HIL GPS precision loss problem

[shupx]

mavros/mavros_extras/src/plugins/hil.cpp

Lines 210 to 238 in 07f497d

	void gps_cb(const mavros_msgs::msg::HilGPS::SharedPtr req)
	{
	mavlink::common::msg::HIL_GPS gps = {};
	gps.time_usec = get_time_usec(req->header.stamp);
	gps.fix_type = req->fix_type;
	gps.lat = req->geo.latitude * 1E7;
	gps.lon = req->geo.longitude * 1E7;
	// @warning geographic_msgs/GeoPoint.msg uses WGS 84 reference ellipsoid
	// @TODO: Convert altitude to AMSL to be received by the FCU
	// related to issue #529
	gps.alt = req->geo.altitude * 1E3;
	// [[[cog:
	// for f in (
	// 'eph', 'epv', 'vel', 'vn', 've', 'vd', 'cog'):
	// cog.outl(f"gps.{f} = req->{f} * 1E2;")
	// ]]]
	gps.eph = req->eph * 1E2;
	gps.epv = req->epv * 1E2;
	gps.vel = req->vel * 1E2;
	gps.vn = req->vn * 1E2;
	gps.ve = req->ve * 1E2;
	gps.vd = req->vd * 1E2;
	gps.cog = req->cog * 1E2;
	// [[[end]]] (sum: txtOM75FdG)
	gps.satellites_visible = req->satellites_visible;
	uas->send_message(gps);
	}

In the HIL plugin's gps callback function, all variables such as gps.lat, gps.lon, and gps.alt are obtained by multiplying the value in the req of type mavros_msgs::msg::HilGPS by 1E7 or 1E2. This was originally intended to preserve decimal information for float or double types. However, reading the definition of the mavros_msgs::msg::HilGPS type reveals that all members of mavros_msgs::msg::HilGPS are already set to int or uint type, indicating that decimal places have been lost.

mavros/mavros_msgs/msg/HilGPS.msg

Lines 1 to 17 in 07f497d

	# HilControls.msg
	#
	# ROS representation of MAVLink HIL_GPS
	# See mavlink message documentation here:
	# https://mavlink.io/en/messages/common.html#HIL_GPS
	std_msgs/Header header
	uint8 fix_type
	geographic_msgs/GeoPoint geo
	uint16 eph
	uint16 epv
	uint16 vel
	int16 vn
	int16 ve
	int16 vd
	uint16 cog
	uint8 satellites_visible

Therefore, I recommend redefine the mavros_msgs::msg::HilGPS message to preserve the decimal part of the values. For example, the lat and lon etc. should use float64 rather than int or uint.

Alternatively, the HIL plugin should be rewritten. These multiplications by 1E2 and 1E7 should be removed because the mavros_msgs::msg::HilGPS message is already considered a processed mavlink message (int and uint type, already multiplied by 1E2 or 1E7).

This problem lies both in ROS1 and ROS2 branch.