Actual case of ROS communication

ROS Built in turtlesim Case study

difference

/turtle1/cmd_vel： The node that controls the movement of the little turtle

Release ：rostopic info /turtle1/cmd_vel(turtle1/cmd_vel Is the node )

Type: geometry_msgs/Twist
Publishers: /teleop_turtle (http://rosnoetic-VirtualBox:33275/)
Subscribers: /turtlesim (http://rosnoetic-VirtualBox:40025/)

subscribe ：rostopic info /turtle1/pose

Type: turtlesim/Pose
Publishers: /turtle1 (http://rosnoetic-VirtualBox:46159/)
Subscribers: None

Topic Publishing

1. Get the topic /turtle1/cmd_vel

rqt_graph： Start the calculation chart
The left and right ends are node information

2. Get message type

rostopic info /turtle1/cmd_vel(turtle/cmd_vel It's a topic )

Type: geometry_msgs/Twist
Publishers: /teleop_turtle (http://rosnoetic-VirtualBox:33275/)
Subscribers: /turtlesim (http://rosnoetic-VirtualBox:40025/)

perhaps rostopic type /turtle1/cmd_vel

geometry_msgs/Twist

3. Get message format

• rosmsg show geometry_msgs/Twist（ Be similar to plumbing_pub_sub/Person） Get internal parameters
• rosmsg info geometry_msgs/Twist

geometry_msgs/Vector3 linear（ Linear velocity ）
float64 x
float64 y
float64 z
geometry_msgs/Vector3 angular（ angular velocity ）
float64 x
float64 y
float64 z

• linear( Linear velocity ) Under the xyz Corresponding to x、y and z Speed in direction ( The unit is m/s), The data type is floating point double
• angular( angular velocity ) Under the xyz They correspond to each other x Roll on the shaft 、y On axis pitch and z Yaw speed on axis ( The unit is rad/s)

radian : The unit radian is defined as the center angle when the arc length is equal to the radius . That is... In the picture radian
The perimeter of 2pir, turn 1 Radius is 1 radian , turn 1 The circle is equivalent to 6.28 Radius , Namely 6.28 A radian ,1 Second turn 1 Circle is 6.28rad/s.

With 10Hz The way to subscribe ：rostopic pub -r 10 /turtle1/cmd_vel geometry_msgs/Twist

4. Control tortoise movement

4.1 C++ Realization ：test01_pub_twist

function

step ：

1. roscore
2. rosrun turtlesim turtlesim_node
3. cd demo02_ws
4. source ./devel/setup.bash
5. rosrun plumbing_test test01_pub_twist

#include"ros/ros.h"
#include"geometry_msgs/Twist.h"

/*  demand ： Post topic news   topic of conversation ： /turtle1/cmd_vel  news ： geometry_msgs/Twist 1. Include header file  2. initialization ROS node  3. Create node handle  4. Create a publishing object  5. Release logic implementation  6.spinOnce()  Circular Publishing  */

int main(int argc, char *argv[])
{
    
    //  Solve the mess 
    setlocale(LC_ALL,"");

    // 2. Initialize node 
    ros::init(argc,argv,"my_control");

    // 3. Create node handle 
    ros::NodeHandle nh;

    // 4. Create a publishing object 
    ros::Publisher pub = nh.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel",10);//  Topic name /tur...

    // 5. Release logic implementation  10Hz 1 second 10 Time 
    // 5.1  Set the release frequency 
    ros::Rate rate(10);

    // 5.2  Organize the messages that are published 
    geometry_msgs::Twist twist;
    twist.linear.x = 1.0;// The data type is floating point double
    twist.linear.y = 0.0;
    twist.linear.z = 0.0;
    twist.angular.z = 1.0;// Only yaw angle 
    twist.angular.x = 0.0;
    twist.angular.y = 0.0;

    // 5.3  Circular Publishing 
    while(ros::ok())
    {
    
        pub.publish(twist);
        
        //  Sleep 
        rate.sleep();

        // 6.spinOnce()  Circular Publishing 
        ros::spinOnce();
    }
    
    return 0;
}

4.2 Python Realization ： test01_pub_twist_p.py

function

step

1. Add executable rights
   chmod +x *.py
   ll
2. compile ——catkin Part of the modified
3. perform
   roscore
   rosrun turtlesim turtlesim_node
   rosrun plumbing_test test01_pub_twist_p.py

#! /usr/bin/eny python

"""  Issued by ： Release speed news   topic of conversation ： /turtle1/cmd_vel  news ： geometry_msgs/Twist 1.  Guide pack  2.  initialization ROS node  3.  Create publisher object  4.  Organization data , Release data  """

import rospy
from geometry_msgs.msg import Twist

if __name__ == "__main__":

    # 2.  initialization ROS node 
    rospy.init_node("my_control_p")

    # 3.  Create publisher object 
    pub = rospy.Publisher("/turtle/cmd_vel",Twist,queue_size = 10)

    # 4.  Organization data , Release data 
    # 4.1  Set the release frequency 
    rate = rospy.Rate(10)

    # 4.2  Message creation speed 
    twist = Twist()
    twist.linear.x = 0.5
    twist.linear.y = 0.0
    twist.linear.z = 0.0
    
    twist.angular.x = 0.0
    twist.angular.y = 0.0
    twist.angular.z = 1.0

    # 4.3  Circular Publishing 
    while not rospy.is_shutdown():
        pub.publish(twist)
        rate.sleep()

Topic subscription

1. Get the topic /turtle1/pose

rostopic list

/rosout
/rosout_agg
/turtle1/cmd_vel
/turtle1/color_sensor
/turtle1/pose

2. Get message type

rostopic info /turtle1/pose

Type: turtlesim/Pose
Publishers: /turtle1 (http://rosnoetic-VirtualBox:46159/)
Subscribers: None

3. Get message format

rosmsg info turtlesim/Pose

float32 x( coordinate )
float32 y
float32 theta（ toward ）
float32 linear_velocity（ Linear velocity ）
float32 angular_velocity（ angular velocity ）

rostopic echo /turtle1/pose： Print information

4. Code implementation

4.1 C++ Realization ：test02_sub_pose

function

1. window 1：vscode terminal
   source ./devel/setup.bash
   roslaunch plumbing_test start_turtle.launch
2. window 2：ctrl+alt+t
   cd demo02_ws
   source ./devel/setup.bash
   rosrun plumbing_test test02_sub_pose
   You can control the tortoise movement according to the keyboard , Print out the turtle's movement information in real time .

#include"ros/ros.h"
#include"turtlesim/Pose.h"

/*  demand ： Subscribe to tortoise pose information  1.  Include header file  2.  initialization ROS node  3.  Create node handle  4.  Create subscription object  5.  Process subscribed data （ Callback function ） 6. spin() come back  */
void doPose(const turtlesim::Pose::ConstPtr &pose)
{
    
    ROS_INFO(" Turtle pose information ： coordinate (%.2f,%.2f), toward (%.2f), Linear velocity :%.2f, angular velocity :%.2f",
            pose->x,pose->y,pose->theta,pose->linear_velocity,pose->angular_velocity);
}

int main(int argc, char *argv[])
{
    
    //  Chinese garbled 
    setlocale(LC_ALL,"");

    // 2.  initialization ROS node 
    ros::init(argc,argv,"sub_pose");

    // 3.  Create node handle 
    ros::NodeHandle nh;

    // 4.  Create subscription object 
    ros::Subscriber sub = nh.subscribe("/turtle1/pose",100,doPose); //doPose It's a callback function 

    // 5.  Process subscribed data （ Callback function ）
    // 6. spin() come back 
    ros::spin();
    return 0;
}

4.2 Python Realization ：test02_sub_pose_p.py

function

1. Add executable rights
   chmod +x *.py
   ll
2. compile ——catkin Part of the modified
3. perform
   window 1：vscode terminal
   source ./devel/setup.bash
   roslaunch plumbing_test start_turtle.launch
   window 2：ctrl+alt+t
   cd demo02_ws
   source ./devel/setup.bash
   rosrun plumbing_test test02_sub_pose_p.py

#! /usr/bin/env python

"""  demand ： Subscribe and output tortoise's position information  1.  Guide pack  2.  initialization ROS node  3.  Create subscription object  4.  Use the callback function to process the subscribed information  5. spin() """
import  rospy
from turtlesim.msg import Pose

def doPose(pose):
    rospy.loginfo("p-> Turtle pose information ： coordinate (%.2f,%.2f), toward (%.2f), Linear velocity :%.2f, angular velocity :%.2f",
                pose.x,pose.y,pose.theta,pose.linear_velocity,pose.angular_velocity)

if __name__ == "__main__":
    
    # 2.  initialization ROS node 
    rospy.init_node("sub_pose_p")

    # 3.  Create subscription object 
    sub = rospy.Subscriber("/turtle1/pose",Pose,doPose,queue_size=100)#  The message type is Pose
    # 4.  Use the callback function to process the subscribed information 
    # 5. spin()
    rospy.spin()

The service call

1. Get the topic /spawn( lay eggs )

rosservice list

/clear
/key/get_loggers
/key/set_logger_level
/kill
/reset
/rosout/get_loggers
/rosout/set_logger_level
/spawn
/turtle1/get_loggers
/turtle1/set_logger_level
/turtle1/set_pen
/turtle1/teleport_absolute
/turtle1/teleport_relative

2. Get message type

rosservice info /spawn： obtain turtlesim/Spawn

Node: /turtle1
URI: rosrpc://rosnoetic-VirtualBox:60831
Type: turtlesim/Spawn
Args: x y theta name

3. Get message format

rossrv info turtlesim/Spawn

float32 x （ The first half is the request ）
float32 y
float32 theta
string name

---

string name（ The second half is the response ）

theta It's the radian system , The scope is 3.14rad——(-3.14)rad, Counter clockwise is positive , Clockwise is negative

4. Code implementation

4.1 C++ Realization test03_server_client.cpp

1. window 1：vscode terminal
   source ./devel/setup.bash
   roslaunch plumbing_test start_turtle.launch
2. window 2：ctrl+alt+t
   cd demo02_ws
   source ./devel/setup.bash
   rosrun plumbing_test test03_service_client

function

#include"ros/ros.h"
#include"turtlesim/Spawn.h"

/*  demand ： Send request to server , Generate a new tortoise   topic of conversation ：/spawn  news ：turtlesim/Spawn 1. Include header file  2. initialization ROS node  3. Create node handle  4. Create client objects  5. Organize data and send  6. Process response  */

int main(int argc, char *argv[])
{
    
    setlocale(LC_ALL,"");

    // 2. initialization ROS node 
    ros::init(argc,argv,"service_call");

    // 3. Create node handle 
    ros::NodeHandle nh;

    // 4. Create client objects 
    ros::ServiceClient client = nh.serviceClient<turtlesim::Spawn>("/spawn"); // /spawn It's the topic name 

    // 5. Organize data and send 
    // 5.1  Organization request data 
    turtlesim::Spawn spawn;
    spawn.request.x = 1.0;
    spawn.request.y = 4.0;
    spawn.request.theta = 4.0;
    spawn.request.name = "turtle2";

    // 5.2  Send a request 
    // Determine the server status 
    // ros::service::waitForService("/spawn");
    client.waitForExistence();
    bool flag = client.call(spawn);//flag  Accept response status , The response result will also be set into spawn object 
    
    // 6. Process response 
    if(flag) //  Response successful 
    {
    
        ROS_INFO(" Tortoise generation succeeded , The new turtle is called ：%s",spawn.response.name.c_str());
    }
    else
    {
    
        ROS_INFO(" request was aborted !!!");
    }

    return 0;
}

4.2 Python Realization test03_server_client_p.py

function

1. Add executable rights
   chmod +x *.py
   ll
2. compile ——catkin Part of the modified
3. perform
   window 1：vscode terminal
   source ./devel/setup.bash
   roslaunch plumbing_test start_turtle.launch
   window 2：ctrl+alt+t
   cd demo02_ws
   source ./devel/setup.bash
   rosrun plumbing_test test03_service_client_p.py

#! /usr/bin/env python


"""  demand ： Send a request to the server to generate a turtle   topic of conversation ：/spawn  Message type ：turtlesim/Spawn 1.  Guide pack  2.  initialization ROS node  3.  Create the client object of the service  4.  Organize data and send requests  5.  Process response results  """

import rospy
from turtlesim.srv import Spawn,SpawnRequest,SpawnResponse

if __name__ == "__main__":
    # 2.  initialization ROS node 
    rospy.init_node("service_call")
    # 3.  Create the client object of the service 
    client = rospy.ServiceProxy("/spawn",Spawn) # /spawn It's the topic name 
    # 4.  Organize data and send requests 
    # 4.1  Organization data 
    request = SpawnRequest()
    request.x = 4.5
    request.y = 2.0
    request.theta = -3 #  turn right 3 individual rad
    request.name = "turtle3"
    # 4.2  Determine the server status and send 
    client.wait_for_service() #  When the server is turned on, execute , Otherwise hang 
    #  Prevent throwing exceptions 
    try:
        response = client.call(request)
        # 5.  Process response results 
        rospy.loginfo(" The name of the tortoise is ：%s",response.name)
    except Exception as e:
        rospy.logerr(" Request handling exception ")

Parameter setting

1. Get parameter name

Get parameter list rosparam list

/rosdistro
/roslaunch/uris/host_rosnoetic_virtualbox__43129
/rosversion
/run_id
/turtlesim/background_b
/turtlesim/background_g
/turtlesim/background_r

Get parameter value rosparam get /turtlesim/background_r

2. Code implementation

2.1 C++ Realization test04_param

function

rescore
cd demo02_ws
source ./devel/setup.bash
rosrun plumbing_test test04_param
rosrun turtlesim turtlesim_node（ Finally start ）

#include"ros/ros.h"

/*
     demand ： Modify parameters in the server turtlesim Background color related parameters 

    1. initialization ROS node 
    2. It is not necessary to create a node handle （ And the subsequent API of ）
    3. Modify the parameters 
*/


int main(int argc, char *argv[])
{
    
    // 1. initialization ROS node 
    ros::init(argc,argv,"change_bgcolor");
    // 2. It is not necessary to create a node handle （ And the subsequent API of ）
    // ros::NodeHandle nh("turtlesim");// Set namespace 
    // nh.setParam("background_r",255);
    // nh.setParam("background_g",255);
    // nh.setParam("background_b",255);

    ros::NodeHandle nh;
    nh.setParam("/turtlesim/background_r",0);
    nh.setParam("/turtlesim/background_g",50);
    nh.setParam("/turtlesim/background_b",100);

    // 3. Modify the parameters 
    //  The way 1： If the ros::param  There is no need to create a node handle 
    // ros::param::set("/turtlesim/background_r",0);
    // ros::param::set("/turtlesim/background_g",0);
    // ros::param::set("/turtlesim/background_b",0);

    //  The way 2： Use nodehandle
    return 0;
}

2.2 Python Realization test04_param_p.py

function

1. Add executable rights
   chmod +x *.py
   ll
2. compile ——catkin Part of the modified
3. perform

rescore
cd demo02_ws
source ./devel/setup.bash
rosrun plumbing_test test04_param_p.py
rosrun turtlesim turtlesim_node（ Finally start ）

#! /usr/bin/env python
"""  demand ： Modify tortoise GUI Background color of  1. initialization ros node  2. Set parameters  """

import rospy

if __name__ == "__main__":
    rospy.init_node("change_bgcolor")

    #  Modify background color 
    rospy.set_param("/turtlesim/background_r",100)
    rospy.set_param("/turtlesim/background_g",50)
    rospy.set_param("/turtlesim/background_b",200)