ROS 话题消息的定义与使用

如何自定义话题消息

创建 msg 文件，新建一个 /msg 文件夹

Person.msg

string name
unit8 sex
unit8 age

unit8 ubknown = 8
unit8 male = 1
unit8 female = 2

在 package.xml 中添加功能包依赖

• <build_depend>message_generation</build_depend>

• <exec_depend>message_runtime</exec_depend>

在 CMakeLists.txt 中添加编译选项

• 在 find_package() 中添加 message_generation

• 在 Declare ROS messages, services and actions 部分添加

  • add_message_files(FILES Person.msg)
  • generate_messages(DEPENDENCIES std_msgs)

• 在 catkin_package() 中添加 message_runtime

  • 取消掉 CATKIN_DEPENDS 部分的注释

编译生成语言相关文件

在 catkin_ws/ 根目录下

catkin_make

• 编译时可能报错，提示

  File "/opt/ros/melodic/lib/python2.7/dist-packages/genmsg/template_tools.py", line 39, in <module>
    import em
ImportError: No module named em
    ···
    ···
  File "/opt/ros/melodic/lib/python2.7/dist-packages/genpy/message.py", line 48, in <module>
    import yaml
ImportError: No module named yaml

按照提示安装相关依赖

• python -m pip install empy

• pip install pyyaml

再次编译后成功

---

创建 Publisher & Subscriber

在 learning_topic 功能包的 src 目录中新建 person_publisher.cpp 和 person_subscriber.cpp 文件

编辑内容如下

person_publisher.cpp

/**
 * @file person_publisher.cpp
 * @brief 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 node;

    // 创建一个 publisher 注册
    // 发布名为 /person_info 的 topic
    // learning_topic::Person
    // 队列长度是 10
    ros::Publisher person_info_pub = node.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 geometry_msgs::Twist 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("Publsh 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

/**
 * @file person_subscriber.cpp
 * @brief 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) {
    // ROS 节点初始化
    ros::init(argc, argv, "person_subscriber");

    // 创建节点句柄
    ros::NodeHandle node;

    // 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 = node.subscribe("/person_info", 10, personInfoCallback);

    // 循环等待回调函数
    ros::spin();
    
    return 0;
}

配置 CMakeList.txt

编辑 learning_topic/CMakeList.txt ，在文件中的 build 部分添加以下内容

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)

-自定义的话题消息编译时会生成一些动态文件，需要用 add_dependencies() 来进行链接

编译功能包

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

运行

开启三个终端分别运行

终端 1 roscore

cd ~/catkin_ws/
roscore

终端 2 person_publisher

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

终端 3 person_subscriber

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

效果如下

可以看到自定义的消息结构成功的发布和订阅