FITSIO - An Interface to FITS Format Files for Fortran Programmers

                    William D Pence, HEASARC, NASA/GSFC
                              Version 3.0

[Note: This file contains various formatting command symbols in the first 
column which are used when generating the LATeX version of this document.]

*I.  Introduction

This document describes the Fortran-callable subroutine interface that
is provided as part of the CFITSIO library (which is written in ANSI
C).  This is a companion document to the CFITSIO User's Guide which
should be consulted for further information about the underlying
CFITSIO library.  In the remainder of this document, the terms FITSIO
and CFITSIO are interchangeable and refer to the same library.

FITSIO/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 was written to provide a powerful yet simple
interface for accessing FITS files which will run on most commonly used
computers and workstations. FITSIO supports all the features described
in the official NOST 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
FITSIO subroutines 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.

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.

The latest version of the CFITSIO source code, documentation, and
example programs are available on the World-Wide Web or via anonymous
ftp from:
-
        http://heasarc.gsfc.nasa.gov/fitsio
        ftp://legacy.gsfc.nasa.gov/software/fitsio/c
-
\newpage
Any questions, bug reports, or suggested enhancements related to the CFITSIO
package should be sent to the primary author:
-
        Dr. William Pence                 Telephone:  (301) 286-4599
        HEASARC, Code 662                 E-mail: pence@tetra.gsfc.nasa.gov
        NASA/Goddard Space Flight Center
        Greenbelt, MD 20771, USA
-
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 {\tt http://fits.gsfc.nasa.gov}.  In particular, the
'NOST FITS Standard' gives the authoritative definition of the FITS data
format, and the  `FITS User's Guide' provides additional historical background
and practical advice on using FITS files.

CFITSIO users may also be interested in the FTOOLS package of programs
that can be used to manipulate and analyze FITS format files.
Information about FTOOLS can be obtained on the Web or via anonymous
ftp at:
-
        http://heasarc.gsfc.nasa.gov/ftools
        ftp://legacy.gsfc.nasa.gov/software/ftools/release
-

*II.  Creating FITSIO/CFITSIO 
 
**A.  Building the Library

To use the FITSIO subroutines one must first build the CFITSIO library,
which requires a C compiler. gcc is ideal, or most other ANSI-C
compilers will also work.  The CFITSIO code is contained in about 40 C
source files (*.c) and header files (*.h). On VAX/VMS systems 2
assembly-code files (vmsieeed.mar and vmsieeer.mar) are also needed.

The Fortran interface subroutines to the C CFITSIO routines are located
in the f77\_wrap1.c, through f77\_wrap4.c files.  These are relatively simple
'wrappers' that translate the arguments in the Fortran subroutine into
the appropriate format for the corresponding C routine.  This
translation is performed transparently to the user by a set of C macros
located in the cfortran.h file.  Unfortunately cfortran.h does not
support every combination of C and Fortran compilers so the Fortran
interface is not supported on all platforms. (see further notes below).  

A standard combination of C and Fortran compilers will be assumed by
default, but one may also specify a particular Fortran compiler by
doing:
-
 >  setenv CFLAGS -DcompilerName=1
-
(where 'compilerName' is the name of the compiler) before running 
the configure command.  The currently recognized compiler
names are: 
-
 g77Fortran
 IBMR2Fortran
 CLIPPERFortran
 pgiFortran
 NAGf90Fortran
 f2cFortran
 hpuxFortran
 apolloFortran
 sunFortran
 CRAYFortran
 mipsFortran
 DECFortran
 vmsFortran
 CONVEXFortran
 PowerStationFortran
 AbsoftUNIXFortran
 AbsoftProFortran
 SXFortran
-
Alternatively, one may edit the CFLAGS line in the Makefile to add the
'-DcompilerName' flag after running the './configure' command.

The CFITSIO library is built on Unix systems by typing:
-
 >  ./configure [--prefix=/target/installation/path]
 >  make          (or  'make shared')
 >  make install  (this step is optional)
-
at the operating system prompt.  The configure command customizes the
Makefile for the particular system, then the `make' command compiles the
source files and builds the library.  Type `./configure' and not simply
`configure' to ensure that the configure script in the current directory
is run and not some other system-wide configure script.  The optional
'prefix' argument to configure gives the path to the directory where
the CFITSIO library and include files should be installed via the later
'make install' command. For example,
-
   > ./configure --prefix=/usr1/local
-
will cause the 'make install' command to copy the CFITSIO libcfitsio file 
to /usr1/local/lib and the necessary include file to /usr1/local/include
(assuming of course that the process has permission to write to these 
directories).

By default this also builds the set of Fortran-callable
wrapper routines whose calling sequences are described later in this
document.

The 'make shared' option builds a shared or dynamic version of the
CFITSIO library.  When using the shared library the executable code is
not copied into your program at link time and instead the program
locates the necessary library code at run time, normally through
LD\_LIBRARY\_PATH or some other method. The advantages of using a shared
library are:
-
   1.  Less disk space if you build more than 1 program
   2.  Less memory if more than one copy of a program using the shared
       library is running at the same time since the system is smart
       enough to share copies of the shared library at run time.
   3.  Possibly easier maintenance since a new version of the shared
       library can be installed without relinking all the software
       that uses it (as long as the subroutine names and calling
       sequences remain unchanged).
   4.  No run-time penalty.
-
The disadvantages are:
-
   1. More hassle at runtime.  You have to either build the programs
      specially or have LD_LIBRARY_PATH set right.
   2. There may be a slight start up penalty, depending on where you are
      reading the shared library and the program from and if your CPU is
      either really slow or really heavily loaded.
-

On HP/UX systems, the environment variable CFLAGS should be set
to -Ae before running configure to enable "extended ANSI" features.

It may not be possible to staticly link programs that use CFITSIO on
some platforms (namely, on Solaris 2.6) due to the network drivers
(which provide FTP and HTTP access to FITS files).  It is possible to
make both a dynamic and a static version of the CFITSIO library, but
network file access will not be possible using the static version. 

On VAX/VMS and ALPHA/VMS systems the make\_gfloat.com command file may
be executed to build the cfitsio.olb object library using the default
G-floating point option for double variables.  The make\_dfloat.com and
make\_ieee.com files may be used instead to build the library with the
other floating point options. Note that the getcwd function that is
used in the group.c module may require that programs using CFITSIO be
linked with the ALPHA\$LIBRARY:VAXCRTL.OLB library.  See the example
link line in the next section of this document.

On Windows IBM-PC type platforms the situation is more complicated
because of the wide variety of Fortran compilers that are available and
because of the inherent complexities of calling the CFITSIO C routines
from Fortran.  Two different versions of the CFITSIO dll library are
available, compiled with the Borland C++ compiler and the Microsoft
Visual C++ compiler, respectively, in the files
cfitsiodll\_2xxx\_borland.zip and cfitsiodll\_2xxx\_vcc.zip, where
'2xxx' represents the current release number.  Both these dll libraries
contain a set of Fortran wrapper routines which may be compatible with
some, but probably not all, available Fortran compilers.  To test if
they are compatible, compile the program testf77.f and try linking to
these dll libraries.  If these libraries do not work with a particular
Fortran compiler, then there are 2 possible solutions.  The first
solution would be to modify the file cfortran.h for that particular
combination of C and Fortran compilers, and then rebuild the CFITSIO
dll library.  This will require, however, a some expertise in
mixed language programming.
The other solution is to use the older v5.03 Fortran-77 implementation
of FITSIO that is still available from the FITSIO web-site.  This
version is no longer supported, but it does provide the basic functions
for reading and writing FITS files and should be compatible with most
Fortran compilers.

CFITSIO has currently been tested on the following platforms:
-
  OPERATING SYSTEM           COMPILER
   Sun OS                     gcc and cc (3.0.1)
   Sun Solaris                gcc and cc
   Silicon Graphics IRIX      gcc and cc
   Silicon Graphics IRIX64    MIPS
   Dec Alpha OSF/1            gcc and cc
   DECstation  Ultrix         gcc
   Dec Alpha OpenVMS          cc 
   DEC VAX/VMS                gcc and cc
   HP-UX                      gcc
   IBM AIX                    gcc
   Linux                      gcc
   MkLinux                    DR3
   Windows 95/98/NT           Borland C++ V4.5
   Windows 95/98/NT/ME/XP     Microsoft/Compaq Visual C++ v5.0, v6.0
   Windows 95/98/NT           Cygwin gcc
   OS/2                       gcc + EMX
   MacOS 7.1 or greater       Metrowerks 10.+
-
CFITSIO will probably run on most other Unix platforms.  Cray
supercomputers are currently not supported.

**B.  Testing the Library
 
The CFITSIO library should be tested by building and running
the testprog.c program that is included with the release. 
On Unix systems type:
-
    % make testprog
    % testprog > testprog.lis
    % diff testprog.lis testprog.out
    % cmp testprog.fit testprog.std
-
 On VMS systems,
(assuming cc is the name of the C compiler command), type:
-
    $ cc testprog.c
    $ link testprog, cfitsio/lib, alpha$library:vaxcrtl/lib
    $ run testprog
-
The testprog program should produce a FITS file called `testprog.fit'
that is identical to the `testprog.std' FITS file included with this
release.  The diagnostic messages (which were piped to the file
testprog.lis in the Unix example) should be identical to the listing
contained in the file testprog.out.  The 'diff' and 'cmp' commands
shown above should not report any differences in the files.  (There
may be some minor formatting differences, such as the presence or
absence of leading zeros, or 3 digit exponents in numbers,
which can be ignored).

The Fortran wrappers in CFITSIO may be tested with the testf77
program.  On Unix systems the fortran compilation and link command
may be called 'f77' or 'g77', depending on the system.
-
   % f77 -o testf77 testf77.f -L. -lcfitsio -lnsl -lsocket  
 or
   % f77 -f -o testf77 testf77.f -L. -lcfitsio    (under SUN O/S)
 or
   % f77 -o testf77 testf77.f -Wl,-L. -lcfitsio -lm -lnsl -lsocket (HP/UX)
 or
   % g77 -o testf77 -s testf77.f -lcfitsio -lcc_dynamic -lncurses (Mac OS-X)

   % testf77 > testf77.lis
   % diff testf77.lis testf77.out
   % cmp testf77.fit testf77.std
-
On machines running SUN O/S, Fortran programs must be compiled with the
'-f' option to force double precision variables to be aligned on 8-byte
boundarys to make the fortran-declared variables compatible with C.  A
similar compiler option may be required on other platforms.  Failing to
use this option may cause the program to crash on FITSIO routines that
read or write double precision variables.

Also note that on some systems, the output listing of the testf77
program may differ slightly from the testf77.std template, if leading
zeros are not printed by default before the decimal point when using F
format.

A few other utility  programs are included with CFITSIO: 
-
    speed - measures the maximum throughput (in MB per second)
              for writing and reading FITS files with CFITSIO

    listhead - lists all the header keywords in any FITS file

    fitscopy - copies any FITS file (especially useful in conjunction
                 with the CFITSIO's extended input filename syntax)

    cookbook - a sample program that performs common read and
                 write operations on a FITS file.

    iter_a, iter_b, iter_c - examples of the CFITSIO iterator routine
-

The first 4 of these utility programs can be compiled and linked by typing
-
   %  make program_name
-

**C.  Linking Programs with FITSIO

When linking applications software with the FITSIO library, several system libraries usually need to be specified on the link command line.  On 
Unix systems, the most reliable way to determine what libraries are required
is to type 'make testprog' and see what libraries the configure script has 
added.  The typical libraries that may need to be added are -lm (the math 
library) and -lnsl and -lsocket (needed only for FTP and HTTP file access).
These latter 2 libraries are not needed on VMS and Windows platforms, 
because FTP file access is not currently supported on those platforms.
 
Note that when upgrading to a newer version of CFITSIO it is usually
necessay to recompile, as well as relink, the programs that use CFITSIO,
because the definitions in fitsio.h often change.
 
**D.  Getting Started with FITSIO

In order to effectively use the FITSIO library as quickly as possible,
it is recommended that new users follow these steps:

1.  Read the following `FITS Primer' chapter for a brief
overview of the structure of FITS files.  This is especially important
for users who have not previously dealt with the FITS table and image
extensions.

2.  Write a simple program to read or write a FITS file using the Basic
Interface routines. 

3.  Refer to the cookbook.f program that is included with this release
for examples of routines that perform various common FITS file
operations.

4. Read Chapters 4 and 5 to become familiar with the conventions and
advanced features of the FITSIO interface.

5.  Scan through the more extensive set of routines that are provided
in the `Advanced Interface'.  These routines perform more specialized
functions than are provided by the Basic Interface routines.

**E.  Example Program

The following listing shows an example of how to use the FITSIO
routines in a Fortran program.  Refer to the cookbook.f program that
is included with the FITSIO distribution for examples of other
FITS programs.
-
      program writeimage

C     Create a FITS primary array containing a 2-D image

      integer status,unit,blocksize,bitpix,naxis,naxes(2)
      integer i,j,group,fpixel,nelements,array(300,200)
      character filename*80
      logical simple,extend

      status=0
C     Name of the FITS file to be created:
      filename='ATESTFILE.FITS'

C     Get an unused Logical Unit Number to use to create the FITS file
      call ftgiou(unit,status)

C     create the new empty FITS file
      blocksize=1
      call ftinit(unit,filename,blocksize,status)

C     initialize parameters about the FITS image (300 x 200 16-bit integers)
      simple=.true.
      bitpix=16
      naxis=2
      naxes(1)=300
      naxes(2)=200
      extend=.true.

C     write the required header keywords
      call ftphpr(unit,simple,bitpix,naxis,naxes,0,1,extend,status)

C     initialize the values in the image with a linear ramp function
      do j=1,naxes(2)
          do i=1,naxes(1)
              array(i,j)=i+j
          end do
      end do

C     write the array to the FITS file
      group=1
      fpixel=1
      nelements=naxes(1)*naxes(2)
      call ftpprj(unit,group,fpixel,nelements,array,status)

C     write another optional keyword to the header
      call ftpkyj(unit,'EXPOSURE',1500,'Total Exposure Time',status)

C     close the file and free the unit number
      call ftclos(unit, status)
      call ftfiou(unit, status)
      end
-

**F.  Legal Stuff

Copyright (Unpublished--all rights reserved under the copyright laws of
the United States), U.S. Government as represented by the Administrator
of the National Aeronautics and Space Administration.  No copyright is
claimed in the United States under Title 17, U.S. Code.

Permission to freely use, copy, modify, and distribute this software
and its documentation without fee is hereby granted, provided that this
copyright notice and disclaimer of warranty appears in all copies.
(However, see the restriction on the use of the gzip compression code,
below).

DISCLAIMER:

THE SOFTWARE IS PROVIDED 'AS IS' WITHOUT ANY WARRANTY OF ANY KIND,
EITHER EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO,
ANY WARRANTY THAT THE SOFTWARE WILL CONFORM TO SPECIFICATIONS, ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
PURPOSE, AND FREEDOM FROM INFRINGEMENT, AND ANY WARRANTY THAT THE
DOCUMENTATION WILL CONFORM TO THE SOFTWARE, OR ANY WARRANTY THAT THE
SOFTWARE WILL BE ERROR FREE.  IN NO EVENT SHALL NASA BE LIABLE FOR ANY
DAMAGES, INCLUDING, BUT NOT LIMITED TO, DIRECT, INDIRECT, SPECIAL OR
CONSEQUENTIAL DAMAGES, ARISING OUT OF, RESULTING FROM, OR IN ANY WAY
CONNECTED WITH THIS SOFTWARE, WHETHER OR NOT BASED UPON WARRANTY,
CONTRACT, TORT , OR OTHERWISE, WHETHER OR NOT INJURY WAS SUSTAINED BY
PERSONS OR PROPERTY OR OTHERWISE, AND WHETHER OR NOT LOSS WAS SUSTAINED
FROM, OR AROSE OUT OF THE RESULTS OF, OR USE OF, THE SOFTWARE OR
SERVICES PROVIDED HEREUNDER."

The file compress.c contains (slightly modified) source code that
originally came from gzip-1.2.4, copyright (C) 1992-1993 by Jean-loup
Gailly.  This gzip code is distributed under the GNU General Public
License and thus requires that any software that uses the CFITSIO
library (which in turn uses the gzip code) must conform to the
provisions in the GNU General Public License.  A copy of the GNU
license is included at the beginning of compress.c file.

Similarly, the file wcsutil.c contains 2 slightly modified routines
from the Classic AIPS package that are also distributed under the GNU
General Public License.

Alternate versions of the compress.c and wcsutil.c files (called
compress\_alternate.c and wcsutil\_alternate.c) are provided for users 
who want to use the CFITSIO
library but are unwilling or unable to publicly release their software
under the terms of the GNU General Public License.   These alternate
versions contains non-functional stubs for the file compression and
uncompression routines and the world coordinate transformation routines
used by CFITSIO.  Replace the file `compress.c'
with `compress\_alternate.c' and 'wcsutil.c' with 'wcsutil\_alternate.c
before compiling the CFITSIO library.  This
will produce a version of CFITSIO which does not support reading or
writing compressed FITS files, or doing image coordinate transformations,
but is otherwise identical to the standard version.  

**G.  Acknowledgements

The development of many of the 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.

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.

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.

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).

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, 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, John Mattox, Carsten Meyer, Emi
Miyata, Stefan Mochnacki, Mike Noble, Oliver Oberdorf, Clive Page,
Arvind Parmar, Jeff Pedelty, Tim Pearson, Maren Purves, Scott Randall,
Chris Rogers, Arnold Rots, 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.


*III.  A FITS Primer

This section gives a brief overview of the structure of FITS files.
Users should refer to the documentation available from the NOST, as
described in the introduction, for more detailed information on FITS
formats.

FITS was first developed in the late 1970's as a standard data
interchange format between various astronomical observatories.  Since
then FITS has become the defacto standard data format supported by most
astronomical data analysis software packages.  

A FITS file consists of one or more Header + Data Units (HDUs), where
the first HDU is called the `Primary HDU', or `Primary Array'.  The
primary array contains an N-dimensional array of pixels, such as a 1-D
spectrum, a 2-D image, or a 3-D data cube.  Six different primary
datatypes are supported: Unsigned 8-bit bytes, 16, 32, and 64-bit signed
integers, and 32 and 64-bit floating point reals.  FITS also has a
convention for storing unsigned integers (see the later
section entitled `Unsigned Integers' for more details). The primary HDU
may also consist of only a header with a null array containing no
data pixels.

Any number of additional HDUs may follow the primary array; these
additional HDUs are called FITS `extensions'.  There are currently 3
types of extensions defined by the FITS standard:

\begin{itemize}
\item
  Image Extension - a N-dimensional array of pixels, like in a primary array
\item
  ASCII Table Extension - rows and columns of data in ASCII character format
\item
  Binary Table Extension - rows and columns of data in binary representation
\end{itemize}

In each case the HDU consists of an ASCII Header Unit followed by an optional
Data Unit.  For historical reasons, each Header or Data unit must be an
exact multiple of 2880 8-bit bytes long.  Any unused space is padded
with fill characters (ASCII blanks or zeros).

Each Header Unit consists of any number of 80-character keyword records
or `card images' which have the general form:
-
  KEYNAME = value / comment string
  NULLKEY =       / comment: This keyword has no value
-
The keyword names may be up to 8 characters long and can only contain
uppercase letters, the digits 0-9, the hyphen, and the underscore
character. The keyword name is (usually) followed by an equals sign and
a space character (= ) in columns 9 - 10 of the record, followed by the
value of the keyword which may be either an integer, a floating point
number, a character string (enclosed in single quotes), or a boolean
value (the letter T or F).   A keyword may also have a null or undefined
value if there is no specified value string, as in the second example.

The last keyword in the header is always the `END' keyword which has no
value or comment fields. There are many rules governing the exact
format of a keyword record (see the NOST FITS Standard) so it is better
to rely on standard interface software like FITSIO to correctly
construct or to parse the keyword records rather than try to deal
directly with the raw FITS formats.

Each Header Unit begins with a series of required keywords which depend
on the type of HDU.  These required keywords specify the size and
format of the following Data Unit.  The header may contain other
optional keywords to describe other aspects of the data, such as the
units or scaling values.  Other COMMENT or HISTORY keywords are also
frequently added to further document the data file.

The optional Data Unit immediately follows the last 2880-byte block in
the Header Unit.  Some HDUs do not have a Data Unit and only consist of
the Header Unit.

If there is more than one HDU in the FITS file, then the Header Unit of
the next HDU immediately follows the last 2880-byte block of the
previous Data Unit (or Header Unit if there is no Data Unit).

The main required keywords in FITS primary arrays or image extensions are:
\begin{itemize}
\item
BITPIX -- defines the datatype of the array: 8, 16, 32, 64, -32, -64 for
unsigned 8--bit byte, 16--bit signed integer, 32--bit signed integer,
64--bit signed integer,
32--bit IEEE floating point, and 64--bit IEEE double precision floating
point, respectively.
\item
NAXIS --  the number of dimensions in the array, usually 0, 1, 2, 3, or 4.
\item
NAXISn -- (n ranges from 1 to NAXIS) defines the size of each dimension.
\end{itemize}

FITS tables start with the keyword XTENSION = `TABLE' (for ASCII
tables) or XTENSION = `BINTABLE' (for binary tables) and have the
following main keywords:
\begin{itemize}
\item
TFIELDS -- number of fields or columns in the table
\item
NAXIS2 -- number of rows in the table
\item
TTYPEn -- for each column (n ranges from 1 to TFIELDS) gives the
name of the column
\item
TFORMn -- the datatype of the column
\item
TUNITn -- the physical units of the column (optional)
\end{itemize}

Users should refer to the FITS Support Office at {\tt http://fits.gsfc.nasa.gov}
for futher information about the FITS format and related software 
packages.


*V.  FITSIO Conventions and Guidelines

**A.  CFITSIO Size Limitations

CFITSIO places few restrictions on the size of FITS files that it
reads or writes.  There are a few limits, however, which may affect
some extreme cases:

1.  The maximum number of FITS files that may be simultaneously opened
by CFITSIO is set by NMAXFILES as defined in fitsio2.h.  It is currently
set = 300 by default.  CFITSIO will allocate about 80 * NMAXFILES bytes
of memory for internal use.  Note that the underlying C compiler or
operating system, may have a smaller limit on the number of opened files.
The C symbolic constant FOPEN\_MAX is intended to define the maximum
number of files that may open at once (including any other text or
binary files that may be open, not just FITS files).  On some systems it
has been found that gcc supports a maximum of 255 opened files.

Note that opening and operating on many FITS files simultaneously in
parallel may be less efficient than operating on smaller groups of files
in series.  CFITSIO only has NIOBUF number of internal buffers (set = 40
by default) that are used for temporary storage of the most recent data
records that have been read or written in the FITS files.  If the number
of opened files is greater than NIOBUF, then CFITSIO may waste more time
flushing and re-reading or re-writing the same records in the FITS files.

2.  By default, CFITSIO can handle FITS files up to 2.1 GB in size (2**31
bytes).  This file size limit is often imposed by 32-bit operating
systems.  More recently, as 64-bit operating systems become more common, an
industry-wide standard (at least on Unix systems) has been developed to
support larger sized files (see http://ftp.sas.com/standards/large.file/). 
Starting with version 2.1 of CFITSIO, larger FITS files up to 6 terabytes
in size may be read and written on supported platforms.  In order
to support these larger files, CFITSIO must be compiled with the
'-D\_LARGEFILE\_SOURCE' and `-D\_FILE\_OFFSET\_BITS=64' compiler flags. 
Some platforms may also require the `-D\_LARGE\_FILES' compiler flag.
 This causes the compiler to allocate 8-bytes instead of
4-bytes for the `off\_t' datatype which is used to store file offset
positions.  It appears that in most cases it is not necessary to
also include these compiler flags when compiling programs that link to
the CFITSIO library.

If CFITSIO is compiled with the -D\_LARGEFILE\_SOURCE 
and -D\_FILE\_OFFSET\_BITS=64 flags on a
platform that supports large files, then it can read and write FITS
files that contain up to 2**31 2880-byte FITS records, or approximately
6 terabytes in size.  It is still required that the value of the NAXISn
and PCOUNT keywords in each extension be within the range of a signed
4-byte integer (max value = 2,147,483,648).  Thus, each dimension of an
image (given by the NAXISn keywords), the total width of a table
(NAXIS1 keyword), the number of rows in a table (NAXIS2 keyword), and
the total size of the variable-length array heap in binary tables
(PCOUNT keyword) must be less than this limit.

Currently, support for large files within CFITSIO has been tested
on the Linux, Solaris, and IBM AIX operating systems.

**B.  Multiple Access to the Same FITS File

CFITSIO supports simultaneous read and write access to multiple HDUs in
the same FITS file.  Thus, one can open the same FITS file twice within
a single program and move to 2 different HDUs in the file, and then
read and write data or keywords to the 2 extensions just as if one were
accessing 2 completely separate FITS files.   Since in general it is
not possible to physically open the same file twice and then expect to
be able to simultaneously (or in alternating succession) write to 2
different locations in the file, CFITSIO recognizes when the file to be
opened (in the call to fits\_open\_file) has already been opened and
instead of actually opening the file again, just logically links the
new file to the old file.  (This only applies if the file is opened
more than once within the same program, and does not prevent the same
file from being simultaneously opened by more than one program).  Then
before CFITSIO reads or writes to either (logical) file, it makes sure
that any modifications made to the other file have been completely
flushed from the internal buffers to the file.  Thus, in principle, one
could open a file twice, in one case pointing to the first extension
and in the other pointing to the 2nd extension and then write data to
both extensions, in any order, without danger of corrupting the file,
There may be some efficiency penalties in doing this however, since
CFITSIO has to flush all the internal buffers related to one file
before switching to the  other, so it would still be prudent to
minimize the number of times one switches back and forth between doing
I/O to different HDUs in the same file.

**C.  Current Header Data Unit (CHDU)

In general, a FITS file can contain multiple Header Data Units, also
called extensions.  CFITSIO only operates within one HDU at any given
time, and the currently selected HDU is called the Current Header Data
Unit (CHDU).  When a FITS file is first created or opened the CHDU is
automatically defined to be the first HDU (i.e., the primary array).
CFITSIO routines are provided to move to and open any other existing
HDU within the FITS file or to append or insert a new HDU in the FITS
file which then becomes the CHDU.

**D.  Subroutine Names

All FITSIO subroutine names begin with the letters 'ft' to distinguish
them from other subroutines and are 5 or 6 characters long. Users should
not name their own subroutines beginning with 'ft' to avoid conflicts.
(The SPP interface routines all begin with 'fs'). Subroutines which read
or get information from the FITS file have names beginning with
'ftg...'. Subroutines which write or put information into the FITS file
have names beginning with 'ftp...'.

**E.  Subroutine Families and Datatypes

Many of the subroutines come in families which differ only in the
datatype of the associated parameter(s) .  The datatype of these
subroutines is indicated by the last letter of the subroutine name
(e.g., 'j' in 'ftpkyj') as follows:
-
        x - bit 
        b - character*1 (unsigned byte)  
        i - short integer (I*2)
        j - integer (I*4, 32-bit integer)
        k - long long integer (I*8, 64-bit integer)
        e - real exponential floating point (R*4)
        f - real fixed-format floating point (R*4)
        d - double precision real floating-point (R*8)
        g - double precision fixed-format floating point (R*8)
        c - complex reals (pairs of R*4 values)
        m - double precision complex (pairs of R*8 values)
        l - logical (L*4)
        s - character string
-

When dealing with the FITS byte datatype, it is important to remember
that the raw values (before any scaling by the BSCALE and BZERO, or
TSCALn and TZEROn keyword values) in byte arrays (BITPIX = 8) or byte
columns (TFORMn = 'B') are interpreted as unsigned bytes with values
ranging from 0 to 255. Some Fortran compilers support a non-standard
byte datatype such as INTEGER*1, LOGICAL*1, or BYTE, which can sometimes
be used instead of CHARACTER*1 variables. Many machines permit passing a
numeric datatype (such as INTEGER*1) to the FITSIO subroutines which are
expecting a CHARACTER*1 datatype, but this technically violates the
Fortran-77 standard and is not supported on all machines (e.g., on a VAX/VMS
machine one must use the VAX-specific \%DESCR function).

One feature of the CFITSIO routines is that they can operate on a `X'
(bit) column in a binary table as though it were a `B' (byte) column.
For example a `11X' datatype column can be interpreted the same as a
`2B' column (i.e., 2 unsigned 8-bit bytes).  In some instances, it can
be more efficient to read and write whole bytes at a time, rather than
reading or writing each individual bit.

The double precision complex datatype is not a standard Fortran-77
datatype.  If a particular Fortran compiler does not directly support
this datatype,  then one may instead pass an array of pairs of double
precision values to these subroutines.  The first  value in each pair
is the real part, and the second is the imaginary part.

**F.  Implicit Data Type Conversion

The FITSIO routines that read and write numerical data can perform
implicit data type conversion.  This means that the data type of the
variable or array in the program does not need to be the same as the
data type of the value in the FITS file.  Data type conversion is
supported for numerical and string data types (if the string contains a
valid number enclosed in quotes) when reading a FITS header keyword
value and for numeric values when reading or writing values in the
primary array or a table column.  CFITSIO returns status =
NUM\_OVERFLOW  if the converted data value exceeds the range of the
output data type.  Implicit data type conversion is not supported
within binary tables for string, logical, complex, or double complex
data types.

In addition, any table column may be read as if it contained string values.
In the case of numeric columns the returned string will be formatted
using the TDISPn display format if it exists.

**G.  Data Scaling

When reading numerical data values in the primary array or a
table column, the values will be scaled automatically by the BSCALE and
BZERO (or TSCALn and TZEROn) header keyword values if they are
present in the header.  The scaled data that is returned to the reading
program will have
-
        output value = (FITS value) * BSCALE + BZERO
-
(a corresponding formula using TSCALn and TZEROn is used when reading
from table columns).  In the case of integer output values the floating
point scaled value is truncated to an integer (not rounded to the
nearest integer).  The ftpscl and fttscl subroutines may be used to
override the scaling parameters defined in the header (e.g., to turn
off the scaling so that the program can read the raw unscaled values
from the FITS file).

When writing numerical data to the primary array or to a table
column the data values will generally be automatically inversely scaled
by the value of the BSCALE and BZERO (or TSCALn and TZEROn) header
keyword values if they they exist in the header.  These keywords must
have been written to the header before any data is written for them to
have any effect.  Otherwise, one may use the ftpscl and fttscl
subroutines to define or override the scaling keywords in the header
(e.g., to turn off the scaling so that the program can write the raw
unscaled values into the FITS file). If scaling is performed, the
inverse scaled output value that is written into the FITS file will
have
-
         FITS value = ((input value) - BZERO) / BSCALE
-
(a corresponding formula using TSCALn and TZEROn is used when
writing to table columns).  Rounding to the nearest integer, rather
than truncation, is performed when writing integer datatypes to the
FITS file.

**H.  Error Status Values and the Error Message Stack

The last parameter in nearly every FITSIO subroutine is the error
status value which is both an input and an output parameter.  A
returned positive value for this parameter indicates an error was
detected.  A listing of all the FITSIO status code values is given at
the end of this document.

The FITSIO library uses an `inherited status' convention for the status
parameter which means that if a subroutine is called with a positive
input value of the status parameter, then the subroutine will exit
immediately without changing the value of the status parameter.  Thus,
if one passes the status value returned from each FITSIO routine as
input to the next FITSIO subroutine, then whenever an error is detected
all further FITSIO processing will cease.  This convention can simplify
the error checking in application programs because it is not necessary
to check the value of the status parameter after every single FITSIO
subroutine call.  If a program contains a sequence of several FITSIO
calls, one can just check the status value after the last call.  Since
the returned status values are generally distinctive, it should be
possible to determine which subroutine originally returned the error
status.  

FITSIO also maintains an internal stack of error messages (80-character
maximum length) which in many cases provide a more detailed explanation
of the cause of the error than is provided by the error status number
alone. It is recommended that the error message stack be printed out
whenever a program detects a FITSIO error. To do this, call the FTGMSG
routine repeatedly to get the successive messages on the stack. When the
stack is empty FTGMSG will return a blank string. Note that this is a
`First In -- First Out' stack, so the oldest error message is returned
first by ftgmsg.

**I.  Variable-Length Array Facility in Binary Tables

FITSIO provides easy-to-use support for reading and writing data in
variable length fields of a binary table. The variable length columns
have TFORMn keyword values of the form `1Pt(len)' or `1Qt(len)' where `t' is the
datatype code (e.g., I, J, E, D, etc.) and `len' is an integer
specifying the maximum length of the vector in the table.  If the value
of `len' is not specified when the table is created (e.g., if the TFORM
keyword value is simply specified as '1PE' instead of '1PE(400) ), then
FITSIO will automatically scan the table when it is closed to
determine the maximum length of the vector and will append this value
to the TFORMn value.

The same routines which read and write data in an ordinary fixed length
binary table extension are also used for variable length fields,
however, the subroutine parameters take on a slightly different
interpretation as described below.

All the data in a variable length field is written into an area called
the `heap' which follows the main fixed-length FITS binary table.  The
size of the heap, in bytes, is specified with the PCOUNT keyword in the
FITS header.  When creating a new binary table, the initial value of
PCOUNT should usually be set to zero.  FITSIO will recompute the size
of the heap as the data is written and will automatically update the
PCOUNT keyword value when the table is closed.  When writing variable
length data to a table, CFITSIO will automatically extend the size
of the heap area if necessary, so that any following HDUs do not
get overwritten.

By default the heap data area starts immediately after the last row of
the fixed-length table.  This default starting location may be
overridden by the THEAP keyword, but this is not recommended.  
If additional rows of data are added to the table, CFITSIO will
automatically shift the the heap down to make room for the new
rows, but it is obviously be more efficient to initially
create the table with the necessary number of blank rows, so that
the heap does not needed to be constantly moved.

When writing to a variable length field, the entire array of values for
a given row of the table must be written with a single call to FTPCLx.
The total length of the array is calculated from (NELEM+FELEM-1). One
cannot append more elements to an existing field at a later time; any
attempt to do so will simply overwrite all the data which was previously
written. Note also that the new data will be written to a new area of
the heap and the heap space used by the previous write cannot be
reclaimed. For this reason it is advised that each row of a variable
length field only be written once. An exception to this general rule
occurs when setting elements of an array as undefined. One must first
write a dummy value into the array with FTPCLx, and then call FTPCLU to
flag the desired elements as undefined. (Do not use the FTPCNx family
of routines with variable length fields). Note that the rows of a table,
whether fixed or variable length, do not have to be written
consecutively and may be written in any order.

When writing to a variable length ASCII character field (e.g., TFORM =
'1PA') only a single character string written.  FTPCLS writes the whole
length of the input string (minus any trailing blank characters), thus
the NELEM and FELEM parameters are ignored.  If the input string is
completely blank then FITSIO will write one blank character to the FITS
file.  Similarly, FTGCVS and FTGCFS read the entire string (truncated
to the width of the character string argument in the subroutine call)
and also ignore the NELEM and FELEM parameters.

The FTPDES subroutine is useful in situations where multiple rows of a
variable length column have the identical array of values.  One can
simply write the array once for the first row, and then use FTPDES to
write the same descriptor values into the other rows (use the FTGDES
routine to read the first descriptor value);  all the rows will then
point to the same storage location thus saving disk space.

When reading from a variable length array field one can only read as
many elements as actually exist in that row of the table; reading does
not automatically continue with the next row of the table as occurs
when reading an ordinary fixed length table field.  Attempts to read
more than this will cause an error status to be returned.  One can
determine the number of elements in each row of a variable column with
the FTGDES subroutine.

**I.  Support for IEEE Special Values

The ANSI/IEEE-754 floating-point number standard defines certain
special values that are used to represent such quantities as
Not-a-Number (NaN), denormalized, underflow, overflow, and infinity.
(See the Appendix in the NOST FITS standard or the NOST FITS User's
Guide for a list of these values).  The FITSIO subroutines that read
floating point data in FITS files recognize these IEEE special values
and by default interpret the overflow and infinity values as being
equivalent to a NaN, and convert the underflow and denormalized values
into zeros.  In some cases programmers may want access to the raw IEEE
values, without any modification by FITSIO.  This can be done by
calling the FTGPVx or FTGCVx routines while specifying 0.0 as the value
of the NULLVAL parameter.  This will force FITSIO to simply pass the
IEEE values through to the application program, without any
modification.  This does not work for double precision values on
VAX/VMS machines, however, where there is no easy way to bypass the
default interpretation of the IEEE special values.

**J.  When the Final Size of the FITS HDU is Unknown

It is not required to know the total size of a FITS data array or table
before beginning to write the data to the FITS file.  In the case of
the primary array or an image extension, one should initially create
the array with the size of the highest dimension (largest NAXISn
keyword) set to a dummy value, such as 1.  Then after all the data have
been written and the true dimensions are known, then the NAXISn value
should be updated using the fits\_ update\_key routine before moving to
another extension or closing the FITS file.

When writing to FITS tables, CFITSIO automatically keeps track of the
highest row number that is written to, and will increase the size of
the table if necessary.  CFITSIO will also automatically insert space
in the FITS file if necessary, to ensure that the data 'heap', if it
exists, and/or any additional HDUs that follow the table do not get
overwritten as new rows are written to the table.

As a general rule it is best to specify the initial number of rows = 0
when the table is created, then let CFITSIO keep track of the number of
rows that are actually written.  The application program should not
manually update the number of rows in the table (as given by the NAXIS2
keyword) since CFITSIO does this automatically.  If a table is
initially created with more than zero rows, then this will usually be
considered as the minimum size of the table, even if fewer rows are
actually written to the table.  Thus, if a table is initially created
with NAXIS2 = 20, and CFITSIO only writes 10 rows of data before
closing the table, then NAXIS2 will remain equal to 20.  If however, 30
rows of data are written to this table, then NAXIS2 will be increased
from 20 to 30.  The one exception to this automatic updating of the
NAXIS2 keyword is if the application program directly modifies the
value of NAXIS2 (up or down) itself just before closing the table.  In this
case, CFITSIO does not update NAXIS2 again, since it assumes that the
application program must have had a good reason for changing the value
directly.  This is not recommended, however, and is only provided for
backward compatibility with software that initially creates a table
with a large number of rows, than decreases the NAXIS2 value to the
actual smaller value just before closing the table.

**K.  Local FITS Conventions supported by FITSIO

CFITSIO supports several local FITS conventions which are not
defined in the official NOST FITS standard and which are not
necessarily recognized or supported by other FITS software packages.
Programmers should be cautious about using these features, especially
if the FITS files that are produced are expected to be processed by
other software systems which do not use the CFITSIO interface.

***1.  Support for Long String Keyword Values.

The length of a standard FITS string keyword is limited to 68
characters because it must fit entirely within a single FITS header
keyword record.  In some instances it is necessary to encode strings
longer than this limit, so FITSIO supports a local convention in which
the string value is continued over multiple keywords. This
continuation convention uses an ampersand character at the end of each
substring to indicate that it is continued on the next keyword, and the
continuation keywords all have the name CONTINUE without an equal sign
in column 9. The string value may be continued in this way over as many
additional CONTINUE keywords as is required.  The following lines
illustrate this continuation convention which is used in the value of
the STRKEY keyword:
-
LONGSTRN= 'OGIP 1.0'           / The OGIP Long String Convention may be used.
STRKEY  = 'This is a very long string keyword&'  / Optional Comment
CONTINUE  ' value that is continued over 3 keywords in the &  '
CONTINUE  'FITS header.' / This is another optional comment.
-
It is recommended that the LONGSTRN keyword, as shown
here, always be included in any HDU that uses this longstring
convention.  A subroutine called FTPLSW
has been provided in CFITSIO to write this keyword if it does not
already exist.

This long string convention is supported by the following FITSIO
subroutines that deal with string-valued keywords:
-
      ftgkys - read a string keyword
      ftpkls - write (append) a string keyword
      ftikls - insert a string keyword
      ftmkls - modify the value of an existing string keyword
      ftukls - update an existing keyword, or write a new keyword
      ftdkey - delete a keyword
-
These routines will transparently read, write, or delete a long string
value in the FITS file, so programmers in general do not have to be
concerned about the details of the convention that is used to encode
the long string in the FITS header.  When reading a long string, one
must ensure that the character string parameter used in these
subroutine calls has been declared long enough to hold the entire
string, otherwise the returned string value will be truncated.

Note that the more commonly used FITSIO subroutine to write string
valued keywords (FTPKYS) does NOT support this long string convention
and only supports strings up to 68 characters in length.  This has been
done deliberately to prevent programs from inadvertently writing
keywords using this non-standard convention without the explicit intent
of the programmer or user.   The FTPKLS subroutine must be called
instead to write long strings.  This routine can also be used to write
ordinary string values less than 68 characters in length.

***2.  Arrays of Fixed-Length Strings in Binary Tables

The definition of the FITS binary table extension format does not
provide a simple way to specify that a character column contains an
array of fixed-length strings.  To support this feature, FITSIO uses a
local convention for the format of the TFORMn keyword value of the form
'rAw' where 'r' is an integer specifying the total width in characters
of the column, and 'w' is an integer specifying the (fixed) length of
an individual unit string within the vector.  For example, TFORM1 =
'120A10' would indicate that the binary table column is 120 characters
wide and consists of 12 10-character length strings.  This convention
is recognized by the FITSIO subroutines that read or write strings in
binary tables.   The Binary Table definition document specifies that
other optional characters may follow the datatype code in the TFORM
keyword, so this local convention is in compliance with the
FITS standard, although other FITS readers are not required to
recognize this convention.

The Binary Table definition document that was approved by the IAU in
1994 contains an appendix describing an alternate convention for
specifying arrays of fixed or variable length strings in a binary table
character column (with the form 'rA:SSTRw/nnn)'.  This appendix was not
officially voted on by the IAU and hence is still provisional.  FITSIO
does not currently support this proposal.

***3.  Keyword Units Strings

One deficiency of the current FITS Standard is that it does not define
a specific convention for recording the physical units of a keyword
value.  The TUNITn keyword can be used to specify the physical units of
the values in a table column, but there is no analogous convention for
keyword values.  The comment field of the keyword is often used for
this purpose, but the units are usually not specified in a well defined
format that FITS readers can easily recognize and extract.

To solve this deficiency, FITSIO uses a local convention in which the
keyword units are enclosed in square brackets as the first token in the
keyword comment field; more specifically, the opening square bracket
immediately follows the slash '/' comment field delimiter and a single
space character.  The following examples illustrate keywords that use
this convention:

-
EXPOSURE=               1800.0 / [s] elapsed exposure time
V_HELIO =                16.23 / [km s**(-1)] heliocentric velocity
LAMBDA  =                5400. / [angstrom] central wavelength
FLUX    = 4.9033487787637465E-30 / [J/cm**2/s] average flux
-

In general, the units named in the IAU(1988) Style Guide are
recommended, with the main exception that the preferred unit for angle
is 'deg' for degrees.

The FTPUNT and FTGUNT subroutines in FITSIO write and read,
respectively, the keyword unit strings in an existing keyword.

***4.  HIERARCH Convention for Extended Keyword Names

CFITSIO supports the HIERARCH keyword convention which allows keyword
names that are longer then 8 characters and may contain the full range
of printable ASCII text characters.  This convention 
was developed at the European Southern Observatory (ESO)  to support 
hierarchical FITS keyword such as:
-
HIERARCH ESO INS FOCU POS = -0.00002500 / Focus position
-
Basically, this convention uses the FITS keyword 'HIERARCH' to indicate
that this convention is being used, then the actual keyword name
({\tt'ESO INS FOCU POS'} in this example) begins in column 10 and can
contain any printable ASCII text characters, including spaces.  The
equals sign marks the end of the keyword name and is followed by the
usual value and comment fields just as in standard FITS keywords.
Further details of this convention are described at
http://arcdev.hq.eso.org/dicb/dicd/dic-1-1.4.html (search for
HIERARCH).

This convention allows a much broader range of keyword names 
than is allowed by the FITS Standard.  Here are more examples
of such keywords:
-
HIERARCH LongKeyword = 47.5 / Keyword has > 8 characters, and mixed case
HIERARCH XTE$TEMP = 98.6 / Keyword contains the '$' character
HIERARCH Earth is a star = F / Keyword contains embedded spaces
-
CFITSIO will transparently read and write these keywords, so application
programs do not in general need to know anything about the specific
implementation details of the HIERARCH convention.  In particular,
application programs do not need to specify the `HIERARCH' part of the
keyword name when reading or writing keywords (although it
may be included if desired).  When writing a keyword, CFITSIO first
checks to see if the keyword name is legal as a standard FITS keyword
(no more than 8 characters long and containing only letters, digits, or
a minus sign or underscore). If so it writes it as a standard FITS
keyword, otherwise it uses the hierarch convention to write the
keyword.   The maximum keyword name length is 67 characters, which
leaves only 1 space for the value field.  A more practical limit is
about 40 characters, which leaves enough room for most keyword values.
CFITSIO returns an error if there is not enough room for both the
keyword name and the keyword value on the 80-character card, except for
string-valued keywords which are simply truncated so that the closing
quote character falls in column 80.  In the current implementation,
CFITSIO preserves the case of the letters when writing the keyword
name, but it is case-insensitive when reading or searching for a
keyword.  The current implementation allows any ASCII text character
(ASCII 32 to ASCII 126) in the keyword name except for the '='
character.  A space is also required on either side of the equal sign.

**L.  Optimizing Code for Maximum Processing Speed

CFITSIO has been carefully designed to obtain the highest possible
speed when reading and writing FITS files.  In order to achieve the
best performance, however, application programmers must be careful to
call the CFITSIO routines appropriately and in an efficient sequence;
inappropriate usage of CFITSIO routines can greatly slow down the
execution speed of a program.

The maximum possible I/O speed of CFITSIO depends of course on the type
of computer system that it is running on.  As a rough guide, the
current generation of workstations can achieve speeds of 2 -- 10 MB/s
when reading or writing FITS images and similar, or slightly slower
speeds with FITS binary tables.  Reading of FITS files can occur at
even higher rates (30MB/s or more) if the FITS file is still cached in
system memory following a previous read or write operation on the same
file.  To more accurately predict the best performance that is possible
on any particular system, a diagnostic program called ``speed.c'' is
included with the CFITSIO distribution which can be run to
approximately measure the maximum possible speed of writing and reading
a test FITS file.

The following 2 sections provide some background on how CFITSIO
internally manages the data I/O and describes some strategies that may
be used to optimize the processing speed of software that uses
CFITSIO.

***1.  Background Information: How CFITSIO Manages Data I/O

Many CFITSIO operations involve transferring only a small number of
bytes to or from the FITS file (e.g, reading a keyword, or writing a
row in a table); it would be very inefficient to physically read or
write such small blocks of data directly in the FITS file on disk,
therefore CFITSIO maintains a set of internal Input--Output (IO)
buffers in RAM memory that each contain one FITS block (2880 bytes) of
data.  Whenever CFITSIO needs to access data in the FITS file, it first
transfers the FITS block containing those bytes into one of the IO
buffers in memory.  The next time CFITSIO needs to access bytes in the
same block it can then go to the fast IO buffer rather than using a
much slower system disk access routine.  The number of available IO
buffers is determined by the NIOBUF parameter (in fitsio2.h) and is
currently set to 40.

Whenever CFITSIO reads or writes data it first checks to see if that
block of the FITS file is already loaded into one of the IO buffers.
If not, and if there is an empty IO buffer available, then it will load
that block into the IO buffer (when reading a FITS file) or will
initialize a new block (when writing to a FITS file).  If all the IO
buffers are already full, it must decide which one to reuse (generally
the one that has been accessed least recently), and flush the contents
back to disk if it has been modified before loading the new block.

The one major exception to the above process occurs whenever a large
contiguous set of bytes are accessed, as might occur when reading or
writing a FITS image.  In this case CFITSIO bypasses the internal IO
buffers and simply reads or writes the desired bytes directly in the
disk file with a single call to a low-level file read or write
routine.  The minimum threshold for the number of bytes to read or
write this way is set by the MINDIRECT parameter and is currently set
to 3 FITS blocks = 8640 bytes.  This is the most efficient way to read
or write large chunks of data and can achieve IO transfer rates of
5 -- 10MB/s or greater.  Note that this fast direct IO process is not
applicable when accessing columns of data in a FITS table because the
bytes are generally not contiguous since they are interleaved by the
other columns of data in the table.  This explains why the speed for
accessing FITS tables is generally slower than accessing
FITS images.

Given this background information, the general strategy for efficiently
accessing FITS files should now be apparent:  when dealing with FITS
images, read or write large chunks of data at a time so that the direct
IO mechanism will be invoked;  when accessing FITS headers or FITS
tables, on the other hand, once a particular FITS block has been
loading into one of the IO buffers, try to access all the needed
information in that block before it gets flushed out of the IO buffer.
It is important to avoid the situation where the same FITS block is
being read then flushed from a IO buffer multiple times.

The following section gives more specific suggestions for optimizing
the use of CFITSIO.

1.  When dealing with a FITS primary array or IMAGE extension, it is
more efficient to read or write large chunks of the  image at a time
(at least 3 FITS blocks = 8640 bytes) so that the direct IO mechanism
will be used as described in the previous section.  Smaller chunks of
data are read or written via the IO buffers, which is somewhat less
efficient because of the extra copy operation and additional
bookkeeping steps that are required.  In principle it is more efficient
to read or write as big an array of image pixels at one time as
possible, however, if the array becomes so large that the operating
system cannot store it all in RAM, then the performance may be degraded
because of the increased swapping of virtual memory to disk.

2.  When dealing with FITS tables, the most important efficiency factor
in the software design is to read or write the data in the FITS file in
a single pass through the file.  An example of poor program design
would be to read a large, 3-column table by sequentially reading the
entire first column, then going back to read the 2nd column, and
finally the 3rd column; this obviously requires 3 passes through the
file which could triple the execution time of an I/O limited program.
For small tables this is not important, but when reading multi-megabyte
sized tables these inefficiencies can become significant.  The more
efficient procedure in this case is to read or write only as many rows
of the table as will fit into the available internal I/O buffers, then
access all the necessary columns of data within that range of rows.
Then after the program is completely finished with the data in those
rows it can move on to the next range of rows that will fit in the
buffers, continuing in this way until the entire file has been
processed.  By using this procedure of accessing all the columns of a
table in parallel rather than sequentially, each block of the FITS file
will only be read or written once.

The optimal number of rows to read or write at one time in a given
table depends on the width of the table row, on the number of I/O
buffers that have been allocated in FITSIO, and also on the number of
other FITS files that are open at the same time (since one I/O buffer
is always reserved for each open FITS file).  Fortunately, a FITSIO
routine is available that will return the optimal number of rows for a
given table:  call ftgrsz(unit, nrows, status).  It is not critical to
use exactly the value of nrows returned by this routine, as long as one
does not exceed it.  Using a very small value however can also lead to
poor performance because of the overhead from the larger number of
subroutine calls.

The optimal number of rows returned by ftgrsz is valid only as long as
the application program is only reading or writing data in the
specified table.  Any other calls to access data in the table header or
in any other FITS file would  cause additional blocks of data to be
loaded into the I/O buffers displacing data from the original table,
and should be avoided during the critical period while the table is
being read or written.

Occasionally it is necessary to simultaneously access more than one
FITS table, for example when transferring values from an input table to
an output table.  In cases like this, one should call ftgrsz to get the
optimal number of rows for each table separately, than reduce the
number of rows proportionally.  For example, if the optimal number of
rows in the input table is 3600 and is 1400 in the output table, then
these values should be cut in half to 1800 and 700, respectively, if
both tables are going to be accessed at the same time.

3.  Use binary table extensions rather than ASCII table
extensions for better efficiency  when dealing with tabular data.  The
I/O to ASCII tables is slower because of the overhead in formatting or
parsing the ASCII data fields, and because ASCII tables are about twice
as large as binary tables with the same information content.

4. Design software so that it reads the FITS header keywords in the
same order in which they occur in the file.  When reading keywords,
FITSIO searches forward starting from the position of the last keyword
that was read.  If it reaches the end of the header without finding the
keyword, it then goes back to the start of the header and continues the
search down to the position where it started.  In practice, as long as
the entire FITS header can fit at one time in the available internal I/O
buffers, then the header keyword access will be very fast and it makes
little difference which order they are accessed.

5. Avoid the use of scaling (by using the BSCALE and BZERO or TSCAL and
TZERO keywords) in FITS files since the scaling operations add to the
processing time needed to read or write the data.  In some cases it may
be more efficient to temporarily turn off the scaling (using ftpscl or
fttscl) and then read or write the raw unscaled values in the FITS
file.

6. Avoid using the 'implicit datatype conversion' capability in
FITSIO.  For instance, when reading a FITS image with BITPIX = -32
(32-bit floating point pixels), read the data into a single precision
floating point data array in the program.  Forcing FITSIO to convert
the data to a different datatype can significantly slow the program.

7. Where feasible, design FITS binary tables using vector column
elements so that the data are written as a contiguous set of bytes,
rather than as single elements in multiple rows.  For example, it is
faster to access the data in a table that contains a single row
and 2 columns with TFORM keywords equal to  '10000E' and '10000J', than
it is to access the same amount of data in a table with 10000 rows
which has columns with the TFORM keywords equal to '1E' and '1J'.  In
the former case the 10000 floating point values in the first column are
all written in a contiguous block of the file which can be read or
written quickly, whereas in the second case each floating point value
in the first column is interleaved with the integer value in the second
column of the same row so CFITSIO has to explicitly move to the
position of each element to be read or written.

8. Avoid the use of variable length vector columns in binary tables,
since any reading or writing of these data requires that CFITSIO first
look up or compute the starting address of each row of data in the
heap.

9. When copying data from one FITS table to another, it is faster to
transfer the raw bytes instead of reading then writing each column of
the table.  The FITSIO subroutines FTGTBS and FTPTBS (for ASCII
tables), and  FTGTBB and FTPTBB (for binary tables) will perform
low-level reads or writes of any contiguous range of bytes in a table
extension.  These routines can be used to read or write a whole row (or
multiple rows) of a table with a single subroutine call.   These
routines are fast because they bypass all the usual data scaling, error
checking and machine dependent data conversion that is normally done by
FITSIO, and they allow the program to write the data to the output file
in exactly the same byte order.  For these same reasons, use of these
routines can be somewhat risky because no validation or machine
dependent conversion is performed by these routines.  In general these
routines are only recommended for optimizing critical pieces of code
and should only be used by programmers who thoroughly understand the
internal byte structure of the FITS tables they are reading or
writing.

10. Another strategy for improving the speed of writing a FITS table,
similar to the previous one, is to directly construct the entire byte
stream for a whole table row (or multiple rows) within the application
program and then write it to the FITS file with
ftptbb.  This avoids all the overhead normally present
in the column-oriented CFITSIO write routines.  This technique should
only be used for critical applications, because it makes the code more
difficult to understand and maintain, and it makes the code more system
dependent (e.g., do the bytes need to be swapped before writing to the
FITS file?).

11.  Finally, external factors such as the type of magnetic disk
controller (SCSI or IDE), the size of the disk cache, the average seek
speed of the disk, the amount of disk fragmentation, and the amount of
RAM available on the system can all have a significant impact on
overall I/O efficiency.  For critical applications, a system
administrator should review the proposed system hardware to identify any
potential I/O bottlenecks.



*VII.  Basic Interface Routines

This section defines a basic set of subroutines that can be
used to perform the most common types of read and write operations
on FITS files.  New users should start with these subroutines and
then, as needed, explore the more advance routines described in
the following chapter to perform more complex or specialized operations.

A right arrow symbol ($>$) is used to separate the input parameters from
the output parameters in the  definition of each routine.  This symbol
is not actually part of the calling sequence.  Note that
the status parameter is both an input and an output parameter
and must be initialized = 0 prior to calling the FITSIO subroutines.

Refer to Chapter 9 for the definition of all the parameters 
used by these interface routines.

**A.  FITSIO Error Status Routines \label{FTVERS}

>1  Return the current version number of the fitsio library.
    The version number will be incremented with each new
>   release of CFITSIO.
-
        FTVERS( > version)
-
>2  Return the descriptive text string corresponding to a FITSIO error
    status code.   The 30-character length string contains a brief
>   description of the cause of the error.
-
        FTGERR(status, > errtext)
-
>3  Return the top (oldest) 80-character error message from the
    internal FITSIO stack of error messages and shift any remaining
    messages on the stack up one level.  Any FITSIO error will
    generate one or more messages on the stack.  Call this routine
    repeatedly to get each message in sequence.  The error stack is empty
>   when a blank string is returned.
-
        FTGMSG( > errmsg)
-
>4 The FTPMRK routine puts an invisible marker on the 
   CFITSIO error stack.  The FTCMRK routine can then be
   used to delete any more recent error messages on the stack, back to
   the position of the marker.  This preserves any older error messages
   on the stack.  FTCMSG simply clears the entire error message stack.
>  These routines are called without any arguments.
-
        FTPMRK
        FTCMRK
        FTCMSG
-

>5  Print out the error message corresponding to the input status
    value and all the error messages on the FITSIO stack  to the specified
    file stream  (stream can be either the string 'STDOUT' or 'STDERR').
>   If the input status value = 0 then this routine does nothing.
-
       FTRPRT (stream, > status)
-
>6  Write an 80-character message to the FITSIO error stack.  Application
    programs should not normally write to the stack, but there may be
>   some situations where this is desirable.
-
        FTPMSG(errmsg)
-

**B.  File I/O Routines

>1 Open an existing FITS file with readonly or readwrite access.
   This routine always opens the primary array (the first HDU) of 
   the file, and does not move to a following extension, if one was
   specified as part of the filename.   Use the FTNOPN routine to
   automatically move to the extension.  This routine will also
   open IRAF images (.imh format files) and raw binary data arrays
   with READONLY access by first converting them on the fly into
   virtual FITS images.  See the `Extended File Name Syntax' chapter
   for more details.  The FTDKOPEN routine simply opens the specified
   file without trying to interpret the filename using the extended
>  filename syntax.
-
        FTOPEN(unit,filename,rwmode, > blocksize,status)
        FTDKOPEN(unit,filename,rwmode, > blocksize,status)
-
>2 Open an existing FITS file with readonly or readwrite access
   and move to a following extension, if one was specified as
   part of the filename.  (e.g.,  'filename.fits+2' or
   'filename.fits[2]' will move to the 3rd HDU in the file).
   Note that this routine differs from FTOPEN in that it does not
>  have the redundant blocksize argument.
-
        FTNOPN(unit,filename,rwmode, > status)
-
>3 Open an existing FITS file with readonly or readwrite access
   and then move to the first HDU containing significant data, if a) an HDU
   name or number to open was not explicitly specified as part of the
   filename, and b) if the FITS file contains a null primary array (i.e.,
   NAXIS = 0).  In this case, it will look for the first IMAGE HDU with
   NAXIS > 0, or the first table that does not contain the strings `GTI'
   (Good Time Interval) or `OBSTABLE' in the EXTNAME keyword value.  FTTOPN
   is similar, except it will move to the first significant table HDU
   (skipping over any image HDUs) in the file if a specific HDU name
   or number is not specified.  FTIOPN will move to the first non-null
>  image HDU, skipping over any tables.
-
        FTDOPN(unit,filename,rwmode, > status)
        FTTOPN(unit,filename,rwmode, > status)
        FTIOPN(unit,filename,rwmode, > status)
-
>4 Open and initialize a new empty FITS file.   A template file may also be
   specified to define the structure of the new file (see section 4.2.4).
   The FTDKINIT routine simply creates the specified
   file without trying to interpret the filename using the extended
>  filename syntax.
-
        FTINIT(unit,filename,blocksize, > status)
        FTDKINIT(unit,filename,blocksize, > status)
-
>>5 Close a FITS file previously opened with ftopen or ftinit
-
        FTCLOS(unit, > status)
-
>6  Move to a specified (absolute) HDU in the FITS file (nhdu = 1 for the
>   FITS primary array)
-
        FTMAHD(unit,nhdu, > hdutype,status)
-
>7  Create a primary array (if none already exists), or insert a 
    new IMAGE extension immediately following the CHDU, or
    insert a new Primary Array at the beginning of the file.  Any
    following extensions in the file will be shifted down to make room
    for the new extension.  If the CHDU is the last HDU in the file
    then the new image extension will simply be appended to the end of
    the file.   One can force a new primary array to be inserted at the
    beginning of the FITS file by setting status = -9 prior
    to calling the routine.  In this case the existing primary array will be
    converted to an IMAGE extension. The new extension (or primary
    array) will become the CHDU.  The FTIIMGLL routine is identical
    to the FTIIMG routine except that the 4th parameter (the length
    of each axis) is an array of 64-bit integers rather than an array
>   of 32-bit integers.
-
        FTIIMG(unit,bitpix,naxis,naxes, > status) 
        FTIIMGLL(unit,bitpix,naxis,naxesll, > status) 
-
>8  Insert a new ASCII TABLE extension immediately following the CHDU.
    Any following extensions will be shifted down to make room for
    the new extension.  If there are no other following extensions
    then the new table extension will simply be appended to the
    end of the file.  The new extension will become the CHDU. The FTITABLL
    routine is identical
    to the FTITAB routine except that the 2nd and 3rd parameters (that give
    the size of the table) are 64-bit integers rather than 
>   32-bit integers.
-
        FTITAB(unit,rowlen,nrows,tfields,ttype,tbcol,tform,tunit,extname, >
               status)
        FTITABLL(unit,rowlenll,nrowsll,tfields,ttype,tbcol,tform,tunit,extname, >
               status)
-
>9  Insert a new binary table extension immediately following the CHDU.
    Any following extensions will be shifted down to make room for
    the new extension.  If there are no other following extensions
    then the new bintable extension will simply be appended to the
     end of the file.  The new extension will become the CHDU. The FTIBINLL
    routine is identical
    to the FTIBIN routine except that the 2nd parameter (that gives
    the length of the table) is a 64-bit integer rather than 
>   a 32-bit integer.
-
        FTIBIN(unit,nrows,tfields,ttype,tform,tunit,extname,varidat > status)
        FTIBINLL(unit,nrowsll,tfields,ttype,tform,tunit,extname,varidat > status)

-
**C.  Keyword I/O Routines

>>1 Put (append) an 80-character record into the CHU. 
-
        FTPREC(unit,card, > status)
-
>2  Put (append) a new keyword of the appropriate datatype into the CHU. 
     The E and D versions of this routine have the added feature that
     if the 'decimals' parameter is negative, then the 'G' display
     format rather then the 'E' format will be used when constructing
     the keyword value, taking the absolute value of 'decimals' for the
     precision.  This will suppress trailing zeros, and will use a
     fixed format rather than an exponential format,
>    depending on the magnitude of the value.
-
        FTPKY[JKLS](unit,keyword,keyval,comment, > status)
        FTPKY[EDFG](unit,keyword,keyval,decimals,comment, > status)  
-
>3 Get the nth 80-character header record from the CHU.  The first keyword
   in the header is at key\_no = 1;  if key\_no = 0 then this subroutine
   simple moves the internal pointer to the beginning of the header
   so that subsequent keyword operations will start at the top of 
>  the header; it also returns a blank card value in this case.
-
        FTGREC(unit,key_no, > card,status)
-
>4  Get a keyword value (with the appropriate datatype) and comment from 
>   the CHU 
-
        FTGKY[EDJKLS](unit,keyword, > keyval,comment,status)
-
>>5  Delete an existing keyword record.  
-
        FTDKEY(unit,keyword, > status)
-

**D.  Data I/O Routines

The following routines read or write data values in the current HDU of
the FITS file.  Automatic datatype conversion 
will be attempted for numerical datatypes if the specified datatype is 
different from the actual datatype of the FITS array or table column.

>>1 Write elements into the primary data array or image extension.
-
        FTPPR[BIJKED](unit,group,fpixel,nelements,values, > status)
-
>2  Read elements from the primary data array or image extension.  
    Undefined array elements will be 
    returned with a value = nullval, unless nullval = 0 in which case no 
    checks for undefined pixels will be performed. The anyf parameter is 
    set to true (= .true.) if any of the returned
>   elements were undefined.
-
        FTGPV[BIJKED](unit,group,fpixel,nelements,nullval, > values,anyf,status)
-
>3  Write elements into an ASCII or binary table column. The `felem'
    parameter applies only to vector columns in binary tables and is 
>   ignored when writing to ASCII tables.
-
        FTPCL[SLBIJKEDCM](unit,colnum,frow,felem,nelements,values, > status)
-
>4  Read elements from an ASCII or binary table column.  Undefined
    array elements will be returned with a value = nullval, unless nullval = 0 
    (or = ' ' for ftgcvs) in which case no checking for undefined values will
    be performed. The ANYF parameter is set to true if any of the returned
    elements are undefined. 

    Any column, regardless of it's intrinsic datatype, may be read as a
    string.  It should be noted however that reading a numeric column
    as a string is 10 - 100 times slower than reading the same column
    as a number due to the large overhead in constructing the formatted
    strings.  The display format of the returned strings will be
    determined by the TDISPn keyword, if it exists, otherwise by the
    datatype of the column.  The length of the returned strings  can be
    determined with the ftgcdw routine.  The following TDISPn display
    formats are currently supported:
-
    Iw.m   Integer
    Ow.m   Octal integer
    Zw.m   Hexadecimal integer
    Fw.d   Fixed floating point
    Ew.d   Exponential floating point
    Dw.d   Exponential floating point
    Gw.d   General; uses Fw.d if significance not lost, else Ew.d
-
  where w is the width in characters of the displayed values, m is the minimum
  number of digits displayed, and d is the number of digits to the right of the 
>  decimal.  The .m field is optional.

-
        FTGCV[SBIJKEDCM](unit,colnum,frow,felem,nelements,nullval, > 
                       values,anyf,status)
-
>5  Get the table column number and full name of the column whose name
    matches the input template string.  See the `Advanced Interface Routines' 
>   chapter for a full description of this routine.
- 
        FTGCNN(unit,casesen,coltemplate, > colname,colnum,status)
-


*VIII   Advanced Interface Subroutines

This chapter defines all the available subroutines in the FITSIO user
interface. For completeness, the basic subroutines described in the
previous chapter are also repeated here. A right arrow symbol is used
here to separate the input parameters from the output parameters in the
definition of each subroutine. This symbol is not actually part of the
calling sequence. An alphabetical list and definition of all the
parameters is given at the end of this section. 

**A.  FITS File Open and Close Subroutines: \label{FTOPEN}

>1 Open an existing FITS file with readonly or readwrite access. The 
FTDKOPEN routine simply opens the specified file without trying to 
interpret the filename using the extended filename syntax. FTDOPN opens
the file and 
also moves to the first HDU containing significant data, if no specific
HDU is specified as part of the filename.  FTTOPN and FTIOPN are similar
except that they will move to the first table HDU or image HDU, respectively,
>if a HDU name or number is not specified as part of the filename.
-
        FTOPEN(unit,filename,rwmode, > blocksize,status)
        FTDKOPEN(unit,filename,rwmode, > blocksize,status)

        FTDOPN(unit,filename,rwmode, > status)
        FTTOPN(unit,filename,rwmode, > status)
        FTIOPN(unit,filename,rwmode, > status)
-

>2 Open an existing FITS file with readonly or readwrite access
   and move to a following extension, if one was specified as
   part of the filename.  (e.g.,  'filename.fits+2' or
   'filename.fits[2]' will move to the 3rd HDU in the file).
   Note that this routine differs from FTOPEN in that it does not
>  have the redundant blocksize argument.
-
        FTNOPN(unit,filename,rwmode, > status)
-
>3  Reopen a FITS file that was previously opened with 
    FTOPEN, FTNOPN, or FTINIT.  The newunit number
    may then be treated as a separate file, and one may
    simultaneously read or write to 2 (or more)  different extensions in
    the same file.   The FTOPEN and FTNOPN routines (above) automatically
    detects cases where a previously opened file is being opened again,
    and then internally call FTREOPEN, so programs should rarely
>   need to explicitly call this routine.
-
       FTREOPEN(unit, > newunit, status)
-
>4 Open and initialize a new empty FITS file.
   The FTDKINIT routine simply creates the specified
   file without trying to interpret the filename using the extended
>  filename syntax.
-
       FTINIT(unit,filename,blocksize, > status)
       FTDKINIT(unit,filename,blocksize, > status)
-

>5   Create a new FITS file, using a template file to define its
  initial size and structure.  The template may be another FITS HDU
  or an ASCII template file.  If the input template file name
  is blank, then this routine behaves the same as FTINIT.
  The currently supported format of the ASCII template file is described
  under the fits\_parse\_template routine (in the general Utilities 
  section), but this may change slightly later releases of
> CFITSIO.
-
       FTTPLT(unit, filename, tplfilename, > status)
-
>6 Flush internal buffers of data to the output FITS file 
   previously opened with ftopen or ftinit.  The routine usually
   never needs to be called, but doing so will ensure that
   if the program subsequently aborts, then the FITS file will
>  have at least been closed properly.
-
        FTFLUS(unit, > status)
-
>>7 Close a FITS file previously opened with ftopen or ftinit
-
        FTCLOS(unit, > status)
-
>8  Close and DELETE a FITS file previously opened with ftopen or ftinit.
    This routine may be  useful in cases where a FITS file is created, but
>   an error occurs which prevents the complete file from being written.
-
        FTDELT(unit, > status)
-
>9  Get the value of an unused I/O unit number which may then be used
    as input to FTOPEN or FTINIT.  This routine searches for the first
    unused unit number in the range from with 99 down to 50.   This
    routine just keeps an internal list of the allocated unit numbers
    and does not physically check that the Fortran unit is available (to be
    compatible with the SPP version of FITSIO).  Thus users must not
    independently allocate any unit numbers in the range 50 - 99 
    if this routine is also to be used in the same program.  This 
    routine is provided for convenience only, and it is not required 
>   that the unit numbers used by FITSIO be allocated by this routine.
-
        FTGIOU( > iounit, status)
-
>10  Free (deallocate) an I/O unit number which was previously allocated
    with FTGIOU.   All previously allocated unit numbers may be
>   deallocated at once by calling FTFIOU with iounit = -1.
-
        FTFIOU(iounit, > status)
-
>11  Return the Fortran unit number that corresponds to the C fitsfile
pointer value, or vice versa.  These 2 C routines may be useful in 
mixed language programs where both C and Fortran subroutines need
to access the same file.  For example, if a FITS file is opened
with unit 12 by a Fortran subroutine, then a C routine within the
same program could get the fitfile pointer value to access the same file
by calling  'fptr = CUnit2FITS(12)'.  These routines return a value
>of zero if an error occurs.
-
      int       CFITS2Unit(fitsfile *ptr);
      fitsfile* CUnit2FITS(int unit);
-

>11  Parse the input filename and return the HDU number that would be
moved to if the file were opened with FTNOPN.    The returned HDU
number begins with 1 for the primary array, so for example, if the
input filename = `myfile.fits[2]' then hdunum = 3 will be returned.
FITSIO does not open the file to check if the extension actually exists
if an extension number is specified. If an extension *name* is included
in the file name specification (e.g.  `myfile.fits[EVENTS]' then this
routine will have to open the FITS file and look for the position of
the named extension, then close file again.  This is not possible if
the file is being read from the stdin stream, and an error will be
returned in this case.  If the filename does not specify an explicit
extension (e.g. 'myfile.fits') then hdunum = -99 will be returned,
which is functionally equivalent to hdunum = 1. This routine is mainly
used for backward compatibility in the ftools software package and is
not recommended for general use.  It is generally better and more
efficient to first open the FITS file with FTNOPN, then use FTGHDN to
determine which HDU in the file has been opened, rather than calling
> FTEXTN followed by a call to FTNOPN.
-
        FTEXTN(filename, > nhdu, status)
-
>>12 Return the name of the opened FITS file. 
-
        FTFLNM(unit, > filename, status)
-
>>13 Return the I/O mode of the open FITS file (READONLY = 0, READWRITE = 1).
-
        FTFLMD(unit, > iomode, status)
-
>14 Return the file type of the opened FITS file (e.g. 'file://', 'ftp://',
>  etc.).
-
        FTURLT(unit, > urltype, status)
-
>15  Parse the input filename or URL into its component parts: the file
type (file://, ftp://, http://, etc), the base input file name, the
name of the output file that the input file is to be copied to prior
to opening, the HDU or extension specification, the filtering
specifier, the binning specifier, and the column specifier.  Blank
strings will be returned for any components that are not present
>in the input file name.
-
       FTIURL(filename, > filetype, infile, outfile, extspec, filter, 
               binspec, colspec, status)
-
>16 Parse the input file name and return the root file name.  The root
name includes the file type if specified, (e.g.  'ftp://' or 'http://')
and the full path name, to the extent that it is specified in the input
filename.  It does not include the HDU name or number, or any filtering
>specifications.
-
       FTRTNM(filename, > rootname, status)
-

>16 Test if the input file or a compressed version of the file (with
a .gz, .Z, .z, or .zip extension) exists on disk.  The returned value of 
the 'exists' parameter will have 1 of the 4 following values:
-
   2:  the file does not exist, but a compressed version does exist
   1:  the disk file does exist
   0:  neither the file nor a compressed version of the file exist
  -1:  the input file name is not a disk file (could be a ftp, http,
       smem, or mem file, or a file piped in on the STDIN stream)
-
> 
-
      FTEXIST(filename, > exists, status);
-
**B.  HDU-Level Operations \label{FTMAHD}

When a FITS file is first opened or created, the internal buffers in
FITSIO automatically point to the first HDU in the file.  The following
routines may be used to move to another HDU in the file.  Note that
the HDU numbering convention used in FITSIO  denotes the primary array
as the first HDU, the first extension in a FITS file is the second HDU,
and so on.

>1  Move to a specified (absolute) HDU in the FITS file (nhdu = 1 for the
>   FITS primary array)
-
        FTMAHD(unit,nhdu, > hdutype,status)
-
>>2 Move to a new (existing) HDU forward or backwards relative to the CHDU
-
        FTMRHD(unit,nmove, > hdutype,status)  
-
>3  Move to the (first) HDU which has the specified extension type and
    EXTNAME (or HDUNAME) and EXTVER keyword values.  The hdutype parameter
    may have
    a value of IMAGE\_HDU, ASCII\_TBL, BINARY\_TBL, or ANY\_HDU where
    ANY\_HDU means that only the extname and extver values will be
    used to locate the correct extension.  If the input value of
    extver is 0 then the EXTVER keyword is ignored and the first HDU
    with a matching EXTNAME (or HDUNAME) keyword will be found.  If no
    matching HDU is found in the file then the current HDU will remain
    unchanged
>   and a status = BAD\_HDU\_NUM (301) will be returned. 
-
        FTMNHD(unit, hdutype, extname, extver, > status)
-
>>4 Get the number of the current HDU in the FITS file (primary array = 1)
-
        FTGHDN(unit, > nhdu)
-
>5  Return the type of the current HDU in the FITS file.  The possible
>   values for hdutype are IMAGE\_HDU (0), ASCII\_TBL (1), or BINARY\_TBL (2).  
-
        FTGHDT(unit, > hdutype, status)
-
>6  Return the total number of HDUs in the FITS file.
>   The CHDU remains unchanged. 
-
        FTTHDU(unit, > hdunum, status)
-
>7 Create (append) a new empty HDU following the last extension that
    has been previously accessed by the program.   This will overwrite
    any extensions in an existing FITS file if the program has not already
    moved to that (or a later) extension using the FTMAHD or FTMRHD routines.
    For example, if an existing FITS file contains a primary array and 5 
    extensions and a program (1) opens the FITS file, (2) moves to
    extension 4, (3) moves back to the primary array, and (4) then calls
    FTCRHD, then the new extension will be written following the 4th
>   extension, overwriting the existing 5th extension. 
-
        FTCRHD(unit, > status)
-

>8  Create a primary array (if none already exists), or insert a 
    new IMAGE extension immediately following the CHDU, or
    insert a new Primary Array at the beginning of the file.  Any
    following extensions in the file will be shifted down to make room
    for the new extension.  If the CHDU is the last HDU in the file
    then the new image extension will simply be appended to the end of
    the file.   One can force a new primary array to be inserted at the
    beginning of the FITS file by setting status = -9 prior
    to calling the routine.  In this case the existing primary array will be
    converted to an IMAGE extension. The new extension (or primary
    array) will become the CHDU.  The FTIIMGLL routine is identical
    to the FTIIMG routine except that the 4th parameter (the length
    of each axis) is an array of 64-bit integers rather than an array
>   of 32-bit integers.
-
        FTIIMG(unit,bitpix,naxis,naxes, > status) 
        FTIIMGLL(unit,bitpix,naxis,naxesll, > status) 
-
>9  Insert a new ASCII TABLE extension immediately following the CHDU.
    Any following extensions will be shifted down to make room for
    the new extension.  If there are no other following extensions
    then the new table extension will simply be appended to the
    end of the file.  The new extension will become the CHDU. The FTITABLL
    routine is identical
    to the FTITAB routine except that the 2nd and 3rd parameters (that give
    the size of the table) are 64-bit integers rather than 
>   32-bit integers.
-
        FTITAB(unit,rowlen,nrows,tfields,ttype,tbcol,tform,tunit,extname, >
               status)
        FTITABLL(unit,rowlenll,nrowsll,tfields,ttype,tbcol,tform,tunit,extname, >
               status)
-

>10  Insert a new binary table extension immediately following the CHDU.
    Any following extensions will be shifted down to make room for
    the new extension.  If there are no other following extensions
    then the new bintable extension will simply be appended to the
    end of the file.  The new extension will become the CHDU. The FTIBINLL
    routine is identical
    to the FTIBIN routine except that the 2nd parameter (that gives
    the length of the table) is a 64-bit integer rather than 
>   a 32-bit integer.
-
        FTIBIN(unit,nrows,tfields,ttype,tform,tunit,extname,varidat > status)
        FTIBINLL(unit,nrowsll,tfields,ttype,tform,tunit,extname,varidat > status)

-

>11  Resize an image by modifing the size, dimensions, and/or datatype of the 
    current primary array or image extension. If the new image, as specified
    by the input arguments, is larger than the current existing image
    in the FITS file then zero fill data will be inserted at the end
    of the current image and any following extensions will be moved 
    further back in the file.  Similarly, if the new image is
    smaller than the current image then any following extensions
    will be shifted up towards the beginning of the FITS file
    and the image data will be truncated to the new size.
    This routine rewrites the BITPIX, NAXIS, and NAXISn keywords
    with the appropriate values for new image. The FTRSIMLL routine is identical
    to the FTRSIM routine except that the 4th parameter (the length
    of each axis) is an array of 64-bit integers rather than an array
>   of 32-bit integers.
-
        FTRSIM(unit,bitpix,naxis,naxes,status)
        FTRSIMLL(unit,bitpix,naxis,naxesll,status)
-
>12 Delete the CHDU in the FITS file.  Any following HDUs will be shifted
    forward in the file, to fill in the gap created by the deleted
    HDU.  In the case of deleting the primary array (the first HDU in
    the file) then the current primary array will be replace by a null
    primary array containing the minimum set of required keywords and
    no data.  If there are more extensions in the file following the
    one that is deleted, then the the CHDU will be redefined to point
    to the following extension.  If there are no following extensions
    then the CHDU will be redefined to point to the previous HDU.  The
    output HDUTYPE parameter indicates the type of the new CHDU after
>   the previous CHDU has been deleted.
-
        FTDHDU(unit, > hdutype,status)
-
>13  Copy all or part of the input FITS file and append it
    to the end of the output FITS file.  If 'previous' (an integer parameter) is
    not equal to 0, then any HDUs preceding the current HDU in the input file
    will be copied to the output file.  Similarly, 'current' and 'following'
    determine whether the current HDU, and/or any following HDUs in the input
    file will be copied to the output file. If all 3 parameters are not equal
    to zero, then the entire input file will be copied.  On return, the current
    HDU in the input file will be unchanged, and the last copied HDU will be the 
>   current HDU in the output file.     
-
        FTCPFL(iunit, ounit, previous, current, following, > status)
-
>14 Copy the entire CHDU from the FITS file associated with IUNIT to the CHDU 
    of the FITS file associated with OUNIT. The output HDU must be empty and
    not already contain any keywords.  Space will be reserved for MOREKEYS
    additional  keywords in the output header if there is not already enough 
>   space. 
-
        FTCOPY(iunit,ounit,morekeys, > status)
-
>15 Copy the header (and not the data) from the CHDU associated with inunit
    to the CHDU associated with outunit.  If the current output HDU
    is not completely empty, then the CHDU will be closed and a new
    HDU will be appended to the output file.  This routine will automatically
    transform the necessary keywords when copying a primary array to
    and image extension, or an image extension to a primary array. 
>   An empty output data unit will be created (all values = 0). 
-
        FTCPHD(inunit, outunit, > status)
-
>16 Copy just the data from the CHDU associated with IUNIT 
    to the CHDU associated with OUNIT. This will overwrite 
    any data previously in the OUNIT CHDU.  This low level routine is used
    by FTCOPY, but it may also be useful in certain application programs
    which want to copy the data from one FITS file to another but also
    want to modify the header keywords in the process. all the required 
    header keywords must be written to the OUNIT CHDU before calling
>   this routine 
-
        FTCPDT(iunit,ounit, > status)
-

**C.  Define or Redefine the structure of the CHDU \label{FTRDEF}

It should rarely be necessary to call the subroutines in this section.
FITSIO internally calls these routines whenever necessary, so any calls
to these routines by application programs will likely be redundant.

>1  This routine forces FITSIO to scan the current header keywords that
    define the structure of the HDU (such as the NAXISn, PCOUNT and GCOUNT
    keywords) so that it can initialize the internal buffers that describe
    the HDU structure.  This routine may be used instead of the more
    complicated calls to ftpdef, ftadef or ftbdef.  This routine is
    also very useful for reinitializing the structure of an HDU, 
    if the number of rows in a table, as specified by the NAXIS2 keyword,
>   has been modified from its initial value.
-
        FTRDEF(unit, > status)   (DEPRECATED)
-
>2 Define the structure of the primary array or IMAGE extension.  When
   writing GROUPed FITS files that by convention set the NAXIS1 keyword
   equal to 0, ftpdef must be called with naxes(1) = 1, NOT 0, otherwise
   FITSIO will report an error status=308 when trying to write data
   to a group. Note: it is usually simpler to call FTRDEF rather
>  than this routine.
-
        FTPDEF(unit,bitpix,naxis,naxes,pcount,gcount, > status)  (DEPRECATED)
-
>3  Define the structure of an ASCII table (TABLE) extension. Note: it 
>   is usually simpler to call FTRDEF rather than this routine.
-
        FTADEF(unit,rowlen,tfields,tbcol,tform,nrows > status) (DEPRECATED)
-
>4  Define the structure of a binary table (BINTABLE) extension. Note: it 
>   is usually simpler to call FTRDEF rather than this routine.
-
        FTBDEF(unit,tfields,tform,varidat,nrows > status) (DEPRECATED)
-
>5  Define the size of the Current Data Unit, overriding the length
    of the data unit as previously defined by ftpdef, ftadef, or ftbdef.
    This is useful if one does not know the total size of the data unit until
    after the data have been written.  The size (in bytes) of an ASCII or 
    Binary table is given by NAXIS1 * NAXIS2.  (Note that to determine the
    value of NAXIS1 it is often more convenient to read the value of the
    NAXIS1 keyword from the output file, rather than computing the row 
    length directly from all the TFORM keyword values).  Note: it 
>   is usually simpler to call FTRDEF rather than this routine.
-
        FTDDEF(unit,bytlen, > status) (DEPRECATED)
-
>6  Define the zero indexed byte offset of the 'heap' measured from
    the start of the binary table data.  By default the heap is assumed
    to start immediately following the regular table data, i.e., at
    location NAXIS1 x NAXIS2.  This routine is only relevant for 
    binary tables which contain variable length array columns (with
    TFORMn = 'Pt').  This subroutine also automatically writes
    the value of theap to a keyword in the extension header.  This 
    subroutine must be called after the required keywords have been
    written (with ftphbn) and after the table structure has been defined
>   (with ftbdef) but before any data is written to the table.
-
        FTPTHP(unit,theap, > status)
-

**D.  FITS Header I/O Subroutines

***1.  Header Space and Position Routines \label{FTHDEF}

>1  Reserve space in the CHU for MOREKEYS more header keywords.  
    This subroutine may be called to reserve space for keywords which are
    to be written at a later time, after the data unit or subsequent
    extensions have been written to the FITS file.  If this subroutine is
    not explicitly called, then the initial size of the FITS header will be
    limited to the space available at the time that  the first data is written
    to the associated data unit.   FITSIO has the ability to dynamically
    add more space to the header if needed, however it is more efficient
>   to preallocate the required space if the size is known in advance.
-
        FTHDEF(unit,morekeys, > status)
-
>2  Return the number of existing keywords in the CHU (NOT including the
    END keyword which is not considered a real keyword) and the remaining
    space available to write additional keywords in the CHU.  (returns
    KEYSADD = -1 if the header has not yet been closed).
    Note that FITSIO will attempt to dynamically add space for more 
>   keywords if required when appending new keywords to a header.
-
        FTGHSP(iunit, > keysexist,keysadd,status)
-
>3  Return the number of keywords in the header and the current position 
    in the header.  This returns the number of the keyword record that 
    will be read next (or one greater than the position of the last keyword 
    that was read or written). A value of 1 is returned if the pointer is
>   positioned at the beginning of the header.  
-
        FTGHPS(iunit, > keysexist,key_no,status)
-
***2.  Read or Write Standard Header Routines \label{FTPHPR}

These subroutines provide a simple method of reading or writing most of
the keyword values that are normally required in a FITS files.  These
subroutines are provided for convenience only and are not required to
be used.  If preferred, users may call the lower-level subroutines
described in the previous section to individually read or write the
required keywords.  Note that in most cases, the required keywords such
as NAXIS, TFIELD, TTYPEn, etc, which define the structure of the HDU
must be written to the header before any data can be written to the
image or table.

>1  Put the primary header or IMAGE extension keywords into the CHU.
There are 2 available routines: The simpler FTPHPS routine is
equivalent to calling ftphpr with the default values of SIMPLE = true,
pcount = 0, gcount = 1, and EXTEND = true.  PCOUNT, GCOUNT and EXTEND
keywords are not required in the primary header and are only written if
pcount is not equal to zero, gcount is not equal to zero or one, and if
extend is TRUE, respectively.  When writing to an IMAGE extension, the
>SIMPLE and EXTEND parameters are ignored.
-
        FTPHPS(unit,bitpix,naxis,naxes, > status)

        FTPHPR(unit,simple,bitpix,naxis,naxes,pcount,gcount,extend, > status)
-
>2  Get primary header or IMAGE extension keywords from the CHU.  When
    reading from an IMAGE extension the SIMPLE and EXTEND parameters are
>   ignored.
-
        FTGHPR(unit,maxdim, > simple,bitpix,naxis,naxes,pcount,gcount,extend,
               status)
-
>3  Put the ASCII table header keywords into the CHU. The optional
TUNITn and EXTNAME keywords are written only if the input string
>values are not blank.
-
        FTPHTB(unit,rowlen,nrows,tfields,ttype,tbcol,tform,tunit,extname, >
               status)
-
>>4  Get the ASCII table header keywords from the CHU
-
        FTGHTB(unit,maxdim, > rowlen,nrows,tfields,ttype,tbcol,tform,tunit,
               extname,status)
-
>5 Put the binary table header keywords into the CHU. The optional
   TUNITn and EXTNAME keywords are written only if the input string
   values are not blank.  The pcount parameter, which specifies the
   size of the variable length array heap, should initially = 0;
   FITSIO will automatically update the PCOUNT keyword value if any
   variable length array data is written to the heap.  The TFORM keyword
   value for variable length vector columns should have the form 'Pt(len)'
   or '1Pt(len)' where `t' is the data type code letter (A,I,J,E,D, etc.)
   and  `len' is an integer specifying the maximum length of the vectors
   in that column (len must be greater than or equal to the longest
   vector in the column).  If `len' is not specified when the table is
   created (e.g., the input TFORMn value is just '1Pt') then FITSIO will
   scan the column when the table is first closed and will append the
   maximum length to the TFORM keyword value.  Note that if the table
   is subsequently modified to increase the maximum length of the vectors
   then the modifying program is responsible for also updating the TFORM 
>  keyword value.

-
        FTPHBN(unit,nrows,tfields,ttype,tform,tunit,extname,varidat, > status)
-
>>6 Get the binary table header keywords from the CHU
-
        FTGHBN(unit,maxdim, > nrows,tfields,ttype,tform,tunit,extname,varidat,
               status)
-
***3.  Write Keyword Subroutines \label{FTPREC}

>>1 Put (append) an 80-character record into the CHU. 
-
        FTPREC(unit,card, > status)
-
>2  Put (append) a COMMENT keyword into the CHU.  Multiple COMMENT keywords
>   will be written if the input comment string is longer than 72 characters. 
-
        FTPCOM(unit,comment, > status)
-
>3 Put (append) a HISTORY keyword into the CHU.  Multiple HISTORY keywords
>   will be written if the input history string is longer than 72 characters.
-
        FTPHIS(unit,history, > status)
-
>4  Put (append) the DATE keyword into the CHU.  The keyword value will contain
    the current system date as a character string in 'dd/mm/yy' format. If
    a DATE keyword already exists in the header, then this subroutine will
>   simply update the keyword value in-place with the current date.
-
        FTPDAT(unit, > status)
-
>5  Put (append) a new keyword of the appropriate datatype into the CHU. 
    Note that FTPKYS will only write string values up to 68 characters in 
    length; longer strings will be truncated.  The FTPKLS routine can be 
    used to write longer strings, using a non-standard FITS convention.
     The E and D versions of this routine have the added feature that
     if the 'decimals' parameter is negative, then the 'G' display
     format rather then the 'E' format will be used when constructing
     the keyword value, taking the absolute value of 'decimals' for the
     precision.  This will suppress trailing zeros, and will use a
     fixed format rather than an exponential format,
>    depending on the magnitude of the value.
-
        FTPKY[JKLS](unit,keyword,keyval,comment, > status)
        FTPKY[EDFG](unit,keyword,keyval,decimals,comment, > status)  
-
>6  Put (append) a string valued keyword into the CHU which may be longer 
    than 68 characters in length.  This uses the Long String Keyword
    convention that is described in the "Usage Guidelines and Suggestions"
    section of this document.  Since this uses a non-standard FITS 
    convention to encode the long keyword string, programs which use
    this routine should also call the FTPLSW routine to add some COMMENT
    keywords to warn users of the FITS file that this convention is
    being used.  FTPLSW also writes a keyword called LONGSTRN to record
    the version of the longstring convention that has been used, in case
    a new convention is adopted at some point in the future.   If the
    LONGSTRN keyword is already present in the header, then FTPLSW will
>   simply return and will not write duplicate keywords.
-
        FTPKLS(unit,keyword,keyval,comment, > status)
        FTPLSW(unit, > status)
-
>7  Put (append) a new keyword with an undefined, or null, value into the CHU.
>   The value string of the keyword is left blank in this case.
-
        FTPKYU(unit,keyword,comment, > status)
-
>8  Put (append) a numbered sequence of keywords into the CHU.   One may
    append the same comment to every keyword (and eliminate the need
    to have an array of identical comment strings, one for each keyword) by
    including the ampersand character as the last non-blank character in the
    (first) COMMENTS string parameter.  This same string 
    will then be used for the comment field in all the keywords. (Note
    that the SPP version of these routines only supports a single comment
>   string).
-
        FTPKN[JKLS](unit,keyroot,startno,no_keys,keyvals,comments, > status)
        FTPKN[EDFG](unit,keyroot,startno,no_keys,keyvals,decimals,comments, > 
                   status)
-
>9 Copy an indexed keyword from one HDU to another, modifying
    the index number of the keyword name in the process.  For example,
    this routine could read the TLMIN3 keyword from the input HDU
    (by giving keyroot = "TLMIN" and innum = 3) and write it to the
    output HDU with the keyword name TLMIN4 (by setting outnum = 4).
    If the input keyword does not exist, then this routine simply
>   returns without indicating an error. 
-
        FTCPKY(inunit, outunit, innum, outnum, keyroot, > status)
-
>10 Put (append) a 'triple precision' keyword into the CHU in F28.16 format.
    The floating point keyword value is constructed by concatenating the 
    input integer value with the input double precision fraction value
    (which must have a value between 0.0 and 1.0). The FTGKYT routine should 
    be used to read this keyword value, because the other keyword reading
>   subroutines will not preserve the full precision of the value.
-
        FTPKYT(unit,keyword,intval,dblval,comment, > status)
-
>11 Write keywords to the CHDU that are defined in an ASCII template file.
   The format of the template file is described under the ftgthd
>  routine below. 
-
        FTPKTP(unit, filename, > status)
-
>12 Append the physical units string to an existing keyword.  This
    routine uses a local convention, shown in the following example,
    in which the keyword units are enclosed in square brackets in the
>   beginning of the keyword comment field.
   
-
     VELOCITY=                 12.3 / [km/s] orbital speed

        FTPUNT(unit,keyword,units, > status)
-
***4.  Insert Keyword Subroutines \label{FTIREC}

>1  Insert a new keyword record into the CHU at the specified position
    (i.e., immediately preceding the (keyno)th keyword in the header.)
    This 'insert record' subroutine is somewhat less efficient
    then the 'append record' subroutine (FTPREC) described above because
>   the remaining keywords in the header have to be shifted down one slot.
-
        FTIREC(unit,key_no,card, > status)
-
>2  Insert a new keyword into the CHU.  The new keyword is inserted
    immediately following the last keyword that has been read from the header.
    The FTIKLS subroutine works the same as the FTIKYS subroutine, except
    it also supports long string values greater than 68 characters in length.
    These 'insert keyword' subroutines are somewhat less efficient then 
    the 'append keyword' subroutines described above because the remaining
>   keywords in the header have to be shifted down one slot.
-
        FTIKEY(unit, card, > status)
        FTIKY[JKLS](unit,keyword,keyval,comment, > status)
        FTIKLS(unit,keyword,keyval,comment, > status)
        FTIKY[EDFG](unit,keyword,keyval,decimals,comment, > status)  
-
>3  Insert a new keyword with an undefined, or null, value into the CHU.
>   The value string of the keyword is left blank in this case.
-
        FTIKYU(unit,keyword,comment, > status)
-
***5.  Read Keyword Subroutines \label{FTGREC}

These routines return the value of the specified keyword(s).  Wild card
characters (*, ?, or \#) may be used when specifying the name of the keyword 
to be read: a '?' will match any single character at that position in the
keyword name and a '*' will match any length (including zero) string of
characters.  The '\#' character will match any consecutive string of
decimal digits (0 - 9). Note that when a wild card is used in the input 
keyword name, the routine will only search for a match from the current 
header position to the end of the header.  It will not resume the search 
from the top of the header back to the original header position as is done
when no wildcards are included in the keyword name.  If the desired
keyword string is 8-characters long (the maximum length of a keyword
name) then a '*' may be appended as the ninth character of the input
name to force the keyword search to stop at the end of the header
(e.g., 'COMMENT *' will search for the next COMMENT keyword).  The
ffgrec routine may be used to set the starting position when doing
wild card searches.

>1 Get the nth 80-character header record from the CHU.  The first keyword
   in the header is at key\_no = 1;  if key\_no = 0 then this subroutine
   simple moves the internal pointer to the beginning of the header
   so that subsequent keyword operations will start at the top of 
>  the header; it also returns a blank card value in this case.
-
        FTGREC(unit,key_no, > card,status)
-
>2  Get the name, value (as a string), and comment of the nth keyword in CHU.
    This routine also checks that the returned keyword name (KEYWORD) contains
    only legal ASCII characters.  Call FTGREC and FTPSVC to bypass this error
>   check.
-
        FTGKYN(unit,key_no, > keyword,value,comment,status)
-
>>3  Get the 80-character header record for the named keyword
-
        FTGCRD(unit,keyword, > card,status)
-
>4  Get the next keyword whose name matches one of the strings in
    'inclist' but does not match any of the strings in 'exclist'.
    The strings in inclist and exclist may contain wild card characters
    (*, ?, and \#) as described at the beginning of this section.
    This routine searches from the current header position to the
    end of the header, only, and does not continue the search from
    the top of the header back to the original position.  The current
    header position may be reset with the ftgrec routine.  Note
    that nexc may be set = 0 if there are no keywords to be excluded.
    This routine returns status = 202 if a matching
>   keyword is not found.
-
        FTGNXK(unit,inclist,ninc,exclist,nexc, > card,status)
-
>5   Get the literal keyword value as a character string.  Regardless
     of the datatype of the keyword, this routine simply returns the
     string of characters in the value field of the keyword along with
>    the comment field.
-
        FTGKEY(unit,keyword, > value,comment,status) 
-
>6  Get a keyword value (with the appropriate datatype) and comment from 
>   the CHU 
-
        FTGKY[EDJKLS](unit,keyword, > keyval,comment,status)
-
>7  Get a sequence of numbered keyword values.  These
>   routines do not support wild card characters in the root name.
-
        FTGKN[EDJKLS](unit,keyroot,startno,max_keys, > keyvals,nfound,status)
-
>8  Get the value of a floating point keyword, returning the integer and
    fractional parts of the value in separate subroutine arguments.
    This subroutine may be used to read any keyword but is especially
>   useful for reading the 'triple precision' keywords written by FTPKYT.
-
        FTGKYT(unit,keyword, > intval,dblval,comment,status)
-
>9  Get the physical units string in an existing keyword.  This
    routine uses a local convention, shown in the following example,
    in which the keyword units are
    enclosed in square brackets in the beginning of the keyword comment
    field.  A blank string is returned if no units are defined
>    for the keyword. 
-
    VELOCITY=                 12.3 / [km/s] orbital speed

        FTGUNT(unit,keyword, > units,status)
-
***6.  Modify Keyword Subroutines \label{FTMREC}

Wild card characters, as described in the Read Keyword section, above,
may be used when specifying the name of the keyword to be modified.

>>1  Modify (overwrite) the nth 80-character header record in the CHU
-
        FTMREC(unit,key_no,card, > status)
-
>2  Modify (overwrite) the 80-character header record for the named keyword
    in the CHU.  This can be used to overwrite the name of the keyword as
>   well as its value and comment fields.
-
        FTMCRD(unit,keyword,card, > status)
-
>3  Modify (overwrite) the name of an existing keyword in the CHU 
>   preserving the current value and comment fields.
-
        FTMNAM(unit,oldkey,keyword, > status)
-
>>4  Modify (overwrite) the comment field of an existing keyword in the CHU
-
        FTMCOM(unit,keyword,comment, > status)
-
>5  Modify the value and comment fields of an existing keyword in the CHU.
    The FTMKLS subroutine works the same as the FTMKYS subroutine, except
    it also supports long string values greater than 68 characters in length.
    Optionally, one may modify only the value field and leave the comment
    field unchanged by setting the input COMMENT parameter equal to
    the ampersand character (\&).
     The E and D versions of this routine have the added feature that
     if the 'decimals' parameter is negative, then the 'G' display
     format rather then the 'E' format will be used when constructing
     the keyword value, taking the absolute value of 'decimals' for the
     precision.  This will suppress trailing zeros, and will use a
     fixed format rather than an exponential format,
>    depending on the magnitude of the value.
-
        FTMKY[JKLS](unit,keyword,keyval,comment, > status)
        FTMKLS(unit,keyword,keyval,comment, > status)
        FTMKY[EDFG](unit,keyword,keyval,decimals,comment, > status)
-
>6  Modify the value of an existing keyword to be undefined, or null.
    The value string of the keyword is set to blank.
    Optionally, one may leave the comment field unchanged by setting the 
>   input COMMENT parameter equal to the ampersand character (\&).
-
        FTMKYU(unit,keyword,comment, > status)
-
***7.  Update Keyword Subroutines \label{FTUCRD}

>1  Update an 80-character record in the CHU.  If the specified keyword
    already exists then that header record will be replaced with 
    the input CARD string.  If it does not exist then the new record will 
    be added to the header.
    The FTUKLS subroutine works the same as the FTUKYS subroutine, except
>   it also supports long string values greater than 68 characters in length.
-
        FTUCRD(unit,keyword,card, > status)
-
>2  Update the value and comment fields of a keyword in the CHU.
    The specified keyword is modified if it already exists (by calling
    FTMKYx) otherwise a new keyword is created by calling FTPKYx.
     The E and D versions of this routine have the added feature that
     if the 'decimals' parameter is negative, then the 'G' display
     format rather then the 'E' format will be used when constructing
     the keyword value, taking the absolute value of 'decimals' for the
     precision.  This will suppress trailing zeros, and will use a
     fixed format rather than an exponential format,
>    depending on the magnitude of the value.
-
        FTUKY[JKLS](unit,keyword,keyval,comment, > status)
        FTUKLS(unit,keyword,keyval,comment, > status)
        FTUKY[EDFG](unit,keyword,keyval,decimals,comment, > status)
-
>3  Update the value of an existing keyword to be undefined, or null,
    or insert a new undefined-value keyword if it doesn't already exist.
>   The value string of the keyword is left blank in this case.
-
        FTUKYU(unit,keyword,comment, > status)
-
***8.  Delete Keyword Subroutines \label{FTDREC}

>1  Delete an existing keyword record.  The space previously occupied by  
    the keyword is reclaimed by moving all the following header records up
    one row in the header.  The first routine deletes a keyword at a
    specified position in the header (the first keyword is at position 1),
    whereas the second routine deletes a specifically named keyword.
    Wild card characters, as described in the Read Keyword section, above,
    may be used when specifying the name of the keyword to be deleted
>   (be careful!).
-
        FTDREC(unit,key_no, > status)
        FTDKEY(unit,keyword, > status)
-

**F.  Data Scaling and Undefined Pixel Parameters  \label{FTPSCL}

These subroutines define or modify the internal parameters used by
FITSIO to either scale the data or to represent undefined pixels.
Generally FITSIO will scale the data according to the values of the BSCALE
and BZERO (or TSCALn and TZEROn) keywords, however these subroutines
may be used to override the keyword values.  This may be useful when
one wants to read or write the raw unscaled values in the FITS file.
Similarly, FITSIO generally uses the value of the BLANK or TNULLn
keyword to signify an undefined pixel, but these routines may be used
to override this value.  These subroutines do not create or modify the
corresponding header keyword values.

>1  Reset the scaling factors in the primary array or image extension; does 
    not change the BSCALE and BZERO keyword values and only affects the
    automatic scaling performed when the data elements are written/read
    to/from the FITS file.   When reading from a FITS file the returned
    data value = (the value given in the FITS array) * BSCALE + BZERO.
    The inverse formula is used when writing data values to the FITS
    file.  (NOTE: BSCALE and BZERO must be declared as Double Precision
>   variables).
-
        FTPSCL(unit,bscale,bzero, > status)
-
>2  Reset the scaling parameters for a table column; does not change
    the TSCALn or TZEROn keyword values and only affects the automatic
    scaling performed when the data elements are written/read to/from
    the FITS file.  When reading from a FITS file the returned data
    value = (the value given in the FITS array) * TSCAL + TZERO.  The
    inverse formula is used when writing data values to the FITS file.
    (NOTE: TSCAL and TZERO  must be declared as Double Precision
>   variables).
-
        FTTSCL(unit,colnum,tscal,tzero, > status)
-
>3  Define the integer value to be used to signify undefined pixels in the
    primary array or image extension.  This is only used if BITPIX = 8, 16, 
    32. or 64  This does not create or change the value of the BLANK keyword in 
    the header. FTPNULLL is identical to FTPNUL except that the blank
>   value is a 64-bit integer instead of a 32-bit integer.
-
        FTPNUL(unit,blank, > status)
        FTPNULLL(unit,blankll, > status)
-
>4  Define the string to be used to signify undefined pixels in 
    a column in an ASCII table.  This does not create or change the value
>   of the TNULLn keyword.
-
        FTSNUL(unit,colnum,snull > status)
-
>5  Define the value to be used to signify undefined pixels in 
    an integer column in a binary table (where TFORMn = 'B', 'I', 'J', or 'K').  
    This does not create or  change the value of the TNULLn keyword. 
    FTTNULLL is identical to FTTNUL except that the tnull
>   value is a 64-bit integer instead of a 32-bit integer.
-
        FTTNUL(unit,colnum,tnull > status)
        FTTNULLL(unit,colnum,tnullll > status)
-

**G.  FITS Primary Array or IMAGE Extension I/O Subroutines \label{FTPPR}

    These subroutines put or get data values in the primary data array
(i.e., the first HDU in the FITS file) or an IMAGE extension.  The
data array is represented as a single one-dimensional array of
pixels regardless of the actual dimensionality of the array, and the
FPIXEL parameter gives the position within this 1-D array of the first
pixel to read  or write.  Automatic data type conversion is performed
for numeric data (except for complex data types) if the data type of
the primary array (defined by the BITPIX keyword) differs from the data
type of the array in the calling subroutine.  The data values are also
scaled by the BSCALE and BZERO header values as they are being written
or read from the FITS array.  The ftpscl subroutine MUST be
called to define the scaling parameters when writing data to the FITS
array or to override the default scaling value given in the header when
reading the FITS array.

    Two sets of subroutines are provided to read the data array which
differ in the way undefined pixels are handled.  The first set of
routines (FTGPVx) simply return an array of data elements in which
undefined pixels are set equal to a value specified by the user in the
'nullval' parameter.  An additional feature of these subroutines is
that if the user sets nullval = 0, then no checks for undefined pixels
will be performed, thus increasing the speed of the program.  The
second set of routines (FTGPFx) returns the data element array and, in
addition, a logical array which defines whether the corresponding data
pixel is undefined.  The latter set of subroutines may be more
convenient to use in some circumstances, however, it requires an
additional array of logical values which can be unwieldy when working
with large data arrays.  Also for programmer convenience, sets of
subroutines to directly read or write 2 and 3 dimensional arrays  have
been provided, as well as a set of subroutines to read or write any
contiguous rectangular subset of pixels within the n-dimensional array.

>1  Get the data type of the image (= BITPIX value).  Possible returned 
    values are: 8, 16, 32, 64, -32, or -64 corresponding to unsigned byte,
    signed 2-byte integer, signed 4-byte integer, signed 8-byte integer,
    real, and double.

    The second subroutine is similar to FTGIDT, except that if the image
    pixel values are scaled, with non-default values for the BZERO and
    BSCALE keywords, then this routine will return the 'equivalent'
    data type that is needed to store the scaled values.  For example,
    if BITPIX = 16 and BSCALE = 0.1 then the equivalent data type is
    floating point, and -32 will be returned.  There are 2 special cases:
    if the image contains unsigned 2-byte integer values, with BITPIX =
    16, BSCALE = 1, and BZERO = 32768, then this routine will return
    a non-standard value of 20 for the bitpix value.  Similarly if the
    image contains unsigned 4-byte integers, then bitpix will
>   be returned with a value of 40. 

-
        FTGIDT(unit, > bitpix,status)
        FTGIET(unit, > bitpix,status)
-
>>2  Get the dimension (number of axes = NAXIS) of the image 
-
        FTGIDM(unit, > naxis,status)
-
>3   Get the size of all the dimensions of the image. The FTGISZLL
>    routine returns an array of 64-bit integers instead of 32-bit integers.
-
        FTGISZ(unit, maxdim, > naxes,status)
        FTGISZLL(unit, maxdim, > naxesll,status)
-
>4   Get the parameters that define the type and size of the image.  This
     routine simply combines calls to the above 3 routines. The FTGIPRLL
>    routine returns an array of 64-bit integers instead of 32-bit integers.

-
        FTGIPR(unit, maxdim, > bitpix, naxis, naxes, int *status)
        FTGIPRLL(unit, maxdim, > bitpix, naxis, naxesll, int *status)
-
>>5 Put elements into the data array  
-
        FTPPR[BIJKED](unit,group,fpixel,nelements,values, > status)
-
>6 Put elements into the data array, substituting the appropriate FITS null
   value for all elements which are equal to the value of NULLVAL.  For 
   integer FITS arrays, the null value defined by the previous call to FTPNUL
   will be substituted;  for floating point FITS arrays (BITPIX = -32
   or -64) then the special IEEE NaN (Not-a-Number) value will be
>  substituted.
-
        FTPPN[BIJKED](unit,group,fpixel,nelements,values,nullval > status)
-
>>7 Set data array elements as undefined 
-
        FTPPRU(unit,group,fpixel,nelements, > status)
-
>8  Get elements from the data array.  Undefined array elements will be 
    returned with a value = nullval, unless nullval = 0 in which case no 
>   checks for undefined pixels will be performed.
-
        FTGPV[BIJKED](unit,group,fpixel,nelements,nullval, > values,anyf,status)
-
>9  Get elements and nullflags from data array. 
    Any undefined array elements will have the corresponding flagvals element 
>   set equal to .TRUE.
-
        FTGPF[BIJKED](unit,group,fpixel,nelements, > values,flagvals,anyf,status)
-
>>10  Put values into group parameters
-
        FTPGP[BIJKED](unit,group,fparm,nparm,values, > status)
-
>>11  Get values from group parameters
-
        FTGGP[BIJKED](unit,group,fparm,nparm, > values,status)
-
The following 4 subroutines transfer FITS images with 2 or 3 dimensions
to or from a data array which has been declared in the calling program.  
The dimensionality of the FITS image is passed by the naxis1, naxis2,
and naxis3 parameters and the declared dimensions of the program array
are passed in the dim1 and dim2 parameters.  Note that the program array
does not have to have the same dimensions as the FITS array, but must
be at least as big.  For example if a FITS image with NAXIS1 = NAXIS2 = 400
is read into a program array which is dimensioned as 512 x 512 pixels,
then the image will just fill the lower left corner of the array
with pixels in the range 1 - 400 in the X an Y directions.  This has
the effect of taking a contiguous set of pixel value in the FITS array
and writing them to a non-contiguous array in program memory
(i.e., there are now some blank pixels around the edge of the image
in the program array).

>>11  Put 2-D image into the data array
-
        FTP2D[BIJKED](unit,group,dim1,naxis1,naxis2,image, > status)
-
>>12  Put 3-D cube into the data array 
-
        FTP3D[BIJKED](unit,group,dim1,dim2,naxis1,naxis2,naxis3,cube, > status)
-
>13  Get 2-D image from the data array.  Undefined
     pixels in the array will be set equal to the value of 'nullval',
     unless nullval=0 in which case no testing for undefined pixels will
>    be performed.
-
        FTG2D[BIJKED](unit,group,nullval,dim1,naxis1,naxis2, > image,anyf,status)
-
>14 Get 3-D cube from the data array.   Undefined
    pixels in the array will be set equal to the value of 'nullval',
    unless nullval=0 in which case no testing for undefined pixels will
>   be performed.
-
        FTG3D[BIJKED](unit,group,nullval,dim1,dim2,naxis1,naxis2,naxis3, >
                     cube,anyf,status)
-

The following subroutines transfer a rectangular subset of the pixels
in a FITS N-dimensional image to or from an array which has been
declared in the calling program.  The fpixels and lpixels parameters
are integer arrays which specify the starting and ending pixels in each
dimension of the FITS image that are to be read or written.  (Note that
these are the starting and ending pixels in the FITS image, not in the
declared array). The array parameter is treated simply as a large
one-dimensional array of the appropriate datatype containing the pixel
values; The pixel values in the FITS array are read/written  from/to
this program array in strict sequence without any gaps;  it is up to
the calling routine to correctly interpret the dimensionality of this
array.  The two families of FITS reading routines (FTGSVx and FTGSFx
subroutines) also have an 'incs' parameter which defines the
data sampling interval in each dimension of the FITS array.  For
example, if incs(1)=2 and incs(2)=3 when reading a 2-dimensional
FITS image, then only every other pixel in the first dimension
and every 3rd pixel in the second dimension will be returned in
the 'array' parameter. [Note: the FTGSSx family of routines which
were present in previous versions of FITSIO have been superseded
by the more general FTGSVx family of routines.]

>>15   Put an arbitrary data subsection into the data array.
-
        FTPSS[BIJKED](unit,group,naxis,naxes,fpixels,lpixels,array, > status)
-
>16    Get an arbitrary data subsection from the data array.  Undefined
       pixels in the array will be set equal to the value of 'nullval',
       unless nullval=0 in which case no testing for undefined pixels will
>      be performed.
-
        FTGSV[BIJKED](unit,group,naxis,naxes,fpixels,lpixels,incs,nullval, >
                     array,anyf,status)
-
>17    Get an arbitrary data subsection from the data array.  Any Undefined
       pixels in the array will have the corresponding 'flagvals'
>      element set equal to .TRUE.
-
        FTGSF[BIJKED](unit,group,naxis,naxes,fpixels,lpixels,incs, >
                     array,flagvals,anyf,status)
-

**H.  FITS ASCII and Binary Table Data I/O Subroutines 

***1.  Column Information Subroutines \label{FTGCNO}

>1   Get the number of rows or columns in the current FITS table.
     The number of rows is given by the NAXIS2 keyword and the
     number of columns is given by the TFIELDS keyword in the header
     of the table.  The FTGNRWLL routine is identical to FTGNRW except
     that the number of rows is returned as a 64-bit integer rather
>    than a 32-bit integer.
-
        FTGNRW(unit, > nrows, status)
        FTGNRWLL(unit, > nrowsll, status)
        FTGNCL(unit, > ncols, status)
-
>2  Get the table column number (and name) of the column whose name
matches an input template name.  The table column names are defined by
the TTYPEn keywords in the FITS header.  If a column does not have a
TTYPEn keyword, then these routines assume that the name consists of
all blank characters.  These 2 subroutines perform the same function
except that FTGCNO only returns the number of the matching column whereas
FTGCNN also returns the name of the column.  If CASESEN = .true. then
the column name match will be case-sensitive.

The input column name template (COLTEMPLATE) is (1) either the exact
name of the column to be searched for, or (2) it may contain wild cards
characters (*, ?, or \#), or (3) it may contain the number of the desired
column (where the number is expressed as ASCII digits).  The first 2 wild 
cards behave similarly to UNIX filename matching:  the '*' character matches 
any sequence of characters (including zero characters) and the '?'
character matches any single character.  The \# wildcard will match
any consecutive string of decimal digits (0-9).  As an example, the template
strings 'AB?DE', 'AB*E', and 'AB*CDE' will all match the string
'ABCDE'.  If more than one column name in the table matches the
template string, then the first match is returned and the status value
will be set to 237 as a warning that a unique match was not found.  To
find the other cases that match the template, simply call the
subroutine again leaving the input status value equal to  237 and the
next matching name will then be returned.  Repeat this process until a
status = 219 (column name not found) is returned.  If these subroutines
fail to match the template to any of the columns in the table, they
lastly check if the template can be interpreted as a simple positive
integer (e.g., '7', or '512') and if so, they return that column
number.  If no matches are found then a status = 219 error is
returned.

Note that the FITS Standard recommends that only letters, digits, and
the underscore character be used in column names (with no embedded
spaces in the name).  Trailing blank characters are not significant.
It is recommended that the column names in a given table be unique
>within the first 8 characters.
- 
        FTGCNO(unit,casesen,coltemplate, > colnum,status)
        FTGCNN(unit,casesen,coltemplate, > colname,colnum,status)
-
>3  Get the datatype of a column in an ASCII or binary table.  This 
    routine returns an integer code value corresponding to the datatype
    of the column. (See the FTBNFM and FTASFM subroutines in the Utilities
    section of this document for a list of the code values).  The vector
    repeat count (which is alway 1 for ASCII table columns) is also returned.
    If the specified column has an ASCII character datatype (code = 16) then
    the width of a unit string in the column is also returned.  Note that
    this routine supports the local convention for specifying arrays of
    strings within a binary table character column, using the syntax 
    TFORM = 'rAw' where 'r' is the total number of characters (= the width 
    of the column) and 'w' is the width of a unit string within the column.  
    Thus if the column has TFORM = '60A12' then this routine will return 
    datacode = 16, repeat = 60, and width = 12.

   The second routine, FTEQTY is similar except that in
   the case of scaled integer columns it returns the 'equivalent' data
   type that is needed to store the scaled values, and not necessarily
   the physical data type of the unscaled values as stored in the FITS
   table.  For example if a '1I' column in a binary table has TSCALn =
   1 and TZEROn = 32768, then this column effectively contains unsigned
   short integer values, and thus the returned value of typecode will
   be the code for an unsigned short integer, not a signed short integer.
   Similarly, if a column has TTYPEn = '1I'
   and TSCALn = 0.12, then the returned typecode
>  will be the code for a 'real' column.
-
        FTGTCL(unit,colnum, > datacode,repeat,width,status)
        FTEQTY(unit,colnum, > datacode,repeat,width,status)
-
>4  Return the display width of a column.  This is the length
    of the string that will be returned  
    when reading the column as a formatted string.  The display width is
    determined by the TDISPn keyword, if present, otherwise by the data
>   type of the column.
-
        FTGCDW(unit, colnum, > dispwidth, status)
-
>5  Get information about an existing ASCII table column.  (NOTE: TSCAL and
    TZERO must be declared as Double Precision variables).  All the
>   returned parameters are scalar quantities.
-
        FTGACL(unit,colnum, >
               ttype,tbcol,tunit,tform,tscal,tzero,snull,tdisp,status)
-
>6  Get information about an existing binary table column. (NOTE: TSCAL and
    TZERO must be declared as Double Precision variables). DATATYPE is a 
    character string which returns the datatype of the column as defined
    by the TFORMn keyword (e.g., 'I', 'J','E', 'D', etc.).  In the case
    of an ASCII character column, DATATYPE will have a value of the 
    form 'An' where 'n' is an integer expressing the width of the field
    in characters.  For example, if TFORM = '160A8' then FTGBCL will return
    DATATYPE='A8' and REPEAT=20.   All the returned parameters are scalar
>   quantities.
-
        FTGBCL(unit,colnum, >
               ttype,tunit,datatype,repeat,tscal,tzero,tnull,tdisp,status)
-
>7  Put (append) a TDIMn keyword whose value has the form '(l,m,n...)'
    where l, m, n... are the dimensions of a multidimension array
>   column in a binary table.
-
        FTPTDM(unit,colnum,naxis,naxes, > status)
-
>8  Return the number of and size of the dimensions of a table column.
    Normally this information is given by the TDIMn keyword, but if 
    this keyword is not present then this routine returns NAXIS = 1
>   and NAXES(1) equal to the repeat count in the TFORM keyword.
-
        FTGTDM(unit,colnum,maxdim, > naxis,naxes,status)
-
>9  Decode the input TDIMn keyword string (e.g. '(100,200)') and return the
    number of and size of the dimensions of a binary table column. If the input
    tdimstr character string is null, then this routine returns naxis = 1
    and naxes[0] equal to the repeat count in the TFORM keyword. This routine
>   is called by FTGTDM.
-
        FTDTDM(unit,tdimstr,colnum,maxdim, > naxis,naxes, status)
-
>10  Return the optimal number of rows to read or write at one time for
    maximum I/O efficiency.  Refer to the ``Optimizing Code'' section
>   in Chapter 5 for more discussion on how to use this routine.

-
        FFGRSZ(unit, > nrows,status)
-

***2.  Low-Level Table Access Subroutines \label{FTGTBS}

The following subroutines provide low-level access to the data in ASCII
or binary tables and are mainly useful as an efficient way to copy all
or part of a table from one location to another.  These routines simply
read or write the specified number of consecutive bytes in an ASCII or
binary table, without regard for column boundaries or the row length in
the table.  The first two subroutines read or write consecutive bytes
in a table to or from a character string variable, while the last two
subroutines read or write consecutive bytes to or from a variable
declared as a numeric data type (e.g., INTEGER, INTEGER*2, REAL, DOUBLE
PRECISION).  These routines do not perform any machine dependent data
conversion or byte swapping, except that conversion to/from ASCII
format is performed by the FTGTBS and FTPTBS routines on machines which
do not use ASCII character codes in the internal data representations
(e.g., on IBM mainframe computers).

>1  Read a consecutive string of characters from an ASCII table 
    into a character variable (spanning columns and multiple rows if necessary)
    This routine should not be used with binary tables because of
>   complications related to passing string variables between C and Fortran.
-
        FTGTBS(unit,frow,startchar,nchars, > string,status)
-
>2  Write a consecutive string of characters to an ASCII table 
    from a character variable (spanning columns and multiple rows if necessary)
    This routine should not be used with binary tables because of
>   complications related to passing string variables between C and Fortran.
-
        FTPTBS(unit,frow,startchar,nchars,string, > status)
-
>3  Read a consecutive array of bytes from an ASCII or binary table 
    into a numeric variable (spanning columns and multiple rows if necessary).
    The array parameter may be declared as any numerical datatype as long
    as the array is at least 'nchars' bytes long, e.g., if nchars = 17,
>   then declare the array as INTEGER*4 ARRAY(5).
-
        FTGTBB(unit,frow,startchar,nchars, > array,status)
-
>4  Write a consecutive array of bytes to an ASCII or binary table 
    from a numeric variable (spanning columns and multiple rows if necessary)
    The array parameter may be declared as any numerical datatype as long
    as the array is at least 'nchars' bytes long, e.g., if nchars = 17,
>   then declare the array as INTEGER*4 ARRAY(5).
-
        FTPTBB(unit,frow,startchar,nchars,array, > status)
-

***3.  Edit Rows or Columns \label{FTIROW}

>1  Insert blank rows into an existing ASCII or binary table (in the CDU).
    All the rows FOLLOWING row FROW are shifted down by NROWS rows.  If
    FROW or FROWLL equals 0 then the blank rows are inserted at the beginning of the 
    table.  These routines modify the NAXIS2 keyword to reflect the new 
>   number of rows in the table.  
-
        FTIROW(unit,frow,nrows, > status)
        FTIROWLL(unit,frowll,nrowsll, > status)
-
>2  Delete rows from an existing ASCII or binary table (in the CDU).
    The NROWS (or NROWSLL) is the number of rows are deleted, starting 
    with row FROW (or FROWLL), and
    any remaining rows in the table are shifted up to fill in the space.
    These routines modify the NAXIS2 keyword to reflect the new number
>   of rows in the table. 
-
        FTDROW(unit,frow,nrows, > status)
        FTDROWLL(unit,frowll,nrowsll, > status)
-
>3  Delete a list of rows from an ASCII or binary table (in the CDU).
    In the first routine, 'rowrange' is a character string listing the
    rows or row ranges to delete (e.g., '2-4, 5, 8-9'). In the second
    routine, 'rowlist' is an integer array of row numbers to be deleted
    from the table.  nrows is the number of row numbers in the list.
    The first row in the table is 1 not 0.  The list of row numbers
>   must be sorted in ascending order.
-
        FTDRRG(unit,rowrange, > status)
        FTDRWS(unit,rowlist,nrows, > status)
-
>4  Insert a blank column (or columns) into an existing ASCII or binary 
    table (in the CDU).  COLNUM specifies the column number that the (first)
    new column should occupy in the table.  NCOLS specifies how many 
    columns are to be inserted. Any existing columns from this position and
    higher are moved over to allow room for the new column(s).  
    The index number on all the following keywords will be incremented
    if necessary to reflect the new position of the column(s) in the table:
    TBCOLn, TFORMn, TTYPEn, TUNITn, TNULLn, TSCALn, TZEROn, TDISPn, TDIMn,
    TLMINn, TLMAXn, TDMINn, TDMAXn, TCTYPn, TCRPXn, TCRVLn, TCDLTn, TCROTn,
>   and TCUNIn.
-
        FTICOL(unit,colnum,ttype,tform, > status)
        FTICLS(unit,colnum,ncols,ttype,tform, > status)
-
>5  Modify the vector length of a binary table column (e.g.,
    change a column from TFORMn = '1E' to '20E').  The vector
>   length may be increased or decreased from the current value.
-
        FTMVEC(unit,colnum,newveclen, > status)
-
>6  Delete a column from an existing ASCII or binary table (in the CDU).
    The index number of all the keywords listed above (for FTICOL) will be 
    decremented if necessary to reflect the new position of the column(s) in 
    the table.  Those index keywords that refer to the deleted column will
    also be deleted.  Note that the physical size of the FITS file will
    not be reduced by this operation, and the empty FITS blocks if any
>   at the end of the file will be padded with zeros.
-
        FTDCOL(unit,colnum, > status)
-
>7  Copy a column from one HDU to another (or to the same HDU).  If
    createcol = TRUE, then a new column will be inserted in the output
    table, at position `outcolumn', otherwise the existing output column will
    be overwritten (in which case it must have a compatible datatype).  
>   Note that the first column in a table is at colnum = 1. 
-
        FTCPCL(inunit,outunit,incolnum,outcolnum,createcol, > status);
-
***4.  Read and Write Column Data Routines \label{FTPCLS}

These subroutines put or get data values in the current ASCII or Binary table
extension.  Automatic data type conversion is performed for numerical data
types (B,I,J,E,D) if the data type of the column (defined by the TFORM keyword)
differs from the data type of the calling subroutine.  The data values are also
scaled by the TSCALn and TZEROn header values as they are being written to
or read from the FITS array.  The fttscl subroutine MUST be used to define the
scaling parameters when writing data to the table or to override the default
scaling values given in the header
when reading from the table. 

    In the case of binary tables with vector elements, the 'felem'
parameter defines the starting pixel within the element vector.  This
parameter is ignored with ASCII tables. Similarly, in the case of
binary tables the 'nelements' parameter specifies the total number of
vector values read or written (continuing on subsequent rows if
required) and not the number of table elements.  Two sets of
subroutines are provided to get the column data which differ in the way
undefined pixels are handled.  The first set of routines (FTGCV)
simply return an array of data elements in which undefined pixels are
set equal to a value specified by the user in the 'nullval' parameter.
An additional feature of these subroutines is that if the user sets
nullval = 0, then no checks for undefined pixels will be performed,
thus increasing the speed of the program.  The second set of routines
(FTGCF) returns the data element array and in addition a logical array
of flags which defines whether the corresponding data pixel is undefined.

    Any column, regardless of it's intrinsic datatype, may be read as a
    string.  It should be noted however that reading a numeric column
    as a string is 10 - 100 times slower than reading the same column as
    a number due to the large overhead in constructing the formatted
    strings.    The display format of the returned strings will be
    determined by the TDISPn keyword, if it exists, otherwise by the
    datatype of the column.  The length of the returned strings can be
    determined with the ftgcdw routine.  The following TDISPn display
    formats are currently supported:
-
    Iw.m   Integer
    Ow.m   Octal integer
    Zw.m   Hexadecimal integer
    Fw.d   Fixed floating point
    Ew.d   Exponential floating point
    Dw.d   Exponential floating point
    Gw.d   General; uses Fw.d if significance not lost, else Ew.d
-
  where w is the width in characters of the displayed values, m is the minimum
  number of digits displayed, and d is the number of digits to the right of the 
  decimal.  The .m field is optional.

>1  Put elements into an ASCII or binary table column (in the CDU).
    (The SPP FSPCLS routine has an additional integer argument after 
    the VALUES character string which specifies the size of the 1st 
>   dimension of this 2-D CHAR array).
-
        FTPCL[SLBIJKEDCM](unit,colnum,frow,felem,nelements,values, > status)
-
>2  Put elements into an ASCII or binary table column (in the CDU)
    substituting the appropriate FITS null value for any elements that
    are equal to NULLVAL.   For ASCII TABLE extensions, the
    null value defined by the previous call to FTSNUL will be substituted;
    For integer FITS columns, in a binary table  the null value
    defined by the previous call to FTTNUL will be substituted;
    For floating point FITS columns a special IEEE NaN (Not-a-Number)
>   value will be substituted.
-
        FTPCN[BIJKED](unit,colnum,frow,felem,nelements,values,nullval > status)
-
>3  Put bit values into a binary byte ('B') or bit ('X') table column (in the
    CDU).  LRAY is an array of logical values corresponding to the sequence of
    bits to be written.  If LRAY is true then the corresponding bit is
    set to 1, otherwise the bit is set to 0.  Note that in the case of
    'X' columns, FITSIO will write to all 8 bits of each byte whether
    they are formally valid or not.  Thus if the column is defined as
    '4X', and one calls FTPCLX with  fbit=1 and nbit=8, then all 8 bits
    will be written into the first byte (as opposed to writing the
    first 4 bits into the first row and then the next 4 bits into the
    next row), even though the last 4 bits of each byte are formally
>   not defined.
-
        FTPCLX(unit,colnum,frow,fbit,nbit,lray, > status)
-
>>4  Set table elements in a column as undefined
-
        FTPCLU(unit,colnum,frow,felem,nelements, > status)
-
>5  Get elements from an ASCII or binary table column (in the CDU).  These
    routines return the values of the table column array elements.  Undefined
    array elements will be returned with a value = nullval, unless nullval = 0 
    (or = ' ' for ftgcvs) in which case no checking for undefined values will
    be performed. The ANYF parameter is set to true if any of the returned
    elements are undefined. (Note: the ftgcl routine simple gets an array
    of logical data values without any checks for undefined values;  use
    the ftgcfl routine to check for undefined logical elements).
    (The SPP FSGCVS routine has an additional integer argument after 
    the VALUES character string which specifies the size of the 1st 
>   dimension of this 2-D CHAR array).
-
        FTGCL(unit,colnum,frow,felem,nelements, > values,status)
        FTGCV[SBIJKEDCM](unit,colnum,frow,felem,nelements,nullval, > 
                       values,anyf,status)
-
>6  Get elements and null flags from an ASCII or binary table column (in the
    CHDU).  These routines return the values of the table column array elements.
    Any undefined array elements will have the corresponding flagvals element 
    set equal to .TRUE. The ANYF parameter is set to true if any of the 
    returned elements are undefined.
    (The SPP FSGCFS routine has an additional integer argument after 
    the VALUES character string which specifies the size of the 1st 
>   dimension of this 2-D CHAR array).
-
        FTGCF[SLBIJKEDCM](unit,colnum,frow,felem,nelements, > 
                         values,flagvals,anyf,status)
-
>7  Get an arbitrary data subsection from an N-dimensional array
    in a binary table vector column.  Undefined pixels 
    in the array will be set equal to the value of 'nullval',
    unless nullval=0 in which case no testing for undefined pixels will
    be performed.  The first and last rows in the table to be read
    are specified by fpixels(naxis+1) and lpixels(naxis+1), and hence
    are treated as the next higher dimension of the FITS N-dimensional
    array.  The INCS parameter specifies the sampling interval in
>   each dimension between the data elements that will be returned.
-
        FTGSV[BIJKED](unit,colnum,naxis,naxes,fpixels,lpixels,incs,nullval, >
                     array,anyf,status)
-
>8  Get an arbitrary data subsection from an N-dimensional array
    in a binary table vector column.  Any Undefined
    pixels in the array will have the corresponding 'flagvals'
    element set equal to .TRUE.   The first and last rows in the table 
    to be read are specified by fpixels(naxis+1) and lpixels(naxis+1), 
    and hence are treated as the next higher dimension of the FITS 
    N-dimensional array.  The INCS parameter specifies the sampling 
    interval in each dimension between the data elements that will be 
>   returned.
-
        FTGSF[BIJKED](unit,colnum,naxis,naxes,fpixels,lpixels,incs, >
                     array,flagvals,anyf,status)
-
>9  Get bit values from a byte ('B') or bit (`X`) table column (in the
    CDU).  LRAY is an array of logical values corresponding to the
    sequence of bits to be read.  If LRAY is true then the
    corresponding bit was set to 1, otherwise the bit was set to 0.
    Note that in the case of 'X' columns, FITSIO will read  all 8 bits
    of each byte whether they are formally valid or not.  Thus if the
    column is defined as '4X', and one calls FTGCX with  fbit=1 and
    nbit=8, then all 8 bits will be read from the first byte (as
    opposed to reading the first 4 bits from the first row and then the
    first 4 bits from the next row), even though the last 4 bits of
>   each byte are formally not defined.
-
        FTGCX(unit,colnum,frow,fbit,nbit, > lray,status)
-
>10 Read any consecutive set of bits from an 'X' or 'B' column and
    interpret them as an unsigned n-bit integer. NBIT must be less than
    or equal to 16 when calling FTGCXI, and less than or equal to 32 when
    calling FTGCXJ; there is no limit on the value of NBIT for FTGCXD, but
    the returned double precision value only has 48 bits of precision on
    most 32-bit word machines.  The NBITS bits are interpreted as an
    unsigned integer unless NBITS = 16 (in FTGCXI) or 32 (in FTGCXJ) in which
    case the string of bits are interpreted as 16-bit or 32-bit 2's 
    complement signed integers.  If NROWS is greater than 1 then the
    same set of bits will be read from sequential rows in the table
    starting with row FROW.  Note that the numbering convention
    used here for the FBIT parameter adopts 1 for the first element of the
>   vector of bits;  this is the Most Significant Bit of the integer value.    
-
        FTGCX[IJD](unit,colnum,frow,nrows,fbit,nbit, > array,status)
-
>11 Get the descriptor for a variable length column in a binary table.
    The descriptor consists of 2 integer parameters: the number of elements
    in the array and the starting offset relative to the start of the heap.
    The first routine returns a single descriptor whereas the second routine
>   returns the descriptors for a range of rows in the table.
-
        FTGDES(unit,colnum,rownum, > nelements,offset,status) 
        FTGDESLL(unit,colnum,rownum, > nelementsll,offsetll,status) 

        FFGDESS(unit,colnum,firstrow,nrows > nelements,offset, status)
        FFGDESSLL(unit,colnum,firstrow,nrows > nelementsll,offsetll, status)
-
>12  Write the descriptor for a variable length column in a binary table. 
    These subroutines can be used in conjunction with FTGDES to enable
    2 or more arrays to point to the same storage location to save
>   storage space if the arrays are identical.
-
        FTPDES(unit,colnum,rownum,nelements,offset, > status) 
        FTPDESLL(unit,colnum,rownum,nelementsll,offsetll, > status) 
-
        
**I.  Row Selection and Calculator Routines \label{FTFROW}

These routines all parse and evaluate an input string containing a user
defined arithmetic expression.  The first 3 routines select rows in a
FITS table, based on whether the expression evaluates to true (not
equal to zero) or false (zero).  The other routines evaluate the
expression and calculate a value for each row of the table.  The
allowed expression syntax is described in the row filter section in the
earlier `Extended File Name Syntax' chapter of this document.  The
expression may also be written to a text file, and the name of the
file, prepended with a '@' character may be supplied for the 'expr'
parameter (e.g.  '@filename.txt'). The  expression  in  the  file can
be arbitrarily complex and extend over multiple lines of the file.
Lines  that begin with 2 slash characters ('//') will  be ignored and
may be used to add comments to the file.

>1  Evaluate a boolean expression over the indicated rows, returning an     
> array of flags indicating which rows evaluated to TRUE/FALSE 
-
         FTFROW(unit,expr,firstrow, nrows, > n_good_rows, row_status, status)
-
>>2  Find the first row which satisfies the input boolean expression 
-
         FTFFRW(unit, expr, > rownum, status)             
-
>3 Evaluate an expression on all rows of a table.  If the input and output  
files are not the same, copy the TRUE rows to the output file.  If the   
>files are the same, delete the FALSE rows (preserve the TRUE rows). 
-
         FTSROW(inunit, outunit, expr, > status)
-
>4  Calculate an expression for the indicated rows of a table, returning     
the results, cast as datatype (TSHORT, TDOUBLE, etc), in array.  If      
nulval==NULL, UNDEFs will be zeroed out.  For vector results, the number 
of elements returned may be less than nelements if nelements is not an   
even multiple of the result dimension.  Call FTTEXP to obtain    
>the dimensions of the results.    
-
         FTCROW(unit,datatype,expr,firstrow,nelements,nulval, > 
             array,anynul,status)
-
>5 Evaluate an expression and write the result either to a column (if
the expression is a function of other columns in the table) or to a
keyword (if the expression evaluates to a constant and is not a
function of other columns in the table).  In the former case, the
parName parameter is the name of the column (which may or may not already
exist) into which to write the results, and parInfo contains an
optional TFORM keyword value if a new column is being created.  If a
TFORM value is not specified then a default format will be used,
depending on the expression.  If the expression evaluates to a constant,
then the result will be written to the keyword name given by the
parName parameter, and the parInfo parameter may be used to supply an
optional comment for the keyword.  If the keyword does not already
exist, then the name of the keyword must be preceded with a '\#' character,
>otherwise the result will be written to a column with that name.
        
-
         FTCALC(inunit, expr, outunit, parName, parInfo, > status) 
-
>6  This calculator routine is similar to the previous routine, except
that the expression is only evaluated over the specified 
row ranges.  nranges specifies the number of row ranges, and firstrow
>and lastrow give the starting and ending row number of each range.
-
         FTCALC_RNG(inunit, expr, outunit, parName, parInfo,
            nranges, firstrow, lastrow, > status)
-
>>7 Evaluate the given expression and return information on the result. 
-
         FTTEXP(unit, expr, > datatype, nelem, naxis, naxes, status)        
-
 

**J.  Celestial Coordinate System Subroutines \label{FTGICS}

The FITS community has adopted a set of keyword conventions that define
the transformations needed to convert between pixel locations in an
image and the corresponding celestial coordinates on the sky, or more
generally, that define world coordinates that are to be associated with
any pixel location in an n-dimensional FITS array. CFITSIO is distributed
with a couple of self-contained World Coordinate System (WCS) routines,
however, these routines DO NOT support all the latest WCS conventions,
so it is STRONGLY RECOMMENDED that software developers use a more robust
external WCS library.  Several recommended libraries are:
-
  WCSLIB -  supported by Mark Calabretta
  WCSTools - supported by Doug Mink
  AST library - developed by the U.K. Starlink project
-

More information about the WCS keyword conventions and links to all of
these WCS libraries can be found on the FITS Support Office web site at
http://fits.gsfc.nasa.gov under the WCS link.

The functions provided in these external WCS libraries will need access to
the  WCS information contained in the FITS file headers.  One convenient
way to pass this information to the extermal library is to use  FITSIO
to copy the header keywords into one long character string, and then
pass this string to an interface routine in the external library that
will extract the necessary WCS information (e.g., see the astFitsChan
and astPutCards routines in the Starlink AST library).

The following FITSIO routines DO NOT support the more recent WCS conventions
that have been approved as part of the FITS standard.  Consequently,
the following routines ARE NOW DEPRECATED.  It is STRONGLY RECOMMENDED
that software developers not use these routines, and instead use an
external WCS library, as described above.

These routines are included mainly for backward compatibility with
existing software.  They support the following standard map 
projections: -SIN, -TAN, -ARC, -NCP, -GLS, -MER, and -AIT (these are the
legal values for the coordtype parameter).  These routines are based
on similar functions in Classic AIPS.  All the angular quantities are
given in units of degrees.

>1  Get the values of all the standard FITS celestial coordinate system
    keywords from the header of a FITS image (i.e., the primary array or
    an image extension).  These values may then be passed to the subroutines
    that perform the coordinate transformations.  If any or all of the WCS 
    keywords are not present, then default values will be returned. If
    the first coordinate axis is the declination-like coordinate, then
    this routine will swap them so that the longitudinal-like coordinate
    is returned as the first axis.

    If the file uses the newer 'CDj\_i' WCS transformation matrix
    keywords instead of old style 'CDELTn' and 'CROTA2' keywords, then
    this routine will calculate and return the values of the equivalent
    old-style keywords.    Note that the conversion from the new-style
    keywords to the old-style values is sometimes only an
    approximation, so if the approximation is larger than an internally
    defined threshold level, then CFITSIO will still return the
    approximate WCS keyword values, but will also return with status =
    506, to warn the calling program that approximations have been
    made.  It is then up to the calling program to decide whether the
    approximations are sufficiently accurate for the particular
    application, or whether more precise WCS transformations must be
>   performed using new-style WCS keywords directly.
-
        FTGICS(unit, > xrval,yrval,xrpix,yrpix,xinc,yinc,rot,coordtype,status)
-
>2  Get the values of all the standard FITS celestial coordinate system
    keywords from the header of a FITS table where the X and Y (or RA and
    DEC coordinates are stored in 2 separate columns of the table.
    These values may then be passed to the subroutines that perform the
>   coordinate transformations.
-
        FTGTCS(unit,xcol,ycol, > 
               xrval,yrval,xrpix,yrpix,xinc,yinc,rot,coordtype,status)
-
>3   Calculate the celestial coordinate corresponding to the input 
>    X and Y pixel location in the image.
-
        FTWLDP(xpix,ypix,xrval,yrval,xrpix,yrpix,xinc,yinc,rot,
                          coordtype, > xpos,ypos,status)
-
>4   Calculate the X and Y pixel location corresponding to the input 
>    celestial coordinate in the image.
-
        FTXYPX(xpos,ypos,xrval,yrval,xrpix,yrpix,xinc,yinc,rot,
                          coordtype, > xpix,ypix,status)
-
        
**K.  File Checksum Subroutines \label{FTPCKS}

The following routines either compute or validate the checksums for the
CHDU.  The DATASUM keyword is used to store the numerical value of the
32-bit, 1's complement checksum for the data unit alone.  If there is
no data unit then the value is set to zero. The numerical value is
stored as an ASCII string of digits, enclosed in quotes, because the
value may be too large to represent as a 32-bit signed integer.  The
CHECKSUM keyword is used to store the ASCII encoded COMPLEMENT of the
checksum for the entire HDU.  Storing the complement, rather than the
actual checksum, forces the checksum for the whole HDU to equal zero.
If the file has been modified since the checksums were computed, then
the HDU checksum will usually not equal zero.  These checksum keyword
conventions are based on a paper by Rob Seaman published in the
proceedings of the ADASS IV conference in Baltimore in November 1994
and a later revision in June 1995.

>1  Compute and write the DATASUM and CHECKSUM keyword values for the CHDU
    into the current header.  The DATASUM value is the 32-bit checksum
    for the data unit, expressed as a decimal integer enclosed in single 
    quotes. The CHECKSUM keyword value is a 16-character string which
    is the ASCII-encoded value for the complement of the checksum for 
    the whole HDU.  If these keywords already exist, their values
    will be updated only if necessary (i.e., if the file has been modified 
>   since the original keyword values were computed).
-
        FTPCKS(unit, > status) 
-
>2  Update the CHECKSUM keyword value in the CHDU, assuming that the
    DATASUM keyword exists and already has the correct value.  This routine
    calculates the new checksum for the current header unit, adds it to the 
    data unit checksum, encodes the value into an ASCII string, and writes
>   the string to the CHECKSUM keyword.
-
        FTUCKS(unit, > status) 
-
>3  Verify the CHDU by computing the checksums and comparing
    them with the keywords.  The data unit is verified correctly
    if the computed checksum equals the value of the DATASUM
    keyword.  The checksum for the entire HDU (header plus data unit) is 
    correct if it equals zero.  The output DATAOK and HDUOK parameters
    in this subroutine are integers which will have a value = 1
    if the data or HDU is verified correctly, a value = 0
    if the DATASUM or CHECKSUM keyword is not present, or value = -1
>   if the computed checksum is not correct. 
-
        FTVCKS(unit, > dataok,hduok,status) 
-
>4  Compute and return the checksum values for the CHDU (as 
    double precision variables) without creating or modifying the 
    CHECKSUM and DATASUM keywords.  This routine is used internally by 
>   FTVCKS, but may be useful in other situations as well.
-
        FTGCKS(unit, > datasum,hdusum,status) 
-
>5  Encode a checksum value (stored in a double precision variable)
    into a 16-character string.  If COMPLEMENT = .true. then the 32-bit  
>   sum value will be complemented before encoding.
-
        FTESUM(sum,complement, > checksum)
-
>6  Decode a 16 character checksum string into a double precision value.
    If COMPLEMENT = .true. then the 32-bit sum value will be complemented 
>   after decoding.
-
        FTDSUM(checksum,complement, > sum)
-
        
**L.   Date and Time Utility Routines \label{FTGSDT}

The following routines help to construct or parse the FITS date/time
strings.   Starting in the year 2000, the FITS DATE keyword values (and
the values of other `DATE-' keywords) must have the form 'YYYY-MM-DD'
(date only) or 'YYYY-MM-DDThh:mm:ss.ddd...' (date and time) where the
number of decimal places in the seconds value is optional.  These times
are in UTC.  The older 'dd/mm/yy' date format may not be used for dates
after 01 January 2000.

>1  Get the current system date.  The returned year has 4 digits
>    (1999, 2000, etc.) 
-
        FTGSDT( > day, month, year, status )
-

>2  Get the current system date and time string ('YYYY-MM-DDThh:mm:ss').
The time will be in UTC/GMT if available, as indicated by a returned timeref 
value = 0.  If the returned value of timeref = 1 then this indicates that
it was not possible to convert the local time to UTC, and thus the local
>time was returned.
-
        FTGSTM(> datestr, timeref, status)
-

>3  Construct a date string from the input date values.  If the year
is between 1900 and 1998, inclusive, then the returned date string will
have the old FITS format ('dd/mm/yy'), otherwise the date string will
have the new FITS format ('YYYY-MM-DD').  Use FTTM2S instead
> to always return a date string using the new FITS format. 
-
        FTDT2S( year, month, day, > datestr, status)
-

>4  Construct a new-format date + time string ('YYYY-MM-DDThh:mm:ss.ddd...').
  If the year, month, and day values all = 0 then only the time is encoded
  with format 'hh:mm:ss.ddd...'.  The decimals parameter specifies how many
  decimal places of fractional seconds to include in the string.  If `decimals'
> is negative, then only the date will be return ('YYYY-MM-DD').
-
        FTTM2S( year, month, day, hour, minute, second, decimals, 
                > datestr, status)
-

>5  Return the date as read from the input string, where the string may be
in either the old ('dd/mm/yy')  or new ('YYYY-MM-DDThh:mm:ss' or
>'YYYY-MM-DD') FITS format.  
-
        FTS2DT(datestr, > year, month, day, status)
-

>6  Return the date and time as read from the input string, where the
string may be in either the old  or new FITS format.  The returned hours,
minutes, and seconds values will be set to zero if the input string
does not include the time ('dd/mm/yy' or 'YYYY-MM-DD') .  Similarly,
the returned year, month, and date values will be set to zero if the
>date is not included in the input string ('hh:mm:ss.ddd...'). 
-
        FTS2TM(datestr, > year, month, day, hour, minute, second, status)
-

**M.  General Utility Subroutines \label{FTGHAD}

The following utility subroutines may be useful for certain applications:

>>1  Return the starting byte address of the CHDU and the next HDU.
-
        FTGHAD(iunit, > curaddr, nextaddr)
-
>>2  Convert a character string to uppercase (operates in place).
-
        FTUPCH(string)
-
>3  Compare the input template string against the reference string
    to see if they match.  The template string may contain wildcard
    characters: '*' will match any sequence of characters (including
    zero characters) and '?' will match any single character in the
    reference string. The '\#' character will match any consecutive string
    of decimal digits (0 - 9).  If CASESN = .true. then the match will be
    case sensitive.  The returned MATCH parameter will be .true. if
    the 2 strings match, and EXACT will be .true. if the match is
    exact (i.e., if no wildcard characters were used in the match).
>   Both strings must be 68 characters or less in length.
-
        FTCMPS(str_template, string, casesen, > match, exact)
-

>4  Test that the keyword name contains only legal characters: A-Z,0-9,
>   hyphen, and underscore.
-
        FTTKEY(keyword, > status)
-
>5  Test that the keyword record contains only legal printable ASCII
>     characters
-
        FTTREC(card, > status)
-
>6  Test whether the current header contains any NULL (ASCII 0) characters.
    These characters are illegal in the header, but they will go undetected
    by most of the CFITSIO keyword header routines, because the null is 
    interpreted as the normal end-of-string terminator.  This routine returns
    the position of the first null character in the header, or zero if there
    are no nulls.  For example a returned value of 110 would indicate that
    the first NULL is located in the 30th character of the second keyword
    in the header (recall that each header record is 80 characters long).
    Note that this is one of the few FITSIO routines in which the returned
>   value is not necessarily equal to the status value).   
-
        FTNCHK(unit, > status)
-
>7  Parse a header keyword record and return the name of the keyword
    and the length of the name.
    The keyword name normally occupies the first 8 characters of the
    record, except under the HIERARCH convention where the name can
>   be up to 70 characters in length.
-
        FTGKNM(card, > keyname, keylength, staThe '\#' character will match any consecutive string
    of decimal digits (0 - 9). tus)
-  
>8  Parse a header keyword record.
    This subroutine parses the input header record to return the value (as
    a character string) and comment strings.  If the keyword has no
    value (columns 9-10 not equal to '= '), then the value string is returned
    blank and the comment string is set equal to column 9 - 80 of the
>   input string.
-
        FTPSVC(card, > value,comment,status)
-
>9  Construct a sequence keyword name (ROOT + nnn).
    This subroutine appends the sequence number to the root string to create
>   a keyword name (e.g., 'NAXIS' + 2 = 'NAXIS2')
-
        FTKEYN(keyroot,seq_no, > keyword,status)
-
>10 Construct a sequence keyword name (n + ROOT).
    This subroutine concatenates the sequence number to the front of the
>   root string to create a keyword name (e.g., 1 + 'CTYP' = '1CTYP')
-
        FTNKEY(seq_no,keyroot, > keyword,status)
-
>11 Determine the datatype of a keyword value string.
    This subroutine parses the keyword value string (usually columns 11-30
>   of the header record) to determine its datatype.  
-
        FTDTYP(value, > dtype,status)
-
>11 Return the class of input header record.  The record is classified
    into one of the following categories (the class values are
    defined in fitsio.h).  Note that this is one of the few FITSIO
>   routines that does not return a status value. 
-
       Class  Value             Keywords
  TYP_STRUC_KEY  10  SIMPLE, BITPIX, NAXIS, NAXISn, EXTEND, BLOCKED,
                     GROUPS, PCOUNT, GCOUNT, END
                     XTENSION, TFIELDS, TTYPEn, TBCOLn, TFORMn, THEAP,
                     and the first 4 COMMENT keywords in the primary array
                     that define the FITS format.
  TYP_CMPRS_KEY  20  The experimental keywords used in the compressed 
                     image format ZIMAGE, ZCMPTYPE, ZNAMEn, ZVALn,
                     ZTILEn, ZBITPIX, ZNAXISn, ZSCALE, ZZERO, ZBLANK
  TYP_SCAL_KEY   30  BSCALE, BZERO, TSCALn, TZEROn
  TYP_NULL_KEY   40  BLANK, TNULLn
  TYP_DIM_KEY    50  TDIMn
  TYP_RANG_KEY   60  TLMINn, TLMAXn, TDMINn, TDMAXn, DATAMIN, DATAMAX
  TYP_UNIT_KEY   70  BUNIT, TUNITn
  TYP_DISP_KEY   80  TDISPn
  TYP_HDUID_KEY  90  EXTNAME, EXTVER, EXTLEVEL, HDUNAME, HDUVER, HDULEVEL
  TYP_CKSUM_KEY 100  CHECKSUM, DATASUM
  TYP_WCS_KEY   110  CTYPEn, CUNITn, CRVALn, CRPIXn, CROTAn, CDELTn
                     CDj_is, PVj_ms, LONPOLEs, LATPOLEs
                     TCTYPn, TCTYns, TCUNIn, TCUNns, TCRVLn, TCRVns, TCRPXn,
                     TCRPks, TCDn_k, TCn_ks, TPVn_m, TPn_ms, TCDLTn, TCROTn
                     jCTYPn, jCTYns, jCUNIn, jCUNns, jCRVLn, jCRVns, iCRPXn,
                     iCRPns, jiCDn,  jiCDns, jPVn_m, jPn_ms, jCDLTn, jCROTn
                     (i,j,m,n are integers, s is any letter)
  TYP_REFSYS_KEY 120 EQUINOXs, EPOCH, MJD-OBSs, RADECSYS, RADESYSs
  TYP_COMM_KEY   130 COMMENT, HISTORY, (blank keyword)
  TYP_CONT_KEY   140 CONTINUE
  TYP_USER_KEY   150 all other keywords

         class = FTGKCL (char *card)
-
>12 Parse the 'TFORM' binary table column format string.
    This subroutine parses the input TFORM character string and returns the
    integer datatype code, the repeat count of the field, and, in the case
    of character string fields, the length of the unit string.  The following
    datatype codes are returned (the negative of the value is returned
>   if the column contains variable-length arrays):
-
                Datatype                DATACODE value
                bit, X                   1 
                byte, B                 11
                logical, L              14
                ASCII character, A      16
                short integer, I        21
                integer, J              41
                real, E                 42
                double precision, D     82
                complex                 83
                double complex          163

        FTBNFM(tform, > datacode,repeat,width,status)
-
>13 Parse the 'TFORM' keyword value that defines the column format in
    an ASCII table.  This routine parses the input TFORM character
    string and returns the datatype code, the width of the column,
    and (if it is a floating point column) the number of decimal places
    to the right of the decimal point.  The returned datatype codes are
    the same as for the binary table, listed above, with the following
    additional rules:  integer columns that are between 1 and 4 characters
    wide are defined to be short integers (code = 21).  Wider integer
    columns are defined to be regular integers (code = 41).  Similarly,
    Fixed decimal point columns (with TFORM = 'Fw.d') are defined to
    be single precision reals (code = 42) if w is between 1 and 7 characters
    wide, inclusive.  Wider 'F' columns will return a double precision
    data code (= 82).  'Ew.d' format columns will have datacode = 42,
>   and 'Dw.d' format columns will have datacode = 82.
-
        FTASFM(tform, > datacode,width,decimals,status)
-
>14 Calculate the starting column positions and total ASCII table width
    based on the input array of ASCII table TFORM values.  The SPACE input
    parameter defines how many blank spaces to leave between each column
    (it is recommended to have one space between columns for better human
>   readability).
-
        FTGABC(tfields,tform,space, > rowlen,tbcol,status)
-
>15 Parse a template string and return a formatted 80-character string
    suitable for appending to (or deleting from) a FITS header file.  
    This subroutine is useful for parsing lines from an ASCII template file
    and reformatting them into legal FITS header records.  The formatted
    string may then be passed to the FTPREC, FTMCRD, or FTDKEY subroutines 
>   to append or modify a FITS header record.
-
        FTGTHD(template, > card,hdtype,status)
-
    The input TEMPLATE character string generally should contain 3 tokens:
    (1) the KEYNAME, (2) the VALUE, and (3) the COMMENT string.  The
    TEMPLATE string must adhere to the following format:

>-      The KEYNAME token must begin in columns 1-8 and be a maximum  of 8
        characters long.  If the first 8 characters of the template line are
        blank then the remainder of the line is considered to be a FITS comment
        (with a blank keyword name).  A legal FITS keyword name may only
        contain the characters A-Z, 0-9, and '-' (minus sign) and
        underscore.  This subroutine will automatically convert any lowercase
        characters to uppercase in the output string.  If KEYNAME = 'COMMENT'
        or 'HISTORY' then the remainder of the line is considered to be a FITS
>       COMMENT or HISTORY record, respectively.

>-      The VALUE token must be separated from the KEYNAME token by one or more
        spaces and/or an '=' character.  The datatype of the VALUE token
        (numeric, logical, or character string) is automatically determined
        and  the output CARD string is formatted accordingly.  The value
        token may be forced to be interpreted as a string (e.g. if it is a
>       string of numeric digits) by enclosing it in single quotes.

>-      The COMMENT token is optional, but if present must be separated from
        the VALUE token by at least one blank space.  A leading '/' character
        may be used to mark the beginning of the comment field, otherwise the
        comment field begins with the first non-blank character following the
>       value token.

>-      One exception to the above rules is that if the first non-blank
        character in the template string is a minus sign ('-') followed
        by a single token, or a single token followed by an equal sign, 
        then it is interpreted as the name of a keyword which is to be  
>       deleted from the FITS header.  

>-      The second exception is that if the template string starts with
        a minus sign and is followed by 2 tokens then the second token
        is interpreted as the new name for the keyword specified by
        first token.  In this case the old keyword name (first token)
        is returned in characters 1-8 of the returned CARD string, and
        the new keyword name (the second token) is returned in characters
        41-48 of the returned CARD string.  These old and new names
        may then be passed to the FTMNAM subroutine which will change
>       the keyword name.

    The HDTYPE output parameter indicates how the returned CARD string
    should be interpreted:
-
        hdtype                  interpretation
        ------           -------------------------------------------------
           -2            Modify the name of the keyword given in CARD(1:8)
                         to the new name given in CARD(41:48)

           -1            CARD(1:8) contains the name of a keyword to be deleted
                         from the FITS header.

            0            append the CARD string to the FITS header if the
                         keyword does not already exist, otherwise update
                         the value/comment if the keyword is already present
                         in the header.

            1            simply append this keyword to the FITS header (CARD
                         is either a HISTORY or COMMENT keyword).

            2            This is a FITS END record; it should not be written
                         to the FITS header because FITSIO automatically
                         appends the END record when the header is closed.
-
     EXAMPLES:  The following lines illustrate valid input template strings:
-
      INTVAL 7 This is an integer keyword
      RVAL           34.6   /     This is a floating point keyword
      EVAL=-12.45E-03  This is a floating point keyword in exponential notation
      lval F This is a boolean keyword
                  This is a comment keyword with a blank keyword name
      SVAL1 = 'Hello world'   /  this is a string keyword
      SVAL2  '123.5'  this is also a string keyword
      sval3  123+  /  this is also a string keyword with the value '123+    '
      # the following template line deletes the DATE keyword
      - DATE 
      # the following template line modifies the NAME keyword to OBJECT
      - NAME OBJECT
-                
>16  Parse the input string containing a list of rows or row ranges, and
     return integer arrays containing the first and last row in each
     range.  For example, if rowlist = "3-5, 6, 8-9" then it will
     return numranges = 3, rangemin = 3, 6, 8 and rangemax = 5, 6, 9.
     At most, 'maxranges' number of ranges will be returned.  'maxrows'
     is the maximum number of rows in the table; any rows or ranges
     larger than this will be ignored.  The rows must be specified in
     increasing order, and the ranges must not overlap. A minus sign
     may be use to specify all the rows to the upper or lower bound, so
     "50-" means all the rows from 50 to the end of the table, and "-"
>    means all the rows in the table, from 1 - maxrows.
-
    FTRWRG(rowlist, maxrows, maxranges, >  
           numranges, rangemin, rangemax, status)
-



*VI.  The CFITSIO Iterator Function

The fits\_iterate\_data function in CFITSIO provides a unique method of
executing an arbitrary user-supplied `work' function that operates on
rows of data in  FITS tables or on pixels in FITS images.  Rather than
explicitly reading and writing the FITS images or columns of data, one
instead calls the CFITSIO iterator routine, passing to it the name of
the user's work function that is to be executed along with a list of
all the table columns or image arrays that are to be passed to the work
function.  The CFITSIO iterator function then does all the work of
allocating memory for the arrays, reading the input data from the FITS
file, passing them to the work function, and then writing any output
data back to the FITS file after the work function exits.  Because
it is often more efficient to process only a subset of the total table
rows at one time, the iterator function can determine the optimum
amount of data to pass in each iteration and repeatly call the work
function until the entire table been processed.

For many applications this single CFITSIO iterator function can
effectively replace all the other CFITSIO routines for reading or
writing data in FITS images or tables.  Using the iterator has several
important advantages over the traditional method of reading and writing
FITS data files:

\begin{itemize}
\item
It cleanly separates the data I/O from the routine that operates on
the data.  This leads to a more modular and `object oriented'
programming style.  

\item
It simplifies the application program by eliminating the need to allocate
memory for the data arrays and eliminates most of the calls to the CFITSIO
routines that explicitly read and write the data.

\item
It ensures that the data are processed as efficiently as possible.
This is especially important when processing tabular data since
the iterator function will calculate the most efficient number
of rows in the table to be passed at one time to the user's work 
function on each iteration.

\item
Makes it possible for larger projects to develop a library of work
functions that all have a uniform calling sequence and are all
independent of the details of the FITS file format.

\end{itemize}

There are basically 2 steps in using the CFITSIO iterator function.
The first step is to design the work function itself which must have a
prescribed set of input parameters.  One of these parameters is a
structure containing pointers to the arrays of data; the work function
can perform any desired operations on these arrays and does not need to
worry about how the input data were read from the file or how the
output data get written back to the file.

The second step is to design the driver routine that opens all the
necessary FITS files and initializes  the input parameters to the
iterator function.  The driver program calls the CFITSIO iterator
function which then reads the data and passes it to the user's work
function.

Further details on using the iterator function can be found in the
companion CFITSIO User's Guide, and in the iter\_a.f, iter\_b.f and
iter\_c.f example programs.



*IV.   Extended File Name Syntax

**A.  Overview

CFITSIO supports an extended syntax when specifying the name of the
data file to be opened or created  that includes the following
features:

\begin{itemize}
\item
CFITSIO can read IRAF format images which have header file names that
end with the '.imh' extension, as well as reading and writing FITS
files,   This feature is implemented in CFITSIO by first converting the
IRAF image into a temporary FITS format file in memory, then opening
the FITS file.  Any of the usual CFITSIO routines then may be used to
read the image header or data.  Similarly, raw binary data arrays can
be read by converting them on the fly into virtual FITS images.

\item
FITS files on the internet can be read (and sometimes written) using the FTP,
HTTP, or ROOT protocols.

\item
FITS files can be piped between tasks on the stdin and stdout streams.

\item
FITS files can be read and written in shared memory.  This can potentially
achieve much better data I/O performance compared to reading and
writing the same FITS files on magnetic disk.

\item
Compressed FITS files in gzip or Unix COMPRESS format can be directly read.

\item
Output FITS files can be written directly in compressed gzip format,
thus saving disk space.

\item
FITS table columns can be created, modified, or deleted 'on-the-fly' as
the table is opened by CFITSIO.  This creates a virtual FITS file containing
the modifications that is then opened by the application program.

\item
Table rows may be selected, or filtered out, on the fly when the table
is opened by CFITSIO, based on an arbitrary user-specified expression.
Only rows for which the expression evaluates to 'TRUE' are retained
in the copy of the table that is opened by the application program.

\item
Histogram images may be created on the fly by binning the values in
table columns, resulting in a virtual N-dimensional FITS image.  The
application program then only sees the FITS image (in the primary
array) instead of the original FITS table.
\end{itemize}

The latter 3 features in particular add very powerful data processing
capabilities directly into CFITSIO, and hence into every task that uses
CFITSIO to read or write FITS files.  For example, these features
transform a very simple program that just copies an input FITS file to
a new output file (like the `fitscopy' program that is distributed with
CFITSIO) into a multipurpose FITS file processing tool.  By appending
fairly simple qualifiers onto the name of the input FITS file, the user
can perform quite complex table editing operations (e.g., create new
columns, or filter out rows in a table) or create FITS images by
binning or histogramming the values in table columns.  In addition,
these functions have been coded using new state-of-the art algorithms
that are, in some cases, 10 - 100 times faster than previous widely
used implementations.

Before describing the complete syntax for the extended FITS file names
in the next section, here are a few examples of FITS file names that
give a quick overview of the allowed syntax:

\begin{itemize}
\item
{\tt 'myfile.fits'}: the simplest case of a FITS file on disk in the current
directory.

\item
{\tt 'myfile.imh'}: opens an IRAF format image file and converts it on the
fly into a temporary FITS format image in memory which can then be read with
any other CFITSIO routine.

\item
{\tt rawfile.dat[i512,512]}: opens a raw binary data array (a 512 x 512
short integer array in this case) and converts it on the fly into a
temporary FITS format image in memory which can then be read with any
other CFITSIO routine.

\item
{\tt myfile.fits.gz}: if this is the name of a new output file, the '.gz'
suffix will cause it to be compressed in gzip format when it is written to 
disk.

\item
{\tt 'myfile.fits.gz[events, 2]'}:  opens and uncompresses the gzipped file
myfile.fits then moves to the extension which has the keywords EXTNAME
= 'EVENTS' and EXTVER = 2.

\item
{\tt '-'}:  a dash (minus sign) signifies that the input file is to be read
from the stdin file stream, or that the output file is to be written to
the stdout stream. 

\item
{\tt 'ftp://legacy.gsfc.nasa.gov/test/vela.fits'}:  FITS files in any ftp
archive site on the internet may be directly opened with read-only
access.

\item
{\tt 'http://legacy.gsfc.nasa.gov/software/test.fits'}: any valid URL to a
FITS file on the Web may be opened with read-only access.

\item
{\tt 'root://legacy.gsfc.nasa.gov/test/vela.fits'}: similar to ftp access
except that it provides write as well as read access to the files
across the network. This uses the root protocol developed at CERN.

\item
{\tt 'shmem://h2[events]'}: opens the FITS file in a shared memory segment and
moves to the EVENTS extension.  

\item
{\tt 'mem://'}:  creates a scratch output file in core computer memory.  The
resulting 'file' will disappear when the program exits, so this
is mainly useful for testing purposes when one does not want a
permanent copy of the output file.

\item
{\tt 'myfile.fits[3; Images(10)]'}: opens a copy of the image contained in the
10th row of the 'Images' column in the binary table in the 3th extension
of the FITS file.  The application just sees this single image as the 
primary array.

\item
{\tt 'myfile.fits[1:512:2, 1:512:2]'}: opens a section of the input image
ranging from the 1st to the 512th pixel in  X and Y, and selects every 
second pixel in both dimensions, resulting in a 256 x 256 pixel image 
in this case.

\item
{\tt 'myfile.fits[EVENTS][col Rad = sqrt(X**2 + Y**2)]'}:  creates and opens
a temporary file on the fly (in memory or on disk) that is identical to
myfile.fits except that it will contain a new column in the EVENTS
extension called 'Rad' whose value is computed using the indicated
expresson which is a function of the values in the X and Y columns.

\item
{\tt 'myfile.fits[EVENTS][PHA > 5]'}:  creates and opens a temporary FITS
files that is identical to 'myfile.fits' except that the EVENTS table
will only contain the rows that have values of the PHA column greater
than 5.  In general, any arbitrary boolean expression using a C or
Fortran-like syntax, which may combine AND and OR operators,
may be used to select rows from a table.

\item
{\tt 'myfile.fits[EVENTS][bin (X,Y)=1,2048,4]'}:  creates a temporary FITS
primary array image which is computed on the fly by binning (i.e,
computing the 2-dimensional histogram) of the values in the X and Y
columns of the EVENTS extension.  In this case the X and Y coordinates
range from 1 to 2048 and the image pixel size is 4 units in both
dimensions, so the resulting image is 512 x 512 pixels in size.

\item
The final example combines many of these feature into one complex
expression (it is broken into several lines for clarity):
-
  'ftp://legacy.gsfc.nasa.gov/data/sample.fits.gz[EVENTS]
   [col phacorr = pha * 1.1 - 0.3][phacorr >= 5.0 && phacorr <= 14.0]
   [bin (X,Y)=32]' 
-
In this case, CFITSIO (1) copies and uncompresses the FITS file from
the ftp site on the legacy machine, (2) moves to the 'EVENTS'
extension, (3) calculates a new column called 'phacorr', (4) selects
the rows in the table that have phacorr in the range 5 to 14, and
finally (5) bins the remaining rows on the X and Y column coordinates,
using a pixel size = 32 to create a 2D image.  All this processing is
completely transparent to the application program, which simply sees
the final 2-D image in the primary array of the opened file.
\end{itemize}

The full extended CFITSIO FITS file name can contain several different
components depending on the context.  These components are described in
the following sections:
-
When creating a new file:
   filetype://BaseFilename(templateName)

When opening an existing primary array or image HDU:
   filetype://BaseFilename(outName)[HDUlocation][ImageSection]

When opening an existing table HDU:
   filetype://BaseFilename(outName)[HDUlocation][colFilter][rowFilter][binSpec]
-
The filetype, BaseFilename, outName, HDUlocation, and ImageSection
components, if present, must be given in that order, but the colFilter,
rowFilter, and binSpec specifiers may follow in any order.  Regardless
of the order, however, the colFilter specifier, if present, will be
processed first by CFITSIO, followed by the rowFilter specifier, and
finally by the binSpec specifier.

**A.  Filetype

The type of file determines the medium on which the file is located
(e.g., disk or network) and, hence, which internal device driver is used by
CFITSIO to read and/or write the file.  Currently supported types are
-
        file://  - file on local magnetic disk (default)
        ftp://   - a readonly file accessed with the anonymous FTP protocol.
                   It also supports  ftp://username:password@hostname/...
                   for accessing password-protected ftp sites.
        http://  - a readonly file accessed with the HTTP protocol.  It
                   does not  support username:password like the ftp driver.
                   Proxy HTTP servers are supported using the http_proxy
                   environment variable.
        root://  - uses the CERN root protocol for writing as well as
                   reading files over the network.
        shmem:// - opens or creates a file which persists in the computer's
                   shared memory.
        mem://   - opens a temporary file in core memory.  The file 
                   disappears when the program exits so this is mainly
                   useful for test purposes when a permanent output file
                   is not desired.
-
If the filetype is not specified, then type file:// is assumed.
The double slashes '//' are optional and may be omitted in most cases.

***1.  Notes about HTTP proxy servers

A proxy HTTP server may be used by defining the address (URL) and port 
number of the proxy server with the http\_proxy environment variable.
For example
-
    setenv http_proxy http://heasarc.gsfc.nasa.gov:3128
-
will cause CFITSIO to use port 3128 on the heasarc proxy server whenever
reading a FITS file with HTTP.

***2.  Notes about the root filetype

The original rootd server can be obtained from:
\verb-ftp://root.cern.ch/root/rootd.tar.gz-
but, for it to work correctly with CFITSIO one has to use a modified
version which supports a command to return the length of the file. 
This modified version is available in rootd subdirectory
in the CFITSIO ftp area at
-
      ftp://legacy.gsfc.nasa.gov/software/fitsio/c/root/rootd.tar.gz.  
-

This small server is started either by inetd when a client requests a
connection to a rootd server or by hand (i.e. from the command line).
The rootd server works with the ROOT TNetFile class. It allows remote
access to ROOT database files in either read or write mode. By default
TNetFile assumes port 432 (which requires rootd to be started as root).
To run rootd via inetd add the following line to /etc/services:
-                                                                          
  rootd     432/tcp                                                    
-                                                                    
and to /etc/inetd.conf, add the following line: 
-
  rootd stream tcp nowait root /user/rdm/root/bin/rootd rootd -i       
-                                                                    
Force inetd to reread its conf file with "kill -HUP <pid inetd>".    
You can also start rootd by hand running directly under your private 
account (no root system privileges needed). For example to start     
rootd listening on port 5151 just type:   \verb+rootd -p 5151+  
Notice: no \& is needed. Rootd will go into background by itself.       
-
  Rootd arguments:                                                     
    -i                says we were started by inetd                    
    -p port#          specifies a different port to listen on          
    -d level          level of debug info written to syslog            
                      0 = no debug (default)                           
                      1 = minimum                                      
                      2 = medium                                       
                      3 = maximum                                      
-
Rootd can also be configured for anonymous usage (like anonymous ftp).
To setup rootd to accept anonymous logins do the following (while being
logged in as root):                                  
-
   - Add the following line to /etc/passwd:                             
                                                                     
     rootd:*:71:72:Anonymous rootd:/var/spool/rootd:/bin/false          
                                                                     
     where you may modify the uid, gid (71, 72) and the home directory  
     to suite your system.                                              
                                                                     
   - Add the following line to /etc/group:                              
                                                                     
     rootd:*:72:rootd                                                   
                                                                     
     where the gid must match the gid in /etc/passwd.                   
                                                                     
   - Create the directories:                                            
                                                                     
     mkdir /var/spool/rootd                                             
     mkdir /var/spool/rootd/tmp                                         
     chmod 777 /var/spool/rootd/tmp                                     
                                                                     
     Where /var/spool/rootd must match the rootd home directory as      
     specified in the rootd /etc/passwd entry.                          
                                                                     
   - To make writeable directories for anonymous do, for example:       
                                                                     
     mkdir /var/spool/rootd/pub                                         
     chown rootd:rootd /var/spool/rootd/pub                             
-
That's all.  Several additional remarks:  you can login to an anonymous
server either with the names "anonymous" or "rootd".  The password should
be of type user@host.do.main. Only the @ is enforced for the time
being.  In anonymous mode the top of the file tree is set to the rootd
home directory, therefore only files below the home directory can be
accessed.  Anonymous mode only works when the server is started via
inetd.

***3.  Notes about the shmem filetype:

Shared memory files are currently supported on most Unix platforms,
where the shared memory segments are managed by the operating system
kernel and `live' independently of processes. They are not deleted (by
default) when the process which created them terminates, although they
will disappear if the system is rebooted.  Applications can create
shared memory files in CFITSIO by calling:
-
   fit_create_file(&fitsfileptr, "shmem://h2", &status);
-
where the root `file' names are currently restricted to be 'h0', 'h1',
'h2', 'h3', etc., up to a maximumn number defined by the the value of
SHARED\_MAXSEG (equal to 16 by default).  This is a prototype
implementation of the shared memory interface and a more robust
interface, which will have fewer restrictions on the number of files
and on their names, may be developed in the future.

When opening an already existing FITS file in shared memory one calls
the usual CFITSIO routine:
-
   fits_open_file(&fitsfileptr, "shmem://h7", mode, &status)
-
The file mode can be READWRITE or READONLY just as with disk files.
More than one process can operate on READONLY mode files at the same
time.  CFITSIO supports proper file locking (both in READONLY and
READWRITE modes), so calls to fits\_open\_file may be locked out until
another other process closes the file.

When an application is finished accessing a FITS file in a shared
memory segment, it may close it  (and the file will remain in the
system) with fits\_close\_file, or delete it with fits\_delete\_file.
Physical deletion is postponed until the last process calls
ffclos/ffdelt.  fits\_delete\_file tries to obtain a READWRITE lock on
the file to be deleted, thus it can be blocked if the object was not
opened in READWRITE mode.

A shared memory management utility program called `smem', is included
with the CFITSIO distribution.  It can be built by typing `make smem';
then type `smem -h' to get a list of valid options.  Executing smem
without any options causes it to list all the shared memory segments
currently residing in the system and managed by the shared memory
driver. To get a list of all the shared memory objects, run the system
utility program `ipcs  [-a]'.

**B.  Base Filename

The base filename is the name of the file optionally including the
director/subdirectory path, and in the case of `ftp', `http', and `root'
filetypes, the machine identifier.  Examples:
-
    myfile.fits
    !data.fits
    /data/myfile.fits
    fits.gsfc.nasa.gov/ftp/sampledata/myfile.fits.gz
-

When creating a new output file on magnetic disk (of type file://) if
the base filename begins with an exclamation point (!) then any
existing file with that same basename will be deleted prior to creating
the new FITS file.  Otherwise if the file to be created already exists,
then CFITSIO will return an error and will not overwrite the existing
file.  Note  that the exclamation point,  '!', is a special UNIX character,
so if it is used  on the command line rather than entered at a task
prompt, it must be  preceded by a backslash to force the UNIX
shell to pass it verbatim to the application program.

If the output disk file name ends with the suffix '.gz', then CFITSIO
will compress the file using the gzip compression algorithm before
writing it to disk.  This can reduce the amount of disk space used by
the file.  Note that this feature requires that the uncompressed file
be constructed in memory before it is compressed and written to disk,
so it can fail if there is insufficient available memory.

An input FITS file may be compressed with the gzip or Unix compress
algorithms, in which case CFITSIO will uncompress the file on the fly
into a temporary file (in memory or on disk).  Compressed files may
only be opened with read-only permission.  When specifying the name of
a compressed FITS file it is not necessary to append the file suffix
(e.g., `.gz' or `.Z').  If CFITSIO cannot find the input file name
without the suffix, then it will automatically search for a compressed
file with the same root name.  In the case of reading ftp and http type
files, CFITSIO generally looks for a compressed version of the file
first, before trying to open the uncompressed file.  By default,
CFITSIO copies (and uncompressed if necessary) the ftp or http FITS
file into memory on the local machine before opening it.  This will
fail if the local machine does not have enough memory to hold the whole
FITS file, so in this case, the output filename specifier (see the next
section) can be used to further control how CFITSIO reads ftp and http
files.

If the input file is an IRAF image file (*.imh file) then CFITSIO will
automatically convert it on the fly into a virtual FITS image before it
is opened by the application program.  IRAF images can only be opened
with READONLY file access.

Similarly, if the input file is a raw binary data array, then CFITSIO
will convert it on the fly into a virtual FITS image with the basic set
of required header keywords before it is opened by the application
program (with READONLY access).  In this case the data type and
dimensions of the image must be specified in square brackets following
the filename (e.g. rawfile.dat[ib512,512]). The first character (case
insensitive) defines the datatype of the array:
-
     b         8-bit unsigned byte
     i        16-bit signed integer
     u        16-bit unsigned integer
     j        32-bit signed integer
     r or f   32-bit floating point
     d        64-bit floating point
-
An optional second character specifies the byte order of the array
values: b or B indicates big endian (as in FITS files and the native
format of SUN UNIX workstations and Mac PCs) and l or L indicates
little endian (native format of DEC OSF workstations and IBM PCs).  If
this character is omitted then the array is assumed to have the native
byte order of the local machine.  These datatype characters are then
followed by a series of one or more integer values separated by commas
which define the size of each dimension of the raw array.  Arrays with
up to 5 dimensions are currently supported.  Finally, a byte offset to
the position of the first pixel in the data file may be specified by
separating it with a ':' from the last dimension value.  If omitted, it
is assumed that the offset = 0.  This parameter may be used to skip
over any header information in the file that precedes the binary data.
Further examples:
-
  raw.dat[b10000]           1-dimensional 10000 pixel byte array
  raw.dat[rb400,400,12]     3-dimensional floating point big-endian array
  img.fits[ib512,512:2880]  reads the 512 x 512 short integer array in 
                            a FITS file, skipping over the 2880 byte header
-

One special case of input file is where the filename = `-' (a dash or
minus sign) or 'stdin' or 'stdout', which signifies that the input file
is to be read from the stdin stream, or written to the stdout stream if
a new output file is being created.  In the case of reading from stdin,
CFITSIO first copies the whole stream into a temporary FITS file (in
memory or on disk), and subsequent reading of the FITS file occurs in
this copy.  When writing to stdout, CFITSIO first constructs the whole
file in memory (since random access is required), then flushes it out
to the stdout stream when the file is closed.   In addition, if the
output filename = '-.gz' or 'stdout.gz' then it will be gzip compressed
before being written to stdout.

This ability to read and write on the stdin and stdout steams allows
FITS files to be piped between tasks in memory rather than having to
create temporary intermediate FITS files on disk.  For example if task1
creates an output FITS file, and task2 reads an input FITS file, the
FITS file may be piped between the 2 tasks by specifying
-
   task1 - | task2 - 
-
where the vertical bar is the Unix piping symbol.  This assumes that the 2
tasks read the name of the FITS file off of the command line.

**C.  Output File Name when Opening an Existing File

An optional output filename may be specified in parentheses immediately
following the base file name to be opened.  This is mainly useful in
those cases where CFITSIO creates a temporary copy of the input FITS
file before it is opened and passed to the application program.  This
happens by default when opening a network FTP or HTTP-type file, when
reading a compressed FITS file on a local disk, when reading from the
stdin stream, or when a column filter, row filter, or binning specifier
is included as part of the input file specification.  By default this
temporary file is created in memory.  If there is not enough memory to
create the file copy, then CFITSIO will exit with an error.   In these
cases one can force a permanent file to be created on disk, instead of
a temporary file in memory, by supplying the name in parentheses
immediately following the base file name.  The output filename can
include the '!' clobber flag.

Thus, if the input filename to CFITSIO is:
\verb+file1.fits.gz(file2.fits)+
then CFITSIO will uncompress `file1.fits.gz' into the local disk file
`file2.fits' before opening it.  CFITSIO does not automatically delete
the output file, so it will still exist after the application program
exits.

In some cases, several different temporary FITS files will be created
in sequence, for instance, if one opens a remote file using FTP, then
filters rows in a binary table extension, then create an image by
binning a pair of columns.  In this case, the remote file will be
copied to a temporary local file, then a second temporary file will be
created containing the filtered rows of the table, and finally a third
temporary file containing the binned image will be created.  In cases
like this where multiple files are created, the outfile specifier will
be interpreted the name of the final file as described below, in descending
priority:

\begin{itemize}
\item
as the name of the final image file if an image within a single binary
table cell is opened or if an image is created by binning a table column.
\item
as the name of the file containing the filtered table if a column filter
and/or a row filter are specified.
\item
as the name of the local copy of the remote FTP or HTTP file.
\item
as the name of the uncompressed version of the FITS file, if a
compressed FITS file on local disk has been opened.
\item
otherwise, the output filename is ignored.
\end{itemize}

The output file specifier is useful when reading FTP or HTTP-type
FITS files since it can be used to create a local disk copy of the file
that can be reused in the future.  If the output file name = `*' then a
local file with the same name as the network file will be created.
Note that CFITSIO will behave differently depending on whether the
remote file is compressed or not as shown by the following examples:
\begin{itemize}
\item
`ftp://remote.machine/tmp/myfile.fits.gz(*)' - the remote compressed
file is copied to the local compressed file `myfile.fits.gz', which
is then uncompressed in local memory before being opened and passed
to the application program.

\item
`ftp://remote.machine/tmp/myfile.fits.gz(myfile.fits)' - the remote
compressed file is copied and uncompressed into the local file
`myfile.fits'.  This example requires less local memory than the
previous example since the file is uncompressed on disk instead of
in memory.

\item
`ftp://remote.machine/tmp/myfile.fits(myfile.fits.gz)' - this will
usually produce an error since CFITSIO itself cannot compress files.
\end{itemize}

The exact behavior of CFITSIO in the latter case depends on the type of
ftp server running on the remote machine and how it is configured.  In
some cases, if the file `myfile.fits.gz' exists on the remote machine,
then the server will copy it to the local machine.  In other cases the
ftp server will automatically create and transmit a compressed version
of the file if only the uncompressed version exists.  This can get
rather confusing, so users should use a certain amount of caution when
using the output file specifier with FTP or HTTP file types, to make
sure they get the behavior that they expect.

**D.  Template File Name when Creating a New File

When a new FITS file is created with a call to fits\_create\_file, the
name of a template file may be supplied in parentheses immediately
following the name of the new file to be created.  This template is
used to define the structure of one or more HDUs in the new file.  The
template file may be another FITS file, in which case the newly created
file will have exactly the same keywords in each HDU as in the template
FITS file, but all the data units will be filled with zeros.  The
template file may also be an ASCII text file, where each line (in
general) describes one FITS keyword record.  The format of the ASCII
template file is described below.

**E.  HDU Location Specification

The optional HDU location specifier defines which HDU (Header-Data
Unit, also known as an `extension') within the FITS file to initially
open.  It must immediately follow the base file name (or the output
file name if present).  If it is not specified then the first HDU (the
primary array) is opened.  The HDU location specifier is required if
the colFilter, rowFilter, or binSpec specifiers are present, because
the primary array is not a valid HDU for these operations. The HDU may
be specified either by absolute position number, starting with 0 for
the primary array, or by reference to the HDU name, and optionally, the
version number and the HDU type of the desired extension.  The location
of an image within a single cell of a binary table may also be 
specified, as described below.

The absolute position of the extension is specified either by enclosed
the number in square brackets (e.g., `[1]' = the first extension
following the primary array) or by preceded the number with a plus sign
(`+1').  To specify the HDU by name, give the name of the desired HDU
(the value of the EXTNAME or HDUNAME keyword) and optionally the
extension version number (value of the EXTVER keyword) and the
extension type (value of the XTENSION keyword: IMAGE, ASCII or TABLE,
or BINTABLE), separated by commas and all enclosed in square brackets.
If the value of EXTVER and XTENSION are not specified, then the first
extension with the correct value of EXTNAME is opened. The extension
name and type are not case sensitive, and the extension type may be
abbreviated to a single letter (e.g., I = IMAGE extension or primary
array, A or T = ASCII table extension, and B = binary table BINTABLE
extension).   If the HDU location specifier is equal to `[PRIMARY]' or
`[P]', then the primary array (the first HDU) will be opened.

FITS images are most commonly stored in the primary array or an image
extension, but images can also be stored as a vector in a single cell
of a binary table (i.e. each row of the vector column contains a
different image).  Such an image can be opened with CFITSIO by
specifying the desired column  name and the row number after the binary
table HDU specifier as shown in the following examples. The column name
is separated from the HDU specifier by a semicolon and the row number
is enclosed in parentheses.  In this case CFITSIO copies the image from
the table cell into a temporary primary array before it is opened.  The
application program then just sees the image in the primary array,
without any extensions.  The particular row to be opened may be
specified either by giving an absolute integer row number (starting
with 1 for the first row), or by specifying a boolean expression that
evaluates to TRUE for the desired row.  The first row that satisfies
the expression will be used.  The row selection expression has the same
syntax as described in the Row Filter Specifier section, below.

 Examples:
-
   myfile.fits[3] - open the 3rd HDU following the primary array
   myfile.fits+3  - same as above, but using the FTOOLS-style notation  
   myfile.fits[EVENTS] - open the extension that has EXTNAME = 'EVENTS'
   myfile.fits[EVENTS, 2]  - same as above, but also requires EXTVER = 2
   myfile.fits[events,2,b] - same, but also requires XTENSION = 'BINTABLE'
   myfile.fits[3; images(17)] - opens the image in row 17 of the 'images'
                                column in the 3rd extension of the file.
   myfile.fits[3; images(exposure > 100)] - as above, but opens the image
                   in the first row that has an 'exposure' column value
                   greater than 100.
-

**F.  Image Section

A virtual file containing a rectangular subsection of an image can be
extracted and opened by specifying the range of pixels (start:end)
along each axis to be extracted from the original image.  One can also
specify an optional pixel increment (start:end:step) for each axis of
the input image.  A pixel step = 1 will be assumed if it is not
specified.  If the start pixel is larger then the end pixel, then the
image will be flipped (producing a mirror image) along that dimension.
An asterisk, '*', may be used to specify the entire range of an axis,
and '-*' will flip the entire axis. The input image can be in the
primary array, in an image extension, or contained in a vector cell of
a binary table. In the later 2 cases the extension name or number must
be specified before the image section specifier.

 Examples:
-
  myfile.fits[1:512:2, 2:512:2] -  open a 256x256 pixel image
              consisting of the odd numbered columns (1st axis) and 
              the even numbered rows (2nd axis) of the image in the 
              primary array of the file.

  myfile.fits[*, 512:256] - open an image consisting of all the columns
              in the input image, but only rows 256 through 512.  
              The image will be flipped along the 2nd axis since
              the starting pixel is greater than the ending pixel.

  myfile.fits[*:2, 512:256:2] - same as above but keeping only
              every other row and column in the input image.

  myfile.fits[-*, *] - copy the entire image, flipping it along
              the first axis.

  myfile.fits[3][1:256,1:256] - opens a subsection of the image that
              is in the 3rd extension of the file.

  myfile.fits[4; images(12)][1:10,1:10] - open an image consisting
	      of the first 10 pixels in both dimensions. The original
	      image resides in the 12th row of the 'images' vector
	      column in the table in the 4th extension of the file.
-

When CFITSIO opens an image section it first creates a temporary file
containing the image section plus a copy of any other HDUs in the
file.  This temporary file is then opened by the application program,
so it is not possible to write to or modify the input file when
specifying an image section.  Note that CFITSIO automatically updates
the world coordinate system keywords in the header of the image
section, if they exist, so that the coordinate associated with each
pixel in the image section will be computed correctly.

**G.  Column and Keyword Filtering Specification

The optional column/keyword filtering specifier is used to modify the
column structure and/or the header keywords in the HDU that was
selected with the previous HDU location specifier. This filtering
specifier must be enclosed in square brackets and can be distinguished
from a general row filter specifier (described below) by the fact that
it begins with the string 'col ' and is not immediately followed by an
equals sign.  The original file is not changed by this filtering
operation, and instead the modifications are made on a copy of the
input FITS file (usually in memory), which also contains a copy of all
the other HDUs in the file.  This temporary file is passed to the
application program and will persist only until the file is closed or
until the program exits, unless the outfile specifier (see above) is
also supplied.

The column/keyword filter can be used to perform the following
operations.  More than one operation may be specified by separating
them with semi-colons.

\begin{itemize}

\item
Copy only a specified list of columns columns to the filtered input file.
The list of column name should be separated by semi-colons.  Wild card
characters may be used in the column names to match multiple columns.
If the expression contains both a list of columns to be included and
columns to be deleted, then all the columns in the original table 
except the explicitly deleted columns will appear in the filtered
table (i.e., there is no need to explicitly list the columns to
be included if any columns are being deleted).

\item
Delete a column or keyword by listing the name preceded by a minus
sign or an exclamation mark (!), e.g., '-TIME' will delete the TIME
column if it exists, otherwise the TIME keyword.  An error is returned
if neither a column nor keyword with this name exists.  Note  that the
exclamation point,  '!', is a special UNIX character, so if it is used
on the command line rather than entered at a task prompt, it must be
preceded by a backslash to force the UNIX shell to ignore it.

\item
Rename an existing column or keyword with the syntax 'NewName ==
OldName'.  An error is returned if neither a column nor keyword with
this name exists.

\item
Append a new column or keyword to the table.  To create a column,
give the new name, optionally followed by the datatype in parentheses,
followed by a single equals sign and an  expression to be used to
compute the value (e.g., 'newcol(1J) = 0' will create a new 32-bit
integer column called 'newcol' filled with zeros).  The datatype is
specified using the same syntax that is allowed for the value of the
FITS TFORMn keyword (e.g., 'I', 'J', 'E', 'D', etc. for binary tables,
and 'I8', F12.3', 'E20.12', etc. for ASCII tables).  If the datatype is
not specified then an appropriate datatype will be chosen depending on
the form of the expression (may be a character string, logical, bit, long
integer, or double column). An appropriate vector count (in the case
of binary tables) will also be added if not explicitly specified.

When creating a new keyword, the keyword name must be preceded by a 
pound sign '\#', and the expression must evaluate to a scalar
(i.e., cannot have a column name in the expression).  The comment
string for the keyword may be specified in parentheses immediately
following the keyword name (instead of supplying a datatype as in
the case of creating a new column).  If the keyword name ends with a
pound sign '\#', then cfitsio will substitute the number of the 
most recently referenced column for the \# character .  
This is especially useful when writing
a column-related keyword like TUNITn for a newly created column,
as shown in the following examples.

\item
Recompute (overwrite) the values in an existing column or keyword by
giving the name followed by an equals sign and an arithmetic
expression.
\end{itemize}

The expression that is used when appending or recomputing columns or
keywords can be arbitrarily complex and may be a function of other
header keyword values and other columns (in the same row).  The full
syntax and available functions for the expression are described below
in the row filter specification section.

If the expression contains both a list of columns to be included and
columns to be deleted, then all the columns in the original table 
except the explicitly deleted columns will appear in the filtered
table.  If no columns to be deleted are specified, then only the
columns that are explicitely listed will be included in the filtered
output table.  To include all the columns, add the '*' wildcard
specifier at the end of the list, as shown in the examples.

For  complex  or commonly used operations,  one  can also  place the
operations into an external text  file and import it  into the  column
filter using  the syntax '[col @filename.txt]'.   The operations can
extend over multiple lines of the  file, but multiple operations must
still be separated by semicolons.   Any lines in the external text file
that begin with 2 slash characters ('//') will be ignored and may be
used to add comments into the file.

Examples:
-
   [col Time;rate]               - only the Time and rate columns will
                                   appear in the filtered input file.

   [col Time;*raw]               - include the Time column and any other
                                   columns whose name ends with 'raw'.

   [col -TIME; Good == STATUS]   - deletes the TIME column and
                                   renames the status column to 'Good'

   [col PI=PHA * 1.1 + 0.2; #TUNIT#(column units) = 'counts';*]
                                 - creates new PI column from PHA values
                                   and also writes the TUNITn keyword
                                   for the new column.  The final '*'
                                   expression means preserve all the
                                   columns in the input table in the
                                   virtual output table;  without the '*'
                                   the output table would only contain
                                   the single 'PI' column.

   [col rate = rate/exposure; TUNIT#(&) = 'counts/s';*]
                                 - recomputes the rate column by dividing
                                   it by the EXPOSURE keyword value. This
                                   also modifies the value of the TUNITn
                                   keyword for this column. The use of the
                                   '&' character for the keyword comment
                                   string means preserve the existing
                                   comment string for that keyword. The
                                   final '*' preserves all the columns
                                   in the input table in the virtual
                                   output table.
-

**H.  Row Filtering Specification

    When entering the name of a FITS table that is to be opened by a
    program, an optional row filter may be specified to select a subset
    of the rows in the table.  A temporary new FITS file is created on
    the fly which contains only those rows for which the row filter
    expression evaluates to true.  (The primary array and any other
    extensions in the input file are also copied to the temporary
    file).  The original FITS file is closed and the new virtual file
    is opened by the application program.  The row filter expression is
    enclosed in square brackets following the file name and extension
    name (e.g., 'file.fits[events][GRADE==50]'  selects only those rows
    where the GRADE column value equals 50).   When dealing with tables
    where each row has an associated time and/or 2D spatial position,
    the row filter expression can also be used to select rows based on
    the times in a Good Time Intervals (GTI) extension, or on spatial
    position as given in a SAO-style region file.

***1.  General Syntax

    The row filtering  expression can be an arbitrarily  complex series
    of operations performed  on constants,  keyword values,  and column
    data taken from the specified FITS TABLE extension.  The expression
    must evaluate to a boolean  value for each row  of the table, where
    a value of FALSE means that the row will be excluded.

    For complex or commonly  used filters, one can place the expression
    into a text file and import it into the row filter using the syntax
    '[@filename.txt]'.  The expression can be  arbitrarily complex and
    extend over multiple lines of the file.  Any lines in the external
    text file that begin with 2 slash characters ('//') will be ignored
    and may be used to add comments into the file.

    Keyword and   column data  are referenced by   name.  Any  string of
    characters not surrounded by    quotes (ie, a constant  string)   or
    followed by   an open parentheses (ie,   a  function name)   will be
    initially interpreted   as a column  name and  its contents for the
    current row inserted into the expression.  If no such column exists,
    a keyword of that  name will be searched for  and its value used, if
    found.  To force the  name to be  interpreted as a keyword (in case
    there is both a column and keyword with the  same name), precede the
    keyword name with a single pound sign, '\#', as in '\#NAXIS2'.  Due to
    the generalities of FITS column and  keyword names, if the column or
    keyword name  contains a space or a  character which might appear as
    an arithmetic  term then inclose  the  name in '\$'  characters as in
    \$MAX PHA\$ or \#\$MAX-PHA\$.  Names are case insensitive.

    To access a table entry in a row other  than the current one, follow
    the  column's name  with  a row  offset  within  curly  braces.  For
    example, 'PHA\{-3\}' will evaluate to the value  of column PHA, 3 rows
    above  the  row currently  being processed.   One  cannot specify an
    absolute row number, only a relative offset.  Rows that fall outside
    the table will be treated as undefined, or NULLs.

    Boolean   operators can be  used in  the expression  in either their
    Fortran or C forms.  The following boolean operators are available:
-
    "equal"         .eq. .EQ. ==  "not equal"          .ne.  .NE.  !=
    "less than"     .lt. .LT. <   "less than/equal"    .le.  .LE.  <= =<
    "greater than"  .gt. .GT. >   "greater than/equal" .ge.  .GE.  >= =>
    "or"            .or. .OR. ||  "and"                .and. .AND. &&
    "negation"     .not. .NOT. !  "approx. equal(1e-7)"  ~
-

Note  that the exclamation
point,  '!', is a special UNIX character, so if it is used  on the
command line rather than entered at a task prompt, it must be  preceded
by a backslash to force the UNIX shell to ignore it.

    The expression may  also include arithmetic operators and functions.
    Trigonometric  functions use  radians,  not degrees.  The  following
    arithmetic  operators and  functions  can be  used in the expression
    (function names are case insensitive). A null value will be returned
    in case of illegal operations such as divide by zero, sqrt(negative)
    log(negative), log10(negative), arccos(.gt. 1), arcsin(.gt. 1).

-
    "addition"           +          "subtraction"          -
    "multiplication"     *          "division"             /
    "negation"           -          "exponentiation"       **   ^
    "absolute value"     abs(x)     "cosine"               cos(x)
    "sine"               sin(x)     "tangent"              tan(x)
    "arc cosine"         arccos(x)  "arc sine"             arcsin(x)
    "arc tangent"        arctan(x)  "arc tangent"          arctan2(y,x)
    "hyperbolic cos"     cosh(x)    "hyperbolic sin"       sinh(x)
    "hyperbolic tan"     tanh(x)    "round to nearest int" round(x)
    "round down to int"  floor(x)   "round up to int"      ceil(x)
    "exponential"        exp(x)     "square root"          sqrt(x)
    "natural log"        log(x)     "common log"           log10(x)
    "modulus"            x % y      "random # [0.0,1.0)"   random()
    "minimum"            min(x,y)   "maximum"              max(x,y)
    "cumulative sum"    accum(x)   "sequential difference" seqdiff(x)
    "if-then-else"       b?x:y
    "angular separation"  angsep(ra1,dec1,ra2,de2) (all in degrees)
-

    An alternate syntax for the min and max functions  has only a single
    argument which  should be  a  vector value (see  below).  The result
    will be the minimum/maximum element contained within the vector.

    The accum(x) function forms the cumulative sum of x, element by element.
    Vector columns are supported simply by performing the summation process
    through all the values.  Null values are treated as 0.  The seqdiff(x) 
    function forms the sequential difference of x, element by element.  
    The first value of seqdiff is the first value of x.  A single null 
    value in x causes a pair of nulls in the output.  The seqdiff and 
    accum functions are functional inverses, i.e., seqdiff(accum(x)) == x
    as long as no null values are present.
    
    The angsep function computes the angular separation in degrees 
    between 2 celestial positions, where the first 2 parameters
    give the RA-like and Dec-like coordinates (in decimal degrees)
    of the first position, and the 3rd and 4th parameters give the
    coordinates of the second position.
    
    The  following  type  casting  operators  are  available,  where the
    inclosing parentheses are required and taken  from  the  C  language
    usage. Also, the integer to real casts values to double precision:
-
                "real to integer"    (int) x     (INT) x
                "integer to real"    (float) i   (FLOAT) i
-

    In addition, several constants are built in  for  use  in  numerical
    expressions:

-
        #pi              3.1415...      #e             2.7182...
        #deg             #pi/180        #row           current row number
        #null         undefined value   #snull         undefined string
-

    A  string constant must  be enclosed  in quotes  as in  'Crab'.  The
    "null" constants  are useful for conditionally  setting table values
    to a NULL, or undefined, value (eg., "col1==-99 ? \#NULL : col1").

    There is also a function for testing if  two  values  are  close  to
    each  other,  i.e.,  if  they are "near" each other to within a user
    specified tolerance. The  arguments,  value\_1  and  value\_2  can  be
    integer  or  real  and  represent  the two values who's proximity is
    being tested to be within the specified tolerance, also  an  integer
    or real:
-
                    near(value_1, value_2, tolerance)
-
    When  a  NULL, or undefined, value is encountered in the FITS table,
    the expression will evaluate to NULL unless the undefined  value  is
    not   actually   required  for  evaluation,  e.g. "TRUE  .or.  NULL" 
    evaluates to TRUE. The  following  two  functions  allow  some  NULL
    detection  and  handling:
-
         "a null value?"              ISNULL(x)
         "define a value for null"    DEFNULL(x,y)
-
    The former
    returns a boolean value of TRUE if the  argument  x  is  NULL.   The
    later  "defines"  a  value  to  be  substituted  for NULL values; it
    returns the value of x if x is not NULL, otherwise  it  returns  the
    value of y.
    
***2.  Bit Masks

    Bit  masks can be used to select out rows from bit columns (TFORMn =
    \#X) in FITS files. To represent the mask,  binary,  octal,  and  hex
    formats are allowed:

-
                 binary:   b0110xx1010000101xxxx0001
                 octal:    o720x1 -> (b111010000xxx001)
                 hex:      h0FxD  -> (b00001111xxxx1101)
-
   
    In  all  the  representations, an x or X is allowed in the mask as a
    wild card. Note that the x represents a  different  number  of  wild
    card  bits  in  each  representation.  All  representations are case
    insensitive.
    
    To construct the boolean expression using the mask  as  the  boolean
    equal  operator  described above on a bit table column. For example,
    if you had a 7 bit column named flags in a  FITS  table  and  wanted
    all  rows  having  the bit pattern 0010011, the selection expression
    would be:

-
                            flags == b0010011
    or
                            flags .eq. b10011
-

    It is also possible to test if a range of bits is  less  than,  less
    than  equal,  greater  than  and  greater than equal to a particular
    boolean value:

-
                            flags <= bxxx010xx
                            flags .gt. bxxx100xx
                            flags .le. b1xxxxxxx
-
   
    Notice the use of the x bit value to limit the range of  bits  being
    compared.
    
    It  is  not necessary to specify the leading (most significant) zero
    (0) bits in the mask, as shown in the second expression above.
    
    Bit wise AND, OR and NOT operations are  also  possible  on  two  or
    more  bit  fields  using  the  '\&'(AND),  '$|$'(OR),  and the '!'(NOT)
    operators. All of these operators result in a bit  field  which  can
    then be used with the equal operator. For example:

-
                          (!flags) == b1101100
                          (flags & b1000001) == bx000001
-

    Bit  fields can be appended as well using the '+' operator.  Strings
    can be concatenated this way, too.
    
***3.  Vector Columns

    Vector columns can also be used  in  building  the  expression.   No
    special  syntax  is required if one wants to operate on all elements
    of the vector.  Simply use the column name as for a  scalar  column.
    Vector  columns  can  be  freely  intermixed  with scalar columns or
    constants in virtually all expressions.  The result will be  of  the
    same dimension as the vector.  Two vectors in an expression, though,
    need to  have  the  same  number  of  elements  and  have  the  same
    dimensions.   The  only  places  a vector column cannot be used (for
    now, anyway) are the SAO  region  functions  and  the  NEAR  boolean
    function.

    Arithmetic and logical operations are all performed on an element by
    element basis.  Comparing two vector columns,  eg  "COL1  ==  COL2",
    thus  results  in  another vector of boolean values indicating which
    elements of the two vectors are equal.  

    Eight functions are available that operate on a vector and return a
    scalar result:
-
    "minimum"      MIN(V)          "maximum"               MAX(V)
    "average"      AVERAGE(V)      "median"                MEDIAN(V)
    "sumation"     SUM(V)          "standard deviation"    STDDEV(V)
    "# of values"  NELEM(V)        "# of non-null values"  NVALID(V)
-
    where V represents the name of a vector column or a manually 
    constructed vector using curly brackets as described below.  The
    first 6 of these functions ignore any null values in the vector when
    computing the result.
    
    The SUM function literally sums all  the elements in x,  returning a 
    scalar value.   If x  is  a  boolean  vector, SUM returns the number
    of TRUE elements. The NELEM function  returns the number of elements
    in vector x whereas NVALID return the number of non-null elements in
    the  vector.   (NELEM  also  operates  on  bit  and string  columns, 
    returning their column widths.)  As an example, to  test whether all 
    elements of two vectors satisfy a  given logical comparison, one can
    use the expression
-
              SUM( COL1 > COL2 ) == NELEM( COL1 )
-

    which will return TRUE if all elements  of  COL1  are  greater  than
    their corresponding elements in COL2.
    
    To  specify  a  single  element  of  a  vector, give the column name
    followed by  a  comma-separated  list  of  coordinates  enclosed  in
    square  brackets.  For example, if a vector column named PHAS exists
    in the table as a one dimensional, 256  component  list  of  numbers
    from  which  you  wanted to select the 57th component for use in the
    expression, then PHAS[57] would do the  trick.   Higher  dimensional
    arrays  of  data  may appear in a column.  But in order to interpret
    them, the TDIMn keyword must appear in the header.  Assuming that  a
    (4,4,4,4)  array  is packed into each row of a column named ARRAY4D,
    the  (1,2,3,4)  component  element  of  each  row  is  accessed   by 
    ARRAY4D[1,2,3,4].    Arrays   up   to   dimension  5  are  currently 
    supported.  Each vector index can itself be an expression,  although
    it  must  evaluate  to  an  integer  value  within the bounds of the
    vector.  Vector columns which contain spaces or arithmetic operators
    must   have   their   names  enclosed  in  "\$"  characters  as  with 
    \$ARRAY-4D\$[1,2,3,4].
    
    A  more  C-like  syntax  for  specifying  vector  indices  is   also 
    available.   The element used in the preceding example alternatively
    could be specified with the syntax  ARRAY4D[4][3][2][1].   Note  the
    reverse  order  of  indices  (as in C), as well as the fact that the
    values are still ones-based (as  in  Fortran  --  adopted  to  avoid
    ambiguity  for  1D vectors).  With this syntax, one does not need to
    specify all of the indices.  To  extract  a  3D  slice  of  this  4D
    array, use ARRAY4D[4].
    
    Variable-length vector columns are not supported.
    
    Vectors can  be manually constructed  within the expression  using a
    comma-separated list of  elements surrounded by curly braces ('\{\}').
    For example, '\{1,3,6,1\}' is a 4-element vector containing the values
    1, 3, 6, and 1.  The  vector can contain  only boolean, integer, and
    real values (or expressions).  The elements will  be promoted to the
    highest  datatype   present.  Any   elements   which  are themselves
    vectors, will be expanded out with  each of its elements becoming an
    element in the constructed vector.

***4.  Good Time Interval Filtering

    A common filtering method involves selecting rows which have a time
    value which lies within what is called a Good Time Interval or GTI.
    The time intervals are defined in a separate FITS table extension
    which contains 2 columns giving the start and stop time of each
    good interval.  The filtering operation accepts only those rows of
    the input table which have an associated time which falls within
    one of the time intervals defined in the GTI extension. A high
    level function, gtifilter(a,b,c,d), is available which evaluates
    each row of the input table  and returns TRUE  or FALSE depending
    whether the row is inside or outside the  good time interval.  The
    syntax is
-
      gtifilter( [ "gtifile" [, expr [, "STARTCOL", "STOPCOL" ] ] ] )
-
    where  each "[]" demarks optional parameters.  Note that  the quotes
    around the gtifile and START/STOP column are required.  Either single
    or double quotes may be used.  In cases where this expression is 
    entered on the Unix command line, enclose the entire expression in
    double quotes, and then use single quotes within the expression to
    enclose the 'gtifile' and other terms.  It is also usually possible
    to do the reverse, and enclose the whole expression in single quotes
    and then use double quotes within the expression.  The gtifile,
    if specified,  can be blank  ("") which will  mean to use  the first
    extension  with   the name "*GTI*"  in   the current  file,  a plain
    extension  specifier (eg, "+2",  "[2]", or "[STDGTI]") which will be
    used  to  select  an extension  in  the current  file, or  a regular
    filename with or without an extension  specifier which in the latter
    case  will mean to  use the first  extension  with an extension name
    "*GTI*".  Expr can be   any arithmetic expression, including  simply
    the time  column  name.  A  vector  time expression  will  produce a
    vector boolean  result.  STARTCOL and  STOPCOL are the  names of the
    START/STOP   columns in the    GTI extension.  If   one  of them  is
    specified, they both  must be.

    In  its  simplest form, no parameters need to be provided -- default
    values will be used.  The expression "gtifilter()" is equivalent to
-   
       gtifilter( "", TIME, "*START*", "*STOP*" )
-    
    This will search the current file for a GTI  extension,  filter  the
    TIME  column in the current table, using START/STOP times taken from
    columns in the GTI  extension  with  names  containing  the  strings
    "START"  and "STOP".  The wildcards ('*') allow slight variations in
    naming conventions  such  as  "TSTART"  or  "STARTTIME".   The  same
    default  values  apply for unspecified parameters when the first one
    or  two  parameters  are  specified.   The  function   automatically 
    searches   for   TIMEZERO/I/F   keywords  in  the  current  and  GTI 
    extensions, applying a relative time offset, if necessary.

***5.  Spatial Region Filtering

    Another common  filtering method selects rows based on whether the
    spatial position associated with each row is located within a given 
    2-dimensional region.  The syntax for this high-level filter is
-
       regfilter( "regfilename" [ , Xexpr, Yexpr [ , "wcs cols" ] ] )
-
    where each "[]" demarks optional parameters. The region file name
    is required and must be  enclosed in quotes.  The remaining
    parameters are optional.  The region file is an ASCII text file
    which contains a list of one or more geometric shapes (circle,
    ellipse, box, etc.) which defines a region on the celestial sphere
    or an area within a particular 2D image.  The region file is
    typically generated using an image display program such as fv/POW
    (distribute by the HEASARC), or ds9 (distributed by the Smithsonian
    Astrophysical Observatory).  Users should refer to the documentation
    provided with these programs for more details on the syntax used in
    the region files.

    In its simpliest form, (e.g., regfilter("region.reg") ) the
    coordinates in the default 'X' and 'Y' columns will be used to
    determine if each row is inside or outside the area specified in
    the region file.  Alternate position column names, or expressions,
    may be entered if needed, as in
-
        regfilter("region.reg", XPOS, YPOS)
-
    Region filtering can be applied most unambiguously if the positions
    in the region file and in the table to be filtered are both give in
    terms of absolute celestial coordinate units.  In this case the
    locations and sizes of the geometric shapes in the region file are
    specified in angular units on the sky (e.g., positions given in
    R.A. and Dec.  and sizes in arcseconds or arcminutes).  Similarly,
    each row of the filtered table will have a celestial coordinate
    associated with it.  This association is usually implemented using
    a set of so-called 'World Coordinate System' (or WCS) FITS keywords
    that define the coordinate transformation that must be applied to
    the values in the 'X' and 'Y' columns to calculate the coordinate.

    Alternatively, one can perform spatial filtering using unitless
    'pixel' coordinates for the regions and row positions.  In this
    case the user must be careful to ensure that the positions in the 2
    files are self-consistent.  A typical problem is that the region
    file may be generated using a binned image, but the unbinned
    coordinates are given in the event table.  The ROSAT events files,
    for example, have X and Y pixel coordinates that range from 1 -
    15360.  These coordinates are typically binned by a factor of 32 to
    produce a 480x480 pixel image.  If one then uses a region file
    generated from this image (in image pixel units) to filter the
    ROSAT events file, then the X and Y column values must be converted
    to corresponding pixel units as in:
-
        regfilter("rosat.reg", X/32.+.5, Y/32.+.5)
-
    Note that this binning conversion is not necessary if the region
    file is specified using celestial coordinate units instead of pixel
    units because CFITSIO is then able to directly compare the
    celestial coordinate of each row in the table with the celestial
    coordinates in the region file without having to know anything
    about how the image may have been binned.

    The last "wcs cols" parameter should rarely be needed. If supplied,
    this  string contains the names of the 2 columns (space or comma
    separated) which have the associated WCS keywords. If not supplied,
    the filter  will scan the X  and Y expressions for column names.
    If only one is found in each  expression, those columns will be
    used, otherwise an error will be returned.

    These region shapes are supported (names are case insensitive):
-
       Point         ( X1, Y1 )               <- One pixel square region
       Line          ( X1, Y1, X2, Y2 )       <- One pixel wide region
       Polygon       ( X1, Y1, X2, Y2, ... )  <- Rest are interiors with
       Rectangle     ( X1, Y1, X2, Y2, A )       | boundaries considered
       Box           ( Xc, Yc, Wdth, Hght, A )   V within the region
       Diamond       ( Xc, Yc, Wdth, Hght, A )
       Circle        ( Xc, Yc, R )
       Annulus       ( Xc, Yc, Rin, Rout )
       Ellipse       ( Xc, Yc, Rx, Ry, A )
       Elliptannulus ( Xc, Yc, Rinx, Riny, Routx, Routy, Ain, Aout )
       Sector        ( Xc, Yc, Amin, Amax )
-
    where (Xc,Yc) is  the coordinate of  the shape's center; (X\#,Y\#) are
    the coordinates  of the shape's edges;  Rxxx are the shapes' various
    Radii or semimajor/minor  axes; and Axxx  are the angles of rotation
    (or bounding angles for Sector) in degrees.  For rotated shapes, the
    rotation angle  can  be left  off, indicating  no rotation.   Common
    alternate  names for the regions  can also be  used: rotbox = box;
    rotrectangle = rectangle;  (rot)rhombus = (rot)diamond;  and pie
    = sector.  When a  shape's name is  preceded by a minus sign, '-',
    the defined region  is instead the area  *outside* its boundary (ie,
    the region is inverted).  All the shapes within a single region
    file are OR'd together to create the region, and the order is
    significant. The overall way of looking at region files is that if
    the first region is an excluded region then a dummy included region
    of the whole detector is inserted in the front. Then each region
    specification as it is processed overrides any selections inside of
    that region specified by previous regions. Another way of thinking
    about this is that if a previous excluded region is completely
    inside of a subsequent included region the excluded region is
    ignored.

    The positional coordinates may be given either in pixel units,
    decimal degrees or hh:mm:ss.s, dd:mm:ss.s units.  The shape sizes
    may be given in pixels, degrees, arcminutes, or arcseconds.  Look
    at examples of region file produced by fv/POW or ds9 for further
    details of the region file format.

    There are three functions that are primarily for use with SAO region
    files and the  FSAOI  task, but they  can  be  used  directly.  They
    return  a  boolean true   or  false  depending   on  whether a   two
    dimensional point is in the region or not:
-
    "point in a circular region"
          circle(xcntr,ycntr,radius,Xcolumn,Ycolumn)
    
    "point in an elliptical region"
         ellipse(xcntr,ycntr,xhlf_wdth,yhlf_wdth,rotation,Xcolumn,Ycolumn)
    
    "point in a rectangular region"
             box(xcntr,ycntr,xfll_wdth,yfll_wdth,rotation,Xcolumn,Ycolumn)
    
    where 
       (xcntr,ycntr) are the (x,y) position of the center of the region
       (xhlf_wdth,yhlf_wdth) are the (x,y) half widths of the region
       (xfll_wdth,yfll_wdth) are the (x,y) full widths of the region
       (radius) is half the diameter of the circle
       (rotation) is the angle(degrees) that the region is rotated with
             respect to (xcntr,ycntr)
       (Xcoord,Ycoord) are the (x,y) coordinates to test, usually column
             names
       NOTE: each parameter can itself be an expression, not merely a
             column name or constant.
-

***5.  Example Row Filters
-
    [ binary && mag <= 5.0]        - Extract all binary stars brighter
                                     than  fifth magnitude (note that
                                     the initial space is necessary to
                                     prevent it from being treated as a
                                     binning specification)

    [#row >= 125 && #row <= 175]   - Extract row numbers 125 through 175

    [IMAGE[4,5] .gt. 100]          - Extract all rows that have the
                                     (4,5) component of the IMAGE column
                                     greater than 100

    [abs(sin(theta * #deg)) < 0.5] - Extract all rows having the
                                     absolute value of the sine of theta
                                     less  than a half where the angles
                                     are tabulated in degrees

    [SUM( SPEC > 3*BACKGRND )>=1]  - Extract all rows containing a
                                     spectrum, held in vector column
                                     SPEC, with at least one value 3
                                     times greater than the background
                                     level held in a keyword, BACKGRND

    [VCOL=={1,4,2}]                - Extract all rows whose vector column
                                     VCOL contains the 3-elements 1, 4, and
                                     2.

    [@rowFilter.txt]               - Extract rows using the expression
                                     contained within the text file
                                     rowFilter.txt

    [gtifilter()]                  - Search the current file for a GTI
				     extension,  filter  the TIME
				     column in the current table, using
				     START/STOP times taken from
				     columns in the GTI  extension

    [regfilter("pow.reg")]         - Extract rows which have a coordinate
                                     (as given in the X and Y columns) 
                                     within the spatial region specified
                                     in the pow.reg region file. 

    [regfilter("pow.reg", Xs, Ys)] - Same as above, except that the
                                     Xs and Ys columns will be used to 
                                     determine the coordinate of each
                                     row in the table.
-

**I.   Binning or Histogramming Specification

The optional binning specifier is enclosed in square brackets and can
be distinguished from a general row filter specification by the fact
that it begins with the keyword 'bin'  not immediately followed by an
equals sign.  When binning is specified, a temporary N-dimensional FITS
primary array is created by computing the histogram of the values in
the specified columns of a FITS table extension.  After the histogram
is computed the input FITS file containing the table is then closed and
the temporary FITS primary array is opened and passed to the
application program.  Thus, the application program never sees the
original FITS table and only sees the image in the new temporary file
(which has no additional extensions).  Obviously, the application
program must be expecting to open a FITS image and not a FITS table in
this case.

The data type of the FITS histogram image may be specified by appending
'b' (for 8-bit byte), 'i' (for 16-bit integers), 'j' (for 32-bit
integer), 'r' (for 32-bit floating points), or 'd' (for 64-bit double
precision floating point)  to the 'bin' keyword (e.g. '[binr X]'
creates a real floating point image).  If the datatype is not
explicitly specified then a 32-bit integer image will be created by
default, unless the weighting option is also specified in which case
the image will have a 32-bit floating point data type by default.

The histogram image may have from 1 to 4 dimensions (axes), depending
on the number of columns that are specified.  The general form of the
binning specification is:
-
 [bin{bijrd}  Xcol=min:max:binsize, Ycol= ..., Zcol=..., Tcol=...; weight]
-
in which up to 4 columns, each corresponding to an axis of the image,
are listed. The column names are case insensitive, and the column
number may be given instead of the name, preceded by a pound sign
(e.g., [bin \#4=1:512]).  If the column name is not specified, then
CFITSIO will first try to use the 'preferred column' as specified by
the CPREF keyword if it exists (e.g., 'CPREF = 'DETX,DETY'), otherwise
column names 'X', 'Y', 'Z', and 'T' will be assumed for each of the 4
axes, respectively.  In cases where the column name could be confused
with an arithmetic expression, enclose the column name in parentheses to
force the name to be interpreted literally.

Each column name may be followed by an equals sign and then the lower
and upper range of the histogram, and the size of the histogram bins,
separated by colons.  Spaces are allowed before and after the equals
sign but not within the 'min:max:binsize' string.  The min, max and
binsize values may be integer or floating point numbers, or they may be
the names of keywords in the header of the table.  If the latter, then
the value of that keyword is substituted into the expression.

Default values for the min, max and binsize quantities will be
used if not explicitly given in the binning expression as shown
in these examples:
-
    [bin x = :512:2]  - use default minimum value
    [bin x = 1::2]    - use default maximum value
    [bin x = 1:512]   - use default bin size
    [bin x = 1:]      - use default maximum value and bin size
    [bin x = :512]    - use default minimum value and bin size
    [bin x = 2]       - use default minimum and maximum values
    [bin x]           - use default minimum, maximum and bin size
    [bin 4]           - default 2-D image, bin size = 4 in both axes
    [bin]             - default 2-D image
-
CFITSIO  will use the value of the TLMINn, TLMAXn, and TDBINn keywords,
if they exist, for the default min, max, and binsize, respectively.  If
they do not exist then CFITSIO will use the actual minimum and maximum
values in the column for the histogram min and max values.  The default
binsize will be set to 1, or (max - min) / 10., whichever is smaller,
so that the histogram will have at least 10 bins along each axis.

A shortcut notation is allowed if all the columns/axes have the same
binning specification.  In this case all the column names may be listed
within parentheses, followed by the (single) binning specification, as
in:
-
    [bin (X,Y)=1:512:2]
    [bin (X,Y) = 5]
-

The optional weighting factor is the last item in the binning specifier
and, if present, is separated from the list of columns by a
semi-colon.  As the histogram is accumulated, this weight is used to
incremented the value of the appropriated bin in the histogram.  If the
weighting factor is not specified, then the default weight = 1 is
assumed.  The weighting factor may be a constant integer or floating
point number, or the name of a keyword containing the weighting value.
Or the weighting factor may be the name of a table column in which case
the value in that column, on a row by row basis, will be used.

In some cases, the column or keyword may give the reciprocal of the
actual weight value that is needed.  In this case, precede the weight
keyword or column name by a slash '/' to tell CFITSIO to use the
reciprocal of the value when constructing the histogram. 

For  complex or commonly  used  histograms, one  can also  place its
description  into  a  text  file and  import   it  into  the binning
specification  using the  syntax '[bin  @filename.txt]'.  The file's
contents  can extend over   multiple lines, although  it must still
conform to the  no-spaces rule  for the min:max:binsize syntax and each
axis specification must still be comma-separated.  Any lines in the
external text file that begin with 2 slash characters ('//') will be
ignored and may be used to add comments into the file.

 Examples:

-
    [bini detx, dety]                - 2-D, 16-bit integer histogram
                                       of DETX and DETY columns, using
                                       default values for the histogram
                                       range and binsize

    [bin (detx, dety)=16; /exposure] - 2-D, 32-bit real histogram of DETX
                                       and DETY columns with a bin size = 16
                                       in both axes. The histogram values
                                       are divided by the EXPOSURE keyword
                                       value.

    [bin time=TSTART:TSTOP:0.1]      - 1-D lightcurve, range determined by
                                       the TSTART and TSTOP keywords, 
                                       with 0.1 unit size bins.  
 
    [bin pha, time=8000.:8100.:0.1]  - 2-D image using default binning
                                       of the PHA column for the X axis,
                                       and 1000 bins in the range 
                                       8000. to 8100. for the Y axis.
    
    [bin @binFilter.txt]             - Use the contents of the text file
                                       binFilter.txt for the binning
                                       specifications.

-


*V.  Template Files

When a new FITS file is created with a call to fits\_create\_file, the
name of a template file may be supplied in parentheses immediately
following the name of the new file to be created.  This template is
used to define the structure of one or more HDUs in the new file.  The
template file may be another FITS file, in which case the newly created
file will have exactly the same keywords in each HDU as in the template
FITS file, but all the data units will be filled with zeros.  The
template file may also be an ASCII text file, where each line (in
general) describes one FITS keyword record.  The format of the ASCII
template file is described in the following sections.

**A   Detailed Template Line Format

The format of each ASCII template line closely follows the format of a
FITS keyword record:
-
  KEYWORD = KEYVALUE / COMMENT
-
except that free format may be used (e.g., the equals sign may appear
at any position in the line) and TAB characters are allowed and are
treated the same as space characters.  The KEYVALUE and COMMENT fields
are optional.  The equals sign character is also optional, but it is
recommended that it be included for clarity.  Any template line that
begins with the pound '\#' character is ignored by the template parser
and may be use to insert comments into the template file itself.

The KEYWORD name field is limited to 8 characters in length and only
the letters A-Z, digits 0-9, and the hyphen and underscore characters
may be used, without any embedded spaces. Lowercase letters in the
template keyword name will be converted to uppercase.  Leading spaces
in the template line preceding the keyword name are generally ignored,
except if the first 8 characters of a template line are all blank, then
the entire line is treated as a FITS comment keyword (with a blank
keyword name) and is copied verbatim into the FITS header.

The KEYVALUE field may have any allowed  FITS  data type: character
string, logical, integer, real, complex integer, or complex real.  The
character string values need not be enclosed in single quote characters
unless they are necessary to distinguish the string from a different
data type (e.g.  2.0 is a real but '2.0' is a string).  The keyword has
an undefined (null) value if the template record only contains blanks
following the "=" or between the "=" and the "/" comment field
delimiter.

String keyword values longer than 68 characters (the maximum length
that will fit in a single FITS keyword record) are permitted using the
CFITSIO long string convention. They can either be specified as a
single long line in the template, or by using multiple lines where the
continuing lines contain the 'CONTINUE' keyword, as in this example:
- 
  LONGKEY = 'This is a long string value that is contin&'
  CONTINUE  'ued over 2 records' / comment field goes here
-
The format of template lines with CONTINUE keyword is very strict:  3
spaces must follow CONTINUE and the rest of the line is copied verbatim
to the FITS file.

The start of the optional COMMENT field must be preceded by "/", which
is used to separate it from the keyword value field. Exceptions are if
the KEYWORD name field contains COMMENT, HISTORY, CONTINUE, or if the
first 8 characters of the template line are blanks.

More than one Header-Data Unit (HDU) may be defined in the template
file.  The start of an HDU definition is denoted with a SIMPLE or
XTENSION template line:

1) SIMPLE begins a Primary HDU definition. SIMPLE may only appear as
the  first keyword in the template file. If the template file begins
with XTENSION instead of SIMPLE, then a default empty Primary HDU is
created, and the template is then assumed to define the keywords
starting with the first extension following the Primary HDU.

2) XTENSION marks the beginning of a new extension HDU definition.  The
previous HDU will be closed at this point and processing of the next
extension begins.

**B   Auto-indexing of Keywords

If a template keyword name ends with a "\#" character, it is said to be
'auto-indexed'.   Each "\#" character will be replaced by the current
integer index value, which gets reset = 1 at the start of each new HDU
in the file (or 7 in the special case of a GROUP definition).  The
FIRST indexed keyword in each template HDU definition is used as the
'incrementor';  each subsequent occurrence of this SAME keyword will
cause the index value to be incremented.  This behavior can be rather
subtle, as illustrated in the following examples in which the TTYPE
keyword is the incrementor in both cases:
-
  TTYPE# = TIME
  TFORM# = 1D
  TTYPE# = RATE
  TFORM# = 1E
-
will create TTYPE1, TFORM1, TTYPE2, and TFORM2 keywords.  But if the
template looks like,
-
  TTYPE# = TIME
  TTYPE# = RATE
  TFORM# = 1D
  TFORM# = 1E
-
this results in a FITS files with  TTYPE1, TTYPE2, TFORM2, and TFORM2,
which is probably not what was intended!

**C   Template Parser Directives

In addition to the template lines which define individual keywords, the
template parser recognizes 3 special directives which are each preceded
by the backslash character:  \verb+ \include, \group+, and \verb+ \end+.

The 'include' directive must be followed by a filename. It forces the
parser to temporarily stop reading the current template file and begin
reading the include file. Once the parser reaches the end of the
include file it continues parsing the current template file.  Include
files can be nested, and HDU definitions can span multiple template
files.

The start of a GROUP definition is denoted with the 'group' directive,
and the end of a GROUP definition is denoted with the 'end' directive.
Each GROUP contains 0 or more member blocks (HDUs or GROUPs). Member
blocks of type GROUP can contain their own member blocks. The GROUP
definition itself occupies one FITS file HDU of special type (GROUP
HDU), so if a template specifies 1 group with 1 member HDU like:
-
\group
grpdescr = 'demo'
xtension bintable
# this bintable has 0 cols, 0 rows
\end
-
then the parser creates a FITS file with 3 HDUs :
-
1) dummy PHDU
2) GROUP HDU (has 1 member, which is bintable in HDU number 3)
3) bintable (member of GROUP in HDU number 2)
-
Technically speaking, the GROUP HDU is a BINTABLE with 6 columns. Applications
can define additional columns in a GROUP HDU using TFORMn and TTYPEn
(where n is 7, 8, ....) keywords or their auto-indexing equivalents.

For a more complicated example of a template file using the group directives,
look at the sample.tpl file that is included in the CFITSIO distribution.

**D   Formal Template Syntax

The template syntax can formally be defined as follows:
-
    TEMPLATE = BLOCK [ BLOCK ... ]

       BLOCK = { HDU | GROUP }

       GROUP = \GROUP [ BLOCK ... ] \END

         HDU = XTENSION [ LINE ... ] { XTENSION | \GROUP | \END | EOF }

        LINE = [ KEYWORD [ = ] ] [ VALUE ] [ / COMMENT ]

    X ...     - X can be present 1 or more times
    { X | Y } - X or Y
    [ X ]     - X is optional
-

At the topmost level, the template defines 1 or more template blocks. Blocks
can be either HDU (Header Data Unit) or a GROUP. For each block the parser
creates 1 (or more for GROUPs) FITS file HDUs.

**E   Errors

In general the fits\_execute\_template() function tries to be as atomic
as possible, so either everything is done or nothing is done. If an
error occurs during parsing of the template, fits\_execute\_template()
will (try to) delete the top level BLOCK (with all its children if any)
in which the error occurred, then it will stop reading the template file
and it will return with an error.

**F   Examples

1. This template file will create a 200 x 300 pixel image, with 4-byte
integer pixel values, in the primary HDU:
-
  SIMPLE = T 
  BITPIX = 32
  NAXIS = 2     / number of dimensions
  NAXIS1 = 100  / length of first axis
  NAXIS2 = 200  / length of second axis
  OBJECT = NGC 253 / name of observed object
-
The allowed values of BITPIX are 8, 16, 32, -32, or -64,
representing, respectively, 8-bit integer, 16-bit integer, 32-bit
integer, 32-bit floating point, or 64 bit floating point pixels.

2.  To create a FITS  table, the template first needs to include
XTENSION = TABLE or BINTABLE to define whether it is an ASCII or binary
table, and NAXIS2 to define the number of rows in the table.  Two
template lines are then needed to define the name (TTYPEn) and FITS data
format (TFORMn) of the columns, as in this example:
-
  xtension = bintable
  naxis2 = 40
  ttype# = Name
  tform# = 10a
  ttype# = Npoints
  tform# = j
  ttype# = Rate
  tunit# = counts/s
  tform# = e
-
The above example defines a null primary array followed by a 40-row
binary table extension with 3 columns called 'Name', 'Npoints', and
'Rate', with data formats of '10A' (ASCII character string), '1J'
(integer) and '1E' (floating point), respectively.  Note that the other
required FITS keywords (BITPIX, NAXIS, NAXIS1, PCOUNT, GCOUNT, TFIELDS,
and END) do not need to be explicitly defined in the template because
their values can be inferred from the other keywords in the template.
This example also illustrates that the templates are generally
case-insensitive (the keyword names and TFORMn values are converted to
upper-case in the FITS file) and that string keyword values generally
do not need to be enclosed in quotes.

     
*IX    Summary of all FITSIO User-Interface Subroutines 

 Error Status Routines  page~\pageref{FTVERS}
-
        FTVERS( > version)
        FTGERR(status, > errtext)
        FTGMSG( > errmsg)
        FTRPRT (stream, > status)
        FTPMSG(errmsg)
        FTPMRK
        FTCMSG
        FTCMRK
-
 FITS File Open and Close Subroutines: page~\pageref{FTOPEN}
-
        FTOPEN(unit,filename,rwmode, > blocksize,status)
        FTDKOPEN(unit,filename,rwmode, > blocksize,status)
        FTNOPN(unit,filename,rwmode, > status)
        FTDOPN(unit,filename,rwmode, > status)
        FTTOPN(unit,filename,rwmode, > status)
        FTIOPN(unit,filename,rwmode, > status)
        FTREOPEN(unit, > newunit, status)
        FTINIT(unit,filename,blocksize, > status)
        FTDKINIT(unit,filename,blocksize, > status)
        FTTPLT(unit, filename, tplfilename, > status)
        FTFLUS(unit, > status)
        FTCLOS(unit, > status)
        FTDELT(unit, > status)
        FTGIOU( > iounit, status)
        FTFIOU(iounit, > status)
	CFITS2Unit(fitsfile *ptr)   (C routine)
        CUnit2FITS(int unit)        (C routine)
        FTEXTN(filename, > nhdu, status)
        FTFLNM(unit, > filename, status)
        FTFLMD(unit, > iomode, status)
        FFURLT(unit, > urltype, status)
        FTIURL(filename, > filetype, infile, outfile, extspec, filter, 
               binspec, colspec, status)
        FTRTNM(filename, > rootname, status)
        FTEXIST(filename, > exist, status)
-
 HDU-Level Operations: page~\pageref{FTMAHD}
-
        FTMAHD(unit,nhdu, > hdutype,status)
        FTMRHD(unit,nmove, > hdutype,status)  
        FTGHDN(unit, > nhdu)
        FTMNHD(unit, hdutype, extname, extver, > status)
        FTGHDT(unit, > hdutype, status)
        FTTHDU(unit, > hdunum, status)
        FTCRHD(unit, > status)
        FTIIMG(unit,bitpix,naxis,naxes, > status) 
        FTITAB(unit,rowlen,nrows,tfields,ttype,tbcol,tform,tunit,extname, >
               status)
        FTIBIN(unit,nrows,tfields,ttype,tform,tunit,extname,varidat > status)
        FTRSIM(unit,bitpix,naxis,naxes,status)
        FTDHDU(unit, > hdutype,status)
        FTCPFL(iunit,ounit,previous, current, following, > status)
        FTCOPY(iunit,ounit,morekeys, > status)
        FTCPHD(inunit, outunit, > status)
        FTCPDT(iunit,ounit, > status)
-
 Subroutines to specify or modify the structure of the CHDU: page~\pageref{FTRDEF}
-
        FTRDEF(unit, > status)  (DEPRECATED)
        FTPDEF(unit,bitpix,naxis,naxes,pcount,gcount, > status)  (DEPRECATED)
        FTADEF(unit,rowlen,tfields,tbcol,tform,nrows > status)  (DEPRECATED)
        FTBDEF(unit,tfields,tform,varidat,nrows > status)  (DEPRECATED)
        FTDDEF(unit,bytlen, > status)  (DEPRECATED)
        FTPTHP(unit,theap, > status)
-
 Header Space and Position Subroutines: page~\pageref{FTHDEF}
-
        FTHDEF(unit,morekeys, > status)
        FTGHSP(iunit, > keysexist,keysadd,status)
        FTGHPS(iunit, > keysexist,key_no,status)
-
 Read or Write Standard Header Subroutines: page~\pageref{FTPHPR}
-
        FTPHPS(unit,bitpix,naxis,naxes, > status)
        FTPHPR(unit,simple,bitpix,naxis,naxes,pcount,gcount,extend, > status)
        FTGHPR(unit,maxdim, > simple,bitpix,naxis,naxes,pcount,gcount,extend,
               status)
        FTPHTB(unit,rowlen,nrows,tfields,ttype,tbcol,tform,tunit,extname, >
               status)
        FTGHTB(unit,maxdim, > rowlen,nrows,tfields,ttype,tbcol,tform,tunit,
               extname,status)
        FTPHBN(unit,nrows,tfields,ttype,tform,tunit,extname,varidat > status)
        FTGHBN(unit,maxdim, > nrows,tfields,ttype,tform,tunit,extname,varidat,
               status)
-
 Write Keyword Subroutines: page~\pageref{FTPREC}
-
        FTPREC(unit,card, > status)
        FTPCOM(unit,comment, > status)
        FTPHIS(unit,history, > status)
        FTPDAT(unit, > status)
        FTPKY[JKLS](unit,keyword,keyval,comment, > status)
        FTPKY[EDFG](unit,keyword,keyval,decimals,comment, > status)  
        FTPKLS(unit,keyword,keyval,comment, > status)
        FTPLSW(unit, > status)
        FTPKYU(unit,keyword,comment, > status)
        FTPKN[JKLS](unit,keyroot,startno,no_keys,keyvals,comments, > status)
        FTPKN[EDFG](unit,keyroot,startno,no_keys,keyvals,decimals,comments, > 
                   status)
        FTCPKYinunit, outunit, innum, outnum, keyroot, > status)
        FTPKYT(unit,keyword,intval,dblval,comment, > status)
        FTPKTP(unit, filename, > status)
        FTPUNT(unit,keyword,units, > status)
-
 Insert Keyword Subroutines: page~\pageref{FTIREC}
-
        FTIREC(unit,key_no,card, > status)
        FTIKY[JKLS](unit,keyword,keyval,comment, > status)
        FTIKLS(unit,keyword,keyval,comment, > status)
        FTIKY[EDFG](unit,keyword,keyval,decimals,comment, > status)  
        FTIKYU(unit,keyword,comment, > status)
-
 Read Keyword Subroutines: page~\pageref{FTGREC}
-
        FTGREC(unit,key_no, > card,status)
        FTGKYN(unit,key_no, > keyword,value,comment,status)
        FTGCRD(unit,keyword, > card,status)
        FTGNXK(unit,inclist,ninc,exclist,nexc, > card,status)
        FTGKEY(unit,keyword, > value,comment,status) 
        FTGKY[EDJKLS](unit,keyword, > keyval,comment,status)
        FTGKN[EDJKLS](unit,keyroot,startno,max_keys, > keyvals,nfound,status)
        FTGKYT(unit,keyword, > intval,dblval,comment,status)
        FTGUNT(unit,keyword, > units,status)
-
 Modify Keyword Subroutines: page~\pageref{FTMREC}
-
        FTMREC(unit,key_no,card, > status)
        FTMCRD(unit,keyword,card, > status)
        FTMNAM(unit,oldkey,keyword, > status)
        FTMCOM(unit,keyword,comment, > status)
        FTMKY[JKLS](unit,keyword,keyval,comment, > status)
        FTMKLS(unit,keyword,keyval,comment, > status)
        FTMKY[EDFG](unit,keyword,keyval,decimals,comment, > status)
        FTMKYU(unit,keyword,comment, > status)
-
 Update Keyword Subroutines: page~\pageref{FTUCRD}
-
        FTUCRD(unit,keyword,card, > status)
        FTUKY[JKLS](unit,keyword,keyval,comment, > status)
        FTUKLS(unit,keyword,keyval,comment, > status)
        FTUKY[EDFG](unit,keyword,keyval,decimals,comment, > status)
        FTUKYU(unit,keyword,comment, > status)
-
 Delete Keyword Subroutines: page~\pageref{FTDREC}
-
        FTDREC(unit,key_no, > status)
        FTDKEY(unit,keyword, > status)
-
 Define Data Scaling Parameters and Undefined Pixel Flags: page~\pageref{FTPSCL}
-
        FTPSCL(unit,bscale,bzero, > status)
        FTTSCL(unit,colnum,tscal,tzero, > status)
        FTPNUL(unit,blank, > status)
        FTSNUL(unit,colnum,snull > status)
        FTTNUL(unit,colnum,tnull > status)
-
 FITS Primary Array or IMAGE Extension I/O Subroutines: page~\pageref{FTPPR}
-
        FTGIDT(unit, > bitpix,status)
        FTGIET(unit, > bitpix,status)
        FTGIDM(unit, > naxis,status)
        FTGISZ(unit, maxdim, > naxes,status)
        FTGIPR(unit, maxdim, > bitpix,naxis,naxes,status)
        FTPPR[BIJKED](unit,group,fpixel,nelements,values, > status)
        FTPPN[BIJKED](unit,group,fpixel,nelements,values,nullval > status)
        FTPPRU(unit,group,fpixel,nelements, > status)
        FTGPV[BIJKED](unit,group,fpixel,nelements,nullval, > values,anyf,status)
        FTGPF[BIJKED](unit,group,fpixel,nelements, > values,flagvals,anyf,status)
        FTPGP[BIJKED](unit,group,fparm,nparm,values, > status)
        FTGGP[BIJKED](unit,group,fparm,nparm, > values,status)
        FTP2D[BIJKED](unit,group,dim1,naxis1,naxis2,image, > status)
        FTP3D[BIJKED](unit,group,dim1,dim2,naxis1,naxis2,naxis3,cube, > status)
        FTG2D[BIJKED](unit,group,nullval,dim1,naxis1,naxis2, > image,anyf,status)
        FTG3D[BIJKED](unit,group,nullval,dim1,dim2,naxis1,naxis2,naxis3, >
                     cube,anyf,status)
        FTPSS[BIJKED](unit,group,naxis,naxes,fpixels,lpixels,array, > status)
        FTGSV[BIJKED](unit,group,naxis,naxes,fpixels,lpixels,incs,nullval, >
                     array,anyf,status)
        FTGSF[BIJKED](unit,group,naxis,naxes,fpixels,lpixels,incs, >
                     array,flagvals,anyf,status)
-
 Table Column Information Subroutines: page~\pageref{FTGCNO}
-
        FTGNRW(unit, > nrows, status)
        FTGNCL(unit, > ncols, status)
        FTGCNO(unit,casesen,coltemplate, > colnum,status)
        FTGCNN(unit,casesen,coltemplate, > colnam,colnum,status)
        FTGTCL(unit,colnum, > datacode,repeat,width,status)
        FTEQTY(unit,colnum, > datacode,repeat,width,status)
        FTGCDW(unit,colnum, > dispwidth,status)
        FTGACL(unit,colnum, >
               ttype,tbcol,tunit,tform,tscal,tzero,snull,tdisp,status)
        FTGBCL(unit,colnum, >
               ttype,tunit,datatype,repeat,tscal,tzero,tnull,tdisp,status)
        FTPTDM(unit,colnum,naxis,naxes, > status)
        FTGTDM(unit,colnum,maxdim, > naxis,naxes,status)
        FTDTDM(unit,tdimstr,colnum,maxdim, > naxis,naxes, status)
        FFGRSZ(unit, > nrows,status)
-
 Low-Level Table Access Subroutines: page~\pageref{FTGTBS}
-
        FTGTBS(unit,frow,startchar,nchars, > string,status)
        FTPTBS(unit,frow,startchar,nchars,string, > status)
        FTGTBB(unit,frow,startchar,nchars, > array,status)
        FTPTBB(unit,frow,startchar,nchars,array, > status)
-
 Edit Rows or Columns page~\pageref{FTIROW}
-
        FTIROW(unit,frow,nrows, > status)
        FTDROW(unit,frow,nrows, > status)
        FTDRRG(unit,rowrange, > status)
        FTDRWS(unit,rowlist,nrows, > status)
        FTICOL(unit,colnum,ttype,tform, > status)
        FTICLS(unit,colnum,ncols,ttype,tform, > status)
        FTMVEC(unit,colnum,newveclen, > status)
        FTDCOL(unit,colnum, > status)
        FTCPCL(inunit,outunit,incolnum,outcolnum,createcol, > status);
-
 Read and Write Column Data Routines page~\pageref{FTPCLS}
-
        FTPCL[SLBIJKEDCM](unit,colnum,frow,felem,nelements,values, > status)
        FTPCN[BIJKED](unit,colnum,frow,felem,nelements,values,nullval > status)
        FTPCLX(unit,colnum,frow,fbit,nbit,lray, > status)
        FTPCLU(unit,colnum,frow,felem,nelements, > status)
        FTGCL(unit,colnum,frow,felem,nelements, > values,status)
        FTGCV[SBIJKEDCM](unit,colnum,frow,felem,nelements,nullval, > 
                       values,anyf,status)
        FTGCF[SLBIJKEDCM](unit,colnum,frow,felem,nelements, > 
                         values,flagvals,anyf,status)
        FTGSV[BIJKED](unit,colnum,naxis,naxes,fpixels,lpixels,incs,nullval, >
                     array,anyf,status)
        FTGSF[BIJKED](unit,colnum,naxis,naxes,fpixels,lpixels,incs, >
                     array,flagvals,anyf,status)
        FTGCX(unit,colnum,frow,fbit,nbit, > lray,status)
        FTGCX[IJD](unit,colnum,frow,nrows,fbit,nbit, > array,status)
        FTGDES(unit,colnum,rownum, > nelements,offset,status) 
        FTPDES(unit,colnum,rownum,nelements,offset, > status) 
-
 Row Selection and Calculator Routines: page~\pageref{FTFROW}
-
        FTFROW(unit,expr,firstrow, nrows, > n_good_rows, row_status, status)
        FTFFRW(unit, expr, > rownum, status)             
        FTSROW(inunit, outunit, expr, > status )
        FTCROW(unit,datatype,expr,firstrow,nelements,nulval, > 
             array,anynul,status)
        FTCALC(inunit, expr, outunit, parName, parInfo, > status) 
        FTCALC_RNG(inunit, expr, outunit, parName, parInfo,
            nranges, firstrow, lastrow, > status)
        FTTEXP(unit, expr, > datatype, nelem, naxis, naxes, status)
-
 Celestial Coordinate System Subroutines: page~\pageref{FTGICS}
-
        FTGICS(unit, > xrval,yrval,xrpix,yrpix,xinc,yinc,rot,coordtype,status)
        FTGTCS(unit,xcol,ycol, > 
               xrval,yrval,xrpix,yrpix,xinc,yinc,rot,coordtype,status)
        FTWLDP(xpix,ypix,xrval,yrval,xrpix,yrpix,xinc,yinc,rot,
                          coordtype, > xpos,ypos,status)
        FTXYPX(xpos,ypos,xrval,yrval,xrpix,yrpix,xinc,yinc,rot,
                          coordtype, > xpix,ypix,status)
-
 File Checksum Subroutines: page~\pageref{FTPCKS}
-
        FTPCKS(unit, > status) 
        FTUCKS(unit, > status) 
        FTVCKS(unit, > dataok,hduok,status) 
        FTGCKS(unit, > datasum,hdusum,status) 
        FTESUM(sum,complement, > checksum)
        FTDSUM(checksum,complement, > sum)

-
 Time and Date Utility Subroutines: page~\pageref{FTGSDT}
-
        FTGSDT( > day, month, year, status )
        FTGSTM(> datestr, timeref, status)
        FTDT2S( year, month, day, > datestr, status)
        FTTM2S( year, month, day, hour, minute, second, decimals, 
                > datestr, status)
        FTS2DT(datestr, > year, month, day, status)
        FTS2TM(datestr, > year, month, day, hour, minute, second, status)
-
 General Utility Subroutines: page~\pageref{FTGHAD}
-
        FTGHAD(unit, > curaddr,nextaddr)
        FTUPCH(string)
        FTCMPS(str_template,string,casesen, > match,exact)
        FTTKEY(keyword, > status)
        FTTREC(card, > status)
        FTNCHK(unit, > status)
        FTGKNM(unit, > keyword, keylength, status)
        FTPSVC(card, > value,comment,status)
        FTKEYN(keyroot,seq_no, > keyword,status)
        FTNKEY(seq_no,keyroot, > keyword,status)
        FTDTYP(value, > dtype,status)
        class = FTGKCL(card)
        FTASFM(tform, > datacode,width,decimals,status)
        FTBNFM(tform, > datacode,repeat,width,status)
        FTGABC(tfields,tform,space, > rowlen,tbcol,status)
        FTGTHD(template, > card,hdtype,status)
        FTRWRG(rowlist, maxrows, maxranges, > numranges, rangemin, 
               rangemax, status)
-

*X.   Parameter Definitions
-
anyf - (logical) set to TRUE if any of the returned data values are undefined
array - (any datatype except character) array of bytes to be read or written. 
bitpix - (integer) bits per pixel: 8, 16, 32, -32, or -64
blank - (integer) value used for undefined pixels in integer primary array
blank - (integer*8) value used for undefined pixels in integer primary array
blocksize - (integer) 2880-byte logical record blocking factor 
          (if 0 < blocksize < 11) or the actual block size in bytes 
          (if 10 < blocksize < 28800).  As of version 3.3 of FITSIO, 
          blocksizes greater than 2880 are no longer supported.
bscale - (double precision) scaling factor for the primary array
bytlen - (integer) length of the data unit, in bytes
bzero - (double precision) zero point for primary array scaling
card - (character*80) header record to be read or written
casesen - (logical) will string matching be case sensitive?
checksum - (character*16) encoded checksum string
colname - (character) ASCII name of the column
colnum - (integer) number of the column (first column = 1)
coltemplate - (character) template string to be matched to column names
comment - (character) the keyword comment field
comments - (character array) keyword comment fields
compid - (integer) the type of computer that the program is running on
complement - (logical) should the checksum be complemented?
coordtype - (character) type of coordinate projection (-SIN, -TAN, -ARC, 
          -NCP, -GLS, -MER, or -AIT)
cube - 3D data cube of the appropriate datatype
curaddr - (integer) starting address (in bytes) of the CHDU
current - (integer) if not equal to 0, copy the current HDU
datacode - (integer) symbolic code of the binary table column datatype
dataok - (integer) was the data unit verification successful (=1) or 
         not (= -1).  Equals zero if the DATASUM keyword is not present.      
datasum - (double precision) 32-bit 1's complement checksum for the data unit
datatype - (character) datatype (format) of the binary table column 
datestr  - (string) FITS date/time string: 'YYYY-MM-DDThh:mm:ss.ddd',
           'YYYY-MM-dd', or 'dd/mm/yy'
day - (integer) current day of the month
dblval - (double precision) fractional part of the keyword value
decimals - (integer) number of decimal places to be displayed
dim1 - (integer) actual size of the first dimension of the image or cube array
dim2 - (integer) actual size of the second dimension of the cube array
dispwidth - (integer) - the display width (length of string) for a column
dtype - (character) datatype of the keyword ('C', 'L', 'I',  or 'F')
                C = character string
                L = logical
                I = integer
                F = floating point number
errmsg - (character*80) oldest error message on the internal stack
errtext - (character*30) descriptive error message corresponding to error number
casesen - (logical) true if column name matching is case sensitive
exact - (logical) do the strings match exactly, or were wildcards used?
exclist  (character array) list of names to be excluded from search
exists   - flag indicating whether the file or compressed file exists on disk
extend - (logical) true if there may be extensions following the primary data
extname - (character) value of the EXTNAME keyword (if not blank)
fbit - (integer) first bit in the field to be read or written
felem - (integer) first pixel of the element vector (ignored for ASCII tables)
filename - (character) name of the FITS file
flagvals - (logical array) True if corresponding data element is undefined
following - (integer) if not equal to 0, copy all following HDUs in the input file
fparm - (integer) sequence number of the first group parameter to read or write
fpixel - (integer) the first pixel position
fpixels - (integer array) the first included pixel in each dimension
frow - (integer) beginning row number (first row of table = 1)
frowll - (integer*8) beginning row number (first row of table = 1)
gcount - (integer) value of the GCOUNT keyword (usually = 1)
group - (integer) sequence number of the data group (=0 for non-grouped data)
hdtype - (integer) header record type: -1=delete;  0=append or replace;
                   1=append; 2=this is the END keyword
hduok - (integer) was the HDU verification successful (=1) or 
         not (= -1).  Equals zero if the CHECKSUM keyword is not present.      
hdusum - (double precision) 32 bit 1's complement checksum for the entire CHDU
hdutype - (integer) type of HDU: 0 = primary array or IMAGE, 1 = ASCII table,
                   2 = binary table, -1 = unknown
history - (character) the HISTORY keyword comment string
hour - (integer) hour from 0 - 23
image - 2D image of the appropriate datatype
inclist  (character array) list of names to be included in search
incs - (integer array) sampling interval for pixels in each FITS dimension
intval - (integer) integer part of the keyword value
iounit - (integer) value of an unused I/O unit number
iunit - (integer) logical unit number associated with the input FITS file, 1-199
key_no - (integer) sequence number (starting with 1) of the keyword record
keylength - (integer) length of the keyword name
keyroot - (character) root string for the keyword name
keysadd -(integer) number of new keyword records which can fit in the CHU
keysexist - (integer) number of existing keyword records in the CHU
keyval - value of the keyword in the appropriate datatype
keyvals - (array) value of the keywords in the appropriate datatype
keyword - (character*8) name of a keyword
lray - (logical array) array of logical values corresponding to the bit array
lpixels - (integer array) the last included pixel in each dimension
match - (logical) do the 2 strings match?
maxdim - (integer) dimensioned size of the NAXES, TTYPE, TFORM or TUNIT arrays
max_keys - (integer) maximum number of keywords to search for
minute - (integer) minute of an hour (0 - 59)
month - (integer) current month of the year (1 - 12)
morekeys - (integer) will leave space in the header for this many more keywords
naxes - (integer array) size of each dimension in the FITS array
naxesll - (integer*8 array) size of each dimension in the FITS array
naxis - (integer) number of dimensions in the FITS array 
naxis1 - (integer) length of the X/first axis of the FITS array
naxis2 - (integer) length of the Y/second axis of the FITS array
naxis3 - (integer) length of the Z/third axis of the FITS array
nbit - (integer) number of bits in the field to read or write
nchars - (integer) number of characters to read and return
ncols - (integer) number of columns
nelements - (integer) number of data elements to read or write
nelementsll - (integer*8) number of data elements to read or write
nexc   (integer)  number of names in the exclusion list (may = 0)
nhdu - (integer) absolute number of the HDU (1st HDU = 1)
ninc   (integer)  number of names in the inclusion list
nmove - (integer) number of HDUs to move (+ or -), relative to current position
nfound - (integer) number of keywords found (highest keyword number)
no_keys - (integer) number of keywords to write in the sequence
nparm - (integer) number of group parameters to read or write
nrows - (integer) number of rows in the table
nrowsll - (integer*8) number of rows in the table
nullval - value to represent undefined pixels, of the appropriate datatype
nextaddr - (integer) starting address (in bytes) of the HDU following the CHDU
offset - (integer) byte offset in the heap to the first element of the array
offsetll - (integer*8) byte offset in the heap to the first element of the array
oldkey - (character) old name of keyword to be modified
ounit - (integer) logical unit number associated with the output FITS file 1-199
pcount - (integer) value of the PCOUNT keyword (usually = 0)
previous - (integer) if not equal to 0, copy all previous HDUs in the input file
repeat - (integer) length of element vector (e.g. 12J); ignored for ASCII table
rot - (double precision) celestial coordinate rotation angle (degrees)
rowlen - (integer) length of a table row, in characters or bytes
rowlenll - (integer*8) length of a table row, in characters or bytes
rowlist - (integer array) list of row numbers to be deleted in increasing order
rownum - (integer) number of the row (first row = 1)
rowrange- (string) list of rows or row ranges to be deleted
rwmode - (integer) file access mode: 0 = readonly, 1 = readwrite 
second   (double)- second within minute (0 - 60.9999999999) (leap second!)
seq_no - (integer) the sequence number to append to the keyword root name
simple - (logical) does the FITS file conform to all the FITS standards
snull - (character) value used to represent undefined values in ASCII table
space - (integer) number of blank spaces to leave between ASCII table columns
startchar - (integer) first character in the row to be read
startno - (integer) value of the first keyword sequence number (usually 1)
status - (integer) returned error status code (0 = OK)
str_template (character) template string to be matched to reference string
stream - (character) output stream for the report: either 'STDOUT' or 'STDERR'
string - (character) character string
sum - (double precision) 32 bit unsigned checksum value
tbcol - (integer array) column number of the first character in the field(s)
tdisp - (character) Fortran type display format for the table column
template-(character) template string for a FITS header record
tfields - (integer) number of fields (columns) in the table
tform - (character array) format of the column(s); allowed values are:
         For ASCII tables:  Iw, Aw, Fww.dd, Eww.dd, or Dww.dd
         For binary tables: rL, rX, rB, rI, rJ, rA, rAw, rE, rD, rC, rM
         where 'w'=width of the field, 'd'=no. of decimals, 'r'=repeat count
         Note that the 'rAw' form is non-standard extension to the
         TFORM keyword syntax that is not specifically defined in the
         Binary Tables definition document.
theap - (integer) zero indexed byte offset of starting address of the heap
         relative to the beginning of the binary table data
tnull - (integer) value used to represent undefined values in binary table
tnullll - (integer*8) value used to represent undefined values in binary table
ttype - (character array) label for table column(s)
tscal - (double precision) scaling factor for table column
tunit - (character array) physical unit for table column(s)
tzero - (double precision) scaling zero point for table column
unit  - (integer) logical unit number associated with the FITS file (1-199)
units - (character) the keyword units string (e.g., 'km/s')
value - (character) the keyword value string
values - array of data values of the appropriate datatype
varidat - (integer) size in bytes of the 'variable length data area'
           following the binary table data (usually = 0)
version - (real) current revision number of the library
width - (integer) width of the character string field
xcol - (integer) number of the column containing the X coordinate values
xinc - (double precision) X axis coordinate increment at reference pixel (deg)
xpix - (double precision) X axis pixel location
xpos - (double precision) X axis celestial coordinate (usually RA) (deg)
xrpix - (double precision) X axis reference pixel array location
xrval - (double precision) X axis coordinate value at the reference pixel (deg)
ycol - (integer) number of the column containing the X coordinate values
year - (integer) last 2 digits of the year (00 - 99)
yinc - (double precision) Y axis coordinate increment at reference pixel (deg)
ypix - (double precision) y axis pixel location
ypos - (double precision) y axis celestial coordinate (usually DEC) (deg)
yrpix - (double precision) Y axis reference pixel array location
yrval - (double precision) Y axis coordinate value at the reference pixel (deg)
-

*XI.    FITSIO Error Status Codes
-
Status codes in the range -99 to -999  and 1 to 999 are reserved for future
FITSIO use.

  0  OK, no error
101  input and output files are the same
103  too many FITS files open at once; all internal buffers full
104  error opening existing file
105  error creating new FITS file; (does a file with this name already exist?)
106  error writing record to FITS file
107  end-of-file encountered while reading record from FITS file
108  error reading record from file
110  error closing FITS file
111  internal array dimensions exceeded
112  Cannot modify file with readonly access
113  Could not allocate memory
114  illegal logical unit number; must be between 1 - 199, inclusive
115  NULL input pointer to routine
116  error seeking position in file

121  invalid URL prefix on file name 
122  tried to register too many IO drivers 
123  driver initialization failed 
124  matching driver is not registered 
125  failed to parse input file URL
126  parse error in range list

151  bad argument in shared memory driver
152  null pointer passed as an argument
153  no more free shared memory handles
154  shared memory driver is not initialized
155  IPC error returned by a system call
156  no memory in shared memory driver
157  resource deadlock would occur
158  attempt to open/create lock file failed
159  shared memory block cannot be resized at the moment

201  header not empty; can't write required keywords
202  specified keyword name was not found in the header  
203  specified header record number is out of bounds 
204  keyword value field is blank
205  keyword value string is missing the closing quote character 
207  illegal character in keyword name or header record
208  keyword does not have expected name. Keyword out of sequence? 
209  keyword does not have expected integer value 
210  could not find the required END header keyword
211  illegal BITPIX keyword value 
212  illegal NAXIS keyword value 
213  illegal NAXISn keyword value: must be 0 or positive integer 
214  illegal PCOUNT keyword value
215  illegal GCOUNT keyword value
216  illegal TFIELDS keyword value
217  negative ASCII or binary table width value (NAXIS1)
218  negative number of rows in ASCII or binary table (NAXIS2)
219  column name (TTYPE keyword) not found
220  illegal SIMPLE keyword value
221  could not find the required SIMPLE header keyword 
222  could not find the required BITPIX header keyword 
223  could not find the required NAXIS header keyword
224  could not find all the required NAXISn keywords in the header 
225  could not find the required XTENSION header keyword
226  the CHDU is not an ASCII table extension
227  the CHDU is not a binary table extension 
228  could not find the required PCOUNT header keyword
229  could not find the required GCOUNT header keyword
230  could not find the required TFIELDS header keyword
231  could not find all the required TBCOLn keywords in the header
232  could not find all the required TFORMn keywords in the header  
233  the CHDU is not an IMAGE extension
234  illegal TBCOL keyword value; out of range
235  this operation only allowed for ASCII or BINARY table extension
236  column is too wide to fit within the specified width of the ASCII table
237  the specified column name template matched more than one column name
241  binary table row width is not equal to the sum of the field widths
251  unrecognizable type of FITS extension
252  unrecognizable FITS record
253  END keyword contains non-blank characters in columns 9-80 
254  Header fill area contains non-blank characters
255  Data fill area contains non-blank on non-zero values
261  unable to parse the TFORM keyword value string
262  unrecognizable TFORM datatype code
263  illegal TDIMn keyword value

301  illegal HDU number; less than 1 or greater than internal buffer size
302  column number out of range (1 - 999)
304  attempt to move to negative file record number
306  attempted to read or write a negative number of bytes in the FITS file
307  illegal starting row number for table read or write operation
308  illegal starting element number for table read or write operation
309  attempted to read or write character string in non-character table column
310  attempted to read or write logical value in non-logical table column
311  illegal ASCII table TFORM format code for attempted operation
312  illegal binary table TFORM format code for attempted operation
314  value for undefined pixels has not been defined
317  attempted to read or write descriptor in a non-descriptor field
320  number of array dimensions out of range
321  first pixel number is greater than the last pixel number
322  attempt to set BSCALE or TSCALn scaling parameter = 0
323  illegal axis length less than 1

340 NOT_GROUP_TABLE 340   Grouping function error
341  HDU_ALREADY_MEMBER    
342 MEMBER_NOT_FOUND      
343 GROUP_NOT_FOUND       
344 BAD_GROUP_ID          
345 TOO_MANY_HDUS_TRACKED 
346 HDU_ALREADY_TRACKED   
347 BAD_OPTION            
348 IDENTICAL_POINTERS    
349 BAD_GROUP_ATTACH
350 BAD_GROUP_DETACH

360 NGP_NO_MEMORY              malloc failed
361 NGP_READ_ERR               read error from file
362 NGP_NUL_PTR                null pointer passed as an argument.
                                 Passing null pointer as a name of
                                 template file raises this error
363 NGP_EMPTY_CURLINE          line read seems to be empty (used
                                 internally)
364 NGP_UNREAD_QUEUE_FULL      cannot unread more then 1 line (or single
                                 line twice)
365 NGP_INC_NESTING            too deep include file nesting (infinite
                                 loop, template includes itself ?)
366 NGP_ERR_FOPEN              fopen() failed, cannot open template file
367 NGP_EOF                    end of file encountered and not expected
368 NGP_BAD_ARG                bad arguments passed. Usually means
                                 internal parser error. Should not happen
369 NGP_TOKEN_NOT_EXPECT       token not expected here

401  error attempting to convert an integer to a formatted character string
402  error attempting to convert a real value to a formatted character string
403  cannot convert a quoted string keyword to an integer
404  attempted to read a non-logical keyword value as a logical value
405  cannot convert a quoted string keyword to a real value
406  cannot convert a quoted string keyword to a double precision value
407  error attempting to read character string as an integer
408  error attempting to read character string as a real value
409  error attempting to read character string as a double precision value
410  bad keyword datatype code 
411  illegal number of decimal places while formatting floating point value
412  numerical overflow during implicit datatype conversion
413  error compressing image
414  error uncompressing image
420  error in date or time conversion

431  syntax error in parser expression 
432  expression did not evaluate to desired type 
433  vector result too large to return in array 
434  data parser failed not sent an out column 
435  bad data encounter while parsing column 
436  parse error: output file not of proper type

501  celestial angle too large for projection
502  bad celestial coordinate or pixel value
503  error in celestial coordinate calculation
504  unsupported type of celestial projection
505  required celestial coordinate keywords not found
506  approximate wcs keyword values were returned
-
\end{document}