How to transform the rotation around Z axis in Lidar to Y axis in Camera frame?

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Hey all,

I need to label the lidar point cloud for object detection according to kitti data set labelling. But kitti labels are in camera co-odinate frame. I am getting the rotation around Z axis in lidar frame(assume pitch and roll are 0). Now I need to convert the rot_z_lid into rot_y_cam?

I have the transformation matrix between lidar_to_camera, see below:

MATRIX_T_VELO_2_CAM = ([
        [7.49916597e-03, -9.99971248e-01, -8.65110297e-04, -6.71807577e-03],
        [1.18652889e-02, 9.54520517e-04, -9.99910318e-01, -7.33152811e-02],
        [9.99882833e-01, 7.49141178e-03, 1.18719929e-02, -2.78557062e-01],
        [0, 0, 0, 1]
    ])

How can I do this transformation?

When I look into other codes, they are just using a simple formula: rot_y = -rot_z - 3.14/2.

But I don't think this is the right way of transformation!

Could anyone help me with this?

Thanks in advance