def law_of_cosines_distance_from(p2)
      Math.acos(Math.sin(latr) * Math.sin(p2.latr) + Math.cos(latr) * Math.cos(p2.latr) * Math.cos(p2.lonr - lonr)) * RADIUS
    end
def law_of_cosines_distance_from(p2)
      Math.acos(Math.sin(latr) * Math.sin(p2.latr) + Math.cos(latr) * Math.cos(p2.latr) * Math.cos(p2.lonr - lonr)) * RADIUS
    end
Units are in km