mola_sm_loop_closure

Simplemap loop-closure postprocessing library and CLI tool

Links

README

Distro	Build dev	Build releases	Stable version
ROS 2 Humble (u22.04)		amd64 arm64
ROS 2 Jazzy @ u24.04		amd64 arm64
ROS 2 Kilted @ u24.04		amd64 arm64
ROS 2 Rolling (u24.04)		amd64 arm64

mola_sm_loop_closure

Offline loop-closure engine for MOLA CSimpleMap files. Given an input simplemap produced by any MOLA odometry front-end, the package re-optimises all keyframe poses by detecting and closing loops, then writes the corrected simplemap back to disk.

Two algorithms

Algorithm	Class	Best for
SimplemapLoopClosure	`mola::SimplemapLoopClosure`	Long maps with noticeable drift; groups keyframes into submaps and runs heavy point-cloud ICP between submap pairs
FrameToFrameLoopClosure	`mola::FrameToFrameLoopClosure`	GNSS-augmented datasets or quick re-optimisation; runs frame-to-frame ICP with a GNC graph optimizer

CLI usage

# SimplemapLoopClosure (default algorithm):
mola-sm-lc-cli -i in.simplemap -o out.simplemap \
    -p pipelines/loop-closure-lidar3d-gicp.yaml

# FrameToFrameLoopClosure:
mola-sm-lc-cli -i in.simplemap -o out.simplemap \
    -a mola::FrameToFrameLoopClosure \
    -p pipelines/loop-closure-f2f-lidar3d-gicp.yaml

Available pipelines

YAML file	Sensor type	Algorithm
`loop-closure-lidar3d-gicp.yaml`	3-D LiDAR (GICP)	SimplemapLoopClosure
`loop-closure-lidar3d-icp.yaml`	3-D LiDAR (point-to-point ICP)	SimplemapLoopClosure
`loop-closure-lidar2d.yaml`	2-D LiDAR	SimplemapLoopClosure
`loop-closure-f2f-lidar3d-gicp.yaml`	3-D LiDAR (GICP)	FrameToFrameLoopClosure

Key YAML knobs

SimplemapLoopClosure

submap_max_absolute_length / submap_min_absolute_length — controls submap granularity.
assume_planar_world: true enables annealed soft planar constraints (z, roll, pitch).
- planar_world_initial_sigma_z, planar_world_initial_sigma_ang, planar_world_annealing_rounds — tune the annealing schedule.
- planar_world_hard_flatten: true restores the old hard-flattening behaviour.
use_gnss: true / gnss_add_horizontality: true — GNSS-assisted global alignment.

FrameToFrameLoopClosure

lc_candidate_strategy — DISTANCE_STRATIFIED (default), PROXIMITY_ONLY, or MULTI_OBJECTIVE.
assume_planar_world: true — planar-world annealing.
use_gnss: true — per-keyframe GNSS factors (FactorGnssEnu).

See the online tutorial for a step-by-step example.

License

This package is released under the GNU GPL v3 license as open source, with the main intention of being useful for research and evaluation purposes. Commercial licenses available upon request.

Contributions require acceptance of the Contributor License Agreement (CLA).