ROS2学习笔记：Launch脚本

Launch可以实现同时启动多节点，这一不需要在终端一个一个窗口进行ros2 run

运行launch文件：

ros2 launch （功能包）（launch文件）

1 编写一个launch文件：

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
	return LaunchDescription([
		Node(
			package = 'learning_topic',
			executable = 'topic_helloworld_pub',
		),
		Node(
			package = 'learning_topic',
			executable = 'topic_helloworld_sub',
		),
	])
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1 from launch import LaunchDescription
from launch_ros.actions import Node
引入launch相关库，LaunchDescription描述了需要运行的节点

2 Node(
package = ‘learning_topic’,
executable = ‘topic_helloworld_pub’,
),
在LaunchDescription里声明要调用的节点，这里的调用内容可见（https://blog.csdn.net/Raine_Yang/article/details/125349724?spm=1001.2014.3001.5501）

3 def generate_launch_description():
generate_launch_description为自动生成Launch文件的函数

2 launch文件作为软件启动配置文件
（以rviz2为例）

ros2 run rviz2 rviz2 -d (launch文件完整路径)

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():
	rviz_config = os.path.join(
		get_package_share_directory('learning_launch'),
		'rviz',
		'turtle_rviz.rviz'
	)

	return LaunchDescription([
		Node(
			package = 'rviz2',
			executable = 'rviz2',
			name = 'rviz2',
			arguments = ['-d', rviz_config]
		)
	]) 
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1 rviz_config = os.path.join(
get_package_share_directory(‘learning_launch’),
‘rviz’,
‘turtle_rviz.rviz’
)
在这里标明配置文件路径，类似于使用-d后面的文件完整路径

2 name = ‘rviz2’,
对节点重命名为rviz2。在launch文件里可以覆盖节点在源码里的名称，进行重命名

3 launch文件对节点和话题的重命名

该程序会打开两个turtlesim程序

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
	return LaunchDescription([
		Node(
			package = 'turtlesim',
			namespace = 'turtlesim1',
			executable = 'turtlesim_node',
			name = 'sim'
		),
		Node(
			package = 'turtlesim',
			namespace = 'turtlesim2',
			executable = 'turtlesim_node'
			name = 'sim'
		),
		Node(
			package = ‘turtlesim’,
			executable = 'mimic'
			name = 'mimic',
			remappings = [
				('/input/pose', '/turtlesim1/turtle1/pose'),
				('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),
			]
		)
	])
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1 命名空间
namespace = ‘turtlesim1’,
namespace = ‘turtlesim2’,

ROS2里不允许同名节点，因此直接打开两个turtlesim会报错。可以在launch文件里加入namespace进行区分，如下图

2 话题重定向
remappings = [
(‘/input/pose’, ‘/turtlesim1/turtle1/pose’),
(‘/output/cmd_vel’, ‘/turtlesim2/turtle1/cmd_vel’),
]
用remappings可以对话题发布者和接受者进行重定向。这里把输入话题名/input/pose改为/turtlesim1/turtle1/pose，把输出话题’/output/cmd_vel改为/turtlesim2/turtle1/cmd_vel

这样turtlesim1的pose会被mimic节点订阅，再由mimic发布到turtlesim2.turtlesim2会执行和turtlesim1一样的动作

4 在launch文件里配置参数

from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration, TextSubstitution

from launch_ros.actions import Node

def generate_launch_description():
	background_r_launch_arg = DeclareLaunchArgument(
		'background_r', default_value = TextSubstitution(text = "0")
	)
	background_g_launch_arg = DeclareLaunchArgument(
		'background_g', default_value = TextSubstitution(text = "84")
	)
	background_b_launch_arg = DeclareLaunchArgument(
		'background_b', default_value = TextSubstitution(text = "122")
	)

	return LaunchDescription([
		background_r_launch_arg,
		background_g_launch_arg,
		background_b_launch_arg,
		Node(
			package = 'turtlesim',
			executable = 'turtlesim_node',
			name = 'sim',
			parameters = [{
				'background_r': LaunchConfiguration('background_r'),
				'background_g': LaunchConfiguration('background_g'),
				'background_b': LaunchConfiguration('background_b'),
			}]
		),
	])
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1 def generate_launch_description():
background_r_launch_arg = DeclareLaunchArgument(
‘background_r’, default_value = TextSubstitution(text = “0”)
)
background_g_launch_arg = DeclareLaunchArgument(
‘background_g’, default_value = TextSubstitution(text = “84”)
)
background_b_launch_arg = DeclareLaunchArgument(
‘background_b’, default_value = TextSubstitution(text = “122”)
)
创建launch文件内参数修改R G B数值

2 parameters = [{
‘background_r’: LaunchConfiguration(‘background_r’),
‘background_g’: LaunchConfiguration(‘background_g’),
‘background_b’: LaunchConfiguration(‘background_b’),
}]
在返回值里parameters修改参数

对参数yaml文件修改可以简化以上代码

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_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
   config = os.path.join(              # 找到参数文件的完整路径
      get_package_share_directory('learning_launch'),
      'config',
      'turtlesim.yaml'
      )

   return LaunchDescription([          # 返回launch文件的描述信息
      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
      )
   ])
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1 config = os.path.join(
get_package_share_directory(‘learning_launch’),
‘config’,
‘turtlesim.yaml’
)
找到参数yaml文件的路径，我这里在learning_launch功能包，config文件夹，turtlesim.yaml文件

2 parameters=[config]
在返回值里加入parameters来加载参数文件

turtlesim.yaml参数文件：

/turtlesim2/sim:
   ros__parameters:
      background_b: 0
      background_g: 0
      background_r: 0

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注意这里命名空间turtlesim2，节点名称sim都要和launch文件里保持一致，否则无法运行

5 在launch文件里包含其他launch文件

在一些大型系统可能会有多个launch文件，可以把多个launch文件嵌套在一个launch文件会更方便

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

def generate_launch_description():                   # 自动生成launch文件的函数
   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('learning_launch'), 'launch'),
         '/parameters_nonamespace.launch.py'])
      )
  
   parameter_yaml_with_namespace = GroupAction(      # 对指定launch文件中启动的功能加上命名空间
      actions=[
         PushRosNamespace('turtlesim2'),
         parameter_yaml]
      )

   return LaunchDescription([                        # 返回launch文件的描述信息
      parameter_yaml_with_namespace
   ])

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1 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(‘learning_launch’), ‘launch’),
‘/parameters_nonamespace.launch.py’])
)
获取另一个launch文件的完整地址。文件在learning_launch功能包，launch文件夹下parameters_nonamespace.launch.py文件

2 actions=[
PushRosNamespace(‘turtlesim2’),
parameter_yaml]
对加载的launch文件重命名功能空间turtlesim2。这样可以防止原launch文件命名出现冲突

在setup里面对launch文件进行声明

from setuptools import setup
import os
from glob import glob

package_name = 'learning_launch'

setup(
    name=package_name,
    version='0.0.0',
    packages=[package_name],
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
        (os.path.join('share', package_name, 'launch'), glob(os.path.join('launch', '*.launch.py'))),
        (os.path.join('share', package_name, 'config'), glob(os.path.join('config', '*.*'))),
        (os.path.join('share', package_name, 'rviz'), glob(os.path.join('rviz', '*.*'))),
    ],
    install_requires=['setuptools'],
    zip_safe=True,
    maintainer='hcx',
    maintainer_email='huchunxu@guyuehome.com',
    description='TODO: Package description',
    license='TODO: License declaration',
    tests_require=['pytest'],
    entry_points={
        'console_scripts': [
        ],
    },
)

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1 data_files=[
(‘share/ament_index/resource_index/packages’,
[‘resource/’ + package_name]),
(‘share/’ + package_name, [‘package.xml’]),
(os.path.join(‘share’, package_name, ‘launch’), glob(os.path.join(‘launch’, ‘.launch.py’))),
(os.path.join(‘share’, package_name, ‘config’), glob(os.path.join(‘config’, '.'))),
(os.path.join(‘share’, package_name, ‘rviz’), glob(os.path.join(‘rviz’, '.*’))),
],

这一步把所有launch文件夹下，config文件夹下，和rviz文件夹下的文件进行声明（ * 代表所有文件），这样编译器会把这些文件复制到install文件夹下，可以后续运行