\defgroup gnc Guidance, Navigation & Control

The Guidance, Navigation & Control subsystem is responsible for tracking the robot's pose and controlling the robot's motion.

GNC Subsystems

GNC consists of four main subsystems, that run in a chain:

1. EKF: The extended Kalman filter integrates IMU measurements, as well as visual measurements from the localization subsystem, to track the robot's pose.
2. CTL: The control subsystem takes the robot's current state from the EKF, and determines the forces and torques needed to execute the commands sent from the mobility subsystem.
3. FAM: The force allocation module takes the force and torque commands from the control subsystem, and determines the PMC speeds and nozzle positions to best execute these forces and torques.
4. SIM: The simulator simulates the inputs to the EKF, and simulates the robot's motion based on the outputs of the FAM.

GNC Code Organization

Unlike the rest of flight software, the GNC systems are written mainly in Simulink. Simulink drag and drop box diagrams are then converted to automatically generated C code. The structure of the GNC code is:

1. [EKF](@ref ekf), [CTL](@ref ctl) and [FAM](@ref fam) are GN&C ROS Wrapper. [Sim Wrapper](@ref simwrapper) is the model side of the GN&C ROS Wrapper. These folders contain ROS nodelets that mainly convert inputs and outputs between ROS messages and Simulink.
2. [GNC Autocode](@ref gncautocode): This folder contains a thin C++ wrapper around the auto-generated C functions, which are all compiled in this package into a library.
3. [Matlab](@ref matlab): This folder contains the Matlab / Simulink code. This is where all the core functionality is located.