library or algorithm to compute viewable GPS satellites

Question

Does anyone know of a library or algorithm (whether freely or commercially available) to compute viewable GPS satellites for a particular location? Even better, does anyone know of a library or algorithm to compute the footprints of GPS satellites given almanac or ephemeris data?

Thanks, Jacob

Answer 1

There are a number of software packages, many of them free, which can generate satellite pass predictions from publicly available orbital elements. T.S. Kelso's web site celestrak.com is a great resource - here's a list of some satellite tracking software packages.

Most satellite tracking software uses orbital elements (TLEs or "two line element" sets) published by NORAD. You will want a relatively fresh elset (no more than a couple of weeks old) in order to generate reasonably accurate predictions, since the predictions lose accuracy over time, and the orbit can change due to maneuvers or stationkeeping. celestrak.com maintains up to date TLEs for many satellites, including the GPS constellation.