code: def start_centroid_distance(item_a, item_b, max_value):
      
      start_a = item_a.center_of_mass(item_a.times[0])
      start_b = item_b.center_of_mass(item_b.times[0])
      start_distance = np.sqrt((start_a[0] - start_b[0]) ** 2 + (start_a[1] - start_b[1]) ** 2)
      return np.minimum(start_distance, max_value) / float(max_value)
docs: Distance between the centroids of the first step in each object.
  
      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.