Camera yaw to global yaw

Hi, considering that we have yaw orientation of a bounding box:

heading_angle = boxes[0].orientation
v =, np.array([1, 0, 0]))
yaw_cam = -np.arctan2(v[2], v[0])

where boxes are in camera frame, how can we convert yaw_cam to yaw in the global frame, i.e., convert it to the suitable label format.
Thanks and cheers!

Have a look at the devkit, to learn how we deal with the various transformations, e.g.:

Thanks for the tip! Could you help me figure out what am I doing wrong here?

from pyquaternion import Quaternion
import numpy as np
from nuscenes.nuscenes import NuScenes
from nuscenes.utils.geometry_utils import BoxVisibility

def quaternion_yaw(q: Quaternion, in_image_frame: bool=True) -> float:
    if in_image_frame:
        v =, np.array([1, 0, 0]))
        yaw = -np.arctan2(v[2], v[0])
        v =, np.array([1, 0, 0]))
        yaw = np.arctan2(v[1], v[0])

    return yaw

nusc = NuScenes()

scene = nusc.scene[0]
sample = nusc.get('sample', scene['first_sample_token'])

annotation_token = sample['anns'][0]

box_global = nusc.get('sample_annotation', annotation_token) # in global frame
gt_yaw_global = quaternion_yaw(Quaternion(box_global['rotation']), False)

boxes = []
cams = [key for key in sample['data'].keys() if 'CAM' in key]
for cam in cams:
    _, boxes, _ = nusc.get_sample_data(sample['data'][cam], box_vis_level=BoxVisibility.ANY, selected_anntokens=[annotation_token])
    if len(boxes) > 0:
        break  # found image match

cam_data = nusc.get('sample_data', sample['data'][cam])
cam_pose = nusc.get('calibrated_sensor', cam_data['calibrated_sensor_token'])
car_from_cam = Quaternion(cam_pose['rotation'])

ego_pose_cam = nusc.get('ego_pose', cam_data['ego_pose_token'])
global_from_car = Quaternion(ego_pose_cam['rotation'])

yaw_cam = quaternion_yaw(boxes[0].orientation)
q_yaw_cam = Quaternion(axis=(0, 0, 1), radians=yaw_cam)

q_yaw_global = global_from_car * (car_from_cam * q_yaw_cam)
yaw_global = quaternion_yaw(q_yaw_global,  False)

print(yaw_cam, gt_yaw_global)

For mini dataset I get output -3.120828115749234 -0.36810739253486857.

Hi. I am not exactly sure. Here are 3 things I’d take a closer look at:

  • quaternion_yaw: Does the modified version for in_image_frame really work? is the vector in v (1, 0, 0) the same?
  • get_sample_data: Use use_flat_vehicle_coordinates=True for exact results.
  • q_yaw_cam: You are rotating around the z axis. In camera coordinates yaw should be a rotation around the y axis. See