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/**
 * @file gps_fusion.cpp
 * Function for fusing gps measurements
 */

/* #include <mathlib/mathlib.h> */
#include "ekf.h"

void Ekf::fuseGpsVelPos()
{
	Vector3f gps_pos_obs_var;

	// correct velocity for offset relative to IMU
	const Vector3f pos_offset_body = _params.gps_pos_body - _params.imu_pos_body;
	const Vector3f vel_offset_body = _ang_rate_delayed_raw % pos_offset_body;
	const Vector3f vel_offset_earth = _R_to_earth * vel_offset_body;
	_gps_sample_delayed.vel -= vel_offset_earth;

	// correct position and height for offset relative to IMU
	const Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
	_gps_sample_delayed.pos -= pos_offset_earth.xy();
	_gps_sample_delayed.hgt += pos_offset_earth(2);

	const float lower_limit = fmaxf(_params.gps_pos_noise, 0.01f);

	if (isOtherSourceOfHorizontalAidingThan(_control_status.flags.gps)) {
		// if we are using other sources of aiding, then relax the upper observation
		// noise limit which prevents bad GPS perturbing the position estimate
		gps_pos_obs_var(0) = gps_pos_obs_var(1) = sq(fmaxf(_gps_sample_delayed.hacc, lower_limit));

	} else {
		// if we are not using another source of aiding, then we are reliant on the GPS
		// observations to constrain attitude errors and must limit the observation noise value.
		float upper_limit = fmaxf(_params.pos_noaid_noise, lower_limit);
		gps_pos_obs_var(0) = gps_pos_obs_var(1) = sq(math::constrain(_gps_sample_delayed.hacc, lower_limit, upper_limit));
	}

	_gps_sample_delayed.sacc = fmaxf(_gps_sample_delayed.sacc, _params.gps_vel_noise);

	const float vel_var = sq(_gps_sample_delayed.sacc);
	const Vector3f gps_vel_obs_var{vel_var, vel_var, vel_var * sq(1.5f)};

	// calculate innovations
	_gps_vel_innov = _state.vel - _gps_sample_delayed.vel;
	_gps_pos_innov.xy() = Vector2f(_state.pos) - _gps_sample_delayed.pos;

	// set innovation gate size
	const float pos_innov_gate = fmaxf(_params.gps_pos_innov_gate, 1.f);
	const float vel_innov_gate = fmaxf(_params.gps_vel_innov_gate, 1.f);

	// fuse GPS measurement
	fuseHorizontalVelocity(_gps_vel_innov, vel_innov_gate, gps_vel_obs_var, _gps_vel_innov_var, _gps_vel_test_ratio);
	fuseVerticalVelocity(_gps_vel_innov, vel_innov_gate, gps_vel_obs_var, _gps_vel_innov_var, _gps_vel_test_ratio);
	fuseHorizontalPosition(_gps_pos_innov, pos_innov_gate, gps_pos_obs_var, _gps_pos_innov_var, _gps_pos_test_ratio);
}