Facade of the Basilica of San Petronio

April/October 2013
Factum Arte
High-resolution scanning of the sculptural works on the
Facade of the Basilica of San Petronio
Constantly updating: http://www.factum-arte.com/pag/593/The-Church-of-San-Petronio
Main Door
Main Door: Jacopo della Quercia.
The areas highlighted in red indicate the areas that have been scanned
Left Door
Left Door: The Resurrection of Christ.
Right Door
The areas highlighted in red indicate the areas
that have been scanned
Right Door: The Entombment of Christ.
The areas highlighted in red indicate the areas
that have been scanned
Scanning systems
The scanning has been carried out at different resolutions using three complementary white-light 3D scanning systems.
NUB 3D Sidio scanning system: used at three different resolutions: 75 microns, 135 microns, 250 microns.
Breukmann smart SCAN3D: used at a resolution of 250
microns.
David scanning system.
The majority the sculptural elements were
scanned with this system. NUB 3D are based in
Barcelona and Factum Arte has worked with their
systems for the past 10 years.
This light-weight versatile scanner was used
during the final phase of the work on the
facade; the Breuckmann is ideally suited to
work on scaffolding where a fast exposure is
essential to limit the effects of vibrations on the
data. This is a twin-camera scanner that is easy
to handle and operate.
This agile, low-cost scanner was used to record
areas that were otherwise inaccessable to the
Breuckmann and Nub 3D. Due to its size and the
shallow depth of field the David scanner had a
limited but important role. This is an inferior system in terms of its precision, however it helped to
complete any missing data. It was able to retrieve
the general form of the scanned object whilst sacrificing surface detail.
NUB 3D Sidio scanning system
The Sidio white-light scanner projects linear patterns of light onto the
surface of an object permitting the software to interpret the geometric
deformations over the surface. This non-contact technology facilitates
the capture of a precise model of the scanned object. No markers or
external reference points are attached to the object.
The Sidio is a single-camera system linked to a projector which in
turn is
connected to two external projectors (markers) that locate and register
the scanned area. The projectors enable the user to visualise the parts
that have been successfully captured. The markers are also used to
pre-align the different 3D images which are used to generate the final
cloud point.
Patterns projected on the surface.
The projection of a green reference marker is an aid to ensuring that the entire
surface has been captured.
Scanning one of the pilasters of the left door.
Scanning the architectural details of one of the pilasters of
the right door and of one of the sections of the arch.
Scanning the tiles of the left arch.
Scanning one of the sculptures above the left door.
Image of the scanning of the turban of San Giuseppe, from
the statue of The Entombment of Christ, by Amico Aspertini.
The turban, belonging to the figure of San Giuseppe was removed during the restoration. This
was scanned separately making it possible to scan
it from all sides, top and bottom. There is some
evidence to suggest that it was put back in the
wrong position during the 1978 restoration. The
captured data will make it possible to evaluate
these claims.
The turban scanned at the resolution of 135 microns.
Different colours identify the different shots
needed to successfully scan the object. In this image they are pre-aligned to make it possible for the
operator to know which parts of the surface have
already been recorded.
Scanning of the faces of San Petronio and Madonna con
Bambino, Jacopo Della Quercia, Main Door, The faces and
hands of the main figures were scanned at a 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 smartScan is a white-light scanner that uses a projector to a pattern of light onto the surface of the object being recorded.
A pair of optical sensors placed with two different angles of incidence
record the pattern. This happens in a couple of seconds and significantly reduces the problems with vibrations that can happen when
recording at high-resolution on scaffolding. The projector is analogue
and the patterns are produced from a set of transparences.
In the Breukmann software the pre-alignment is 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 helps the
operator see areas that need attention or re-scanning.
The patterns projected on the surface of the stone.
The scanned object visualized by the two cameras in the Breukmann software.
Part of the Main Door scanned at a resolution of 140 microns.
Part of the Main Door scanned at a resolution of 250 microns.
Part of the Right Door scanned at a resolution of 250 microns.
David scanning system
This is a low-cost scanning system. Like the Sidio and smartSCAN it
is a non-contact white-light system. Thanks to the size and configuration of the scanner it is possible to access areas that are 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 areas at high resolution. The scanner is useful
for obtaining information about the shape of the object rather than
the complex surface. During the work on the façade of San Petronio it
has been used 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 detailed photographic documentation has been undertaken for
every section of the facade. The photos taken from different angles
help in the integration of the 3D models and provide an important
documentation of the condition of the facade.
Conbinationsof data of different types are intrinsic to Factum Arte’s
working methods. The photographic documentation provides important information that can be cross- referenced with the 3D data. This
can be about colour differences, restorations or the general condition
of the works.
Details of two sections of the arch of the Main Door: Prophets, by Jacopo della
Quercia.
Details of one of the half pilasters of the Main Door by Jacopo della Quercia.
One of the sections of the arch of the Main Door: Prophets
by Jacopo della Quercia.
Virtual visualisation of the scanned art works
Points cloud:
This is the direct output of the scanner. The positioned points within a three-dimensional space coincide
with the scanned areas.
Mesh:
The mesh is created by an algorithm using a triangulation system based on the point cloud. The software
generates a 3D surface coinciding with the point cloud- rather like dropping a piece of silk aver a frame..
Holes:
The white light scanner uses an optical system and a projector positioned with a angle of incidence between
them; for this reason some parts of the surface are invisible to the scanner and cannot be recorded . Repositioning the scanner can sometimes result in the gaps being filled with data.
Filling:
To create a model without holes, Factum Arte has developed a system that can recognise the gaps and generate a coherent surface All files are archived both with ‘holes filled’ and as raw data. It is essential that any
modification is transparent and does not obscure or alter the ‘original’ 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 arch of the left door.
Render of one of the panels of
main pilaster of the main door,
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 Main Door.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Main Door, scanned at a resolution of 250 microns.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Main Door, plaster cast reproduction made by Oroinzio
Lelli in 1886.
In 1886 the Victoria and Albert Museum in London commissioned Oronzo Lelli to make plaster casts of the sculptures by Jacopo della Quercia on the Main
Door of the facade of San Petronio. By comparing the casts made in the C19th cenury, with the original sculptures in their current condition and the 3D scans
made over the last 9 months some starting things emerged.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Main Door, plaster cast reproduction of Lelli.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Main Door, scanning of the plaster cast reproduction of
Lelli.
Detail: Birth of Christ, Jacopo Della Quercia, architrave of
the Main Door.
A plaster cast is a full contact recording. While it can damage the surface of decaying marble and will remove any traces of colour it should retain a true record
of the surface and shape of any sculpture. However the process of piece moulding is demanding and requires high levels of manual skill. Through a comparative
analysis it is obvious that the copies do not coincide completely to the original carvings and an experienced eye can easily find the joins of the piece moulds and
irregularities of the process. It appears that the moulds made by Lelli were done quickly with the intention from the start that the casts would be finished by hand
with a rasp- Resulting is a accurate sense of shape but a less exact record of the surface. Further distortions and deformations happen when making plaster positives and this can be seen as secondary moulds were made from the plaster casts.
The plaster casts are a great record of the condition of the facade in 1886 but they are a mix of objective accuracy and subjective interpretations. The same could
be said for the 3 D recordings that have recently been made of the sculptures that decorate the 3 main doors. While the 3D scans have recorded both the surface
and shape in remarkable detail with objective accuracy there are still parts of the recording process that rely on human skill and ‘post-procesing’ - In order to
facilitate a forensic study of the sculptures and ensure the data is meaningful to monitor their condition in the future every attempt is being made to track any
changes or modifications that are made to the files.
Every copy reveals something important about the original work- A comparison between the marble carvings, the original plastercasts, the casts made from
casts and the 3D data recorded with 3 different systems can facilitate an intimate understanding of these important works - it also reveals how the works have
been cared for over time..
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.
To complete our research we thought it could be interesting to scan Lelli’s plastercasts and compare them with our scans of the original works. A digital analysis
can reveal losses and additions to the volume. A simple visual comparison reveals other types of change - for example the donkey’s face or in the angle of the
angel’s head in the upper left corner.
With naked eye it can be difficult to stuty the surface characteristics of the Candoglia’s marble. Photographs can also be confusing as the colour or tonal information can obscure as well as reveal. The varoius renderings of the 3D data can facilitate a meaningful study of the fragility of the surface.
Factum Arte thanks: the Basilica of San Petronio, the Studio Cavina e Terra Architetti, the Opificio delle Pietre Dure and mostly Don Oreste for making this project possible, Mari Lending and Victor Borges.
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