Meaningful colouring of spectral cube data with volume rendering
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ascl:1704.003 Documentation Status astropy

About shwirl

shwirl is a custom standalone Python program to visualise spectral data cubes with ray-tracing volume rendering. The program has been developed to investigate transfer functions and graphics shaders as enablers for scientific visualisation of astronomical data. Details about transfer functions and shaders developed and implemented in shwirl can be found in a full length article by Vohl, Fluke, Barnes & Hassan (2017).

A transfer function is an arbitrary function that combines volumetric elements (or voxels) to set the colour, intensity, or transparency level of each pixel in the final image. A graphics shader is an algorithmic kernel used to compute several properties of the final image such as colour, depth, and/or transparency. Shaders are particularly suited to computing transfer functions, and are an integral part of the graphics pipeline on Graphics Processing Units.

The program utilises Astropy to handle FITS files and World Coordinate System, Qt (and PyQt) for the user interface, and VisPy, an object-oriented Python visualisation library binding onto OpenGL. We implemented the algorithms in the fragment shader using the GLSL language.

The software has been tested on Linux, Mac, and Windows machines, including remote desktop on cloud computing infrastructure.

Disclaimer: While the software is available for download and ready to visualise data, this is not intended as a full software release just yet.


Documentation can be found at readthedocs.


You need Qt5, PyQt5. See documentation for more details.


When Qt and PyQt is installed, you can install via pip, e.g.

pip3 install shwirl

and run with


Issues, requests and general inquiries

Please list issues, feature requests and/or general inquiries by creating a new issue.

Want to contribute?

As mentioned above, shwirl is not intended to be a finished product yet. If you would like to contribute, pull requests are welcomed.


shwirl is licensed under the terms of the (new) BSD license. A copy of the license is included within this repository.


Copyright (c) 2017, Dany Vohl All rights reserved.