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hyye / lio-mapping

Implementation of Tightly Coupled 3D Lidar Inertial Odometry and Mapping (LIO-mapping)
https://sites.google.com/view/lio-mapping
GNU General Public License v3.0
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hardware time synchronization is not required? #8

Closed tuandle closed 5 years ago

tuandle commented 5 years ago

Hi @hyye, Thank you for releasing the source code. I have a question about time synchronization between lidar and IMU. My understanding is that for tightly couple approach, you need to have a precise timing of measurement messages. If I understand the code correctly, in this function from src/imu_processor//MeasurementManager.cc, you simply compare the timestamp of IMU and lidar, which I think they are timestamped on arrival at the host PC and not being externally triggered, for buffering. Is it one of the reasons why you need such a high output rate (at 400 Hz) for IMU?

hyye commented 5 years ago

Hi @tuandle, actually it is not necessary to use an IMU with 400 Hz, but required for relatively higher than lidar’s.

I tested IMUs with stable time stamp and rate typically greater than 100 Hz. Our algorithm can still work.

Time synchronization is indeed an important fact. It is one of the reasons to use IMU with high output rate to reduce its effects. You may try PPS port on lidar to synchronize with IMU, if you want.

tuandle commented 5 years ago

Thanks for your clarification!