分别有CLI-launch，Python XML YAML对比，launch教程三部分：
代码语言：javascript复制docs.ros.org/en/humble/Tutorials/Launch/CLI-Intro.html
docs.ros.org/en/humble/How-To-Guides/Launch-file-different-formats.html
docs.ros.org/en/humble/Tutorials/Launch/Launch-Main.htmlros2 launch -h
代码语言：javascript复制usage: ros2 launch [-h] [-n] [-d] [-p | -s] [-a] [--launch-prefix LAUNCH_PREFIX]
[--launch-prefix-filter LAUNCH_PREFIX_FILTER]
package_name [launch_file_name] [launch_arguments ...]
Run a launch file
positional arguments:
package_name Name of the ROS package which contains the launch file
launch_file_name Name of the launch file
launch_arguments Arguments to the launch file; '<name>:=<value>' (for duplicates, last one wins)
options:
-h, --help show this help message and exit
-n, --noninteractive Run the launch system non-interactively, with no terminal associated
-d, --debug Put the launch system in debug mode, provides more verbose output.
-p, --print, --print-description
Print the launch description to the console without launching it.
-s, --show-args, --show-arguments
Show arguments that may be given to the launch file.
-a, --show-all-subprocesses-output
Show all launched subprocesses' output by overriding their output configuration using the
OVERRIDE_LAUNCH_PROCESS_OUTPUT envvar.
--launch-prefix LAUNCH_PREFIX
Prefix command, which should go before all executables. Command must be wrapped in quotes if
it contains spaces (e.g. --launch-prefix 'xterm -e gdb -ex run --args').
--launch-prefix-filter LAUNCH_PREFIX_FILTER
Regex pattern for filtering which executables the --launch-prefix is applied to by matching
the executable name.例如：
ros2 launch turtlesim multisim.launch.py
其中，multisim.launch.py 如下：
代码语言：javascript复制# turtlesim/launch/multisim.launch.py
from launch import LaunchDescription
import launch_ros.actions
def generate_launch_description():
return LaunchDescription([
launch_ros.actions.Node(
namespace= "turtlesim1", package='turtlesim', executable='turtlesim_node', output='screen'),
launch_ros.actions.Node(
namespace= "turtlesim2", package='turtlesim', executable='turtlesim_node', output='screen'),
])控制其中的小乌龟用rqt工具或如下指令：
1：ros2 topic pub /turtlesim1/turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 1.8}}"
2：ros2 topic pub /turtlesim2/turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: -1.8}}"
启动launch教程 ROS 2 Launch 文件允许同时启动和配置多个包含 ROS 2 节点的可执行文件。
学习启动 1 创建 ROS 2 启动文件。
本教程将展示如何创建一个启动文件，该文件将同时启动节点及其配置。
代码语言：javascript复制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'),
]
)
])2 使用 Launch 启动和监控多个节点。
关于启动文件如何工作以及可用的资源和文档的更高级概述。
代码语言：javascript复制import platform
import launch
import launch.actions
import launch.substitutions
import launch_ros.actions
env_var_name = 'USER' if platform.system() != 'Windows' else 'USERNAME'
def generate_launch_description():
return launch.LaunchDescription([
launch.actions.DeclareLaunchArgument(
'node_prefix',
default_value=[launch.substitutions.EnvironmentVariable(env_var_name), '_'],
description='Prefix for node names'),
launch_ros.actions.Node(
package='demo_nodes_cpp', executable='talker', output='screen',
name=[launch.substitutions.LaunchConfiguration('node_prefix'), 'talker']),
])3 使用替代品。
在描述可重用的启动文件时，可以使用替换来提供更大的灵活性。
代码语言：javascript复制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],
)
])4 使用事件处理程序。
事件处理程序可用于监视进程的状态或定义一组复杂的规则，这些规则可用于动态修改启动文件。
ROS 2 中的 Launch 是一个执行和管理用户定义流程的系统。 它负责监控它启动的进程的状态，以及报告和响应这些进程的状态变化。 这些更改称为事件，可以通过向启动系统注册事件处理程序来处理。 可以为特定事件注册事件处理程序，并可用于监视进程的状态。 此外，它们可用于定义一组复杂的规则，可用于动态修改启动文件。
本教程展示了 ROS 2 启动文件中事件处理程序的使用示例。
代码语言：javascript复制from launch_ros.actions import Node
from launch import LaunchDescription
from launch.actions import (DeclareLaunchArgument, EmitEvent, ExecuteProcess,
LogInfo, RegisterEventHandler, TimerAction)
from launch.conditions import IfCondition
from launch.event_handlers import (OnExecutionComplete, OnProcessExit,
OnProcessIO, OnProcessStart, OnShutdown)
from launch.events import Shutdown
from launch.substitutions import (EnvironmentVariable, FindExecutable,
LaunchConfiguration, LocalSubstitution,
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=[[
FindExecutable(name='ros2'),
' service call ',
turtlesim_ns,
'/spawn ',
'turtlesim/srv/Spawn ',
'"{x: 2, y: 2, theta: 0.2}"'
]],
shell=True
)
change_background_r = ExecuteProcess(
cmd=[[
FindExecutable(name='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=[[
FindExecutable(name='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,
RegisterEventHandler(
OnProcessStart(
target_action=turtlesim_node,
on_start=[
LogInfo(msg='Turtlesim started, spawning turtle'),
spawn_turtle
]
)
),
RegisterEventHandler(
OnProcessIO(
target_action=spawn_turtle,
on_stdout=lambda event: LogInfo(
msg='Spawn request says "{}"'.format(
event.text.decode().strip())
)
)
),
RegisterEventHandler(
OnExecutionComplete(
target_action=spawn_turtle,
on_completion=[
LogInfo(msg='Spawn finished'),
change_background_r,
TimerAction(
period=2.0,
actions=[change_background_r_conditioned],
)
]
)
),
RegisterEventHandler(
OnProcessExit(
target_action=turtlesim_node,
on_exit=[
LogInfo(msg=(EnvironmentVariable(name='USER'),
' closed the turtlesim window')),
EmitEvent(event=Shutdown(
reason='Window closed'))
]
)
),
RegisterEventHandler(
OnShutdown(
on_shutdown=[LogInfo(
msg=['Launch was asked to shutdown: ',
LocalSubstitution('event.reason')]
)]
)
),
])5 使用 ROS 2 启动大型项目。
本教程描述了为大型项目编写启动文件的一些技巧。重点是如何构建启动文件，以便在不同情况下尽可能多地重用它们。此外，它还涵盖了不同 ROS 2 启动工具的使用示例，例如参数、YAML 文件、重新映射、命名空间、默认参数和 RViz 配置。
机器人上的大型应用程序通常涉及多个相互连接的节点，每个节点都可以有许多参数。 在海龟模拟器中模拟多只海龟就是一个很好的例子。 海龟模拟由多个海龟节点、世界配置以及 TF 广播器和侦听器节点组成。 在所有节点之间，存在大量影响这些节点行为和外观的 ROS 参数。 ROS 2 启动文件允许我们在一个地方启动所有节点并设置相应的参数。 在教程结束时，将在 launch_tutorial 包中构建 launch_turtlesim.launch.py 启动文件。 这个启动文件会调出不同的节点，负责模拟两个turtlesim模拟，启动TF广播器和监听器，加载参数，启动一个RViz配置。 在本教程中，将介绍这个启动文件和使用的所有相关功能。
Python、XML 或 YAML：应该使用哪个？
提示：ROS 1 中的启动文件是用 XML 编写的，因此来自 ROS 1 的人可能最熟悉 XML。要查看发生了什么变化，可以访问将启动文件从 ROS 1 迁移到 ROS 2。
对于大多数应用程序，选择哪种 ROS 2 启动格式取决于开发人员的偏好。 但是，如果启动文件需要 XML 或 YAML 无法实现的灵活性，可以使用 Python 编写启动文件。 由于以下两个原因，使用 Python 启动 ROS 2 更加灵活：
- Python 是一种脚本语言，因此可以在启动文件中利用该语言及其库。
- ros2/launch（一般启动功能）和 ros2/launch_ros（ROS 2 特定启动功能）是用 Python 编写的，因此对 XML 和 YAML 可能未公开的启动功能具有较低级别的访问权限。
话虽如此，用 Python 编写的启动文件可能比用 XML 或 YAML 编写的启动文件更复杂和冗长。
同一功能对比如下：
Python
代码语言：javascript复制# example.launch.py
import os
from ament_index_python import get_package_share_directory
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.actions import IncludeLaunchDescription
from launch.actions import GroupAction
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch.substitutions import LaunchConfiguration
from launch.substitutions import TextSubstitution
from launch_ros.actions import Node
from launch_ros.actions import PushRosNamespace
def generate_launch_description():
# args that can be set from the command line or a default will be used
background_r_launch_arg = DeclareLaunchArgument(
"background_r", default_value=TextSubstitution(text="0")
)
background_g_launch_arg = DeclareLaunchArgument(
"background_g", default_value=TextSubstitution(text="255")
)
background_b_launch_arg = DeclareLaunchArgument(
"background_b", default_value=TextSubstitution(text="0")
)
chatter_ns_launch_arg = DeclareLaunchArgument(
"chatter_ns", default_value=TextSubstitution(text="my/chatter/ns")
)
# include another launch file
launch_include = IncludeLaunchDescription(
PythonLaunchDescriptionSource(
os.path.join(
get_package_share_directory('demo_nodes_cpp'),
'launch/topics/talker_listener.launch.py'))
)
# include another launch file in the chatter_ns namespace
launch_include_with_namespace = GroupAction(
actions=[
# push_ros_namespace to set namespace of included nodes
PushRosNamespace(LaunchConfiguration('chatter_ns')),
IncludeLaunchDescription(
PythonLaunchDescriptionSource(
os.path.join(
get_package_share_directory('demo_nodes_cpp'),
'launch/topics/talker_listener.launch.py'))
),
]
)
# start a turtlesim_node in the turtlesim1 namespace
turtlesim_node = Node(
package='turtlesim',
namespace='turtlesim1',
executable='turtlesim_node',
name='sim'
)
# start another turtlesim_node in the turtlesim2 namespace
# and use args to set parameters
turtlesim_node_with_parameters = Node(
package='turtlesim',
namespace='turtlesim2',
executable='turtlesim_node',
name='sim',
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
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'),
]
)
return LaunchDescription([
background_r_launch_arg,
background_g_launch_arg,
background_b_launch_arg,
chatter_ns_launch_arg,
launch_include,
launch_include_with_namespace,
turtlesim_node,
turtlesim_node_with_parameters,
forward_turtlesim_commands_to_second_turtlesim_node,
])xml
代码语言：javascript复制<!-- example.launch.xml -->
<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_ns" default="my/chatter/ns"/>
<!-- include another launch file -->
<include file="$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener.launch.py"/>
<!-- include another launch file in the chatter_ns namespace-->
<group>
<!-- push_ros_namespace to set namespace of included nodes -->
<push_ros_namespace namespace="$(var chatter_ns)"/>
<include file="$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener.launch.py"/>
</group>
<!-- start a turtlesim_node in the turtlesim1 namespace -->
<node pkg="turtlesim" exec="turtlesim_node" name="sim" namespace="turtlesim1"/>
<!-- start another turtlesim_node in the turtlesim2 namespace
and use args to set parameters -->
<node pkg="turtlesim" exec="turtlesim_node" name="sim" namespace="turtlesim2">
<param name="background_r" value="$(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
代码语言：javascript复制# example.launch.yaml
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_ns"
default: "my/chatter/ns"
# include another launch file
- include:
file: "$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener.launch.py"
# include another launch file in the chatter_ns namespace
- group:
- push_ros_namespace:
namespace: "$(var chatter_ns)"
- include:
file: "$(find-pkg-share demo_nodes_cpp)/launch/topics/talker_listener.launch.py"
# start a turtlesim_node in the turtlesim1 namespace
- node:
pkg: "turtlesim"
exec: "turtlesim_node"
name: "sim"
namespace: "turtlesim1"
# start another turtlesim_node in the turtlesim2 namespace and use args to set parameters
- node:
pkg: "turtlesim"
exec: "turtlesim_node"
name: "sim"
namespace: "turtlesim2"
param:
-
name: "background_r"
value: "$(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"
