Heading sensor (THD)

A transmitting heading device, THD, is the bridge sensor that outputs the ship’s true heading as a continuous digital and analog signal to radar, ARPA, ECDIS, AIS, and autopilot, so all systems share one common heading reference. Its performance is set by IMO Resolution MSC.116(73), which requires accuracy and a data output suitable for north-stabilized radar and track control. The THD may be fed by a gyrocompass, a GNSS-compass, or a magnetic compass with a transmitting element. A reliable heading input is required for stabilized radar presentations, course-up displays, and target tracking under SOLAS Chapter V.