【嵌入式系统应用开发】ROS通信模式编程

1 话题、服务模式的ROS程序设计

1.1 创建工作空间

创建工作空间

mkdir -p ~/comm_ws/src
cd ~/comm_ws/src
catkin_init_workspace

编译工作空间，返回上一目录进行编译

cd ..
catkin_make

进入src目录，创建功能包

catkin_create_pkg learning_communication std_msgs rospy roscpp

编译功能包

cd ..
catkin_make
source ~/comm_ws/devel/setup.bash

1.2 话题编程

1.2.1 步骤

1. 创建发布者
   • 初始化ROS节点
   • 向ROS Master注册节点信息，包括发布的话题名和话题中的消息类型
   • 按照一定频率循环发布消息
2. 创建订阅者
   • 初始化ROS节点
   • 订阅需要的话题
   • 循环等待话题消息，接收到消息后进行回调函数
   • 回调函数中完成消息处理
3. 添加编译选项
   • 设置需要编译的代码和生成的可执行文件
   • 设置链接库
   • 设置依赖
4. 运行可执行程序

1.2.2 实践

1. 添加文件

listener.cpp

#include"ros/ros.h"
#include"std_msgs/String.h"
//接收到订阅的消息，会进入消息的回调函数
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
    
    
	//将接收到的消息打印处理
	ROS_INFO("I heard:{%s}",msg->data.c_str());
}
int main(int argc,char **argv)
{
    
    
	//初始化ROS节点
	ros::init(argc,argv,"listener");
	//创建节点句柄
	ros::NodeHandle n;
	//创建一个Subscriber，订阅名为chatter的topic，注册回调函数chatterCallback
	ros::Subscriber sub=n.subscribe("chatter",1000,chatterCallback);
	//循环等待回调函数
	ros::spin();
	return 0;
}

talker.cpp

#include<sstream>
#include"ros/ros.h"
#include"std_msgs/String.h"
int main(int argc,char **argv)
{
    
    
	//ROS节点初始化
	ros::init(argc,argv,"talker");
	//创建节点句柄
	ros::NodeHandle n;
	//创建一个Publisher，发布名为chatter的topic，消息类型为std_msgs::String
	ros::Publisher chatter_pub=n.advertise<std_msgs::String>("chatter",1000);
	//设置循环的频率
	ros::Rate loop_rate(10);
	int count=0;
	while(ros::ok())
	{
    
    
		//初始化std_msgs::String类型的消息
		std_msgs::String msg;
		std::stringstream ss;
		ss<<"hello world"<<count;
		msg.data=ss.str();
		//发布消息
		ROS_INFO("%s",msg.data.c_str());
		chatter_pub.publish(msg);
		//循环等待回调函数
		ros::spinOnce();
		//接受循环频率延时
		loop_rate.sleep();
		++count;
	}
	return 0;
}

2. CMakeLists.txt文件

进入工程包目录下，打开CMakeLists.txt添加如下内容

add_executable(talker src/talker.cpp)
target_link_libraries(talker ${
    
    catkin_LIBRARIES})

add_executable(listener src/listener.cpp)
target_link_libraries(listener ${
    
    catkin_LIBRARIES})

3. 编译

cd ~/comm_ws/
catkin_make

4. 运行可执行文件

启动ros

roscore

打开两个新的终端分别输入：

cd  ~/comm_ws/
source devel/setup.bash
rosrun learning_communication talker 

cd  ~/comm_ws/
source devel/setup.bash
rosrun learning_communication listener 

5. 自定义话题消息

定义msg文件

mkdir ~/comm_ws/src/learning_communication/msg
cd ~/comm_ws/src/learning_communication/msg
vim Person.msg

在package.xml中添加功能包依赖

<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

修改CMakeLists.txt

编译

查看自定义消息

rosmsg show Person

2 动作编程

练习ROS动作编程：客户端发送一个运动坐标，模拟机器人运动到目标位置的过程。包括服务端和客户端的代码实现，要求带有实时位置反馈。

2.1 创建文件

创建小乌龟移动的“服务文件”turtleMove.cpp

/*  
　　　此程序通过通过动作编程实现由client发布一个目标位置
　　　然后控制Turtle运动到目标位置的过程
 */
#include <ros/ros.h>
#include <actionlib/server/simple_action_server.h>
#include "learning_communication/TurtleMoveAction.h"
#include <turtlesim/Pose.h> 
#include <turtlesim/Spawn.h>
#include <geometry_msgs/Twist.h>
 
typedef actionlib::SimpleActionServer<learning_communication::TurtleMoveAction> Server;
 
struct Myturtle
{
    
    
    float x;
    float y;
    float theta;
}turtle_original_pose,turtle_target_pose;
 
ros::Publisher turtle_vel;
 
void posecallback(const turtlesim::PoseConstPtr& msg) 
{
    
     
  ROS_INFO("Turtle1_position:(%f,%f,%f)",msg->x,msg->y,msg->theta);
  turtle_original_pose.x=msg->x; 
  turtle_original_pose.y=msg->y;
  turtle_original_pose.theta=msg->theta;
 }
 
// 收到action的goal后调用该回调函数
void execute(const learning_communication::TurtleMoveGoalConstPtr& goal, Server* as)
{
    
    
    learning_communication::TurtleMoveFeedback feedback;
 
    ROS_INFO("TurtleMove is working.");
    turtle_target_pose.x=goal->turtle_target_x;
    turtle_target_pose.y=goal->turtle_target_y; 
    turtle_target_pose.theta=goal->turtle_target_theta;
    
    geometry_msgs::Twist vel_msgs;
    float break_flag;
    
    while(1)
    {
    
      
        ros::Rate r(10);
        
        vel_msgs.angular.z = 4.0 * (atan2(turtle_target_pose.y-turtle_original_pose.y,
                                   turtle_target_pose.x-turtle_original_pose.x)-turtle_original_pose.theta);
        vel_msgs.linear.x = 0.5 * sqrt(pow(turtle_target_pose.x-turtle_original_pose.x, 2) +
                                      pow(turtle_target_pose.y-turtle_original_pose.y, 2)); 
        break_flag=sqrt(pow(turtle_target_pose.x-turtle_original_pose.x, 2) +
                                        pow(turtle_target_pose.y-turtle_original_pose.y, 2));
        turtle_vel.publish(vel_msgs);
 
        feedback.present_turtle_x=turtle_original_pose.x;
        feedback.present_turtle_y=turtle_original_pose.y;
        feedback.present_turtle_theta=turtle_original_pose.theta;
        as->publishFeedback(feedback);
        ROS_INFO("break_flag=%f",break_flag);
        if(break_flag<0.1) break;
        r.sleep();
    }
        // 当action完成后，向客户端返回结果
        ROS_INFO("TurtleMove is finished.");
        as->setSucceeded();
}
 
int main(int argc, char** argv)
{
    
    
    ros::init(argc, argv, "TurtleMove");
    ros::NodeHandle n,turtle_node;
    ros::Subscriber sub = turtle_node.subscribe("turtle1/pose",10,&posecallback); //订阅小乌龟的位置信息
    turtle_vel = turtle_node.advertise<geometry_msgs::Twist>("turtle1/cmd_vel",10);//发布控制小乌龟运动的速度
    // 定义一个服务器
        Server server(n, "TurtleMove", boost::bind(&execute, _1, &server), false);
        // 服务器开始运行
        server.start();
        ROS_INFO("server has started.");
    ros::spin();
 
    return 0;
}

创建小乌龟“发布目标位置文件”turtleMoveClient.cpp

#include <actionlib/client/simple_action_client.h>
#include "learning_communication/TurtleMoveAction.h"
#include <turtlesim/Pose.h> 
#include <turtlesim/Spawn.h>
#include <geometry_msgs/Twist.h>
 
typedef actionlib::SimpleActionClient<learning_communication::TurtleMoveAction> Client;
 
struct Myturtle
{
    
    
    float x;
    float y;
    float theta;
}turtle_present_pose;
 
// 当action完成后会调用该回调函数一次
void doneCb(const actionlib::SimpleClientGoalState& state,
        const learning_communication::TurtleMoveResultConstPtr& result)
{
    
    
    ROS_INFO("Yay! The TurtleMove is finished!");
    ros::shutdown();
}
 
// 当action激活后会调用该回调函数一次
void activeCb()
{
    
    
    ROS_INFO("Goal just went active");
}
 
// 收到feedback后调用该回调函数
void feedbackCb(const learning_communication::TurtleMoveFeedbackConstPtr& feedback)
{
    
    
    ROS_INFO(" present_pose : %f  %f  %f", feedback->present_turtle_x,
                   feedback->present_turtle_y,feedback->present_turtle_theta);
}
 
int main(int argc, char** argv)
{
    
    
    ros::init(argc, argv, "TurtleMove_client");
 
    // 定义一个客户端
    Client client("TurtleMove", true);
 
    // 等待服务器端
    ROS_INFO("Waiting for action server to start.");
    client.waitForServer();
    ROS_INFO("Action server started, sending goal.");
 
    // 创建一个action的goal
    learning_communication::TurtleMoveGoal goal;
    goal.turtle_target_x = 1;
    goal.turtle_target_y = 1;
    goal.turtle_target_theta = 0;
 
    // 发送action的goal给服务器端，并且设置回调函数
    client.sendGoal(goal,  &doneCb, &activeCb, &feedbackCb);
 
    ros::spin();
 
    return 0;
}

2.2 创建action文件夹

在功能包目录下创建action文件夹，并在此文件夹下创建TurtleMove.action文件

添加如下内容：

# Define the goal
float64 turtle_target_x  # Specify Turtle's　target position
float64 turtle_target_y
float64 turtle_target_theta
---
# Define the result
float64 turtle_final_x
float64 turtle_final_y
float64 turtle_final_theta
---
# Define a feedback message
float64 present_turtle_x
float64 present_turtle_y
float64 present_turtle_theta

2.3 修改文件

修改CMakeList.txt文件
在文件尾添加如下内容

add_executable(turtleMoveClient src/turtleMoveClient.cpp)
target_link_libraries(turtleMoveClient ${
    
    catkin_LIBRARIES})
add_dependencies(turtleMoveClient ${
    
    PROJECT_NAME}_gencpp)
add_executable(turtleMove src/turtleMove.cpp)
target_link_libraries(turtleMove ${
    
    catkin_LIBRARIES})
add_dependencies(turtleMove ${
    
    PROJECT_NAME}_gencpp)

其他修改内容如下：

修改package.xml文件

<build_depend>message_generation</build_depend>
<build_depend>actionlib</build_depend>
<build_depend>actionlib_msgs</build_depend>
  
<exec_depend>message_runtime</exec_depend>
<exec_depend>actionlib</exec_depend>
<exec_depend>actionlib_msgs</exec_depend> 

2.4 编译运行

编译

在四个终端按顺序分别运行下面命令

roscore
rosrun turtlesim turtlesim_node
rosrun learning_communication turtleMove
rosrun learning_communication turtleMoveClient

3 分布式通信

在两台电脑上演示ROS的分布式通信

3.1 主机

开启ros

roscore

新建一个终端，输入

export ROS_IP=xxx.xxx.xxx							#本机IP
export ROS_MASTER_URI=http://xxx.xxx.xxx:11311/		#主机IP
rosrun turtlesim turtlesim_node
source ~/.bashrc

3.2 从机

终端中输入

export ROS_IP=X.X.X.X 						#本机ip
export ROS_MASTER_URI=http://x.x.x.x:11311	#主机IP
source ~/.bashrc
rosrun turtlesim turtle_teleop_key

主机：

从机：

即可实现从机上控制小海龟行走

总结

通过本次实验，学习了解了ROS相关控制机制，学习了话题、服务、动作的相关知识，同时也学习了解到了分布式通信，实现了从机控制主机的小海龟的行走。

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参考
https://blog.csdn.net/qq_43279579/article/details/114764633
https://blog.csdn.net/xiongmingkang/article/details/81203329