Why invert the pitch Angle in the tag, when using biwi data

[zn1966]

In RankPose/src/dataset/biwi.py

with open(filename, 'r') as f: # data/biwi_dataset_list.txt for i, line in enumerate(f.readlines()): ls = line.strip().split(' ') bbox = [float(ls[i]) for i in range(1,5)] pose = [float(ls[i]) for i in range(5,8)] pose[1] = - pose[1] if True and (abs(pose[0])>99 or abs(pose[1])>99 or abs(pose[2])>99): continue

I mean why need to invert pose[1]?