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前言

本篇文章属于ROS2humble的学习笔记，来源于B站鱼香ROSup主。下面是这位up主的视频链接。本文为个人学习笔记，只能做参考，细节方面建议观看视频，肯定受益匪浅。

《ROS 2机器人开发从入门到实践》课程介绍_哔哩哔哩_bilibili

 一、Python节点的订阅和发布

1.下载小说，并通过话题间隔5s发送一行

（1）创建工作空间

在终端中输入：

mkdir -p topic_ws/src

（2）在src目录下创建软件包

处于src目录下，在终端中输入：

ros2 pkg create demo_python_topic --build-type ament_python --dependencies rclpy example_interfaces --license Apache-2.0

回到topic_ws目录下，再输入：

colcon build                 构建文件

 （3）在有__init__.py文件的目录下创建节点文件novel_pub_node.py，节点代码部分如下

import rclpy
from rclpy.node import Node
import requests
from example_interfaces.msg import String
from queue import Queueclass NovelNode(Node):def __init__(self, node_name):super().__init__(node_name)self.get_logger().info(f'{node_name},启动！')self.novel_queue = Queue()  #创建队列self.novel_publisher = self.create_publisher(String, 'novel', 100)self.create_timer(5, self.timer_callback)def timer_callback(self):if self.novel_queue.qsize()>0:line = self.novel_queue.get()msg = String()msg.data = lineself.novel_publisher.publish(msg)self.get_logger().info(f'发布了：{msg}')def download(self, url):responese = requests.get(url)responese.encoding = 'utf-8'text = responese.textself.get_logger().info(f'下载{url},{len(text)}')for line in text.splitlines():self.novel_queue.put(line)def main():rclpy.init()node = NovelNode('novel_pub')node.download('https://fanqienovel.com/reader/7173216089122439711?enter_from=page')rclpy.spin(node)rclpy.shutdown()

（4）执行代码

先找到

entry_points={

'console_scripts': [

],

},

改为

entry_points={

        'console_scripts': [

                'novel_pub_node=demo_python_topic.novel_pub_node:main'

],

},

等号左边是可执行文件的名字，等号右边是软件包名和节点名

然后回到 topic_ws目录下，再输入：

colcon build                 构建文件

再在终端中输入source install/setup.bash

修改一下环境变量

再运行即可：ros2 run demo_python_topic novel_pub_node

2.订阅小说并合成语音

import espeakng
import rclpy
from rclpy.node import Node
from example_interfaces.msg import String
from queue import Queue
import threading
import timeclass NovelSubNode(Node):def __init__(self, node_name):super().__init__(node_name)self.get_logger().info(f'{node_name},启动！')self.novel_queue = Queue()self.create_subscription(String, 'novel', self.novel_callback, 10)self.speech_thread_ = threading.Thread(target=self.speaker_thread)self.speech_thread_.start()def novel_callback(self, msg):self.novel_queue.put(msg.data)passdef speaker_thread(self):speaker = espeakng.Speaker()speaker.voice = 'zh'while rclpy.ok():   #检测ROS当前上下文是否okif self.novel_queue.qsize()>0:text = self.novel_queue.get()self.get_logger().info(f'朗读：{text}')speaker.say(text)       #说speaker.wait()        #等说完else:#让当前线程休眠1stime.sleep(1)def main():rclpy.init()node = NovelSubNode('novel_sub')rclpy.spin(node)rclpy.shutdown()

espeakng为朗读引入的库

注意当前线程休眠1s的操作很关键，这能降低CPU功耗

 二、C++节点的订阅和发布

1.发布速度控制海龟画圆

（1）在工作空间的src目录下创建软件包

处于src目录下，在终端中输入：

ros2 pkg create demo_cpp_topic --build-type ament_cmake --dependencies rclcpp geometry_msgs turtlesim  --license Apache-2.0

（2）在软件包下的src目录下创建节点文件turtle_circle.cpp

出现该报错要配置includePath

配置成这样即可

节点代码如下：

#include "rclcpp/rclcpp.hpp"
#include "geometry_msgs/msg/twist.hpp"
#include <chrono>using namespace std::chrono_literals;class TurtleCircleNode: public rclcpp::Node
{
private:rclcpp::TimerBase::SharedPtr timer_;rclcpp::Publisher<geometry_msgs::msg::Twist>::SharedPtr publisher_;//发布者的共享指针public:explicit TurtleCircleNode(const std::string& node_name):Node(node_name){publisher_ = this->create_publisher<geometry_msgs::msg::Twist>("/turtle1/cmd_vel",10);timer_ = this->create_wall_timer(1000ms,std::bind(&TurtleCircleNode::timer_callback,this));}void timer_callback(){auto msg = geometry_msgs::msg::Twist();msg.linear.x = 1.0;msg.angular.z = 0.5;publisher_->publish(msg);}
}; int main(int argc,char *argv[])
{rclcpp::init(argc,argv);auto node = std::make_shared<TurtleCircleNode>("turtle_circle");rclcpp::spin(node);rclcpp::shutdown();return 0;
}

（4）执行代码

首先去CMakeLists文件

add_executable(turtle_circle src/turtle_circle.cpp) #添加可执行文件

ament_target_dependencies(turtle_circle rclcpp geometry_msgs)        #添加依赖

install(TARGETS turtle_circle

DESTINATION lib/${PROJECT_NAME}

) #拷贝文件到人ros2 run的文件目录上，便于ros2 run启动

 然后回到topic_ws工作空间下colcon build 编译文件

生成完后输入source install/setup.bash配置环境变量

ros2 run demo_cpp_topic turtle_circle 即可运行

2.订阅pose实现闭环控制

#include "rclcpp/rclcpp.hpp"
#include "geometry_msgs/msg/twist.hpp"
#include <chrono>
#include "turtlesim/msg/pose.hpp"using namespace std::chrono_literals;class TurtleControlNode: public rclcpp::Node
{
private:rclcpp::TimerBase::SharedPtr timer_;rclcpp::Publisher<geometry_msgs::msg::Twist>::SharedPtr publisher_;//发布者的共享指针rclcpp::Subscription<turtlesim::msg::Pose>::SharedPtr subscriber_;//订阅者的共享指针double target_x_{1.0};double target_y_{1.0};double k{0.5};double max_speed_{3.0};public:explicit TurtleControlNode(const std::string& node_name):Node(node_name){publisher_ = this->create_publisher<geometry_msgs::msg::Twist>("/turtle1/cmd_vel",10);subscriber_ = this->create_subscription<turtlesim::msg::Pose>("/turtle1/pose",10,std::bind(&TurtleControlNode::sub_callback,this,std::placeholders::_1));// timer_ = this->create_wall_timer(1500ms,std::bind(&TurtleControlNode::timer_callback,this));}void sub_callback(const turtlesim::msg::Pose::SharedPtr pose){//1. 获取当前位置auto current_x = pose->x;auto current_y = pose->y;RCLCPP_INFO(get_logger(),"当前:x=%f,y=%f",current_x,current_y);//2. 计算当前海龟位置跟目标位置之间的距离差和角度差auto distance = std::sqrt((target_x_-current_x)*(target_x_-current_x)+(target_y_-current_y)*(target_y_-current_y));auto angle = std::atan2((target_y_-current_y),(target_x_-current_x))-pose->theta;//3.控制策略auto msg = geometry_msgs::msg::Twist();if (distance>0.1){if (fabs(angle)>0.2){msg.angular.z = k*angle;}else{msg.linear.x = k*distance;}}//4.限制速度if (msg.linear.x > max_speed_){msg.linear.x = max_speed_;}publisher_->publish(msg);}
}; int main(int argc,char *argv[])
{rclcpp::init(argc,argv);auto node = std::make_shared<TurtleControlNode>("turtle_control");rclcpp::spin(node);rclcpp::shutdown();return 0;
}

三、话题通信最佳实践（获取系统信息并显示）

1.自定义消息类型

在src目录下创建status_interfaces功能包，在功能包目录下，创建msg文件夹，在msg文件夹下创建SystemStatus.msg文件

builtin_interfaces/Time stamp # 记录时间戳
string host_name #主机名字
float32 cpu_percent #CPU使用率
float32 memory_percent #内存使用率
float32 memory_total #内存总大小
float32 memory_available #内存剩余量
float64 net_sent #网络数据发送总量
float64 net_rece #网络数据接受总量

 在SystemStatus.msg文件中编写如上代码

在CMakeLists文件中添加cmake函数

# find dependencies
find_package(ament_cmake REQUIRED)
find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)
#cmake函数，来自依赖rosidl_default_generators 用于将msg消息接口定义文件转换成库或者头文件夹
rosidl_generate_interfaces(${PROJECT_NAME}"msg/SystemStatus.msg"DEPENDENCIES builtin_interfaces
)

再在package.xml文件中添加声明，声明该功能包是包含消息接口的功能包

<member_of_group>rosidl_interface_packages</member_of_group>

2.发布者节点代码

import rclpy
from status_interfaces.msg import SystemStatus
from rclpy.node import Node 
import psutil
import platformclass SysStatusPub(Node):def __init__(self,node_name):super().__init__(node_name)self.status_publisher_ = self.create_publisher(SystemStatus,'sys_status',10)self.timer_ = self.create_timer(1.0,self.timer_callback)def timer_callback(self):cpu_percent =  psutil.cpu_percent()memory_info = psutil.virtual_memory()net_io_counters = psutil.net_io_counters()msg = SystemStatus()msg.stamp = self.get_clock().now().to_msg()msg.host_name = platform.node()msg.cpu_percent = cpu_percentmsg.memory_percent = memory_info.percentmsg.memory_total = memory_info.total / 1024 / 1024msg.memory_available = memory_info.available / 1024 / 1024msg.net_sent = net_io_counters.bytes_sent / 1024 / 1024msg.net_recv = net_io_counters.bytes_recv / 1024 / 1024self.get_logger().info(f'发布:{str(msg)}')self.status_publisher_.publish(msg)def main():rclpy.init()node = SysStatusPub('sys_status_pub')rclpy.spin(node)rclpy.shutdown()

3.订阅者节点代码

#include <QApplication>
#include <QLabel>
#include <QString>
#include <rclcpp/rclcpp.hpp>
#include "status_interfaces/msg/system_status.hpp"using SystemStatus = status_interfaces::msg::SystemStatus;class SysStatusDisplay : public rclcpp::Node
{
private:rclcpp::Subscription<SystemStatus>::SharedPtr subscriber_;QLabel *label_;public:SysStatusDisplay() : Node("sys_status_display"){label_ = new QLabel();subscriber_ = this->create_subscription<SystemStatus>("sys_status", 10, [&](const SystemStatus::SharedPtr msg) -> void{ label_->setText(get_qstr_from_msg(msg));});label_->setText(get_qstr_from_msg(std::make_shared<SystemStatus>()));label_->show();}QString get_qstr_from_msg(const SystemStatus::SharedPtr msg){std::stringstream show_str;show_str << "=============状态可视化显示工具=============\n"<< "数 据 时 间:\t" << msg->stamp.sec << "\ts\n"<< "主 机 名 字\t" << msg->host_name << "\t\n"<< "CPU 使用率:\t" << msg->cpu_percent << "\t%\n"<< "内存使用率:\t" << msg->memory_percent << "\t%\n"<< "内存总大小:\t" << msg->memory_total << "\tMB\n"<< "剩余有效内存:\t" << msg->memory_available << "\tMB\n"<< "网络发送量:\t" << msg->net_sent << "\tMB\n"<< "网络接受量:\t" << msg->net_recv << "\tMB\n"<< "=========================================";return QString::fromStdString(show_str.str());                }
};int main(int argc, char *argv[])
{rclcpp::init(argc, argv);QApplication app(argc, argv);auto node = std::make_shared<SysStatusDisplay>();std::thread spin_thread([&]() -> void{rclcpp::spin(node);});spin_thread.detach();app.exec();return 0;
}

这里由于rclcpp::spin()和app.exec()都会阻塞代码进程，所以要多开一个线程

四、Git入门