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ros2: turtlebot3 gazebo /scan topic subscriber is not calling the callback function

asked 2019-10-05 13:26:35 -0500

shivaang12 gravatar image

updated 2019-10-06 12:37:19 -0500

I am trying to simply subscribe to /scan topic after launching launch file in turtlebot3_gazebo pkg. For that I am creating a ros2 node which subscribes to /scan topic and logs it into the console.

Thanks in advance!


/scan works from terminal using ros2 topic echo /scan but when run my pkg it simple not calling the callback function. This is how my subscriber class looks like.

class ScanPrinter:public rclcpp::Node{

    sub_ = this->create_subscription<sensor_msgs::msg::LaserScan>(
    std::bind(&ScanPrinter::LaserCallback, this, std::placeholders::_1)

void LaserCallback(const sensor_msgs::msg::LaserScan::SharedPtr msg){
    RCLCPP_INFO(this->get_logger(), std::to_string(msg->ranges[90]).c_str());
rclcpp::Subscription<sensor_msgs::msg::LaserScan>::SharedPtr sub_;
  • Operating System:
    • Ubuntu 18.04
  • Version or commit hash:
    • Compiled from github
  • DDS implementation:
    • Default

Steps I do in order

  • export TURTLEBOT3_MODEL=burger
  • I launch the file which opens up the gazebo with the spawned turtle bot.

  • I try to run my subscriber node and it prints nothing on the console log, as it suppose to according to the LaseCallback function. By which I deduce that its not calling the call back function.

  • Then I tried ros2 topic echo /scan and it prints the message correctly.

  • Then I tried to see if my subscribers has really subscribed this topic by ros2 topic info /scan and then it prints publisher: 1, subscriber 1 by which I deduce it does.

  • Then I tried to subscribe custom string publisher by making necessary changes in the code, and it behaves perfectly.

I don't know what is wrong here.

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It's unlikely members here will analyse your complete package for you -- especially if you just post a link here. We don't run a debugging service here.

Please provide some excerpts of your code, especially the parts having to do with creating subscribers, an overview of the topics that do exist, a description of how you start everything (also: in what order), versions of things like Fast-RTPS (or any other DDS implementation you are using), etc, etc.

gvdhoorn gravatar image gvdhoorn  ( 2019-10-06 05:38:54 -0500 )edit

Sorry, I couldn't figured out earlier how to post code, which is why I provided the link. But I made the necessary changes as per you suggestion.

shivaang12 gravatar image shivaang12  ( 2019-10-06 12:35:08 -0500 )edit

3 Answers

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answered 2019-10-08 09:48:54 -0500

shivaang12 gravatar image

I made it work at the end. The /scan topic publishes the data with Sensor QoS profile, qos_profile_sensor_data. So it is mandatory to use qos_profile_sensor_data QoS profile in the subscriber.

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This worked for me! Thank you!

For those that need help with this in python it should be: rclpy.qos.qos_profile_sensor_data

For C++, it should be: rmw_qos_profile_sensor_data

zmk5 gravatar image zmk5  ( 2019-10-15 17:08:49 -0500 )edit

answered 2019-12-03 04:33:38 -0500

greggScutum gravatar image

You can also take a look at the Dolly demo for Gazebo ( They are using rclcpp::QoS(rclcpp::SystemDefaultsQoS()).

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answered 2022-01-23 14:24:42 -0500

mac137 gravatar image

Python code for those who are still in doubt about how to implement the qos_profile_sensor_data for the subscriber of a 2d lidar (found here):

from sensor_msgs.msg import LaserScan


qos_policy = rclpy.qos.QoSProfile(reliability=rclpy.qos.ReliabilityPolicy.BEST_EFFORT, history=rclpy.qos.HistoryPolicy.KEEP_LAST, depth=1)

self.subscription = self.create_subscription(LaserScan, 'scan', self.listener_callback, qos_profile=qos_policy)

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Asked: 2019-10-05 13:26:35 -0500

Seen: 1,666 times

Last updated: Jan 23 '22