====== Thruster Plugin ======
The thruster plugin runs the thrusters for our simulated sub. It is responsible for:
  * Running a ROS node that receives thruster messages and then adds forces as appropriate.
  * Visualizing the thruster output graphically by sending visual messages to the gazebo server. These are distinct from ROS messages and will covered in the next section.
  * Add buoyancy to the submarine. We do this manually in the thruster plugin instead of utilizing the built-in buoyancy plugin because we found the buoyancy plugin to behave weirdly.

====== Thruster Visualizer ======
When gazebo is run it starts both a server (gzserver) and a client (gzclient). Since model plugins are run on the server but visuals are run on the client gazebo messages must be sent from the thruster plugin (which is a model plugin) to the client in order to add visuals to the simulator.

To visualize each thruster a very narrow cylinder is defined for each. This cylinder is then scaled and positioned each time a new thruster message is recieved. To see how the visual messages are defined see [[https://github.com/PalouseRobosub/robosub_simulator/blob/master/src/thruster.cpp#L88|here]].

To see the actual scaling and resizing steps see [[https://github.com/PalouseRobosub/robosub_simulator/blob/master/src/thruster.cpp#L145|UpdateVisualizers]].