Global loop closure with lidar

[dinossht]

Does RTAB-Map support loading a previously mapped database file and using LiDAR-only loop closure (e.g., by setting Reg/Strategy to LiDAR-based registration) to relocalize within the existing map and continue mapping from that point? This would be similar to using camera-based bag-of-words for relocalization in the old map to resume mapping.

[matlabbe]

There is no built-in way to do it. You would need an approach like https://github.com/MarvinStuede/cmr_lidarloop or https://github.com/gisbi-kim/scancontext_tro

[dinossht]

Ah allright, so what does setting reg/strategy=1 achieve?

[matlabbe]

Reg/Strategy=1 enables ICP registration between nodes of a visual loop closure. If nodes have laser scans, then we apply ICP registration to refine the loop closure transform. That parameter enables that part from section 3.4 of this paper:

When a laser scan or a point cloud is available, link’s transformation is refined using the same ICP Registration approach than with lidar odometry (described in Section 3.1.2).

[dinossht]

Allright, so the scan data is for refinement. Does this refinement take place also when odometry is lost and the system needs loop closure to continue mapping?