Lidar pointcloud details: cut angle and motion distortion

#1

What is the exact cut angle of the pointcloud?
By “cut angle” I am referring to an angle where lidar sweep is cut and packed into a pointcloud.

At the “Data collection” page I have found information “…the timestamp of the LIDAR scan is the time when the full rotation of the current LIDAR frame is achieved.”
Furthermore, by observing the timestamps of the reference samples and corresponding camera images I have noticed a consistent time difference for each camera which suggests there is a consistent cut angle, but I am not able to reverse engineer it precisely.
It seems that the cut angle is somewhere in the middle of the rear left camera and that the lidar rotates in a clockwise direction, please correct me if I’m wrong.
Since we need some reference frame we can assume 0° is at lidar’s y-axis (forward direction) and that the angle increases in clockwise direction to 360° (x-axis would then be at 90°).

Lastly, is the motion distortion compensated in the lidar pointclouds using ego-motion?

#2

Hi, you are correct. The lidar sweep starts from the left side and proceeds clockwise and ends after completing the revolution. During a revolution a number of individual packages with smaller subsections are received, each of which has a timestamp. The timestamp of a lidar pointcloud is the timestamp of the last package. We perform motion compensation for each of the packages.
The cameras are triggered whenever the lidar sweep comes across the center of a camera’s FOV. The triggering is near-instantaneous.
I guess what you chose as a reference depends on your application. I believe our annotations start at your 90 degree orientation (“right”).

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