Really well done!
I particularly like the little details, like the “radiating” markers spreading thinner until they vanish, and them not being in sync with each other. Then of course the very gentle backface culling transition zone for the labels. So you quite elegantly avoided one of the downsides of labels being a 2D-effect.
In my entry, the labels are textured 3D-planes, and as such benefit from the full range of 3D features like:
automatic visibility handling
various billboarding options
dynamic content updating
sensitivity for fog
plus the rest I didn’t think of
Be warned, that the code is a monolithic mess (it contains an earlier version of TexFont) - please take this only as an MVP to see what this approach can do in terms of visual impact.
Please take particular note of the one label at latitude 0°, longitude 0° (Gulf of Guinea), which can be configured (GUI) as having [No | 2D | 3D] billboarding properties. In addition, its contents is dynamcally updated and displays pitch and yaw angles, as well as distance from the target of the OrbitControlled camera.