April/October 2013 Factum Artescanning in high resolution the sculptural works of the

Facade of San Petronio

Porta Magna

In red the zones that have been scanned.Porta Magna: Jacopo della Quercia.

In red the zones that have been scanned. Porta destra: Th e Entombment of Christ.Porta sinistra: Th e Resurrection of Christ.

Porta Destra Porta Sinistra

In red the zones that have been scanned.

Scanning systems

Scanning has been realized with diff erent resolutions thanks to the use of three complementary white light systems.

Most of the tiles were scanned with this system. Th e Sidio systems are being used by Factum Arte for 10 years.

Th e scanner was used during the fi nal part of the work on the facade; the Breuckmann is more suitable for the scaff olding conditions, lighter and easier to handle, also it limits risks of vibration during the scanning.

Th is small scanner permits scanning parts which would be impossible to reach with the other two systems due to their size and the depth of fi eld needed by the optical systems of Breukmann and Sidio. Th e David is surely less precise but still off ers the possibility of fi lling the missing parts, retrieving at least the actual form of the scanned object.

Sidio scanning system: used resolution 75 microns, 135 microns, 250 microns

Breukmann scanning system: used resolution 250 microns

David scanning system.

Sidio scanning system

Th e Sidio scanning system is a white light 3D scanner; the machine projects linear patterns of shadow and light on the surface which per-mit the soft ware to identify the diff erent depths of the object. Th e no-contact technology allows to obtain a precise model of the scanned surface without damaging the piece of art.

Th e Sidio system needs also two external projectors to scan. Th anks to that it is possible to visualize on the surface the parts already been scanned from the system. Th ese references are also used by the soft ware to pre-aligning the diff erent shots which will form the fi nal cloud point.

Patterns projected on the surface. Th e 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 scan-ner’s soft ware.

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.

Th e turban, removed during the restoration, was scanned separately making it possible to scan it entirely.

Image of the scanning of the turban of San Giuseppe, from the statue of Th e Entombment of Christ, by Amico Asper-tini.

Th e turban scanned at the resolution of 135 microns.

Diff erent colours identify the diff erent 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 two of the tiles of the Porta Destra at the resolu-tion of 250 microns.

Scanning of the faces of Christ and San Giuseppe, Amico Aspertini at the resolution of 135 microns.

Breukmann scanning system

Th e Breukmann scanning system is a white light scanner also project-ing light and shadow patterns on the surface. Th anks to a pair of opti-cal sensors placed with two diff erent 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 fl ipping slides.

In the Breukmann soft ware the pre-alignment is being done manu-ally. 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 al-lows the operator to be aware of the evolution of the scanning work.

Th e patterns projected on the surface of the stone. Th e scanned object visualized by the two cameras of the scanner in the Breukmann soft ware.

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

Th is 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. Th is is a white light system too and therefore it is a no-contact one. Th anks to the size of the scanner it is possible to access areas which would be impossible to reach by the other two systems.

Th e David scanner soft ware has a limited memory and therefore it is not possible to scan big surfaces. Th e scanner is useful for obtain-ing 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.

Th e pattern projected on the surface of the stone. Th e scanned object visualised in the David soft ware.

Photographic Documentation

A very detailed photographic documentation has been realized for every tile and sculpture on the facade. Th e photos taken from diff er-ent angles will help in the integration of the 3D models and they pro-vide a precious documentation of the actual condition of the facade.

Th e photographic documentation provides important information about the chromatic features of the art works but also about the con-servation 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, Proph-ets, Jacopo della Quercia.

Th e case of the Christ’s arm by Amico Aspertini

Th e Entombment of Christ, work of Amico Aspertini, pic-ture taken during the restoration.

Th e Entombment of Christ, work of Amico Aspertini, pic-ture taken before the restoration.

Image of the scanning of the same composition of Amico Aspertini.

Th e left arm of the statue “Th e 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. Diff erent 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.

Th e scanning has been carried out in diff erent sessions in order to collect the biggest possible amount of information present on the surface of the arm.

Porta Destra, Th e Entombment of Christ, of Amico Asper-tini, 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 scaff old of San Petronio.

Working closely with the restorers has permitted us to be present during crucial moments of the restoration. Th e Opifi cio delle Pietre Dure commissioned to Factum the reproduction of the arm of the statue “Th e Entombment of Christ” by Amico Aspertini.

A 360 ° model of the arm, scanned at the resolution of 135 microns.

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 soft ware of the point cloud and the processing data.

Scanning of the forearm. Virtual reintegration of the arm. Virtual view of the point of the attachment of the arm.

Th e scanning also allowed us to determine the ori-entation 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. Th is 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. Th e facsimile will be lighter than the original one and with higher resistance to the atmospheric agents than the one made by stone. Th is allows the preservation of the original arm avoiding further damages and also gives the possibility to study it in order to avoid similar problems.

Th e modelled arm has been already prototyped. Th e 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.

Fitting of the prototyped 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.Th anks 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. Th e photo of the facsimile in this page is only a test as the fi nal facsimile will be casted by the Opifi cio 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:

Th is is the direct output of the scanner. Th e positioned points in the three-dimensional space coincide with the scanned areas. Th e points cloud is a format adequate to be used in the future in case of an improvement in the fi eld of processing data technology and that is because it is nothing more than points in the space.

Mesh:

Th e mesh is created by an algorithm using a triangulation system based on the points cloud. In this way the soft ware creates the 3D surface coinciding with the points cloud.

Holes:

Th e 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 fi rst 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.

Th e diff erent colours identify the diff erent scans which were necessary for completing the scanning of the whole “For-mella”.

Visualisation of the same “Formella” in the processing data soft ware.

Rendering of the same fi gure.

Render of the central fi gure of the Porta Sinistra arch.

For the visualisation of the scanned art works it has been used a totally neutral texture. Th e white colour off ers a clear view of the surface of the stone without distractions due to its chromatic variations. Th e 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 scaff olding will be disassembled.

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.

Th e plaster casts of the Victorian Age

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. Th rough 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 fi nalized by hand, adding some details which did not exist in the original works. Th anks to a comparison with our scans we were able to defi ne that our collected data are instead more accurate to the originals.

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.

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 diffi cult 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 diff erent 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.

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.

Visualization of the casted “Formella” in the data processing program and a render of the same piece.

Visualization of the original “Formella” in the data process-ing program and a render of the same piece.

Plaster cast of the Porta Magna, Oronzio Lelli 1886, Victo-rian Albert Museum, London.

Factum Arte thanks: the Basilica of San Petronio, the Studio Cavina Architetti, the Opifi cio delle Pietre Dure and mostly Don Oreste for making this project pos-sible.

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