Navigation in curved space-time, Thomas B. Bahder, Am. J. Phys. 69(3), March 2001
A covariant and invariant theory of navigation in curved space-time with respect to the electromagnetic beacons is written in terms if J.L. Synge's two-point invariant world function. Explicit equations are given for navigation in space-time in the vicinity of the Earth in Schwarzschild coordinates and in rotating coordinates. The restricted problem of determining an observer's coordinate time when his or her spatial position is known is also considered.