PX4-Autopilot/src/modules/uavcan/gnss_receiver.cpp

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/**
 * @file gnss_receiver.cpp
 *
 * @author Pavel Kirienko <pavel.kirienko@gmail.com>
 * @author Andrew Chambers <achamber@gmail.com>
 *
 */

#include "gnss_receiver.hpp"
#include <systemlib/err.h>
#include <mathlib/mathlib.h>

#define MM_PER_CM 			10	// Millimeters per centimeter

UavcanGnssReceiver::UavcanGnssReceiver(uavcan::INode &node) :
_node(node),
_uavcan_sub_status(node),
_report_pub(-1)
{
}

int UavcanGnssReceiver::init()
{
	int res = -1;

	// GNSS fix subscription
	res = _uavcan_sub_status.start(FixCbBinder(this, &UavcanGnssReceiver::gnss_fix_sub_cb));
	if (res < 0)
	{
		warnx("GNSS fix sub failed %i", res);
		return res;
	}

	// Clear the uORB GPS report
	memset(&_report, 0, sizeof(_report));

	return res;
}

void UavcanGnssReceiver::gnss_fix_sub_cb(const uavcan::ReceivedDataStructure<uavcan::equipment::gnss::Fix> &msg)
{
	_report.timestamp_position = hrt_absolute_time();
	_report.lat = msg.lat_1e7;
	_report.lon = msg.lon_1e7;
	_report.alt = msg.alt_1e2 * MM_PER_CM;	// Convert from centimeter (1e2) to millimeters (1e3)

	_report.timestamp_variance = _report.timestamp_position;


	// Check if the msg contains valid covariance information
	const bool valid_position_covariance = !msg.position_covariance.empty();
	const bool valid_velocity_covariance = !msg.velocity_covariance.empty();

	if (valid_position_covariance) {
		float pos_cov[9];
		msg.position_covariance.unpackSquareMatrix(pos_cov);

		// Horizontal position uncertainty
		const float horizontal_pos_variance = math::max(pos_cov[0], pos_cov[4]);
		_report.eph = (horizontal_pos_variance > 0) ? sqrtf(horizontal_pos_variance) : -1.0F;

		// Vertical position uncertainty
		_report.epv = (pos_cov[8] > 0) ? sqrtf(pos_cov[8]) : -1.0F;
	} else {
		_report.eph = -1.0F;
		_report.epv = -1.0F;
	}

	if (valid_velocity_covariance) {
	    float vel_cov[9];
	    msg.velocity_covariance.unpackSquareMatrix(vel_cov);
		_report.s_variance_m_s = math::max(math::max(vel_cov[0], vel_cov[4]), vel_cov[8]);

		/* There is a nonlinear relationship between the velocity vector and the heading.
		 * Use Jacobian to transform velocity covariance to heading covariance
		 *
		 * Nonlinear equation:
		 * heading = atan2(vel_e_m_s, vel_n_m_s)
		 * For math, see http://en.wikipedia.org/wiki/Atan2#Derivative
		 *
		 * To calculate the variance of heading from the variance of velocity,
		 * cov(heading) = J(velocity)*cov(velocity)*J(velocity)^T
		 */
		float vel_n = msg.ned_velocity[0];
		float vel_e = msg.ned_velocity[1];
		float vel_n_sq = vel_n * vel_n;
		float vel_e_sq = vel_e * vel_e;
		_report.c_variance_rad =
				(vel_e_sq * vel_cov[0] +
						-2 * vel_n * vel_e * vel_cov[1] +	// Covariance matrix is symmetric
						vel_n_sq* vel_cov[4]) / ((vel_n_sq + vel_e_sq) * (vel_n_sq + vel_e_sq));

	} else {
		_report.s_variance_m_s = -1.0F;
		_report.c_variance_rad = -1.0F;
	}

	_report.fix_type = msg.status;

	_report.timestamp_velocity = _report.timestamp_position;
	_report.vel_n_m_s = msg.ned_velocity[0];
	_report.vel_e_m_s = msg.ned_velocity[1];
	_report.vel_d_m_s = msg.ned_velocity[2];
	_report.vel_m_s = sqrtf(_report.vel_n_m_s * _report.vel_n_m_s + _report.vel_e_m_s * _report.vel_e_m_s + _report.vel_d_m_s * _report.vel_d_m_s);
	_report.cog_rad = atan2f(_report.vel_e_m_s, _report.vel_n_m_s);
	_report.vel_ned_valid = true;

	_report.timestamp_time = _report.timestamp_position;
	_report.time_gps_usec = uavcan::UtcTime(msg.gnss_timestamp).toUSec();	// Convert to microseconds

	_report.satellites_used = msg.sats_used;

	if (_report_pub > 0) {
		orb_publish(ORB_ID(vehicle_gps_position), _report_pub, &_report);

	} else {
		_report_pub = orb_advertise(ORB_ID(vehicle_gps_position), &_report);
	}

}