You'd either need to know your starting location, or have a clock synced with a known observatory, (which in combination with an overhead observation, is just a

You'd either need to know your starting location, or have a clock synced with a known observatory, (which in combination with an overhead observation, is just another way to determine your approximate starting location). You don't measure angle to the horizon, but angle from gravitational/geodetic "up", so you'd need probably a good leveling mechanism plus an inertial device, (if you want to be moving). And a reference to correct geodetic up to elliptical up (similar to a magnetic declination, but for gravity). But even military quality geodetic transits can only get your longitude +/-100yds, plus they weigh a few hundred pounds, need to be manually set up, leveled, and a person has to do the actual observation (click a button as a star passes through the crosshair). Granted this is decades old technology, (and I think actually used a electronic-mechanical computer) but I don't know that much has changed since then, at least in the unclassified world. I believe ships at sea doing it manually with a sextant or similar device are only going for accuracy in the magnitude of 1-10 nautical miles. So depending on what you're trying to do, it's questionable how much this might help you.