Open-source software-defined GNSS receiver. Takes raw L-band I/Q from an SDR and runs the full receive chain — acquisition, tracking, telemetry decoding of the navigation message, and PVT (position/velocity/time) computation — for GPS L1/L2/L5, Galileo, GLONASS and BeiDou. The reference way to receive and decode a live civilian GNSS signal in software.