A COMMERCIAL OF THE SHELF COMPONENTS FOR A UNMANNED AIR VEHICLE PHOTOGRAMMETRY

A photogrammetry from a unmanned aerial vehicle (UAV) can be understood as a new measurement tool. Is introduces a low-cost alternatives for a traditional aerial photogrammetry. A commercial off-the-shelf products (COTS), that are commercially available for a costumers, are the standard manufactures products, not custom. COTS products are available in the commercial market and can be bought and used under government contract. That fact makes it cheaper and available for all. Motivations for using COTS components is a reduction of overall system-development and costs and long-term maintenance costs. An aviation offers a different types of aircraft. Aircraft may be classified by different criteria, such as lift type, aircraft propulsion. All those types offers different attributes, that are more or less desirable for UAV photogrammetry. A methodology for determining a platform type was developed in this research, and the most suitable platform for a photogrammetry measurements was chosen. In order to build a UAV platform for photogrammetry tasks, products available on commercial market were analyzed with characteristics and technical data.


INTRODUCTION
Commercial off-the-shelf (COTS) products can be defined as an items, including services, sold in the commercial marketplace.This is a standard manufactures products, not specially designed for custom purposes.This item is commercially available, leased, licensed and sold to the general public.COTS products not require special modification or maintenance over its life cycle.It means that all components can be purchased on the market, connected and programed for a final product.
Unmanned aerial vehicle (UAV), also called drone, is defined as a generic aircraft design to operate with no human pilot onboard.Initially, UAV systems and platforms were designed for a military applications.Military UAV are very complicated, specially designed for a military operations.UAV technology was unavailable to a wider community.During recent years UAV technology was commercialized.Nowadays, it is possible to purchase small, simple and cheap drone for a home usage.So called professional drones, but still commercial, are available on the market and equipped with more advanced technology, better cameras, represents better stability, endurance and maneuverability during flight.All components are available on markets, can be replaced, modified, upgraded.It means, that UAV technology becomes very popular and affordable for community.UAV photogrammetry should be understood as a new photogrammetric measurement tool.This technology opens a new applications in the close range domain, combining aerial and terrestrial photogrammetry, but also introduces low-cost alternatives to the classical manned aerial photogrammetry.UAV photogrammetry describes photogrammetric measurement platforms, which operate as either remotely controlled, semi-autonomously, or autonomously [1].

UAV PHOTOGRAMMETRY
Recent years showed that a the range of measurement technique published in [7] and modified in [4], now can be revised again (Fig. 1), since NASA launched X-37 project, also known as the Orbital Test Vehicle (OTV), which is a reusable unmanned spacecraft.Since that moment unmanned aerial vehicle are enable to operate in outer space.
Based on this information, new classification of geomatics 3D measurement technique found in [6] should be revised as well (Fig. 2).Since UAV reached the space, its capability to take a photogrammetry measurements reach ability close to measurements taken from satellites.

UAV PLATFORMS
UAV platform (body) can be considered as a mechanical structure, typically including a fuselage, wings and the propulsion system and aviation electronics, excluding payload.Platforms design is a field of aerospace engineering that combines aerodynamics, materials technology and manufacturing methods to achieve balances of performance, reliability and cost.UAV platforms can be categorized using the main characteristics of aircrafts.Table 1 shows a classification of the UAV platforms, which can be used for photogrammetric applications.UAV is a part of system named Unmanned Aerial System (UAS).A typical UAS consists of an unmanned aerial vehicle, ground control station (GCS) and a communication and control link (C2) between GCS and UAV.Critical UAV modules are placed on board unnamed platform, such as navigation module (NM), flight control module (FCM), mechanical servos.Depends on UAV main purpose and tasks payload is different.In case of photogrammetry and remote sensing, payload could be defined as a data acquisition module (DAM) (Fig. 3).GCS can be defined as a stationary or transportable devices to monitor, command and control the unmanned aircraft.Ground control station can operate form ground, sea or air.It is a connection between machine and an operator.The design of a GCS for UAV are to have a certain functional requirements.Crucial functionalities are [5]: air vehicle control -a capability to effectively control and fly the UAV during is mission, payload control -ability to operate sensors from ground, mission planning -functionality that aids UAVs operator in planning the mission providing required knowledge inputs concerning capabilities and UAVs limitations, payload data analysis and dissemination -capability to disseminate the data form payload to an eventual users, system/air vehicle diagnosticsautomatic test facility for UAV and GCS effective maintenance and deployment, operator training -facility to train he air vehicle controller in handling the aircraft, practicing mission plans and emergency procedures, post-flight analysis -capability to store flight data and payload data and to analyses it after the flight.
NM is most critical module on board UAV.Navigation module repeatedly provide the aircraft's position, velocity and altitude to FCM.Navigation module feeding FCM with a crucial data to guide unmanned platform.NM is equipped with navigation systems (NS) to fix a platforms position (usually uses GNSS) and orientation system (OS) with motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate orientation and velocity (direction and speed of movement) of a platform (inertial measurement unit -IMU).Where NM (NS+OS) and FCM are integrated in one module can be called autopilots.
FCM is defined as a devices commanding a flight, means leading UAV to designated position and putting on the right orientation and speed.FCM consists of two main parts: data analysis -this part is receiving commands from system operator and current flight parameters form NM, analyses I and prepare commands for an executive part in order to correct flight parameters.Second part is an executive part with mechanical servos, engine electronic speed controller, designed to move all control surfaces and regulate speed of engines.
DAM includes optical remote sensing instruments.Depends on characters of desirable data the data acquisition module can be equipped with different type of sensor including airborne image acquisition systems (from visible band to the near infrared (NIR) up to the thermal infrared (TIR)), microwaves systems, active and passive ranging instruments.

METHODOLOGY
In order to select the most suitable platform for a photogrammetry task platform a parameters matrix was developed (Tab.2).According to the classification (Tab.1) a specified parameters have been assigned with an appropriate weight.The weights range is 1 to 5. The weights for each type of platform have been developed on the basis of own experience and research results [4] [6].The parameter values varies from 0 to 2, with 0 being the lowest characteristics (ability) platform in the specified parameter, while the 2 highest.The result for the type of platform, was calculated from the expression: Tab.As a results present, the most suitable platform for a photogrammetry task, with specified parameters, is motor glider with result 54 points.According to a "FAI Sporting Code" moto-glider is a fixed-wing aerodyne equipped with a means of propulsion (MoP), capable of sustained soaring flight without thrust from the means of propulsion.Motor gliders are equipped with a propeller, which may be fixed, feathering, or retractable.Motor with fixed or full feathering propellers can take off and cruise like an airplane or soar with power off, like a glider.Self-launching retractable propeller motor gliders have sufficient thrust and initial climb rate to take off without assistance, or they may be launched as with a conventional glider.
The glider (sailplane) is characterized by a high aerodynamic efficiency, much higher than in other platform types.Currently the technology of building the gliders is based on composite materials (carbon and glass fibers) formed in CNC milled molds.That technology enables engineers to produce the wings and fuselages with a very high precision accurately determined by numerical models, resulting in a lightweight yet extremely rugged structure.The composite material forms complex shapes at relatively low cost, and can exhibit incredible strength and stiffness.
The propulsion system in motor glider type UAV platforms consists of brushless electric motor with electronic speed controller (ESC) powered by a Lithium-polymer batteries.That configuration is the most efficient for UAV and can be assembled completely of low-cost commercial-off-the-shelf products.

DATA ACQUISITION MODULE
Data acquisition module integrates in one physical element all sensing instruments and auxiliary elements.As for the sensing elements for photogrammetry tasks we concentrated only on commercial visible light, spectral and thermal cameras with weight less than 1500 g, basing on [8] (Tab.3).An auxiliary elements are mainly active or passive stabilization system, additional data storage, and optionally recovery system.
In case of chosen platform type (motor glider) DAM components should closed in be housing or placed within fuselage, in order to diminish an aerodynamic drag.In that particular platform aerodynamic drag forces can negatively influence on gliders overall performance.On the other hand, that problem is minimalized on different platform type typical vertical takeoff and landing (VTOL) like single of multirotor copters.

NAVIGATION AND ORIENTATION MODULE
Form the photogrammetric point of view NM and OS are responsible for camera extrinsic parameters determination.Geodetic-grade light-weight GNSS modules are available on the commercial market (Tab.4) with weight less than 100 g.Unfortunately, light-weight geodetic-grade IMUs are not yet available [3].A light-weight IMU modules are based on MEMS (microelectromechanical systems) technology, therefore are not able to provide very accurate data, in compare to a heavy weight FOG IMU system (Fiber Optic Gyro).Commercial IMU for navigation purposes, with weight less than 250 g are presented in Tab. 5. Tables 6 and 7 presents an integrated modulesautopilots and hybrid navigation units (HNU) with weight less than 250 g.

CONCLUSION
As the results shows the moto glider is the most suitable platform for a photogrammetry tasks.A crucial modules for navigation and data acquisition are commercially available on the market with weight suitable for small UAV like moto glider.Still, light-weight with geodetic-grade IMU modules are unavailable, however in connection with sensor fusion or other navigation methods [1], a camera extrinsic parameters can be determined with affordable accuracy.
2 Evaluation of UAV platforms employed for photogrammetry applications.