ardupilot/libraries/AP_Common/Location.h

#pragma once

#include <AP_Math/AP_Math.h>

class AP_Terrain;

#define LOCATION_ALT_MAX_M  83000   // maximum altitude (in meters) that can be fit into Location structure's alt field

class Location
{
public:

    uint8_t relative_alt : 1;           // 1 if altitude is relative to home
    uint8_t loiter_ccw   : 1;           // 0 if clockwise, 1 if counter clockwise
    uint8_t terrain_alt  : 1;           // this altitude is above terrain
    uint8_t origin_alt   : 1;           // this altitude is above ekf origin
    uint8_t loiter_xtrack : 1;          // 0 to crosstrack from center of waypoint, 1 to crosstrack from tangent exit location

    // note that mission storage only stores 24 bits of altitude (~ +/- 83km)
    int32_t alt;
    int32_t lat;
    int32_t lng;

    /// enumeration of possible altitude types
    enum class AltFrame {
        ABSOLUTE = 0,
        ABOVE_HOME = 1,
        ABOVE_ORIGIN = 2,
        ABOVE_TERRAIN = 3
    };

    /// constructors
    Location();
    Location(int32_t latitude, int32_t longitude, int32_t alt_in_cm, AltFrame frame);
    Location(const Vector3f &ekf_offset_neu, AltFrame frame);

    static void set_terrain(AP_Terrain* terrain) { _terrain = terrain; }

    // set altitude
    void set_alt_cm(int32_t alt_cm, AltFrame frame);

    // get altitude (in cm) in the desired frame
    // returns false on failure to get altitude in the desired frame which
    // can only happen if the original frame or desired frame is above-terrain
    bool get_alt_cm(AltFrame desired_frame, int32_t &ret_alt_cm) const WARN_IF_UNUSED;

    // get altitude frame
    AltFrame get_alt_frame() const;

    // converts altitude to new frame
    // returns false on failure to convert which can only happen if
    // the original frame or desired frame is above-terrain
    bool change_alt_frame(AltFrame desired_frame);

    // get position as a vector from origin (x,y only or x,y,z)
    // return false on failure to get the vector which can only
    // happen if the EKF origin has not been set yet
    // x, y and z are in centimetres
    bool get_vector_xy_from_origin_NE(Vector2f &vec_ne) const WARN_IF_UNUSED;
    bool get_vector_from_origin_NEU(Vector3f &vec_neu) const WARN_IF_UNUSED;

    // return distance in meters between two locations
    float get_distance(const struct Location &loc2) const;

    // return the distance in meters in North/East/Down plane as a N/E/D vector to loc2
    Vector3f get_distance_NED(const Location &loc2) const;

    // return the distance in meters in North/East plane as a N/E vector to loc2
    Vector2f get_distance_NE(const Location &loc2) const;

    // extrapolate latitude/longitude given distances (in meters) north and east
    void offset(float ofs_north, float ofs_east);

    // extrapolate latitude/longitude given bearing and distance
    void offset_bearing(float bearing, float distance);
    
    // extrapolate latitude/longitude given bearing, pitch and distance
    void offset_bearing_and_pitch(float bearing, float pitch, float distance);

    // longitude_scale - returns the scaler to compensate for
    // shrinking longitude as you move north or south from the equator
    // Note: this does not include the scaling to convert
    // longitude/latitude points to meters or centimeters
    float longitude_scale() const;

    bool is_zero(void) const WARN_IF_UNUSED;

    void zero(void);

    // return bearing in centi-degrees from location to loc2
    int32_t get_bearing_to(const struct Location &loc2) const;
    // return the bearing in radians
    float get_bearing(const struct Location &loc2) const { return radians(get_bearing_to(loc2) * 0.01f); } ;

    // check if lat and lng match. Ignore altitude and options
    bool same_latlon_as(const Location &loc2) const;

    /*
     * convert invalid waypoint with useful data. return true if location changed
     */
    bool sanitize(const struct Location &defaultLoc);

    // return true when lat and lng are within range
    bool check_latlng() const;

    // see if location is past a line perpendicular to
    // the line between point1 and point2 and passing through point2.
    // If point1 is our previous waypoint and point2 is our target waypoint
    // then this function returns true if we have flown past
    // the target waypoint
    bool past_interval_finish_line(const Location &point1, const Location &point2) const;

    /*
      return the proportion we are along the path from point1 to
      point2, along a line parallel to point1<->point2.
      This will be more than 1 if we have passed point2
     */
    float line_path_proportion(const Location &point1, const Location &point2) const;

    bool initialised() const { return (lat !=0 || lng != 0 || alt != 0); }

private:
    static AP_Terrain *_terrain;

    // scaling factor from 1e-7 degrees to meters at equator
    // == 1.0e-7 * DEG_TO_RAD * RADIUS_OF_EARTH
    static constexpr float LOCATION_SCALING_FACTOR = 0.011131884502145034f;
    // inverse of LOCATION_SCALING_FACTOR
    static constexpr float LOCATION_SCALING_FACTOR_INV = 89.83204953368922f;
};