话题消息的订阅与使用

一、话题模型

二、自定义话题消息

自定义话题消息(Person.msg)
string name
uint8 sex
uint8 age
uint8 unknown = 0
uint 8 male = 1
unit8 female = 2

1. 定义msg文件；

2. 在package.xml中添加功能包依赖

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

3. 在CMakeLists.txt添加编译选项

   find_package(....... message_generation)
   
   add_message_files(FILES Person.msg)
   generate_messages(DEPENDENCIES std_msgs)
   
   catkin_package(....... message_runtime)
   

4. 编译生成语言相关文件

三、创建发布者、订阅者

/**
 * 该例程将发布/person_info话题，自定义消息类型learning_topic::Person
 */
 
#include <ros/ros.h>
#include "learning_topic/Person.h"

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

    // 创建节点句柄
    ros::NodeHandle n;

    // 创建一个Publisher，发布名为/person_info的topic，消息类型为learning_topic::Person，队列长度10
    ros::Publisher person_info_pub = n.advertise<learning_topic::Person>("/person_info", 10);

    // 设置循环的频率
    ros::Rate loop_rate(1);

    int count = 0;
    while (ros::ok())
    {
        // 初始化learning_topic::Person类型的消息
    	learning_topic::Person person_msg;
		person_msg.name = "ZhangQiYue";
		person_msg.age  = 21;
		person_msg.sex  = learning_topic::Person::male;

        // 发布消息
		person_info_pub.publish(person_msg);

       	ROS_INFO("Publish Person Info: name:%s  age:%d  sex:%d", 
				  person_msg.name.c_str(), person_msg.age, person_msg.sex);

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

    return 0;
}

/**
 * 该例程将订阅/person_info话题，自定义消息类型learning_topic::Person
 */
 
#include <ros/ros.h>
#include "learning_topic/Person.h"

// 接收到订阅的消息后，会进入消息回调函数
void personInfoCallback(const learning_topic::Person::ConstPtr& msg)
{
    // 将接收到的消息打印出来
    ROS_INFO("Subcribe Person Info: name:%s  age:%d  sex:%d", 
			 msg->name.c_str(), msg->age, msg->sex);
}

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

    // 创建节点句柄
    ros::NodeHandle n;

    // 创建一个Subscriber，订阅名为/person_info的topic，注册回调函数personInfoCallback
    ros::Subscriber person_info_sub = n.subscribe("/person_info", 10, personInfoCallback);

    // 循环等待回调函数
    ros::spin();

    return 0;
}

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

# 该例程将发布/person_info话题，自定义消息类型learning_topic::Person

import rospy
from learning_topic.msg import Person

def velocity_publisher():
	# ROS节点初始化
    rospy.init_node('person_publisher', anonymous=True)

	# 创建一个Publisher，发布名为/person_info的topic，消息类型为learning_topic::Person，队列长度10
    person_info_pub = rospy.Publisher('/person_info', Person, queue_size=10)

	#设置循环的频率
    rate = rospy.Rate(10) 

    while not rospy.is_shutdown():
		# 初始化learning_topic::Person类型的消息
    	person_msg = Person()
    	person_msg.name = "ChenQian";
    	person_msg.age  = 20;
    	person_msg.sex  = Person.male;

		# 发布消息
        person_info_pub.publish(person_msg)
    	rospy.loginfo("Publsh person message[%s, %d, %d]", 
				person_msg.name, person_msg.age, person_msg.sex)

		# 按照循环频率延时
        rate.sleep()

if __name__ == '__main__':
    try:
        velocity_publisher()
    except rospy.ROSInterruptException:
        pass

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

# 该例程将订阅/person_info话题，自定义消息类型learning_topic::Person

import rospy
from learning_topic.msg import Person

def personInfoCallback(msg):
    rospy.loginfo("Subcribe Person Info: name:%s  age:%d  sex:%d", 
			 msg.name, msg.age, msg.sex)

def person_subscriber():
	# ROS节点初始化
    rospy.init_node('person_subscriber', anonymous=True)

	# 创建一个Subscriber，订阅名为/person_info的topic，注册回调函数personInfoCallback
    rospy.Subscriber("/person_info", Person, personInfoCallback)

	# 循环等待回调函数
    rospy.spin()

if __name__ == '__main__':
    person_subscriber()

如何实现一个发布者

• 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
• 创建消息数据
• 按照一定频率循环发布消息

如何实现一个订阅者

• 初始化ROS节点
• 订阅需要的话题
• 循环等待话题消息，接收到消息后进入回调函数
• 在回调函数中完成消息处理

四、配置代码编译规则

add_executable(person_publisher src/person_publisher.cpp)
target_link_libraries(person_publisher ${catkin_LIBRARIES})
add_dependencies(person_publisher ${PROJECT_NAME}_generate_messages_cpp)


add_executable(person_subscriber src/person_subscriber.cpp)
target_link_libraries(person_subscriber ${catkin_LIBRARIES})
add_dependencies(person_subscriber ${PROJECT_NAME}_generate_messages_cpp)

如何配置CMakeLists.txt中的编译规则

• 设置需要编译的代码和生成的可执行文件
• 设置链接库
• 添加依赖项

五、编译并运行发布者和订阅者

 cd ~/catkin_ws
 catkin_make
 source devel/setup.bash
 roscore
 
 rosrun learning_topic person_publisher
 rosrun learning_topic person_subscriber