ROS1学习第二弹

本文纯属记录学习过程，所学教程来自B站古月居ROS入门21讲

ROS1学习第一弹

二、关于代码

1.必有内容：

   // ROS节点初始化
   ros::init(argc, argv, "parameter_config");

   // 创建节点句柄
   ros::NodeHandle node;

2. 文件结构：/catkin_ws/src 中
   src
   ├── CMakeLists.txt -> /opt/ros/noetic/share/catkin/cmake/toplevel.cmake
   ├── learning_parameter
   │ ├── CMakeLists.txt
   │ ├── include
   │ │ └── learning_parameter
   │ ├── package.xml
   │ └── src
   │ └── parameter_config.cpp
   ├── learning_service
   │ ├── CMakeLists.txt
   │ ├── include
   │ │ └── learning_service
   │ ├── package.xml
   │ ├── src
   │ │ ├── person_client.cpp
   │ │ ├── person_server.cpp
   │ │ ├── turtle_command_server.cpp
   │ │ └── turtle_spawn.cpp
   │ └── srv
   │ └── Person.srv
   └── learning_topic
   ├── CMakeLists.txt
   ├── include
   │ └── learning_topic
   ├── msg
   │ └── Person.msg
   ├── package.xml
   └── src
   ├── person_publisher.cpp
   ├── person_subscriber.cpp
   ├── pose_subscriber.cpp
   └── velocity_publisher.cpp
   其中比如 └── learning_topic就是一个功能包，靠catkin_create_pkg生成，语法是catkin_create_pkg my_cpp_pkg roscpp std_msgs

3.Topic ：Publisher 与 Subscriber
在功能包下面建立msg文件夹，里面.msg文件定义消息类型，整个包编译一边就能在/devel/include/下面看见具体实现定义消息类型的文件

publisher:

#include<ros/ros.h>
#include"learning_topic/Person.h"

int main(int argc,char **argv)
{
    ros::init(argc, argv, "person_publisher");
    ros::NodeHandle n;

    // 创建Publisher对象（话题名、队列长度）
    ros::Publisher person_info_pub=n.advertise<learning_topic::Person>("/person_info",10);
    // 设置循环频率
    ros::Rate loop_rate(1);

    int count=0;
    while(ros::ok())
    {
        learning_topic::Person person_msg; // 创建消息对象
        person_msg.name="Tom";
        person_msg.age=18;
        person_msg.sex=learning_topic::Person::male;

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

        ROS_INFO("Publish Person Info: name: %s, age: %d, sex: %d", 
                 person_msg.name.c_str(), person_msg.age, person_msg.sex);
        
        loop_rate.sleep(); // 控制循环频率
    }
    return 0;
}

subscriber:

#include<ros/ros.h>
#include"learning_topic/Person.h"

void personInfoCallback(const learning_topic::Person::ConstPtr& msg)
{
    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::init(argc,argv,"person_subscriber");
    ros::NodeHandle n;

    // learning_topic::Person是自定义的消息类型
    // person_info_sub是订阅者对象
    // "/person_info"是话题名称 与publisher发布的名称一致
    // 10是队列长度，表示订阅者的消息队列长度
    // 当消息队列满时，旧消息会被丢弃
    // personInfoCallback是回调函数，当有新消息到来时会调用此函数处理消息
    // 该函数的参数是一个指向ConstPtr的指针，ConstPtr是指向常量的智能指针
    // 这样可以避免复制消息，提高效率
    // 订阅者会在后台自动处理消息队列
    // 当有新消息到来时，回调函数会被调用
    // 回调函数可以访问消息内容，并进行相应的处理
    ros::Subscriber person_info_sub=n.subscribe("/person_info",10,personInfoCallback);//
    ros::spin();
    return 0;
}

4.Service：Client 与 Server
在功能包下面建立srv文件夹，里面.srv文件定义消息类型，整个包编译一边就能在/devel/include/下面看见具体实现定义消息类型的文件

client:

#include<ros/ros.h>
#include<learning_service/Person.h>

int main(int argc,char ** argv)
{
    ros::init(argc,argv,"person_client");
    ros::NodeHandle node;

    // 等待服务可用（类似中断）
    ros::service::waitForService("/show_person");
    // 创建服务客户端
    ros::ServiceClient person_client=node.serviceClient<learning_service::Person>("/show_person");

    learning_service::Person srv;
    srv.request.name="Tom";
    srv.request.age=20;
    srv.request.sex=learning_service::Person::Request::male;

    ROS_INFO("Call service to show person[name:%s, age:%d, sex:%d]",
             srv.request.name.c_str(), srv.request.age,srv.request.sex);

    person_client.call(srv); // 调用服务
    ROS_INFO("Showperson result: %s", srv.response.result.c_str());
    
    return 0;
}

server:

#include<ros/ros.h>
#include"learning_service/Person.h"

bool personCallback(learning_service::Person::Request &req, // 引用传递，接绑定到客户端发送的请求对象
                   learning_service::Person::Response &res) {
    ROS_INFO("Person: Name: %s, Age: %d, sex:%d", req.name.c_str(), req.age,req.sex);
    
    res.result="OK";
    return true;
}

int main(int argc,char **argv)
{
    ros::init(argc,argv,"person_server");
    ros::NodeHandle n;

    // 创建服务
    ros::ServiceServer person_service=n.advertiseService("/show_person",personCallback); 
    ROS_INFO("Person service is ready.");
    ros::spin();
    return 0;
}

5.rosparam的使用：

rosparam is a command-line tool for getting, setting, and deleting parameters from the ROS Parameter Server.

Commands:
rosparam set set parameter
rosparam get get parameter
rosparam load load parameters from file
rosparam dump dump parameters to file
rosparam delete delete parameter
rosparam list list parameter names