目录
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。
<launch.substitutions.launch_configuration.LaunchConfiguration object at 0x7f26d46805b0>
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}])
])
