ECEF vector API

[NiklasPhabian]

It might be useful to have STARE being able to convert between ECEF vectors and SIDs.

When a user interpolates between points on the sphere, they might to choose to work in ECEF in the first place. And it would be sad if they had to convert back to lat/lon to interact with STARE.

[michaelleerilee]

This suggests having ECEF functions in the API.

[NiklasPhabian]

right. And we have them already under the hood in SpatialVectors

[michaelleerilee]

Just have to watch out for the reference frame coordinate system.