TODO docs.

def miles(kilometers=0, meters=0, feet=0, nautical=0):
    """
    TODO docs.
    """
    ret = 0.
    if nautical:
        kilometers += nautical / nm(1.)
    if feet:
        kilometers += feet / ft(1.)
    if meters:
        kilometers += meters / 1000.
    ret += kilometers / 1.609344
    return ret