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Terrestrial laser scanning technology is nowadays more and more used for the documentation of cultural heritage monuments. The thorough exploitation of the main advantage of terrestrial laser scanners (TLS) that is the acquisition of extremely dense discrete points in a relatively small time period leads to detailed 3D representation of the monument, overcoming possible difficulties such as limited accessibility. Most often, this 3D representation is used for the monument's documentation as well as for virtual tours in, out or around it. This detailed documentation can be used for one more purpose: the estimation of the deformation that its elements have experienced through the centuries and, following, the monument's restoration, provided that, its' initial, constructional geometry is known. In this paper, research towards this goal is presented, dealing with the estimation of the deformations of a column of the ancient temple of Zeus in Nemea Greece using TLS technology. This column is standing erect since the temple's construction in 330 BC and it has been subject to serious deformations because of various causes.
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Survey Review
ISSN: 0039-6265 (Print) 1752-2706 (Online) Journal homepage:
The contribution of laser scanning technology
in the estimation of ancient Greek monuments'
G. D. Georgopoulos, E. C. Telioni & A. Tsontzou
To cite this article: G. D. Georgopoulos, E. C. Telioni & A. Tsontzou (2016): The contribution
of laser scanning technology in the estimation of ancient Greek monuments' deformations,
Survey Review
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The contribution of laser scanning technology
in the estimation of ancient Greek monuments’
G. D. Georgopoulos
, E. C. Telioni*
and A. Tsontzou
Terrestrial laser scanning technology is nowadays more and more used for the documentation of
cultural heritage monuments. The thorough exploitation of the main advantage of terrestrial laser
scanners (TLS) that is the acquisition of extremely dense discrete points in a relatively small time
period leads to detailed 3D representation of the monument, overcoming possible difficulties
such as limited accessibility. Most often, this 3D representation is used for the monument’s
documentation as well as for virtual tours in, out or around it. This detailed documentation can be
used for one more purpose: the estimation of the deformation that its elements have experienced
through the centuries and, following, the monument’s restoration, provided that, its’ initial,
constructional geometry is known. In this paper, research towards this goal is presented, dealing
with the estimation of the deformations of a column of the ancient temple of Zeus in Nemea Greece
using TLS technology. This column is standing erect since the temple’s construction in 330 BC
and it has been subject to serious deformations because of various causes.
Keywords: Cultural heritage monuments, Ancient Greek monuments, Laser scanning technology, Estimation of deformations, Geodetic methodology
In recent years, an increasing interest on the application
of terrestrial laser scanners (TLS) in deformation
estimation is observed (Alba et al., 2006; Kersten et al.,
2009; Roberts and Hirst, 2005). This interest arrises
from the advantages of TLS that can be summarised to
the direct 3D coordinates estimation of a dense points
set on the object monitored, the high degree of
automation, the user-friendly software that accompanies
the hardware and the creation of the examined object’s
model (Monserat et al., 2007). An important and very
interesting part of deformation monitoring using TLS is
that concerning cultural heritage monuments
(Castagnietti et al., 2012; Pesci et al., 2011; Teza and
Pesci, 2013; Pieraccini et al., 2014). This monitoring
deals not only with ‘current time’ deformations because
of various causes (seismic hazard, underground works,
etc.) but also with the deformations the parts of the
monument have undergone through the centuries: this is
of crucial importance when planning interventions con-
cerning restoration of the monument.
The possibility of obtaining a large amount of object
points is considered as an extremely important advan-
tage of laser scanners compared to classic geodetic
methodology. In the later case, the estimation of the
object’s deformation is achieved through the
establishment of a geodetic control network and the
monitoring of discrete control points on the monument
under consideration. On the contrary, when TLS
technology is applied, the object’s deformations are
determined after the creation of a 3D model from the
points cloud either through an appropriate software or
through the estimation of a surface that fits best, using
least squares techniques (Gruen and Akca, 2005;
Pesci et al., 2011; Teza and Pesci, 2013). From this
modelled surface, all the information, concerning the
way the monument’s elements have deformed, is derived.
This is achieved through the comparison of the modelled
surface with the initially constructed one. The high
redundancy of points ameliorates the accuracy in
deformation estimation, provided that the appropriate
methodology is applied, in order to estimate statistically
significant small scale deformations. The later is
extremely important in cases of restoration of cultural
heritage monuments where high accuracy is crucial for
correct interventions. This fact holds especially for the
restoration of monuments of the Greek Antiquity
(temples, theatres, etc.), since it is known that they were
constructed on the basis of strict plans, demanding high
accuracy in construction, and therefore, the same accu-
racy must be achieved during the restoration project.
The purpose of this paper is to present an approach
on the estimation of ancient Greek monuments’ defor-
mations that takes advantage of laser scanner technol-
ogy but is based on the principles of classic geodetic
methodology. This approach is applied and presented
here for the estimation of the deformations of a
column of the ancient temple of Zeus in Nemea, Greece,
that is standing erect since the temple’s construction.
School of Rural and Surveying Engineering, National Technical
University, 9, H. Polytechneiou Str., Zografou, Athens 157 80, Greece
18, Ioannou Theodorou Str., Koropi, Athens 19400, Greece
*Corresponding author, email
Ñ2016 Survey Review Ltd
Received 08 December 2014; accepted 04 May 2015
DOI 10.1179/1752270615Y.0000000035 Survey Review 2016 1
Downloaded by [National Technial University of Athens], [Doctor E. C. Telioni] at 01:03 01 March 2016
The proposed methodology
In the majority of cases, deformations in ancient Greek
monuments are determined from direct measurements.
These measurements are of high metric accuracy but are
time consuming, may demand special construction
(scaffold) for the measurements, and, what is more
important, cannot be related to each other.
In the cases where classic geodetic methodology is
used, the deformations are estimated using a geodetic
control network. This network consists of reference
points, established in stable areas in the vicinity of the
monument, and control points, established in carefully
selected positions on the monument itself. The elements
of the network are measured and adjusted using least
squares and the coordinates of the network’s points are
estimated in a local or global reference frame.
On the contrary, when using TLS technology,
the monument’s deformations are estimated from the
entire modelled object rather than from discrete points
of the cloud, which are difficult to be identified and
isolated. The points of a local geodetic network, esta-
blished, measured and adjusted for this reason in the
area of the monument, are used as scan positions.
In order to ensure the accurate registration of successive
scans as well as the high accuracy of the geo-referenced
point clouds, special (planar or spherical) targets are
positioned at the network’s points. Finally, the extracted
deformations are referred to the same reference frame of
the network and can be associated and compared
to each other, so that a complete and detailed ‘picture’ of
the deformed monument is derived.
As far as the scanning resolution is concerned, it is
proposed to perform the scans with maximum sampling
provided by the scanner. Before any operation, it is
necessary to calibrate both its hardware and software,
in order to ensure the proper operation of the scanner.
The procedure of the monument’s modelling requires
the creation of a surface best-fitting to the points cloud.
The creation and elaboration of the optimum surface are
a complex process, mainly because of the fact that it is
non-parametric and the primary data are often quite
noisy. The basic steps of the creation of the surface
- The data pre-processing for noise reduction and
deletion of those points that do not belong to the
- The specification of the object’s features that should be
maintained during the modelling (e.g. edges or break
lines). For example, when modelling the surface of an
ancient temple’s column, the break lines, indicating the
parts of the column (drums, capital, etc.) must be
- The creation of triangular or tetrahedral meshes and
the generation of the surface. The generated surface
can also be mathematical (parametric) if the geometry
of the object is simple. The majority of the used
software performs the technique of triangulation,
where a set of points is changed to a polygonal mesh.
Further refinement of the generated surface, such as
hole filling and smoothening, is usually required.
- Right after the surface generation, specifically selected
point sets are extracted. These points belong to planes,
lines, curves, etc. that describe the object’s current
geometry. From these extracted point sets, the best-
fitting plane or line is determined, using least squares
techniques, and is compared to the initial,
constructional one in order to estimate statistically
significant deformations of the monument’s elements.
It is very important to have a good knowledge of the
monument’s initial, constructional geometry for the
correct interpretation of the results. For example,
when dealing with the estimation of ancient temples’
deformations, one must keep in mind that the main
lines expressing the monument’s geometry are
either curved or inclined with rates in correlation to
each other.
Deformation estimation of a column of
the ancient temple of Zeus in Nemea,
The proposed methodology was applied for the
estimation of the deformations of a column of the
ancient temple of Zeus in Nemea. The temple, of Doric
order, was constructed in 330 BC. It was an important
Greek sanctuary and was the centre of the Panhellenic
Nemean Games. The temple had an exterior colonnade
(called peristyle) with six columns on the short sides and
12 on the long ones. The systematic demolition of the
temple began between 600 and 700 AD, in order to use
its elements for the construction of a church situated
about 100 m south of the temple. The external Doric
columns were knocked down and about 1300 parts of
the temple were removed. Only three of the 36 Doric
columns remained in place, one of which is the column
under consideration. The parts of the temple remaining
in place (the stepped base and the three Doric columns)
show significant displacements because of human
destruction (mostly in the early Christian period) as well
as because of settlements, since the foundation of the
temple is not on solid mass. The restoration works on
the temple of Zeus began in 1984. Up till now, two
restoration programmes have been completed, during
which, part of the temple’s stepped base (the crepis) and
six of the peristyle columns those of the northeastern
corner were completely restored (summer 2013).
The column under consideration is the only one of the
peristyle columns, that stands erect since the temple’s
construction (Fig. 1). It is standing next to the lately
restored columns at the eastern side of the temple.
The column has a total height of 9.726 m (without the
capital), and consists of 13 superimposed parts (drums)
that have a mean height of 0.75 m. Each drum has
20 carved shafts ( flutes) and was connected to the
adjacent drums through a wooden dowel. The drums’
diameters reduce gradually from 1.522 m (lower face of
first drum) to 1.237 m (upper face of thirteenth drum).
A typical cross-section of a drum is depicted in Fig. 3.
Significant displacements and rotations between the
column’s drums are visible. In order to plan restoration
interventions, it was decided to estimate the column’s
deformations using TLS technology.
Data acquisition modelled surface
A geodetic control network was already established at
the temple’s surroundings, as well as on its body, for the
needs of the two restoration programmes mentioned
above (Georgopoulos and Telioni, 2005). Three new
points were established for the scanning purposes.
The network’s elements were measured and adjusted,
Georgopoulos et al. Contribution of laser scanning technology
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and the point’s coordinates in a local reference system
were estimated with an accuracy of few millimetres
(Tsontzou, 2014).
Terrestrial laser scanner ScanStation2 of Leica Geo-
systems was used for the column’s scanning. For the
referencing and registration of the points clouds, HDS
sphere targets were used. The instrument has, according
to the manufacturers, an accuracy of +4 mm in distance
measurement, an angular accuracy of +60 mrad (120),
while the accuracy in point positioning is +6 mm. Taking
into account the above mentioned accuracies, as well as
the error because of the beam’s diameter, the centring and
levelling errors of the scanner and targets (Lichti and
Gordon, 2004), the horizontal and vertical accuracy of
direct geo-referencing was estimated to be +5 mm.
Four of the network’s points were used for the
scanning. The Cyclone software was used for the
definition of the scan parameters and the processing of
the field data. The scanning resolution was set to 2 mm.
When each scan was completed, the point cloud was
georeferenced directly to the local reference frame of the
network. The geo-referencing errors were small, up to
4 mm. The whole procedure was completed in a 5-h
interval. The modelled surface of the column is depicted
in Fig. 2 (Tsontzou, 2014).
Estimation of deformations
After the creation of the column’s modelled surface
(Fig. 2), the 13 drums of the column were isolated
from each other. For each drum, three horizontal cross-
sections were created: at the upper and lower face of the
drum and one at the middle, 39 sections as a whole. The
exact position of each section depended on the existing
damages of the drum. These 39 sections were extracted
in Cad environment and converted into point sets.
In Fig. 3, the modelled surface of a drum is depicted,
together with the result of the extracted middle section in
Cad environment and the corresponding point set.
For each point set, after it was extracted in Cad
environment, the coordinates of the inner points of the
flutes were determined. These points (one for each flute,
20 as a whole) lie on the circumference of the circle
escribed in the section (Fig. 3). The circle’s components
(centre’s coordinates and radius) were estimated using
the following equation (1)
: the coordinates of the escribed circle’s
: the coordinates of the inner point of i flute
(i¼1,..., 20)
R: the escribed circle’s radius
Thus, 20 observation equations were formulated for
each section. After the adjustment, the coordinates
) of the circle’s centre, as well as its radius R, were
estimated. Their standard deviations ranged between
¡0.1 mm and ¡1.3 mm.
In order to check the precision achieved, the diameters,
corresponding to the section at the lower face of each of the
1 Column K31 of the temple of Zeus in Nemea
2 Modelled surface of the column
Georgopoulos et al. Contribution of laser scanning technology
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13 drums, were compared to the direct measurements,
made with a mechanical calliper that had an accuracy of
¡0.1 mm (Zambas, 2000). The diameters were, also,
compared to the corresponding ones of the adjacent
column that, as it has been mentioned above, was restored
recently. In both cases, differences did not exceed 2 mm.
The constructional, initial positions of the centres of
the columns’ bases (lower face of the first drum) are
determined from previous surveys of the temple, for the
restoration projects (Georgopoulos and Telioni, 2005).
They belong to a straight line, parallel, at a distance of
0.900 m, to the upper step (the stylobate) of the temple’s
base. The distance between the centres is constant
(3.745 m), with the exception of the four corner
columns, where the distance is about 0.20 m smaller.
Thus, the initial, constructional position of the column
monitored is known. It was realised, however, from the
estimated coordinates of the centre of the column’s
base that the column has moved, as a rigid body,
from its initial, constructional position 0.066 m with a
south-western direction.
As it has been mentioned above, for the correct
interpretation of the estimated deformations, a good
knowledge of the monument’s constructional geometry
is needed. Thus, when dealing with deformations of
ancient columns, it must be kept in mind that the peristyle
columns were constructed with a given inwards
inclination with respect to the plumb line. This inclination
was imposed, because the surface of the temple’s stepped
base (on which the columns were erected) was constructed
curved, with different transversal and longitudinal
gradients. The inwards inclination of the columns’ axis
has a rate equal to the transverse inclination of the base
and can be estimated from direct measurements on the
columns’ first drum (Zambas, 1998). For the temple of
Nemean Zeus, this inwards inclination, of all the columns’
axes, is estimated (from direct measurements with a
mechanical calliper) 3.5‰ (Zambas, 2000). Therefore, the
initial, constructional positions of the drums can also be
estimated, and compared with the current ones, in order
to estimate correctly the drums’ displacement vectors.
The displacement vectors between every two
successive drums were estimated and their statistical
significance was tested for confidence level 95%. For this
purpose, the centres of each drum’s middle section were
used. Significant displacements ranging up to 21 mm
were detected (Tsontzou, 2014). The displacement
vectors (length d
and direction a
) are depicted in
Table 1 and presented in Fig. 4.
From Fig. 4, it can be seen that, besides the 0.066 m
column’s movement as a rigid body, its eight first drums
show a movement, varying in magnitude, but with the
same north–northwestern direction. For the rest five
drums, the direction of the displacement vectors changes
completely, having a direction towards the south.
In Fig. 4, the initial, constructional position of the
column’s drums centres is also given for comparison
3 Cross-section of a drum and the corresponding point set. The circle described in the section is also presented
Table 1 Displacement vectors between the column’s
successive drums
Drums d
(mm) s
(mm) a
First–second 12 ¡0.6 325
Second–third 4 ¡0.6 367
Third–fourth 4 ¡0.5 354
Fourth–fifth 12 ¡0.7 347
Fifth–sixth 6 ¡0.8 351
Sixth–seventh 6 ¡0.7 346
Seventh–eighth 21 ¡0.6 365
Eighth–ninth 9 ¡0.7 344
Ninth–tenth 3 ¡0.8 267
Tenth–eleventh 8 ¡0.8 201
Eleventh–twelfth 5 ¡0.7 175
Twelfth–thirteenth 5 ¡0.8 173
4 Displacement vectors between the column’s successive
Georgopoulos et al. Contribution of laser scanning technology
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The displacement vectors of all the drums, with
respect to the first one, were also estimated (Table 2) and
are presented in Fig. 5. Displacements ranging up to
7 cm were detected.
Apart from the drums’ linear displacements, the
rotation Qof each drum (with respect to the first one),
and the corresponding arc length on the escribed circle,
were also estimated (Table 3, Fig. 6).
As it can be seen, all the drums show a counter-
clockwise rotation with respect to the first one: the
maximum rotation of 5 g occurs from the eighth up to
the eleventh drum that seem to have rotated as a
rigid body.
The proposed methodology and its application show
that, laser scanning technology can be an indispensable
tool for the estimation of the deformations that their
parts have undergone during the centuries of their life.
The establishment of a high precision geodetic network
and the use of its points as stations for the monument’s
scanning ensures the prerequisite of accurate registration
and geo-referencing of points clouds. In fact,
geo-referencing errors did not exceed +3 mm in the case
study presented in the context of this paper.
The main difference on deformation estimation when
using TLS technology is that one deals with big point
sets rather than discrete points as in classic geodetic
monitoring. To overcome this problem, the approxi-
mation of carefully selected point sets with the appro-
priate line or surface, using least squares techniques, is
proposed in order to determine the structural geometry
of the object examined. In the case examined above, this
led to the estimation of the necessary geometric features
with +1 mm accuracy. It is important to note the good
agreement of these features from the directly measured
ones, the differences been all statistically insignificant.
Table 2 Displacements of the column’s drums with respect
to the first one
Drums d
(mm) a
First–second 12 325
First–third 15 334
First–fourth 18 337
First–fifth 30 341
First–sixth 35 343
First–seventh 41 343
First–eighth 61 351
First–ninth 70 350
First–tenth 71 347
First–eleventh 66 341
First–twelfth 62 338
First–thirteenth 58 336
5 Displacements of the column’s drums as seen from the
southern and eastern side of the temple
Table 3 Rotations of the column’s drums with respect to the
first one
Drums Rotation Q(g) Arc length (mm)
First–second 21.1 13
First–third 20.4 5
First–fourth 20.6 7
First–fifth 21.9 22
First–sixth 21.6 18
First–seventh 22.0 23
First–eighth 24.5 50
First–ninth 24.7 51
First–tenth 25.0 54
First–eleventh 25.0 52
First–twelfth 22.0 21
First–thirteenth 21.8 18
6 Rotations of the column’s drums with respect to the first
one and the corresponding linear movements
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The estimated deformation parameters (displacement
vectors and drums’ rotations) had the same accuracy of
+1 mm. The selection of the appropriate line or surface
for the approximation of the extracted point sets is of
utmost importance, therefore, the cooperation with
architects specialised in restoration is a prerequisite.
Moreover, a good knowledge of the monument’s initial
geometry is needed, for the correct interpretation of the
results of deformation estimation.
It must be pointed out that, since all the points clouds are
referenced to the network’s reference frame, the estimated
deformations are related to each other, thus giving a
complete ‘picture’ of the way the monument has deformed.
This can be used for the estimation of the monument’s
vulnerability and the decision of needed interventions.
Taking into account the small time interval needed for
the points cloud acquisition, when compared to the
amount of information gained, the proposed method-
ology can be applied for a quick, but accurate, check of
the monument’s condition, after a sudden event, such as
an earthquake, has occurred.
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The United Nations aims to preserve, evaluate, and conserve cultural heritage (CH) structures as part of sustainable development. The design life expectancy of many CH structures is slowly approaching its end. It is thus imperative to conduct frequent visual inspections of CH structures following conservation guidelines to ensure their structural integrity. This study implements a custom defect detection, and localization supervised deep learning model based on the you only look once (YOLO) v5 real-time object detection algorithm by implementing a case study of the Dadi-Poti tombs in Hauz Khas Village, New Delhi. The custom YOLOv5 model is trained to automatically detect four defects, namely, discoloration, exposed bricks, cracks, and spalling, and tested on a dataset comprising 10291 images. The validity and performance of the custom YOLOv5 model are compared with a ResNet 101 architecture-based faster region-based convolutional neural network (R CNN), and conventional manual visual inspection methods are used to convey the significance of the developed artificial intelligence-based model. The maximum average precision (mAP) of the custom YOLOv5 model and faster R-CNN is 93.7% and 85.1%, respectively.
... Terrestrial laser scanning has been successfully used by archaeologists and heritage practitioners to document heritage resources throughout the world (Cai et al., 2021;Gardzinska, 2021;Tait et al., 2016;Mills and Andrews, 2014;Dawson et al., 2009Dawson et al., , 2013Van Genechten et al., 2011;Gibb et al., 2011;Entwistle et al., 2009;Al-Khedera et al., 2009). However, few studies have explored the analytical potential of point clouds for detecting changes to heritage sites over long periods of time (Mahasuwanchai et al., 2021;Lercari, 2019;Lerones et al., 2016;Georgopoulos et al., 2015). If documentation is the only objective, then heritage resources are rarely scanned more than once. ...
Purpose Designing and implementing effective strategies for managing heritage resources throughout the world has become critically important as the impacts of climate change and human-caused destruction are increasingly felt. Of particular importance is the ability to identify and track fast- and slow-moving processes associated with weathering, erosion and the movement or removal of heritage objects by natural and human agents. In this paper, the authors demonstrate how 3D laser scanning can be used to detect and monitor changes to the Okotoks Erratic “Big Rock” Provincial Historic Resource in Alberta, Canada, over a period of 7 years. Design/methodology/approach Terrestrial laser scanning surveys of the Okotoks Erratic “Big Rock” Provincial Historic Resource were undertaken in 2013, 2016 and 2020. Registration was used to place the three epochs of point clouds into a unique datum for comparison using the cloud-to-cloud distance function in Cloud Compare. Findings The movement/repositioning of rocks around the base of the erratic, the emergence of “unofficial” paths and changes to interpretive trails and fencing were all identified at the site over the time period of the study. Practical implications Current conservation at the Okotoks Big Rock focus primarily on the rock art panels that are scattered over the erratic. The results of this study indicate they should be broadened so that the geological integrity of the site, which is intrinsically linked to its cultural value, can also be maintained. Originality/value This is the first study the authors are aware of that utilizes terrestrial laser scanning + change detection analysis to identify and track changes to a heritage site over a period as long as 7 years.
... Nowadays, a laser scanning and photogrammetry, as surveying and three-dimensional (3D) modelling techniques, are extremely important for documentation of cultural heritage (Guarnieri et al. 2013). In all the branches of cultural heritage field the 3D survey is an essential support for a number of activities: the object documentation, different kinds of analysis (statistical analysis, historical reconstructions, etc.), the communication and promotion of the sites, deformation estimation, adoption of BIM (Building Information Modelling) etc. (Aicardi et al. 2018, Georgopoulos et al. 2016, Rodríguez-Moreno et al. 2016. Aside from providing a record for future generations, photogrammetry can aid in the more practical quantitative planning of conservation and restoration. ...
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This paper describes the preparation of documentation of a part of the cultural and historical heritage of Bosnia and Herzegovina, the famous chapel on the Orthodox cemetery ‘Holy Archangels George and Gabriel’ located in Saraje�vo, by the method of UAV photogrammetry. Two aircrafts (semi-professional and amateur) DJI Phantom 4 Pro and DJI Mavic Pro were used, and 3D models were made based on the photos taken. The quality of chapel 3D models was evaluated by estimating the geometrical accuracy, with different aspects and combinations. The obtained absolute 3D accuracy of the high-resolution model is 14 mm, while the relative accuracy is 9 mm.
... Both ToF and PS scanners are extensively used for deformation monitoring of historic structures. The geometric deformations are estimated by comparing measured point clouds with an idealized shape [65][66][67][68][69][70][71][72][73] or by performing multitemporal measurements [74][75][76][77]. Furthermore, laser scanning appears to be particularly suitable for obtaining the necessary geometric data to generate numerical models for structural health analysis, in terms of rapidity and spatial resolution [78][79][80][81][82]. ...
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Built cultural heritage is under constant threat due to environmental pressures, anthropogenic damages, and interventions. Understanding the preservation state of monuments and historical structures, and the factors that alter their architectural and structural characteristics through time, is crucial for ensuring their protection. Therefore, inspection and monitoring techniques are essential for heritage preservation, as they enable knowledge about the altering factors that put built cultural heritage at risk, by recording their immediate effects on monuments and historic structures. Nondestructive evaluations with close-range sensing techniques play a crucial role in monitoring. However, data recorded by different sensors are frequently processed separately, which hinders integrated use, visualization, and interpretation. This article’s aim is twofold: i) to present an overview of close-range sensing techniques frequently applied to evaluate built heritage conditions, and ii) to review the progress made regarding the fusion of multi-sensor data recorded by them. Particular emphasis is given to the integration of data from metric surveying and from recording techniques that are traditionally non-metric. The article attempts to shed light on the problems of the individual and integrated use of image-based modeling, laser scanning, thermography, multispectral imaging, ground penetrating radar, and ultrasonic testing, giving heritage practitioners a point of reference for the successful implementation of multidisciplinary approaches for built cultural heritage scientific investigations.
... Actualmente existen muchos tipos de escáneres 3D con diferentes características atendiendo al rango de distancia medida, la tecnología usada o la exactitud conseguida (Georgopoulos et al., 2016). El uso de los escáneres 3D en el estudio y conservación del patrimonio cultural es un hecho ya consolidado con aplicaciones sobre objetos y sitios arqueológicos de diferentes tamaños, características y épocas (Fehér, 2013;Neiß et al., 2016;Rodríguez-Gonzálvez et al., 2015). ...
... Using 3-D model, damaged part and details of the structure were easily detected and geometrically identified. The interesting method of estimation the deformations in heritage structure by TLS was presented in [13]. The column of an ancient Temple in Greece, which was built in 330 B.C., was chosen for the study. ...
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Historical structures, buildings, bridges, and walls are very sensitive to deformations which can be caused by many factors, such as winds, heavy rains, extreme temperature variations, ground and soil settlements, tectonic loadings, and others. The mapping of 3-D deformation maps of building provides an opportunity not only to understand the structural changes, but also to detect zones with a potential risk of damage. The high spatial resolution of terrestrial laser scanning (TLS) technology allows monitoring historical buildings with millimeter accuracy. Two towers of Istanbul Land Walls were surveyed three times with the 5-month time interval. The accurate deviation maps were obtained from TLS’s data by comparing epochs. Between first two campaigns, there happened an earthquake with the magnitude of Mw 5.7 with the epicenter of approximately 60kmfromthe study area. The findings and outputs of this article indicate that earthquake had a great impact on the monitored structures and deformations were found up to 15 mm for the tower I and up to 20 mm for the tower II.
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The Post-2015 UN Development Agenda includes culture and links the preservation of cultural heritage (CH) to sustainable development. In principle, sustainable redevelopment of CH should preserve historical qualities and ensure the financial profitability of the asset. Still, being a construction process, it has to be under constant change monitoring. Bearing in mind the quality of data achieved by measurement systems, TLS instruments can be used to capture 3D spatial data for cultural heritage. The authors analyse the usefulness of TLS data as the spatial database for the redevelopment and functional reuse of a historical granary. Following measurements on various stages of the redevelopment of the CH asset, TLS data undergo principally simple and rapid analyses (shape analysis, determination of the pace and scope of redevelopment, detection of conservation effort results, HBIM) to improve decision-making capabilities within the project. Contrary to the universal approach, periodic CH redevelopment scanning involves the entire structure, not merely its most valuable heritage components. As a result, not only doesthe remote-sensing data acquisition for monitoring of sustainable redevelopment of cultural heritage record the state of the revitalised building, but it also demonstrates the potential of periodic measurements as the primary source of insight into the heritage asset and the directions and quality of changes it undergoes.
There are two main ways of building 3D models of archaeological objects. The first way is to use photogrammetry by means of image-based modelling systems. The second way is the use of 3D scanners. Both methods have advantages and problems. In this work, we propose a simple way to merge both methods to preserve the best of each method and obtain 3D models with high accuracy and excellent resolution and texture fidelity. Building on the work of other proposals offering an alternative solution, we demonstrate a model with absolute units, where the colour of the texture is calibrated to assure a very good photo finish. Fidelity results produced by RMS estimation of the deviations of the colour patches offer better results for the photo camera than for the cameras in the scanners used. The final model maintains the metric properties of the scanned model, which was our metric reference.
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The paper presents a synergic and multidisciplinary approach where laser scanner survey, radar interfer-ometric monitoring and finite element (FE) numerical modelling are used for expeditious and no-contact dynamic identification of monumental masonry towers. The methodology is applied to a real case of great historical interest: the "Torre del Mangia" (Mangia's tower) in Siena (Italy). The tower geometry was acquired through Terrestrial Laser Scanning (TLS) techniques. The tower oscillations were detected using an interferometric radar in "Piazza del Campo", the square facing the Mangia's Tower, along three alignments, and movement of the structure at several heights were recorded. A FE model, built on the basis of the geometry acquired through the TLS, was used to interpret and verify the physical meaning of the experimental results. Through the discussion of the case study, the paper shows that the proposed approach can be considered as an effective and expeditious method for assessing the dynamic behavior of monumental buildings (and to plan interventions) on territorial scale.
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SUMMARY The terrestrial laser scanning system Trimble GS100 was used in two projects for geometrical building inspection. In this paper, two projects, a water tower and an underground tunnel in Hamburg, are presented wherein geometrical building parameters and discrete points are de- rived from laser scanning data with the goal of inspecting existing buildings relative to con- struction plans. Using data acquired by laser scanning as-built measurements could be com- pared with building plans to determine deviations and possible collisions. The results achieved in these projects demonstrate clearly that terrestrial laser scanning data allows very extensive inspection of buildings due to the high geometrical quality of the point clouds. However, if increased precision (of better than 2mm) is required, the performance potential of the laser scanning system is limited. Since extensive CAD modelling was not necessary for these particular projects very fast results (up to a factor of 1:1 for the ratio of scanning to data processing) have been produced. ZUSAMMENFASSUNG Das terrestrische Laserscanning System Trimble GS100 wurde in zwei Projekten zur Untersuchung von Bauwerken eingesetzt. In diesem Beitrag werden mit dem Wasserturm und dem U-Bahntunnel in Hamburg zwei Projekte vorgestellt, bei denen geometrische Parameter des Gebäudes und diskrete Punkte aus Laserscanningdaten abgeleitet werden, um existierende Gebäude mit Bauplänen zu überprüfen. Anhand der mit dem Laserscanner gewonnenen Daten konnten Bauwerksplanungen mit dem Ist-Bestand hinsichtlich Abweichungen und Kollisionen überprüft werden. Die Ergebnisse zeigen, dass aus Laserscanningdaten abgeleitete Werte sehr umfangreiche Prüfungen zulassen, und dass jedoch bei erhöhten Genauigkeitsanforderungen (von besser als 2 mm) das System an seine Grenzen stößt. Da umfangreiche CAD-Modellierungsarbeiten nicht erforderlich waren, konnten sehr schnell Ergebnisse (bis zu Faktor 1:1 für das Verhältnis Erfassung/Auswertung) erzeugt werden.
The Asinelli and Garisenda towers are the main symbols of the city of Bologna (Italy). These leaning towers, whose heights are about 97 and 48 m respectively, were built during the early 12th century and are two of the few surviving ones from about 100 tall medieval buildings that once characterized the city. Therefore, they are part of the Italian cultural heritage and their safeguard is extremely important. In order to evaluate in detail the deformations of these towers, in particular the deviations from a regular inclination of their walls, the terrestrial laser scanning (TLS) has been used and an efficient direct analysis method has been developed. The towers have been scanned from six viewpoints, providing 19-point clouds with a complete coverage of the visible surfaces with large overlap areas. For each tower, after the registration of the partial point clouds into a common reference frame, an accurate morphological analysis of the acquired surfaces has been carried out. The results show several zones affected by significant deformations and inclination changes. In the case of the Asinelli tower, for which a finite element model is available, the results have also been interpreted on the basis of the static load and normal modes. The correspondence between the measured deformation and the theoretically expected deformation, caused by a seismic sequence, is clear. This fact suggests a high sensibility of the tower to dynamic loads. Although a direct evaluation of the risk cannot be carried out with the obtained results, they lead to the general indication that the structural health of these buildings must be frequently checked and that man-made loads (e.g. vibration due to vehicular traffic) should be avoided or at least reduced.
SUMMARY Cultural heritage recording is a prime application for terrestrial laser scanners due to the high spatial resolution, high accuracy and fast data capture rates offered by this technology. To date, insufficient attention has been given to the many error sources contributing to the uncertainty of scanner datasets. A full error budget is derived for directly georeferenced terrestrial laser scanner networks that considers both relevant error sources fundamental to surveying and those unique to sampled laser scanner systems. In the case of the latter, new probabilistic models are proposed for angular positional uncertainty due to laser beamwidth and target centroid pointing. Analysis of a cultural heritage recording project in Ayutthaya, Thailand, highlights the disparity between 'expected' precision and the more realistic precision indicated by the error budget, to which the laser beamwidth is demonstrated to be a significant contributor.
The romanesque-byzantine style, 1000 year old leaning bell tower of Caorle (Venice Province, Italy) is a unique masonry structure, characterized by single and double lancet windows harmonically distributed on a cylinder-shaped shaft surmounted by a conic cusp. A terrestrial laser scanning (TLS) survey was carried out in 2011 and some analyses were performed on the resulting point cloud to provide the following: bell tower leaning angle, wall inclination/tapering and radius, local deviation from circular shape, and local curvature. Emphasis was placed on the changes of these quantities with elevation. In order to perform these analyses, a MATLAB/Octave toolbox was developed and is available as supplementary material of this paper. In this way, a reliable picture of the current geometry of the bell tower was obtained. In particular, a correlation between leaning angle (average value 1.4° towards East-South-East) and some surface deformations and damage (bulges, brick displacements or also material loss) was found. These results are useful for cultural heritage preservation purposes. © 2012.
The use of Terrestrial Laser Scanning (TLS) data for deformation measurement is gaining increasing interest. This paper is focused on a new procedure for land deformation monitoring based on repeated TLS scans. The kernel of the procedure is the least squares 3D surface matching proposed by Gruen and Akca [Gruen, A., Akca, D., 2005. Least squares 3D surface and curve matching. ISPRS Journal of Photogrammetry and Remote Sensing 59 (3), 151−174]. This paper describes the three main steps of the procedure, namely the acquisition of the TLS data, the global co-registration of the point clouds, and the estimation of the deformation parameters using local surface matchings. The paper briefly outlines the key advantages of the proposed approach, such as the capability to exploit the available high data redundancy using advanced analysis tools, the flexibility of the proposed solution, and the capability of providing fully 3D deformation measurements, including displacement vectors and rotations. Furthermore, it illustrates the performance of the proposed procedure with a validation experiment where a deformation measurement scenario was simulated and TLS and topographic data were acquired. From the analysis of this experiment, interesting features are highlighted: the validation errors below 1 cm in the displacements and below 1 gon in the rotations of small targets measured at a distance of 134 m; the increase by factor two of the errors when the same scene is measured from a distance of 225 m; and the importance of an accurate global co-registration in order to avoid systematic errors in the estimated deformation parameters. It is interesting to note that the above results were achieved under non-optimal conditions, e.g. using non-calibrated data and sub-optimal targets from the matching viewpoint. Besides the simulation experiment, the validation results achieved on landslide test site are briefly discussed.
The automatic co-registration of point clouds, representing 3D surfaces, is a relevant problem in 3D modeling. This multiple registration problem can be defined as a surface matching task. We treat it as least squares matching of overlapping surfaces. The surface may have been digitized/sampled point by point using a laser scanner device, a photogrammetric method or other surface measurement techniques. Our proposed method estimates the transformation parameters of one or more 3D search surfaces with respect to a 3D template surface, using the Generalized Gauss–Markoff model, minimizing the sum of squares of the Euclidean distances between the surfaces. This formulation gives the opportunity of matching arbitrarily oriented 3D surface patches. It fully considers 3D geometry. Besides the mathematical model and execution aspects we address the further extensions of the basic model. We also show how this method can be used for curve matching in 3D space and matching of curves to surfaces. Some practical examples based on the registration of close-range laser scanner and photogrammetric point clouds are presented for the demonstration of the method. This surface matching technique is a generalization of the least squares image matching concept and offers high flexibility for any kind of 3D surface correspondence problem, as well as statistical tools for the analysis of the quality of final matching results.
Geodetic surveys at the temple of Zeus
  • G Georgopoulos
  • E Telioni
Georgopoulos, G. and Telioni, E. 2005. Geodetic surveys at the temple of Zeus, in Nemea, Greece, Technical report (in Greek).
Geometrical building inspection by terrestrial laser scanning Surveyors key role in accelerated development
  • T Kersten
  • H Sternberg
  • C Mechelke
Deformation monitoring and analysis of structures using laser scanners
  • G Roberts
  • L Hirst
Roberts, G. and Hirst, L. 2005. Deformation monitoring and analysis of structures using laser scanners. In: FIG Working Week 2005 and GSDI-8. From Pharaohs to Geoinformatics, Cairo, Egypt, 16-21