Accuracy Measurement With Ground Truth

[achmadrizalmustaqim]

I constructed the map using hdl_graph_slam, then I used interactive_slam for map correction. Now, I would like to measure the accuracy of the 3D map after using interactive slam. Note: I use 3D LiDAR measurement data only.
In the paper it is said: "We used the measured 3D LIDAR trajectory as the ground truth and evaluated the accuracy of the mapping results by comparing the estimated sensor trajectory with the ground truth."
My questions:

1. May I know how to get the data of measured 3D LiDAR trajectory? How can I extract this data to be my ground truth?
2. How to get the estimated sensor trajectory? Is it the distance travelled of keyframe that we can see in each odometry file directory after performing interactive slam?

If anybody knows, please help.

cc: @koide3 @kkoide3