code: def keypoint_vflip(kp, rows, cols):
      
      x, y, angle, scale = kp
      c = math.cos(angle)
      s = math.sin(angle)
      angle = math.atan2(-s, c)
      return [x, (rows - 1) - y, angle, scale]
docs: Flip a keypoint vertically around the x-axis.