Node unable to subscribe the specified topic

kinetic

asked 2019-09-27 03:07:48 -0600

sumant

77 ●16 ●21 ●28 http://bcrlab.wordpress.com/

updated 2019-09-27 03:16:04 -0600

Specification: Ubuntu 16.04, ROS kinetic, Gazebo, turtlebot3

Here is my rqt_graph image description

There is a node /negotiator which should subscribe cca_cmd_vel and publish to cmd_vel.

turtlebot3_teleop_keyboard and move_base publish on cca_cmd_vel.

Here is the code

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

void cca_cmd_velCallback(const geometry_msgs::Twist::ConstPtr& vel)
{
  geometry_msgs::Twist new_vel = *vel;
  cmd_vel_pub.publish(new_vel);
}

int main(int argc, char **argv)
{
//Negotiator Subscribe cmd_vel

  ros::init(argc, argv, "negotiator");
  ros::NodeHandle n;


  ros::Subscriber sub = n.subscribe("cca_cmd_vel", 1000, cca_cmd_velCallback);


//Negotiator Publish to GAZEBO
  ros::Publisher cmd_vel_pub = n.advertise<geometry_msgs::Twist>("cmd_vel", 1000);
//ros::Publisher cmd_vel_pub = n.advertise<geometry_msgs::Twist>("cmd_vel", 1000);
ros::spin();

  return 0;
}

Kindly suggest where to improve

Few More add on information

crlab@crlab-500-100IX:~$ rostopic info cca_cmd_vel

Type: geometry_msgs/Twist

Publishers: 
 * /move_base (http://localhost:34459/)
 * /turtlebot3_teleop_keyboard (http://localhost:41875/)

Subscribers: None

crlab@crlab-500-100IX:~$ rostopic info cmd_vel

Type: geometry_msgs/Twist

Publishers: None

Subscribers: 
 * /gazebo (http://localhost:33175/)
 * /negotiator (http://localhost:35659/)

crlab@crlab-500-100IX:~$ rosnode info negotiator

--------------------------------------------------------------------------------
Node [/negotiator]
Publications: 
 * /rosout [rosgraph_msgs/Log]

Subscriptions: 
 * /clock [rosgraph_msgs/Clock]
 * /cmd_vel [unknown type]

Services: 
 * /negotiator/get_loggers
 * /negotiator/set_logger_level


contacting node http://localhost:35659/ ...
Pid: 4967
Connections:
 * topic: /rosout
    * to: /rosout
    * direction: outbound
    * transport: TCPROS
 * topic: /clock
    * to: /gazebo (http://localhost:33175/)
    * direction: inbound
    * transport: TCPROS

crlab@crlab-500-100IX:~$ rosnode info turtlebot3_teleop_keyboard

--------------------------------------------------------------------------------
Node [/turtlebot3_teleop_keyboard]
Publications: 
 * /cca_cmd_vel [geometry_msgs/Twist]
 * /rosout [rosgraph_msgs/Log]

Subscriptions: 
 * /clock [rosgraph_msgs/Clock]

Services: 
 * /turtlebot3_teleop_keyboard/get_loggers
 * /turtlebot3_teleop_keyboard/set_logger_level


contacting node http://localhost:41875/ ...
Pid: 4938
Connections:
 * topic: /rosout
    * to: /rosout
    * direction: outbound
    * transport: TCPROS
 * topic: /clock
    * to: /gazebo (http://localhost:33175/)
    * direction: inbound
    * transport: TCPROS

crlab@crlab-500-100IX:~$ `rosnode info move_base`

Node [/move_base]
Publications: 
 * /cca_cmd_vel [geometry_msgs/Twist]
 * /move_base/DWAPlannerROS/cost_cloud [sensor_msgs/PointCloud2]
 * /move_base/DWAPlannerROS/global_plan [nav_msgs/Path]
 * /move_base/DWAPlannerROS/local_plan [nav_msgs/Path]
 * /move_base/DWAPlannerROS/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/DWAPlannerROS/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/DWAPlannerROS/trajectory_cloud [sensor_msgs/PointCloud2]
 * /move_base/NavfnROS/plan [nav_msgs/Path]
 * /move_base/current_goal [geometry_msgs/PoseStamped]
 * /move_base/feedback [move_base_msgs/MoveBaseActionFeedback]
 * /move_base/global_costmap/costmap [nav_msgs/OccupancyGrid]
 * /move_base/global_costmap/costmap_updates [map_msgs/OccupancyGridUpdate]
 * /move_base/global_costmap/footprint [geometry_msgs/PolygonStamped]
 * /move_base/global_costmap/inflation_layer/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/global_costmap/inflation_layer/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/global_costmap/obstacle_layer/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/global_costmap/obstacle_layer/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/global_costmap/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/global_costmap/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/global_costmap/static_layer/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/global_costmap/static_layer/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/goal [move_base_msgs/MoveBaseActionGoal]
 * /move_base/local_costmap/costmap [nav_msgs/OccupancyGrid]
 * /move_base/local_costmap/costmap_updates [map_msgs/OccupancyGridUpdate]
 * /move_base/local_costmap/footprint [geometry_msgs/PolygonStamped]
 * /move_base/local_costmap/inflation_layer/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/local_costmap/inflation_layer/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/local_costmap/obstacle_layer/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/local_costmap/obstacle_layer/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/local_costmap/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/local_costmap/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/parameter_descriptions [dynamic_reconfigure/ConfigDescription]
 * /move_base/parameter_updates [dynamic_reconfigure/Config]
 * /move_base/result [move_base_msgs/MoveBaseActionResult]
 * /move_base/status [actionlib_msgs/GoalStatusArray]
 * /rosout [rosgraph_msgs/Log]

Subscriptions: 
 * /clock [rosgraph_msgs/Clock]
 * /map [nav_msgs/OccupancyGrid]
 * /move_base/cancel [unknown type]
 * /move_base/global_costmap/footprint [geometry_msgs/PolygonStamped]
 * /move_base/goal [move_base_msgs/MoveBaseActionGoal]
 * /move_base/local_costmap/footprint [geometry_msgs/PolygonStamped]
 * /move_base_simple/goal [geometry_msgs/PoseStamped]
 * /odom [nav_msgs/Odometry]
 * /scan [sensor_msgs/LaserScan]
 * /tf [tf2_msgs/TFMessage]
 * /tf_static [tf2_msgs/TFMessage]

Services: 
 * /move_base/DWAPlannerROS/set_parameters
 * /move_base/NavfnROS/make_plan
 * /move_base/clear_costmaps
 * /move_base/get_loggers
 * /move_base/global_costmap/inflation_layer/set_parameters
 * /move_base/global_costmap/obstacle_layer ...

(more)

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Comments

How are you launching your nodes, maybe you can post the launch files as well. From the negotiator node you have posted you don't seem to do anything other than republishing the messages as a different topic, do you have plans to add some processing on the input? If you don't need processing on the topic, then you do not need a node to use a different topic name, you could just use the remap tag to change the topic when launching the publishing or subscribing node.

Roslaunch xml documentation

You can search this forum for examples on how to remap topics.

Reamees ( 2019-09-27 04:44:17 -0600 )edit

Seeing the output of rostopic info cmd_vel it looks like the negotiator is subscribing to cmd_vel, which is really weird since the code clearly states differently. Something in either your launch files or the posted code can't be correct. Are you already remapping cca_cmd_vle to cmd_vel?

LeoE ( 2019-09-27 04:52:53 -0600 )edit

@Reamees I am executing node through

rosrun ecca negotiator

Once I can republish the data , I will later do some processing.

sumant ( 2019-09-27 04:59:13 -0600 )edit

@LeoE 1. Whatever I have copied is correct. 2. This is the first node I am writing. There is no other remapping taking place.

sumant ( 2019-09-27 05:39:16 -0600 )edit

Well there are no publishers in your negotiator node, and the "wrong" subscriber. Please try to delete your build and devel folder, rebuild your project and try it again. If the code is correct there must be a problem in either building or running the node. It could be, that an old version of your node is still somewhere in the system an is actually launched instead of the new one. Have you had the negotiator node subscribe to the cmd_vel topic before?

LeoE ( 2019-09-27 06:00:54 -0600 )edit

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answered 2019-09-27 06:21:30 -0600

Delb

3907 ●16 ●105 ●68

updated 2019-10-18 02:52:49 -0600

Your code can't compile as it is. You define cmd_vel_pub within the main function and then use it in the callback. That's not the same scope so that can't compile.

You need to define it as a global variable to use your code like this or use the publisher in a while (ros::ok()) loop in your main function and store the data in the callback with a global variable.

Anyway all the informations you gave are the result of a previous executable, since your code can't compile all your informations are related to another code that has previously been compiled. Try correcting this issue and then update all the rostopic/rosnode info with your new code (the rostopic list could be a good help too).

Edit : Glad it works for you but I would make some remarks to help you improve your code :

    ros::NodeHandle p;
    ros::NodeHandle n;
    ros::NodeHandle vel_sub;

You don't need different NodeHandle for each subscriber and/or publisher, you can use the same for all of them. See #q68182 for a more extensive answer/description
```
ros::Subscriber sub = n.subscribe<geometry_msgs::Twist>("tele_cmd_vel", 0, negotiatorCallback);
```
Your subscriber as a queue size of 0, meaning it will never throw messages even if they arrive faster than the callback execution that could lead you to some troubles
```
ros::Subscriber tele_cmd_vel_sub = vel_sub.subscribe<geometry_msgs::Twist>("move_base_cmd_vel", 1000, negotiatorCallback);
```
Is it intended to have the same callback for two subscribers ? This behavior looks like you can use a velocity multiplexer (see the wiki)

Instead of ros::spin() you should use this :

while (ros::ok())
{
    ros::spinOnce();
}

This allows you do things in your loop instead of being blocked by ros::spin(). Like that you can publish data wihtin this loop instead of the callback.

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Comments

What @Delb said, also, you might want to have a look at this question for an example implementation.

Reamees ( 2019-09-27 06:34:41 -0600 )edit

thanks @Reamees , your link solved my problem.

sumant ( 2019-10-01 06:27:15 -0600 )edit

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Node unable to subscribe the specified topic

crlab@crlab-500-100IX:~$ `rosnode info move_base`

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crlab@crlab-500-100IX:~$ rosnode info move_base

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Node unable to subscribe the specified topic

crlab@crlab-500-100IX:~$ `rosnode info move_base`