Returns the ground distance in metres between two LocationGlobal objects.

    This method is an approximation, and will not be accurate over large distances and close to the 
    earth's poles. It comes from the ArduPilot test code: 
    https://github.com/diydrones/ardupilot/blob/master/Tools/autotest/common.py

def get_distance_metres(aLocation1, aLocation2):
    """
    Returns the ground distance in metres between two LocationGlobal objects.

    This method is an approximation, and will not be accurate over large distances and close to the 
    earth's poles. It comes from the ArduPilot test code: 
    https://github.com/diydrones/ardupilot/blob/master/Tools/autotest/common.py
    """
    dlat = aLocation2.lat - aLocation1.lat
    dlong = aLocation2.lon - aLocation1.lon
    return math.sqrt((dlat*dlat) + (dlong*dlong)) * 1.113195e5