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This tutorial covers the toolchain to build a package.

[/vc_column_text][vc_tour interval=”0″][vc_tab title=”Prerequisites” tab_id=”1394605844-1-1″][vc_column_text][/vc_column_text][vc_column_text]For this tutorial we will use a lightweight simulator, please install it using

$ sudo apt-get install ros-<distro>-ros-tutorials

Replace ‘<distro>’ with the name of your ROS distribution (e.g. hydro, groovy, electric, fuerte etc.)[/vc_column_text][/vc_tab][vc_tab title=”Quick Overview of Graph Concepts” tab_id=”1394605844-2-63″][vc_column_text]

• Nodes: A node is an executable that uses ROS to communicate with other nodes.
• Messages: ROS data type used when subscribing or publishing to a topic.
• Topics: Nodes can publish messages to a topic as well as subscribe to a topic to receive messages.
• Master: Name service for ROS (i.e. helps nodes find each other)
• rosout: ROS equivalent of stdout/stderr
• roscore: Master + rosout + parameter server (parameter server will be introduced later)

[/vc_column_text][/vc_tab][vc_tab title=”Nodes” tab_id=”1394606195229-2-4″][vc_column_text]A node really isn’t much more than an executable file within a ROS package. ROS nodes use a ROS client library to communicate with other nodes. Nodes can publish or subscribe to a Topic. Nodes can also provide or use a Service.[/vc_column_text][/vc_tab][vc_tab title=”Client Libraries” tab_id=”1394606196452-3-2″][vc_column_text]ROS client libraries allow nodes written in different programming languages to communicate:

• rospy = python client library
• roscpp = c++ client library

[/vc_column_text][/vc_tab][vc_tab title=”Roscore” tab_id=”1394607183584-4-0″][vc_column_text]roscore is the first thing you should run when using ROS.

Please run:

$ roscore
You will see something similar to:

… logging to ~/.ros/log/9cf88ce4-b14d-11df-8a75-00251148e8cf/roslaunch-machine_name-13039.log Checking log directory for disk usage. This may take awhile. Press Ctrl-C to interrupt Done checking log file disk usage. Usage is <1GB. started roslaunch server http://machine_name:33919/ ros_comm version 1.4.7 SUMMARY ======== PARAMETERS * /rosversion * /rosdistro NODES auto-starting new master process[master]: started with pid [13054] ROS_MASTER_URI=http://machine_name:11311/ setting /run_id to 9cf88ce4-b14d-11df-8a75-00251148e8cf process[rosout-1]: started with pid [13067] started core service [/rosout]

If roscore does not initialize, you probably have a network configuration issue. See Network Setup – Single Machine Configuration

If roscore does not initialize and sends a message about lack of permissions, probably the ~/.ros folder is owned by root, change recursively the ownership of that folder with:

$ sudo chown -R <your_username> ~/.ros

[/vc_column_text][/vc_tab][vc_tab title=”Using rosnode” tab_id=”1394607184691-5-4″][vc_column_text][/vc_column_text][vc_column_text]rosrun allows you to use the package name to directly run a node within a package (without having to know the package path).

Usage:

$ rosrun [package_name] [node_name]

So now we can run the turtlesim_node in the turtlesim package.

Then, in a new terminal:

$ rosrun turtlesim turtlesim_node

You will see the turtlesim window:

NOTE: The turtle may look different in your turtlesim window. Don’t worry about it – there are many types of turtle and yours is a surprise!

In a new terminal:

$ rosnode list

You will see something similar to:

• /rosout
  /turtlesim

One powerful feature of ROS is that you can reassign Names from the command-line.

Close the turtlesim window to stop the node (or go back to the rosrun turtlesim terminal and use ctrl-C). Now let’s re-run it, but this time use a Remapping Argument to change the node’s name:

$ rosrun turtlesim turtlesim_node __name:=my_turtle

Now, if we go back and use rosnode list:

$ rosnode list

• You will see something similar to:

• /rosout
  /my_turtle

Note: If you still see /turtlesim in the list, it might mean that you stopped the node in the terminal using ctrl-C instead of closing the window, or that you don’t have the $ROS_HOSTNAME environment variable defined as described in Network Setup – Single Machine Configuration. You can try cleaning the rosnode list with: $ rosnode cleanup

We see our new /my_turtle node. Let’s use another rosnode command, ping, to test that it’s up:

$ rosnode ping my_turtle

• rosnode: node is [/my_turtle]
  pinging /my_turtle with a timeout of 3.0s
  xmlrpc reply from http://aqy:42235/     time=1.152992ms
  xmlrpc reply from http://aqy:42235/     time=1.120090ms
  xmlrpc reply from http://aqy:42235/     time=1.700878ms
  xmlrpc reply from http://aqy:42235/     time=1.127958ms

[/vc_column_text][/vc_tab][vc_tab title=”Using rosrun” tab_id=”1394607254525-6-10″][vc_column_text]rosrun allows you to use the package name to directly run a node within a package (without having to know the package path).

Usage:

 $ rosrun [package_name] [node_name]

So now we can run the turtlesim_node in the turtlesim package.

Then, in a new terminal:

$ rosrun turtlesim turtlesim_node

You will see the turtlesim window:

NOTE: The turtle may look different in your turtlesim window. Don’t worry about it – there are many types of turtle and yours is a surprise!

In a new terminal:

$ rosnode list

You will see something similar to:

• /rosout
  /turtlesim

One powerful feature of ROS is that you can reassign Names from the command-line.

Close the turtlesim window to stop the node (or go back to the rosrun turtlesim terminal and use ctrl-C). Now let’s re-run it, but this time use a Remapping Argument to change the node’s name:

$ rosrun turtlesim turtlesim_node __name:=my_turtle

Now, if we go back and use rosnode list:

 $ rosnode list

• You will see something similar to:

• /rosout
  /my_turtle

We see our new /my_turtle node. Let’s use another rosnode command, ping, to test that it’s up:

$ rosnode ping my_turtle

• rosnode: node is [/my_turtle]
  pinging /my_turtle with a timeout of 3.0s
  xmlrpc reply from http://aqy:42235/     time=1.152992ms
  xmlrpc reply from http://aqy:42235/     time=1.120090ms
  xmlrpc reply from http://aqy:42235/     time=1.700878ms
  xmlrpc reply from http://aqy:42235/     time=1.127958ms

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