ardupilot/ArduSub/commands.cpp

#include "Sub.h"

// checks if we should update ahrs/RTL home position from the EKF
void Sub::update_home_from_EKF()
{
    // exit immediately if home already set
    if (ahrs.home_is_set()) {
        return;
    }

    // special logic if home is set in-flight
    if (motors.armed()) {
        set_home_to_current_location_inflight();
    } else {
        // move home to current ekf location (this will set home_state to HOME_SET)
        if (!set_home_to_current_location(false)) {
            // ignore this failure
        }
    }
}

// set_home_to_current_location_inflight - set home to current GPS location (horizontally) and EKF origin vertically
void Sub::set_home_to_current_location_inflight()
{
    // get current location from EKF
    Location temp_loc;
    Location ekf_origin;
    if (ahrs.get_location(temp_loc) && ahrs.get_origin(ekf_origin)) {
        temp_loc.alt = ekf_origin.alt;
        if (!set_home(temp_loc, false)) {
            // ignore this failure
        }
    }
}

// set_home_to_current_location - set home to current GPS location
bool Sub::set_home_to_current_location(bool lock)
{
    // get current location from EKF
    Location temp_loc;
    if (ahrs.get_location(temp_loc)) {

        // Make home always at the water's surface.
        // This allows disarming and arming again at depth.
        // This also ensures that mission items with relative altitude frame, are always
        // relative to the water's surface, whether in a high elevation lake, or at sea level.
        temp_loc.alt -= barometer.get_altitude() * 100.0f;
        return set_home(temp_loc, lock);
    }
    return false;
}

// set_home - sets ahrs home (used for RTL) to specified location
//  returns true if home location set successfully
bool Sub::set_home(const Location& loc, bool lock)
{
    // check if EKF origin has been set
    Location ekf_origin;
    if (!ahrs.get_origin(ekf_origin)) {
        return false;
    }

    // set ahrs home (used for RTL)
    if (!ahrs.set_home(loc)) {
        return false;
    }

    // lock home position
    if (lock) {
        ahrs.lock_home();
    }

    // return success
    return true;
}