ardupilot/ArduCopter/inertia.cpp

#include "Copter.h"

// read_inertia - read inertia in from accelerometers
void Copter::read_inertia()
{
    // inertial altitude estimates. Use barometer climb rate during high vibrations
    inertial_nav.update(vibration_check.high_vibes);

    // pull position from ahrs
    Location loc;
    ahrs.get_position(loc);
    current_loc.lat = loc.lat;
    current_loc.lng = loc.lng;

    // exit immediately if we do not have an altitude estimate
    if (!inertial_nav.get_filter_status().flags.vert_pos) {
        return;
    }

    // current_loc.alt is alt-above-home, converted from inertial nav's alt-above-ekf-origin
    const int32_t alt_above_origin_cm = inertial_nav.get_position_z_up_cm();
    current_loc.set_alt_cm(alt_above_origin_cm, Location::AltFrame::ABOVE_ORIGIN);
    if (!ahrs.home_is_set() || !current_loc.change_alt_frame(Location::AltFrame::ABOVE_HOME)) {
        // if home has not been set yet we treat alt-above-origin as alt-above-home
        current_loc.set_alt_cm(alt_above_origin_cm, Location::AltFrame::ABOVE_HOME);
    }
}