# Class Hierarchy (high level)

## LinkManager, LinkInterface

A "Link" in QGC is a specific type of communication pipe with the vehicle such as a serial port or UDP over WiFi. The base class for all links is LinkInterface. Each link runs on it's own thread and sends bytes to MAVLinkProtocol.

The `LinkManager` object keeps track of all open links in the system. `LinkManager` also manages automatic connections through serial and UDP links.

## MAVLinkProtocol

There is a single `MAVLinkProtocol` object in the system. It's job is to take incoming bytes from a link and translate them into MAVLink messages. MAVLink HEARTBEAT messages are routed to `MultiVehicleManager`. All MAVLink messages are routed to Vehicle's which are associated with the link.

## MultiVehicleManager

There is a single `MultiVehicleManager` object within the system. When it receives a HEARTBEAT on a link which has not been previously seen it creates a Vehicle object. `MultiVehicleManager` also keeps tracks of all Vehicles in the system and handles switching from one active vehicle to another and correctly handling a vehicle being removed.

## Vehicle

The Vehicle object is the main interface through which the QGC code communicates with the physical vehicle.

Note: There is also a UAS object associated with each Vehicle which is a deprecated class and is slowly being phased out with all functionality moving to the Vehicle class. No new code should be added here.

## FirmwarePlugin, FirmwarePluginManager

The FirmwarePlugin class is the base class for firmware plugins. A firmware plugin contains the firmware specific code, such that the Vehicle object is clean with respect to it supporting a single standard interface to the UI.

FirmwarePluginManager is a factory class which creates a FirmwarePlugin instance based on the MAV_AUTOPILOT/MAV_TYPE combination for the Vehicle.