In general, one aspect disclosed features a computer-implemented method comprising: determining whether Global Positioning System (GPS) location data are available; responsive to determining the GPS location data are available, causing transmission of a first message in National Marine Electronics Association (NMEA) format, the first message comprising the GPS location data; and responsive to determining the GPS location data are not available: determining a location based on non-GPS location data, generating a second message in NMEA format, the second message representing the determined location, and transmitting the second message.