ROS2+发布者+订阅者示例

2023-12-14 20:28
文章标签 订阅 示例 ros2 发布者

本文主要是介绍ROS2+发布者+订阅者示例,希望对大家解决编程问题提供一定的参考价值,需要的开发者们随着小编来一起学习吧!

Writing a simple publisher and subscriber (C++)

Goal: Create and run a publisher and subscriber node using C++.

Tutorial level: Beginner

Time: 20 minutes

​​​Background

Nodes are executable processes that communicate over the ROS graph. In this tutorial, the nodes will pass information in the form of string messages to each other over a topic. The example used here is a simple “talker” and “listener” system; one node publishes data and the other subscribes to the topic so it can receive that data.

The code used in these examples can be found here.

Prerequisites

In previous tutorials, you learned how to create a workspace and create a package.

Tasks

1 Create a package

Open a new terminal and source your ROS 2 installation so that ros2 commands will work.

Navigate into the ros2_ws directory created in a previous tutorial.

Recall that packages should be created in the src directory, not the root of the workspace. So, navigate into ros2_ws/src, and run the package creation command:

ros2 pkg create --build-type ament_cmake cpp_pubsub

Copy to clipboard

Your terminal will return a message verifying the creation of your package cpp_pubsub and all its necessary files and folders.

Navigate into ros2_ws/src/cpp_pubsub/src. Recall that this is the directory in any CMake package where the source files containing executables belong.

2 Write the publisher node

Download the example talker code by entering the following command:

LinuxmacOSWindows

wget -O publisher_member_function.cpp https://raw.githubusercontent.com/ros2/examples/humble/rclcpp/topics/minimal_publisher/member_function.cpp

Copy to clipboard

Now there will be a new file named publisher_member_function.cpp. Open the file using your preferred text editor.

#include <chrono>
#include <functional>
#include <memory>
#include <string>#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"using namespace std::chrono_literals;/* This example creates a subclass of Node and uses std::bind() to register a
* member function as a callback from the timer. */class MinimalPublisher : public rclcpp::Node
{public:MinimalPublisher(): Node("minimal_publisher"), count_(0){publisher_ = this->create_publisher<std_msgs::msg::String>("topic", 10);timer_ = this->create_wall_timer(500ms, std::bind(&MinimalPublisher::timer_callback, this));}private:void timer_callback(){auto message = std_msgs::msg::String();message.data = "Hello, world! " + std::to_string(count_++);RCLCPP_INFO(this->get_logger(), "Publishing: '%s'", message.data.c_str());publisher_->publish(message);}rclcpp::TimerBase::SharedPtr timer_;rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;size_t count_;
};int main(int argc, char * argv[])
{rclcpp::init(argc, argv);rclcpp::spin(std::make_shared<MinimalPublisher>());rclcpp::shutdown();return 0;
}

Copy to clipboard

2.1 Examine the code

The top of the code includes the standard C++ headers you will be using. After the standard C++ headers is the rclcpp/rclcpp.hpp include which allows you to use the most common pieces of the ROS 2 system. Last is std_msgs/msg/string.hpp, which includes the built-in message type you will use to publish data.

#include <chrono>
#include <functional>
#include <memory>
#include <string>#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"using namespace std::chrono_literals;

Copy to clipboard

These lines represent the node’s dependencies. Recall that dependencies have to be added to package.xml and CMakeLists.txt, which you’ll do in the next section.

The next line creates the node class MinimalPublisher by inheriting from rclcpp::Node. Every this in the code is referring to the node.

class MinimalPublisher : public rclcpp::Node

Copy to clipboard

The public constructor names the node minimal_publisher and initializes count_ to 0. Inside the constructor, the publisher is initialized with the String message type, the topic name topic, and the required queue size to limit messages in the event of a backup. Next, timer_ is initialized, which causes the timer_callback function to be executed twice a second.

public:MinimalPublisher(): Node("minimal_publisher"), count_(0){publisher_ = this->create_publisher<std_msgs::msg::String>("topic", 10);timer_ = this->create_wall_timer(500ms, std::bind(&MinimalPublisher::timer_callback, this));}

Copy to clipboard

The timer_callback function is where the message data is set and the messages are actually published. The RCLCPP_INFO macro ensures every published message is printed to the console.

private:void timer_callback(){auto message = std_msgs::msg::String();message.data = "Hello, world! " + std::to_string(count_++);RCLCPP_INFO(this->get_logger(), "Publishing: '%s'", message.data.c_str());publisher_->publish(message);}

Copy to clipboard

Last is the declaration of the timer, publisher, and counter fields.

rclcpp::TimerBase::SharedPtr timer_;
rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;
size_t count_;

Copy to clipboard

Following the MinimalPublisher class is main, where the node actually executes. rclcpp::init initializes ROS 2, and rclcpp::spin starts processing data from the node, including callbacks from the timer.

int main(int argc, char * argv[])
{rclcpp::init(argc, argv);rclcpp::spin(std::make_shared<MinimalPublisher>());rclcpp::shutdown();return 0;
}

Copy to clipboard

2.2 Add dependencies

Navigate one level back to the ros2_ws/src/cpp_pubsub directory, where the CMakeLists.txt and package.xml files have been created for you.

Open package.xml with your text editor.

As mentioned in the previous tutorial, make sure to fill in the <description><maintainer> and <license> tags:

<description>Examples of minimal publisher/subscriber using rclcpp</description>
<maintainer email="you@email.com">Your Name</maintainer>
<license>Apache License 2.0</license>

Copy to clipboard

Add a new line after the ament_cmake buildtool dependency and paste the following dependencies corresponding to your node’s include statements:

<depend>rclcpp</depend>
<depend>std_msgs</depend>

Copy to clipboard

This declares the package needs rclcpp and std_msgs when its code is built and executed.

Make sure to save the file.

2.3 CMakeLists.txt

Now open the CMakeLists.txt file. Below the existing dependency find_package(ament_cmake REQUIRED), add the lines:

find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

Copy to clipboard

After that, add the executable and name it talker so you can run your node using ros2 run:

add_executable(talker src/publisher_member_function.cpp)
ament_target_dependencies(talker rclcpp std_msgs)

Copy to clipboard

Finally, add the install(TARGETS...) section so ros2 run can find your executable:

install(TARGETStalkerDESTINATION lib/${PROJECT_NAME})

Copy to clipboard

You can clean up your CMakeLists.txt by removing some unnecessary sections and comments, so it looks like this:

cmake_minimum_required(VERSION 3.5)
project(cpp_pubsub)# Default to C++14
if(NOT CMAKE_CXX_STANDARD)set(CMAKE_CXX_STANDARD 14)
endif()if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")add_compile_options(-Wall -Wextra -Wpedantic)
endif()find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)add_executable(talker src/publisher_member_function.cpp)
ament_target_dependencies(talker rclcpp std_msgs)install(TARGETStalkerDESTINATION lib/${PROJECT_NAME})ament_package()

Copy to clipboard

You could build your package now, source the local setup files, and run it, but let’s create the subscriber node first so you can see the full system at work.

3 Write the subscriber node

Return to ros2_ws/src/cpp_pubsub/src to create the next node. Enter the following code in your terminal:

LinuxmacOSWindows

wget -O subscriber_member_function.cpp https://raw.githubusercontent.com/ros2/examples/humble/rclcpp/topics/minimal_subscriber/member_function.cpp

Copy to clipboard

Check to ensure that these files exist:

publisher_member_function.cpp  subscriber_member_function.cpp

Copy to clipboard

Open the subscriber_member_function.cpp with your text editor.

#include <memory>#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"
using std::placeholders::_1;class MinimalSubscriber : public rclcpp::Node
{public:MinimalSubscriber(): Node("minimal_subscriber"){subscription_ = this->create_subscription<std_msgs::msg::String>("topic", 10, std::bind(&MinimalSubscriber::topic_callback, this, _1));}private:void topic_callback(const std_msgs::msg::String & msg) const{RCLCPP_INFO(this->get_logger(), "I heard: '%s'", msg.data.c_str());}rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscription_;
};int main(int argc, char * argv[])
{rclcpp::init(argc, argv);rclcpp::spin(std::make_shared<MinimalSubscriber>());rclcpp::shutdown();return 0;
}

Copy to clipboard

3.1 Examine the code

The subscriber node’s code is nearly identical to the publisher’s. Now the node is named minimal_subscriber, and the constructor uses the node’s create_subscription class to execute the callback.

There is no timer because the subscriber simply responds whenever data is published to the topic topic.

public:MinimalSubscriber(): Node("minimal_subscriber"){subscription_ = this->create_subscription<std_msgs::msg::String>("topic", 10, std::bind(&MinimalSubscriber::topic_callback, this, _1));}

Copy to clipboard

Recall from the topic tutorial that the topic name and message type used by the publisher and subscriber must match to allow them to communicate.

The topic_callback function receives the string message data published over the topic, and simply writes it to the console using the RCLCPP_INFO macro.

The only field declaration in this class is the subscription.

private:void topic_callback(const std_msgs::msg::String & msg) const{RCLCPP_INFO(this->get_logger(), "I heard: '%s'", msg.data.c_str());}rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscription_;

Copy to clipboard

The main function is exactly the same, except now it spins the MinimalSubscriber node. For the publisher node, spinning meant starting the timer, but for the subscriber it simply means preparing to receive messages whenever they come.

Since this node has the same dependencies as the publisher node, there’s nothing new to add to package.xml.

3.2 CMakeLists.txt

Reopen CMakeLists.txt and add the executable and target for the subscriber node below the publisher’s entries.

add_executable(listener src/subscriber_member_function.cpp)
ament_target_dependencies(listener rclcpp std_msgs)install(TARGETStalkerlistenerDESTINATION lib/${PROJECT_NAME})

Copy to clipboard

Make sure to save the file, and then your pub/sub system should be ready.

4 Build and run

You likely already have the rclcpp and std_msgs packages installed as part of your ROS 2 system. It’s good practice to run rosdep in the root of your workspace (ros2_ws) to check for missing dependencies before building:

LinuxmacOSWindows

rosdep install -i --from-path src --rosdistro humble -y

Copy to clipboard

Still in the root of your workspace, ros2_ws, build your new package:

LinuxmacOSWindows

colcon build --packages-select cpp_pubsub

Copy to clipboard

Open a new terminal, navigate to ros2_ws, and source the setup files:

LinuxmacOSWindows

. install/setup.bash

Copy to clipboard

Now run the talker node:

ros2 run cpp_pubsub talker

Copy to clipboard

The terminal should start publishing info messages every 0.5 seconds, like so:

[INFO] [minimal_publisher]: Publishing: "Hello World: 0"
[INFO] [minimal_publisher]: Publishing: "Hello World: 1"
[INFO] [minimal_publisher]: Publishing: "Hello World: 2"
[INFO] [minimal_publisher]: Publishing: "Hello World: 3"
[INFO] [minimal_publisher]: Publishing: "Hello World: 4"

Copy to clipboard

Open another terminal, source the setup files from inside ros2_ws again, and then start the listener node:

ros2 run cpp_pubsub listener

Copy to clipboard

The listener will start printing messages to the console, starting at whatever message count the publisher is on at that time, like so:

[INFO] [minimal_subscriber]: I heard: "Hello World: 10"
[INFO] [minimal_subscriber]: I heard: "Hello World: 11"
[INFO] [minimal_subscriber]: I heard: "Hello World: 12"
[INFO] [minimal_subscriber]: I heard: "Hello World: 13"
[INFO] [minimal_subscriber]: I heard: "Hello World: 14"

Copy to clipboard

Enter Ctrl+C in each terminal to stop the nodes from spinning.

Summary

You created two nodes to publish and subscribe to data over a topic. Before compiling and running them, you added their dependencies and executables to the package configuration files.

Next steps

Next you’ll create another simple ROS 2 package using the service/client model. Again, you can choose to write it in either C++ or Python.

Related content

There are several ways you could write a publisher and subscriber in C++; check out the minimal_publisher and minimal_subscriber packages in the ros2/examples repo.

这篇关于ROS2+发布者+订阅者示例的文章就介绍到这儿,希望我们推荐的文章对编程师们有所帮助!



http://www.chinasem.cn/article/493811

相关文章

MySQL 8 中的一个强大功能 JSON_TABLE示例详解

《MySQL8中的一个强大功能JSON_TABLE示例详解》JSON_TABLE是MySQL8中引入的一个强大功能,它允许用户将JSON数据转换为关系表格式,从而可以更方便地在SQL查询中处理J... 目录基本语法示例示例查询解释应用场景不适用场景1. ‌jsON 数据结构过于复杂或动态变化‌2. ‌性能要

Python实现MQTT通信的示例代码

《Python实现MQTT通信的示例代码》本文主要介绍了Python实现MQTT通信的示例代码,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友们下面随着小编来一... 目录1. 安装paho-mqtt库‌2. 搭建MQTT代理服务器(Broker)‌‌3. pytho

Java中Arrays类和Collections类常用方法示例详解

《Java中Arrays类和Collections类常用方法示例详解》本文总结了Java中Arrays和Collections类的常用方法,涵盖数组填充、排序、搜索、复制、列表转换等操作,帮助开发者高... 目录Arrays.fill()相关用法Arrays.toString()Arrays.sort()A

MySQL进行数据库审计的详细步骤和示例代码

《MySQL进行数据库审计的详细步骤和示例代码》数据库审计通过触发器、内置功能及第三方工具记录和监控数据库活动,确保安全、完整与合规,Java代码实现自动化日志记录,整合分析系统提升监控效率,本文给大... 目录一、数据库审计的基本概念二、使用触发器进行数据库审计1. 创建审计表2. 创建触发器三、Java

MySQL 主从复制部署及验证(示例详解)

《MySQL主从复制部署及验证(示例详解)》本文介绍MySQL主从复制部署步骤及学校管理数据库创建脚本,包含表结构设计、示例数据插入和查询语句,用于验证主从同步功能,感兴趣的朋友一起看看吧... 目录mysql 主从复制部署指南部署步骤1.环境准备2. 主服务器配置3. 创建复制用户4. 获取主服务器状态5

Spring Boot中的路径变量示例详解

《SpringBoot中的路径变量示例详解》SpringBoot中PathVariable通过@PathVariable注解实现URL参数与方法参数绑定,支持多参数接收、类型转换、可选参数、默认值及... 目录一. 基本用法与参数映射1.路径定义2.参数绑定&nhttp://www.chinasem.cnbs

Spring StateMachine实现状态机使用示例详解

《SpringStateMachine实现状态机使用示例详解》本文介绍SpringStateMachine实现状态机的步骤,包括依赖导入、枚举定义、状态转移规则配置、上下文管理及服务调用示例,重点解... 目录什么是状态机使用示例什么是状态机状态机是计算机科学中的​​核心建模工具​​,用于描述对象在其生命

PostgreSQL中rank()窗口函数实用指南与示例

《PostgreSQL中rank()窗口函数实用指南与示例》在数据分析和数据库管理中,经常需要对数据进行排名操作,PostgreSQL提供了强大的窗口函数rank(),可以方便地对结果集中的行进行排名... 目录一、rank()函数简介二、基础示例:部门内员工薪资排名示例数据排名查询三、高级应用示例1. 每

使用Python删除Excel中的行列和单元格示例详解

《使用Python删除Excel中的行列和单元格示例详解》在处理Excel数据时,删除不需要的行、列或单元格是一项常见且必要的操作,本文将使用Python脚本实现对Excel表格的高效自动化处理,感兴... 目录开发环境准备使用 python 删除 Excphpel 表格中的行删除特定行删除空白行删除含指定

SpringBoot线程池配置使用示例详解

《SpringBoot线程池配置使用示例详解》SpringBoot集成@Async注解,支持线程池参数配置(核心数、队列容量、拒绝策略等)及生命周期管理,结合监控与任务装饰器,提升异步处理效率与系统... 目录一、核心特性二、添加依赖三、参数详解四、配置线程池五、应用实践代码说明拒绝策略(Rejected