Interpolate data on global geographic coordinates

[santisoler]

Description of the desired feature

The current interpolators in Verde are not able to interpolate data on global geographic coordinates.
This is a not just a software problem, but rather a mathematical one.
Wessel and Becker (2008) present a method to interpolate global data based on Green's functions and splines.
Would be nice to have this implemented on Verde.

Are you willing to help implement and maintain this feature? Yes

[leouieda]

It would indeed be very good to have this in there! I imagine you could pretty much copy the Spline class and change the Green's functions. The controlling parameters are also a bit different so it might not be worth the effort of subclassing. This will be a nice test to see if we should redesign Spline to be more subclass friendly.