Launching Other Launch Files

COM2009 Assignment #1 Checkpoint

It helps if you've already completed Part 2 up to and including Exercise 4 before working on this as, in this example, we'll build on the move_circle.py node.

We need a simulation of our Waffle active in order to run this, which we can enable with the following command:

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, navigate to your part2_navigation package and create a launch directory (if you haven't done so):
```
roscd part2_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="part2_navigation" type="move_circle.py" name="circle_node" output="screen" />
</launch>
```
Having completed Assignment #1 Part 1, the <node> tag should already be familiar to you. The <include> tag before it however, 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 part2_navigation circle.launch
```
The Waffle will be launched in the "empty world" Gazebo environment, and the robot should start moving in a circle straight away!