Q: Subscribe to a Gazebo topic and publish in a ROS node
A: If you are working with that [turtlebot3 simulation](https://turtlebot3.readthedocs.io/en/latest/simulation.html), you don’t have to subscribe a gazebo topic, since the simulation is configured already with ROS.
To subscribe the laser scanner and publish something else in the same node, you can do the following:
Create a pkg with these dependencies
More ROS Learning Resources: https://goo.gl/DuTPtK
Q: How to add takeoff and land to teleop_twist_keyboard Python script?
Original question here: https://answers.ros.org/question/273938/adding-take-off-and-landing-into-teleop_twist_keyboardpy/
A: Here you can see an example script that does that.
RELATED LINKS:
* ROS Development Studio: rds.theconstructsim.com
* Robot Ignite Academy: www.robotigniteacademy.com
![[ROS Q&A] 49 – How to navigate while avoiding obstacles](https://www.theconstruct.ai/wp-content/uploads/2017/10/ROS-QA-How-to-navigate-while-avoiding-obstacles.png)
Q: How to navigate while avoiding obstacles? Original question here: https://answers.ros.org/question/274391/could-use-some-guidance-on-how-to-navigate-while-avoiding-obstacles/?answer=274526#post-id-274526
A: In order to do navigation using a laser for localization and obstacle avoidance, you need to do first a map of the environment you want to move through. For that, you need to use the gmapping package. Launch the gmapping package, and then move the robot around using the keyboard or joystick so it can build the map.
Once the map is done, you need to save it using the following command:
rosrun map_server map_saver -f name_of_map
Then you are ready to use that map for localization and sending the robot to different locations in the map, while avoiding obstacles. Kill the gmapping node and launch now the localization package (the amcl). Together with the amcl you need to launch the map_server (to use the map you created on the previous step) and the move_base (to make the robot move around while avoiding obstacles).
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Q: How to use ira_laser_tools package to merge laser data
A: the reason why you cannot see in the /scan_multi the obstacles of the back is because you are using the default configuration of the ira_laser_tool. By default, the ira_laser_toolpackage does not produce the /scan_multi from -PI to +PI, but some other weird values.
The solution, is to use the rqt_reconfigure tool to set the angle_min and angle_max parameters to -PI and +PI respectively. To do that, open the tool with the command:
rosrun rqt_reconfigure rqt_reconfigure
You should see something like in the picture attached. Then, just change the angle values. I recommend you change that while watching the scan in rviz so you will see clearly how the scan changes based on your values.
The original question can be found here: https://answers.ros.org/question/273572/how-to-use-ira_laser_tools-package-to-merge-laser-datas/#273809
Q: I’m trying to assemble some readings from a Hokuyo laser simulated in gazebo.
A: The following example can help you understand how to use the laser_assembler package in order to assemble the readings from a Hokuyo laser.