Launch 文件允许您同时启动和配置多个包含 ROS 2 节点的可执行文件。

launch文件编写

创建文件夹用来存储launch文件
```
mkdir launch
```
创建launch文件
```
touch launch/first.launch.py
```
编写launch文件 ```python from launch import LaunchDescription from launch_ros.actions import Node

def generate_launch_description(): return LaunchDescription([ Node( package=’turtlesim’, executable=’turtlesim_node’, ), Node( package=’turtlesim’, executable=’turtlesim_node’, ) ])


4. 进入launch文件夹启动launch文件
```bash
ros2 launch turtlesim_mimic_launch.py

python工程包中launch文件编写

在python工程包下创建launch文件夹编写launch文件
在setup.py中配置 ```python import os from glob import glob from setuptools import setup

package_name = ‘my_package’

setup(

# Other parameters ...
data_files=[
    # ... Other data files
    # Include all launch files. This is the most important line here!
    (os.path.join('share', package_name), glob('launch/*.launch.py'))
]

)

启动launch文件
```bash
ros2 launch 包名 launch文件名

指定节点名和命名空间

Node(
    package='turtlesim',
    namespace='tutle',
    executable='turtlesim_node',
    name='tutrtle1'
)

topic重定向

Node(                             # 配置一个节点的启动
            package='turtlesim',          # 节点所在的功能包
            namespace='turtlesim2',       # 节点所在的命名空间
            executable='turtlesim_node',  # 节点的可执行文件名
            name='sim',                    # 对节点重新命名
            remappings=[                  # 资源重映射列表
                ('/turtlesim2/turtle1/cmd_vel', '/my_cmd_vel'),         # 将/input/pose话题名修改为/turtlesim1/turtle1/pose
              ]
        ),

param参数修改

定义参数:

from launch import LaunchDescription                   # launch文件的描述类
from launch.actions import DeclareLaunchArgument       # 声明launch文件内使用的Argument类
from launch.substitutions import LaunchConfiguration, TextSubstitution
from launch_ros.actions import Node                    # 节点启动的描述类
def generate_launch_description():                     # 自动生成launch文件的函数
   background_r_launch_arg = DeclareLaunchArgument(
      'background_r', default_value=TextSubstitution(text='0')     # 创建一个Launch文件内参数（arg）background_r
   )
   background_g_launch_arg = DeclareLaunchArgument(
      'background_g', default_value=TextSubstitution(text='84')    # 创建一个Launch文件内参数（arg）background_g
   )
   background_b_launch_arg = DeclareLaunchArgument(
      'background_b', default_value=TextSubstitution(text='122')   # 创建一个Launch文件内参数（arg）background_b
   )

使用param参数:

return LaunchDescription([                                      # 返回launch文件的描述信息
      background_r_launch_arg,                                     # 调用以上创建的参数（arg）
      background_g_launch_arg,
      background_b_launch_arg,
      Node(                                                        # 配置一个节点的启动
         package='turtlesim',
         executable='turtlesim_node',                              # 节点所在的功能包
         name='sim',                                               # 对节点重新命名
         parameters=[{                                             # ROS参数列表
            'background_r': LaunchConfiguration('background_r'),   # 创建参数background_r
            'background_g': LaunchConfiguration('background_g'),   # 创建参数background_g
            'background_b': LaunchConfiguration('background_b'),   # 创建参数background_b
         }]
      ),
   ])

加载yaml参数文件

在package下创建config文件夹

在config下创建turtlesim.yaml

/turtlesim:
ros__parameters:
   background_b: 0
   background_g: 0
   background_r: 0

配置setup.py

(os.path.join('share', package_name, 'config'), glob(os.path.join('config', '*.*'))),

param文件路径

from ament_index_python.packages import get_package_share_directory  # 查询功能包路径的方法
config = os.path.join(              # 找到参数文件的完整路径
   get_package_share_directory('launch_pkg'),
   'config',
   'turtlesim.yaml'
   )

配置节点param文件

Node(                            # 配置一个节点的启动
  package='turtlesim',          # 节点所在的功能包
  executable='turtlesim_node',  # 节点的可执行文件名
  namespace='turtlesim2',       # 节点所在的命名空间
  name='sim',                   # 对节点重新命名
  parameters=[config]           # 加载参数文件
)

包含launch文件

找到另外一个launch文件 ```python

from launch_ros.actions import Node

import os

from ament_index_python.packages import get_package_share_directory # 查询功能包路径的方法

from launch import LaunchDescription # launch文件的描述类 from launch.actions import IncludeLaunchDescription # 节点启动的描述类 from launch.launch_description_sources import PythonLaunchDescriptionSource from launch.actions import GroupAction # launch文件中的执行动作 from launch_ros.actions import PushRosNamespace # ROS命名空间配置

parameter_yaml = IncludeLaunchDescription( # 包含指定路径下的另外一个launch文件 PythonLaunchDescriptionSource([os.path.join( get_package_share_directory(‘launch_pkg’)), ‘/first.launch.py’]) )


2. launch文件的描述中
```python
return LaunchDescription([
        parameter_yaml,
        Node(
            package='rviz2',
            executable='rviz2',
        )
    ])