terrain_estimator.h

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/**
 * @file terrain_estimator.h
 */

#pragma once

#include <lib/mathlib/mathlib.h>
#include <matrix/math.hpp>
#include <uORB/topics/sensor_combined.h>
#include <uORB/topics/vehicle_gps_position.h>
#include <uORB/topics/vehicle_attitude.h>
#include <uORB/topics/distance_sensor.h>


/*
* This class can be used to estimate distance to the ground using a laser range finder.
* It's assumed that the laser points down vertically if the vehicle is in it's neutral pose.
* The predict(...) function will do a state prediciton based on accelerometer inputs. It also
* considers accelerometer bias.
* The measurement_update(...) function does a measurement update based on range finder and gps
* velocity measurements. Both functions should always be called together when there is new
* acceleration data available.
* The is_valid() function provides information whether the estimate is valid.
*/

class __EXPORT TerrainEstimator
{
public:
    TerrainEstimator();
    ~TerrainEstimator() = default;

    bool is_valid() {return _terrain_valid;}
    float get_distance_to_ground() {return -_x(0);}
    float get_velocity() {return _x(1);}

    void predict(float dt, const struct vehicle_attitude_s *attitude, const struct sensor_combined_s *sensor,
             const struct distance_sensor_s *distance);
    void measurement_update(uint64_t time_ref, const struct vehicle_gps_position_s *gps,
                const struct distance_sensor_s *distance,
                const struct vehicle_attitude_s *attitude);

private:
    enum {n_x = 3};

    float _distance_last;
    bool _terrain_valid;

    // kalman filter variables
    matrix::Vector<float, n_x> _x;      // state: ground distance, velocity, accel bias in z direction
    float  _u_z;            // acceleration in earth z direction
    matrix::Matrix<float, 3, 3> _P; // covariance matrix

    // timestamps
    uint64_t _time_last_distance;
    uint64_t _time_last_gps;

    /*
    struct {
        float var_acc_z;
        float var_p_z;
        float var_p_vz;
        float var_lidar;
        float var_gps_vz;
    } _params;
    */

    bool is_distance_valid(float distance);

};