def trajectory(flags, data):
    """
    Returns a set of lines connecting each camera poses world frame position.
    returns: [open3d.geometry.LineSet]
    """
    line_sets = []
    previous_pose = None
    for i, T_WC in enumerate(data['poses']):
        if previous_pose is not None:
            points = o3d.utility.Vector3dVector([previous_pose[:3, 3], T_WC[:3, 3]])
            lines = o3d.utility.Vector2iVector([[0, 1]])
            line = o3d.geometry.LineSet(points=points, lines=lines)
            line_sets.append(line)
        previous_pose = T_WC
    return line_sets