E-heritage : the future for integrated applications in cultural heritage

A number of factors are combining to change the structure and contents of documentation of cultural heritage: 1) the exponential growth in data generated by imaging techniques makes it possible for a site or an artifact to be recorded at a resolution of over 16 megapixels and at a density of several hundred million cloud points; 2) high-resolution imaging is becoming more affordable and/or available; 3) the economics and legal constraints of conservation practice are gradually pushing towards more stringent documentation standards; 4) improved communications infrastructure and mobile computing facilities are changing the way that data is recorded, processed, stored and – inevitably - used; 5) increasingly available computerized expert systems will be integrated into the very systems that conservators and documentation specialists carry around with them or access on a daily basis; 6) the advent of web-based systems will afford super-computer processing power and large-system database handling to the documentation specialist and the conservator in the field and permit greater flexibility for teleworking; 7) Computerised Project-based Management techniques will gradually spread from the realm of large institutions to SME’s and individual practitioners making digital image processing in architecture and archaeology more akin to the exchange of engineering drawings in automobile design industry. 8) The availability of cheap local or distributed processing power means that most of the above advantages will be present in both developed and developing countries. This paper explores. e-heritage as an integrated project which aims at providing a seamless yet structurally and inherently up-gradeable technological platform for all activities within cultural heritage conservation and management.peer-reviewe

Verification of micro-scale photogrammetry for smooth three-dimensional object measurement

By using sub-millimetre laser speckle pattern projection we show that photogrammetry systems are able to measure smooth three-dimensional objects with surface height deviations less than 1 μm. The projection of laser speckle patterns allows correspondences on the surface of smooth spheres to be found, and as a result, verification artefacts with low surface height deviations were measured. A combination of VDI/VDE and ISO standards were also utilised to provide a complete verification method, and determine the quality parameters for the system under test. Using the proposed method applied to a photogrammetry system, a 5 mm radius sphere was measured with an expanded uncertainty of 8.5 μm for sizing errors, and 16.6 μm for form errors with a 95 % confidence interval. Sphere spacing lengths between 6 mm and 10 mm were also measured by the photogrammetry system, and were found to have expanded uncertainties of around 20 μm with a 95 % confidence interval

Rejuvenation of metallic glasses by non-affine thermal strain.

When a spatially uniform temperature change is imposed on a solid with more than one phase, or on a polycrystal of a single, non-cubic phase (showing anisotropic expansion-contraction), the resulting thermal strain is inhomogeneous (non-affine). Thermal cycling induces internal stresses, leading to structural and property changes that are usually deleterious. Glasses are the solids that form on cooling a liquid if crystallization is avoided--they might be considered the ultimate, uniform solids, without the microstructural features and defects associated with polycrystals. Here we explore the effects of cryogenic thermal cycling on glasses, specifically metallic glasses. We show that, contrary to the null effect expected from uniformity, thermal cycling induces rejuvenation, reaching less relaxed states of higher energy. We interpret these findings in the context that the dynamics in liquids become heterogeneous on cooling towards the glass transition, and that there may be consequent heterogeneities in the resulting glasses. For example, the vibrational dynamics of glassy silica at long wavelengths are those of an elastic continuum, but at wavelengths less than approximately three nanometres the vibrational dynamics are similar to those of a polycrystal with anisotropic grains. Thermal cycling of metallic glasses is easily applied, and gives improvements in compressive plasticity. The fact that such effects can be achieved is attributed to intrinsic non-uniformity of the glass structure, giving a non-uniform coefficient of thermal expansion. While metallic glasses may be particularly suitable for thermal cycling, the non-affine nature of strains in glasses in general deserves further study, whether they are induced by applied stresses or by temperature change.This research was supported by the World Premier International Research Center Initiative (WPI), MEXT, Japan, by NSF China and MOST 973 China, and by the Engineering and the Engineering and Physical Sciences Research Council, UK (Materials World Network project). Y.H.S. acknowledges support from a China Scholarship Council (CSC) scholarship.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature1467

3-D Acquisition and Representation: theory and applications

Tutoria

Acquisizione 3D e modellazione poligonale

Con l’evoluzione della tecnologia il costo di un apparato per il rilievo tridimensionale è divenuto abbordabile anche per piccole imprese e singoli professionisti: per questo le tecniche di digitalizzazione 3D divengono via via più richieste sia in ambito didattico sia applicativo. Il testo si propone di illustrare il principio di funzionamento dei diversi sensori 3D ormai disponibili sul mercato, li inquadra in un contesto generale specificandone i principi di funzionamento, motivandone le prestazioni e fornendo dei criteri per permettere anche all’utente finale una caratterizzazione dei sistemi consentendone un uso consapevole. Descrive le modalità con cui questi sensori devono essere utilizzati per trasformare le superfici di un oggetto in un insieme di dati manipolabili con gli strumenti della rappresentazione digitale, come deve essere pianificato un progetto di acquisizione e quali sono gli errori da evitare. Vengono inoltre analizzate le procedure per il post-processing dei dati grezzi prodotti da un sensore 3D che consentono di arrivare ad un modello tridimensionale completo di texture e ci si sofferma sulle modalità di applicazione delle tecniche di acquisizione 3D a due campi applicativi in particolare: l’Industrial Design e la conservazione dei Beni Culturali. Infine, vengono esposti una serie di casi di studio, presi da differenti ambiti disciplinari, che illustrano come le tecniche descritte nella prima parte del libro possano essere utilmente applicate per far fronte alle difficoltà pratiche

Improvement of Metric Accuracy of Digital 3D Models through Digital Photogrammetry. A Case Study: Donatello's Maddalena

In spite of an undoubted richness of information produced by 3D optical technologies, in some cases, the method for generating a digital model from single 3D acquisitions involves the propagation of errors. These errors limit the overall metric accuracy attainable with such procedure. This happens when small 3D images are assembled together in order to model a large object. The authors present a procedure by which the metric reliability of the 3D model, obtained through iterative alignments of single range maps, can be guaranteed to an acceptable level. For this purpose, non-impeding optical targets were specifically designed for placement around the object. These are measured using a close range digital photogrammetry technique and by the 3D range camera system. From these measurements, transformation matrices have been calculated. Each matrix allows for the roto-translation (pose) of the 3D images from the local coordinate system of the range camera to an accurate global coordinate system determined by the digital photogrammetric procedure.Malgr\ue9 la richesse certaine des informations produites au moyen des techniques optiques 3D, dans certains cas, la m\ue9thode de g\ue9n\ue9ration d'un mod\ue8le num\ue9rique \ue0 partir d'images 3D isol\ue9es entra\ueene la propagation d'erreurs. Ces erreurs restreignent la pr\ue9cision m\ue9trique globale qu'il est possible d'obtenir avec de telles m\ue9thodes. Cela se produit en particulier lorsque de petites images 3D sont assembl\ue9es ensemble afin de mod\ue9liser un gros objet. Les auteurs pr\ue9sentent une m\ue9thode gr\ue2ce \ue0 laquelle la fiabilit\ue9 m\ue9trique du mod\ue8le 3D, obtenu par alignement it\ue9ratif d'images \ue0 \ue9chelle unique, peut \ueatre garantie, ce \ue0 un niveau acceptable. \uc0 cette fin, des cibles optiques non masquantes ont \ue9t\ue9 sp\ue9cifiquement con\ue7ues pour \ueatre plac\ue9es autour de l'objet. Ces cibles sont mesur\ue9es au moyen d'une technique de photogramm\ue9trie num\ue9rique \ue0 distance rapproch\ue9e, ainsi que gr\ue2ce \ue0 une cam\ue9ra de t\ue9l\ue9m\ue9trie 3D. \uc0 partir de ces mesures, des matrices de transformation ont \ue9t\ue9 calcul\ue9es. Chaque matrice permet la translation-rotation (pose) des images 3D, depuis le syst\ue8me de coordonn\ue9es local de la cam\ue9ra de t\ue9l\ue9m\ue9trie, vers un syst\ue8me de coordonn\ue9es global pr\ue9cis d\ue9termin\ue9 par la m\ue9thode de photogramm\ue9trie num\ue9rique.NRC publication: Ye

Accuracy Verification and Enhancement in 3D Modeling: Application to Donatello's Maddelena

The three-dimensional acquisition and modeling of Donatello's Maddalena was started in order to create a methodology that aims at monitoring fragile wooden sculptures over the years. Hence a set of new approaches in 3D modeling was needed for obtaining the necessary metric reliability. The main focus of the work is modeling accuracy, therefore quality control procedures based both of the self check of 3D data and the use of complementary 3D sensors were developed for testing the model. Sensor fusion was also extensively used in order to correct a few alignment errors after the ICP phase leading to a not negligible overall metric discrepancy. All the steps of the acquisition procedure, from the project planning to the solution of the various technical and logistical problems are reported. Although few commercial systems claim to use a similar approach, for the first time, the non-invasive integration of photogrammetry and 3D scanning, specifically designed for applications in Cultural Heritage, is here extensively documented.l'acquisition et la mod\ue9lisation tridimensionnelles de la Maddalena de Donatello ont \ue9t\ue9 lanc\ue9es afin d'\ue9laborer une m\ue9thodologie qui vise \ue0 surveiller des sculptures de bois fragiles au fil des ann\ue9es. Par cons\ue9quent, il a fallu un ensemble de nouvelles m\ue9thodes de mod\ue9lisation 3D pour obtenir la fiabilit\ue9 de mesure n\ue9cessaire. Le travail met l'accent sur la pr\ue9cision de la mod\ue9lisation, de sorte que des proc\ue9dures de contr\uf4le de la qualit\ue9 bas\ue9es tant sur l'auto-v\ue9rification des donn\ue9es 3D que sur l'utilisation de capteurs 3D compl\ue9mentaires ont \ue9t\ue9 \ue9labor\ue9es pour essayer le mod\ue8le. Nous avons syst\ue9matiquement fait appel \ue0 la fusion des donn\ue9es des capteurs, afin de corriger quelques erreurs d'alignement apr\ue8s la phase ICP, qui donnait lieu \ue0 un \ue9cart de mesure global non n\ue9gligeable. Nous d\ue9crivons toutes les \ue9tapes de la proc\ue9dure d'acquisition, allant de la planification du projet \ue0 la r\ue9solution des divers probl\ue8mes techniques et logistiques. Bien que peu de syst\ue8mes commerciaux r\ue9clament d'utiliser une m\ue9thode semblable, pour la premi\ue8re fois, l'int\ue9gration non effractive de la photogramm\ue9trie et du balayage 3D, con\ue7ue sp\ue9cialement pour des applications dans le domaine du patrimoine culturel, est document\ue9e ici de fa\ue7on exhaustive.NRC publication: Ye