HRSC2COCO.py: NameError: name 'distance' is not defined

[Feeeeeel]

File "D:/project/mydesign/Rotated_Object/HRSC2016_dataset/HRSC2016_COCO/tool/HRSC2COCO.py", line 167, in parse_voc_poly
object_struct['long-axis'] = max(distance(poly[0], poly[1]), distance(poly[1], poly[2]))

NameError: name 'distance' is not defined