Skip to content
Anima Mundi Anima Mundi

Launch 文件不同格式

ROS 2 launch 文件支持 XML、YAML 和 Python 三种格式。本指南将用三种格式实现同一功能，并讨论各自的适用场景。

Launch 文件示例

Section titled “Launch 文件示例”

下面是用 XML、YAML 和 Python 编写的 launch 文件。 每个 launch 文件完成以下操作：

  • 设置带默认值的命令行参数
  • 包含另一个 launch 文件
  • 在另一个命名空间中包含另一个 launch 文件
  • 启动一个节点并设置其命名空间
  • 启动一个节点，设置其命名空间，并通过 args 设置参数
  • 启动一个节点并将消息从一个话题重映射到另一个话题

XML 版本

Section titled “XML 版本”
<?xml version="1.0" encoding="UTF-8"?>
<launch>
  <!-- args that can be set from the command line or a default will be used -->
  <arg name="background_r" default="0" />
  <arg name="background_g" default="255" />
  <arg name="background_b" default="0" />
  <arg name="chatter_py_ns" default="chatter/py/ns" />
  <arg name="chatter_xml_ns" default="chatter/xml/ns" />
  <arg name="chatter_yaml_ns" default="chatter/yaml/ns" />


  <!-- include another launch file -->
  <include file="$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.py" />


  <!-- include a Python launch file in the chatter_py_ns namespace-->
  <group>
    <!-- push_ros_namespace to set namespace of included nodes -->
    <push_ros_namespace namespace="$(var chatter_py_ns)" />
    <include file="$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.py" />
  </group>


  <!-- include a xml launch file in the chatter_xml_ns namespace-->
  <group>
    <!-- push_ros_namespace to set namespace of included nodes -->
    <push_ros_namespace namespace="$(var chatter_xml_ns)" />
    <include file="$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.xml" />
  </group>


  <!-- include a yaml launch file in the chatter_yaml_ns namespace-->
  <group>
    <!-- push_ros_namespace to set namespace of included nodes -->
    <push_ros_namespace namespace="$(var chatter_yaml_ns)" />
    <include file="$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.yaml" />
  </group>


  <!-- start a turtlesim_node in the turtlesim1 namespace and use args to set the log level -->
  <node pkg="turtlesim" exec="turtlesim_node" name="sim" namespace="turtlesim1" args="--ros-args --log-level info" />


  <!-- start another turtlesim_node in the turtlesim2 namespace, use ros_args to set the log level, and child elements to set the parameters -->
  <node pkg="turtlesim" exec="turtlesim_node" name="sim" namespace="turtlesim2" ros_args="--log-level warn">
    <param name="background_r" value="$(var background_r)" />
    <param name="background_g" value="$(var background_g)" />
    <param name="background_b" value="$(var background_b)" />
  </node>


  <!-- perform remap so both turtles listen to the same command topic -->
  <node pkg="turtlesim" exec="mimic" name="mimic">
    <remap from="/input/pose" to="/turtlesim1/turtle1/pose" />
    <remap from="/output/cmd_vel" to="/turtlesim2/turtle1/cmd_vel" />
  </node>
</launch>

YAML 版本

Section titled “YAML 版本”
%YAML 1.2
---
launch:
# args that can be set from the command line or a default will be used
- arg:
    name: "background_r"
    default: "0"
- arg:
    name: "background_g"
    default: "255"
- arg:
    name: "background_b"
    default: "0"
- arg:
    name: "chatter_py_ns"
    default: "chatter/py/ns"
- arg:
    name: "chatter_xml_ns"
    default: "chatter/xml/ns"
- arg:
    name: "chatter_yaml_ns"
    default: "chatter/yaml/ns"


# include another launch file
- include:
    file: "$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.py"


# include a Python launch file in the chatter_py_ns namespace
- group:
    - push_ros_namespace:
        namespace: "$(var chatter_py_ns)"
    - include:
        file: "$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.py"


# include a xml launch file in the chatter_xml_ns namespace
- group:
    - push_ros_namespace:
        namespace: "$(var chatter_xml_ns)"
    - include:
        file: "$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.xml"


# include a yaml launch file in the chatter_yaml_ns namespace
- group:
    - push_ros_namespace:
        namespace: "$(var chatter_yaml_ns)"
    - include:
        file: "$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener_launch.yaml"


# start a turtlesim_node in the turtlesim1 namespace and use args to set the log level
- node:
    pkg: "turtlesim"
    exec: "turtlesim_node"
    name: "sim"
    namespace: "turtlesim1"
    args: "--ros-args --log-level info"


# start another turtlesim_node in the turtlesim2 namespace, use ros_args to set the log level, and param to set the parameters
- node:
    pkg: "turtlesim"
    exec: "turtlesim_node"
    name: "sim"
    namespace: "turtlesim2"
    ros_args: "--log-level warn"
    param:
    - name: "background_r"
      value: "$(var background_r)"
    - name: "background_g"
      value: "$(var background_g)"
    - name: "background_b"
      value: "$(var background_b)"


# perform remap so both turtles listen to the same command topic
- node:
    pkg: "turtlesim"
    exec: "mimic"
    name: "mimic"
    remap:
    - from: "/input/pose"
      to: "/turtlesim1/turtle1/pose"
    - from: "/output/cmd_vel"
      to: "/turtlesim2/turtle1/cmd_vel"

Python 版本

Section titled “Python 版本”
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, GroupAction, IncludeLaunchDescription
from launch.substitutions import LaunchConfiguration, PathJoinSubstitution
from launch_ros.actions import Node, PushROSNamespace
from launch_ros.substitutions import FindPackageShare




def generate_launch_description():
    launch_dir = PathJoinSubstitution([FindPackageShare('demo_nodes_cpp'), 'launch', 'topics'])
    return LaunchDescription([
        # args that can be set from the command line or a default will be used
        DeclareLaunchArgument('background_r', default_value='0'),
        DeclareLaunchArgument('background_g', default_value='255'),
        DeclareLaunchArgument('background_b', default_value='0'),
        DeclareLaunchArgument('chatter_py_ns', default_value='chatter/py/ns'),
        DeclareLaunchArgument('chatter_xml_ns', default_value='chatter/xml/ns'),
        DeclareLaunchArgument('chatter_yaml_ns', default_value='chatter/yaml/ns'),


        # include another launch file
        IncludeLaunchDescription(
            PathJoinSubstitution([launch_dir, 'talker_listener_launch.py'])
        ),


        # include a Python launch file in the chatter_py_ns namespace
        GroupAction(
            actions=[
                # push_ros_namespace first to set namespace of included nodes for following actions
                PushROSNamespace('chatter_py_ns'),
                IncludeLaunchDescription(
                    PathJoinSubstitution([launch_dir, 'talker_listener_launch.py'])),
            ]
        ),


        # include a xml launch file in the chatter_xml_ns namespace
        GroupAction(
            actions=[
                # push_ros_namespace first to set namespace of included nodes for following actions
                PushROSNamespace('chatter_xml_ns'),
                IncludeLaunchDescription(
                    PathJoinSubstitution([launch_dir, 'talker_listener_launch.xml'])),
            ]
        ),


        # include a yaml launch file in the chatter_yaml_ns namespace
        GroupAction(
            actions=[
                # push_ros_namespace first to set namespace of included nodes for following actions
                PushROSNamespace('chatter_yaml_ns'),
                IncludeLaunchDescription(
                    PathJoinSubstitution([launch_dir, 'talker_listener_launch.yaml'])),
            ]
        ),


        # start a turtlesim_node in the turtlesim1 namespace and use arguments to set the log level
        Node(
            package='turtlesim',
            namespace='turtlesim1',
            executable='turtlesim_node',
            name='sim',
            arguments=['--ros-args', '--log-level', 'info']
        ),


        # start another turtlesim_node in the turtlesim2 namespace,
        # use ros_arguments to set the log level, and parameters to set the parameters
        Node(
            package='turtlesim',
            namespace='turtlesim2',
            executable='turtlesim_node',
            name='sim',
            ros_arguments=['--log-level', 'warn'],
            parameters=[{
                'background_r': LaunchConfiguration('background_r'),
                'background_g': LaunchConfiguration('background_g'),
                'background_b': LaunchConfiguration('background_b'),
            }]
        ),


        # perform remap so both turtles listen to the same command topic
        Node(
            package='turtlesim',
            executable='mimic',
            name='mimic',
            remappings=[
                ('/input/pose', '/turtlesim1/turtle1/pose'),
                ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),
            ]
        ),
    ])

从命令行使用 Launch 文件

Section titled “从命令行使用 Launch 文件”

启动

Section titled “启动”

上面的任何 launch 文件都可以用 ros2 launch 运行。要在本地试用，你可以创建一个新包，然后使用：

Terminal window
ros2 launch <package_name> <launch_file_name>

或者通过指定 launch 文件的路径直接运行：

Terminal window
ros2 launch <path_to_launch_file>

设置参数

Section titled “设置参数”

要向 launch 文件传递参数，请使用 key:=value 语法。例如，设置 background_r 的值：

Terminal window
ros2 launch <package_name> <launch_file_name> background_r:=255

或：

Terminal window
ros2 launch <path_to_launch_file> background_r:=255

控制乌龟

Section titled “控制乌龟”

要测试重映射是否正常工作，你可以在另一个终端中运行以下命令来控制乌龟：

Terminal window
ros2 run turtlesim turtle_teleop_key --ros-args --remap __ns:=/turtlesim1

XML、YAML 还是 Python：应该使用哪种？

Section titled “XML、YAML 还是 Python：应该使用哪种？”

注意： ROS 1 中的 launch 文件是用 XML 编写的，因此对于从 ROS 1 迁移过来的用户来说，XML 可能是最熟悉的。 要了解变化内容，你可以访问 迁移 Launch 文件。

对于大多数应用来说，选择哪种 ROS 2 launch 格式主要取决于个人偏好。不过，如果 XML 或 YAML 无法满足你对灵活性的需求，可以选择用 Python 编写。Python 格式主要有两大优势：

  • Python 是一种脚本语言，你可以在 launch 文件中直接利用 Python 语言本身及其丰富的标准库。
  • ros2/launch（通用 launch 功能）和 ros2/launch_ros（ROS 2 特定的 launch 功能）都是用 Python 编写的，因此你可以接触到 XML 和 YAML 可能未暴露的底层 launch 功能。

不过，Python 格式的 launch 文件往往比 XML 或 YAML 更复杂、更冗长。