The Use of UAVs for Cultural Heritage and Archaeology

Abstract

This chapter focuses on the uses of unmanned aerial vehicles (UAVs) for documenting and monitoring cultural heritage and archaeological sites. High-resolution aerial imagery from UAVs also allows the rapid generation of 3D digital surface models for documentation and model reconstruction in a variety of applications. This chapter provides various examples of cultural heritage and archaeological sites in Cyprus that have been documented with high-resolution cameras aboard UAVs. Photogrammetry is also used to create 3D models of the site, which can also be printed using a digital printer.

Full text

241© Springer Nature Switzerland AG 2020
D. G. Hadjimitsis et al. (eds.), Remote Sensing for Archaeology and Cultural
Landscapes, Springer Remote Sensing/Photogrammetry,
https://doi.org/10.1007/978-3-030-10979-0_14
The Use ofUAVs forCultural Heritage
andArchaeology
KyriacosThemistocleous
Abstract This chapter focuses on the uses of unmanned aerial vehicles (UAVs) for
documenting and monitoring cultural heritage and archaeological sites. High-
resolution aerial imagery from UAVs also allows the rapid generation of 3D digital
surface models for documentation and model reconstruction in a variety of applica-
tions. This chapter provides various examples of cultural heritage and archaeologi-
cal sites in Cyprus that have been documented with high-resolution cameras aboard
UAVs. Photogrammetry is also used to create 3D models of the site, which can also
be printed using a digital printer.
Keywords UAVs · Cultural heritage · Archaeology · Photogrammetry
Introduction
The documentation of architectural cultural heritage sites has traditionally been
expensive and labor-intensive. Innovative technologies, such as unmanned aerial
vehicles (UAVs), provide an affordable, reliable, and straightforward method of
capturing cultural heritage sites, thereby providing a more efcient and sustainable
approach to documentation of cultural heritage structures. UAVs have proven to be
invaluable in the elds of archaeology and cultural heritage, as they provide a non-
invasive, time- and cost-efcient way to document cultural heritage sites. Most
importantly, they are able to include the cultural landscape in which ancient vestiges
are located in the documentation process. UAVs are a low-cost, nonintrusive, non-
contact, cost- and time-efcient alternative to traditional methods of archaeological
documentation and monitoring as they are able to acquire high spatial resolution
data with high temporal frequencies over large areas. Aerial imagery from UAVs
also allows the rapid generation of 3D digital surface models for documentation and
model reconstruction in a variety of applications.
K. Themistocleous ()
Department of Civil Engineering and Geomatics, Faculty of Engineering and Technology,
Cyprus University of Technology, Limassol, Cyprus
e-mail: k.themistocleous@cut.ac.cy
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This chapter presents an overview of case studies conducted using UAVs to
document and monitor archaeological and cultural heritage sites in Cyprus with
high resolution. The case studies include the use of UAVs for the purposes of aerial
photography and photogrammetry, which produces ortho-images and generates 3D
models of the site.
UAVs
Although airborne and satellite sensors are the most widely used methods in remote
sensing to date, UAVs are becoming an alternative remote sensing method, as they
are easier to use and are accessible to a wider audience. Currently, unmanned aerial
vehicles (UAVs) such as gliders and copters provide a low-cost, high-quality image
comparable to airborne sensors. The use of UAVs for monitoring purposes provides
a low-cost, non-invasive technique to acquire high spatial resolution data with high
temporal frequencies, especially in areas that have limited coverage and are inacces-
sible to humans. Research indicates that aerial remote sensing and imaging can be
conducted using large-scale low-altitude imaging and geospatial information
(Colomina and Molina 2014; Cho et al. 2013; Mayr 2013; Petrie 2013). Recent
developments in photogrammetry technology provide a simple and cost-effective
method of generating relatively accurate 3D models from 2D images (Ioannides
etal. 2013; Themistocleous etal. 2014b, 2015a, b, c). These techniques provide a
set of new tools to capture, store, process, share, visualize, and annotate 3D models
in the eld (Themistocleous etal. 2014a, 2015b).
The use of cost-effective unmanned aerial vehicles (UAVs) are becoming com-
mon tools for researchers for numerous applications. According to Burkart (Burkhart
etal. 2014), the emerging development of small versatile UAVs for use in remote
sensing offers simple and affordable observation from the air. Since UAVs vary in
size and payload capacity, various sensors can be installed onto the UAV platform
(Fig.1). The sensors that can be added to the UAV platform include visible spec-
trum cameras and multispectral, infrared, and thermal cameras (Themistocleous
etal. 2014a), thereby creating an unmanned aerial system appropriate for remote
sensing applications. Due to the decreasing size of the sensors, receivers, and anten-
nas, it is now possible to create an integration of various sensors, as their low weight
Fig. 1 Left—Sony NEX 7visible spectrum camera. Center—Tetracam multispectral camera.
Right—FLIR thermal camera
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and small size render them ideal for use on UAVs (Colomina and Molina 2014;
Kostrzewa etal. 2003; Rufno and Moccia 2005; Scholtz etal. 2011).
UAVs can be divided into two types: xed-wing copter and glider. Each type of UAV
has its own advantages and limitations, which are discussed in the sections below.
Fixed-Wing Copter
A copter system is a very powerful aerial platform with enhanced stability and
maneuverability and powerful enough to lift a payload of several kilograms. For
autonomous ight and improved maneuverability, the copter can be equipped with
an internal GPS, gyros, compass, altitude control, telemetry, acceleration, and baro-
metric sensors for altitude control. Copters are available with 4, 6, or 8 motorized
propellers and can carry a payload of up to 2.5kg on the mechanized viewing plat-
form (Fig.2). The main advantage of this conguration is that the copter can remain
steady in the air and respond smoothly to ight commands from the operator, due to
the ve separate sensors and three gyroscopes that work together to maintain stable
and controlled ight. The ground station transmitters allow the operator to easily
control the copter system and the viewing angle of the camera. Using a video sys-
tem, the live video of the camera is transmitted to a ground station. Flight times
range from 8 to 25minutes, depending on the payload and battery. To maximize
ight time, two batteries can be connected in series to provide a ight time up to
40minutes. The copter can be programmed to y planned waypoint routes by using
the GPS onboard navigation system and photographs can be triggered automati-
cally. During the ight, the current position of the copter can be shown using a
portable computer or a tablet.
Due to the internal GPS of the copter, the operator is able to take measurements of
the same target at different heights by using the wireless PDA.The copter has a mech-
Fig. 2 Selected xed-wing copters used in the case studies
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anized camera mount that could be controlled remotely. The cameras and video
recorders are attached to the camera mount and aerial photographs can be taken using
the manual trigger through the ground control systems. The system can also be pre-
programmed to take photographs at certain points and angles on a planned waypoint
route. The camera mount is balanced horizontally and vertically by servomotors,
which allows the camera to be vertical to the ground at all times. The copter had the
capability to be raised up to 3km in the air, thus providing data acquisition at higher
elevations that the helium balloon platform. However, at high elevations, it was dif-
cult for the operator to keep the copter within his line of sight and control the unit.
One of the main limitations of the xed-wing copter is the battery capacity. Flight
times are approximately 10min when the payload was at maximum capacity and
20min with normal payload, thereby minimizing the utilization of the copter for data
collection. As well, the copter required calibration every time it was switched on in
order to calibrate the internal GPS.The copter required that the operator have con-
siderable experience in lift-off and landing copters to operate the copter and avoid
damage to the instrument. The operator needs to be aware of the time limitations of
the battery to avoid any crashes and possible damage to the copter. Special care is
necessary in urban areas to avoid any collisions with electrical cables, buildings, etc.
An additional problem of the copter is that it is quite large and bulky, which makes
transport difcult.
Recently, there has been an inux of smaller copters with integrated cameras, such
as the DJI Phantom series. These UAVs have an integrated 20 megapixel camera,
which is extremely light and easy to manage. The unit has a built-in high- precision
three-axis camera stabilization system that allows for smooth aerial photography.
The integrated GPS autopilot system includes position holding, altitude lock, and
stable hovering, thereby providing constant stability in ight. The UAV has a Wi-Fi
wireless connection up to a distance of 300 meters, as well as real-time telemetry data
and ight parameters. However, a main drawback of the copter is that the battery
ight time is only 25min. The unit has an intelligent operator control that displays
the current position of the UAV in relation to the pilot as well as ground station
support, thereby enabling extensive ight planning for automated ights.
Gliders
One of the benets of the glider is that it has a ight duration of up to 90min, which
is four times the ight duration of other UAVs. The QuestUAV Q-POD is a glider
UAV that can be used with different payload bays (Fig.3). Q-Pods are designed to
Fig. 3 QuestUAV glider
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be easily interchangeable. The modular design consists of one airframe and multiple
sensor pods (Q-Pods). The A-frame carries the permanent equipment including the
wings, motor, avionics, and autopilot. The Q-Pods slip easily into the A-frame and
carry single or multiple sensors and the battery pack. The unit contains aircraft
system status indicators, including current mode, critical sensor condition, GPS,
onboard voltage monitoring, and communication link quality. As well, there is a
real-time, auto-scaling moving map automatically linked with the planned way-
points and ight path. The UAV has a 100km range and has an operational ceiling
of 10,000ft.
One of the biggest drawbacks of the Quest UAV system is that it required two to
three people to operate it. As the glider is in constant motion, there are limitations
on the types of sensors that can be used while the unit is in motion. The price point
is more expensive than the previous systems examined. Also, extensive training and
practice are required in order to operate the glider, due to safety requirements and
ight regulations.
UAV Applications forCultural Heritage
UAVs are being used for surveying cultural heritage sites due to their affordability,
reliability, ease of use, and the quality of the processed measurements (Colomina
and Molina 2014; Themistocleous etal. 2015a; Lo Brutto etal. 2014; Rinaudo etal.
2012). Research indicates that aerial remote sensing and imaging can be conducted
using large-scale low-altitude imaging and geospatial information (Colomina and
Molina 2014; Cho etal. 2013; Mayr 2013; Petrie 2013). Research indicates that
UAV data provide more detailed surveys of the archaeological site (Hassani 2015;
Remondino and Rizzi 2009; El-Hakim etal. 2004; Gruen etal. 2005; Rönnholm
etal. 2007; Guidi etal. 2009), which are used to document the site. UAVs are also
useful to survey inaccessible and/or dangerous areas which cannot be accessed
directly using other systems or piloted aerial systems (Everaerts 2008; Eisenbeiss
2009). Several cultural heritage researchers have used UAVs for archaeological sites
in the Mediterranean (Rinaudo etal. 2012; Brumana etal. 2013; Remondino etal.
2011) as well as in Germany, Cambodia, and Hungary (Seitz and Altenbach 2011;
Meszaros 2011). Also, researchers have used the combination of aerial imagery for
3D reconstruction of the cultural heritage site (Eisenbeiss 2009; Fiorillo etal. 2012).
Remote sensing technologies on a UAV platform are extremely useful for the
detection and monitoring of cultural heritage features (Themistocleous etal. 2014a,
b, c; Agapiou et al. 2013). UAVs can be an efcient, non-invasive, and low-cost
resource to document cultural heritage sites (Themistocleous et al. 2014a, b, c;
Agapiou etal. 2013) and can be tted with sensors which are able to produce an
unprecedented volume of high-resolution, geo-tagged image sets of cultural heritage
sites from above (Themistocleous etal. 2014a, b; Kostrzewa etal. 2003; Rufno
and Moccia 2005; Scholtz etal. 2011). Researchers have used the combination of
aerial imagery for 3D reconstruction of the cultural heritage site (Eisenbeiss 2009;
Fiorillo etal. 2012) through the use of photogrammetry.
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The methodology followed for the case studies presented in this chapter begins
with a UAV survey where high-resolution aerial images are acquired. These images
are then processed using Structure from Motion software, which creates a 3D digital
model. The 3D model can then be exported into a BIM model, where the structure
can be documented in terms of oor plans, elevations, and sections (Fig.4).
Photogrammetry
Photogrammetry is a three-dimensional coordinate technique that uses computer
analysis of photographic images for measurement. The fundamental principle of
photogrammetry is aerial triangulation, where images from at least two different
locations can be developed from each camera to point on the object and processed
to produce the three-dimensional coordinates of the point of interest. Photogrammetry
is used to conduct the image processing of the images acquired with the UAV, where
the digital images are interpolated in order to create high-resolution, scaled, and
geo-referenced 3D models from them. Photogrammetry generates the creation of
3D models by reconstructing a dense point cloud and generating polygonal mesh
model based on the dense cloud data. In addition, the software has an automatic tool
of texture projection, which makes automatic projection from the color directly on
the surfaces possible (Meszaros 2011).
The rst step in the program’s procedure is called Structure from Motion (SFM)
(Scopigno etal. 2015; Ingwer etal. 2015; Giuliano 2014). Structure from Motion is
a photogrammetric method for creating three-dimensional models of a feature or
topography from overlapping two-dimensional photographs taken from many loca-
tions and orientations to reconstruct the photographed scene. SfM analyses the data-
set, detecting geometrical patterns in order to reconstruct the virtual positions of the
cameras that were used in order to align the images, including building a sparse
point cloud (tie points).
The second step involves the creation of a complete geometry of the scene using
a multi-viewpoint stereo algorithms to build a dense point cloud. At this stage the
dataset of images are employed to produce a high-resolution geometry of the surface.
This step successfully creates a 3D model, also known as a digital surface model
(DSM). The processing began with the orthomosaic production from these multiple
images, which was used for digital terrain modeling (DTM) production from which
Fig. 4 Methodology
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a contour map can be generated. All images derived from the UAV can be included
in processing or it is possible to select a sub- set of images on key sites with the study
area for more detailed analysis ensuring sufcient overlap and ground control points
(GCPs) allow for this. Photogrammetry software allows generation of high-resolu-
tion geo-referenced orthomosaics, exceptionally detailed DTMs and textured
polygonal models through the use of the image overlay (Eisenbeiss 2009).
Following, surfacing algorithms employ the dense cloud’s 3D point positions
and the look angles from the photos to the matched points to build the geometrical
mesh. The coordinates from the GCPs are then applied in order to scale the model
to the correct dimensions. The software automatically aligns images based on
pairing of features and creates a “sparse cloud” of elevations based on these points.
The completed alignment is then used to develop a dense point cloud which is used
to create a surface which allows draping of the imagery over the model by creating
and building a texture from the original images and overlays the imagery onto the
model mesh (Themistocleous et al. 2014c). The photogrammetry software then
builds a polygon mesh and calculates a texture for the mesh. The software generates
the building of 3D models by reconstructing a dense point cloud and generating
polygonal mesh model based on the dense cloud data. In addition, photogrammetry
has an automatic tool of texture projection, which makes automatic projection from
the color directly on the surfaces possible (Meszaros 2011).
Image Processing
When cameras used in acquiring images have a wide-angle lens, lens distortion
removal is required by calibrating the camera and removing the distortion by esti-
mating the camera calibration parameters of center principal point, square pixels,
and distortion models using the Brown distortion model (Brown 1966). Camera
calibration data can also be calculated by the Agisoft Lens software (and exported
if needed) or imported from an external source.
In the examples presented in this chapter, Agisoft PhotoScan Pro photogrammetry
software was used to conduct the image processing. Agisoft PhotoScan is capable of
interpolating digital images in order to create high-resolution, scaled, and geo-refer-
enced 3D models from them. All clear images with sufcient overlap were included
in the processing in order to generate a dense point cloud of the church. Ground con-
trol points (GCP) were applied to correct the scale and geo-reference the model. To
complete the geo-referencing task, the program requires either Global Positioning
System (GPS) coordinates associated with cameras, provided in an EXIF/plain text
le, or GCP coordinates that can be used to achieve higher accuracy (up to 1cm).
Based on the latest multi-view 3D reconstruction technology, the software operates
with arbitrary images and is efcient in both controlled and uncontrolled conditions
(Remondino etal. 2011). Photos can be taken from any position, providing that
the object to be reconstructed is visible on at least two photos with sufcient overlay.
Both image alignment and 3D model reconstruction are fully automated.
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Building Information Modeling
After the 3D model generation, the point cloud model is converted to the .rcp indexed
format and imported into Autodesk Revit software to generate a Building Information
Model (BIM). BIM is an intelligent 3D model-based process that involves the genera-
tion and management of digital representations of physical and functional character-
istics of places. It can also be dened as a BIM virtual information model. BIM design
tools allow extraction of different views from a building model for drawing produc-
tion and other uses. After the BIM model is constructed, drawings of the plans,
elevations, and sections of the church can be generated directly from the BIM model
for documentation purposes. Also, information such as material, color, height,
thickness, etc. can be added to each component in the BIM database.
Case Studies
The below case studies feature a variety of examples of how UAVs were used in
order to acquire aerial images and document different types of cultural heritage and
archaeological sites. Different UAVs were utilized based on the survey area. Gliders
were used for surveying an extensive area, whereas drones were used for smaller
areas and structures. As previously mentioned, the methodology used was the same
in all case studies. First, GCPs were established at each site and the high-resolution
aerial images were acquired using UAVs with different sensors. Second, once the
aerial imagery was obtained using the UAV, the images were processed using SfM
software to create a 3D model and then produce an ortho-image and digital eleva-
tion model. In some of the structures, the 3D model was imported into BIM in order
to produce drawings, oor plans, and elevations.
Curium Case Study
The study took place in the southwest of Cyprus, in the archaeological site of Curium,
which is situated outside the modern city of Limassol, Cyprus. Curium is considered
one of the most signicant archaeological sites on the island. Although the Kingdom
of Curium was established in the Cypro-Geometric period (1050–750 BC), the
majority of the archaeological remains within the Curium archaeological area date to
the Roman and Late Roman/Early Byzantine periods. The area is particularly noted
for its magnicent Greco-Roman theater, which was initially constructed in the late
second century BC, until being abandoned in the later fourth century AD, most likely
following successive earthquakes in the area.
In the Curium study, the QuestUAV Q-Pod Surveyor was used (Themistocleous
etal. 2014a) in order to cover the entire site with a 20MP high-resolution camera.
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Quest UAV Q-Pods are small unmanned airborne vehicle (UAV) capable of carrying
a payload in ight and ying a pre-programmed route that is created in its ight
planning software. All the necessary ight permissions were acquired from the
Cyprus Aviation Authority (CAA) and the Sovereign Bases Area Administration
(SBAA). The selected UAV was own at a low altitude of 125 meters to provide
high- resolution data for survey. Single images were taken automatically with a 60%
overlap in an x and y direction in order to build a large detailed ortho-image and
create a 3D model for accurate survey work (Themistocleous et al. 2015b). A
20minute ight was needed to survey a 1 square km area with a 3cm resolution.
The UAV included a GPS unit that geo-tagged all the aerial images with the latitude
and longitude within the metadata le of every image (Themistocleous etal. 2014a).
Fixed ground control points distributed throughout the site were used in order to
geo-reference the image with an accuracy up to 2cm. The result was a high-resolu-
tion ortho-rectied image of the Curium site, which included the ancient hill,
amphitheater, and all the monuments (Figs.5 and 6).
The aerial images were processed in Agisoft Photoscan in order to create a 3D
textured model of the amphitheater, as well as a digital terrain model (DTM)
(Themistocleous etal. 2014a) (Figs. 7 and 8). The survey of the Curium site was
conducted in order to document the entire site and examine the capabilities of the
SfM technique in large archaeological sites, such as the Curium site area.
The process used in this case study is very useful in documenting large archaeo-
landscapes as satellite imagery cannot provide the resolution that is available with
UAV images. Ortho- images that are produced by UAV using photogrammetric meth-
ods are more accurate when used with GCPs and can provide more information since
the resolution is very high, especially with cameras exceeding 20MP resolution. The
capabilities of the state-of-the-art drones, UAVs, and multi-copters provide stable
Fig. 5 Ortho-image of the ancient Curium archaeological site
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aerial images using mechanisms to stabilize the camera, which are known as gimbles,
thereby providing sharp and clear images that are geo-referenced due to the internal
GPS of the UAV.This assists in the photogrammetry and modeling process, since the
images are providing enough geo-referenced information in order to create an accu-
rate and geometrically correct geo-referenced model.
Fig. 6 Orthomosaic and reconstructed DTM of the ancient Curium archaeological site
Fig. 7 3D textured model of Curium in Agisoft PhotoScan Professional
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The DTM of the amphitheater of the Curium archaeological site was used to
print a 3D model (Fig.9). The model was printed by “CUTing Edge” of Cyprus
University of Technology, and it is now exhibited in the local museum of Curium.
The model serves both for educational reasons as well as for visually impaired
people (Themistocleous etal. 2016a).
Nea Paphos Mosaics andArchaeological Park Case Study
Nea Paphos was established at the end of the fourth century BC and was the capital
city of Cyprus during the Roman period. The Nea Paphos archaeological park is a
vast archaeological area, with remains of villas, palaces, theaters, fortresses, and
tombs and is also a UNESCO World Heritage Site. Among the most signicant
remains discovered to date are four large and elaborate Roman villas (the House of
Dionysos, the House of Aion, the House of Theseus, and the House of Orpheus), all
with superb preserved mosaic oors. These mosaics constitute an illuminated album
of ancient Greek mythology, with representations of Greek gods, goddesses, and
heroes, as well as activities of everyday life. The mosaics of Nea Paphos are
Fig. 8 DTM from Agisoft PhotoScan Professional
Fig. 9 3D model and 3D printed model of Curium amphitheater
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extremely rare and are considered among the nest specimens in the world; they
cover the Hellenistic period to the Byzantine period (UNESCO 2017).
Due to the size of the site, different UAVs were used to document archaeological
sites in Nea Paphos, Cyprus (Themistocleous etal. 2014c, 2015a, b). Aerial images
were taken with different UAV systems, including gliders and multi-rotors in order
to survey the site. Archaeologists estimate that only 10% of Nea Paphos has been
excavated. Therefore, researchers have been unable to reconstruct what Nea Paphos
must have looked like at the time of its creation. Therefore, UAV surveys are impor-
tant in assisting archaeologists and cultural heritage experts to manage the site and
monitor environmental changes from erosion and pollution, since the site is located
next to the sea and the modern city of Paphos.
In order to survey the entire site, 350 images were taken, and 56 GCPs were
distributed over the site, generating a 3cm per pixel resolution ortho-image and
13 cm per pixel DEM (Fig. 10). Contour lines were created to determine the
topography of the area. Due to the high-resolution images derived from the UAVs,
compared with satellite images, many crop marks are visible, which suggests
possible underground archaeological features.
In order to document the famous mosaics in the archaeological park, multi- copters
with a 20 MP high-resolution camera were own at a low altitude of 50 meters and
80% overlap in both directions (forward and side overlap). This provided the ability
to capture a higher-resolution model of 1cm per pixel and create a more accurate
3D model of the site (Fig.11).
Fig. 10 Left: Ortho-image of Nea Paphos using a glider. Right: DEM with contour lines created
from the 3D model
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As a result, the images and the model generated from the high resolution images
are extremely detailed to the point where the individual mosaics can be seen, as
shown in Fig.12.
Using all the images and GCPs acquired from the UAVs, a geo-referenced model
and ortho-image were produced using the methodology described in this chapter
and as shown in Fig.13.
The geo-referenced ortho-images generated in this site will be compared with
other images of the same study area at different times in order to identify any envi-
ronmental changes in order for the relevant authorities to take the necessary actions
to protect the site from further damage.
Fig. 11 Left: Ortho-image of the House of Aion, the House of Theseus, and the House of Orpheus.
Right: DEM of the House of Aion, the House of Theseus, and the House of Orpheus created from
the 3D model
Fig. 12 Left—Aerial photograph of the archaeological park in Paphos, Cyprus. Center—Aerial
photograph of the mosaic oor. Right—Aerial photograph of the mosaic corridor
Fig. 13 3D model of archaeological park in Paphos using SfM
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Fabrica Hill Case Study
Fabrica Hill is situated near Saint Paul’s Pillar and the Ancient Theater Ruins in the
city of Paphos. The Fabrica Hill most likely dates back to Hellenistic times and was
used during Byzantine times as a quarry and storage area. The hill was named
Fabrica because a textile mill existed at the site during the Middle Ages. The site
includes some minor ancient mosaics that have been partially restores, as well as
several ancient quarry caves from the Hellenistic period. The numerous under-
ground caves are of sizeable proportions, and their coated walls may have been
painted. The presence of these features makes Fabrica a very complex system and a
challenging case study for accurate documentation (Themistocleous etal. 2014b).
During the preparation for the “Paphos 2017- European Capital of Culture,” the
Municipality of Paphos requested that the site be documented in order to redesign
the site and make it more accessible to tourists.
An aerial surveying of Fabrica Hill was conducted using a quadcopter equipped
with a GoPro Hero 3 Camera (Themistocleous etal. 2014b, 2015b). In addition, the
Leica laser scanner was used to support the UAV survey by providing an internal 3D
model of the area. All images acquired by the copter were processed through the use
of Agisoft Photoscan Profession software, while the point cloud data were pro-
cessed in the Cyclone environment. Over 300 high-resolution images were taken
above the Fabrica Hill and were post-processed using Agisoft Photoscan Professional
software. The immediate outcome of the post-processing was the orthomosaic pro-
duction deriving from the merging and layering of these multiple images (Fig.14).
The ortho-image was further exploited in order to produce the digital terrain model
(DTM) of the area in order to generate a contour map. Further to the orthomosaic of
the area, relative 3D models have been also retrieved. The most impressive models
were those of the ancient amphitheater (Fig.15).
All the 3D models and ortho-images were provided to the municipality and the
architects in order to prepare a proposed plan for renovation of the area.
Asinou Church Case Study
The study area is the church of Panagia Phorbiotissa, better known as Asinou
Church, which is located in the north foothills of the Troodos Mountains of Cyprus,
which is a UNESCO World Heritage Site (Themistocleous et al. 2015c). A quad-
copter with an added gimble, telemetry, and GoPro HERO3+ camera was used to
acquire the aerial images of the church in order to create a 3D model. The small
quadcopter was used due to its maneuverability, which was needed to take images
above and around the church (Fig.16).
The copter was own in manual mode to ensure that all the images necessary
for image processing are taken and to avoid any obstacles around the church,
especially trees. During the ight, two operators were required for the aerial survey;
one operator controlled the ight path of the UAV, while the other operator
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monitored the UAV telemetry data. The telemetry information was transmitted to
the operator on a monitor in order to verify the position, distance, height, and bat-
tery life of the quadcopter. This was necessary to guarantee the overlap and correct
position of each image.
Fig. 14 Ortho-image of Fabrica Hills
Fig. 15 3D section of the amphitheater located at Fabrica Hill
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Over 1000 images were taken at Asinou Church, which were post-processed by
removing the lens distortion and then processed using the Agisoft Photoscan
Professional software. Since the GoPro HERO3+ camera used a wide-angle lens,
lens distortion removal was required by calibrating the camera and removing the
distortion using the appropriate distortion lter (Themistocleous et al. 2015c).
Agisoft PhotoScan was used to conduct the image processing, thereby generating
high-resolution geo-referenced orthomosaic, detailed DTMs, and textured polygo-
nal models through the use of image overlay. Due to the manual ight parameters
and low speed of the copter around the structure, the rolling shutter issue usually
associated with the GoPro cameras were not an issue.
The processing began with the orthomosaic production from these multiple
images, which was used for the 3D model (Fig.17). Following the orthomosaic
production, a high-resolution 3D mesh model of the church was generated and
exported to a surface model (Themistocleous etal. 2015c). The surface model was
imported into Autodesk 3DS Max in order to clean up, x, and optimize the mesh.
Any unnecessary noise or busy surroundings were cleaned up, and large mesh
issues, such as particles, holes, spikes and tunnels, were xed. The mesh was then
Fig. 16 Quadcopter with GoPro HERO3+ camera during ight
Fig. 17 Left, photographic image church; center, 3D model; right, 3D printed model
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prepared for printing by exporting the corrected model into a .stl le, where a 3D
printer was used to generate a 3D model. The model was printed using a Makerbot
Replicator 3D printer with PLA lament and layer resolution of 100 microns, which
provided an accurate representation of the church.
Foinikaria Church Case Study
The study focused on the Church of Panagia Chryseleousa in Foinikaria village,
which is located in the Limassol District of Cyprus. The survey was done in coop-
eration with the Holy Bishopric of Lemesos in an effort to document the church in
a short amount of time. In the study, the hexacopter with attached GoPro HERO+
12MP camera was used to take aerial images of the church (Themistocleous etal.
2016b) (Fig.18). The hexacopter was used due to its maneuverability to take images
above and around the church. A gimble was added to the camera to provide high-
precision three-axis camera stabilization system that allows for smooth aerial pho-
tography. The integrated GPS included position holding, altitude lock, and stable
hovering to provide constant stability in ight. The ying altitude was relatively low
at 10 meters in order to produce higher-resolution images. The copter was own in
manual mode to ensure that all the images necessary for image processing are taken
and to avoid any obstacles around the church, especially trees. During the ight, two
operators were required for the aerial survey; one operator controlled the ight
path of the UAV, while the other operator monitored the UAV telemetry data.
The telemetry information was transmitted to the operator on a monitor in order to
verify the position, distance, height, and battery life of the hexacopter.
Fig. 18 Foinikaria church, with UAV yover and ground control point (GCP)
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Over 1000 images were taken at the Foinikaria Church, which were post-
processed by removing the lens distortion and then processed using the Agisoft
Photoscan Professional software. The processing began with the orthomosaic pro-
duction from these multiple images, which was used for the 3D model. Following
the orthomosaic production, the model was exported from Agisoft into SketchFab
for visualization purposes. The study found that particular areas were not well docu-
mented on the 3D model, due to an insufcient number of images in specic loca-
tions, such as the bell tower. This is evident below, where the bell tower is not
clearly modeled.
Autodesk Revit software was used to generate a BIM 3D model of the church,
including the bell tower (Fig.19). The BIM model was overlaid with the point cloud
(Themistocleous etal. 2016b).
The point cloud provided enough information so the structure of the building can
be accurately modeled without the need of any in situ measurements. The point
cloud information was especially necessary to model the roof, bell tower, arches,
and openings. This provided a fast and accurate method for documenting the church.
As well, the point cloud was able to capture the rough surface texture resulting of
weathering (Fig.20).
Sections of the 3D model overlaid with the point cloud. This provides detailed
information regarding the exterior walls of the church and the structure of the
narthex (Fig.21).
Using the Revit software, drawings including oor plans, elevations, and sec-
tions of the church were generated (Fig. 22). A database was created to include
information regarding the structure, including wall height, thickness, material, etc.
This provided a valuable source of documentation of the church, for future restora-
tion and maintenance works. Also, the documentation of the site was important to
study possible expansion projects.
The elevations are also overlaid with the point cloud to provide additional infor-
mation on the building, such as surface texture, color, and materials (Fig.23).
Fig. 19 BIM model of the church
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Fig. 20 Left, 3D model of church; right, 3D point cloud model integrated with BIM model
Fig. 21 Point cloud
section with BIM model
Fig. 22 Drawings of the Foinikaria church generated from BIM
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Choirokoitia Case Study
The Neolithic settlement of Choirokoitia is one of the most important prehistoric
sites in the Eastern Mediterranean (UNESCO 2016). Included in the UNESCO
World Cultural Heritage list since 1988, Choirokoitia is one of the best preserved
Neolithic settlements in Cyprus and the Eastern Mediterranean. Occupied from
the seventh to the fth millennium BC, the site was ofcially abandoned in the
fourth millennium BC for unknown reasons (UNESCO). Under the PROTHEGO
project, which monitors and documents UNESCO cultural heritage sites vulner-
able to geo-hazards, several UAV surveys have been done of the archaeological
site of Choirokoitia, near Limassol Cyprus. Choirokoitia is a UNESCO World
Heritage site that is vulnerable to ground deformations; therefore, UAVs were
used to document the site (Themistocleous etal. 2016c). Surveying techniques,
such as total station, leveling, and Global Navigation Satellite Systems (GNSS),
were used to measure the positional changes of any point on the surface at millime-
ter level accuracy. In order to document the Choirokoitia sites, UAV images were
used to create ortho-photos, dense clouds, 3D model, and digital elevation models
(Themistocleous etal. 2017). Different multi- copter UAVs with a high-resolution
20MP camera were used to acquire images over the site with xed ground control
points for geo-referencing in order to produce a photogrammetric ortho-image
Fig. 23 Drawings of plans and elevations extracted from the BIM model
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and point cloud 3D model of the demonstration site and also for comparison over
temporal intervals (Fig.24).
Aerial images were taken using UAVs on 29 October 2016 and 2 February 2017.
Over 450 images were taken of the Choirokoitia site on 29 October 2016, and over
460 images were taken on 2 February 2017. Ground control points (GCP) were
applied to correct the scale and geo-reference the model. The images were then pre-
processed by removing the lens distortion and then processed using the Agisoft
Photoscan Professional software (Fig.25). The aerial imagery obtained from the
UAVs was imported into SfM software to create rapid and automated generation of
a point cloud model and 3D mesh model in order to document and monitor the
Choirokoitia site for geo-hazards (Themistocleous etal. 2017).
All clear images with sufcient overlap were included in the processing in order
to generate a dense point cloud of the Choirokoitia site. The images taken on 2
February 2017 were able to cover more of the mountain; therefore, the Choirokoitia
site is outlined for clarication. In Fig.26 and 27, the image on the left is from the
Fig. 24 Inspire 2 UAV with 20mp Zenmuse X5S camera and sensors
Fig. 25 Ortho-image of Choirokoitia site 29 October 2016
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survey conducted on 29 October 2016, where the image on the right outlined in red
is from the survey conducted on 2 February 2017.
As is evident, there was a dramatic difference in the level of vegetation present at
the site on the dates that the images were acquired. The October 2016 images show
sparse vegetation, while the images acquired in February 2017 show signicantly
more vegetation present at the site. As it was easier to identify vegetation in the
images acquired in the winter campaign due to the color and morphology of the
vegetation, masking was done in order to subtract the vegetation from the model in
order to generate the DEM of the ground surface (Fig.28). This was done by using
interpolation of the areas where the vegetation was previously present. A contour
Fig. 26 Point cloud generation of Choirokoitia site
Fig. 27 3D surface model of Choirokoitia site
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map of the area was then generated using stitch imaging using the DEM model
without vegetation (Fig.29).
The generated DEM model can assist in creating a simulation model to deter-
mine the rockfall patterns in the area (Fig.30). In these types of simulations, it is
important that vegetation be removed from the model in order to be more accurate
using only the geological features of the landscape.
The ground-based geotechnical monitoring was also compared and validated
with InSAR data to evaluate cultural heritage sites deformation trends and to under-
stand its behavior over the last two decades.
Fig. 28 Vegetation subtraction and contour generation
Fig. 29 Stitch imaging and ortho-generation
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Amathus Necropolis Case Study
The ancient town of Amathus is situated on the south coast of Cyprus, about 7km
east of the town of Lemesos and dates to the Neolithic period. East and west of
Amathus are two important necropolis with carved tombs which date from the
Geometric to the Roman period. During the excavations of the tombs, rich archaeo-
logical material came to light, part of which is now exhibited in the Lemesos District
Museum. The Department of Antiquities also focuses on the management, preserva-
tion and promotion of the archaeological site of Amathus, through the application of
concrete strategies focused on securing its sustainability and development.
In cooperation with the Department of Antiquities, high-resolution digital cam-
eras with VNIR sensors were used to document burial mounds in the Amathus
archaeological site at varying elevations. The UAV survey was conducted as con-
struction was scheduled to begin in the area; therefore, quick documentation of the
archaeological site was necessary while the site was being excavated (Fig. 31).
Since there was ongoing development in the area, the site was backlled at the
end of the archaeological excavation as a method of preservation and conservation.
This example shows how UAVs can be important in documenting archaeological
sites when documentation needs to be done in a limited time for a large area.
The aerial images in Fig.32 were taken within a 1 month period, showing the
excavations that took place on the site. Below, the image on the left shows the area
at the beginning of the excavation, where the image on the right shows the area a
month later, where different tombs were excavated.
At the site, there were various archaeological ndings that were documented
using the UAV while the site was being excavated. For example, the below image
shows the documentation of a tomb that was located on the site. The UAV was able
to enter into the burial chamber and document the entire structure. A 3D model was
Fig. 30 Digital elevation model of Choirokoitia site
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Fig. 31 Ortho-image of the overall excavation site in Amathus, including detail of burial site
Fig. 32 Top, beginning of excavation; bottom, 1 month after the beginning of the excavation
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created to show the capability of the UAV to provide detailed documentation of an
archaeological dig, as shown in Fig.33.
UAVs can be a valuable tool to document archaeological sites, especially when
time is limited and high-resolution documentation is needed.
Conclusion
UAVs have become an extremely important tool for cultural heritage experts for the
documentation and analysis of cultural heritage sites as they provide a cost-effective
and efcient manner to acquire high spatial resolution data with high temporal fre-
quencies, especially in areas that have limited coverage and are inaccessible to
humans. The case studies presented in this chapter highlighted the ability of UAVs
to provide high-resolution data of a cultural heritage site using a non-invasive tech-
nology and high accuracy with the use of ground control points.
The case studies examined various cultural heritage sites in Cyprus, where the
high-resolution aerial imagery obtained from the UAVs was imported into Structure
from Motion photogrammetry to create rapid and automated generation of a point
cloud model and 3D mesh model. The high accuracy of the ortho-image and 3D
model can be used to document and monitor changes of the cultural heritage sites
over time. A printed 3D model can also be made of the structure. Also, the point
cloud generated can be exported into BIM, in order to produce a BIM model and
drawings of the structure. The high-accuracy documentation generated from the
BIM model can be used for future renovation or expansion of the site.
Acknowledgment We would like to thank the ERATOSTHENES Research Centre and its staff
for their invaluable assistance. Special thanks to the Department of Antiquities of Cyprus, the
Cyprus Remote Sensing Society, the Cyprus Research Promotion Foundation, the Holy Bishopric
Fig. 33 3D model of burial chamber at Amathus necropolis
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of Lemesos, QuestUAV, and the Southwestern Baptist Theological Seminary. Also, the author
wishes to acknowledge the Cyprus Aviation Authority (CAA) and the Sovereign Bases Area
Administration (SBAA) for their assistance in providing ight permission. Finally, additional
thanks to the “ATHENA” project H2020-TWINN2015 of the European Commission, No. 691936,
the “PROTection of European Cultural HEritage from GeO - hazards (PROTHEGO)” project
JPICH HERITAGE PLUS/0314/36 and the Cultural Landscape risk Identication, Management
and Assessment (CLIMA) project, JPICH HERITAGE PLUS/0314/07.
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