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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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