Launch Files

Overview¶

As you should know from the COM2009 ROS Course, Nodes can be executed on a ROS network in two ways:

Using the rosrun command:
```
rosrun {package name} {script name}
```
Or by using roslaunch:
```
roslaunch {package name} {launch file}
```

In Assignment #1 Part 1 you learn that a launch file is an xml file with a .launch file extension. Inside this we can ask ROS to do a number of different things from one single roslaunch command-line call.

roslaunch offers a number of advantages over rosrun:

Multiple nodes can be executed simultaneously.
roslaunch will launch the ROS Master for us, if isn't already running (so we don't have to manually call roscore).
From within one .launch file, we can launch other .launch files.
We can pass in additional arguments to launch certain things conditionally, or pass specific arguments to certain ROS nodes.
As if that wasn't enough, there is also a roslaunch Python API, allowing us to launch nodes from within other (Python) nodes!

In this section we'll talk about some of these advanced features that you may find useful.