public GpsPoint(TtPoint p)
     : base(p)
 {
     /*
     if (p.op == TwoTrails.Engine.OpType.Take5 ||
         p.op == TwoTrails.Engine.OpType.GPS ||
         p.op == TwoTrails.Engine.OpType.WayPoint ||
         p.op == TwoTrails.Engine.OpType.Walk)
     */
     if(p.GetType() == typeof(GpsPoint))
     {
         GpsCopy((GpsPoint)p);
         _op = TwoTrails.Engine.OpType.GPS;
     }
     else
     {
         _op = TwoTrails.Engine.OpType.GPS;
         DefaultGpsValues();
     }
 }