From ardupilot/AP_GPS/AP_GPS.h
/// GPS status codes
enum GPS_Status {
NO_GPS = GPS_FIX_TYPE_NO_GPS, ///< No GPS connected/detected
NO_FIX = GPS_FIX_TYPE_NO_FIX, ///< Receiving valid GPS messages but no lock
GPS_OK_FIX_2D = GPS_FIX_TYPE_2D_FIX, ///< Receiving valid messages and 2D lock
GPS_OK_FIX_3D = GPS_FIX_TYPE_3D_FIX, ///< Receiving valid messages and 3D lock
GPS_OK_FIX_3D_DGPS = GPS_FIX_TYPE_DGPS, ///< Receiving valid messages and 3D lock with differential improvements
GPS_OK_FIX_3D_RTK_FLOAT = GPS_FIX_TYPE_RTK_FLOAT, ///< Receiving valid messages and 3D RTK Float
GPS_OK_FIX_3D_RTK_FIXED = GPS_FIX_TYPE_RTK_FIXED, ///< Receiving valid messages and 3D RTK Fixed