about gt_bbox convert

[llq12]

Dear authors；
I have compared tools/data_converter/nuscenes_converter.py#L246 between your code and mmdet3d offcial code,I find that you have changed yaw value by (-rots - np.pi/2),what does that means?I am confused because I need figure out yaw's coordinate system in gt_bbox；could you explain this part,thanks！