5. Launch files

5.1. Basic launch file

Ros launch talker_listener.launch file that execute 2 nodes:

  <node name="listener" pkg="roscpp_tutorials" type="listener_node" output="screen"/>
  <node name="talker" pkg="roscpp_tutorials" type="talker_node" output="screen"/>

The previous launch file execute one instance of the listener_node with a the name listener, and one instance of the executable talker_node with the name talker, that are part of the package roscpp_tutorials. So the type id the name of the compiled node. The name is the name of the instance of the node (process). The tag output have value screen, it tell ROS to show the outputs of the nodes in the terminal. If roscore is not running, roslaunch execute it.

Open a terminal and run the roslaunch command:

roslaunch roscpp_tutorials talker_listener.launch

Of course the package roscpp_tutorials should be in your active workspace or installed on your computer. Or you substitute the package name and node names with your own.

Clone the repository in your workspace

git clone https://github.com/ros/ros_tutorials.git

Or install it

sudo apt-get install ros-kinetic-roscpp-tutorials

5.2. Parameters

You can also set parameters on the Parameter Server. These parameters will be stored on the Parameter Server before any nodes are launched.

  <param name="somestring1" value="bar" />
  <!-- force to string instead of integer -->
  <param name="somestring2" value="10" type="str" />

  <param name="someinteger1" value="1" type="int" />
  <param name="someinteger2" value="2" />

  <param name="somefloat1" value="3.14159" type="double" />
  <param name="somefloat2" value="3.0" />

  <!-- you can set parameters in child namespaces -->
  <param name="wg/childparam" value="a child namespace parameter" />

  <!-- upload the contents of a file to the server -->
  <param name="configfile" textfile="$(find roslaunch)/example.xml" />
  <!-- upload the contents of a file as base64 binary to the server -->
  <param name="binaryfile" binfile="$(find roslaunch)/example.xml" />

5.3. Substitution args

 <arg name="gui" default="true" />
 <param name="foo" value="$(arg my_foo)" />

 <node name="add_two_ints_server" pkg="beginner_tutorials" type="add_two_ints_server" />
 <node name="add_two_ints_client" pkg="beginner_tutorials" type="add_two_ints_client" args="$(arg a) $(arg b)" />

Execution example:

roslaunch beginner_tutorials launch_file.launch a:=1 b:=5

5.4. Namespaces

5.5. Including files