Make planetary radius configurable

[maureenjcohen]

What version of Parcels are you running?

v4

Is your feature request related to a problem?

I'm a planetary scientist and have been using Parcels (v3.1.4) for some simulations of trajectories in the Venus atmosphere. Venus has a very similar radius to Earth, so degrees are a similar size in meters.

However, I'd like to use the package for Mars and potentially Jupiter in the future. The hardcoded degree to meter conversions (1852 * 60) will be way off for these planets.

Describe the solution you'd like

Make radius configurable by adding it as an attribute to the grid (defaulting to Earth radius). Then calculate deg2m = radius * PI/180. Replace instances of 1852 * 60 with the new deg2m constant.

Describe alternatives you've considered

No response

Additional context

I'm happy to fork/implement this myself and try it in v4. I could allow deg2rad to revert to 1852 * 60 whenever Earth's radius or no radius is specified so it's fully back compatible.

[VeckoTheGecko]

Hi @maureenjcohen , thanks for the issue! This is something that we're keen to support and have also discussed internally (cc @fluidnumericsJoe and @michaeldenes ) . I think that the best way to go about this would be by allowing mesh to be a custom object during FieldSet initialisation (e.g., mesh=SphericalMesh(radius=...)) which is then picked up in the rest of the code.

Feel free to put a PR together. I think it would be good to have this on our roadmap