mation about positioning beacons (a generalized term for the reference
    objects that help you determine your position, such as satellites or cell
    towers).

    @ivar seenBeacons: A set of visible beacons. Note that visible beacons are not
        necessarily used in acquiring a positioning fix.
    @type seenBeacons: C{set} of L{IPositioningBeacon}
    @ivar usedBeacons: A set of the beacons that were used in obtaining a
        positioning fix. This only contains beacons that are actually used, not
        beacons for which it is unknown if they are used or not.
    @type usedBeacons: C{set} of L{IPositioningBeacon}
    r