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The research deals with the different image vectorialization techniques for the development of reliable drawings on mosaic systems. Following the restoration of the floor mosaics of the Basilica of the Nativity in Bethlehem, surveys were conducted with digital technologies that produced a 3D database on considerable mosaic surfaces. The problem of the graphic representation, linked to the drawing of these systems, concerns both the optimization of the methodological processes in advantage of a more performing drawing activity, and the definition of the appropriate languages to satisfy requirements related to the documentation and the work restoration. Technical drawers have worked alongside restorers to produce technical drawings and a model to interact with the mosaic system, developing an informative model that can facilitate construction activities and, at the same time, enhance the entire artwork.
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SCIentific RESea rch and Info rmation Technology
Rice rca Scie ntifica e Tecnologie de ll'I nformazione
Vol 9, I ssue 2 (2019), 95-104
e-ISSN 2239-4303, DOI 10.2 423/i22394303v9n2p95
Open acces s ar ticle licensed under CC -BY-NC-ND
CASPUR-CIB ER Publishing, http://www.sciresit.it
VECTORIALIZATION PRACTICES OF THE IMAGES DRAWING OF THE FLOOR
MOSAICS OF THE BASILICA OF NATIVITY IN BETHLEHEM
Sandro Parrinello*, Silvia La Placa*
* Department of Civil Engineering and Architecture (DICAr) Pavia, Italy.
Abstract
The research deals with the different image vectorialization techniques for the development of reliable drawings on mosaic
systems. Following the restoration of the floor mosaics of the Basilica of the Nativity in Bethlehem, surveys were conducted
with digital technologies that produced a 3D database on considerable mosaic surfaces. The problem of the graphic
representation, linked to the drawing of these systems, concerns both the optimization of the methodological processes in
advantage of a more performing drawing activity, and the definition of the appropriate languages to satisfy requirements
related to the documentation and the work restoration. Technical drawers have worked alongside restorers to produce
technical drawings and a model to interact with the mosaic system, developing an informative model that can facilitate
construction activities and, at the same time, enhance the entire artwork.
Keywords
Mosaics Survey, Digital Documentation, Vectorial Drawing, Interactive 3D model, Church of Nativity
1. Introduction
With the aim of structuring a methodology for
the digital documentation and management of
mosaic assets, this research deals with the issue of
automation in the graphic restitution processes
experimented on the case study of floor mosaics of
the Basilica of the Nativity in Bethlehem.
1
The project, conducted by the DAda-LAB
laboratory of the University of Pavia, is regulated
by an agreement with Piacenti S.p.A., the company
charged of the monumental complex restoration
activities. The objective is the definition of reliable
drawings able to reproduce the individual tiles of
the mosaic system on a 4:1 scale to support
analysis, critical interpretations and thematic
drawings useful for the restoration process.
The survey campaigns, conducted in December
2018 and August 2019, have interested the use of
several digital instruments to verify the quality of
the different data acquisition methods, compared
in an integrated survey system
2
(Bertocci, 2006).
1
The paragraphs 1; 2; 3; 6; are due to Sandro Parrinello. The
paragraphs 4; 5, are due to Silvia La Placa.
2
The digital survey activities, conducted by the Dada-LAB
team of researchers Picchio, De Marco and Doria, saw the use
Following the two survey campaigns, in order
to develop a rapid and reliable digital
reconstruction of the decorative apparatus, ortho-
images vectorialization processes of the mosaic
system have been performed, obtaining reliable
drawings and graphic representations for the
computation of the mosaic tiles. At the same time,
the research activities concerned the creation of a
reliable 3D model of the mosaic system and of the
adjoining architectural apparatus in order to allow
the operator to virtually interact with the
individual tiles and to understand the spatial
qualities in relation to the context (Adami, Fassi,
Fregonese & Piana, 2018).
These procedures, which have generated a
functional documentary corpus to the graphic
database of the important ornamental apparatus,
intends to qualify the operational protocols for the
structuring of a survey methodology. Moreover, in
graphic restitution practices, the updating of
language in the digital environment has involved a
reflection on signs, symbols and different levels of
headwords functional organization.
of Laser Scanner technology (FARO FOCUS S 150 of FARO) and
digital photographic instrumentation (Canon EOS 77D with
fixed focal length 18 mm and SONY alpha 6000 with 24mm
fixed focal length).
(2019), n. 2 S. Parrinello, S. La Placa
96
The new design meets the growing
documentary and management requirements, for
3
About the cultural addresses that have guided restoration
practices and in particular the different opinions on the
treatment of gaps and pictorial reintegration.
conservation and, generally, for the enhancement
of the heritage (Fig. 1).
2. The digital representation of mosaic systems
The documentation of mosaic works generally
involves the use of digitization technologies
combined with non-invasive diagnostic analysis.
This integration had required drawings and
graphic representations to define the areas subject
to different pathologies with relative precision, to
combine the metric information with other
qualitative data useful for the definition of some
aspects, such as color necessary to represent the
decoration and the ornament in the mosaic layout.
Measurement practices thus follow the
evolution of the reading methodologies for the
image complexity in terms of reliability of the data
acquired, conservation and restoration of surfaces
(Cantisani, Garzonio & Tucci, 2006) (Monti &
Maino, 2012).
The drawing becomes the container of
construction and restoration site, where different
activities are both marked of cleaning and pictorial
reinstatement of the ornamental apparatus. For
this operation, which has undergone several
critical orientations over the last few decades
3
(Fiori & Vandini, 2002), the survey outputs
become the fundamental tool thanks to which the
restorer can perform his own functional
interpretations to understand the integrity of the
work. Moreover, architectural contexts, in which
such decorative systems are located, are often
characterized by numerous criticalities that
influence the understanding and general state of
conservation of the mosaic. The ancient mosaic,
when it is located in its original architecture, is
often subject to an irregular background linked to
the failures that occurred over time (Tucci, Bonora,
Crocetto, Nobile, & Al Turk, 2010). For these
reasons, the analysis cannot ignore, as is obvious
for any cultural asset, an examination of the
relations that connect the mosaic to the context
(Brumana, Fregonese, Monti, Monti, Monti & Vio,
2007) (Adami & Fregonese, 2018). At the same
time, those relations characterize the components
that determine its image, thus defining a
hierarchical structure of relations to which the
document process must be able to respond
4
(Norberg-Schulz, 1992; Parrinello 2013).
4
The environmental levels, as described by C. Norberg-
Schulz, qualify a hierarchy of sets for which it is possible to
define relational domains. These characterize a structure that
Fig. 1: The floor mosaics in relation to the Basilica of the
Nativity main nave
(2019), n. 2 Vectorialization practices of the images
97
The systematic knowledge of the artwork
starts from an analysis process that defines the
documentation and survey project. The
morphological knowledge requires the application
of digital technologies to be able to successfully
configure different reading scales. These are, in
particular, a detail scale (Fig. 2) in which it is
possible to understand the tiles geometries and
materials, and a larger scale, which contextualizes
finds correlation with that of research, in which the objectives
of the analysis strategies correspond to the descriptive needs
of the relationships identified for the characterization of the
different levels.
the mosaics within the architecture that houses
them and describes the elements represented
(Manferdini, 2010).
In the design of the mosaic the high number of
tiles involves a very onerous process, in terms of
time and of reviewing the contours of each piece.
The attempt to automate this procedure is
considered one of necessary objectives to ensure
that this design and documentation practice is part
of the usual process on mosaic apparatus studies.
The automatic vectorialization of the images aims
at reproducing the geometry and the drawing of
the tiles, in order to obtain a 2D drawing from
which it could be possible to carry out a
computation for the restoration and a 3D
reconstruction for a more effective understanding
of the work in relation to the surroundings.
3. The floor mosaics of the Basilica of the Nativity
The first Nativity factory, dating back to the
time of Constantine, had a floor decorated with a
mosaic carpet that in later centuries was covered,
raising the floor of the Basilica. The decorative
apparatus was discovered in 1934 by the
Englishman William Harvey, during an excavation
campaign conducted following the restoration of
the complex. It was then covered after its
decorative perimeter was accurately documented
with photographs and drawings (Madden, 2012).
In recent years, during the restorations
conducted on the roofs and on the wall facings
5
(Bertocci & Parrinello, 2015), the mosaics were
again excavated to assess the overall integrity and
the state of conservation of the tiles, thus initiating
a restoration process aimed at defining a solution
that would allow the visitors to appreciate the
original drawing of the Basilica.
On the sides of the central nave there are two
large trapdoors through which it is possible to
observe the fragments of the mosaic and
appreciate the general layout, that measured
about 16.36 x 6.80 m. The overall design had to
present two distinct carpets: the first, to the west,
of 6.50 x 6.80 m, with a series of intertwined
medallions, acanthus leaves and plant motifs on a
black background; the second, of 9.86 x 6.80 m,
comprised six square panels adorned with
geometric motifs and a wide range of colors.
5
Since 2013, restoration has been carried out on the roofs, on
the walls and on the mosaic complexes. The Dada-LAB
Research Laboratory immediately collaborated with Piacenti
S.p.A.
Fig. 2: Details of the floor mosaic
(2019), n. 2 S. Parrinello, S. La Placa
98
Since the central portion of the plant has been
lost, it is possible to read only a few portions of the
six panels belonging to the second carpet: the first
one divides squares into swastika motifs; the
second alternates octagonal figures with square
shapes; of the two centrals it is possible to read
only the upper one, representing a round
medallion, with triangular and intertwined motifs,
and the same medallion decoration is visible in the
oriental panels, decorated with complex rings (Fig.
3). Further portions of the floor are visible in the
easternmost area of the central nave, in the
northern arm of the transept and in the south nave.
These panels show plant and zoomorphic motifs
on a white background and, in comparison with
the carpet of the central nave, have free decorative
layout without borders.
Qualitative differences are visible in the tiles
layout: those that constitute backgrounds or
borders are more spaced apart, while the designs,
both geometric and organic, are made with smaller
tiles, closer together. These density variations
have conditioned the graphic restitution project. If,
from one side, the greater thickness of the mortar
between one block and the other facilitated the
6
To improve the management of the levels, the color of the
digital tiles is standardized with reference to the natural
aspect, considering however all the present nuances.
7
In order to obtain a high quality of the photographic data,
during the survey campaing the mosaic was divided into
portions of 15x15 cm, 30x30 cm and 45x45 cm (based on the
complexity of the drawing) by affixing wires over tiles,
arranged from side to side. This grid allowed us to codify each
automatic recognition of the edges with the image
vectorialization on the other side, due to more
decorated areas, with a greater density, this
procedure has been more complicated, also
because of the chromatic variety that imposed a
color coding.
4. The mosaic drawing
Following the acquisition phase, once the
mosaics materic drawings were recomposed, the
goal was to get a vectorial drawing where the
minimum element was identified by a closed
polyline, corresponding to the contours,
differentiated in terms of layer in relation to the
color of the tile
6
.
The point cloud of the Laser Scanner survey
was subdivided by materializing the mosaic
partition, defined in the survey campaing during
the shooting phase
7
. This process has facilitated
the management of the post-production
procedures and of the structuring of an orientation
code of the different s useful for storing data.The
entire mosaic apparatus has been recomposed
through present equal ortho rectified portions of
15x15 cm, 30x30 cm or 45x45 cm, in relation to the
complexity of the layout design and to the
chromatic variations, rich in criticality for edge
detection software (Di Blasi & Gallo, 2005).
Bitmap graphics softwares has been used,
suitable for photo editing, integrated together to
improve their functions (Monti & Maino, 2012)
and using Adobe Photoshop and Lightroom
softwares, the images were adjusted by changing
the tonal values, exposure and the brightness
8
.
Once the images have been optimized in terms
of colors and contrasts (Fig. 4), different
vectorialization software have been evaluated by
comparing the time procedure and the result.
Adobe Illustrator has been chosen for the
possibility to interact with different formats both
inbound and outbound. By adjusting the tolerance
values, thresholds and traces, it has been possible
to isolate the contours of the individual tiles.
Thanks to this, it has been possible to define the
settings according to the different types of tiles,
color, and the lighting conditions, which allowed to
portion, photograph it separately from the others and
obtaining images of great precision and sharpness.
8
Working with the "curves" tool it was possible to adjust the
color dominants for the tiles that had different balance and
brightness for light problems that could not be solved during
the acquisition phase.
Fig. 3: Details of the second carpet scores
(2019), n. 2 Vectorialization practices of the images
99
automate the process thanks to the activation of
precompiled actions.
On one side, the contrast between the dark tiles
(that go from shades of red, to brown until black)
the mortar made the edges easily identifiable, on
the other side, for the lighter tiles (from white to
yellow, to ocher, to pink) the difficulty of
vectorialization required a more complex image
calibration phase. By changing the exposure,
contrast and curves relative to the brightness
values of the tonal range or the individual color
9
The procedure carried out on Adobe Illustrator for white
tiles is the same as for colored portions. The difference is
found only in the management of the threshold instrument:
the setting of a higher threshold level enhances the portions
that are better lit and the tiles with clearer colors; at a lower
channels the tonal values are transformed to make
the tiles completely white and darken the mortar
(Fig. 5). By importing the calibrated image onto
Illustrator, it is possible to visualize only the edges
of the tiles (view contours), adjust the number of
tracks and the disturbance (looking at the
preview), increase or consider the percentage of
corners (set a 0% for greater tiles cleaning,)
through the "trace" tool. Last, it is necessary to
raise or lower the threshold levels, which will be
different for each file
9
. The vectorial image of each
closed boundary tiles obtained can be exported as
a dwg file and opened on AutoCad software. The
file is constituted of Splines, which must be
converted into Polylines to optimize the work in
the subsequent phases.
It is necessary to consider that each tile, during
the automated process, was traced with Spline
overlays by the Adobe Illustrator software
(according to the settings set manually) to ensure
greater accuracy of the final result. This has
generated a certain amount of duplicate elements
in the dwg file that weigh it down in terms of file
size (Fig. 6) (Parrinello & Picchio, 2019).
For each color of the tiles, a corresponding
layer has been created to facilitate computations
and to restore the mosaic representation, even
with chromatic simplifications (Fig. 7).
The applied methodology has produced valid
automation results, although in some cases it was
necessary to integrate the design manually always
working on the source photo by subtraction,
eliminating the mortar from the images, selecting
level corresponds a better reading of the dark tiles. It is
therefore advisable to repeat the process several times,
setting different levels, for each mosaic portion with a wide
chromatic range.
Fig. 5: The white tiles modified to improve the contrast of
the edges
Fig. 4: Detail of the portion of source and modified orthophotos
(2019), n. 2 S. Parrinello, S. La Placa
100
it or deleting it, to then proceed with automatic
vectorialization (Figg. 8-9).
5. Tridimensional modelling
The mosaic drawings have an intrinsic 3D
structure due not only to the tile itself, but also to
the reciprocal position and orientation of these.
The tiles together with the mortar, affected by the
light, give rise to the visual perception of the
mosaic complex (Rivola, Castagnetti, Bertacchini,
& Casagrande, 2016).
This drawing perception, performed on a floor
surface, is also due to the tiles non coplanarity and
Fig. 7: Mosaic reproduced on AutoCAD
Fig. 6: Vectorialization process of the image in Illustrator
(2019), n. 2 Vectorialization practices of the images
101
their inclination which produces light refraction
effects. The thickness of this decorative apparatus,
although minimal, needs to be represented to
ensure a correct reading of the artwork.
The 3D drawing representation aims to
highlight the cognitive data obtained from the
mosaic documentation. Through this visualization
it is possible to obtain immediate reading of the
information content of the model itself. The
researcher is thus facilitated in the understanding
of the analyzed work, just as the restorer is
facilitated in perceiving the information related to
geometry and forms (Limoncelli, 2011).
Digital technologies offer important
perspectives for the graphic rendering of
historical-cultural value artworks. These
technologies are valid especially when they are
applied to artworks, such as the case study treated,
not accessible to the public for conservative needs.
Plants and general sections of the mosaic have
allowed to return the information concerning the
excavation (content, depth, width, length,
Fig. 8: Orthophoto and drawing of the mosaic reproduced on
AutoCad
Fig. 9: Drawing of the mosaic reproduced on AutoCad
(2019), n. 2 S. Parrinello, S. La Placa
102
deformations, etc.) and these graphic drawings,
imported on the Rhinoceros modeling software,
have constituted the prerequisite for the
development of a reliable prerequisite for the
development of a reliable model system.
A first phase saw the return of the excavation
and the laying surface of the tiles. The mosaic
height differences were approximated using the
"multipick" command from Leica Cyclone software
and selecting over 290 control points from the
point cloud. From these points a nurbs surface was
reconstructed using the Patch command of
Rhinoceros (Fig. 10).
During a second phase on this surface the tiles
of the vector mosaic drawing were projected and
extruded. The 3D graphic representation, based on
chromatic intervals, provides defined and
readable information on the drawing, position and
quantity of the tiles present in the mosaic complex
(Fig. 11). The choice of operating with the
extrusion method, which involves the loss of
information in terms of individual inclinations and
deformations of the tile, has allowed us to obtain a
3D model useful for computation and effective
representation of the artwork.
The union of the 3D model of architectural
apparatus portion affected by the excavation with
the mosaic tiles applied to the pavement, gives
consistency to a digital object that is easy to read
and interpret. The simplification made allows
therefore a complete visualization of the
apparatus and not only of some of its portions,
bringing the further advantage of a much lower
weight compared to that obtainable by modeling
the single tile. The model, which is informative and
communicative, can also be used for informative
projects, as well as being implementable from the
point of view of interaction, multimedia and
virtual reality for digital use.
6. Conclusion
The two-dimensional (Fig. 12) and three-
dimensional digital drawing created meet the need
for computation and planning of restoration
processes, maintenance control as well as being
usable also for the creation of digital information
archives. The digital models, or more often
portions of them, can also find material
concreteness, configuring themselves as specific
communicative supports, to be realized with a
view to a more inclusive use of the heritage
(Rivola, Castagnetti, Bertacchini & Casagrande,
2016).
Fig. 10: Elevation map of the mosaic from the cloud of laser
scanner points for the analysis of the height differences of
the mosaic surface
Fig. 11: 3D model of the mosaic
(2019), n. 2 Vectorialization practices of the images
103
In this direction, some 3D prints of a portion of
the mosaic were produced, evaluating the
representative effectiveness on supports such as
wood and plexiglass. The impression of the laser
cut was defined by the pigmentation of the single
mosaic tile and a lighter pigment (white tiles)
corresponded to a smaller incision of the edge,
while to the darker tiles corresponds a greater
impression, to reach a depth of about 3 mm (black
tiles).
The mosaic model can be configured as an
additional opportunity for an independent and
inclusive use of the work, developing tactile maps
and relief models and preparing scenarios in
which the mosaic can exit the basilica to
characterize exhibition and installations,
becoming an element that, between reality and
virtual, manages to create new opportunities for
knowledge.
Fig. 12: Complete mosaic drawing
Fig. 12: Detail of the portion of source and modified orthophotos
Fig. 13: 3D printing of the digital file
(2019), n. 2 S. Parrinello, S. La Placa
104
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... Starting from this segmentation, it is possible to proceed with a semi-automatic mode, in which the obtained contours are vectorized: in this phase, the operator is required to control specific parameters, such as "threshold", "paths" and "noise", that are used by vectorbased software to process the given image and generate corresponding paths [20]. ...
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The floor of Florence Cathedral, result of contribution of numerous craftsmen, shows excellent decorative pattern realized through “white and stained marbles” of different provenance. The relief project, obtained by digital correction of images acquired with high resolution, allows the cataloguing of used lapideous stones and the quantification of their areal extension. The recognition of material is based on macroscopic observation and for each element a data sheet containing dimensional, classificative and conservation state’s informations is produced. For the study of the state a conservation, methods able to evaluate altimetric variations will be used. Scanner system and ortophoto are very useful for the study of planarity defects and erosion state. These methods allow to know the general state of conservation of the whole floor and, in particularly, to define the lithotypes that will need major attention, above all regarding the erosion phenomena, determined by the presence of a huge number of visitors. These information can be useful for the planning of the conservation intervention and for the a sustainable use of the Cathedral.
Conference Paper
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Le superfici musive e lapidee, generalmente complesse e riccamente decorate, necessitano di rilievi multiscala che possano da un lato documentare dettagliatatamente la consistenza geometrica e materica, dall’altro contestualizzarle all’interno delle strutture architettoniche che le contengono. In accordo con la Direzione Generale delle Antichità e dei Musei del Ministero della Cultura siriano, sono stati effettuati rilievi metrici con sistemi a scansione ed immagini digitali ad alta risoluzione, presso il mausoleo del Sultano al-Zahir Baybars in Damasco. Lo spazio analizzato, quadrangolare e coperto da una cupola, è rivestito di marmi colorati e mosaici tipici dello stile architettonico mamelucco. Nel presente lavoro si intende valutare potenzialità e limiti delle nuove tecnologie applicate alla documentazione e al progetto conservativo di opere d’arte musive e più in generale, di paramenti e superfici architettoniche.
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Mosaic’s virtual restoration - Information technologies are increasinglyand usefully applied to the study and conservation of culturalheritage. In this paper we present three different applications ofcomputer science techniques to cataloguing and documentation ofmosaic materials: the multimedia database of the InternationalCentre for Documentation on the Mosaic of Ravenna, the virtual restorationof the mosaics of Ravenna cartoons and three-dimensionalrelief of the mosaic by 3D laser scanner.
Porti e città fortificate in Terrasanta: modelli e tecnologie attraverso il Mediterraneo all'epoca delle Crociate
  • S Bertocci
Bertocci, S. (2016). Porti e città fortificate in Terrasanta: modelli e tecnologie attraverso il Mediterraneo all'epoca delle Crociate. In G. Verdiani (Ed.), Defensive architecture of the mediterranean XV to XVIII Centuries, Vol.IV, (pp. 443-452), Firenze, Italy: DidaPress.
Digital survey and documentation of the archaeological and architectural sities
  • S Bertocci
  • S Parrinello
Bertocci, S., & Parrinello, S. (2015). Digital survey and documentation of the archaeological and architectural sities. Firenze, Italy: Edifir.
Complex analyses of surface, modelling and comparison of the 3D orthophoto to the real scale with historical cartography: mosaic surface of basilica of
  • R Brumana
  • L Fregonese
  • C Monti
  • C C Monti
  • G Monti
  • E Vio
Brumana R., Fregonese L., Monti C., Monti C.C., Monti G., & Vio E. (2007). Complex analyses of surface, modelling and comparison of the 3D orthophoto to the real scale with historical cartography: mosaic surface of basilica of San Marco in Venice. e-Perimetron, 2(4), 224-244.
Teoria e tecniche per la conservazione del mosaico
  • C Fiori
  • M Vandini
Fiori, C., & Vandini, M. (2002). Teoria e tecniche per la conservazione del mosaico. Padova, Italy: Editore Il Prato.
Applicazioni digitali per l'archeologia: il restauro Virtuale. DigItalia
  • M Limoncelli
Limoncelli, M. (2011). Applicazioni digitali per l'archeologia: il restauro Virtuale. DigItalia, 1, 42-59. Retrieved from http://www.digitalia.sbn.it