code: def _load_image_labels(self):
          
          temp = []
  
          # load ground-truths
          for idx in self.image_set_index:
              label_file = self._label_path_from_index(idx)
              with open(label_file, 'r') as f:
                  label = []
                  for line in f.readlines():
                      temp_label = line.strip().split()
                      assert len(temp_label) == 5, "Invalid label file" + label_file
                      cls_id = int(temp_label[0])
                      x = float(temp_label[1])
                      y = float(temp_label[2])
                      half_width = float(temp_label[3]) / 2
                      half_height = float(temp_label[4]) / 2
                      xmin = x - half_width
                      ymin = y - half_height
                      xmax = x + half_width
                      ymax = y + half_height
                      label.append([cls_id, xmin, ymin, xmax, ymax])
                  temp.append(np.array(label))
          return temp
docs: preprocess all ground-truths
  
          Returns:
          ----------
          labels packed in [num_images x max_num_objects x 5] tensor