use OpenCV for SVD instead of eigen

[sgk-000]

Use OpenCV SVD function instead of eigen SVD function because eigen SVD function is not robust. Refer to this issue. #8

[CLboyrobot]

Use OpenCV SVD function instead of eigen SVD function because eigen SVD function is not robust. Refer to this issue. #8

hello，could you tell me some details about the code here,(https://github.com/UMich-BipedLab/LiDARTag/blob/release/src/lidartag_decode.cc#L1778) i am very confused the value 12,could you tell me somethingabout the value 12 ,thank you very much