The software package GNU Data Language (GDL) can be downloaded at the project's homepage (link), then follow the instructions for Win / Mac / Linux to install. In common Linux distibutions (Ubuntu, Debian, …) one can use the package management, too:

sudo apt-get install gnudatalanguage 

For the use in the Laboratory Courses the IDL Astro Library is also required. It can be downloaded at:

http://idlastro.gsfc.nasa.gov/homepage.html

Unpack the archive (astron) and change the following lines of the file readfits.pro in the directory pro:

Line:              ndata = product(dims,/integer)
replace by:        ndata = dims[0]

Additionally create a file fitsconvert.pro with the following content:

function fitsconvert,image
if n_elements(image) eq 0 then begin
  print,'Usage: converted_image=fitsconvert,original_image'
  return,0
endif
erg=(long(image)+65536) mod 65536
return,erg
end

The directory astron and the file fitsconvert.pro can now be moved to an arbitrary place. To use the AstroLib, create an additional start-up script that exports the paths of the libraries. This script can e.g. be saved as hidden file in the home directory (e.g. $HOME/.gdl_startup). If the directory astron and the file fitsconvert.pro are placed in /home/praktikum/opt/gdl-astrolib, the start-up script would look like:

!PATH=!PATH + ':/usr/share/doc/gnudatalanguage/examples/pro'
!PATH=!PATH + ':/usr/bin/'
!PATH=!PATH + ':/home/praktikum/opt/gdl-astrolib/astron/pro'
!PATH=!PATH + ':/home/praktikum/opt/gdl-astrolib'
loadct,0, ncolor=255;
!P.BACKGROUND=255;
!P.COLOR=0;
!X.STYLE=1;
!Y.STYLE=1;
!Z.STYLE=1
print,'';
print, '*********************************************';
print, '** Personal settings are loaded and active **';
print, '*********************************************';
print,'';

The first two lines contain links to the programs that were installed as example gdl programs and the executable gdl file. The third/fourth line contain the path of the astron directory (the .pro files) and the file fitsconvert.pro (adjust paths as needed).

If the start-up script is in the directory /home/praktikum, prepare it for the usage in the Bash-Shell (in $HOME/.bashrc) by adding the following line to the .bashrc script:

export GDL_STARTUP=/home/praktikum/.gdl_startup