how can we get accurate orientation data when we use hector slam

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hector slam can handle slam without any odom param, I can understand when the robot do the linear move, but think about this situation, if the robot just do rotation in the same place, the hector slam can know the rotation accurate? and if it is a round spheric environment, I don't think hector can get the orientation just by lidar scan data. is that right? And how can we supply the accurate orientation info, should we use imu or mechanism odometry? Thank you very much