3、 Topic communication: create your own information format

1、 technological process

1. Create... Under the function pack msg Folder , Used to hold .msg file

2. Definition Person.msg file

string name
uint16 age
float64 height

3. Edit profile

1. package.xml file
   Add two dependent packages , The first is the dependent package at compile time , The second is the runtime dependent package

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

2. CMakeLists.txt file

   find_package(catkin REQUIRED COMPONENTS
    roscpp
    rospy
    std_msgs
    message_generation
    )
   

   To configure msg Source file

   add_message_files(
    FILES
    Person.msg
    )
   

   Add dependencies when generating messages

   generate_messages(
    DEPENDENCIES
    std_msgs
    )
   

   Add execution time dependencies

   catkin_package(
   # INCLUDE_DIRS include
   # LIBRARIES public_massage
   CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
   # DEPENDS system_lib
   )
   

4. compile

After compilation , Some middleware will be generated , These middleware will be used in later programming , Include ：
C++ Middleware invoked in ：
working space /devel/include/ Package name /XXX.h
Python Middleware invoked in ：
working space /devel/lib/python3/dist-packages/ Package name /msg

2、 Code implementation

0.vscode To configure

For the convenience of code prompt , Need to be in .vscode/c_cpp_properties.json Medium includepath Add head Path to file

{
    
  "configurations": [
    {
    
      "browse": {
    
        "databaseFilename": "${workspaceFolder}/.vscode/browse.vc.db",
        "limitSymbolsToIncludedHeaders": false
      },
      "includePath": [
        "/opt/ros/noetic/include/**",
        "/usr/include/**",
        "/media/d102/EPAN/Desktop/code_study_ubuntu/rosdemo_04/devel/include/**"
      ],
      "name": "ROS",
      "intelliSenseMode": "gcc-x64",
      "compilerPath": "/usr/bin/gcc",
      "cStandard": "gnu11",
      "cppStandard": "c++17"
    }
  ],
  "version": 4
}

1.C++ Realization

1. Issued by

#include"ros/ros.h"
//public_massage Bit package name , Specific path  workspace/devel/include/ Package name 
#include"public_massage/Person.h"

int main(int argc,char *argv[]){
    
    setlocale(LC_ALL,"");
    //1. initialization ROS node , Name the node 
    ros::init(argc,argv,"talker");
    //2. establish ROS Handle 
    ros::NodeHandle nh;
    //3. Create publisher object 
    ros::Publisher pub = nh.advertise<public_massage::Person>("chatter",1000);
    //4. Organize the release of information 
    public_massage::Person p;
    p.name = "xiaomage";
    p.age = 24;
    p.height = 1.78;

    // Set the release frequency 
    ros::Rate r(1);
    // When the node is alive 
    while (ros::ok())
    {
    
        pub.publish(p);
        p.age += 1;
        ROS_INFO("my name is:%s,i am %d years old,height is %.2f meter!",p.name.c_str(),p.age,p.height);
        
        r.sleep();
        ros::spinOnce();
    }
    return 0;
    
    
}

2. Subscriber

#include"ros/ros.h"
#include"public_massage/Person.h"

void doPerson(const public_massage::Person::ConstPtr& person_p){
    
    ROS_INFO(" Subscriber information ：%s, %d, %.2f",person_p->name.c_str(),person_p->age,person_p->height);
}

int main(int argc, char *argv[]){
    
    setlocale(LC_ALL,"");
    //1. initialization ROS node 
    ros::init(argc,argv,"listener");
    //2. establish ROS Handle 
    ros::NodeHandle nh;
    //3. Create subscription object 
    ros::Subscriber sub = nh.subscribe<public_massage::Person>("chatter",10,doPerson);
    //4. Callback function Person

    //5.ros::spin()
    ros::spin();
    return 0;
}

3. To configure CMakeLists.txt file
   Be careful to add add_dependencies

add_executable(person_talker src/person_talker.cpp)
add_executable(person_listener src/person_listener.cpp)



add_dependencies(person_talker ${
    PROJECT_NAME}_generate_messages_cpp)
add_dependencies(person_listener ${
    PROJECT_NAME}_generate_messages_cpp)


target_link_libraries(person_talker
  ${
    catkin_LIBRARIES}
)
target_link_libraries(person_listener
  ${
    catkin_LIBRARIES}
)

2.Python Realization

0. To configure .vscode Medium settings.json file , Add the path of message data type

{
    
    "python.autoComplete.extraPaths": [
        "/opt/ros/noetic/lib/python3/dist-packages",
        "~/home/d102/anaconda3/envs/python36/lib/python3.6/site-packages/mediapipe/python",
        "~/home/d102/anaconda3/envs/python36/lib/python3.6/site-packages",
        "/home/d102/catkin_ws/devel/lib/python2.7/dist-packages",
        "/media/d102/EPAN/Desktop/code_study_ubuntu/rosdemo_04/devel/lib/python3/dist-packages"
    ]
}

1. Issued by

#! /usr/bin/env python

import rospy
# Introduce message data type 
from public_massage.msg import Person

if __name__ == "__main__":
    #1. initialization ROS node 
    rospy.init_node("talker_p")
    #2. Create publisher object 
    pub = rospy.Publisher("chatter_p",Person,queue_size=10)
    #3. Organize messages 
    p = Person()
    p.name = "xiaomage"
    p.age = 24
    p.height = 1.78

    #4. Write release logic 
    rate = rospy.Rate(1)
    while not rospy.is_shutdown():
        pub.publish(p)
        rate.sleep()
        rospy.loginfo(" full name ：%s,  Age ：%d,  height ：%.2f",p.name,p.age,p.height)

2. Subscriber

#! /usr/bin/env python

import rospy
from public_massage.msg import Person

def doperson(p):
    rospy.loginfo(" Received personal information ：%s, %d, %.2f",p.name,p.age,p.height)

if __name__ == "__main__":
    rospy.init_node("listener_p")
    sub = rospy.Subscriber("chatter_p",Person,doperson,queue_size=10)
    rospy.spin()

3. Add executable rights
   stay scripts Open the terminal under the folder , perform chmod +x *.py
4. To configure CMakeLists.txt file

catkin_install_python(PROGRAMS
  scripts/talker_p.py
  scripts/listener_p.py
  DESTINATION ${
    CATKIN_PACKAGE_BIN_DESTINATION}
)