ROS知识：消息自定义的操作

我们一般用的消息，是系统定义的；然而系统定义的消息格式往往不够用，需要自定义消息数据， 这里介绍自定义消息的几个步骤。

自定义消息，首先需要定义一个数据结构文件如：

Person.msg

string name
uint8 sex
uint8 age
uint8 unknown = 0
uint8 male =1
uint8 fmale = 2

Person.msg的存放路径：

定义编译依赖 message_generation

定义执行依赖：message_runtime

 message_generation 
message_runtime

1)修改依赖信息find-package

find-package（..., message_generation)

2）追加文件 

add _message_files(FILES Person.msg)

generate_messages(DEPENDENCIES std_msgs)

3)追加包

catkin_package( .... message_runtime )

退回到工作区，然后catkin_make进行编译；注意，这里编译后，将person.msg编译成了person.h

并存放在: <工作空间>/devel/include目录下。

//person_publisher.cpp

 
#include 
//！！！！！关键！！！！！
#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
    //！！！！！关键！！！！！
    ros::Publisher person_info_pub = n.advertise("/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;
}

//person_subscriber.cpp

 
#include 
//！！！！！关键！！！！！
#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
    //！！！！！关键！！！！！
    ros::Subscriber person_info_sub = n.subscribe("/person_info", 10, personInfoCallback);

    // 循环等待回调函数
    ros::spin();

    return 0;
}

*设置需要编译的代码和生成的可执行文件;
*设置链接库;
*添加动态产生的依赖项.

//这里相比之前配置CMakeLists.txt，多了add_dependencies的语句目的是让可执行文件（前两句做的工作）和动态生成的文件产生依赖关系
//位置依旧,找到Install位置的上方，添加以下语句,保存.
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)

实际操作截图： 

cd ~/catkin_ws
catkin_make
source devel/setup.bash
roscore
//新开一个终端，运行subscriber
rosrun learning_topic person_subscriber
//新开一个终端，运行publisher
rosrun learning_topic person_publisher
//ROS Master是帮助节点的创建和链接的。节点一旦创建和链接后，就不受ROS Master影响

10.1 publisher

#!/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 = "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

10.2 subscriber

#!/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()