ROS beginner tutorial
The ROS package beginner_tutorials serves as a tutorial that shows how to write basic publisher and subscriber nodes. The package consists of 2 nodes: a talker and a listener node. The purpose of the talker node is to publish a string message to the network. The purpose of the subscriber node is to listen and receive the messages coming from the talker node. The beginner_tutorials also contains a CMakelist.txt and a package.xml files that provide the the building configuration of the package. There is also a results folder which contains the results obtained from the talker/listener and from the cppcheck and cpplint tools.
In order to build the beginner_tutorials ROS package do the following:
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Move to directory containing your catking workspace: cd ~/catkin_ws
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Once inside catkin_ws build all packages inside workspace: catkin_make
After Build has completed successfully you can run the nodes as follows:
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Open a terminal session by typing: ctrl + alt + T
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Start Roscore by typing: roscore
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Open a second terminal session by typing: ctrl + alt + T
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Run the talker node by typing: rosrun beginner_tutorials talker
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Open a thrid terminal session by typing: ctrl + alt + T
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Run the listener node by typing: rosrun beginner_tutorials listener
Once both nodes are running you will be able to see the published messages in the second console screen as well as the received message in the third terminal.
The server service and client service nodes are ROS nodes that overwrite the messages being published by the talker node. The server node was implemented using and Empty call. The empty call takes no service arguments and only calls the callback function when the server service node is called. This node overwrites the talker node messages published in the chatter topic.
It really is very similar as the steps used above for the beginner tutorials nodes talker and listener. The main difference in this case, is the use of a roslaunch file that will run all nodes at once when invoke. As usual in order to build all nodes type catkin_make inside the catkin workspace. After all nodes are built without errors, the run the roslaunch file as follows: roslaunch beginner_tutorials beginner_tutorials.launch