本文记录了>
/>
/>
/>
</
node>
includeinclude 可以在一个 launch file 中包含另外的 launch file groupgroup 可以把多个 node 组合在一起 疑问4：如何编写一个 launch file?无论是 python、xml 还是 yaml，编写 launch file 的步骤差不多一样。 设置命令行参数的默认值，设置 launch file 的包含关系，通过 标签设置 Node 信息，包括 name、namespace、parameter如果需要设置 remmaping 则设置 remapping 关系官方文档有出示个一个例子# 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",)
)
background_g_launch_arg = DeclareLaunchArgument(
"background_g",)
)
background_b_launch_arg = DeclareLaunchArgument(
"background_b",)
)
chatter_ns_launch_arg = DeclareLaunchArgument(
"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":/>
/>
/>
/>
/>
/>
/>
/>
>
/>
/>
/>
>
/>
/>
</
node>
</
launch>
yaml 要写也很容易。 # 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"
疑问5：如何在/>
把 from 中的 topic，转换成 to 指定的 topic 有 2 种用途：把一个 node 原本来发布的 topic，映射为另外一个名字把其他的 node 发布的原始 topic，映射为所需要的 topicROS2 官方教程的示例中有如下代码Node(
package='turtlesim',
executable='mimic',
name='mimic',
remappings=[
('/input/pose', '/turtlesim1/turtle1/pose'),
('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),
]
)
实践官方教程有很详细的指引，这里简单概述一下。1.创建 launch 文件turtlesim_mimic_launch.pyfrom 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.启动ros2 launch turtlesim_mimic_launch.py
你会看到两个乌龟界面。
3. 调试发送命令让乌龟动起来. 新开一个终端，敲下面的命令。ros2 topic pub -r 1 /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}}"
我们仔细观察看到，发送的是 /turtlesim1/turtle1/cmd_vel 这个 Topic，但 2 只乌龟都运动起来，这是因为我们在 mimic 这个节点中做了remap 动作，相当于进行了消息的透传。 我们可以通过 rqt_graph 查看更详细的信息。 新开一个终端然后输入 rqt_graph。
它们之间的关系还是一目了然的。参考1.ROS2官方文档 2.ROS1官方文档
在麻将等娱乐活动中，往往有一些朋友过于注重麻将技术的高低和游戏胜负结果，自己如果技高一筹，赢了对手，往往兴高采烈，自鸣得意，而一旦发现技术高超的对手则愤愤不平真人棋牌游戏，输了之后久久不能平静，平明搜集挖掘各类所谓的高深的麻将技术，力图提高自己麻将技术水平，甚至希望自己永远不输，能够一直赢下去。按照佛家来说，这是入了执念，太过执着于输赢成败，而忘记了输赢成败，奈争由人算，忘记了麻将游戏这项活动本身原始的意义。
