The system utilised an RTK-GPS correction signal from
a local (located w1 km from the test site) GPS base station
(Trimble Model 4700) to obtain RTK Fixed quality accuracy. An
8 ms clock reference PPS (pulse per second) signal, was
produced by the autopilot receiver to synchronise the geoposition
data with external events. The autopilot receiver was
set to output the “NMEA-0183 GPGGA” string containing the
geographic coordinates (Latitude and Longitude) at 1 Hz rate
via an RS-232 serial connection.