mola_mapper_2d

2D LiDAR Graph-SLAM backend component based on the MOLA and MRPT frameworks, compatible with ROS 2.

Distro	Develop Branch	Releases	Stable Release
ROS2 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

Overview

This repository provides a C++ library mola_mapper_2d implementing a complete 2D LiDAR SLAM system (Simultaneous Localization and Mapping) using pose graph optimization.

The mapper uses:

• GTSAM for factor graph optimization
• mp2p_icp for scan-to-map registration and loop closure detection
• MRPT for common robotics types and utilities
• MOLA framework for system integration and component management

Sensor input is provided via MOLA observation interfaces, making it compatible with various sensor front-ends (odometry, LiDAR, etc.). ROS 2 example launch files are provided in ros2-launches.

A CLI interface mola-mapper-2d-cli is also provided for running on offline datasets.

Features

• Graph-based SLAM: Maintains a pose graph of keyframes with SE(3) constraints
• Loop Closure Detection: Automatic detection and correction of large-scale loops
• Flexible ICP Pipelines: Separate configurable pipelines for odometry and loop closure
• Keyframe Management: Intelligent keyframe selection and old-keyframe replacement
• Robust Optimization: Levenberg-Marquardt optimization with robust noise models
• Multi-Sensor Support: Handles 2D/3D LiDAR observations with flexible sensor labeling
• Session Resumption: Supports resuming SLAM sessions from saved states for multi-session mapping
• Visualization Support: Built-in 3D scene generation for debugging and visualization
• Full State Serialization: Complete state save/load for archival and analysis

Contents

The repository provides:

• Core Library: mola_mapper_2d - The main 2D SLAM backend implementation
• CLI Tool: mola-mapper-2d-cli - Command-line interface for offline processing
• Example Configurations: YAML configuration templates for different scenarios
• ROS 2 Bridges: Integration components for ROS 2 (in separate ROS-specific package)

Quick Start

Build and Install

Refer to: https://docs.mola-slam.org/latest/#installing

# Standard MOLA installation (with ROS 2)
colcon build --packages-select mola_mapper_2d

# Or standalone (without ROS 2)
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
cmake --install build

Basic Usage

#include <mola_mapper_2d/Mapper2D.h>

// Create mapper instance
mola::Mapper2D mapper;

// Initialize from YAML configuration
mapper.initialize("config.yaml");

// Process observations in a loop
mapper.onObservation(observation);

// Get current estimates
auto pose = mapper.get_current_pose();
auto map = mapper.get_current_map();

// Save state for later resumption
auto state = mapper.get_state();
// ... serialize state ...

// Resume from saved state
mapper.resume_session(saved_pose);

Architecture

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