# Chapter 1 Introduction

## 1.1  A Brief Overview

CFITSIO is a machine-independent library of routines for reading and writing data files in the FITS (Flexible Image Transport System) data format. It can also read IRAF format image files and raw binary data arrays by converting them on the fly into a virtual FITS format file. This library is written in ANSI C and provides a powerful yet simple interface for accessing FITS files which will run on most commonly used computers and workstations. CFITSIO supports all the features described in the official definition of the FITS format and can read and write all the currently defined types of extensions, including ASCII tables (TABLE), Binary tables (BINTABLE) and IMAGE extensions. The CFITSIO routines insulate the programmer from having to deal with the complicated formatting details in the FITS file, however, it is assumed that users have a general knowledge about the structure and usage of FITS files.

CFITSIO also contains a set of Fortran callable wrapper routines which allow Fortran programs to call the CFITSIO routines. See the companion “FITSIO User’s Guide” for the definition of the Fortran subroutine calling sequences. These wrappers replace the older Fortran FITSIO library which is no longer supported.

The CFITSIO package was initially developed by the HEASARC (High Energy Astrophysics Science Archive Research Center) at the NASA Goddard Space Flight Center to convert various existing and newly acquired astronomical data sets into FITS format and to further analyze data already in FITS format. New features continue to be added to CFITSIO in large part due to contributions of ideas or actual code from users of the package. The Integral Science Data Center in Switzerland, and the XMM/ESTEC project in The Netherlands made especially significant contributions that resulted in many of the new features that appeared in v2.0 of CFITSIO.

## 1.2 Sources of FITS Software and Information

The latest version of the CFITSIO source code, documentation, and example programs are available on the Web or via anonymous ftp from:

            http://heasarc.gsfc.nasa.gov/fitsio
            ftp://legacy.gsfc.nasa.gov/software/fitsio/c

Any questions, bug reports, or suggested enhancements related to the CFITSIO package should be sent to the FTOOLS Help Desk at the HEASARC:

            http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp

This User’s Guide assumes that readers already have a general understanding of the definition and structure of FITS format files. Further information about FITS formats is available from the FITS Support Office at http://fits.gsfc.nasa.gov. In particular, the ’FITS Standard’ gives the authoritative definition of the FITS data format. Other documents available at that Web site provide additional historical background and practical advice on using FITS files.

The HEASARC also provides a very sophisticated FITS file analysis program called ‘Fv’ which can be used to display and edit the contents of any FITS file as well as construct new FITS files from scratch. Fv is freely available for most Unix platforms, Mac PCs, and Windows PCs. CFITSIO users may also be interested in the FTOOLS package of programs that can be used to manipulate and analyze FITS format files. Fv and FTOOLS are available from their respective Web sites at:

            http://fv.gsfc.nasa.gov
            http://heasarc.gsfc.nasa.gov/ftools

## 1.3 Acknowledgments

The development of the many powerful features in CFITSIO was made possible through collaborations with many people or organizations from around the world. The following in particular have made especially significant contributions:

Programmers from the Integral Science Data Center, Switzerland (namely, Jurek Borkowski, Bruce O’Neel, and Don Jennings), designed the concept for the plug-in I/O drivers that was introduced with CFITSIO 2.0. The use of ‘drivers’ greatly simplified the low-level I/O, which in turn made other new features in CFITSIO (e.g., support for compressed FITS files and support for IRAF format image files) much easier to implement. Jurek Borkowski wrote the Shared Memory driver, and Bruce O’Neel wrote the drivers for accessing FITS files over the network using the FTP, HTTP, and ROOT protocols. Also, in 2009, Bruce O’Neel was the key developer of the thread-safe version of CFITSIO.

The ISDC also provided the template parsing routines (written by Jurek Borkowski) and the hierarchical grouping routines (written by Don Jennings). The ISDC DAL (Data Access Layer) routines are layered on top of CFITSIO and make extensive use of these features.

Giuliano Taffoni and Andrea Barisani, at INAF, University of Trieste, Italy, implemented the I/O driver routines for accessing FITS files on the computational grids using the gridftp protocol.

Uwe Lammers (XMM/ESA/ESTEC, The Netherlands) designed the high-performance lexical parsing algorithm that is used to do on-the-fly filtering of FITS tables. This algorithm essentially pre-compiles the user-supplied selection expression into a form that can be rapidly evaluated for each row. Peter Wilson (RSTX, NASA/GSFC) then wrote the parsing routines used by CFITSIO based on Lammers’ design, combined with other techniques such as the CFITSIO iterator routine to further enhance the data processing throughput. This effort also benefited from a much earlier lexical parsing routine that was developed by Kent Blackburn (NASA/GSFC). More recently, Craig Markwardt (NASA/GSFC) implemented additional functions (median, average, stddev) and other enhancements to the lexical parser.

The CFITSIO iterator function is loosely based on similar ideas developed for the XMM Data Access Layer.

Peter Wilson (RSTX, NASA/GSFC) wrote the complete set of Fortran-callable wrappers for all the CFITSIO routines, which in turn rely on the CFORTRAN macro developed by Burkhard Burow.

The syntax used by CFITSIO for filtering or binning input FITS files is based on ideas developed for the AXAF Science Center Data Model by Jonathan McDowell, Antonella Fruscione, Aneta Siemiginowska and Bill Joye. See http://heasarc.gsfc.nasa.gov/docs/journal/axaf7.html for further description of the AXAF Data Model.

The file decompression code were taken directly from the gzip (GNU zip) program developed by Jean-loup Gailly and others.

The new compressed image data format (where the image is tiled and the compressed byte stream from each tile is stored in a binary table) was implemented in collaboration with Richard White (STScI), Perry Greenfield (STScI) and Doug Tody (NOAO).

Doug Mink (SAO) provided the routines for converting IRAF format images into FITS format.

Martin Reinecke (Max Planck Institute, Garching)) provided the modifications to cfortran.h that are necessary to support 64-bit integer values when calling C routines from fortran programs. The cfortran.h macros were originally developed by Burkhard Burow (CERN).

Julian Taylor (ESO, Garching) provided the fast byte-swapping algorithms that use the SSE2 and SSSE3 machine instructions available on x86_64 CPUs.

In addition, many other people have made valuable contributions to the development of CFITSIO. These include (with apologies to others that may have inadvertently been omitted):

Steve Allen, Carl Akerlof, Keith Arnaud, Morten Krabbe Barfoed, Kent Blackburn, G Bodammer, Romke Bontekoe, Lucio Chiappetti, Keith Costorf, Robin Corbet, John Davis, Richard Fink, Ning Gan, Emily Greene, Gretchen Green, Joe Harrington, Cheng Ho, Phil Hodge, Jim Ingham, Yoshitaka Ishisaki, Diab Jerius, Mark Levine, Todd Karakaskian, Edward King, Scott Koch, Claire Larkin, Rob Managan, Eric Mandel, Richard Mathar, John Mattox, Carsten Meyer, Emi Miyata, Stefan Mochnacki, Mike Noble, Oliver Oberdorf, Clive Page, Arvind Parmar, Jeff Pedelty, Tim Pearson, Philippe Prugniel, Maren Purves, Scott Randall, Chris Rogers, Arnold Rots, Rob Seaman, Barry Schlesinger, Robin Stebbins, Andrew Szymkowiak, Allyn Tennant, Peter Teuben, James Theiler, Doug Tody, Shiro Ueno, Steve Walton, Archie Warnock, Alan Watson, Dan Whipple, Wim Wimmers, Peter Young, Jianjun Xu, and Nelson Zarate.

## 1.4 Legal Stuff

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