private double d(ToaDo a, ToaDo b)
        {
            Coordinates toaDo1 = new Coordinates(a);
            Coordinates toaDo2 = new Coordinates(b);
            double      doDai  = CoordinatesDistanceExtensions.DistanceTo(toaDo1, toaDo2) * 1000;// đơn vị là mét.

            return(doDai);
        }
 public Coordinates(ToaDo toaDo)
 {
     Latitude  = toaDo.getX();
     Longitude = toaDo.getY();
 }