GDL setup with Astronomy library open-source IDL replacement

To setup the IDL/GDL Astronomy library on Linux:

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

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


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


  1. reopen Terminal
  1. 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
  1. from gdl

    FITS_READ, '', data, header

showing an image from Hubble Space Telescope. 3. show FITS headers