M. Guarneri1, S. Ceccarelli2, M. Ciaffi1

1FSN-TECFIS-DIM, 2GARR Scholarship/ENEA Guest

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

Lecce 24/10/2017

Topics

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• The Aurelian Walls Museum, between history divulgation and daily problems • Short introduction to RGB-ITR scanner • Our intervention inside the Tower Room • Actual developments of the ITR tools for answering to the stakeholders’ request • Conclusions and future developments

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

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The Walls Museum: one of the most important, evocative and fragile example of Roman architecture

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

San Sebastian Door

• The Walls Museum entrance is free of charge and the opening times is from 9.00 to 14.00.

• The funds are almost sufficient for the standard maintenance and quality of the site

• A bilateral agreement was signed between the Walls Museum and ENEA Agency during the COBRA Project.

• No deep studies were performed on the charcoal inscriptions before the COBRA project

• The constrains of this intervention were to don’t introduce dangerous and expansive infrastructures (scaffolds) and don’t interdict the area to the visitors

The room digitalised in this work belong to the occidental tower. Before the 19th century a second floor in correspondence of the decorations and a higher third one were present. Nowadays, the tower room consists of a single open space accessible from the bottom floor. The entire structure is about 11 meters high and the most significant and visible drawings are placed at about 5 meters high from the floor, made of charcoal on plaster with dark brown and black colour figures. The history of the room decoration is quite ambiguous because of the uncertain age and authors’ drawings and inscriptions assignment. Several hypothesis has been formulated, but the most reliable one, according with historians, ascribes the decoration elements to soldiers belonging to the papal ranks stationed in the Appia Door between 18th and 19th century. The second supposition distinguishes historically the two elements: the drawings, assigned to Battista Franco, would be dated back to the 16th century as preparatory sketches on which the door decorations were based on for the victory of Carlo V over the Turks. The inscriptions remain attributed to soldiers lived inside the monumental door during the 19th century until Italy unification.

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• Composed by two parts, optical head and electronic equipment, interconnected by fiber optics

• Distance and colour information collected by the use of three laser sources (660, 514, 440 nm) coupled with three photodiodes

• A 2mdeg resolution is ensured by the use of high precision TV raster-like motorised scanning system

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RGB-ITR Scanner

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

• Interface with the ITR scanners hardware • Create a new scanning project • Identify the area to scan • Set the pixels resolution • Programming the acquisition by scripts • Calibration procedure • Drive a laser shutter for eyes-safety

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itrScanSystem

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

• Load RAW data collected by ITR scanners

• Create a 3D coloured mesh by ITR data • Calibrate the colours importing the

calibration curves collected on-site by the scanner

• Inspect the structure (distances, isocurves, profiles) and colour data (colour differences, segmentations, colour profiles)

• 3D viewer with multi layer selection support

• Export to all most common 2D/3D file formats (PNG, TIFF, PLY, OBJ)

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itrAnalyzer

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

Main RGB-ITR features

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Two of the most common questions about RGB-ITR scanner usage is: Why and Where this kind of scanner should be used? Some answers can be summarised as follows:

• (Why) RGB-ITR is a punctual laser scanner based (actually) on three superimposed wavelengths and a focalised spot of 0.5mm at 10 meters (1.2mm at 17 meters)

• (Where) Both high resolution colour and distance information are needed, up to 35 meters and without the use of infrastructures like scaffolds

• (Where) The ambient light influence during the digitalisation phase has a significative weight

• (Why) An in-situ and ready-to-use analysis is needed • (Why) Searching for a customised solution

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

3D laser coloured mesh Acquired by RGB-ITR scanning tool and processed by itrAnalyzer

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Scanner/drawing distance 5500 mm Drawing size (WxH) 1047x1682 mm Drawing resolution 5300x7700 pixels Drawing spatial resolution 0.197x0.218 mm/pixels Average letters size 6.55x6.32 mm Average letters resolution 32x27 pixels ITR average spot-size 0.2 mm

The case study: The Tower Room at S. Sebastian Door

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Detail of one of the charcoal inscription acquired by the laser scanner The decoded inscription part declaim: " Mastro Francesco (…) della sposa Maria Giustini Bari il 1° Aprile 1878 arruolato nel corso della guerra e di passaggio il 2 ottobre 1896 visitata questa torre e aggregato a questa brigata il 18 gennaio 1899. (…) Giovanni "

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The adopted approach for the inscription decoding

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Structural elements and morphological operators

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

RGB to HSV

Hue

Saturation

Lightness

Structural element: Disk(ray=5)

Morph. Operator: OPENING

Background

Morph. Operator: CLOSING

Structural element: Disk(ray=2)

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HSV to RGB

Detail of one of the charcoal inscription acquired by the laser scanner Any optical aberration is automatically and intrinsically corrected by the point-to-point distance information

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Laser colour information stored in a rectangular matrix

Corrected optical aberrations of the laser colour information

Detail of one of the charcoal inscription acquired by the laser scanner At a first sight the drawing appears like a bat, but…

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Detail of one of the charcoal inscription acquired by the laser scanner … after background removal and image enhancement an inscription appears: “Margio”

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Conclusions

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The aim of the intervention was to use this case study for demonstrating the feasibility of an inscriptions study directly using data collected by the RGB-ITR scanner and offering a possible model for reducing intervention costs, not (only and always) by using national and international projects funds, but offering the opportunity to reuse these data for different purposes (cataloguing, monitoring and dissemination). The novelty of this job is not in the single application of the different adopted methodologies, but in the simultaneous hardware and software development of a tool able to act directly in-situ for a prompt analysis and diagnosis of different Cultural Heritage set of problems.

Nowadays no historical researchers and experts were involved for the inscription investigation: the aim is actually to the develop instruments able to decode most of the inscriptions automatically, without interpretation influence. Future developments of the ITR tools for solve this kind of problems will be: • Improve the background removal and image enhancement algorithms robustness • Introduce algorithms based on NN or SVM for automatically decoding the rest of the

phrases surrounding the walls of the Tower Room • Reduce the scanner size and improve the number of wavelengths

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

M. Guarneri massimiliano.guarneri@enea.it

Multi-wavelengths 3D laser scanner for investigation and reconstruction of 19th century charcoal inscriptions

A special thanks to the Capitoline Superintendence for Cultural Heritage of Rome, in particular to its referent and Aurelian Walls Museum Director Ersilia Maria Loreti for the logistic and support during the digitalisation campaign.

Thanks to the ENEA researchers Mario Ferri de Collibus, Giorgio Fornetti, Massimo Francucci S. Mannori, and Marcello Nuvoli for the development and modernization of the system.

The presented work has been performed within COBRA project (lr13/2008 project n.1031) funded by Latium Region and we thank the project responsible Roberta Fantoni for the support during the entire campaign.