Launching Other Launch Files¶

Think back to the move_circle.py node that you created in Week 2. We need a simulation of our robot active in order to run this, which we can enable with the following command (which you should be very familiar with by now):

$ roslaunch turtlebot3_gazebo turtlebot3_empty_world.launch

Suppose you wanted to save yourself some work and launch both the simulation and the move_circle.py node at the same time...

Firstly, return to your week2_navigation package and create a launch directory (if you haven't done so previously):
```
roscd week2_navigation
```
```
mkdir launch
```
```
cd launch/
```
Then create a launch file. You could call this whatever you want, but for the purposes of this example we'll create one called circle.launch:
```
touch circle.launch
```
Inside this file add the following:
```
<launch>
  <include file="$(find turtlebot3_gazebo)/launch/turtlebot3_empty_world.launch" />
  <node pkg="week2_navigation" type="move_circle.py" name="circle_node" output="screen" />
</launch>
```
The <node> tag should already be familiar to you, but the <include> tag before it might not be...

This is what we use to launch other launch files. Here, we are locating the turtlebot3_gazebo package (using find), and asking for the turtlebot3_empty_world.launch file to be executed.
From the command-line, execute your newly created launch file as follows:
```
roslaunch week2_navigation circle.launch
```
The TurtleBot3 Waffle will be launched in the "empty world" simulation, and the robot will start moving in a circle straight away!