1 基本命令

ROS2 中的所有命令都集成在 ros2 命令中，后面参数表示不同的操作目的如 node 表示节点操作，topic 表示话题操作等等，在后面可以再跟参数表示具体干什么。

(1) 帮助命令

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ros2 --help

(2) 运行节点

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ros2 run <package_name> <node_name>
# e.g.
# ros2 run turtlesim turtlesim_node 
# ros2 run turtlesim turtle_teleop_key

(3) 查看节点

打印节点列表：

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ros2 node list

打印节点信息：

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ros2 node info /<node_name>
# ros2 node info /turtlesim

(4) 查看话题

打印话题列表：

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ros2 topic list

订阅话题和打印

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ros2 topic echo <topic_name>
# e.g.
# ros2 topic echo /turtle1/cmd_vel

手动发布话题

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ros2 topic pub --rate <rate> <publish_topic> <data_type> <data>
# e.g.
# ros2 topic pub --rate 1 /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}}"

(5) 服务

调用服务

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ros2 service call <service_name> <service_params>
# e.g.
# ros2 service call_ /_spawn turtlesim_/srv/_Spawn_ "{x: 2, y: 2, theta: 0.2, name: 'turtle2'}"

(6) 数据录制

ROS bag 数据录制

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ros2 bag record <topic_name> -o <save_path>

ROS bag 数据播放

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ros2 bag play <rosbag_filename>

(7) Launch

ROS2 中的 launch 文件是基于 Python 描述的，启动 launch 文件

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ros2 launch <node_name> simple.launch.py

(8) Rviz

启动 Rviz 可视化信息

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ros2 run rviz2 rviz2

2 工作空间

(1) 创建工作空间

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mkdir -p ~/ros2_ws/src
cd ~/ros2_ws/src
git clone https://github.com/ros/ros_tutorials.git -b humble

(2) 自动安装依赖

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cd ~/ros2_ws/
rosdep install -i --from-path src --rosdistro humble -y

(3) 编译工作空间

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cd ~/ros2_ws/
colcon build

(4) 设置环境变量

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source install/local_setup.sh

3 功能包

(1) 创建功能包

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cd ~/ros2_ws/src
ros2 pkg create --build-type ament_cmake c_pkg_name
ros2 pkg create --build-type ament_python python_pkg_name

(2) 编译功能包

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cd ~/ros2_ws/src
colcon build
source install/local_setup.bash

4 基础代码示例

4.1 创建节点

编写节点的 python 程序 scripts/node_helloworld.py

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#!/usr/bin/env python3 
# -*- coding: utf-8 -*-

import rclpy                                     # ROS2 Python接口库
from rclpy.node import Node                      # ROS2 节点类
import time

"""
创建一个HelloWorld节点, 初始化时输出“hello world”日志
"""
class HelloWorldNode(Node):
    def __init__(self, name):
        super().__init__(name)                     # ROS2节点父类初始化
        while rclpy.ok():                          # ROS2系统是否正常运行
            self.get_logger().info("Hello World")  # ROS2日志输出
            time.sleep(0.5)                        # 休眠控制循环时间

def main(args=None):                               # ROS2节点主入口main函数
    rclpy.init(args=args)                          # ROS2 Python接口初始化
    node = HelloWorldNode("node_helloworld_class") # 创建ROS2节点对象并进行初始化
    rclpy.spin(node)                               # 循环等待ROS2退出
    node.destroy_node()                            # 销毁节点对象
    rclpy.shutdown()                               # 关闭ROS2 Python接口

修改功能包的 setup.py 文件

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entry_points={
    'console_scripts': [
     'node_helloworld       = scripts.node_helloworld:main',
    ],

4.2 话题

(1) 发布者

编写发布者的 python 程序：scripts/publisher_node.py

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#!/usr/bin/env python3 
# -*- coding: utf-8 -*-

import rclpy                                     # ROS2 Python接口库
from rclpy.node import Node                      # ROS2 节点类
from std_msgs.msg import String                  # 字符串消息类型

"""
创建一个发布者节点
"""
class PublisherNode(Node):

    def __init__(self, name):
        super().__init__(name)                                    # ROS2节点父类初始化
        self.pub = self.create_publisher(String, "chatter", 10)   # 创建发布者对象（消息类型、话题名、队列长度）
        self.timer = self.create_timer(0.5, self.timer_callback)  # 创建一个定时器（单位为秒的周期，定时执行的回调函数）

    def timer_callback(self):                                     # 创建定时器周期执行的回调函数
        msg = String()                                            # 创建一个String类型的消息对象
        msg.data = 'Hello World'                                  # 填充消息对象中的消息数据
        self.pub.publish(msg)                                     # 发布话题消息
        self.get_logger().info('Publishing: "%s"' % msg.data)     # 输出日志信息，提示已经完成话题发布

def main(args=None):                                 # ROS2节点主入口main函数
    rclpy.init(args=args)                            # ROS2 Python接口初始化
    node = PublisherNode("topic_helloworld_pub")     # 创建ROS2节点对象并进行初始化
    rclpy.spin(node)                                 # 循环等待ROS2退出
    node.destroy_node()                              # 销毁节点对象
    rclpy.shutdown()                                 # 关闭ROS2 Python接口

(2) 订阅者

编写发布者的 python 程序：scripts/subscriber_node.py

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import rclpy                      # ROS2 Python接口库
from rclpy.node   import Node     # ROS2 节点类
from std_msgs.msg import String   # ROS2标准定义的String消息

"""
创建一个订阅者节点
"""
class SubscriberNode(Node):

    def __init__(self, name):
        super().__init__(name)                             # ROS2节点父类初始化
        self.sub = self.create_subscription(\
            String, "chatter", self.listener_callback, 10) # 创建订阅者对象（消息类型、话题名、订阅者回调函数、队列长度）

    def listener_callback(self, msg):                      # 创建回调函数，执行收到话题消息后对数据的处理
        self.get_logger().info('I heard: "%s"' % msg.data) # 输出日志信息，提示订阅收到的话题消息

def main(args=None):                               # ROS2节点主入口main函数
    rclpy.init(args=args)                          # ROS2 Python接口初始化
    node = SubscriberNode("topic_helloworld_sub")  # 创建ROS2节点对象并进行初始化
    rclpy.spin(node)                               # 循环等待ROS2退出
    node.destroy_node()                            # 销毁节点对象
    rclpy.shutdown()                               # 关闭ROS2 Python接口

(3) 修改 setup.py

打开功能包的setup.py文件，加入如下入口点的配置：

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entry_points={
    'console_scripts': [
     'publisher_node  = scripts.publisher_node:main',
     'subscriber_node  = scripts.subscriber_node:main',
    ],
},

4.3 服务

(1) 客户端

客户端发送数据代码如下：scripts/client.py

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import sys

import rclpy                                  # ROS2 Python接口库
from rclpy.node   import Node                 # ROS2 节点类
from learning_interface.srv import AddTwoInts # 自定义的服务接口

class adderClient(Node):
    def __init__(self, name):
        super().__init__(name)                                       # ROS2节点父类初始化
        self.client = self.create_client(AddTwoInts, 'add_two_ints') # 创建服务客户端对象（服务接口类型，服务名）
        while not self.client.wait_for_service(timeout_sec=1.0):     # 循环等待服务器端成功启动
            self.get_logger().info('service not available, waiting again...') 
        self.request = AddTwoInts.Request()                          # 创建服务请求的数据对象

    def send_request(self):                                          # 创建一个发送服务请求的函数
        self.request.a = int(sys.argv[1])
        self.request.b = int(sys.argv[2])
        self.future = self.client.call_async(self.request)           # 异步方式发送服务请求

def main(args=None):
    rclpy.init(args=args)                        # ROS2 Python接口初始化
    node = adderClient("service_adder_client")   # 创建ROS2节点对象并进行初始化
    node.send_request()                          # 发送服务请求

    while rclpy.ok():                            # ROS2系统正常运行
        rclpy.spin_once(node)                    # 循环执行一次节点

        if node.future.done():                   # 数据是否处理完成
            try:
                response = node.future.result()  # 接收服务器端的反馈数据
            except Exception as e:
                node.get_logger().info(
                    'Service call failed %r' % (e,))
            else:
                node.get_logger().info(          # 将收到的反馈信息打印输出
                    'Result of add_two_ints: for %d + %d = %d' % 
                    (node.request.a, node.request.b, response.sum))
            break

    node.destroy_node()                          # 销毁节点对象
    rclpy.shutdown()                             # 关闭ROS2 Python接口

(2) 服务端

服务端请求数据代码如下：scripts/server.py

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import rclpy                                     # ROS2 Python接口库
from rclpy.node   import Node                    # ROS2 节点类
from learning_interface.srv import AddTwoInts    # 自定义的服务接口

class adderServer(Node):
    def __init__(self, name):
        super().__init__(name)                                                           # ROS2节点父类初始化
        self.srv = self.create_service(AddTwoInts, 'add_two_ints', self.adder_callback)  # 创建服务器对象（接口类型、服务名、服务器回调函数）

    def adder_callback(self, request, response):   # 创建回调函数，执行收到请求后对数据的处理
        response.sum = request.a + request.b       # 完成加法求和计算，将结果放到反馈的数据中
        self.get_logger().info('Incoming request\na: %d b: %d' % (request.a, request.b))   # 输出日志信息，提示已经完成加法求和计算
        return response                          # 反馈应答信息

def main(args=None):                             # ROS2节点主入口main函数
    rclpy.init(args=args)                        # ROS2 Python接口初始化
    node = adderServer("service_adder_server")   # 创建ROS2节点对象并进行初始化
    rclpy.spin(node)                             # 循环等待ROS2退出
    node.destroy_node()                          # 销毁节点对象
    rclpy.shutdown()                             # 关闭ROS2 Python接口

(3) 编辑 setup.py

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entry_points={
    'console_scripts': [
     'client  = scripts.client:main',
     'server  = scripts.server:main',
    ],
},

5 URDF 相关

（1）创建功能包

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mkdir -p ~/ros2_ws/src
cd ~/ros2_ws/src
ros2 pkg create urdf_view --build-type ament_python --dependencies rclpy --license Apache-2.0
cd urdf_view

（2）创建 URDF 文件

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mkdir urdf

下载 URDF 文件并保存在 ~/ros2_ws/src/urdf_view/urdf/r2d2.urdf.xml

（3）发布状态

在 ~/ros2_ws/src/urdf_view/urdf_view/ 目录下创建一个文件 state_publisher.py，并粘贴以下内容：

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from math import sin, cos, pi
import rclpy
from rclpy.node import Node
from rclpy.qos import QoSProfile
from geometry_msgs.msg import Quaternion
from sensor_msgs.msg import JointState
from tf2_ros import TransformBroadcaster, TransformStamped

class StatePublisher(Node):

    def __init__(self):
        rclpy.init()
        super().__init__('state_publisher')

        qos_profile = QoSProfile(depth=10)
        self.joint_pub = self.create_publisher(JointState, 'joint_states', qos_profile)
        self.broadcaster = TransformBroadcaster(self, qos=qos_profile)
        self.nodeName = self.get_name()
        self.get_logger().info("{0} started".format(self.nodeName))

        degree = pi / 180.0
        loop_rate = self.create_rate(30)

        # robot state
        tilt = 0.
        tinc = degree
        swivel = 0.
        angle = 0.
        height = 0.
        hinc = 0.005

        # message declarations
        odom_trans = TransformStamped()
        odom_trans.header.frame_id = 'odom'
        odom_trans.child_frame_id = 'axis'
        joint_state = JointState()

        try:
            while rclpy.ok():
                rclpy.spin_once(self)

                # update joint_state
                now = self.get_clock().now()
                joint_state.header.stamp = now.to_msg()
                joint_state.name = ['swivel', 'tilt', 'periscope']
                joint_state.position = [swivel, tilt, height]

                # update transform
                # (moving in a circle with radius=2)
                odom_trans.header.stamp = now.to_msg()
                odom_trans.transform.translation.x = cos(angle)*2
                odom_trans.transform.translation.y = sin(angle)*2
                odom_trans.transform.translation.z = 0.7
                odom_trans.transform.rotation = \
                    euler_to_quaternion(0, 0, angle + pi/2) # roll,pitch,yaw

                # send the joint state and transform
                self.joint_pub.publish(joint_state)
                self.broadcaster.sendTransform(odom_trans)

                # Create new robot state
                tilt += tinc
                if tilt < -0.5 or tilt > 0.0:
                    tinc *= -1
                height += hinc
                if height > 0.2 or height < 0.0:
                    hinc *= -1
                swivel += degree
                angle += degree/4

                # This will adjust as needed per iteration
                loop_rate.sleep()

        except KeyboardInterrupt:
            pass

def euler_to_quaternion(roll, pitch, yaw):
    qx = sin(roll/2) * cos(pitch/2) * cos(yaw/2) - cos(roll/2) * sin(pitch/2) * sin(yaw/2)
    qy = cos(roll/2) * sin(pitch/2) * cos(yaw/2) + sin(roll/2) * cos(pitch/2) * sin(yaw/2)
    qz = cos(roll/2) * cos(pitch/2) * sin(yaw/2) - sin(roll/2) * sin(pitch/2) * cos(yaw/2)
    qw = cos(roll/2) * cos(pitch/2) * cos(yaw/2) + sin(roll/2) * sin(pitch/2) * sin(yaw/2)
    return Quaternion(x=qx, y=qy, z=qz, w=qw)

def main():
    node = StatePublisher()

if __name__ == '__main__':
    main()

（4）创建 launch 文件

创建一个 ~/ros2_ws/src/urdf_view/launch 文件夹，并在其中创建一个 demo.launch.py 文件。

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import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node

def generate_launch_description():

    use_sim_time = LaunchConfiguration('use_sim_time', default='false')

    urdf_file_name = 'r2d2.urdf.xml'
    urdf = os.path.join(
        get_package_share_directory('urdf_view'),
        urdf_file_name)
    with open(urdf, 'r') as infp:
        robot_desc = infp.read()

    return LaunchDescription([
        DeclareLaunchArgument(
            'use_sim_time',
            default_value='false',
            description='Use simulation (Gazebo) clock if true'),
        Node(
            package='robot_state_publisher',
            executable='robot_state+_publisher',
            name='robot_state_publisher',
            output='screen',
            parameters=[{'use_sim_time': use_sim_time, 'robot_description': robot_desc}],
            arguments=[urdf]),
        Node(
            package='urdf_view',
            executable='state_publisher',
            name='state_publisher',
            output='screen'),
    ])

（5）更新 setup.py

为了能够正常安装 python，必须告诉 colcon 编译工具如何安装我们刚才创建的 python 包，编辑 ~/ros2_ws/src/urdf_view/setup.py 如下：

导入必要库

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import os
from glob import glob
from setuptools import setup
from setuptools import find_packages

在 data_files 中添加两行

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data_files=[
  ...
  (os.path.join('share', package_name, 'launch'), glob(os.path.join('launch', '*launch.[pxy][yma]*'))),
  (os.path.join('share', package_name), glob('urdf/*')),
],

修改 entry_points 列表，保证可以从命令行运行 state_publisher

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'console_scripts': [
    'state_publisher = urdf_view.state_publisher:main'
],

（6）安装包

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cd ~/ros2_ws
colcon build --symlink-install --packages-select urdf_view
source install/setup.bash

（7）可视化结果

启动package

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打开一个新终端，运行 Rviz

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rviz2