code: def mean_area_distance(item_a, item_b, max_value):
      
      mean_area_a = np.mean([item_a.size(t) for t in item_a.times])
      mean_area_b = np.mean([item_b.size(t) for t in item_b.times])
      return np.abs(mean_area_a - mean_area_b) / float(max_value)
docs: Absolute difference in the means of the areas of each track over time.
  
      Args:
          item_a: STObject from the first set in TrackMatcher
          item_b: STObject from the second set in TrackMatcher
          max_value: Maximum distance value used as scaling value and upper constraint.
  
      Returns:
          Distance value between 0 and 1.