ROS学习笔记(2) C++例程创建、发送/订阅机制、自定义消息

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本文档介绍了ROS中如何实现publisher和subscriber节点，用于控制小海龟移动，并展示了创建自定义消息类型的流程。通过`velocity_publisher.cpp`发布速度指令，`pose_subscriber.cpp`订阅并打印海龟位置。此外，还详细说明了创建`.msg`文件定义自定义消息`person.msg`，以及相关依赖配置。最后，提供了`person_publisher.cpp`和`person_subscriber.cpp`的代码示例，用于发布和订阅自定义消息。

publisher例程

按照指定频率向小海龟控制频段发送移动数据

//velocity_publisher.cpp
#include <ros/ros.h>
#include <geometry_msgs/Twist.h>

int main(int argc, char **argv){
    ros::init(argc, argv, "velocity_publisher");
    ros::NodeHandle n;
    ros::Publisher turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel",10);
    ros::Rate loop_rate(10);

    int count = 0;
    while(ros::ok()){
        geometry_msgs::Twist vel_msg;
        vel_msg.linear.x = 0.5;
        vel_msg.angular.z = 0.2;
        turtle_vel_pub.publish(vel_msg);
        ROS_INFO("Publish turtle velocity command[%0.2f m/s, %0.2f m/s]",
                    vel_msg.linear.x, vel_msg.angular.z);
        loop_rate.sleep();
    }
    return 0;
}

在CMakeLists.txt中添加编译链接
在这里插入图片描述

add_executable(velocity_publisher src/velocity_publisher.cpp)
target_link_libraries(velocity_publisher ${catkin_LIBRARIES})

subscriber例程

//pose_subscriber.cpp
#include<ros/ros.h>
#include<turtlesim/Pose.h>


void poseCallback(const turtlesim::Pose::ConstPtr &msg){
    ROS_INFO("Turtle pose: x:%0.6f, y:%0.6f", msg->x, msg->y);
}

int main(int argc, char **argv){
    ros::init(argc, argv, "pose_subscriber");
    ros::NodeHandle n;
    ros::Subscriber pose_sub = n.subscribe("/turtle1/pose", 10, poseCallback);
    ros::spin();
    return 0;
}

自定义消息类型

创建一个.msg后缀的消息文件，内容为消息格式的描述文件，会在编译时翻译成对应语言的数据类型格式。
在哪个包里用，就创建在哪个包里
在这里插入图片描述

//person.msg
string name
uint8 sex
uint8 age

uint8 unkown = 0
uint8 male = 1
uint8 female = 2

package.xml中添加自定义消息类型创建的依赖库

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

CMakeLists.txt中添加上述依赖包
在这里插入图片描述

find_package(catkin REQUIRED COMPONENTS
  geometry_msgs
  roscpp
  rospy
  std_msgs
  turtlesim
  message_generation
)

在下面的区域中添加自定义消息的编译链接
在这里插入图片描述

add_message_files(FILES person.msg) 
generate_messages(DEPENDENCIES std_msgs) //自定义消息的依赖包

添加编译依赖项

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES learning_topic
   CATKIN_DEPENDS geometry_msgs roscpp rospy std_msgs turtlesim message_generation
#  DEPENDS system_lib
)

发送和订阅的代码

//person_publisher.cpp
#include<ros/ros.h>
#include<learning_topic/person.h>
int main(int argc, char** argv){
    ros::init(argc, argv, "person_publisher");
    ros::NodeHandle n;
    ros::Publisher person_info_pub = n.advertise<learning_topic::person>("/person_info",10);
    ros::Rate loop_rate(1);

    while(ros::ok()){
        learning_topic::person person_msg;
        person_msg.name = "Tom";
        person_msg.age = 18;
        person_msg.sex = learning_topic::person::male;

        person_info_pub.publish(person_msg);
        ROS_INFO("Published Person info: name:%s, age:%d, sex:%d",
                    person_msg.name.c_str(), person_msg.age, person_msg.sex);
        loop_rate.sleep();
    }
    return 0;
}

//person_subscriber.cpp
#include<ros/ros.h>
#include<learning_topic/person.h>


void poseCallback(const learning_topic::person::ConstPtr &msg){
    ROS_INFO("Get person info name:%s, age:%d, sex:%d", msg->name.c_str(), msg->age, msg->sex);
}

int main(int argc, char **argv){
    ros::init(argc, argv, "person_subscriber");
    ros::NodeHandle n;
    ros::Subscriber person_sub = n.subscribe("/person_info", 10, poseCallback);
    ros::spin();
    return 0;
}

添加编译链接，由于与动态生成代码的地方有依赖关系，故教程上说这里各多了一行add_dependencies
但实际测试并不需要，安全起见加上

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)