Launch file structure

The launch files in spear_rover and spear_simulator are organized into a tree-like hierarchy. At the top, spear_rover/drive.launch launches everything which needs to run on the rover to drive it around manually, and spear_rover/navigate.launch launches everything which needs to run on the rover for autonomous navigation. Both launch files take an argument simulation which controls whether they start with the simulator or with the real robot (so to start navigate.launch in simulation you could run roslaunch spear_rover navigate.launch simulation:=true).

As a general principle, a non-top-level launch file that runs on the robot (simulation or otherwise) should either

• work identically or similarly in or out of simulation, and be in the spear_rover package (e.g. state_estimate.launch)
• work differently in or out of simulation (but present a similar interface), and have two versions: one in spear_rover that runs in the real world, and one in spear_simulator which runs in simulation (e.g. rover.launch)
• only run in simulation, and be in the spear_simulator package (e.g. steering.launch)
• only run in the real world, and be in the spear_rover package (e.g. udp.launch)

The last two usages should be minimized outside of includes to other non-top-level launch files. The idea is to always have a consistent interface whether in or out of simulation.