based on the wiki page - http://en.wikipedia.org/wiki/Great-circle_distance#Formulas it's possible to calculate central angle from known azimuth and elevation of two points (on unit sphere). But is it possible to calculate elevation/azimuth from known azimuth/elevation and central angle (and known elevation and azimuth of the second point)?
My consideration is that at least in the case of known elevation there are two possible results of the azimuth (if it's even possible to calculate).
Is that right? And how to calculate the missing angle?