Add a SphericalAxis function

[aplavin]

Currently, as I understand from earlier discussions with @asinghvi17, GeoAxis assumes some ellipse/geoid for the shape, and takes coordinates in degrees. I (and others in astronomy) typically want to plot a regular sphere, with native units (radians) for lat/lon.
I've been using this snippet (again, adapted from @asinghvi17 recommendations):

SphericalAxis(args...; kwargs...) = GeoAxis(args...; 
	source="""
	GEOGCRS["WGS 84",
	    DATUM["World Geodetic System 1984",
	        ELLIPSOID["WGS 84",6378137,298.257223563,
	            LENGTHUNIT["metre",1]],
	        ID["EPSG",6326]],
	    PRIMEM["Greenwich",0,
	        ANGLEUNIT["radian",1],
	        ID["EPSG",8901]],
	    CS[ellipsoidal,2],
	        AXIS["geodetic latitude (Lat)",north,
	            ORDER[1],
	            ANGLEUNIT["Rad",1]],
	        AXIS["geodetic longitude (Lon)",east,
	            ORDER[2],
	            ANGLEUNIT["Rad",1]]]
	""", kwargs...,)

There is quite some magic here, but it works :) Can such a function be added to GeoMakie?

[asinghvi17]

Not sure about reserving the spherical axis name since that can also mean a 3D sphere. But in general yes, would be nice to host the definition of this CRS in GeoMakie.

Would something like GeoMakie.UNIT_SPHERE_RADIANS_CRS work for this?

[aplavin]

I think specifying source=... is not enough for a true "spherical coordinates axis". In particular, I noticed that while limits=(0±π, 0±π/2) work correctly in radians, ticks don't: e.g., it still needs yticks=[-45, 0, 45] instead of yticks=[-π/4, 0, π/4], even with this source.
That's one of the reasons to have SphericalAxis() (or however it's called) – to have all attributes and coordinates in radians, and to have a perfect sphere as the base.