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  The High Energy Astrophysics Science Archive Research Center (HEASARC) at Goddard Space Flight Center has been active in the development of FITS software and data set design. It has developed and continues to enhance packages of FITS subroutines and tools, which are publicly available and widely used. It has formulated a number of internal conventions, which are primarily related to high energy astrophysics but may have applications in other areas. A number of these conventions are discused in Section 5.6.1. HEASARC material is available through their World Wide Web page at It is also available at

HEASARC has developed two major software packages. FITSIO is a machine-independent subroutine interface for reading or writing FITS files. By using these subroutines, the programmer can avoid having to deal directly with the internal details of the FITS file. FITSIO supports all the standard FITS file formats discussed in section 3. Some of the functions performed are opening and closing files, reading, writing or modifying header keywords, and reading or writing any element of a FITS data array or table. It also includes the VERIFITS program to verify that a FITS file conforms to the FITS standard. In addition to supporting the standard FITS formats, VERIFITS supports the variable length array convention discussed in section 5.2.1.

There are FITSIO versions in portable FORTRAN-77 and in ANSI C. Both versions run on Sun, DECstations, VAX/VMS, DEC Alpha (VMS and OSF/1), SGI, HP, NeXT, IBM PCs (DOS and Linux), Amiga PCs and Macintosh PCs; the FORTRAN version runs on Cray supercomputers and IBM mainframes as well. FITSIO requires random access I/O to the file and therefore does not support direct read or write access to sequential devices such as magnetic tape drives.

FITSIO source code and documentation are available through the Web from the Software item on the HEASARC menu bar or directly from

The other package, FTOOLS, is a collection of utility programs, in ANSI Fortran or C, that allows the user to interactively create, examine, or modify the contents of FITS files, utilizing the FITSIO package. Perl5 scripts are available for combining several FTOOLS to perform complex tasks. FTOOLS supports all the standard FITS file formats discussed in Section 3.

A general FITS file viewer and editor called fv is included as a standard part of the FTOOLS distribution and is available as a standalone package as well. It can be used for viewing and plotting any FITS format data file. It has a graphical user interface (GUI) written in Tcl/Tk that provides spreadsheet-like widgets to display and edit data in any FITS table or image, a scrolling text window to display and edit FITS header keywords, and an image display that uses either the Smithsonian Astrophysical Observatory - The Next Generation (SAOtng) display tool or a custom designed Tk image widget. Users can also produce line plots of the values in two or more columns of a FITS table and export the plots to a PostScript file.

As of this writing, fv is supported on most Unix platforms; support for IBM and Macintosh PCs is planned.

The FTOOLS package, documentation, and installation instructions are available from the Software item on the HEASARC menu block or directly from The fv tool is available at the same location.

The HEASARC FITS Working Group (HFWG), a body within HEASARC established to support present and future multimission needs of the OGIP at NASA, and, in particular, to ensure that the FITS formats and keywords used do not violate the FITS standards, has developed a number of conventions and designs. While use of these conventions and designs is required only for OGIP, the high energy astrophysics community has been consulted during the development process, and many of these conventions are used elsewhere for high energy astrophysics FITS files and other FITS files. A number of these conventions have been described in section 5.6.1. Other conventions specify keywords and strings to be used for such information as quality flags, channel boundaries, exposure times, and units. Among the standard file formats are those for light curves and spectra. Complete documentation on the recommendations and formats that have been adopted by HFWG and on those that are under consideration can be found at or directly by ftp to

The archive of traffic on the heafits mail exploder also is accessible from the HFWG page.

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Next: Some Additional Software Resources Up: Resources Previous: NRAO FITS Resources