Multi-Camera Main Platform Calibration

Similar as stereo camera lidar dataset, We use the open source camera and IMU calibration toolbox Kalibr (modified to run on Ubuntu 20.04) to compute the intrinsic calibration of the Alphasense cameras as well as their extrinsics. We perform spatio-temporal calibration between the cameras and the two IMUs embedded in the Alphasense and the Ouster sensor. The calibration target is a 6 by 6 April grid and each tag size is 8.8cm. The projection model applied is the pinhole model and the distortion model is equidistant. The frontal stereo cameras are first calibrated with IMU, then each lateral single camera is calibrated with IMU. Due to collections being done at different times of the year, we provide all calibration files for each dataset collection.

Synchronization

The Ouster LiDAR and Alphasense synchronize with the recording computer using the Precision Time Protocol (PTP), which achieves sub-microsecond accuracy.

Detailed explanation for Alphasense synchronization can be found at its Github page. And the detailed procedure for Ouster lidar can be found in the software manual Section 16 “PTP Quickstart Guide”.