  Position determination of photon emitters and associated strong field
parallax effects are investigated using relativistic optics when the photon
orbits are confined to the equatorial plane of the Schwarzschild spacetime. We
assume the emitter is at a fixed space position and the receiver moves along a
circular geodesic orbit. This study requires solving the inverse problem of
determining the (spatial) intersection point of two null geodesic initial data
problems, serving as a simplified model for applications in relativistic
astrometry as well as in radar and satellite communications.
