uorb: add AuxGlobalPosition message

Add dedicated AuxGlobalPosition uORB message to replace the previous
approach of reusing VehicleGlobalPosition for auxiliary global position
sources.

msg/versioned/AuxGlobalPosition.msg

@@ -0,0 +1,31 @@
+# Auxiliary global position
+#
+# This message provides global position data from an external source such as
+# pseudolites, visual navigation, or other positioning system.
+
+uint32 MESSAGE_VERSION = 0
+
+uint64 timestamp # [us] Time since system start
+uint64 timestamp_sample # [us] Timestamp of the raw data
+
+uint8 id # [-] Unique identifier for the AGP source
+uint8 source # [@enum SOURCE] Source type of the position data (based on mavlink::GLOBAL_POSITION_SRC)
+uint8 SOURCE_UNKNOWN = 0 # Unknown source
+uint8 SOURCE_GNSS = 1 # GNSS
+uint8 SOURCE_VISION = 2 # Vision
+uint8 SOURCE_PSEUDOLITES = 3 # Pseudolites
+uint8 SOURCE_TERRAIN = 4 # Terrain
+uint8 SOURCE_MAGNETIC = 5 # Magnetic
+uint8 SOURCE_ESTIMATOR = 6 # Estimator
+
+# lat, lon: required for horizontal position fusion, alt: required for vertical position fusion
+float64 lat # [deg] Latitude in WGS84
+float64 lon # [deg] Longitude in WGS84
+float32 alt # [m] [@invalid NaN] Altitude above mean sea level (AMSL)
+
+float32 eph # [m] [@invalid NaN] Std dev of horizontal position, lower bounded by NOISE param
+float32 epv # [m] [@invalid NaN] Std dev of vertical position, lower bounded by NOISE param
+
+uint8 lat_lon_reset_counter # [-] Counter for reset events on horizontal position coordinates
+
+# TOPICS aux_global_position

msg/versioned/VehicleGlobalPosition.msg

@@ -34,4 +34,3 @@ bool dead_reckoning		# True if this position is estimated through dead-reckoning
 
 # TOPICS vehicle_global_position vehicle_global_position_groundtruth external_ins_global_position
 # TOPICS estimator_global_position
-# TOPICS aux_global_position