public Nullable<double> Altitude {get;}

{
    SnapshotChangedEvent.Subscribe(OnSnapshotChanged);
    /// Handles changes to a snapshot by processing the provided snapshot data.
    void OnSnapshotChanged(SnapshotChangedEventArgs args)
    {
        if (args == null)
            return;

        var snapshot = args.Snapshot as NMEASnapshot;
        if (snapshot == null)
            return;
        //Note: Run within a QueuedTask
        var pt = snapshot.GetPositionAsMapPoint();
        if (pt?.IsEmpty ?? true)
            return;

        // access properties
        var alt = snapshot.Altitude;
        var dt = snapshot.DateTime;
        var vdop = snapshot.VDOP;
        var hdop = snapshot.HDOP;
        // etc
        //TODO: use the snapshot
    }
}