Facade of San Petronio

April/October 2013
Factum Arte
scanning in high resolution the sculptural works of the
Facade of San Petronio
Porta Magna
Porta Magna: Jacopo della Quercia.
In red the zones that have been scanned.
Porta Destra
Porta sinistra: The Resurrection of Christ.
Porta Sinistra
In red the zones that have been scanned.
Porta destra: The Entombment of Christ.
In red the zones that have been scanned.
Scanning systems
Scanning has been realized with different resolutions thanks to the use of three complementary white light systems.
Sidio scanning system: used resolution 75 microns, 135
microns, 250 microns
Breukmann scanning system: used resolution 250
microns
David scanning system.
Most of the tiles were scanned with this system.
The Sidio systems are being used by Factum Arte
for 10 years.
The scanner was used during the final part of
the work on the facade; the Breuckmann is
more suitable for the scaffolding conditions,
lighter and easier to handle, also it limits risks
of vibration during the scanning.
This small scanner permits scanning parts which
would be impossible to reach with the other two
systems due to their size and the depth of field
needed by the optical systems of Breukmann and
Sidio. The David is surely less precise but still
offers the possibility of filling the missing parts,
retrieving at least the actual form of the scanned
object.
Sidio scanning system
The Sidio scanning system is a white light 3D scanner; the machine
projects linear patterns of shadow and light on the surface which permit the software to identify the different depths of the object. The nocontact technology allows to obtain a precise model of the scanned
surface without damaging the piece of art.
The Sidio system needs also two external projectors to scan. Thanks
to that it is possible to visualize on the surface the parts already
been scanned from the system. These references are also used by the
software to pre-aligning the different shots which will form the final
cloud point.
Patterns projected on the surface.
The projection of the reference light of the projectors on a “Formella” of the arch of
the left door and the visualisation of the scanned face of San Petronio in the scanner’s software.
Scanning one of the pilasters of the Porta Sinistra.
Scanning the architectural details of one of the pilasters of
the Porta Destra and of one of the tiles of the arch.
Scanning the tiles of the left arch.
Scanning one of the sculptures of the Porta Sinistra.
Image of the scanning of the turban of San Giuseppe, from
the statue of The Entombment of Christ, by Amico Aspertini.
The turban, removed during the restoration, was
scanned separately making it possible to scan it
entirely.
The turban scanned at the resolution of 135 microns.
Different colours identify the different shots
needed to scan the object. In this image are just
pre-aligned as to make it possible to the operator
to know which parts of the surface have already
been scanned.
Scanning of the faces of San Petronio and Madonna con
Bambino, Jacopo Della Quercia, Porta Magna, scanned at
the resolution of 75 microns.
Scanning of the faces of Christ and San Giuseppe, Amico
Aspertini at the resolution of 135 microns.
Scanning of two of the tiles of the Porta Destra at the resolution of 250 microns.
Breukmann scanning system
The Breukmann scanning system is a white light scanner also projecting light and shadow patterns on the surface. Thanks to a pair of optical sensors placed with two different angles of incidence, this system
allows to scan areas which are invisible to the Sidio scanner, that only
has a single optical sensor.
Unlike the Sidio scanner, this projector is analogic and the patterns
are produced from a set of flipping slides.
In the Breukmann software the pre-alignment is being done manually. Each scan needs to have an overlap with the next one. In that way
the operator locates 3 points in common between the two scans and
manually aligns them. Visualizing the point cloud as a 3D image allows the operator to be aware of the evolution of the scanning work.
The patterns projected on the surface of the stone.
The scanned object visualized by the two cameras of the scanner in the Breukmann
software.
One of the cantilever of the Porta Magna, scanned at the
resolution of 140 microns.
One of the “formelle” of the Porta Sinistra scanned at the
resolution of 250 microns.
One of the “formelle” of the Porta Sinistra scanned at the
resolution of 250 microns, point cloud.
David scanning system
This scanning system was acquired in order to test the progress of a
mass produced equipment widely accessible on the market at a lower
price than the professional scanners. This is a white light system too
and therefore it is a no-contact one. Thanks to the size of the scanner
it is possible to access areas which would be impossible to reach by
the other two systems.
The David scanner software has a limited memory and therefore it
is not possible to scan big surfaces. The scanner is useful for obtaining information mostly about the shape of the object rather than the
surface but it is a good complementary solution in combination with
the more precise systems.
The pattern projected on the surface of the stone.
The scanned object visualised in the David software.
Photographic Documentation
A very detailed photographic documentation has been realized for
every tile and sculpture on the facade. The photos taken from different angles will help in the integration of the 3D models and they provide a precious documentation of the actual condition of the facade.
The photographic documentation provides important information
about the chromatic features of the art works but also about the conservation state of the sculptures and the reliefs.
Details of two “formelle” of the arch of the Porta Magna, Prophets, Jacopo della
Quercia.
Details of one of the “formelle” of the half pilaster of the Porta Magna, Jacopo della
Quercia.
One of the “formelle” of the arch of the Porta Magna, Prophets, Jacopo della Quercia.
The case of the Christ’s arm by Amico Aspertini
The Entombment of Christ, work of Amico Aspertini, picture taken before the restoration.
The Entombment of Christ, work of Amico Aspertini, picture taken during the restoration.
Image of the scanning of the same composition of Amico
Aspertini.
Porta Destra, The Entombment of Christ, of Amico Aspertini, detail of the broken part of the left arm of the Christ.
Picture of the detached arm of the sculpture.
Scanning the arm on site, on the scaffold of San Petronio.
The left arm of the statue “The Entombment of
Christ” by Amico Aspertini has been removed
for security reasons. Due to the bad conservation
state of the arm, it has been impossible to reattach
the original piece.
On the surface of the arm it is possible to identify
the various restoration phases done during the
past years. Different materials have been used for
the gluing of the fragments, like resin and mortar.
Some of the resins have made some parts of the
surface translucent and therefore impossible to
scan with a white light system scanner.
The scanning has been carried out in different
sessions in order to collect the biggest possible
amount of information present on the surface of
the arm.
A 360 ° model of the arm, scanned at the resolution of 135
microns.
Working closely with the restorers has permitted us to be present during crucial moments of the restoration. The Opificio delle Pietre Dure commissioned to
Factum the reproduction of the arm of the statue “The Entombment of Christ” by Amico Aspertini.
Scanning of the forearm.
Virtual reintegration of the arm.
Virtual view of the point of the attachment of the arm.
Also the part of the forearm of the Christ was
scanned at the resolution of 135 microns to permit
the perfect corresponding of the two surfaces.
Before creating the real model the precision of the
3D model has been virtually checked thanks to
the alignment software of the point cloud and the
processing data.
The scanning also allowed us to determine the orientation of the brass pivot which joins the original
arm to the forearm.
During the modelling process it has been also
modelled the entry channel in which the glue will
be injected and the space for the quartering of
the pivot with the exact inclination. This makes
possible to use a steel pivot to link the two parts
without damaging further the statue.
Fit trial of the modelled arm.
Using as a prototype the original part and with the data of the 3D scanning, a silicone mould has been made which will allow us to recreate
the arm on marble, adding pigments for a facsimile as closer to the original as possible. The facsimile will be lighter than the original one
and with higher resistance to the atmospheric agents than the one made by stone. This allows the preservation of the original arm avoiding
further damages and also gives the possibility to study it in order to avoid similar problems.
Fitting of the prototyped arm.
The modelled arm has been already prototyped.
The model has been recreated with the use of a very
precise 3D printer which allowed the production of a
very accurate copy of the original arm.
Detail of the entrance hole for the glue that will be use to
reattach the facsimile of the arm back to the statue.
Process of creating the facsimile.
Thanks to the resin 3D printed prototype a silicone mould has been created which will make possible to create an accurate reproduction on a material which is
as closer as possible to the marble of the statue.
The photo of the facsimile in this page is only a test as the final facsimile will be casted by the Opificio delle Pietre Dure with Acristal resin and Carrara marble,
adding also colour pigments which will help to achieve the actual chromaticity of the sculpture.
Virtual visualisation of the scanned art works
Points cloud:
This is the direct output of the scanner. The positioned points in the three-dimensional space coincide with
the scanned areas. The points cloud is a format adequate to be used in the future in case of an improvement
in the field of processing data technology and that is because it is nothing more than points in the space.
Mesh:
The mesh is created by an algorithm using a triangulation system based on the points cloud. In this way the
software creates the 3D surface coinciding with the points cloud.
Holes:
The white light scanner uses an optical system and one projector of light positioned with a angle of incidence
between them; for this reason some parts of the surface are invisible to the scanner and therefore in the scans
some blanks/gaps remain while recreating the 3D model during the first part of the process.
Filling:
To create a model without blanks/gaps, Factum Arte has managed to develop a system able to recognise and
process the replenishments necessary to complete the surface, keeping the model intact and not modifying
the original information on the real surface of the object.
The different colours identify the different scans which were
necessary for completing the scanning of the whole “Formella”.
Visualisation of the same “Formella” in the processing data
software.
Rendering of the same figure.
Render of the central figure of
the Porta Sinistra arch.
Render of one of the “formelle”
of the Porta Magna main
pilaster, work of Jacopo Della
Quercia.
Renders of some of the “formelle” of the right Pilaster of the Porta Destra.
For the visualisation of the scanned art works it has been used a totally neutral texture. The white colour offers a clear view of the surface of the stone without
distractions due to its chromatic variations.
The 3D images of the rendered model permit to see the work from a unique point of view which otherwise will be impossible to recreate once the scaffolding will
be disassembled.
The plaster casts of the Victorian Age
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Porta Magna.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Porta Magna, scanning at the resolution of 250 microns.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Porta Magna, plaster cast reproduction of Oroinzio Lelli.
In 1886, during the Victorian Age, Oronzo Lelli mold the plaster casts of the sculptures on the Porta Magna of the facade of San Petronio, a work of Jacopo della
Quercia. Through a comparative analysis it is obvious that the copies do not coincide completely to the original “formelle”; the moulds had been casted in a short
amount of time and for this reason were finalized by hand, adding some details which did not exist in the original works.
Thanks to a comparison with our scans we were able to define that our collected data are instead more accurate to the originals.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Porta Magna, plaster cast reproduction of Lelli.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Porta Magna, scanning of the plaster cast reproduction
of Lelli.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Porta Magna.
To complete our research we thought it was a good idea to scan Lelli’s reproductions as to be able to compare them with our scans of the original works. Even
only through a visual analysis it is obvious that Lelli’s reproductions are very diverse from the originals, as explained in the images above; for example there is no
accuracy in the donkey’s face or in the angel’s face at the left corner.
With naked eye the demarcation can be difficult due the big quantity of chromatic information which is present on the surface of the reproductions, clearly no
existent in the Candoglia’s marble, which is instead famous for totally different chromatic features. For this reason we have made once again a comparison with
the rendered images, removing any chromatic information and focusing in the plain surface and texture.
Visualization of the original “Formella” in the data processing program and a render of the same piece.
Visualization of the casted “Formella” in the data processing
program and a render of the same piece.
Plaster cast of the Porta Magna, Oronzio Lelli 1886, Victorian Albert Museum, London.
Factum Arte thanks: the Basilica of San Petronio, the Studio Cavina Architetti, the Opificio delle Pietre Dure and mostly Don Oreste for making this project possible.
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