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SLAM

What is SLAM

SLAM stands for Simultaneous Localization and Mapping. It is a computational problem in robotics and computer vision where a robot or device: 1. Localizes itself: Determines its position and orientation within an environment. 2. Maps the environment: Creates a map of its surroundings while navigating through it.

SLAM enables robots to operate autonomously in unknown environments by building a map and tracking their position on that map in real-time.

Starting SLAM from the Terminal

Here are the terminal commands for launching the SLAM toolkit.

# Start robot or robot simulator in this case I wil use the turtlebot3
ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py

# Start nav2
ros2 launch nav2_bringup navigation_launch.py
# Start SLAM
ros2 launch slam_toolbox online_async_launch.py
# Launch rviz2 and add the TF visualization and the map visualization
ros2 run rviz2 rviz2

Custom SLAM Launch File

Here is a custom ROS 2 Launch file

slam.launch.py
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from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, IncludeLaunchDescription
from launch_ros.actions import Node
from ament_index_python.packages import get_package_share_directory
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch.substitutions import LaunchConfiguration
import os

def generate_launch_description():
    # Declare arguments
    use_sim_time = LaunchConfiguration('use_sim_time', default='False')

    # Get package share directories
    nav2_bringup_dir = get_package_share_directory('nav2_bringup')
    slam_toolbox_dir = get_package_share_directory('slam_toolbox')
    locker98_tools_bringup_dir = get_package_share_directory('locker98_tools_bringup')

    # Include the navigation launch file
    navigation_launch = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(nav2_bringup_dir, 'launch', 'navigation_launch.py')
        ),
        launch_arguments={'use_sim_time': use_sim_time}.items()
    )

    # Include the SLAM toolbox launch file
    slam_launch = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(slam_toolbox_dir, 'launch', 'online_async_launch.py')
        ),
        launch_arguments={'use_sim_time': use_sim_time}.items()
    )

    # RViz2 node
    rviz2_node = Node(
        package='rviz2',
        executable='rviz2',
        output='screen',
        arguments=[
            '-d', os.path.join(locker98_tools_bringup_dir, 'rviz', 'slam_config.rviz')
        ]
    )

    return LaunchDescription([
        DeclareLaunchArgument('use_sim_time', default_value='False', description='Use simulation time'),
        navigation_launch,
        slam_launch,
        rviz2_node
    ])
slam.launch.xml
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<launch>
    <arg name="use_sim_time" default="False" />

    <include file="$(find-pkg-share nav2_bringup)/launch/navigation_launch.py">
        <arg name="use_sim_time" value="$(var use_sim_time)"/>
    </include>

    <include file="$(find-pkg-share slam_toolbox)/launch/online_async_launch.py">
        <arg name="use_sim_time" value="$(var use_sim_time)"/>
    </include>

    <node pkg="rviz2" exec="rviz2" output="screen">
        <param name="config" value="$(find-pkg-share locker98_tools_bringup)/rviz/nav2_config.rviz" />
    </node>
</launch>