GDL is a free/libre/open source incremental compiler compatible with IDL (Interactive Data Language) and to some extent with PV-WAVE. Together with its library routines it serves as a tool for data analysis and visualization in such disciplines as astronomy, geosciences and medical imaging. GDL development had been started by Marc Schellens back in early noughties and has since continued with help of a team of maintainers, developers, packagers and thanks to feedback from users.

IDL is a registered trademark of Harris Geospatial Solutions. PV-WAVE is a product of Rogue Wave Software.

GDL is a domain-specific programming language and a data analysis environment. As a language, it is dynamically-typed, array-oriented, vectorised and has object-oriented programming capabilities. GDL library routines handle numerical calculations, data visualisation, signal/image processing, interaction with host OS and data input/output. GDL supports several data formats such as netCDF, HDF4, HDF5, GRIB, PNG, TIFF, DICOM, etc. Graphical output is handled by X11, PostScript, SVG or z-buffer terminals, the last one allowing output graphics (plots) to be saved in a variety of raster graphics formats. GDL features integrated debugging facilities. The built-in widget functionality enables development of GUI-based software. GDL has also a Python bridge (Python code can be called from GDL; GDL can be compiled as a Python module). Development and maintenance of GDL is carried out targeting Linux, BSD, OSX and Windows (MinGW, Cygwin).

Other open-source numerical data analysis tools similar to GDL include SciPy, GNU Octave, Scilab, PDL, NCL, R, Yorick.

Packaged versions of GDL are available for several Linux distributions, BSD and Mac OS X. Please note that several features of GDL depend on compile-time configuration, and might not be available in pre-built or pre-configured packages. The table below summarises GDL mandatory and optional dependencies along with the availability of the optional functionalities in packages (as of April 2018):

Build and test automation is carried out using CMake.

GDL interpreter has been developed using ANTLR v2 but unless you want to change the grammar (*.g files) you don't need ANTLR. All relevant ANTLR files are included in the source tree.

Your comments are welcome! Let us know what you use GDL for. Or if you don't, why not. Which functionality are you missing/would appreciate most for coming versions. Please use the github issue-tracking system to report bugs, complaints, suggestions and comments.

Code enhancements in the form of pull requests are very welcome! Note that contributions can be made in C++, IDL/GDL or Python, as well as by providing enhancements and extensions of the README files, diagnostic messages, etc.

Among the major challenges GDL development is facing currently, there are:

• enhancing test coverage by writing test programs in GDL
• streamlining development and maintainance of GDL reference docs and examples (using the Jupyter kernel?)
• bringing in into the team the needed know-how to address the backlog of ANTLR-related issues
• increasing presence within and interoperability with the Python ecosystem, including adding support for Python 3 (calling GDL from Python 2 and calling Python 2 from GDL is already implemented!)

Help welcome!

As GDL is aimed as a drop-in replacement for IDL, resources for IDL constitute valuable sources of information for GDL users as well. These include:

• the official IDL documentation
• the idl-pvwave Google Group
• the comp.lang.idl-pvwave usenet group archives (dating back to 1991!)
• Wikipedia article on IDL and references therein
• websites of IDL gurus including David Fanning and Michael Galloy
• numerous tutorials and lecture notes introducing IDL

There are several open source packages compatible or interoperable with GDL, including:

• the MPFIT curve fitting library written in IDL (also available as a Debian package)
• the IDL Astronomy User's Library written in IDL (also available as a Debian package)
• the Coyote library of IDL-written utilities (also available as a Debian package)
• the TeXtoIDL package
• the gdlde IDE
• the IDL/GDL Jupyter kernel
• the IDLWAVE Emacs mode
• IDL syntax highlighting module for Vim
• the SingleCompile extension for Vim

Alain Coulais maintains the GDL-accounces mailing list.

There have been quite some mentions of GDL in scientific literature which also provide example use cases. The Coulais et al. papers from the ADASS conferences are the best way to cite GDL as of now.

GDL development had been carried out at SourceForge in years 2003-2018 - thank you!