ardupilot/ArduCopter/navigation.pde

// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-

// run_nav_updates - top level call for the autopilot
// ensures calculations such as "distance to waypoint" are calculated before autopilot makes decisions
// To-Do - rename and move this function to make it's purpose more clear
static void run_nav_updates(void)
{
    // fetch position from inertial navigation
    calc_position();

    // calculate distance and bearing for reporting and autopilot decisions
    calc_distance_and_bearing();

    // run autopilot to make high level decisions about control modes
    run_autopilot();
}

// calc_position - get lat and lon positions from inertial nav library
static void calc_position(){
    if( inertial_nav.position_ok() ) {
        // pull position from interial nav library
        current_loc.lng = inertial_nav.get_longitude();
        current_loc.lat = inertial_nav.get_latitude();
    }
}

// calc_distance_and_bearing - calculate distance and direction to waypoints for reporting and autopilot decisions
static void calc_distance_and_bearing()
{
    Vector3f curr = inertial_nav.get_position();

    // get target from loiter or wpinav controller
    if (control_mode == LOITER || control_mode == CIRCLE) {
        wp_distance = wp_nav.get_loiter_distance_to_target();
        wp_bearing = wp_nav.get_loiter_bearing_to_target();
    }else if (control_mode == AUTO) {
        wp_distance = wp_nav.get_wp_distance_to_destination();
        wp_bearing = wp_nav.get_wp_bearing_to_destination();
    }else{
        wp_distance = 0;
        wp_bearing = 0;
    }

    // calculate home distance and bearing
    if(GPS_ok()) {
        home_distance = pythagorous2(curr.x, curr.y);
        home_bearing = pv_get_bearing_cd(curr,Vector3f(0,0,0));

        // update super simple bearing (if required) because it relies on home_bearing
        update_super_simple_bearing(false);
    }
}

// run_autopilot - highest level call to process mission commands
static void run_autopilot()
{
    if (control_mode == AUTO) {
        // load the next command if the command queues are empty
        update_commands();

        // process the active navigation and conditional commands
        verify_commands();
    }
}

// Keeps old data out of our calculation / logs
static void reset_nav_params(void)
{
    // Will be set by new command
    wp_bearing                      = 0;

    // Will be set by new command
    wp_distance                     = 0;

    // Will be set by nav or loiter controllers
    lon_error                       = 0;
    lat_error                       = 0;
}