ROS入门21讲(3)

七、话题消息的定义和使用

目的：实现Publisher 与 Subscriber 之间的传输

1、自定义话题消息

如何自定义话题消息？

①完成数据接口的定义---定义msg文件

Person.msg

string name
uint8 sex
uint8 age

uint8 unknown = 0
uint8 male = 1
uint8 female = 2

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)

注意：配置完catkin_make一下，会在devel下产生一个Person.h的头文件

④编译生成语言相关文件

2、创建发布者代码

C++代码：

/**
 * 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 = "Tom";
        person_msg.age  = 18;
        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;
}

流程见上一讲(2)

python代码：

# 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 = "Tom";
        person_msg.age  = 18;
        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

3、创建订阅者代码

C++代码：

/**
 * 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;
}

python代码：

# 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()

4、配置代码编译规则

如何配置CMakeLists.txt中的编译规则？

①设置需要配置的代码和生成的可执行文件

②设置链接库

③配置依赖项

CMakeLists.txt中需要添加：

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)

5、编译并且运行发布者和订阅者

命令：

　　$ cd ~/catkin_ws

　　$ catkin_make

　　$ source devel/setup.bash

　　$ roscore

　　$ rosrun learning_topic person_subscriber

　　$ rosrun learning_topic person_publisher

图示：