Digital surveying and 3D modelling structural shape pipelines for instability monitoring in historical buildings: a strategy of versatile mesh models for ruined and endangered heritage


ACTA IMEKO 
ISSN: 2221-870X 
March 2021, Volume 10, Number 1, 84 - 97 

 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 84 

Digital surveying and 3D modelling structural shape pipelines 
for instability monitoring in historical buildings: a strategy of 
versatile mesh models for ruined and endangered heritage  

Sandro Parrinello1, Raffaella De Marco1 

1 DICAR – Department of Civil Engineering and Architecture, University of Pavia, via Ferrata 3, 27100 Pavia, Italy 

 

 

Section: RESEARCH PAPER  

Keywords: Endangered Heritage; reality-based modelling; digital survey; structural modelling; Cultural Heritage Routes 

Citation: Sandro Parrinello, Raffaella De Marco, Digital surveying and 3D modelling structural shape pipelines for instability monitoring in historical buildings: 
a strategy of versatile mesh models for ruined and endangered heritage, Acta IMEKO, vol. 10, no. 1, article 12, March 2021, identifier: IMEKO-ACTA-
10 (2021)-01-12 

Editor: Eulalia Balestrieri, University of Sannio, Italy 

Received June 1, 2020; In final form November 23, 2020; Published March 2021 

Copyright: This is an open-access article distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, 
distribution, and reproduction in any medium, provided the original author and source are credited. 

Funding: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie 
grant agreement No 821870.  

Corresponding author: Raffaella De Marco, e-mail: raffaella.demarco@unipv.it  

 

1. INTRODUCTION: THE DOCUMENTATION OF 
ENDANGERED HERITAGE 

Both the analysis of cultural heritage and the development of 
communitarian guidelines for its protection [1] are determining a 
growing scientific approach to European and worldwide heritage 
sites [2]. The variety of built heritage (historical buildings, 
monuments, historical centres, sites, and territorial landscapes) 
requires a wider field of knowledge and intervention in terms of 
both physical structures and cultural policy. This leads to the 
attendant difficulties in protection and preservation due to a 
fragmented reality of separated protocols and documentation, 
which results in difficulties in the sharing of information and data 
integration, thus hindering the entire approach to an intervention 

programme. This is especially the case for the so-called 
‘endangered heritage’ sites (World Heritage Convention, List of 
World Heritage in Danger 1972), the class of built heritage 
particularly affected by proven or potential threats that pose a 
high level of risk for its preservation [3]. 

In fact, the revision of the sites officially listed as endangered 
heritage has been achieved in terms of the conditions of 
relevance and correspondence with the specified risk criteria and 
indicators (territorial, political, or social dangers). However, the 
statistics in terms of monitoring parameters and protocols 
remain non-uniform, highlighting a lack of scientific and 
technical documentation and a lack of connection between 
intervention activities and ‘reality-based’ updated analysis. The 
framework highlights the coexistence of a dual type of 
emergency issue related to built heritage, with the classification 

ABSTRACT 
Cultural heritage and the attendant variety of built heritage demands a scientific approach from European committees: one related to 
the difficulties in its protection and management. This is primarily due to the lack of emergency protocols related to the structural 
knowledge and documentation pertaining to architecture and its ruins, specifically in terms of the goals of protection and intervention 
for endangered heritage affected by mechanical instabilities. Here, we focus on a rapid and reliable structural documentation pipeline 
for application to historical built heritage, and we introduce a case study of the Church of the Annunciation in Pokcha, Russia, while we 
also review the incorporation of integrated 3D survey products into reality-based models. This practice increases the possibility of 
systematising data through methodological phases and controlling the quality of numerical components into 3D polygonal meshes, with 
millimetric levels of detail and triangulation through the integration of terrestrial laser scanner and unmanned aerial vehicle survey data. 
These models are aimed at emphasising morphological qualities related to structural behaviour, thus highlighting areas of deformation 
and instability of the architectural system for analysis via computational platforms in view of obtaining information related to tensional 
behaviour and emergency risks. 

mailto:raffaella.demarco@unipv.it


 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 85 

of the site as ‘endangered’ for the stability and integrity of its 
physical  
structure on the one hand, and the growing demand for specific 
parameters and protocols for the analysis and quantification of 
the emergency value of the building, thus determining the 
effective intervention. 

Thus, there is a growing demand for the identification of such 
sites [4], both in geographical and typological terms, expanding 
the dissemination and application of appropriate monitoring and 
knowledge practices prior to intervention [4], with the aim of 
triggering a process of safeguarding policies [6].  

The topic of implementing safeguarding methodologies for 
existing heritage is receiving a great deal of attention among 
researchers, with new forms of digital products emerging in 
terms of a survey-based phase of digital documentation related 
to cultural heritage, which is crucial for an accurate and complete 
understanding of the characteristics and parameters of the units 
and contexts of built heritage. This is being combined with 
computer-based cognitive and interactive models, with the 
elaboration of 3D digital products for investigations and 
simulations related to shapes and structures. 

These new representation systems are resulting in new 
expectations related to digital communication, changing the 
objectives and constantly renewing the demand in analytical 
terms for cognitive requirements, in response to the 
requirements linked to the computational nature of interaction 
within the models themselves, which are now capable of 
providing both quantitative and qualitative answers. The 
difficulties in the development of the reliable diagnosis of 
historical structures can be realigned with the need for new 
methods of analysis that can exploit the computational 
opportunities through specific methodologies and cognitive 
practices. These practices relate to the visual and graphic aspects 
of the documentation pertaining to architecture [7], reliably 
representing the present state of stability and linking it to the 
constructive and safeguarding rules.  

2. HISTORICAL STRUCTURES AND INSTABILITIES IN THE 
DIGITAL DOCUMENTATION PROCEDURES 

Historical buildings are traditionally founded on and remain 
linked to their original structural system, from the construction 
phase to later procedures. The demolition of bearing systems and 
elevations, the reconfiguration of horizontal levels and vaults, 
and the construction of expansion blocks thus enrich the 
mechanical experience of the monument (Figure 1).  

The consideration of structural diagnosis applied to historical 
built heritage in terms of the knowledge of the stress behaviours 
and the prevision of damage mechanisms plays a central role in 
the development of the documentation protocols for 
safeguarding. A review of the risks, the on-going kinematics, and 
the priorities of stability related to endangered buildings [8] 
places the focus on the aspect of robustness, that is, the capacity 
of the building and its elements to withstand a certain level of 
stress imposed by a combination of degradation and the changes 
in both the materials and the environments [9]. Thus, considering 
the deep impact that stress-altering phenomena have on the 
geometrical and material aspects of buildings (e.g. deformations, 
drifts, cracks) is part of a comprehensive diagnosis that can be 
achieved through an investigation into the structural shape [10]. 
As such, it is possible to focus the evaluation of the stress 
instabilities on the target of a ‘static morphology' that reflects the 
mechanical and stress traces left by the adaptation schemes of 
the system during its physical history. It also highlights the 
stability principles related to the class and type of resistant 
geometries (Figure 2). 

Nowadays, the analysis of the structural aspects of historical 
buildings involves simplified typological schemes transformed 
into numerical structures, selected to be mechanically 

 

 

 

 

Figure 1. Examples of sites along the Upper Kama route characterised by on-
going risks of abandonment and decay, proving the basis for a classification 
as endangered heritage. From the top, Church of the Exhaltation of the Holy 
Cross in Bondjug, Rubezhskaya Church in Usolye, Church of St. Nicholas in 
Uzhginskay, Church of Paraskeva Friday in Saltanovo.  



 

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controllable in defined levels of physical regularisation and 
abstraction [11]. However, the confidence in the standardisation 
of structural computing has led to underestimating the direct 
‘experience’ of the building, visible in the singular imperfection 
of its shape.  

In fact, structural documentation must be both 'comparative', 
with reference to the archetypes, and 'specific', highlighting the 
accurate variation in formal detail. The testing of specific 
intervention procedures for existing components aimed at 
assessing their instability performance is highlighting the need 
for more precise models for the creation of reliable simulations 
[12]. At the same time, the area of digital documentation has 
developed to include morphometric 3D databases with more 
dense information, which allows for measuring and analysing 
space in terms that is closer to the continuous form [13]. The 
relationships between the shape and mechanics of structural 
systems can determine new descriptive products through reality-
based numeric surfaces in terms of high-poly mesh models, 
which can be morphologically assessed to extract specific 
quantitative parameters that can guide the mechanical 
interpretation. Thus, the reality-based mesh model, the numerical 
component of which reliably determines and characterises the 
geometric aspects, can become an adaptable tool for the 
management of the computational and analytical processes 
related to robustness.  

These considerations are encouraging strategies of data 
integration for the comprehensive adoption of structural reality-
based models related to architectural heritage. On a scientific 
level, the experimentation of reality-based models for structural 
diagnosis will result in a multidisciplinary and implementable 
methodology, one capable of guaranteeing a standardised 
product, that is, the polygonal mesh model, involving different 
levels of detail and integration for the management of the 
existing built heritage. This type of model is aimed at determining 
both emergency and long term interventions, in the calibration 
of their procedural computing in both a scientific and practical-
operational direction through the capacity for the shapes to be 
transformed into morphological and computational platforms of 
analysis, such as finite element analysis (FEA) platforms. Here, 
the methodological process must be as fast, as extendable, and as 
replicable as possible to facilitate interchange and to allow for a 
complete knowledge and management capacity through 3D 
models related to buildings that are in a state of emergency. 

3. AN EXPERIMENTAL CASE STUDY: THE CHURCH OF THE 
ANNUNCIATION IN POKCHA (RUSSIA) 

3.1. The site and its historical/structural characterisation 

The constructive features of built structures relate to the 
technological and material traditions pertaining to specific 
continents, where the stylistic influences and source availability 
of certain elements have determined the specific characteristics 
of the architectural shape. This is especially the case with the built 
sites and monuments along the European Cultural Heritage 
Routes, the architectural value of which is strongly permeated by 
specific structural typologies. These architectural structures have 
thus acquired their own identity, characterisation, and specificity 
over time, evolving specific spatial distributions and constructive 
apparatuses in their historical development and functional 
change. Resilient structures combine a wide framework of 
morphological and static relationships that are reflected in their 
own state of conservation and which influence the robustness-
related approach to their restoration and preservation for 
security and stability.  

The case of Upper Kama, Russia, already the subject of 
international research related to the digital documentation of the 
complexes [14], presents an emblematic example of the Cultural 
Heritage Route and the coexistence of historical structures and 
various phenomena of instability caused by the functional 
experience of the building, reflecting a complex framework of 
diagnosis for the safety and integrity of the various built sites. In 
these terms, the Upper Kama sites form a rich morphological 
abacus of technological modules and elements of structure, along 
with the related pathologies of degradation and conservation [15] 
[16]. 

The cultural tradition of the Upper Kama settlements, more 
stabilised by commercial requirements than most villages of the 
Russian countryside, has determined a global phenomenon of 
transformation regarding the built structural systems, from the 
typical wooden architecture to the constructive solutions of brick 
and stone masonry. Therefore, these architectural structures are 
characterised by a morphological configuration involving 
multiple expansion blocks. During the Soviet period, the demand 
for the conversion of infrastructures for energy or food 
production resulted in the decline of these religious buildings. 
The consequent interventions and the alteration of the 
architectural structures, forcibly adapted to the new functions, 
led to a prevalent abandonment characterised by eventual ruin 
and collapse. 

 

Figure 2. The state of neglect and the lack of conservation present critical situations of widespread instability among the masonry systems, clearly exposing 
the structure to the damage affecting its elements. Robustness instabilities in the structural complex of the Church of the Transfiguration, Pyskor, defining the 
increasing frameworks of damage that will destroy these buildings without specific lines of intervention. 



 

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The case of Blagoveshchenskaya Church, or the Church of 
the Annunciation of the Blessed Virgin, in the village of Pokcha, 
represents a key monumental site of the Cherdyn district, which 
synthesises various different historical-functional evolutions in 
the stratification of its structures and walls, which today lie in 
ruin [17], Figure 3. 

The original wooden complex was replaced in 1785 with a 
new structure composed of stone and brick masonry, subdivided 
into multiple structural blocks, which include the main body, 
with a quadrilateral planimetry, constituting a nucleus for the 
refectory, the southern and northern chapels, the bell tower, and 
the entrance narthex. In 1910, a reconstruction intervention 
resulted in various structural modifications, especially in terms of 
the bell tower, which was entirely replaced, and the eastern 
section of the central vault and the altar, reconstructed with the 
insertion of a five-headed chapter. Meanwhile, the interiors 
formed in plastered stone, with paintings and ornaments dating 
from 1870, remain largely preserved. The face of the building, 
which features an additional red brick facing, contributes to the 
strengthening of the external envelope and allows for the 
possibility of inserting additional devices of tension resistance 
into the stratified walls.  

The history of the site involves attempted restoration works 
dating from 1920 to the complete abandonment in 1940 and to 
the re-conversion into a power central. The energy issues related 
to the new function resulted in the partial collapse of the main 
pavilion vault and the bell tower roof in the 1990s, following 
repeated lightning strikes attracted by the electrical system. 
Following this extensive damage, the church was excluded from 
the list of architectural monuments of interest, precluding any 
new interventions or restoration works, and leaving the site to 
suffer virtual collapse. 

3.2. The current state of the structural ruins 

In 2018, the architectural complex was in a clear state of 
neglected conservation. The wooden roofs had been almost 
entirely destroyed, and the main masonry structure was damaged 
in various areas, particularly in the main vaulted system. 

Meanwhile, the vaulted structure of the spans, the loading on 
the pillars based on a counter-balance scheme involving vault–
vault and vault–support relationships, has been distorted by the 
collapse of the secondary vaults. In terms of the large central 
pavilion vault, only around half of its total span has been 
preserved, with the head brick structure left visible along the 
detachment edge. Both the brick vaults and the wooden roof 
have collapsed into the central environment of the nave, with the 
debris submerging part of the loading pilasters of the vaults, 
which cannot be inspected in their ground basement and have 
been covered by soil and vegetation, creating a natural hill that 
both reduces the access and is the cause of the degradation of 
the preserved supports. The connection with the bell tower, once 
provided by the central nave through the gallery and the 
refectory, has been demolished and thus prevents the direct 
documentation of the state of conservation of the elevated 
structures. 

Following the collapse of the roof, the complex was deprived 
of the main source of protection from atmospheric agents, 
particularly pertinent during the winter months, and has 
therefore suffered a rapid degradation of the remaining portions, 
affected year on year by localised collapses. The site is also totally 
lacking in control services to prevent access to both people and 
animals, who often occupy it and damage the spaces and 
structures. Here, the narthex environments have been 

particularly affected by the frequent presence of herds in 
transhumance, often housed by the shepherds inside the church 
during the summer season (Figure 4). 

3.3. Objectives and targets of the documentation process 

The objective of the documentation of the 
Blagoveshchenskaya Church, in addition to the wider mapping 
and reconnaissance approach for the sites in the Upper Kama 
area, is to encourage a rapid but reliable diagnosis of its structural 
crisis. This is aimed at directing the organisation of possible 
intervention operations, and to safely preserve and promote the 
historical ruins. While the local administration is gradually 
recognising the historical and cultural value of these sites along 
the Kama, the ruined conditions present a clear disadvantage for 
the commitment, both technical and economic, to implementing 
conservation procedures. In this sense, rapid survey and 
quantification methods for recognising and evaluating the 
preserved structural systems and the corresponding risk 
constitute an excellent preliminary tool for accurately 
determining the qualitative and quantitative planning of 
interventions that could halt the exponential cycle of damage. 

The documentation of the current state of conservation of the 
structure of the Blagoveshchenskaya Church has thus 
highlighted the need for structural diagnosis using 3D digital 
survey methods. This involves applying specific integrated 
approaches for the acquisition and modelling of the structural 
shape, one that ensures a descriptive quality of its resistant 
architectural structure through the data collected through a 

 

 

Figure 3. The complex of Blagoveshchenskaya Church in Pokcha. The original 
architectural structure of the church before the revolution in 1956 (above) 
and the ruins as of 2018 (below). 



 

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practical and fast on-site survey. The required knowledge is 
largely related to the shape alteration of the structural ruins, 
ensuring that it can be comprehensively and reliably documented 
and allowing for analysing the degree of safety and determining 
the recovery intervention in relation to the overall mechanical 
scheme. 

4. STRATEGIES OF ANALYSIS FOR THE DIGITISATION OF THE 
RUINED SHAPE 

The documentation of the state of conservation of 
Blagoveshchenskaya Church as of 2018 involved experimenting 
with integrated approaches in digital surveying to focus on the 
static instabilities of the ruins for recovery purposes [18]. Here, 
the morphological analysis of masonry structures was organised 
during the acquisition processes, semantising the spatial 
constructive ruins and linking them to the global volumetric 
macrosystem. Furthermore, the internal inspection of the 

masonry sections in terms of the fractured or collapsed portions 
has allowed for the integration of information related to the 
structural envelope, reliably supporting the digitisation 
procedure [19].  

The ruined shape, the central element of the analysis process, 
has thus become the basis of direct knowledge, supported by the 
repertoire of historical/constructive analysis data, with the dual 
purpose of completing the technical stratigraphic knowledge 
framework and revising it using integrated research in relation to 
the behavioural diagnosis of the structural components. The 
ruined complex of Blagoveshchenskaya Church, for reasons 
attributable to the collapse of the structures and the lack of site 
regulation, has been deprived of the original spatial design of the 
wall system. The absence of the main masonry portions hinders 
the analysis of the current structure in terms of creating defined 
schemes of interpretation in relation to the architectural 
instabilities, and this indicates that the specific evaluation of the 

 

 

Figure 4. Photographic gallery of the Blagoveshchenskaya Church in Pokcha. 
On the left, the state of conservation in 2018, the overall structural system 
and the specific static units that characterise the statics of the entire 
complex. On the right, evolution of the damage to the main vault from 2006 
to 2019, which increased rapidly due to the lack of intervention. Details of 
the constructive system that influences the robustness evaluation of the 
complex. Indication of interventions for the functional conversion into a 
power central, stratigraphic technology of the masonry walls and distribution 
of a steal structure inside the masonry. 

 

 

 



 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 89 

reality-based digital shape is a crucial step for a reliable diagnosis 
of the static robustness [20].  

The ruined complex has been subjected to an integrated, 
extensive, range- and image-based documentation campaign. 
The attendant approach involved calibrating methodologies of 
acquisition and representation in terms of the morphological 
properties of the structural elements, especially in terms of the 
correspondence and integration of spatial information. The 
dimensions of the structure (specifically the elevation of the 
damaged portions of the main vault at over 15 m in height) have 
oriented the morphometric digitisation strategy toward the use 
of multi-instrumental close-range measuring systems, aimed at 
guaranteeing a comprehensive coverage and a high formal 
detailed resolution comparable to the complexly shaped 
geometry of the masonry surfaces and the typological damage of 
the masonries (widely covering the order of dimensions from 5 
to 10 cm). 

At the same time, the colorimetric information has proven to 
be a key aspect in the diagnostics of the structures, evaluating the 
pathologies of mechanical influence on the masonry and 
plastered portions, described through tonal variations in the 
surface colours.  

The on-site campaign was organised on a double acquisition 
level, at the ground level using a terrestrial laser scanner (TLS) 
and at an aerial level using drones for photogrammetry, with the 
aim of obtaining comprehensive morphological data on the 
elevations of the structure (over 15 m) in a single 360 ° point 
cloud database [21].  

4.1. Terrestrial laser scanning acquisition campaign and products  

In the acquisition using a TLS FARO Focus S150, the 
integrated photographic camera was also enabled, ensuring a red, 
green, blue (RGB) information quality for each point (x, y, z) that 
is suitable for surface mapping. Each scan was performed in 
medium or high mode according to the distance of the shooting 
range from the object and provided an additional acquisition 
time of 4.00 minutes to allow for the shooting of 16 frames for 
each camera location (coverage of 360 ° × 320 ° for the scan 
angle). Prior to each photographic shot, the instrument was set 
with an average balance of colour and lighting while considering 
only the horizontal level for the balance of light conditions in the 
outdoor scans, or the entire panoramic space for the interior 
scans. These measures significantly affected the acquisition 
campaign in terms of duplicating the scanning times but were still 
more advantageous for the documentation purposes than a 
parallel photographic campaign from the ground, which requires 
further actions to integrate the photographic material into the 
spatial database. A total of 73 TLS scans were realised to collect 
all external surfaces and to spatially connect the complex 
distribution of the internal environments. The scans were 
performed at an approximate 2-mm laser spot spacing up to a 
height of 5 m, and close to 5 mm in the upper surfaces. The 
quality of TLS acquisition for the bell tower and the central dome 
was ensured by the presence of the inner natural hill over the 
ruins of the roof, which allowed for a higher instrument 
positioning above ground level. The TLS metric survey 
conducted from the ground guaranteed a coverage of 80 % of 
the morphological data related to the structure (Figure 5).  

The processing of the seven source scans on the vaulted 
structure provided an alignment procedure to obtain the unified 
TLS point cloud. Rotation and translation matrixes were then 
applied in semi-automatic mode via the cloud software 
(SCENE), using a cloud-to-cloud alignment set with values of 

0.05 m in subsampling and n° 150 iterations for the alignment 
algorithm. The resulting values of alignment characterising the 
final integrated database are presented in Table 1. 

4.2. Unmanned aerial vehicle acquisition campaign  

 At the same time, the aerial photogrammetric acquisition was 
developed using an unmanned aerial vehicle (UAV, DJI 
Phantom 4 Pro), with the flight plan focused on the points of 
interest of the architectural complex. In fact, the flight plan 
mission was set from the top centre of the complex at a level of 
50 m from the ground in the mode ‘point of interest’. Here, a 
photogrammetric campaign was conducted using the aerial 
camera with a conical acquisition surrounding the monumental 
complex, descending to a height of 10 m above ground and 
developing 329 shots in 10 min of flight. The guaranteed camera 
angle and the adjustable inclination of the gimbal allowed for 
total coverage of the top surfaces, with a quality of photographic 
data suitable for the clear photogrammetric reconstruction of the 
edges of the components (21 MPixel). In addition, specific flight 
plans for the tower blocks and the central vault were planned 
with greater photographic detail, largely due to the close distance 
of shooting. The GPS coordinates defined by the UAV for each 
shot better addressed the alignment algorithms, set to ‘high’ 
precision, simplifying the alignment of the photogrammetric 
structure from motion (SfM) reconstruction. In terms of the 
overall SfM point cloud, there was an error of 0.004 pixels due 
to the camera alignment (Figure 6). 

4.3. Post-processing data and products 

The GPS information in the source data obtained via the 
acquisition campaign provided a preliminary overlapping 
between the TLS- and UAV-acquired point clouds, both in terms 
of vertical and horizontal built surfaces, which was used to 
optimise the referencing in an integrated sparse database of 
morphometric characters. 

To optimise the GPS data, the alignment procedure for the 
TLS and UAV data was set with reference to the TLS point 
cloud, defining six markers from key morphological features that 
were recorded on the UAV point cloud. The resulting values of 
alignment characterising the final integrated database are 
presented in Table 2. The higher errors of reference 
corresponded to the markers with less camera projection in 
terms of photogrammetric alignment. 

The final database featured 51.889.557 and 49.853.646 points 
from the TLS survey on the internal surfaces of the masonry 
structure, and 2.035.911 points from the UAV survey on the 
external surface and the ruins of the vaulted structure. The 
average density in the overall integrated point cloud was 1 
point/3 mm. 

Table 1. Alignment values in cloud-to-cloud reference for TLS data.  

Scan  
Morpho 
feature 

iterations 

Point error 
iterations 

in mm 

Average point 
error  

in mm 

Min 
overlapping  

in % 

Scan 39 4 2.5 2.3 35.5 

Scan 40 12 2.6 1.8 25.8 

Scan 41 7 1.9 1.6 29.5 

Scan 42 6 1.5 1.2 29.5 

Scan 43 5 1.2 1.0 49.4 

Scan 46 6 1.3 1.0 33.8 

Scan 48 4 2.2 2.0 26.3 

Cluster report 44 1.8 1.5 32.8 



 

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From the joint processing of the collected archives, useful 
reference drawings, sections, and plans were produced to obtain 
comprehensive knowledge of the architectural complex and to 
serve as guidance for the intensive mapping of the pathologies 
of degradation and instability documented in the photographic 
repertoire. However, the 2D representation barely described the 
quality of distribution and the volumetric development of the 
main structural elements, rendered even more complex by the 
ruined condition of the site and, as such, by the loss of many of 
the main shapes conventionally identifiable for the classification 
of the elements (intrados of the vaults, opening profiles and local 
collapses, integrity of the elevation structures). 

In addition, the attempt at processing for elevation maps, as 
a standard analysis of deformation mechanisms using the point 

 

Figure 5. Morphometric database from on-site TLS acquisition campaign: the single scans, completed via GPS, compass, and inclinometer information, were 
referenced and registered to control the overall alignment to verify the final point cloud. 

Table 2. Alignment values in TLS and UAV data morphometric reference.  

Marker  
Morpho feature  
correspondence 

Projections Error in m 

Point 1 Vault springer 1 89 0.0383  

Point 2 Vault springer 2 130 0.0472 

Point 3 Vault springer 3 114 0.0483 

Point 4 Vault springer 4 85 0.0439 

Point 5 Vault key 1 
(damaged border) 

87 0.0314 

Point 6 Vault key 2 
(damaged border) 

77 0.0169 

Control points 6 582 0.0392 

 

Figure 6. Morphometric database from the on-site photogrammetric UAV acquisition campaign: the photos were geo-referenced and aligned to define the 
main point cloud on the architectural complex and the surrounding landscape. 



 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 91 

cloud displacement from a reference plane [22], did not satisfy 
the knowledge requirements in terms of the deformation of the 
structural surfaces. The high surface processing of the structural 
envelope, due internally to the collapse conditions and externally 
to the decorative brick structure, resulted in difficult-to-read 
colour maps, where the excessive fragmentation of the level 
indicators failed to provide an overall interpretative picture of the 
deformations. 

5. OPPORTUNITIES FOR 3D INTEGRATED MODELLING FOR 
THE DIAGNOSIS OF THE STRUCTURAL SHAPE 

The aim of the structural representation was focused on the 
development of a continuous mesh modelling protocol, enriched 
with reality-based qualities, achieved as part of the objective of 
digitally surveying detailed and imperfect shapes as confirmed by 
the instability and mechanical features. These shapes, controlled 
and certified within the envelope of the structural object, 
necessarily introduce a need to manage the polygonal geometric 
mesh that defines them, the processes of which are, however, 
improved by the representation of a morphological detail that is 
itself a source of diagnostic reflections on the mechanisms of 
analytical systems [22] [24], Figure 7. 

In this sense, the obtained 3D models not only pursue the 
necessary analysis of the deviation between static surfaces but 
also consolidate a certified practice that defines them both as 
outputs, directly applicable for the quality of structural 
instabilities, and as input data for further implementation, 
specifically on computational platforms.  

As such, a digital data processing was established that will 
exponentially led to the exploitation of the potential of the 3D 
discrete database, namely, the point cloud, and the continuous 
3D object defined by vertex and edges for quantifiable 
evaluations, namely, the model. The application opportunities, 
from FEM platforms to information systems that enhance the 
virtual fruition, can thus provide the grounding for involving the 
models using common languages, thus adapting them 
appropriately [25] [26], Figure 8 and Figure 9. 

The developed research on reality-based mesh models has 
allowed for accurately delineating the causes and effects 
produced by the structural survey in the digitisation and 
modelling processes related to morphometric data, validating the 
compatibility and correspondence of the produced models via a 
multi-instrumental comparison of the measurement practices 
normally applied in the structural field. The integration of the 
products of digital survey protocols applied on the site [26], from 
both terrestrial and aerial image-acquisition tools, was 
complementarily completed through the differentiated visual 
stations, ensuring the capacity to obtain information related to 
both the exterior and the interior parameters, as well as to 
monitor the data related to the roof components and elevation 
units. Focusing on the central pavilion vault, which was largely 
destroyed during the electrical accident, the documentation, 
finalised to the reinstatement of a complete structural shape, 
involved the detection of the vault both from the intrados level, 
also visible in terms of its constructive thickness, and the 
extrados level, dominated by the ruins of the octagonal masonry 
tholobate at the base of the wooden roof, Figure 10.  

5.1. Modelling pipeline 
The pipeline for 3D reality-based modelling was assessed in 

relation to the research objectives regarding the diagnosis of the 
stability of the Blagoveshchenskaya Church in Pokcha. The 

 

 

 

Figure 7. Drawings and elaborations for the 2D description of the main 
structural system of the church. The presence of noise data for elements such 
as the vegetation and collapsed ruins is highlighted. 



 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 92 

choice was oriented both toward a spatial configuration of the 
complex's elements, articulated on several levels and 
environments, and for a correspondence of the actual state of 
ruin of the building, which highlighted various critical issues to 
be transposed automatically in terms of a digitised model through 
non-uniform rational basis spline (NURBS) or parametric 
modelling. First, the data collected from the TLS and UAV 
acquisition campaigns were tested using a compatible procedure 
for the integration of the processed point clouds, also supported 

by common format extensions for their inclusion in the 
modelling platforms. During this phase, various issues emerged 
in the specific management of the vertex and polygon objects. 

Corrections and uniformities of the normal vertex data 
The first aspect related to the difficulty of transferring the 

‘vertex normal’ information for each point of the 
photogrammetric cloud acquired via the UAV on the mesh 
modelling platforms. The compatible formats (mainly .ptx and 
.pts) for the reverse modelling provided a different ASCII code 

 

Figure 8. Quality of processed morpho-metric TLS and UAV data on the external surfaces of the masonry structure. The point cloud from the UAV acquisition 
shows a resolution and density of data comparable with the TLS acquisition, supported by the higher level and resolution of the camera shooting. 

 

Figure 9. Quality of processed morpho-metric TLS and UAV data on the internal surfaces of the masonry structure. The point cloud from the UAV acquisition 
shows a worse resolution in the discrete definition of the main profiles, geometries, and surfaces, largely due to the corner and shadow shooting. 



 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 93 

in the UAV photogrammetric processing environment, and the 
normal information was corrupted within the different matrixes 
of conversion. Following various attempts at comparisons on the 
multiple modelling platforms suitable for the managing of 
architectural scale data, an additional phase of the re-calculation 
of the normal vertex in the UAV point cloud was adopted and 
performed directly in the modelling environment, so as to 
correctly orient the mesh triangulation and to avoid anomalies of 
flipped polygon regions that are not suitable for the mesh 
management as a whole. Due to the high density of points and 
their unstructured distribution, further complicated by the 
geometric articulation of the complex, the automatic normal 
calculation tools did not return uniform and coherent results, 
fragmenting the orientation of the points and, consequently, the 
features of the triangulated mesh. As such, only 70 % of the 
points in the UAV-based point cloud (1.426.256 points) were 
automatically processed for the normal feature.  

To resolve this issue, a single-step triangulation process was 
performed with the TLS and UAV integrated point cloud such 
that the normal vertex data defined in the TLS point cloud could 
mediate the orientation of the entire mesh surface. The 
topological meshing procedure was performed using an HD 
adaptive triangulation set for the following parameters: 

- Geometry capture accuracy: set over 75 % of the details for 
shape accuracy. 

- Scanner accuracy: this related to the overall accuracy 
guaranteed by the source point cloud. Given the source 
TLS and UAV data, and the quality/noise of the 
integrated aligned database, the accuracy was set to 
within 3 mm. 

Filtering and selection of source data for the integration procedure. 
The second aspect related to the different point spacing 

interval of the individual point clouds (on average, 1-3 mm from 
the TLS, and 5-10 mm from the UAV) and its influence on the 
triangulation of an overall polygonal mesh, where a uniform 
reading of structural irregularities was ensured. The two 
discontinuous datasets were refined with an overall filtering 
performed on the point clouds and were checked via a ‘watertight 
remesh’ process on the final mesh, assuming an average edge 
length of 5 mm to define a final model compatible with the main 
standards of deformation analysis in the area of structural 
diagnosis. This range did not compromise the relative 
dimensions of the structural damage quantifiable as a whole and 
related to the geometry of the construction materials (mainly 
bricks and metal chains of larger specific dimensions) and to the 
tolerance threshold set for the analysis (5 mm, also compatible 
with the standards for elastic safety assessments), Figure 11. 

The finalisation of the integrated 3D survey database related 
to the Pokcha complex defined a virtual system of the preserved 
shape, directing the attention toward the metric-spatial 
correspondence of information obtained from the TLS database 
and the UAV photogrammetry, calibrated at different reliability 
values of space reconstruction from the features of the 
instruments applied in the acquisition phase. Specifically, a 
morphological reference and registration was developed in terms 
of the scale of each structural unit of the built complex. Here, for 
the pavilion vault, the two types of data were aligned in terms of 
perimetrical boundaries and façades while considering the 
deviation accuracy of the discreate surfaces and target control 
points. Following this, a segmentation of the overlapped point 
cloud was performed, deleting the overlapped areas and 
maintaining the quality of the TLS data on the intrados surfaces 
and both the TLS and UAV data on the extrados surfaces.  

Finally, the set of points was subjected to standard filtering 
procedures, both automatic and manual, which were aimed at 
cleaning all the spatial information not pertaining to the envelope 
of the structural surface, specifically constituted by the infiltrated 
vegetation both at the base and at the top of the ruins. Further 
attention was paid to the window openings, which were manually 
cleaned for a complete reconstruction of the wall thickness. The 
triangulation phase of the final integrated database highlighted 
certain pieces of missing morphological information, which was 
due to the building masonry areas being covered by vegetation 
during the survey campaign (removed in the point cloud during 
the filtering process). These parts were subsequently integrated 
via a fitting of mesh holes according to the geometric primitives 
derived from the mesh model. The mesh model obtained by 
triangulating and remeshing the surfaces verified the expected 
target of morphological detail, conserving both the main 
structural profiles and the specific geometry qualities of the 
masonry elements, both on the surface and on the edges along 
the collapsed region. 

 
 

 

Figure 10. Alignment and integration of multi-instrumental point clouds for 
the static unit of the central pavilion vault. 



 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 94 

5.2. Non-uniform rational basis spline comparison and deviation 
analysis 

The investigation into the structural instabilities was focused 
on the vaulted unit in the central span, with the aim of comparing 
the specific imperfect geometry of the vault (affected by 
mechanical deformations) with a reliable reconstruction of its 
original shape from the in-site dimensions of the ruins. Using the 
final mesh model, various section planes were set with an 
established pitch of 30 cm along all the surfaces of the unit (vault 
and vertical walls), extracting 3D sketch profiles that adhered to 
the specific morphological surface and importing them into a 
NURBS modelling environment. Using extrusion techniques, the 
structural volumes of the pavilion vault were geometrically 
reconstructed according to the regular project profiles and 
imported into the reverse modelling environment to allow for a 
comparison with the irregular mesh surface, Figure 12. 

The comparison between the NURBS model and the mesh 
model of the vault was performed using the query tool of 
deviation available on the platform to compute the discrepancy 
between the models’ surfaces. The deviation comparison (made 
possible by the same coordinate system maintained between the 
models) indicated an overall failure phenomenon that 
characterised the entire system of the resistant unit, possibly 
attributable to the accidental impact that caused its collapse. 
Within it, various specific portions affected by instability could 
be observed since their colour map obtained via the deviation 
computing was characterised by a colour scale ranging from 
green to red, highlighting the attendant on-course kinematic 
deformation that is increasing over time. These areas are located 
both on the vault and on the supporting walls, within 
deformations that are on a scale of centimetres and that are 
affecting the main loaded parts of the vaulted system, Figure 13. 

Specifically, much like with the collapsed part, the remaining 
structure of the vault exhibits a discharging arch not in line with 
the overall static configuration. In fact, this shape reached 40 mm 
of deformation along entire height, it is subdivided into three 
plastic hinges and presents a serious risk of collapse. The main 
bearing walls also exhibit a buckling deformation that reached a 
maximum of 70 mm, thus increasing the instability of the 
structure in the basement area. 

As such, the reliable mapping of evolving structural 
instabilities using direct survey and mesh models is aimed at 
determining the intervention practices involving targeted 
consolidation actions for the safety and conservation of ruined 
structures. 

6. CONCLUSIONS 

The modelling performed in terms of the Church of the 
Annunciation in Pokcha followed an integrated approach 
involving morphometric data from different instrumental point 
clouds. An overall mesh triangulation strategy was devised to 
produce a reality-based model capable of preserving the 
structural irregularity through the mediation of numerical 
polygonal surfaces. Specific methodological considerations were 
developed for the mesh triangulation of the integrated TLS and 
UAV sparse databases. In order to perform an HD mesh 
construction, a correct alignment of the points was required as 
well as UAV point cloud processing to support the optimisation 
of the poly-face orientation in the mesh. Other filtering processes 
were implemented in terms of the point cloud, specifically 
regarding the presence of opening grids and extensive vegetation, 

 

Figure 11. Final reality-based mesh models following the triangulation and 
optimisation processing of the HD mesh. The mesh preserved the specific 
details of the structural shape of the structural unit. 



 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 95 

to better expose the surface of the structural domain affected by 
the decay and the natural elements of the ruin site. 

The need for a formal approach to the re-drawing analysis and 
intervention for endangered historical sites was the motivation 
behind the operational experimentation of morphological-
structural representation in terms of two specific research targets: 

1) The planning of a documentary strategy aimed at acquiring 
the totality and particularity of the architectural details in 
terms of all typological variants (masonry, metal parts, wall 
coverings) and collocations (main environments, 
underground, in elevation, coverage levels). 

2) The convenience of transferring these detailed systems into 
suitable morpho-metric products capable of providing 
information and analytical opportunities in relation to 
historical masonries through graphic representations.  

These objectives determined the preference for a 3D 
approach to the documentation and visualisation of structures 
directly from the data obtained via digital surveys. The shape 
representation is preserved in both qualitative and quantitative 
structural assessments, aware of the interactions that historical 
architecture can exhibit between its individual preserved 
components and, in terms of restoration, with the intervention 
design, Figure 14. 

Due to its complex nature in terms of compatibility and 
format size, the type of morphometric data represented by high-
poly mesh models is currently affected by the continuous 
developments in the field of Big Data management in relation to 
3D databases pertaining to architectural systems and urban 
aggregates. This possibility for reverse modelling in terms of 
historical architectural heritage allows for revising the 
documentation protocols in a field of application of 
representative systems for structural diagnostics, to aspire to 
technical-professional adoption in the interface with mesh-to-

 

Figure 12. NURBS modelling of the pavilion vault from the sections extracted 
by the mesh surface. The geometric vault was referenced to the mesh model 
and was imported in the same workspace. 

 

Figure 13. Deviation computing on the shape features between the models of the pavilion vault, from the HD mesh and from the NURB modelling. The colour 
map defines a quantitative reading of the deformed portions from the static configuration, highlighting the kinematic mechanisms that are affecting the vault. 
From the comparison, it was possible to identify the areas of instability and to derive diagnostic considerations in relation to the overall static schemes of the 
architectural complex as a whole.  



 

ACTA IMEKO | www.imeko.org March 2021 | Volume 10 | Number 1 | 96 

FEA and mesh-to-BIM protocols. Despite the national risk, the 
lines applied in the digital documentation demonstrate an 
attempt to adapt to the provisions of the Digital Agenda 2020 of 
the European Commission (also included in the Agenda Culture 
2030), regarding the digitation of cultural heritage initiatives for 
the planning of intervention, restoration, and conservation. With 
the possibility of experimenting virtually within a simulated but 
reliable space, the methods and effects of a subsequent physical 
implementation of the intervention for heritage buildings 
emphasises the opportunities for digital preservation and 
eGovernance, expanding the ideas of innovation in relation to 
the type and quality of structural survey products in terms of the 
curation of digital assets and advanced digitisation. The action of 
'structural' documentation, including the knowledge of stress 
behaviours and the prediction of damage mechanisms in 
buildings, can thus be identified within the European guidelines 
for heritage at risk by insisting on the characteristics of 
robustness. 

ACKNOWLEDGEMENTS 

The editorial authorship is granted to Sandro Parrinello for 
sections 1, 3 and the conclusions, and to Raffaella De Marco for 
sections 2, 4 and 5. 

The documentation of the Upper Kama Region is part of a 
wider program of activities carried out, since 2013, by DAda-
LAB - University of Pavia (coordinator prof. S. Parrinello) and 
the Perm National Research Polytechnic University (coordinator 
prof. S. Maximova). The digital survey campaigns of 2018 and 
2019 were conducted by Parrinello S., Picchio F., De Marco R., 
Dell’Amico A. Part of the architectural survey documentation 
data was processed as part of the activities related to the course 
entitled ‘Architectural survey & restoration’ (prof. S. Parrinello, 
prof. G. Minutoli) in the Double Degree Italian/Chinese course 
in Building Engineering and Architecture at the University of 
Pavia. 

The surveying, documentation and modelling of 
Blagoveshchenskaya Church are part of the EU project, 
PROMETHEUS. This project is funded by the EU program 
Horizon 2020-R&I-RISE-Research & Innovation Staff 
Exchange Marie Skłodowska-Curie and involves the 
collaboration between three universities (University of Pavia, 

Italy, Polytechnic University of Valencia, Spain, Perm National 
Research Polytechnic University Perm National Polytechnic 
University Research, Russia) and two companies (EBIME, Spain, 
SISMA, Italy).  

This project has received funding from the European Union’s 
Horizon 2020 research and innovation programme under Marie 
Skłodowska-Curie grant agreement No 821870.  

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http://dx.doi.org/10.1193/1.1623497
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http://www.leviedeimercanti.it/proceeding-x-forum/