publish platform position on uOrb topic.

reused SensorGps.msg with new topic platform_gps_position. Currently
only latitude_deg, longigude_deg and altitude_ellipsoid are set. check
out with listener platform_gps_position.

msg/SensorGps.msg

@@ -69,4 +69,4 @@ uint8 RTCM_MSG_USED_NOT_USED = 1
 uint8 RTCM_MSG_USED_USED = 2
 uint8 rtcm_msg_used		# Indicates if the RTCM message was used successfully by the receiver
 
-# TOPICS sensor_gps vehicle_gps_position
+# TOPICS sensor_gps vehicle_gps_position platform_gps_position

src/modules/simulation/gz_bridge/GZBridge.cpp

@@ -561,6 +561,14 @@ void GZBridge::platformNavsatCallback(const gz::msgs::NavSat &nav_sat)
 	// print d n'ebugging pas
 	// PX4_INFO("Moving Platform NavSat pos: lat=%.2f, lon=%.2f, alt=%.2f",
 	// 	 nav_sat.latitude_deg(), nav_sat.longitude_deg(), nav_sat.altitude());
+	sensor_gps_s gps_output{};
+
+	gps_output.latitude_deg = nav_sat.latitude_deg();
+	gps_output.longitude_deg = nav_sat.longitude_deg();
+	// not sure if this is msl or ellipsoid. consult gz docs.
+	gps_output.altitude_ellipsoid_m = nav_sat.altitude();
+
+	_platform_gps_position_pub.publish(gps_output);
 
 	// TODO publish the corresponding uOrb msg. then in reality we just have
 	// to convert the mavlink msg from the ground station to exactly the

src/modules/simulation/gz_bridge/GZBridge.hpp

@@ -54,6 +54,7 @@
 #include <lib/drivers/device/Device.hpp>
 #include <uORB/topics/sensor_accel.h>
 #include <uORB/topics/sensor_gyro.h>
+#include <uORB/topics/sensor_gps.h>
 #include <uORB/topics/vehicle_angular_velocity.h>
 #include <uORB/topics/vehicle_attitude.h>
 #include <uORB/topics/vehicle_global_position.h>
@@ -190,6 +191,8 @@ private:
 	uORB::Publication<vehicle_local_position_s>   _lpos_ground_truth_pub{ORB_ID(vehicle_local_position_groundtruth)};
 	uORB::PublicationMulti<sensor_baro_s> _sensor_baro_pub{ORB_ID(sensor_baro)};
 
+	uORB::Publication<sensor_gps_s> _platform_gps_position_pub{ORB_ID(platform_gps_position)};
+
 	uORB::PublicationMulti<sensor_accel_s> _sensor_accel_pub{ORB_ID(sensor_accel)};
 	uORB::PublicationMulti<sensor_gyro_s>  _sensor_gyro_pub{ORB_ID(sensor_gyro)};
 	uORB::PublicationMulti<vehicle_odometry_s> _visual_odometry_pub{ORB_ID(vehicle_visual_odometry)};