===== UAV operations characteristics =====

Regarding the range of the operations and requirements for the hardware and software, there are 3 major classes of UAV operations:
  * VLOS - operations within Visual Line Of Sight
  * BVLOS - operations Beyond Visual Line Of Sight
  * FPV - First Person View
We provide a summary and characteristics in the following sections.

==== Flying VLOS ====
VLOS flying is the first drone operators use. And the most common one, requiring the lowest level of certification or no certification at all (depends on the scenario, UAV weight, flight region). The most common question is "How far can I go?". It depends on the regulations, drone size, weather conditions and many others, but in any case, the best approach within the formal limits is given by the following rule: VLOS flying requires UAVO to be able to see and orient the platform using the naked eye ((Indeed, "the naked eye" means you can wear glasses, that you use daily, but you cannot use binoculars or a telescope or a long-range camera with zoom, to observe the drone.)).

<note important>When flying VLOS you not only need to see, where the drone is now, but also need to know its orientation.</note>

VLOS flying does not necessarily mean you need to control the drone in RC: you can use even high level of autonomy modes, but you need to see the drone and be ready to "jump into the action" when needed, i.e. to avoid the collision with another object or modify trajectory. For this reason, VLOS operations require constant observation. In many countries, regulations allow using additional human observers, supporting UAVO during operations. Note, in any case, it is UAVO's responsibility for incident or accident.

As mentioned before, flying VLOS may use virtually any mode from fully manual to fully autonomous. For this reason, a variety of drones fits this category. Depending on the flight mode, there are different requirements for the UAV aerial section and ground section hardware and software, as discussed in the hardware section.

<note tip>It is also natural and allowed by regulations, that UAVO can stop observing the platform for a moment, to check telemetry and ground control systems. Still, in any case, he/she must recover sight contact with the drone quickly, which may be pretty difficult if the platform is far away.</note>

==== Flying BVLOS ====
Flying BVLOS requires more advanced certification than VLOS. It also requires a higher level of communication capabilities between the aerial section (UAV) and ground section (UAVO). The operator needs to be able to control, trace the current location of the drone, and introduce necessary actions remotely. For this reason, the majority of the solutions require good video link (sometimes with multiple cameras/streams). This type of operations has a strong demand on the system reliability, so drones used in BVLOS usually have at least duplicated or even tripled navigation and IMU systems and reliable communication solution. Note, flying BVLOS is flying beyond the horizon of sight, within the line of sight but out of sight range, but also, i.e. beyond the construction (like i.e. a building). All of those situations require more advanced communication systems than in the case of VLOS drones. 

The majority of modern VLOS commercial constructions are ready for BVLOS or at least can be easily adapted. Note, forthcoming regulations will require drone identification using certified devices to let them broadcast ADS-B communicates (as in the passenger planes). More on ADS-B, one can find in Wikipedia ((https://en.wikipedia.org/wiki/Automatic_Dependent_Surveillance%E2%80%93Broadcast)) and FAA websites ((https://www.faa.gov/nextgen/equipadsb/)). Please note, using an ADS-B transmitter requires certification and drone registration while receiving ADS-B from others is considered to be free. And latest FCs contain integrated receivers like i.e. Pixhawk Orange Cube.

In the BVLOS operation, UAVO uses the ground station solely and does not observe the drone. Hence, it requires to provide all necessary information to the operator and also to be able to deliver commands to the UAV reliably.
==== Flying FPV ====
Flying FPV originates from racing, where the operator is "virtually" sitting as a driver or rather a pilot, within a drone's cockpit. Indeed the operator uses a distance video link to see the footage from the front-mounted camera. FPV drones usually do not provide advanced obstacle detection and critical situation handling capabilities, so flight range is limited by law. 

It is worth mentioning that most FPV flights are performed as fully manual controlled ones, even without self-levelling and altitude hold. For this reason, FPV pilots require great skills in space 3D imagination, a deep understanding of flight physics and most of all, huge experience. FPV racing is also considered the class of flights where collisions frequently occur, even leading to total drone damage. For this reason, FPV racing is performed on the dedicated tracks, and pilots are practising away from humans and properties to limit eventual damage cost. 

Obviously, FPV can be used as a part of regular, commercial drone operations, i.e., inspecting a power line. 

FPV flying requires low latency video transmission link (usually analogue) for racing, but digital links are acceptable for non-racing operations, where low video transmission latency is not critical. Indeed, many manufacturers (i.e. DJI, Yuneec) offer FPV sets for regular drones, enabling users to switch from observing a video transmission on their controller/phone to the FPV glasses. While in the case of racing, FPV glasses/headset is a must.

When using FPV glasses/headset, the operator cannot see anything else, but the displays, so FC, related hardware or eventually ground station video processing unit must deliver all necessary information on the screen. That impacts the hardware requirements (usually FC) to let it be able to perform an OSD (on-screen display). Modern FCs that use ARM cortex core (i.e. STM32 F7 series) can deliver this feature out of the box, while there is usually an external, analogue video processing module that supports the FC in this task.