\section{\xlabel{DISP_RECIP}\label{DISP_RECIP}Displaying an Image}

This introductory recipe demonstrates displaying an image, which is the
simplest use of GAIA.  The image used is file {\tt ngc1275jkt.sdf},
a reduced V band CCD image of the galaxy NGC 1275 obtained with the
Jacobus Kapteyn Telescope (JKT) on La Palma.  It was derived from
observations included on the CD-ROM {\it Astronomical Images}\, by
Jaffe\cite{JAFFE98}.  However, the same data are publicly available from
the ING (Isaac Newton Group) data archive maintained at the
\htmladdnormallink{Institute of Astronomy}{http://www.ast.cam.ac.uk/},
\htmladdnormallink{University of Cambridge}{http://www.cam.ac.uk/}.
See URL:

\begin{quote}
\htmladdnormallink{ {\tt http://archive.ast.cam.ac.uk/}}
{http://archive.ast.cam.ac.uk/}
\end{quote}

For technical reasons there are some differences in the arrangement of the
FITS headers in the archive and CD-ROM versions of the files but both
contain identical astronomical information.

{\tt ngc1275jkt.sdf} was created by reducing the raw observations using
CCDPACK (see \xref{SUN/139}{sun139}{}\cite{SUN139}) following the recipe
in \xref{SC/5}{sc5}{}\cite{SC5}.  The data reduction is not considered
further here.  The image is in the NDF data format (see Section~\ref{FORMATS}
for details of the data formats available to GAIA).  If you prefer you could
use an image of your own rather than this one.

Assuming that you have copied all the example data files for the cookbook
into your current directory (as described in Section~\ref{INTRO_RECIP},
above) and configured your terminal or workstation to receive X-output,
then proceed as follows.

\begin{enumerate}

  \item Start GAIA by typing:

  \begin{quote}
   {\tt \%  gaia \&}
  \end{quote}

   The ampersand (`{\tt \&}') is, of course, simply to run GAIA as a
   detached process, so that you can continue to issue Unix commands
   from the command line.  A window displaying a start-up message should
   be displayed, shortly followed by the main GAIA window.  If these
   windows do not appear then GAIA is not properly installed at your site;
   in the first instance seek assistance from your site manager.

  \item Load file {\tt ngc1275jkt.sdf} by clicking the {\sf File} menu
   (leftmost of the options in the menu-bar at the top of the window),
   selecting {\sf Open\ldots} and using the file-picker which appears to
   choose the appropriate file.

  \item The file should open, but the main display window will probably
   be mostly dark, with just a few white dots corresponding to the
   brightest parts of the image.  Set some of the display options as
   follows:

  \begin{enumerate}

    \item select the range of intensities in the image to be displayed:
     click the {\sf Auto Cut:} button (in the middle right of the control
     panel in the centre top of the window) and set it to {\sf 98\%},

    \item set the magnification: click the {\sf Scale:} button (in the
     bottom left of the control panel in the centre top of the window) and
     set it to {\sf 1/2x},

    \item set the colour table: click the {\sf Color Map:} button (in the
     lower right of the control panel in the centre top of the window) and
     set it to {\sf heat}.

  \end{enumerate}

   The display should now look something like Figure~\ref{DISP_R_JKT}.

  \begin{figure}[htbp]
     \centering
     \includegraphics[totalheight=6in]{sc17_disp_r_jkt.ps}
     \begin{quote}
     \caption[A V band CCD image of NGC 1275]
      {A V band CCD image of the galaxy NGC 1275.  The image was obtained
      with the Jacobus Kapteyn Telescope (JKT) on La Palma
     \label{DISP_R_JKT} }
     \end{quote}
  \end{figure}

  \item You can inspect the header information associated with the image
   (see Section~\ref{FORMATS}) by clicking on the {\sf View} menu (second
   on the left on the menu-bar along the top of the main window) and choosing
   the {\sf Fits Header\ldots} option.

   Note that this option will work with images in the NDF format as well
   as those in the FITS format (because the NDF format can contain
   FITS-like header information which GAIA can access).

  \item GAIA has many other functions and options and you may want to spend
   a while exploring some of them.  Similarly, you might also like to
   examine the other images included in the examples.

   On-line help is available from the {\sf Help} menu at the extreme right
   of the menu-bar at the top of the window.  If you click on this menu
   and choose the {\sf Help topics index\ldots} item then the introductory
   page of the GAIA on-line help information will appear (see
   Figure~\ref{DISP_R_HELP}).  From this page you can follow hyper-links
   to further pages giving notes on how to perform numerous common tasks
   with GAIA.  You are likely to find this help information very useful.

  \begin{figure}[htbp]
     \centering
     \includegraphics[totalheight=4in]{sc17_disp_r_help.ps}
     \begin{quote}
     \caption{The introductory GAIA help page
     \label{DISP_R_HELP} }
     \end{quote}
  \end{figure}

  \item When you have finished, close GAIA by clicking on the {\sf File}
   menu and choosing the {\sf Exit} option.

\end{enumerate}


\newpage
