【ROS2概念】系列(十一)——ROS2中的launch启动文件

目录

• 一、ROS2 launch文件简介
• 二、ROS2 launch语法规则
  • 2.1 导入模块
  • 2.2 参数设置
  • 2.3 构建节点
  • 2.4 启动命令
• 三、launch文件中常用到的语句
  • 3.1 获取路径
  • 3.2 设置环境变量
  • 3.3 获取环境变量的值
  • 3.4 包含另外一个python launch文件
  • 3.5 给一组节点添加同一个命名空间
  • 3.6 在launch文件中执行命令
  • 3.7 临时添加parameters的方法
  • 3.8 包含多个其他launch文件
• 四、典型launch文件解析
  • 4.1 turtlebot3启动导航的launch文件
  • 4.2 turtlebot3启动建图
  • 4.3 Navigation2启动定位程序

一、ROS2 launch文件简介

ROS2中的launch文件可以用Python、xml、yaml来写，官方推荐的是使用python来写。

launch文件可以同时配置和启动多个ros节点，使用python编写后，可以执行一些其他的任务（比如新建目录，配置环境变量）。

注意：ROS2与ROS1不同，修改launch文件后也需要重新编译！为避免这种情况，需要在编译时添加选项--symlink-install选项，这样在修改了launch文件，不用编译也是生效的。

二、ROS2 launch语法规则

ROS2的launch文件可分为四个部分，分别是

• 导入模块
• 参数声明
• 构建节点
• 启动命令

2.1 导入模块

ROS2 launch使用python文件编写，需要导入ROS2的包，以便使用ROS2的API对相应的节点进行设置。

from launch import LaunchDescription
import launch_ros.actions

2.2 参数设置

• launch文件可以传值给下级launch文件

• 访问launch文件的入口参数
  有时我们希望能访问到launch文件的入口参数，但是它们通常是LaunchConfiguration类型。常见的形式如下：

use_sim_time = LaunchConfiguration("use_sim_time")

这里的use_sim_time是LaunchConfiguration类型的，不能直接用于if判断。如果你直接按如下方式操作：

if use_sim_time
    print(use_sim_time)

通常会打印下面的信息，并且if的判句永远是True。

我们可以用OpaqueFunction函数来处理。下面是一个示例：

from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, OpaqueFunction
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node, SetParameter


def launch_setup(context, *args, **kwargs):
    use_sim_time = LaunchConfiguration("use_sim_time")
    use_sim_time_str = use_sim_time.perform(context)
    print(f"use_sim_time: {use_sim_time.perform(context)}")
    set_use_sim_time = SetParameter(name="use_sim_time", value=use_sim_time)

    node = Node(
        package="examples_rclcpp_minimal_publisher",
        executable="publisher_lambda",
        name="publisher",
    )

    return [
        set_use_sim_time,
        node,
    ]


def generate_launch_description():
    return LaunchDescription(
        [
            DeclareLaunchArgument("use_sim_time", default_value="false"),
            OpaqueFunction(function=launch_setup),
        ]
    )

其中的use_sim_time_str = use_sim_time.perform(context)将参数内容转换为字符串并返回。例如：use_sim_time的值是True的话，use_sim_time_str将是True字符串。

2.3 构建节点

这个部分主要是写明需要启动哪些节点。并且将节点需要的参数配置好。

 # Nodes launching commands

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

    start_lifecycle_manager_cmd = Node(
            package='nav2_lifecycle_manager',
            executable='lifecycle_manager',
            name='lifecycle_manager_slam',
            output='screen',
            parameters=[{'use_sim_time': use_sim_time},
                        {'autostart': autostart},
                        {'node_names': lifecycle_nodes}])
                        
    start_rviz_cmd = Node(
            package='rviz2',
            executable='rviz2',
            name='rviz2',
            arguments=['-d', rviz_config_dir],
            parameters=[{'use_sim_time': use_sim_time}],
            output='screen')
            
    # perform remap so both turtles listen to the same command topic
    forward_turtlesim_commands_to_second_turtlesim_node = Node(
            package='turtlesim',
            executable='mimic',
            name='mimic',
            remappings=[
                ('/input/pose', '/turtlesim1/turtle1/pose'),
                ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),
            ]
        )

节点中有8个参数。如果不需要配置可以不写，让它保持默认值。

前面已经提到namespace是为了让节点处于不同的命名空间内，这一点可以在上面的图中体现出来。output='screen' 的意思是执行的节点打印的log直接在窗口中输出。除此之外，log也会存在~/.ros/log 目录下（这是默认路径，其实也是可以配置的）。

补充一下其他几个参数

package='nav2_lifecycle_manager' 是指这个节点在哪个ros2包里。executable='lifecycle_manager' 指明需要运行的程序是ros2包中的哪一个执行文件（一个ros包是可以包含多个执行文件的）。

parameters 中可以配置node的参数。这些参数通常会在参数声明部分赋好值，这里直接传给节点即可。同时这里也可以直接传入yaml参数文件。arguments=['-d', rviz_config_dir] 是节点内部实现的参数。通常通过main函数的行参获取。比如下面这个命令：

run rviz2 rviz2 -d $(ros2 pkg prefix --share turtle_tf2_py)/rviz/turtle_rviz.rviz

其中-d就是通过main函数传入进去的参数。

下面的参数用于将两个话题名称对等。左边是节点内部代码内写明的，右边为系统中其他节点提供的话题。

        remappings=[
            ('/input/pose', '/turtlesim1/turtle1/pose'),
            ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),
        ]

给节点配置参数文件的示例

import os

from ament_index_python.packages import get_package_share_directory

from launch import LaunchDescription
from launch_ros.actions import Node


def generate_launch_description():
   config = os.path.join(
      get_package_share_directory('launch_tutorial'),
      'config',
      'turtlesim.yaml'
      )

   return LaunchDescription([
      Node(
         package='turtlesim',
         executable='turtlesim_node',
         namespace='turtlesim2',
         name='sim',
         parameters=[config]
      )
   ])

2.4 启动命令

这一部分只需将前面配置好的命令，用add_action方法加入即可。当然，这里其实有两种写法。一种是下面这种。

    # Create the launch description and populate
    ld = LaunchDescription()

    # Set environment variables
    ld.add_action(stdout_linebuf_envvar)

    # Declare the launch options
    ld.add_action(declare_namespace_cmd)
    ld.add_action(declare_use_namespace_cmd)
    ld.add_action(declare_slam_cmd)
    ld.add_action(declare_map_yaml_cmd)
    ld.add_action(declare_use_sim_time_cmd)
    ld.add_action(declare_params_file_cmd)
    ld.add_action(declare_autostart_cmd)

    # Add the actions to launch all of the navigation nodes
    ld.add_action(bringup_cmd_group)

    return ld

另一种是直接将启动的内容写在return语句中。

    return LaunchDescription([
        DeclareLaunchArgument(
            'map',
            default_value=map_dir,
            description='Full path to map file to load'),

        DeclareLaunchArgument(
            'params_file',
            default_value=param_dir,
            description='Full path to param file to load'),

        DeclareLaunchArgument(
            'use_sim_time',
            default_value='false',
            description='Use simulation (Gazebo) clock if true'),

        IncludeLaunchDescription(
            PythonLaunchDescriptionSource([nav2_launch_file_dir, '/bringup_launch.py']),
            launch_arguments={
                'map': map_dir,
                'use_sim_time': use_sim_time,
                'params_file': param_dir}.items(),
        ),

        Node(
            package='rviz2',
            executable='rviz2',
            name='rviz2',
            arguments=['-d', rviz_config_dir],
            parameters=[{'use_sim_time': use_sim_time}],
            output='screen'),
    ])

三、launch文件中常用到的语句

3.1 获取路径

import os
from ament_index_python.packages import get_package_share_directory

# Get the launch directory
bringup_dir = get_package_share_directory('nav2_bringup')#获取包的路径
launch_dir = os.path.join(bringup_dir, 'launch')#组合包内路径

3.2 设置环境变量

from launch.actions import SetEnvironmentVariable

stdout_linebuf_envvar = SetEnvironmentVariable('RCUTILS_LOGGING_BUFFERED_STREAM', '1')

3.3 获取环境变量的值

import os
TURTLEBOT3_MODEL = os.environ['TURTLEBOT3_MODEL']

3.4 包含另外一个python launch文件

from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource

IncludeLaunchDescription(
    PythonLaunchDescriptionSource([nav2_launch_file_dir, '/bringup_launch.py']),
    launch_arguments={
        'map': map_dir,
        'use_sim_time': use_sim_time,
        'params_file': param_dir}.items(), #这里给内嵌的python launch文件传入参数
),

3.5 给一组节点添加同一个命名空间

from launch.actions import GroupAction
from launch_ros.actions import PushRosNamespace

   ...
   turtlesim_world_2 = IncludeLaunchDescription(
      PythonLaunchDescriptionSource([os.path.join(
         get_package_share_directory('launch_tutorial'), 'launch'),
         '/turtlesim_world_2.launch.py'])
      )
   turtlesim_world_2_with_namespace = GroupAction(
     actions=[
         PushRosNamespace('turtlesim2'),
         turtlesim_world_2,
      ]
   )

3.6 在launch文件中执行命令

from launch_ros.actions import Node

from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, ExecuteProcess, TimerAction
from launch.conditions import IfCondition
from launch.substitutions import LaunchConfiguration, PythonExpression


def generate_launch_description():
    turtlesim_ns = LaunchConfiguration('turtlesim_ns')
    use_provided_red = LaunchConfiguration('use_provided_red')
    new_background_r = LaunchConfiguration('new_background_r')

    turtlesim_ns_launch_arg = DeclareLaunchArgument(
        'turtlesim_ns',
        default_value='turtlesim1'
    )
    use_provided_red_launch_arg = DeclareLaunchArgument(
        'use_provided_red',
        default_value='False'
    )
    new_background_r_launch_arg = DeclareLaunchArgument(
        'new_background_r',
        default_value='200'
    )

    turtlesim_node = Node(
        package='turtlesim',
        namespace=turtlesim_ns,
        executable='turtlesim_node',
        name='sim'
    )
    spawn_turtle = ExecuteProcess(
        cmd=[[
            'ros2 service call ',
            turtlesim_ns,
            '/spawn ',
            'turtlesim/srv/Spawn ',
            '"{x: 2, y: 2, theta: 0.2}"'
        ]],
        shell=True
    )
    change_background_r = ExecuteProcess(
        cmd=[[
            'ros2 param set ',
            turtlesim_ns,
            '/sim background_r ',
            '120'
        ]],
        shell=True
    )
    change_background_r_conditioned = ExecuteProcess(
        condition=IfCondition(
            PythonExpression([
                new_background_r,
                ' == 200',
                ' and ',
                use_provided_red
            ])
        ),
        cmd=[[
            'ros2 param set ',
            turtlesim_ns,
            '/sim background_r ',
            new_background_r
        ]],
        shell=True
    )

    return LaunchDescription([
        turtlesim_ns_launch_arg,
        use_provided_red_launch_arg,
        new_background_r_launch_arg,
        turtlesim_node,
        spawn_turtle,
        change_background_r,
        TimerAction(
            period=2.0,
            actions=[change_background_r_conditioned],
        )
    ])

3.7 临时添加parameters的方法

parameters=[{
    "background_r": LaunchConfiguration('background_r'),
    "background_g": LaunchConfiguration('background_g'),
    "background_b": LaunchConfiguration('background_b'),
}]

parameters=[{'use_sim_time': use_sim_time},
    {'autostart': autostart},
    {'node_names': lifecycle_nodes}
])

3.8 包含多个其他launch文件

import os

from ament_index_python.packages import get_package_share_directory

from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource


def generate_launch_description():
   turtlesim_world_1 = IncludeLaunchDescription(
      PythonLaunchDescriptionSource([os.path.join(
         get_package_share_directory('launch_tutorial'), 'launch'),
         '/turtlesim_world_1.launch.py'])
      )
   turtlesim_world_2 = IncludeLaunchDescription(
      PythonLaunchDescriptionSource([os.path.join(
         get_package_share_directory('launch_tutorial'), 'launch'),
         '/turtlesim_world_2.launch.py'])
      )
   broadcaster_listener_nodes = IncludeLaunchDescription(
      PythonLaunchDescriptionSource([os.path.join(
         get_package_share_directory('launch_tutorial'), 'launch'),
         '/broadcaster_listener.launch.py']),
      launch_arguments={'target_frame': 'carrot1'}.items(),
      )
   mimic_node = IncludeLaunchDescription(
      PythonLaunchDescriptionSource([os.path.join(
         get_package_share_directory('launch_tutorial'), 'launch'),
         '/mimic.launch.py'])
      )
   fixed_frame_node = IncludeLaunchDescription(
      PythonLaunchDescriptionSource([os.path.join(
         get_package_share_directory('launch_tutorial'), 'launch'),
         '/fixed_broadcaster.launch.py'])
      )
   rviz_node = IncludeLaunchDescription(
      PythonLaunchDescriptionSource([os.path.join(
         get_package_share_directory('launch_tutorial'), 'launch'),
         '/turtlesim_rviz.launch.py'])
      )

   return LaunchDescription([
      turtlesim_world_1,
      turtlesim_world_2,
      broadcaster_listener_nodes,
      mimic_node,
      fixed_frame_node,
      rviz_node
   ])

四、典型launch文件解析

4.1 turtlebot3启动导航的launch文件

存放路径：turtlebot3/turtlebot3_navigation2/launch/navigation2.launch.py

import os

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

TURTLEBOT3_MODEL = os.environ['TURTLEBOT3_MODEL']


def generate_launch_description():
    use_sim_time = LaunchConfiguration('use_sim_time', default='false')
    map_dir = LaunchConfiguration(
        'map',
        default=os.path.join(
            get_package_share_directory('turtlebot3_navigation2'),
            'map',
            'map.yaml'))

    param_file_name = TURTLEBOT3_MODEL + '.yaml'

    param_dir = LaunchConfiguration(
        'params_file',
        default=os.path.join(
            get_package_share_directory('turtlebot3_navigation2'),
            'param',
            param_file_name))

    nav2_launch_file_dir = os.path.join(get_package_share_directory('nav2_bringup'), 'launch')

    rviz_config_dir = os.path.join(
        get_package_share_directory('nav2_bringup'),
        'rviz',
        'nav2_default_view.rviz')

    return LaunchDescription([
        DeclareLaunchArgument(
            'map',
            default_value=map_dir,
            description='Full path to map file to load'),

        DeclareLaunchArgument(
            'params_file',
            default_value=param_dir,
            description='Full path to param file to load'),

        DeclareLaunchArgument(
            'use_sim_time',
            default_value='false',
            description='Use simulation (Gazebo) clock if true'),

        IncludeLaunchDescription(
            PythonLaunchDescriptionSource([nav2_launch_file_dir, '/bringup_launch.py']),
            launch_arguments={
                'map': map_dir,
                'use_sim_time': use_sim_time,
                'params_file': param_dir}.items(),
        ),

        Node(
            package='rviz2',
            executable='rviz2',
            name='rviz2',
            arguments=['-d', rviz_config_dir],
            parameters=[{'use_sim_time': use_sim_time}],
            output='screen'),
    ])

4.2 turtlebot3启动建图

存放路径：turtlebot3/turtlebot3_cartographer/launch/cartographer.launch.py

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


def generate_launch_description():
    use_sim_time = LaunchConfiguration('use_sim_time', default='false')
    turtlebot3_cartographer_prefix = get_package_share_directory('turtlebot3_cartographer')
    cartographer_config_dir = LaunchConfiguration('cartographer_config_dir', default=os.path.join(
                                                  turtlebot3_cartographer_prefix, 'config'))
    configuration_basename = LaunchConfiguration('configuration_basename',
                                                 default='turtlebot3_lds_2d.lua')

    resolution = LaunchConfiguration('resolution', default='0.05')
    publish_period_sec = LaunchConfiguration('publish_period_sec', default='1.0')

    rviz_config_dir = os.path.join(get_package_share_directory('turtlebot3_cartographer'),
                                   'rviz', 'tb3_cartographer.rviz')

    return LaunchDescription([
        DeclareLaunchArgument(
            'cartographer_config_dir',
            default_value=cartographer_config_dir,
            description='Full path to config file to load'),
        DeclareLaunchArgument(
            'configuration_basename',
            default_value=configuration_basename,
            description='Name of lua file for cartographer'),
        DeclareLaunchArgument(
            'use_sim_time',
            default_value='false',
            description='Use simulation (Gazebo) clock if true'),

        Node(
            package='cartographer_ros',
            executable='cartographer_node',
            name='cartographer_node',
            output='screen',
            parameters=[{'use_sim_time': use_sim_time}],
            arguments=['-configuration_directory', cartographer_config_dir,
                       '-configuration_basename', configuration_basename]),

        DeclareLaunchArgument(
            'resolution',
            default_value=resolution,
            description='Resolution of a grid cell in the published occupancy grid'),

        DeclareLaunchArgument(
            'publish_period_sec',
            default_value=publish_period_sec,
            description='OccupancyGrid publishing period'),

        IncludeLaunchDescription(
            PythonLaunchDescriptionSource([ThisLaunchFileDir(), '/occupancy_grid.launch.py']),
            launch_arguments={'use_sim_time': use_sim_time, 'resolution': resolution,
                              'publish_period_sec': publish_period_sec}.items(),
        ),

        Node(
            package='rviz2',
            executable='rviz2',
            name='rviz2',
            arguments=['-d', rviz_config_dir],
            parameters=[{'use_sim_time': use_sim_time}],
            output='screen'),
    ])

4.3 Navigation2启动定位程序

路径：navigation2/nav2_bringup/bringup/launch/localization_launch.py

import os

from ament_index_python.packages import get_package_share_directory

from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, SetEnvironmentVariable
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node
from nav2_common.launch import RewrittenYaml


def generate_launch_description():
    # Get the launch directory
    bringup_dir = get_package_share_directory('nav2_bringup')

    namespace = LaunchConfiguration('namespace')
    map_yaml_file = LaunchConfiguration('map')
    use_sim_time = LaunchConfiguration('use_sim_time')
    autostart = LaunchConfiguration('autostart')
    params_file = LaunchConfiguration('params_file')
    lifecycle_nodes = ['map_server', 'amcl']

    # Map fully qualified names to relative ones so the node's namespace can be prepended.
    # In case of the transforms (tf), currently, there doesn't seem to be a better alternative
    # https://github.com/ros/geometry2/issues/32
    # https://github.com/ros/robot_state_publisher/pull/30
    # TODO(orduno) Substitute with `PushNodeRemapping`
    #              https://github.com/ros2/launch_ros/issues/56
    remappings = [('/tf', 'tf'),
                  ('/tf_static', 'tf_static')]

    # Create our own temporary YAML files that include substitutions
    param_substitutions = {
        'use_sim_time': use_sim_time,
        'yaml_filename': map_yaml_file}

    configured_params = RewrittenYaml(
        source_file=params_file,
        root_key=namespace,
        param_rewrites=param_substitutions,
        convert_types=True)

    return LaunchDescription([
        # Set env var to print messages to stdout immediately
        SetEnvironmentVariable('RCUTILS_LOGGING_BUFFERED_STREAM', '1'),

        DeclareLaunchArgument(
            'namespace', default_value='',
            description='Top-level namespace'),

        DeclareLaunchArgument(
            'map',
            default_value=os.path.join(bringup_dir, 'maps', 'turtlebot3_world.yaml'),
            description='Full path to map yaml file to load'),

        DeclareLaunchArgument(
            'use_sim_time', default_value='false',
            description='Use simulation (Gazebo) clock if true'),

        DeclareLaunchArgument(
            'autostart', default_value='true',
            description='Automatically startup the nav2 stack'),

        DeclareLaunchArgument(
            'params_file',
            default_value=os.path.join(bringup_dir, 'params', 'nav2_params.yaml'),
            description='Full path to the ROS2 parameters file to use'),

        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),

        Node(
            package='nav2_lifecycle_manager',
            executable='lifecycle_manager',
            name='lifecycle_manager_localization',
            output='screen',
            parameters=[{'use_sim_time': use_sim_time},
                        {'autostart': autostart},
                        {'node_names': lifecycle_nodes}])
    ])