launch文件是一个包的窗口，通过这个窗口我们可以知道一个软件包能干什么，具体调动了什么节点，需要加载什么参数，下面我们从总体看里面每个launch文件的作用。

环境：utuntu20.04 ros2 foxy nav2不同版本大同小异。

具体怎么安装nav2参考：入门 — Navigation 2 1.0.0 文档

一 nav2_bringup导航包 launch文件结构

二所有的launch文件

1 localization_launch.py

2 slam_launch.py

3 navigation_launch.py

4 rviz_launch.py

5 bringup_launch.py

6 spawn_tb3_launch.py

7 tb3_simulation_launch.py

8 multi_tb3_simulation_launch.py

三每个launch作用

我们按包含关系从简单到复杂说起，lifecycle_manager是一个控制节点启动的，不影响逻辑关系，我们先不考虑。

1 localization_launch.py

启动节点关键代码

        Node(
            package='nav2_map_server',
            executable='map_server',
            name='map_server',
            output='screen',
            parameters=[configured_params],
            remappings=remappings),

        Node(
            package='nav2_amcl',
            executable='amcl',
            name='amcl',
            output='screen',
            parameters=[configured_params],
            remappings=remappings),

executable='map_server', #地图服务

executable='amcl', #基于粒子过滤器的定位技术，用于静态地图的定位。

作用：启动地图服务，在地图上给机器人定位。

2 slam_launch.py

启动节点关键代码

    slam_launch_file = os.path.join(slam_toolbox_dir, 'launch', 'online_sync_launch.py')
    start_slam_toolbox_cmd = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(slam_launch_file),
        launch_arguments={'use_sim_time': use_sim_time}.items())

    start_map_saver_server_cmd = Node(
            package='nav2_map_server',
            executable='map_saver_server',
            output='screen',
            parameters=[configured_params])

start_slam_toolbox_cmd一级套娃，启动了online_sync_launch.py

online_sync_launch.py关键代码

 start_sync_slam_toolbox_node = Node(
        parameters=[
          actual_params_file,
          {'use_sim_time': use_sim_time}
        ],
        package='slam_toolbox',
        executable='sync_slam_toolbox_node',
        name='slam_toolbox',
        output='screen')

executable='sync_slam_toolbox_node', #启动了slam工具箱同步定位建图

executable='map_saver_server', #启动了地图储存服务节点

作用：slam同步定位建图，储存地图。

3 navigation_launch.py

启动节点关键代码

        Node(
            package='nav2_controller',
            executable='controller_server',
            output='screen',
            parameters=[configured_params],
            remappings=remappings),

        Node(
            package='nav2_planner',
            executable='planner_server',
            name='planner_server',
            output='screen',
            parameters=[configured_params],
            remappings=remappings),

        Node(
            package='nav2_recoveries',
            executable='recoveries_server',
            name='recoveries_server',
            output='screen',
            parameters=[configured_params],
            remappings=remappings),

        Node(
            package='nav2_bt_navigator',
            executable='bt_navigator',
            name='bt_navigator',
            output='screen',
            parameters=[configured_params],
            remappings=remappings),

        Node(
            package='nav2_waypoint_follower',
            executable='waypoint_follower',
            name='waypoint_follower',
            output='screen',
            parameters=[configured_params],
            remappings=remappings),

executable='controller_server', #启动机器人控制器

executable='planner_server', #启动机器人规划器

executable='recoveries_server', #启动机器人恢复服务器

executable='bt_navigator', #启动行为树

executable='waypoint_follower', #启动路点跟随

作用：启动导航核心节点，行为树规划器控制器恢复器路点跟随

4 rviz_launch.py

启动节点关键代码

start_rviz_cmd = Node(
        condition=UnlessCondition(use_namespace),
        package='rviz2',
        executable='rviz2',
        name='rviz2',
        arguments=['-d', rviz_config_file],
        output='screen')

executable='rviz2',

作用：启动rviz2可视化机器人及导航

5 bringup_launch.py

启动节点关键代码

        IncludeLaunchDescription(
            PythonLaunchDescriptionSource(os.path.join(launch_dir, 'slam_launch.py')),
            condition=IfCondition(slam),
            launch_arguments={'namespace': namespace,
                              'use_sim_time': use_sim_time,
                              'autostart': autostart,
                              'params_file': params_file}.items()),

        IncludeLaunchDescription(
            PythonLaunchDescriptionSource(os.path.join(launch_dir,
                                                       'localization_launch.py')),
            condition=IfCondition(PythonExpression(['not ', slam])),
            launch_arguments={'namespace': namespace,
                              'map': map_yaml_file,
                              'use_sim_time': use_sim_time,
                              'autostart': autostart,
                              'params_file': params_file,
                              'use_lifecycle_mgr': 'false'}.items()),

        IncludeLaunchDescription(
            PythonLaunchDescriptionSource(os.path.join(launch_dir, 'navigation_launch.py')),
            launch_arguments={'namespace': namespace,
                              'use_sim_time': use_sim_time,
                              'autostart': autostart,
                              'params_file': params_file,
                              'default_bt_xml_filename': default_bt_xml_filename,
                              'use_lifecycle_mgr': 'false',
                              'map_subscribe_transient_local': 'true'}.items()),

通过条件选择condition=IfCondition(slam),二选一启动：

slam_launch.py

localization_launch.py

'slam',default_value='False 所以默认启动 localization_launch.py

启动 navigation_launch.py

作用：这是一个通过launch文件套娃集齐了nav2导航需要的所有节点，按默认设置启动地图服务，在地图上给机器人定位，启动导航行为树规划器控制器恢复器路点跟随。

如果没有实体机器人，开启gazebo仿真机器人+bringup_launch.py+rviz_launch.py

如果有实体机器人，启动机器人底盘程序+bringup_launch.py+rviz_launch.py nav2导航服务全部节点就都集齐了，可以开始自由导航了。

如果想同时建图并导航只需给launch文件加参数，启动 bringup_launch.py slam:=True 这时在陌生环境不需要提供地图，程序会一边建图，一边导航。

注意仿真机器人所有节点 use_sim_time=true （启用仿真时间），实体机器人所有节点use_sim_time=false （不启用仿真时间），时间设置错了会出现莫名其妙的问题。

6 spawn_tb3_launch.py

启动节点关键代码

            package='nav2_gazebo_spawner',
            executable='nav2_gazebo_spawner',
            output='screen',
            arguments=[
                '--robot_name', launch.substitutions.LaunchConfiguration('robot_name'),
                '--robot_namespace', launch.substitutions.LaunchConfiguration('robot_name'),
                '--turtlebot_type', launch.substitutions.LaunchConfiguration('turtlebot_type'),
                '-x', launch.substitutions.LaunchConfiguration('x_pose'),
                '-y', launch.substitutions.LaunchConfiguration('y_pose'),
                '-z', launch.substitutions.LaunchConfiguration('z_pose')]),

executable='nav2_gazebo_spawner',

作用：启动gazebo产卵节点，在gazebo规定位置生成机器人

7 tb3_simulation_launch.py

启动节点关键代码

     start_gazebo_server_cmd = ExecuteProcess(
        condition=IfCondition(use_simulator),
        cmd=['gzserver', '-s', 'libgazebo_ros_init.so', world],
        cwd=[launch_dir], output='screen')

    start_gazebo_client_cmd = ExecuteProcess(
        condition=IfCondition(PythonExpression([use_simulator, ' and not ', headless])),
        cmd=['gzclient'],
        cwd=[launch_dir], output='screen')

   
   
    start_robot_state_publisher_cmd = Node(
        condition=IfCondition(use_robot_state_pub),
        package='robot_state_publisher',
        executable='robot_state_publisher',
        name='robot_state_publisher',
        namespace=namespace,
        output='screen',
        parameters=[{'use_sim_time': use_sim_time}],
        remappings=remappings,
        arguments=[urdf])

    rviz_cmd = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(os.path.join(launch_dir, 'rviz_launch.py')),
        condition=IfCondition(use_rviz),
        launch_arguments={'namespace': '',
                          'use_namespace': 'False',
                          'rviz_config': rviz_config_file}.items())

    bringup_cmd = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(os.path.join(launch_dir, 'bringup_launch.py')),
        launch_arguments={'namespace': namespace,
                          'use_namespace': use_namespace,
                          'slam': slam,
                          'map': map_yaml_file,
                          'use_sim_time': use_sim_time,
                          'params_file': params_file,
                          'default_bt_xml_filename': default_bt_xml_filename,
                          'autostart': autostart}.items())

start_gazebo_server_cmd #启动gazebo服务端，加载ros插件

start_gazebo_client_cmd #启动gazebo客户端

executable='robot_state_publisher', #启动机器人模型

PythonLaunchDescriptionSource(os.path.join(launch_dir, 'rviz_launch.py')), #启动rviz2显示机器人

PythonLaunchDescriptionSource(os.path.join(launch_dir, 'bringup_launch.py')), #启动导航

作用：生成gazebo仿真机器人，启动导航服务，rviz显示机器人导航

7 multi_tb3_simulation_launch.py

作用：这个我也没有仔细研究，总体来说是在gazebo仿真环境生成多个机器人并导航。