docs: def MeterOffset((lat1, lon1), (lat2, lon2)):
      "Return offset in meters of second arg from first."
      dx = EarthDistance((lat1, lon1), (lat1, lon2))
      dy = EarthDistance((lat1, lon1), (lat2, lon1))
      if lat1 < lat2: dy *= -1
      if lon1 < lon2: dx *= -1
      return (dx, dy)