A Critical Comparison of 3D Digitization Techniques for Heritage Objects

Techniques for the three-dimensional digitization of tangible heritage are continuously updated, as regards active and passive sensors, data acquisition approaches, implemented algorithms and employed computational systems. These developments enable higher automation and processing velocities, increased accuracy, and precision for digitizing heritage assets. For large-scale applications, as for investigations on ancient remains, heritage objects, or architectural details, scanning and imagebased modeling approaches have prevailed, due to reduced costs and processing durations, fast acquisition, and the reproducibility of workflows. This paper presents an updated metric comparison of common heritage digitization approaches, providing a thorough examination of sensors, capturing workflows, processing parameters involved, metric and radiometric results produced. A variety of photogrammetric software were evaluated (both commercial and open sourced), as well as photo-capturing equipment of various characteristics and prices, and scanners employing different technologies. The experimentations were performed on case studies of different geometrical and surface characteristics to thoroughly assess the implemented three-dimensional modeling pipelines

Image-based metric heritage modeling in the near-infrared spectrum

Digital photogrammetry and spectral imaging are widely used in heritage sciences towards the comprehensive recording, understanding, and protection of historical artifacts and artworks. The availability of consumer-grade modified cameras for spectral acquisition, as an alternative to expensive multispectral sensors and multi-sensor apparatuses, along with semi-automatic software implementations of Structure-from-Motion (SfM) and Multiple-View-Stereo (MVS) algorithms, has made more feasible than ever the combination of those techniques. In the research presented here, the authors assess image-based modeling from near-infrared (NIR) imagery acquired with modified consumergrade cameras, with applications on tangible heritage. Three-dimensional (3D) meshes, textured with the non-visible data, are produced and evaluated. Specifically, metric evaluations are conducted through extensive comparisons with models produced with image-based modeling from visible (VIS) imagery and with structured light scanning, to check the accuracy of results. Furthermore, the authors observe and discuss, how the implemented NIR modeling approach, affects the surface of the reconstructed models, and may counteract specific problems which arise from lighting conditions during VIS acquisition. The radiometric properties of the produced results are evaluated, in comparison to the respective results in the visible spectrum, on the capacity to enhance observation towards the characterization of the surface and under-surface state of preservation, and consequently, to support conservation interventions

3D photogrammetric data modeling and optimization for multipurpose analysis and representation of Cultural Heritage assets

This research deals with the issues concerning the processing, managing, representation for further dissemination of the big amount of 3D data today achievable and storable with the modern geomatic techniques of 3D metric survey. In particular, this thesis is focused on the optimization process applied to 3D photogrammetric data of Cultural Heritage assets. Modern Geomatic techniques enable the acquisition and storage of a big amount of data, with high metric and radiometric accuracy and precision, also in the very close range field, and to process very detailed 3D textured models. Nowadays, the photogrammetric pipeline has well-established potentialities and it is considered one of the principal technique to produce, at low cost, detailed 3D textured models. The potentialities offered by high resolution and textured 3D models is today well-known and such representations are a powerful tool for many multidisciplinary purposes, at different scales and resolutions, from documentation, conservation and restoration to visualization and education. For example, their sub-millimetric precision makes them suitable for scientific studies applied to the geometry and materials (i.e. for structural and static tests, for planning restoration activities or for historical sources); their high fidelity to the real object and their navigability makes them optimal for web-based visualization and dissemination applications. Thanks to the improvement made in new visualization standard, they can be easily used as visualization interface linking different kinds of information in a highly intuitive way. Furthermore, many museums look today for more interactive exhibitions that may increase the visitors’ emotions and many recent applications make use of 3D contents (i.e. in virtual or augmented reality applications and through virtual museums). What all of these applications have to deal with concerns the issue deriving from the difficult of managing the big amount of data that have to be represented and navigated. Indeed, reality based models have very heavy file sizes (also tens of GB) that makes them difficult to be handled by common and portable devices, published on the internet or managed in real time applications. Even though recent advances produce more and more sophisticated and capable hardware and internet standards, empowering the ability to easily handle, visualize and share such contents, other researches aim at define a common pipeline for the generation and optimization of 3D models with a reduced number of polygons, however able to satisfy detailed radiometric and geometric requests. iii This thesis is inserted in this scenario and focuses on the 3D modeling process of photogrammetric data aimed at their easy sharing and visualization. In particular, this research tested a 3D models optimization, a process which aims at the generation of Low Polygons models, with very low byte file size, processed starting from the data of High Poly ones, that nevertheless offer a level of detail comparable to the original models. To do this, several tools borrowed from the game industry and game engine have been used. For this test, three case studies have been chosen, a modern sculpture of a contemporary Italian artist, a roman marble statue, preserved in the Civic Archaeological Museum of Torino, and the frieze of the Augustus arch preserved in the city of Susa (Piedmont- Italy). All the test cases have been surveyed by means of a close range photogrammetric acquisition and three high detailed 3D models have been generated by means of a Structure from Motion and image matching pipeline. On the final High Poly models generated, different optimization and decimation tools have been tested with the final aim to evaluate the quality of the information that can be extracted by the final optimized models, in comparison to those of the original High Polygon one. This study showed how tools borrowed from the Computer Graphic offer great potentialities also in the Cultural Heritage field. This application, in fact, may meet the needs of multipurpose and multiscale studies, using different levels of optimization, and this procedure could be applied to different kind of objects, with a variety of different sizes and shapes, also on multiscale and multisensor data, such as buildings, architectural complexes, data from UAV surveys and so on

Documentation du patrimoine de l'assemblage de fossiles du site de Kromdraai contenant des hominines (Afrique du Sud) : techniques de numérisation 3D, analyse spatiale quantitative et estimation de volume

Cette thèse explore l'utilisation de données multi-échelles pour modéliser une représentation tridimensionnelle (3D) et générer un registre numérique complet d'un assemblage de fossiles contenant des hominines à partir de l'unité lithostratigraphique P à Kromdraai situé dans le " berceau de l'humanité " classé au patrimoine mondial par l'UNESCO (Province de Gauteng, Afrique du Sud). Les objectifs principaux de cette recherche sont d'illustrer en 3D la progression temporelle et spatiale des fouilles de Kromdraai sur la période 2014-2018, d'analyse la distribution spatiale des vestiges d'homininés et de faune, comme des outils, et finalement, de fournir une documentation sur le patrimoine archéologique de Kromdraai. Nous avons réalisé une analyse multi-scalaire du site, avec l'application de méthodes de photogrammétrie terrestre et aérienne. Conformément aux principes et directives de la gestion du patrimoine archéologique mandatés par les agences internationales telles que l'UNESCO, nous présentons également un protocole de documentation du patrimoine. Nous avons utilisé des technologies de capture de données 3D pour numériser le site de Kromdraai et ses éléments archéologiques découverts entre 2014 et 2018 lors des fouilles. Cette recherche présente une technique originale développée pour la visualisation et la quantification des sédiments volumiques prélevés sur le site à chaque période de fouille par chaque fouilleur. Les estimations de volume calculées à l'aide de la photogrammétrie 3D fournissent un contexte temporel et spatial des sédiments prélevés lors des fouilles successives, et permettent un repositionnement virtuel et plus précis des vestiges découverts ex situ. De plus, nous avons mis en place une modélisation des métadonnées pour démontrer l'utilisation d'un système de gestion de base de données 4D pour la fusion, l'organisation et la diffusion de l'ensemble des données du site de Kromdraai et le partage de la propriété intellectuelle. Nous introduisons également l'une des premières approches statistiques de la modélisation spatiale 3D dans un site Plio-Pléistocène porteurs d'hominines en en Afrique du Sud. En mettant en œuvre des méthodes classiques de tests statistiques telles le partitionnement de données spatiales 3D, nous avons étudié les modèles de l'assemblage de fossiles dans l'unité P, ainsi qu'un échantillon de 810 spécimens catalogués entre 2014 et 2018. Le regroupement de bovidés, de carnivores, d'homininés et de primates non humains a révélé un modèle de distribution spatiale non uniforme des fossiles in situ. Cette recherche présente des méthodes précieuses qui peuvent être appliquées à d'autres sites fossiles contenant des hominines dans le berceau de l'humanité. Ces méthodes peuvent être appliquées pour documenter une fouille archéologique et reconstruire un site en 3D, ainsi que pour documenter des informations patrimoniales. Nos résultats permettent d'améliorer l'interprétation des assemblages fossiles à l'aide d'analyses basées sur des modèles 3D au sein d'un assemblage contenant des hominines.This thesis uses multi-scalar data to create a three-dimensional (3D) representation and, to generate a complete digital record of the early hominin-bearing fossil assemblage from the lithostratigraphic Unit P at Kromdraai in the Cradle of Humankind World Heritage Site (Gauteng Province, South Africa). The main purposes of this research were to illustrate in 3D the temporal and spatial progression of the excavations at Kromdraai since 2014, to investigate the spatial distribution of the hominin, faunal assemblages and artefacts, and ultimately, to provide an archive documenting the archaeological heritage of Kromdraai. We provided a multi-scalar analysis of various aspects of the study site, with the application of methods such as multi-image land and aerial photogrammetry. In alignment with the principles and guidelines for the management of archaeological heritage mandated by international agencies such as UNESCO, we also present a protocol for heritage documentation. We used 3D data capture technologies to record the Kromdraai site and the archaeological evidence discovered between 2014 and 2018 from its main excavation. This research presents an original technique developed for the quantification and visualization of the volume sediments removed from the site during each excavation period. Volume estimations computed using 3D photogrammetry and digitization, provided a temporal and spatial context to the volume and location of material removed by each excavator and, a more precise and virtual repositioning of the fossil material discovered ex situ. Furthermore, we implemented metadata modelling to demonstrate the use of 4D relational database management systems for the fusion, organisation and dissemination of the Kromdraai site dataset and the sharing of intellectual property. We also introduce one of the first statistical approaches of 3D spatial patterning in Plio-Pleistocene early hominin-bearing assemblages in South Africa. Implementing classic statistical testing methods such as k-means and Density-Based Spatial Clustering and Application with Noise (DBSCAN) cluster computation in 3D, we investigated the spatial patterns of the fossil assemblage within Unit P, a sample of 810 individually catalogued specimens recovered between 2014 and 2018. The clustering of bovids, carnivores, hominins, and non-human primates revealed a non-uniform spatial distribution pattern of fossils in-situ. This research presents valuable methods that can be applied at other hominin-bearing fossil sites within the Cradle of Humankind to document an archaeological excavation and to reconstruct of the site in 3D, to document heritage information, and to enhance the interpretation of the fossil assemblages using evidence-based assessment of spatial patterns within a hominin-bearing assemblage

Digitally-Mediated Practices of Geospatial Archaeological Data: Transformation, Integration, & Interpretation

Digitally-mediated practices of archaeological data require reflexive thinking about where archaeology stands as a discipline in regard to the ‘digital,’ and where we want to go. To move toward this goal, we advocate a historical approach that emphasizes contextual source-side criticism and data intimacy—scrutinizing maps and 3D data as we do artifacts by analyzing position, form, material and context of analog and digital sources. Applying this approach, we reflect on what we have learned from processes of digitally-mediated data. We ask: What can we learn as we convert analog data to digital data? And, how does digital data transformation impact the chain of archaeological practice? Primary, or raw data, are produced using various technologies ranging from Global Navigation Satellite System (GNSS)/Global Positioning System (GPS), LiDAR, digital photography, and ground penetrating radar, to digitization, typically using a flat-bed scanner to transform analog data such as old field notes, photographs, or drawings into digital data. However, archaeologists not only collect primary data, we also make substantial time investments to create derived data such as maps, 3D models, or statistics via post-processing and analysis. While analog data is typically static, digital data is more dynamic, creating fundamental differences in digitally-mediated archaeological practice. To address some issues embedded in this process, we describe the lessons we have learned from translating analog to digital geospatial data—discussing what is lost and what is gained in translation, and then applying what we have learned to provide concrete insights to archaeological practice

3D Heterogeneous Dataset for Structural Analysis of Historic Buildings. A Discussion on Process Pipelines

This paper presents a methodology for creating a comprehensive heterogeneous 3D database for the structural evaluation of a historic building by using both non-destructive and destructive surveys combined with historical information. The availability of adequate data on the actual conditions is crucial when assessing the seismic vulnerability and structural behavior of a historic building and validating the results. A reliable 3D database must accept different kinds of data, e.g., the results of destructive/non-destructive surveys, historical information, etc. It must also be interrogated and enriched at any time. Therefore, creating such a 3D database may present several challenges in terms of data-gathering pipeline, comprehensiveness/redundancy, interpretation, organization, and integration with other heterogeneous data. The methodology we present in this paper includes 3D laser scanning, thermal imaging, and endoscopy combined with information regarding the state of conservation, construction history, materials, and techniques. We tested such methodology to create a database that was later used for Finite Element Modeling (FEM) to assess the seismic vulnerability of Diotti Palace, a neoclassical building that has been the seat of the Prefect of Milan since 1859. The results are analytically presented here. In conclusion, we highlight the pros and cons of the proposed methodology by means of a comparative discussion with the state of the art about 3D documentation pipelines for historic buildings and sites

State-of-The-Art and Applications of 3D Imaging Sensors in Industry, Cultural Heritage, Medicine, and Criminal Investigation

3D imaging sensors for the acquisition of three dimensional (3D) shapes have created, in recent years, a considerable degree of interest for a number of applications. The miniaturization and integration of the optical and electronic components used to build them have played a crucial role in the achievement of compactness, robustness and flexibility of the sensors. Today, several 3D sensors are available on the market, even in combination with other sensors in a “sensor fusion” approach. An importance equal to that of physical miniaturization has the portability of the measurements, via suitable interfaces, into software environments designed for their elaboration, e.g., CAD-CAM systems, virtual renders, and rapid prototyping tools. In this paper, following an overview of the state-of-art of 3D imaging sensors, a number of significant examples of their use are presented, with particular reference to industry, heritage, medicine, and criminal investigation applications

INTEGRATED DIGITAL PLATFORMS FOR THE DOCUMENTATION AND MANAGEMENT OF CULTURAL HERITAGE AT RISK

Research definition of strategies and instruments for the prevention, mitigation, and management of hazards resulting from natural or man-made catastrophes is increasingly experimenting with an integrated approach to the digital documentation and visualisation of the built and cultural heritage. In actuality, recent conflicts and events, as well as the rise in natural disasters in previously unaffected regions, demonstrate the growing interest of governments, public administrations and entities, as well as academics, in the development and preservation of the digital memory of man-made landscapes. However, the management of recent catastrophic events allowed for the development of techniques that today enable the transfer of tools and processes from emergency management to routine management.Based on data from recent earthquakes in northern Italy, the current work describes some outcomes of the development of an integrated digital platform for seismic risk management that aims to integrate historical data from previous seismic events, data from existing databases, integrated digital surveys, carried out using integrated survey techniques, and semantically enhanced BIM-based models. The tool is being created as part of a transnational research cooperation initiative with thirteen partners from nations and regions along the Adriatic Sea. The program's overall goal is to improve cross-border emergency services while also raising their degree of safety and efficacy.</p