Why minus pi/2 in yaw?

[yangxpeijiu]

mmdet3d/core/bbox/structures/utils, in mono_cam_box2vis function.

    # convert yaw by (-yaw - np.pi / 2)
    # this is because mono 3D box class such as `NuScenesBox` has different
    # definition of rotation with our `CameraInstance3DBoxes`
     yaw = -yaw - np.pi / 2

I am confused by what means of different definition of rotation with these two boxes?

[Tai-Wang]

It is a legacy issue due to hack of yaw and dimensions in the monocular 3D detection on nuScenes. Basically it is because the rotation definition of nuscenes box class is different from our CameraInstanceBoxes. It has been fixed with #744 . This function will be deprecated soon.