vehicle_gps_position: add heading field

src/modules/mavlink/mavlink_receiver.cpp

@@ -2139,6 +2139,8 @@ MavlinkReceiver::handle_message_hil_gps(mavlink_message_t *msg)
 	hil_gps.fix_type = gps.fix_type;
 	hil_gps.satellites_used = gps.satellites_visible;  //TODO: rename mavlink_hil_gps_t sats visible to used?
 
+	hil_gps.heading = NAN;
+
 	if (_gps_pub == nullptr) {
 		_gps_pub = orb_advertise(ORB_ID(vehicle_gps_position), &hil_gps);
 

src/modules/simulator/gpssim/gpssim.cpp

@@ -178,6 +178,7 @@ GPSSIM::GPSSIM(const char *uart_path, bool fake_gps, bool enable_sat_info,
 {
 	/* we need this potentially before it could be set in task_main */
 	g_dev = this;
+	_report_gps_pos.heading = NAN;
 
 	/* create satellite info data object if requested */
 	if (enable_sat_info) {

src/modules/uavcan/sensors/gnss.cpp

@@ -379,6 +379,8 @@ void UavcanGnssBridge::process_fixx(const uavcan::ReceivedDataStructure<FixType>
 	report.hdop = msg.pdop;
 	report.vdop = msg.pdop;
 
+	report.heading = NAN;
+
 	// Publish to a multi-topic
 	int32_t gps_orb_instance;
 	orb_publish_auto(ORB_ID(vehicle_gps_position), &_report_pub, &report, &gps_orb_instance,