Reference ellipsoids for geodesy and geophysics

This software is in the early stages of design and implementation

This means that will occasionally make backwards incompatible changes as we try to improve the software, test new ideas, and settle on the project scope. We welcome any feedback and ideas! Let us know by submitting issues on Github or send us a message on our Slack chatroom.

See also

Boule is a part of the Fatiando a Terra project.


Boule is Python library for representing Reference Ellipsoids, calculating their gravity fields, and converting coordinates defined on the ellipsoids.

The main use cases are:

  • Calculating normal gravity (for gravity anomalies and disturbances).

  • Spherical gravity modeling, which requires geodetic to geocentric spherical coordinate conversions.

  • Input ellipsoid parameters for spherical harmonic analysis.

Boule is French for “ball” and also a traditional shape of bread resembling a squashed ball (much like the Earth).

Project goals

  • Provide a representation of ellipsoid parameters and derived quantities, including units and citations.

  • Convert between geodetic coordinates and geocentric spherical, topocentric, etc.

  • Calculate the gravity, gravitational, and centrifugal potential (and its derivatives) of ellipsoids in closed form.

  • Include a range ellipsoids for the Earth and other planetary bodies.

Contacting Us


Code of conduct

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

Contributing Guidelines

Please read our Contributing Guide to see how you can help and give feedback.

Imposter syndrome disclaimer

We want your help. No, really.

There may be a little voice inside your head that is telling you that you’re not ready to be an open source contributor; that your skills aren’t nearly good enough to contribute. What could you possibly offer?

We assure you that the little voice in your head is wrong.

Being a contributor doesn’t just mean writing code. Equally important contributions include: writing or proof-reading documentation, suggesting or implementing tests, or even giving feedback about the project (including giving feedback about the contribution process). If you’re coming to the project with fresh eyes, you might see the errors and assumptions that seasoned contributors have glossed over. If you can write any code at all, you can contribute code to open source. We are constantly trying out new skills, making mistakes, and learning from those mistakes. That’s how we all improve and we are happy to help others learn.

This disclaimer was adapted from the MetPy project.


This is free software: you can redistribute it and/or modify it under the terms of the BSD 3-clause License. A copy of this license is provided in LICENSE.txt.