ROS topic name setting

1 rosrun Set topic remapping

Unmapped previous rqt_graph

rosrun Name remapping Syntax : rorun Package name The node name Topic name := New topic name

Realization teleop_twist_keyboard There are two communication schemes with turtle display node ：

1. programme 1

take teleop_twist_keyboard The topic of the node is set to /turtle1/cmd_vel

Start keyboard control node :rosrun teleop_twist_keyboard teleop_twist_keyboard.py /cmd_vel:=/turtle1/cmd_vel

Start the tortoise display node : rosrun turtlesim turtlesim_node

The two can realize normal communication

The modified rqt_graph

 

  At this time, there is no /cmd_vel

2. programme 2

Set the topic of the tortoise display node to /cmd_vel

Start keyboard control node :rosrun teleop_twist_keyboard teleop_twist_keyboard.py

Start the tortoise display node : rosrun turtlesim turtlesim_node /turtle1/cmd_vel:=/cmd_vel

The two can realize normal communication

 2 launch File set topic remapping

launch File set topic remapping Syntax :

<node pkg="xxx" type="xxx" name="xxx">
    <remap from=" The original topic " to=" New topics " />
</node>

Realization teleop_twist_keyboard There are two communication schemes with turtle display node ：

1. programme 1

take teleop_twist_keyboard The topic of the node is set to /turtle1/cmd_vel

<launch>

    <node pkg="turtlesim" type="turtlesim_node" name="t1" />
    <node pkg="teleop_twist_keyboard" type="teleop_twist_keyboard.py" name="key">
        <remap from="/cmd_vel" to="/turtle1/cmd_vel" />
    </node>

</launch>

2. programme 2

Set the topic of the tortoise display node to  /cmd_vel

<!--  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>
    <node pkg="teleop_twist_keyboard" type="teleop_twist_keyboard.py" name="key" />
    <!--  Set the topic controlled by the keyboard to be consistent with the tortoise  -->
</launch>

3 Code and set the topic name

The name of the topic and the namespace of the node 、 The name of the node has a certain relationship , Topic names can be roughly divided into three types :

• overall situation ( Topic reference ROS System , Level with node namespace )
• relative ( The topic refers to the namespace of the node , Level with node name )
• private ( Topic reference node name , Is a child of the node name )

Demonstrate specific relationships with coding .

int main(int argc, char *argv[])
{    
    //1. Initialize the node and set a node name    
    //2. Set different types of topics 
    //3. When starting the node , Pass a  __ns:= xxx
    //4. After the node is started , Use  rostopic  View topic information 
    ros::init(argc,argv,"hello");
    //ros::NodeHandle nh;
    
    // The core ： Set different types of topics 
    //1. overall situation    ---  The topic name needs to be written with / start ( You can also set your own namespace ), In this case, and nodes ( Namespace and name ) It doesn't matter. 
    //ros::Publisher pub = nh.advertise<std_msgs::String>("/chatter",1000);
    //ros::Publisher pub = nh.advertise<std_msgs::String>("/yyy/chatter",1000);
    //2. relative 
    //ros::Publisher pub = nh.advertise<std_msgs::String>("chatter",1000);
    //ros::Publisher pub = nh.advertise<std_msgs::String>("yyy/chatter",1000);
    //3. private    Need to create specific  NodeHandle
    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 and non private 
    // Global topics have higher priority 
    while(ros::ok())
    {
        
    }
    return 0;
}

1.1 Global name

Format : With / The name at the beginning , It has nothing to do with the node name

Example 1:

ros::Publisher pub = nh.advertise<std_msgs::String>("/chatter",1000);

result 1:

/chatter 

  Example 2：

ros::Publisher pub = nh.advertise<std_msgs::String>("/yyy/chatter",1000);

  result 2:

/yyy/chatter

1.2 Relative name

Format : Not / The name at the beginning , Reference namespace ( Level with node name ) To determine the topic name

Example 1:

ros::Publisher pub = nh.advertise<std_msgs::String>("chatter",1000);

  result 1:

xxx/chatter

Example 2:

 ros::Publisher pub = nh.advertise<std_msgs::String>("yyy/chatter",1000);

 xxx/yyy/chatter

1.3 Private name

Format : With ~ The name at the beginning

Example 1:

ros::NodeHandle nh("~");

ros::Publisher pub = nh.advertise<std_msgs::String>("chatter",1000);

  result 1:

/xxx/hello/chatter

Example 2:

ros::NodeHandle nh("~");

ros::Publisher pub = nh.advertise<std_msgs::String>("yyy/chatter",1000);

result 2:

 /xxx/hello/yyy/chatter

 PS: When using ~, And topic names sometimes / At the beginning , Then the topic name is absolute

Example 3:

ros::NodeHandle nh("~");

ros::Publisher pub = nh.advertise<std_msgs::String>("/yyy/chatter",1000);

  result 3:

/yyy/chatter