Add pandas to setup.py as a requirement

[santisoler]

Pandas is needed to run ppigrf but was missing from the setup.py.

[santisoler]

Hi @klaundal! This week I discovered ppigrf and I really like it! I had the need for a pure Python and fast implementation of the IGRF calculator but never had the time to code it. Thanks a lot for tackling it!

I'm one of the core developers of Fatiando a Terra, a project that contains a few open-source libraries for geosciences. I'm leading the development of Harmonica, a library for processing and modelling gravity and magnetic that. Hence ppigrf is a nice companion to our workflows.

I'm going to push some others PRs here, let me know what you think about them and if you have any future ideas for ppigrf. I'm glad to contribute to this project!

[klaundal]

Hi @santisoler , thank you, this is great! And sorry for the slow response, I'm travelling these days. Your additions look good I think.

As for future ideas for ppigrf: The main thing will be to update when new IGRF coefficients become available. Apart from that, it could be good to include functionality for converting to/from dipole coordinates and calculate dipole tilt angle. I have made code for this here https://github.com/klaundal/dipole. But I also like that ppigrf is clean and simple and portable... If you have thoughts on this, or other suggestions, feel free to share.

[santisoler]

Hi @klaundal. No worries for the delay, there's no rush. And thanks for merging my PR!

Would be nice to have the new coefficients once they are out. I think it will be pretty straight forward to add those, since ppigrf just reads the original .shc files. I have a few ideas that I will develop in some Issues.

For example, in Fatiando we have a nice little package called Boule that implements some reference ellipsoids. ppigrf could support computing the IGRF field on any ellipsoid by taking an ellipsoid parameter. It could also use the coordinate conversion methods of the Ellipsoid class we have there: Ellipsoid.geodetic_to_spherical and Ellipsoid.spherical_to_geodetic (ignore the deprecation warnings, we are going to leave those methods).

Another think I would like to add to ppigrf is a function to compute inclination and declination of the magnetic field. I already have some own functions to do it, so it wouldn't be too hard to include them along with tests.

Let me know what you think and thanks again!