uav-based photogrammetric mapping dyah frida

7/22/2019 UAV-Based Photogrammetric Mapping Dyah Frida

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UAV-Based Photogrammetric Mapping

Group 8

Dyah Puspasari W. (38724)

Frida Kurniawati (37820)

KEY WORDS: UAV, Mapping, Photogrammetry,

ABSTRACT

There are two kinds of platform used for mapping system. One is using manned aircraft,

while another is Unmanned Aerial Vehicle (UAV). Manned system is used firstly, and it has

some advantages, one of them is the intelligence of human being piloting the aircraft. But

nowadays, UAV is more efficient to be used because of its low-cost and high-end system.

With a super-wide-angle camera, GPS, and many more sensors combining with a computer at

ground station used to communicate with the aircraft in real-time to monitor flight parameters

and send out control commands, it become easier to do mapping process. This process stage

followed by aerial triangulation, DEM, and DOM process using photogrammetric software to

make 3D model..

1.

INTRODUCTION

1.1.DefinitionUnmanned Aerial Vehicles (UAVs) dont focus to certain kind of vehicle only. Further,

they concern in all aerial vehicles, which are flying in the air with no person onboard;

and with capabilities of controlling the aircraft manually and or automatically [1]. Its

also can be said that UAVs are to be understood as uninhabited and reusable motorized

aerial vehicles [2]. Differed from manned vehicles, it stand-out that in UAV no pilot

exists physically. But, it doesnt mean that this vehicle flies by itselfone hundred

percents autonomously. Instead, in many cases, the crew (operator, backup-pilot etc.)responsible for a UAV is larger than that of a conventional aircraft [2]. The

characteristics of UAV can be simply said as remotely controlled, semi autonomous, or

autonomous; or have combination of those capabilities. Actually, Unmanned Aerial

Vehicles are a part of Unmanned Vehicle Systems which usually used in the various

fields, like computer science, artificial intelligence, etc. to describe the technology of

unmanned.

1.2.Brief HistoryFirstly, unmanned aerial vehicle was used in wars around the world. For example, it wasfirst used in the American Civil War. This concept was also used by the Japanese for


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around a month in World War II, when they tried to launch balloons with incendiary and

other explosives. The idea was that high-altitude winds would carry them to the United

States, where the dropping bombs would cause panic. Apparently, both these ideas were

not effective.

In the 1960s, the US started to develop drones, which were unmanned vehicles built for

spying and reconnaissance. The first such drone was the Firebee drone, a jet propelled

by an engine made by Ryan Aeronautical Company. They were initially used heavily

over Communist China in the 1960s, when major flaws were discovered and corrected.

The Vietnam War was the first time that UAVs, the drones in particular, were used

extensively in reconnaissance and combat roles.

An example of popular UAV is the Global Hawk. This is a jet powered UAV that was

used effectively in Afghanistan. It operates at around 60,000 feet, and carries a wide

range of sensors. UAVs that are in use and under development are both long-range andhigh-endurance vehicles. The Predator, for instance, can stay in the air for around 40

hours. The Global Hawk can stay in the air for 24 hours.

Then, unmanned aircraft are slowing finding their way into commercial applications. The

US government is looking into using UAVs for surveillance over high crime areas, in

order to prevent crimes from happening. They could also be used to control hot spots,

where violence takes place habitually [3].

This paper particularly will discuss about the use of UAV in the field of remote sensing,

especially for photogrammetric mapping.

2. UAV PHOTOGRAMMETRYNowadays, UAV photogrammetry describes a photogrammetric measurement platform,

which operates remotely controlled, semi-autonomously, or autonomously, without a

pilot existing in the vehicle. Photogrammetric measurement system is included in the

platform, but not limited to a small or medium size still-video camera, thermal or infrared

camera systems, airbone LiDAR system, or combination thereof.

There are new various applications offered by UAV photogrammetry, not onlyapplications in the close range domain, combining aeerial and terrestrial photogrammetry,

but also introduces new real time application and low cost alternatives to the clasiccal

manned aerial photogrammetry. See Table below. [2]


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Table 1 : Features of Aerial, close range and UAV photogrammetry.

2.1.AdvantagesIn photogrammetry and remote sensing disciplines, UAVs have a lot of advantages

compared to manned ones. First, UAVs provide a new, controllable platform for remote

data acquisition; manoeuvrability of UAVs permits remote data acquisition in

environments dangerous to human life, and/or inaccessible to direct examination (e.g.

forest fires, volcanoes, toxic spills, transportation disasters, etc.); UAVs provide potential

for acquiring remote data more rapidly and at lower cost than from piloted/manned aerial

vehicles [4]. UAVs are also equipped with high end systems. In many particular case ofhigh-risk situation, UAVs can flight at low altitude and at flight profile close to the object

where manned systems cant be flown. It also offer a real-time processing capability and

the ability for fast data acquisition, while transmitting the image, video, and orientation

data in real time to the ground control station (GCS).

Furthermore, in cloudy and drizzly weather conditions, the data acquisition with UAVs is

still possible, when the distance to the object permits flying below the clouds. Such

weather conditions do not allow the data acquisition with large format cameras integrated

into manned aircrafts due to required larger flight altitude above ground. In addition, one

fundamental advantage of using UAVs is that they are not burdened with the

physiological limitations and economic expenses of human pilots [2].

2.2.LimitationDue to its low-cost system, UAVs have some limitation as below.

1. Use of small or medium format amateur camera due to limitation in weight anddimension. The consequence is UAVs have to acquire a higher number of images in

order to obtain the same image coverage and comparable image resolution.

2. The low-cost sensors are less stable than high-end sensorsreduce image quality.3. Less accurate results for the orientation of the sensors because of low weight

navigation units.

4. Less powerful engineslimiting the reachable altitude.


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5. Existing commercial software packages applied for photogrammetric data processingare rarely set up to support UAV images, as through no standardized workflows and

sensor models are being implemented.

6. There are no benefit from sensing and intelligent features of human beings,especially in unexpected situations.7. There are no sufficient regulations for UAVs given by the civil and securityauthorities

8. They are not equipped with air traffic communication equipments and collisionavoidance system, like manned aircrafts. So, UAVs are restricted to the flight in line-

of-sight and to opertae with a back-up pilot.

9. The operation distance depends on the range of the radio link for rotary and fixedwing UAVs.

10. There are may be interferences of frequencies used for communication between GCSand UAVs caused by other system or may suffer from signal jamming which can

cause flight disorders.

But, seeing that the technology of UAVs is developed rapidly, there is no reason to not

believe that those limitations will can be overcame.

3. UAV SYSTEMThere is a GCS (Ground Control Station) needed to control the aircraft. So, it needs not

only reliable communication links to and from the aircraft, but also to the local Air

Traffic Control (ATC) authorities if required. It usually happens when the aircraft flying

higher than 150-200 m above the ground. The GCS provides a working space for a pilot,

navigator, instrument operator and usually a mission commander [5]. Thats we called it

possibly needs more crew than manned aircraft. The data received by the GCS from the

instruments is either processed on-site or forwarded to a processing centre. This can be

done using standard telecommunication means. Of course, when operating low-cost

systems, most of the GCS functions can be combined in the handheld remote controls

that are typical for these systems. In that case, there is no data transmission for the

instrument; all data are stored on-board.

Figure 1. Ground Control Station [12]. Figure 2. Quadcopter UAV after take off.


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3.1. Physical Components

Figure 3.[6].

Figure 4.

Components

weControl Mini

UAV [1]

3.2.ClassificationTable 2 : Classification of UAVs according to the classes unpowered and powered,

as well as lighter or heavier than air.

Lighter Than Air Heavier Than Air

Flexible wing Fixed wing Rotary wing

Unpowered Balloon Hang glider Gliders Rotorkites

Paraglider

Kites

Powered Airship Paraglider Propeller Single rotor

Jet engines Coaxial

Quadrotors

Multi-rotors


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Table 3 : Classification of the CASA for UAVs.

Class Class I Micro

UAVs

Class II Small

UAVs

Class III Large

UAVsSpecifications Take-off weight of

100g

Take-off weight of

less than 150kg

Take-off weight of

Figure 5. Classification of

UAVs by range and altitude

based on Figure 1 in van

Blyenburgh, 1999[2].

Table 4: Classification of UAVs regarding to the type of georeferencing, real time

capability and application requirements.

Sensors Georeferencin

g

Real-time

capability

Application

requirement

UAV category

No GPS/INS post 0 Low accuracy

[m]

OM-class

GPS and

consumer-grade INS

post/direct + Moderate

accuracy [dm-m]

M- & L-class

DGPS/

navigation- and

tactical grade

INS

post/direct ++ High accuracy

[cm]

M- & L-class

Two kinds of platform are accepted for mapping UAV system. One is remotely-

piloted aircraft. Another is unmanned airship. The useful load required is up to 15 kg.

The photographic flying height is between 100 and 4000 meters, with speed 18160

kilometres per hour. The remote pilot has both manual remote operation and


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automatic programming control functions. A simple constructed two dimensional

stabilization plant are designed to keep the image sensors optical axis directed at

vertical [7].

UVS (Unmanned Aerial System)-International defines a mini UAV system as shown

in table below.

Table 5: A mini UAV system defined by UVS-International [1].

3.3.Sensor System1. Airframe

A modified radio controlled aircraft with primary flight system consisting of the

engine and drive train, main rotor and tail rotor assembly, control actuators, andstructural components.

For example, Airstar International Mongoose airframe helicopter, which is

powered by a 26cc, single cylinder, Zenoah G260H engine producing

approximately 1940 W at 12,000 rpm, an operating head speed

rpm. Its weight 6.1 kg, capable to carry 6.4 kg of payload. Its fuel capacity is

475 cc, which can use for approximately 45 minutes without payload and 30

minutes with payload. The battery 90 minutes of power-on time for the entire

system.

2. Autonomous Flight ControllerIts a combination of Rotomotion Automatic Flight Control System hardware

(AFCS) and custom Mission Control System Software (MCS) to design and

execute pre-programmed waypoint path, monitoring mission-specific intelligent

control software, maintaining full control of the vehicle.

The MCS software runs on the ground base station computer and manages the

guidance and navigation control behavior of the UAV system.

The rotomotion AFCS which has function to stabilize the position of UAV consists

of:

An embedded computer running Linux WAAS (Wide Area Augmentation System)-enabled GPS with unit


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3-axis magnetometer which utillizes PID (Proportional-Integrative-Derivative)controllers to maintain altitude and altitude in translational flight and hover; flight

during a fast-forward flight mode.

GPS provides position of the aircraft and maintain course and speed, as well as

fixed hovering position.

3. Imaging SensorUAV uses USB video camera, or digital camera which supports NEMA sentence

capturing from external GPS units, thus the time of image capture and the exact

position of capture could be recorded into the image header for later review and

correlation. A custom camera trigger is made controller by the AFCS. The camera

will be triggered at preset GPS waypoints.

4. PHOTOGRAMMETRIC PROCESS4.1.Aerial Triangulation

Aerial triangulation inphotogrammetry is methods of determine and calculate 3-

dimensional object coordinates by photogrammetric means, by using photographs

exposed from different positions, covering the same object. With aerial

triangulation in aerial photogrammetry we might be able to calculate 3-dimensional

coordinates for object elements on almost any object. We need at least some points with

known position that are visible in at least some of the photographs. These points we callground control points, or any control points, the control points have to be a part of

the aerial triangulation.

Figure 6. Aerial

triangulation.

Still we need at least

five control points

inside each aerial

photogrammetry modelto be able to do an

absolute orientation of

the model.

In aerial

photogrammetry, to be

able to get that many points a method named aerial triangulation is developed. This

method is that we measure several unknown point clearly visible in the aerial

triangulation in a stereo instrument. These new points together with the ground control

points and the exposures positions for the camera are put together in a big computation.
http://www.photogrammetry-software.com/2010/08/what-is-aerial-triangulation.htmlhttp://www.photogrammetry-software.com/2010/08/what-is-aerial-triangulation.htmlhttp://www.photogrammetry-software.com/2010/08/what-is-aerial-triangulation.htmlhttp://www.photogrammetry-software.com/2010/08/what-is-aerial-triangulation.html


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The result we get out of this is the coordinates in the reference system for all the new

measured points [8].

According to the feature of data get from the UAV acquisition system, a special aerial

triangulation program has been developed. The advantage features of this software are asfollow: 1) Making high precision calibration for the geometric distortion from normal

purpose used digital cameral. 2) Using Pos or GPS data combined with image matching

to reconstruct the topologic relation of the images along the flying direction and between

the neighbouring lines. 3) All the points in the triangulation network are selected and

measured fully automatically. 4) multi-view geometric relations of the images are solved

by large block adjustment with least square method. 5) The coarse error are detected full

automatically by large number of redundant observations. 6) The result of orientation

elements and control points are calculated through alternative solution to achieve 1:2000,

1:1000 or 1:500 scale mapping standard.

Figure 7. Select and measure the observed points fully automatically.

Figure 8. Multi-view geometric relations of the images. [7]


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Figure 9. Aerial Triangulation in LPS Core

4.2.DEM (Digital Elevation Model) ProductionThere are three important terms related to DEM. First, DEM itself. The term DigitalElevation Model is often used as a generic term for DSMs and DTMs, only representing

height information without any further definition about the surface. A DEM can be

represented as a raster (a grid of squares, also known as a heightmap when representing

elevation) or as a vector-basedTriangular Irregular Network (TIN). The TIN DEM

dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is

referred to as a secondary (computed) DEM.

The quality of a DEM is a measure of how accurate elevation is at each pixel (absolute

accuracy) and how accurately is the morphology presented (relative accuracy). Several

factors play an important role for quality of DEM-derived products:

terrain roughness; sampling density (elevation data collection method); grid resolution orpixelsize; interpolationalgorithm; vertical resolution; terrain analysis algorithm; Reference3D products include quality masks that give information on: the coastline,lake, snow, clouds, correlation, etc [9].
http://en.wikipedia.org/wiki/Heightmaphttp://en.wikipedia.org/wiki/Triangular_irregular_networkhttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Interpolationhttp://en.wikipedia.org/wiki/Interpolationhttp://en.wikipedia.org/wiki/Interpolationhttp://en.wikipedia.org/wiki/Pixelhttp://en.wikipedia.org/wiki/Triangular_irregular_networkhttp://en.wikipedia.org/wiki/Heightmap


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Figure 10. DEM

Digital Elevation Models are data files

that contain the elevation of the terrain

over a specified area, usually at a fixed

grid interval over the "Bare Earth". Theintervals between each of the grid

points will always be referenced to

some geographical coordinate system.

This is usually either latitude-longitude

or UTM (Universal Transverse

Mercator) coordinate systems. The closer together the grid points are located, the more

detailed the information will be in the file. The details of the peaks and valleys in the

terrain will be better modeled with small grid spacing than when the grid intervals are

very large. Elevations other than at the specific grid point locations are not contained inthe file. As a result peak points and valley points not coincident with the grid will not be

recorded in the file.

For practical purpose this "Bare Earth" DEM is generally synonymous with aDigital

Terrain Model (DTM). Common uses of DEMs include:

Extracting terrain parameters Modeling water flow or mass movement (for example,landslides) Creation of relief maps

Rendering of 3D visualizations Creation of physical models (including raised-relief maps) Rectification of aerial photography or satellite imagery Reduction (terrain correction) of gravity measurements (gravimetry, physical geodesy)

Terrain analyses ingeomorphology and physical

geography.

Second, a Digital Surface Model

(DSM) which represents the MSL

elevations of the reflective surfaces of

trees, buildings, and other features

elevated above the "Bare Earth".

Figure 11. DSM

Third, TINs which are sets of adjacent, non-overlapping triangles computed from

irregularly spaced points with x/y coordinates and z-values. TIN models are used to

provide better control over terrain slope, aspect, surface areas, volumetric and cut-fill

analysis and generating contours.
http://www.satimagingcorp.com/svc/3dterrain.htmlhttp://www.satimagingcorp.com/svc/3dterrain.htmlhttp://www.satimagingcorp.com/svc/natural_hazards.htmlhttp://www.satimagingcorp.com/svc/natural_hazards.htmlhttp://www.satimagingcorp.com/svc/3dterrain.htmlhttp://www.satimagingcorp.com/svc/3dterrain.html


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Figure 12. Example of TIN.

The TIN's vector data

structure is based on

irregularly-spaced

point, line andpolygon data

interpreted as mass

points and breaklines

and stores the

topological

relationship between

triangles and their

adjacent neighbors

[10].

After aerial triangulation the multi-view images are reorganized to be divided

automatically into basic units as

the stereo pairs in traditional

photogrammetry. Then the DSM is

automatically generated by image

matching and TIN interpolation

within every unit. It need a little

manual interaction operation toseparate the points upon the

building or lie down at grand for

generation DEM. ALL units are

link up to form fully coverage

DEM [7].

Figure 13. The generation of DEM.

4.3. DOM (Digital

Orthophoto Map)

Production

The digital orthophoto

process transforms a

vertical aerial

photograph into the

equivalent of a

traditional map. Yet it

retains the advantages of

a photographvisually


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displaying actual cultural and land features, and the built environment, rather than

representing those features using symbols and lines [11].

The DOM is also produced automatically based on the orientation elements and DEM

results. Because 80 percent overlapping along flying direction have acquired fromaerialphotography, only the centre part of image in the frame have been taken to be

rectified into orthophoto imagery.

Figure 14. Orthophoto imagery.

5. CONCLUSIONUAV-based mapping has became an alternative to produce high resolution digital and

optical image which can support the application of large-scale mapping with lower costthan using manned aircraft. Although it has some limitations, but we can overcome it by

designing the light and small combined super-wide-angle camera which has the self-

calibration function to construct the practical low altitude UAV system combining with

the use of powerful automatic photogrammetric processing software. Hence, mapping

process becomes easier, quicker, and of course, without decrease its quality.

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