ROS Duplicate node name

1. rosrun Set namespace and remap

Open two same nodes

1. The way 1： Set namespace

rosrun turtlesim turtlesim_node __ns:=ergouzi
rosrun turtlesim turtlesim_node __ns:=molvzi

rosnode list

/erGouZi/turtlesim
/molvzi/turtlesim
/rosout
/turtlesim

2. The way 2： Name remapping

rosrun turtlesim turtlesim_node __name:=daqiang
rosrun turtlesim turtlesim_node __name:=xioaqiang

rosnode list

/daqiang
/erGouZi/turtlesim
/molvzi/turtlesim
/rosout
/turtlesim
/xioaqiang

2. launch File set namespace and remap

<!--  Need to start multiple turtles GUI node  -->
<launch>
    <node pkg = "turtlesim" type = "turtlesim_node" name = "turtlesim" /> 
    <!--  Name remapping  -->
    <node pkg = "turtlesim" type = "turtlesim_node" name = "t1" /> 
    <!--  Namespace  -->
    <node pkg = "turtlesim" type = "turtlesim_node" name = "turtlesim" ns = "ergouzi" /> 
    <!--  Namespace  +  Name remapping  -->
    <node pkg = "turtlesim" type = "turtlesim_node" name = "t2" ns = "maolvzi"/> 
</launch>

3. Encoding setting namespace and remapping

ROS Topic name setting

1. rosrun Set topic remapping

rosrun turtlesim turtlesim_node And rosrun teleop_twist_keyboard teleop_twist_keyboard.py
Can't communicate
rostopic list

/cmd_vel——keyboard
/rosout
/rosout_agg
/turtle1/cmd_vel ——node
/turtle1/color_sensor
/turtle1/pose

Use the following

rosrun teleop_twist_keyboard teleop_twist_keyboard.py /cmd_vel:=/turtle1/cmd_vel

perhaps

rosrun turtlesim turtlesim_node /turtle1/cmd_vel:=/cmd_vel

2. launch File set topic remapping

rename_topic——start.launch file

<!--  Keyboard controls tortoise movement  -->
<launch>
    <!--  Set the turtle's topic to be consistent with the keyboard control  -->
    <node pkg = "turtlesim" type = "turtlesim_node" name = "t1" >
        <remap from = "/turtle1/cmd_vel" to = "/cmd_vel" />
    </node>
    <nodep pkg = "teleop_twist_keyboard" type = "teleop_twist_keyboard.py" name = "key1" />
    
    <!--  Set the topic controlled by the keyboard to be consistent with the tortoise  -->
</launch>

3. Code and set the topic name

rosrun rename02_topic topic_name __ns:=xxx( Namespace )
rosnode list And rostopic list
You can define your own namespace

#include"ros/ros.h"
#include"std_msgs/String.h"

/*  demand :  Demonstrate different types of topic name settings   Set topic name and namespace  */

int main(int argc, char *argv[])
{
    
    ros::init(argc,argv,"hello");//hello Is the node 
    // ros::NodeHandle nh;

    // The core : Set different types of topics 
    //1.  overall situation  ----  Topic name with  /  start ( You can also set your own namespace ), In this case, and nodes ( Namespace and name ) It doesn't matter. 
    ros::Publisher pub1 = nh.advertise<std_msgs::String>("/chatter",1000);
    // ros::Publisher pub1 = nh.advertise<std_msgs::String>("/yyy/chatter",1000);
    // The overall topic is /chatter, It can also be used. /yyy/chatter
    
    //2.  relative  ----  Not  /  start 
    ros::Publisher pub2 = nh.advertise<std_msgs::String>("chatter",1000);
    // ros::Publisher pub2 = nh.advertise<std_msgs::String>("yyy/chatter",1000);


    //3.  private  ----  You need to create a specific NodeHandle nh("~")
    ros::NodeHandle nh("~");
    // ros::Publisher pub = nh.advertise<std_msgs::String>("chatter",1000);
    ros::Publisher pub = nh.advertise<std_msgs::String>("yyy/chatter",1000);

    //  Be careful : If private NH Create a topic with  /  start ( Global topics ), The generated topic is global , Non private 
    //  The priority of global topics is higher 


    while(ros::ok())
    {
    

    }

    return 0;
}

python Realization

#! /usr/bin/env python

import rospy
from std_msgs.msg import String

if __name__ == "__main__":
    rospy.init_node("hello")
    """  demand :  Implement different types of topic settings  """

    # 1.  overall situation 
    # pub = rospy.Publisher("/chatter",String,queue_size = 10)

    # 2.  relative 
    pub = rospy.Publisher("chatter",String,queue_size = 10)

    # 3.  private 
    pub = rospy.Publisher("~chatter",String,queue_size = 10)


    while not rospy.is_shutdown():
        pass

ROS Parameter name setting

1. launch File settings parameters

<!--  Set parameters  -->
<launch>
    <!--  Format 1:  overall situation  -->
    <param name = "radius" value = "0.2" />
    
    <!--  Format 2:  private  -->
    <node pkg = "turtlesim" type = "turtlesim_node" name = "t1" ns = "xxx">
        <param name = "radius" value = "0.08" />
    </node>
</launch>

2. Code setting parameters

C++ Realization

#include"ros/ros.h"

int main(int argc, char *argv[])
{
    
    ros::init(argc,argv,"hello");
    ros::NodeHandle nh;

    /*
         Use  ros::param  To set parameters 
    */

    // 1.  overall situation 
    ros::param::set("/radiusA",100);
    // 2.  relative 
    ros::param::set("radiusB",100);
    // 3.  private 
    ros::param::set("~radiusC",100);

    /*
         Use  NodeHandle  Set parameters 
    */

    //  overall situation 
    nh.setParam("/radius_nh_A",1000);

    //  relative 
    nh.setParam("radius_nh_B",1000);

    //  private 
    ros::NodeHandle nh_private("~");
    nh_private.setParam("radius_nh_C",1000);
    
    return 0;
}