NavList:

Bill Lionheart you wrote:
I was thinking of related problems on the sphere. Some of which I can
solve and some I don't know how to solve yet.

For example suppose we have three great circle position lines with
some sensible  assumption about the errors. For example radio
direction finding from distant stations.

Unless you’re a glutton for punishment Bill, I would steer clear of starting with distant radio lines.  Firstly, your normal distribution will widen out with distance from the transmitter.  Secondly, depending upon which type of chart you’re using, the angle you measure at the receiver may not be the angle you plot from the transmitter.  E.g. with a Mercator chart you have to allow for conversion angle, which requires a ch long.  My head’s still hurting from last time.  DaveP