"notes" (or "additional_information") attribute for ellipsoid classes

[MarkWieczorek]

Description of the desired feature: For some ellipsoids, providing a reference might not be enough information to understand the origin of the data in the ellipsoid classes and how to use them. For example:

• Some manuscripts present several ellipsoids: some are constrained to have a geocentric origin whereas others are not. Some coincide with the rotational axis and others not.
• Some manuscripts present ellipsoid shapes, and/or best fitting ellipsoids with respect to the geoid.
• In some cases additional information might be required. For example, many Vesta ellipsoids are not aligned with the coordinate axes.

I propose that we simply add an optional attribute to the 3 ellipsoid classes called "notes" (or perhaps "additional_information") that allows one to add an arbitrary text string with additional information.

edit: Maybe comments would be better.

Are you willing to help implement and maintain this feature?

[MarkWieczorek]

This is incorporated in https://github.com/fatiando/boule/pull/180