SkyCoord adapter: Exception if no lon,lat values on Point

[mcdittmar]

The SkyCoord adapter operates on the coords:Point class
Point

• axis1
• axis2
• axis3
  And has logic for handling Spherical and Cartesian representations.

A nasty exception ensues if axis1 and/or axis2 have no value.
The SkyCoord instructor complains that they are not proper value types.

Another point to consider here.
Point used in Velocity context, underlying Point is still cast to a SkyCoord, but that is not really appropriate.
NOTE: SkyCoord contains position, velocity, proper motion, radial velocity together in the same Frame.

[olaurino]

the astropy adapters weren't much more than proofs of concept, the important part being the framework for being able to create such adapters. Hopefully the framework is fine and you can build on what I did. You did some significant changes in that direction, so hopefully that's true.

[mcdittmar]

They're a real good start. I made a quick-fix for the case I had problems with, but wanted to document the issue so I could go back to it. It can be handy having the adapter auto-convert the coords:Point, but it can also be an issue since you're never really sure which you'll get back. One of the cases has a fine (RA,DEC) coord, but failed to serialize units, so the adapter failed and I got a Point when I expected a SkyCoord. So, I've been considering if maybe the adapter should convert to a Point extension which adds an asSkyCoord() method instead.