LiDAR-based SLAM (gmapping, cartographer) in ROS - Mini Project: Build & Apply

LiDAR-based SLAM with gmapping and cartographer in ROS

📖 Scenario: You are building a robot navigation system that uses LiDAR sensors to create maps and localize itself indoors. You will set up two popular ROS SLAM frameworks: gmapping and cartographer. This project guides you through configuring and running these SLAM packages step-by-step.

🎯 Goal: Set up ROS nodes and configuration files to run LiDAR-based SLAM using gmapping and cartographer. You will create the necessary launch files, parameter configurations, and topic remappings to visualize the generated maps in rviz.

📋 What You'll Learn

Create a ROS launch file to start the gmapping node with LiDAR input

Add a configuration parameter for the LiDAR scan topic name

Implement the core SLAM node launch with correct topic remapping

Add a launch file to start cartographer with its configuration and sensor topics

💡 Why This Matters

🌍 Real World

Robots use LiDAR-based SLAM to build maps and navigate unknown indoor spaces autonomously.

💼 Career

Understanding how to configure and run SLAM frameworks in ROS is essential for robotics engineers working on autonomous navigation.

1

Create a ROS launch file for gmapping node

Create a ROS launch file named gmapping_launch.launch that starts the gmapping node from the slam_gmapping package. Use the node name slam_gmapping and set the output to screen. Do not add any parameters or remappings yet.

ROS

Hint

Use the <node> tag with attributes pkg, type, name, and output.

2

Add LiDAR scan topic parameter

In the gmapping_launch.launch file, add a launch argument named scan_topic with default value /scan. Then add a remap tag inside the node to remap the scan topic to the launch argument $(arg scan_topic).

ROS

Hint

Use <arg> to declare the argument and <remap> inside the node to remap topics.

3

Launch gmapping node with parameters and remapping

Modify the gmapping_launch.launch file to add a parameter base_frame with value base_link inside the node. Keep the existing remap tag for scan. This completes the core logic to run gmapping with LiDAR input and frame configuration.

ROS

Hint

Use the <param> tag inside the node to set parameters.

4

Create a launch file for cartographer with sensor topics

Create a new ROS launch file named cartographer_launch.launch. Inside it, start the cartographer_node from the cartographer_ros package with node name cartographer_node and output screen. Add parameters to load the configuration file $(find cartographer_ros)/configuration_files/backpack_2d.lua. Remap the scan topic to /scan and the tf topic to /tf. This completes the setup to run cartographer SLAM with LiDAR input.

ROS

Hint

Use <param> tags to load configuration files and <remap> tags for topic remapping inside the node.

Practice

1. What is the main purpose of LiDAR-based SLAM in ROS?

easy

A. To process camera images for object detection

B. To control robot motors directly

C. To help robots create maps and know their location using laser scans

D. To send commands to robot arms

Solution

1. Step 1: Understand SLAM basics

   SLAM stands for Simultaneous Localization and Mapping, which means building a map and knowing the robot's position at the same time.

2. Step 2: Identify LiDAR role

   LiDAR uses laser scans to sense the environment, which helps SLAM create accurate maps and localize the robot.

3. Final Answer:

   To help robots create maps and know their location using laser scans -> Option C

4. Quick Check:

   LiDAR-based SLAM = mapping + localization with lasers [OK]

Hint: SLAM = map + location using sensors like LiDAR [OK]

Common Mistakes:

• Confusing SLAM with motor control
• Thinking SLAM processes camera images only
• Assuming SLAM sends commands to robot arms

2. Which ROS launch command correctly starts the gmapping SLAM node?

easy

A. rosstart gmapping slam.launch

B. roslaunch gmapping slam_gmapping.launch

C. rosrun gmapping slam_gmapping.py

D. roslaunch cartographer slam.launch

Solution

1. Step 1: Recall ROS launch syntax

   ROS uses roslaunch to start nodes with launch files, specifying package and launch file name.

2. Step 2: Match gmapping launch file

   The gmapping package provides slam_gmapping.launch to start the SLAM node.

3. Final Answer:

   roslaunch gmapping slam_gmapping.launch -> Option B

4. Quick Check:

   Use roslaunch + package + launch file [OK]

Hint: Use roslaunch with package and launch file name [OK]

Common Mistakes:

• Using rosrun instead of roslaunch for launch files
• Typing rosstart which is invalid
• Confusing cartographer launch with gmapping

3. Given this ROS launch snippet for Cartographer:

<launch>
  <include file="$(find cartographer_ros)/launch/demo_backpack_2d.launch" />
</launch>

What will happen when you run this launch file?

medium

A. It launches a robot simulation without SLAM

B. It starts gmapping SLAM with a 3D map

C. It causes a syntax error due to missing parameters

D. It starts Cartographer SLAM with a 2D LiDAR backpack demo configuration

Solution

1. Step 1: Understand the include tag

   The <include> tag loads another launch file from the cartographer_ros package.

2. Step 2: Identify the included launch file

   demo_backpack_2d.launch is a Cartographer demo for 2D SLAM using a backpack LiDAR sensor.

3. Final Answer:

   It starts Cartographer SLAM with a 2D LiDAR backpack demo configuration -> Option D

4. Quick Check:

   Include demo_backpack_2d.launch = Cartographer 2D SLAM [OK]

Hint: Include demo_backpack_2d.launch means Cartographer 2D SLAM [OK]

Common Mistakes:

• Confusing Cartographer with gmapping
• Assuming missing parameters cause errors here
• Thinking it launches simulation without SLAM

4. You try to run gmapping with this command:

roslaunch gmapping slam_gmapping.launch

But get an error: "Could not find node of type slam_gmapping in package gmapping". What is the likely cause?

medium

A. The gmapping package is not installed or sourced properly

B. You used rosrun instead of roslaunch

C. The launch file name is misspelled

D. Your LiDAR sensor is not connected

Solution

1. Step 1: Analyze the error message

   The error says it cannot find the node type in the gmapping package, meaning the package or node is missing.

2. Step 2: Check common causes

   This usually happens if the gmapping package is not installed or the ROS environment is not sourced to find it.

3. Final Answer:

   The gmapping package is not installed or sourced properly -> Option A

4. Quick Check:

   Missing package or source = node not found error [OK]

Hint: Check package installed and sourced if node not found error [OK]

Common Mistakes:

• Assuming rosrun vs roslaunch causes this error
• Thinking a typo in launch file name causes node type error
• Blaming LiDAR connection for node not found

5. You want to create a 3D map using Cartographer with a LiDAR sensor on a robot. Which approach is best?

hard

A. Use Cartographer's 3D SLAM launch files and configure sensor topics properly

B. Use gmapping with default 2D settings and add a 3D camera

C. Run gmapping and Cartographer simultaneously for better accuracy

D. Use Cartographer's 2D demo launch files and convert output to 3D later

Solution

1. Step 1: Understand SLAM capabilities

   Gmapping supports only 2D SLAM, so it cannot create 3D maps directly.

2. Step 2: Choose Cartographer for 3D

   Cartographer supports 3D SLAM and has launch files designed for 3D mapping with LiDAR sensors.

3. Step 3: Configure sensor topics

   Properly setting sensor topics in Cartographer launch files ensures correct data flow for 3D mapping.

4. Final Answer:

   Use Cartographer's 3D SLAM launch files and configure sensor topics properly -> Option A

5. Quick Check:

   3D map needs Cartographer 3D launch + sensor config [OK]

Hint: 3D mapping needs Cartographer 3D launch and sensor setup [OK]

Common Mistakes:

• Trying to use gmapping for 3D maps
• Running both SLAM systems at once
• Using 2D demos and expecting 3D output