GDL setup with Astronomy library (open-source IDL replacement)

less than 1 minute read

This sets up the IDL/GDL Astronomy library on Linux.

  1. install GDL
    apt install gnudatalanguage
  2. add to ~/.bashrc
    export GDL_STARTUP=~/.gdl/
  3. Download IDL Astronomy Library and extract

    mkdir ~/astrolib
    tar xf astron.dir.tar.gz -C ~/astrolib
  4. create~/.gdl/

    which keeps the current paths and adds all the Astronomy library subdirectories.


  1. reopen Terminal
  2. In GDL:

    and ~/astrolib should be included in the printout.


Astrolib vs. AstroPy

The comparison is with my Astropy-based coordinate conversion library.

  • GDL
    hor2eq, ten(37,54,41), ten(264,55,06), 2466879.7083333d, ra, dec,  /verb, obs='kpno', pres=781.0, temp=273.0
  • Python
    python pymap3d/

revealing less than 2% difference.

reading .fits

  1. Download NASA example FITS file and extract
    tar xf
  2. from gdl
    FITS_READ, '', data, header

    showing an image from Hubble Space Telescope.

  3. show FITS headers

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