之前4.3节例子中，需要分别启动turtle_control、patrol_client、turtlesim_node三个节点，每个节点都需要单独的终端和命令。比较麻烦，ros2 提供了简化启动过程的方法。
4.6.1 使用launch启动多个节点
ros2 支持使用python、xml、YAML 三种格式编写launch脚本。小鱼老师推荐python.
在src/demo_cpp_service下新建文件夹launch，新建文件demo.launch.py,代码如下
import launch
import launch_ros
def generate_launch_description():
action_node_turtle_control = launch_ros.actions.Node(
package='demo_cpp_service',
executable="turtle_control",
output='screen',
)
action_node_patrol_client = launch_ros.actions.Node(
package='demo_cpp_service',
executable="patrol_client",
output='log',
)
action_node_turtlesim_node = launch_ros.actions.Node(
package='turtlesim',
executable='turtlesim_node',
output='both',
)
# 合成启动描述并返回
return launch.LaunchDescription([
action_node_turtlesim_node,
action_node_patrol_client,
action_node_turtle_control,
])导入依赖库launch、launch_ros。函数generate_launch_description中创建3个launch_ros.actions.Node对象，里面指定package功能包、executable可执行文件、output 指定日志输出位置。最后将三个节点合成数组，调用launch.LaunchDescription启动描述并返回。
修改 编译文件CMakeLists.txt增加install,用于吧launch目录复制到install对于功能包share目录下
cmake_minimum_required(VERSION 3.8)
project(demo_cpp_service)
if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
add_compile_options(-Wall -Wextra -Wpedantic)
endif()
# find dependencies
find_package(ament_cmake REQUIRED)
find_package(chapt4_interfaces REQUIRED)
find_package(rclcpp REQUIRED)
find_package(geometry_msgs REQUIRED)
find_package(turtlesim REQUIRED)
add_executable(turtle_control src/turtle_control.cpp)
ament_target_dependencies(turtle_control rclcpp geometry_msgs turtlesim chapt4_interfaces)
add_executable(patrol_client src/patrol_client.cpp)
ament_target_dependencies(patrol_client rclcpp chapt4_interfaces)
if(BUILD_TESTING)
find_package(ament_lint_auto REQUIRED)
# the following line skips the linter which checks for copyrights
# comment the line when a copyright and license is added to all source files
set(ament_cmake_copyright_FOUND TRUE)
# the following line skips cpplint (only works in a git repo)
# comment the line when this package is in a git repo and when
# a copyright and license is added to all source files
set(ament_cmake_cpplint_FOUND TRUE)
ament_lint_auto_find_test_dependencies()
endif()
install(TARGETS
turtle_control patrol_client
DESTINATION lib/${PROJECT_NAME}
)
install(DIRECTORY launch
DESTINATION share/${PROJECT_NAME}
)
ament_package()
对应的demo_python_service 也复制一下launch文件夹。修改setup.py
from setuptools import find_packages, setup
from glob import glob
package_name = 'demo_python_service'
setup(
name=package_name,
version='0.0.0',
packages=find_packages(exclude=['test']),
data_files=[
('share/ament_index/resource_index/packages',
['resource/' + package_name]),
('share/' + package_name, ['package.xml']),
('share/' + package_name+"/resource", ['resource/default.jpg','resource/2.jpg']),
('share/' + package_name+'/launch', glob('launch/*.launch.py')),
],
install_requires=['setuptools'],
zip_safe=True,
description='TODO: Package description',
license='Apache-2.0',
tests_require=['pytest'],
entry_points={
'console_scripts': [
'learn_face_detect=demo_python_service.learn_face_detect:main',
'face_detect_node=demo_python_service.face_detect_node:main',
'face_detect_client_node=demo_python_service.face_detect_client_node:main',
],
},
)
重新构建，启动launch脚本
ros2 launch demo_cpp_service demo.launch.py
效果如下，ctrl+c 中断
同样python 版本执行：ros2 launch demo_python_service demo.launch.py 启动
4.6.2 使用launch 传递参数
先声明参数，再给具体节点使用参数
import launch
import launch_ros
def generate_launch_description():
#1声明一个launch参数
action_declare_arg_bgcolor_g = launch.actions.DeclareLaunchArgument('launch_arg_bg',default_value="150")
action_node_turtle_control = launch_ros.actions.Node(
package='demo_cpp_service',
executable="turtle_control",
output='screen',
)
action_node_patrol_client = launch_ros.actions.Node(
package='demo_cpp_service',
executable="patrol_client",
output='log',
)
#2 把launch的参数手动传递给某个节点
action_node_turtlesim_node = launch_ros.actions.Node(
package='turtlesim',
executable='turtlesim_node',
parameters=[{'background_g': launch.substitutions.LaunchConfiguration('launch_arg_bg',default="150")}],
output='both',
)
return launch.LaunchDescription([
action_declare_arg_bgcolor_g,
action_node_turtlesim_node,
action_node_patrol_client,
action_node_turtle_control,
])书上例子是最大速度，视频例子是修改背景颜色，就是使用launch的参数替换节点的参数。
重新构建后运行：ros2 launch demo_python_service demo.launch.py launch_arg_bg:=255
效果：
4.6.3 launch 使用进阶
Launch三大组件:动作、条件和替换
动作:除了是一个节点外，还可以是一句打印，一段终端指令，甚至是另外一个launch文件
替换:使用launch的参数替换节点的参数值
条件:利用条件可以决定哪些动作启动，那些不启。相当于if
src/demo_cpp_service/launch 文件夹下新建文件：actions.launch.py
代码如下
import launch
import launch.launch_description_sources
import launch_ros
from ament_index_python.packages import get_package_share_directory
def generate_launch_description():
#动作1 -启动其他launch
multisim_launch_path = [get_package_share_directory("turtlesim"),"/launch/","multisim.launch.py"]
action_inlude_launch = launch.actions.IncludeLaunchDescription(
launch.launch_description_sources.PythonLaunchDescriptionSource(
multisim_launch_path
)
)
# 动作2 -打印数据
action_log_info = launch.actions.LogInfo(msg=str(multisim_launch_path))
#动作3 -执行进程 rqt
action_rqt = launch.actions.ExecuteProcess(
cmd=['rqt']
)
#动作4 -组织动作组，把多个动作放到一组
action_group = launch.actions.GroupAction({
#动作5 定时器
launch.actions.TimerAction(period=2.0,actions=[action_inlude_launch]),
launch.actions.TimerAction(period=4.0,actions=[action_rqt])
})
# 合成启动描述并返回
return launch.LaunchDescription([
action_log_info,
action_group
])注意里面的语法不要写错了，不然运行报错
bohu@bohu-TM1701:~/chapt4/chapt4_ws/src/demo_cpp_service/launch$ ros2 launch actions.launch.py
[INFO] [launch]: All log files can be found below /home/bohu/.ros/log/2025-01-10-13-02-59-751143-bohu-TM1701-392500
[INFO] [launch]: Default logging verbosity is set to INFO
[ERROR] [launch]: Caught exception in launch (see debug for traceback): Caught multiple exceptions when trying to load file of format [py]:
- TypeError: 'module' object is not callable
- InvalidFrontendLaunchFileError: The launch file may have a syntax error, or its format is unknown运行日志如下
bohu@bohu-TM1701:~/chapt4/chapt4_ws/src/demo_cpp_service/launch$ ros2 launch actions.launch.py
[INFO] [launch]: All log files can be found below /home/bohu/.ros/log/2025-01-10-13-10-43-357086-bohu-TM1701-393474
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [launch.user]: ['/opt/ros/humble/share/turtlesim', '/launch/', 'multisim.launch.py']
[INFO] [turtlesim_node-1]: process started with pid [393493]
[INFO] [turtlesim_node-2]: process started with pid [393495]
[turtlesim_node-1] qt.qpa.plugin: Could not find the Qt platform plugin "wayland" in ""
[turtlesim_node-2] qt.qpa.plugin: Could not find the Qt platform plugin "wayland" in ""
[turtlesim_node-2] [INFO] [1736485845.707954083] [turtlesim2.turtlesim]: Starting turtlesim with node name /turtlesim2/turtlesim
[turtlesim_node-1] [INFO] [1736485845.708127883] [turtlesim1.turtlesim]: Starting turtlesim with node name /turtlesim1/turtlesim
[turtlesim_node-2] [INFO] [1736485845.716420053] [turtlesim2.turtlesim]: Spawning turtle [turtle1] at x=[5.544445], y=[5.544445], theta=[0.000000]
[turtlesim_node-1] [INFO] [1736485845.716598360] [turtlesim1.turtlesim]: Spawning turtle [turtle1] at x=[5.544445], y=[5.544445], theta=[0.000000]
[INFO] [rqt-3]: process started with pid [393550]
[rqt-3] Could not find the Qt platform plugin "wayland" in ""
使用参数控制
import launch
import launch.launch_description_sources
import launch_ros
from ament_index_python.packages import get_package_share_directory
def generate_launch_description():
#1声明一个launch参数
action_declare_startup_rqt = launch.actions.DeclareLaunchArgument('startup_rqt',default_value="False")
startup_rqt = launch.substitutions.LaunchConfiguration('startup_rqt',default="False")
#动作1 -启动其他launch
multisim_launch_path = [get_package_share_directory("turtlesim"),"/launch/","multisim.launch.py"]
action_inlude_launch = launch.actions.IncludeLaunchDescription(
launch.launch_description_sources.PythonLaunchDescriptionSource(
multisim_launch_path
)
)
# 动作2 -打印数据
action_log_info = launch.actions.LogInfo(msg=str(multisim_launch_path))
#动作3 -执行进程 rqt
action_rqt = launch.actions.ExecuteProcess(
condition = launch.conditions.IfCondition(startup_rqt),
cmd=['rqt']
)
#动作4 -组织动作组，把多个动作放到一组
action_group = launch.actions.GroupAction({
#动作5 定时器
launch.actions.TimerAction(period=2.0,actions=[action_inlude_launch]),
launch.actions.TimerAction(period=4.0,actions=[action_rqt])
})
# 合成启动描述并返回
return launch.LaunchDescription([
action_log_info,
action_group
])可以通过参数控制rqt是否启动。
ros2 launch actions.launch.py startup_rqt:=true
ros2 launch actions.launch.py startup_rqt:=False
