code: def _IDW(self, latitude, longitude, radius=1):
          
          tile = self.get_file(latitude, longitude)
          if tile is None:
              return None
          return tile._InverseDistanceWeighted(latitude, longitude, radius)
docs: Return the interpolated elevation at a point.
  
          Load the correct tile for latitude and longitude given.
          If the tile doesn't exist, return None. Otherwise,
          call the tile's Inverse Distance Weighted function and
          return the elevation.
  
          Args:
              latitude: float with the latitude in decimal degrees
              longitude: float with the longitude in decimal degrees
              radius: int of 1 or 2 indicating the approximate radius
                  of adjacent cells to include
  
          Returns:
              a float of the interpolated elevation with the same unit
              as the .hgt file (meters)