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

edit

I am trying to simply subscribe to /scan topic after launching turtlebot3_world.py 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!

UPDATE:

/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{
public:

ScanPrinter():Node("scan_printer"){
    sub_ = this->create_subscription<sensor_msgs::msg::LaserScan>(
    "scan",
    rclcpp::QoS(rclcpp::KeepLast(10)),
    std::bind(&ScanPrinter::LaserCallback, this, std::placeholders::_1)
    );
}

private:
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
• export GAZEBO_MODEL_PATH=$GAZEBO_MODEL_PATH:<PATH/TO/MODELS>

• I launch the turtlebot3_world.launch.py 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.