
      18 - # of groups written, 19 = gcount.

Side Effects

      The data and header files are accessed.


      Works only for disc files. The data file must have
      must have the extension ".xxd" and the header file must
      have the extension ".xxh" where x is any alphanumeric character


      The header file is opened and each line is read.
      Important parameters are stored in the output
      parameter. If the last two parameters are specified
      the parameter names and values are stored. The common
      block STCOMMN is filled with the type of data, dimensions,
      etc. for use by SXREAD.
      If access is for write, each element of the header
      array, which must be supplied, is written to the
      header file. The common block is filled with
      relevant parameters for SXWRITE. A keyword of "END"
      ends the header.

Modification History

      Written, DMS, May, 1983.
      D. Lindler Feb. 1990
              Modified to allow var. record length header files.
      D. Lindler April 1990 Conversion to new VMS IDL
      Added /BLOCK when opening new .hhd file
      Converted to IDL V5.0 W. Landsman September 1997
      Recognize unsigned datatype for V5.1 or greater W. Landsman Jan 2000
      Assume since V5.5 W. Landsman Sep 2006

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