[ROS study notes] (three) the realization of Publisher Publisher

1. Target function

There are two nodes in ROS Master, one is Subscriber (turtlesim) and the other is Publisher. The publisher implements the program to publish Message. The content of Message includes linear velocity and angle, which are passed to Subscriber through Topic pipeline to control the movement of turtles. .

Second, create a feature package

First create a workspace, refer to the previous section [ROS study notes] (2) Creation of workspace and function package

Then create a feature package

cd ~/catkin_ws/src
catkin_create_pkg learning_topic roscpp rospy std_msgs geometry_msgs turtlesim

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Three, create the publisher code

Enter the src folder of the function package and create a cpp file (you can also create it directly in the graphical interface)

cd ~/catkin_ws/src/learning_topic/src
touch velocity_publisher.cpp
sudo gedit velocity_publisher.cpp

Enter the following code

/**
 * 该例程将发布turtle1/cmd_vel话题，消息类型geometry_msgs::Twist
 */
 
#include <ros/ros.h>
#include <geometry_msgs/Twist.h>

int main(int argc, char **argv)
{
    
    
	// ROS节点初始化
	ros::init(argc, argv, "velocity_publisher");

	// 创建节点句柄
	ros::NodeHandle n;

	// 创建一个Publisher，发布名为/turtle1/cmd_vel的topic，消息类型为geometry_msgs::Twist，队列长度10
	ros::Publisher turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 10);

	// 设置循环的频率
	ros::Rate loop_rate(10);

	int count = 0;
	while (ros::ok())
	{
    
    
	    // 初始化geometry_msgs::Twist类型的消息
		geometry_msgs::Twist vel_msg;
		vel_msg.linear.x = 0.5;
		vel_msg.angular.z = 0.2;

	    // 发布消息
		turtle_vel_pub.publish(vel_msg);
		ROS_INFO("Publsh turtle velocity command[%0.2f m/s, %0.2f rad/s]", 
				vel_msg.linear.x, vel_msg.angular.z);

	    // 按照循环频率延时
	    loop_rate.sleep();
	}

	return 0;
}

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Four, configure publisher code compilation rules

Set the code to be compiled and the executable file generated
Set up the link library

In Learning_topic/CMakeList.txtthe bottom of the file Build (Install above), add the following code

add_executable(velocity_publisher src/velocity_publisher.cpp)	#描述要把哪个程序文件编译成哪个可执行文件
target_link_libraries(velocity_publisher ${catkin_LIBRARIES})	#把可执行文件和库做链接

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Five, compile and run Publisher Publisher

1. Compile

cd ~/catkin_ws
catkin_make
source devel/setup.bash

You can ~/.bashrcadd a source statement at the end of the file, so you don’t have to enter the source command in the terminal every time to create environment variables (replace your own username in the path)
source /home/【Username】/catkin_ws/devel/setup.bash

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2. Run

roscore
rosrun turtlesim turtlesim_node
rosrun learning_topic velocity_publisher

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Reference tutorial: Introduction to Guyue ROS 21 on
GitHub: https://github.com/guyuehome/ros_21_tutorials
Bilibili: https://www.bilibili.com/video/BV1zt411G7Vn