Retraced memories - virtual reconstruction of an architectural landmark

<p class="VARAbstract">This paper addresses the challenge of digitally reconstructing ruined architectural sites and retracing their history, in order to virtually recompose their geometrical, stylistic and material integrity. To this end, the research team analyzed the ruins of the church of Santa Maria de Monasterio Albo, located in the ancient village of Misterbianco (Sicily) and destroyed (together with the entire hamlet) by the 1669 eruption of Mount Etna. In the last years, some excavation campaigns brought the church to the light, unveiling the remains of the main portal and six altars, which are one of the most remarkable examples of Mannerist art in eastern Sicily. This research aimed to three-dimensional (3D) reconstruct both the altars and the portal, ideally reviving their original 17^th century configuration. This goal was achieved through an in-depth archival research (documents dating back to the years between 1300 and 1666 were consulted), an analysis of Classic and Renaissance treatises, and two integrated digital survey campaigns (laser scans and photogrammetry). The outcome is represented by the 3D models of the seven artifacts, which include surviving parts reconstructed as photogrammetric meshes, several fragments were placed in their likely early location through a virtual anastylosis, and NURBS (Non Uniform Rational Basis-Splines) surfaces (recreating the no longer existing elements). The latter were 3D modelled based on the treatises (which provided information on the correct proportioning) or in analogy with other coeval similar artifacts. Overall, the digital reconstruction was based on the ethical principles of transparency of the intervention, recognition of non-original additions and distinction between evidence and hypothesis, according to the London Charter and the Seville Principles. The experimentation provides a valid support for possible interventions in the real world and is the starting point to develop a digital archive of the site, which would make the different accuracy levels the reconstruction explicit.</p><p><strong>Highlights:</strong></p><ul><li><p>3D virtual reconstruction is effective to visualize and bring back to life ruined architectural artefacts.</p></li><li><p>Information about the artefacts original appearance was harvested through digital survey campaigns, archival documents, and comparisons with iconographic sources and coeval buildings.</p></li><li><p>The 3D reconstruction follows ethical principles of transparency and combines photogrammetric meshes (partly relocated through a virtual anastylosis) and NURBS surfaces.</p></li></ul>

Reconstrucción virtual en 3D del castillo de Gauzón (Castrillón, Principado de Asturias)

<p class="VARKeywords">The virtual reconstruction of a site is the mirror in which the archaeological research process is reflected, with all its uncertainties and certainties, generating a space for reflection on the lost materiality while the vestige itself is reconfigured into a didactic and social resource. Here we present the result of the three-dimensional (3D) reconstruction of the archaeological structures preserved in the Peñón de Raíces, in Castrillón (Asturias), which correspond to the ruins of the castle of Gauzón, a famous fortification of the Asturian kings in which La Cruz de la Victoria was made in 908.</p><p>The article begins with an introduction and a first part (Section 2) dedicated to the explanation of the site itself from an archaeological and historical point of view. We believe that this analysis should be the basis of any scientific virtual reconstruction. The virtual reconstruction presented here is dated to the 9-10th centuries and corresponds to the fortification built in the time of the Asturian kings. We offer a detailed analysis of the morphological and architectural components that have been documented in this defensive settlement in the light of archaeological research, and that provide the main foundations for the infographic reconstruction.</p><p>In the second part of the article (Section 3), we analyse the specific sources of historical and archaeological information that support the reconstruction and serve as a reference for it. The historical-archaeological sources used for the representation, for example, of the walls and the palaeoenvironmental environment, are detailed. Likewise, we comment on the process of discussion of the different hypotheses that, finally, lead to the presented result. It is important to note that without this discussion process it is not possible to produce a sound and solid proposal over time.</p><p>In the third part (Section 4), we show the result of the virtual reconstruction with a series of images. To obtain the virtual reconstruction presented in this article, the Blender Geographic Information System (GIS) addon has been used, which allows us to have a digital terrain model (DTM) on our 3D desktop easily so that we can begin to carry out the work from it. The archaeological planimetries were arranged on it and, based on all this information, the modelling process began. In the first place, basic modelling of volumes was carried out that served to raise the first sketches and, on them, to continue discussing the reconstructive hypotheses. Little by little the geometry of the virtual reconstruction was detailed and the castle took shape. The next step was to carry out texturing in a photorealistic way, for which it was decided to use Substance Painter software. We continued with the texturing and addition of details of the surrounding terrain using particle systems, which has been one of the most complex phases to carry out given the level of realism that we set ourselves as a goal. Later, other types of minor details were added: objects, characters and animals, which help to better understand the context. Finally, the final renderings are carried out and their post-processing is developed in Adobe Photoshop, for which matte painting techniques were used that merge 3D images with photographs and digital drawing.</p><p>Our interest was to carry out scientific graphic work, for which we have emphasized the importance of using the scale depicting historical/archaeological evidence for virtual reconstructions, a tool that allows us to ensure the principles of authenticity and scientific transparency of any virtual reconstruction (Aparicio et al., 2016). In this case, thanks to this tool, it is clear that the highest level of evidence is found in the castle itself excavated in the acropolis, while the town and the surrounding palisade clearly show a lower level of evidence. We hope that subsequent excavations in this area will allow us to review the reconstruction and thus also reflect a higher level of evidence in this area.</p><p>We believe that the work presented here constitutes a good example of the use of virtual scientific reconstruction for the development and consolidation of new hypotheses not only reconstructive but also interpretive of an archaeological site. Furthermore, the result presented here demonstrates the power of this graphic resource for the dissemination of historical-archaeological knowledge, a fundamental objective when carrying out any scientific work.</p><p><strong>Highlights:</strong></p><ul><li><p>Reconstrucción infográfica de una de las principales fortificaciones del reino de Asturias (s. VIII-X), a partir de la evidencia material documentada en las campañas de excavación arqueológica realizadas en el yacimiento.</p></li><li><p>Desarrollo de hipótesis reconstructivas de arquitectura militar altomedieval arruinada mediante la interpretación de vestigios arqueológicos aplicando un enfoque multidisciplinar.</p></li><li><p>Ejemplo de uso de la escala de evidencia histórico-arqueológica y de las unidades reconstructivas (UR) como instrumentos que permiten garantizar los principios de autenticidad y transparencia científica.</p></li></ul>

Documentation and modelling of a hypothetical reconstruction of the first Roman watermill in Hispania

<p class="VARKeywords">The accurate graphic survey of an archaeological site is fundamental for its analysis and research. Furthermore, if this site is to be covered by a building and will not be accessible or visible, its documentation is essential, not only to continue with the research, but also to disseminate and enhance the discoveries. An example of this is the "<em>Hoya de los Molinos</em>" archaeological site in Caravaca de la Cruz (Region of Murcia, Spain). This is where the first mark of the wheel of a Roman vertical watermill in the Iberian Peninsula has been found. This fact is crucial because remains of Roman vertical-wheeled watermills have been found across the Mediterranean but not in the Iberian Peninsula. Moreover, the fact that this watermill still has all its structural elements makes this archaeological site in Caravaca de la Cruz very interesting. Due to these facts, it is essential to disseminate this discovery, so that it can be recognized and considered as archaeological and cultural heritage. To that end, the researchers have carried out a three-dimensional (3D) reconstruction of the most characteristic elements, such as the vertical wheel, the gears that allowed grinding the grain, and the building protecting them. A virtual recreation was carried out, based on the historical and building research, which is displayed in an explanatory video. Furthermore, two reproductions were created: one made to scale of the archaeological site with a 3D printer and another one of the hypothetical structure of the Roman watermill. To achieve this result, historians, archaeologists and engineers have collaborated, thus enabling not only its adequate dissemination, but also its accurate documentation, in an inclusive manner. Thanks to all the work that this paper describes, the Roman watermill found in Caravaca de la Cruz can be known, studied and assessed.</p><p><strong>Highlights:</strong></p><ul><li><p>The first Roman watermill in the Iberian Peninsula has been found with all its structural elements, from the imprints left in the stone by the wheel.</p></li><li><p>Virtual reconstruction of the first vertical wheel watermill discovered in Hispania has been made.</p></li><li><p>An animated video of the hydraulic watermill gears performance has been created for documentation and dissemination.</p></li></ul>

Modelling pre-modern flow distances of inland waterways – a GIS study in southern Germany

<p class="VARAbstract">Rivers form major traffic arteries in pre-modern Central Europe and accurate regional to supra-regional network models of inland navigation are crucial for economic history. However, navigation distances have hitherto been based on modern flow distances, which could be a significant source of error due to modern changes in flow distance and channel pattern. Here, we use a systematic comparison of vectorized old maps, which enlighten the fluvial landscape before most of the large-scale river engineering took place, and modern opensource geodata to deduce change ratios of flow distance and channel patterns. The river courses have been vectorised, edited and divided into comparable grid units. Based on the thalweg, meandering and braided/anabranching river sections have been identified and various ratios have been calculated in order to detect changes in length and channel patterns. Our large-scale analytical approach and Geographic Information System (GIS) workflow are transferable to other rivers in order to deduce change ratios on a European scale. The 19^th century flow distance is suitable to model pre-modern navigation distances. As a case study, we have used our approach to reconstruct changes of flow pattern, flow distance and subsequent changes in navigation distance and transportation time for the rivers Altmühl, Danube, Main, Regnitz, Rednitz, Franconian and Swabian Rezat (Southern Germany). The change ratio is rather heterogeneous with length and travel time changes of the main channel up to 24% and an extensive transformation of channel morphology in many river sections. Based on published travel time data, we have modelled the effect of our change ratios. Shipping between the commercial hubs Ulm and Regensburg, to give an example, was up to 5 days longer based on pre-modern distances. This is highly significant and underlines the necessity for river-specific correction values to model supra-regional networks of pre-modern inland waterways and navigation with higher precision.</p><p>Highlights:</p><ul><li><p>Systematic comparison of old maps and modern geodata to deduce river-specific length correction values to improve supra-regional network models of pre-modern inland navigation.</p></li><li><p>Large-scale analytical approach and transferable GIS workflow for flow distance reconstruction with case studies in Southern Germany.</p></li><li><p>Length changes of navigated fairways result in pre-modern period travel times up to 24% higher in corrected models.</p></li></ul>

Linear programming for the analysis and virtual recreation of historical events: the allocation of the artillery during the Siege of Bilbao in 1874

<p class="VARAbstract">The current digital technologies development makes it possible to apply new forms of studying historical events considering the geographical point of view. They rely on the location and the relationships among the different elements that took part in them over a recreated space (e.g. relief, roads, rivers); once these elements have been laid out on the virtual space, Geographic Information Systems (GIS) can be used to analyse several factors, such as distances, visibility, connectivity and so on. Nevertheless, the development of the actions was also driven by the aims, needs and beliefs (either wise or misguided) of the people/actors involved in those situations; therefore, some ways of including reasoning would significantly improve the actual recreation and understanding of the episodes. In this sense, “linear programming” is a very versatile tool for system modelling and optimization that is broadly used in many fields (e.g. industry, transports, agriculture, etc.). Likewise, this technique can also be applied to past scenarios to simulate dynamics and cross-check sources. In this text, two models regarding the distribution and the allocation of supplies during the siege of Bilbao, in the framework of the Third Carlist War (1872-1876), from both parties —beleaguerer and besieged— were established based on the war front textual reports. In these models, the scenario is recreated through the system variables (which define the alternatives that can be or could have been taken) and the constraints (which limit the range of action); moreover, the actors’ goals that guided the course of events are defined by the objective. Despite the simplification in the modelling, the results show very interesting hints about the dynamics involved during the processes and are able to highlight some critical issues that significantly conditioned the final results. Besides, the modelling process itself proved to be an opportunity for collaboration between historians and computer scientists.</p><p><strong>Highlights:</strong></p><ul><li><p>Geographic Information Systems (GIS) allow studying past events through the recreation of the geographical space and the interactions between the elements.</p></li><li><p>Linear programming can be a suitable option to include actors’ reasoning as a part of the modelling process.</p></li><li><p>The usefulness of the system models also enables the identification of critical issues, testing alternative scenarios and sharing information.</p></li></ul>

Multiclass semantic segmentation for digitisation of movable heritage using deep learning techniques

<p class="VARAbstract">Digitisation processes of movable heritage are becoming increasingly popular to document the artworks stored in our museums. A growing number of strategies for the three-dimensional (3D) acquisition and modelling of these invaluable assets have been developed in the last few years. Their objective is to efficiently respond to this documentation need and contribute to deepening the knowledge of the masterpieces investigated constantly by researchers operating in many fieldworks. Nowadays, one of the most effective solutions is represented by the development of image-based techniques, usually connected to a Structure-from-Motion (SfM) photogrammetric approach. However, while images acquisition is relatively rapid, the processes connected to data processing are very time-consuming and require the operator’s substantial manual involvement. Developing deep learning-based strategies can be an effective solution to enhance the automatism level. In this research, which has been carried out in the framework of the digitisation of a wooden maquettes collection stored in the ‘Museo Egizio di Torino’, using a photogrammetric approach, an automatic masking strategy using deep learning techniques is proposed, to increase the level of automatism and therefore, optimise the photogrammetric pipeline. Starting from a manually annotated dataset, a neural network was trained to automatically perform a semantic classification to isolate the maquettes from the background. The proposed methodology allowed the researchers to obtain automatically segmented masks with a high degree of accuracy. The workflow is described (as regards acquisition strategies, dataset processing, and neural network training). In addition, the accuracy of the results is evaluated and discussed. Finally, the researchers proposed the possibility of performing a multiclass segmentation on the digital images to recognise different object categories in the images, as well as to define a semantic hierarchy to perform automatic classification of different elements in the acquired images.</p><p><strong>Highlights:</strong></p><ul><li><p>In the framework of movable heritage digitisation processes, many procedures are very time-consuming, and they still require the operator’s substantial manual involvement.</p></li><li><p>This research proposes using deep learning techniques to enhance the automatism level in the generation of exclusion masks, improving the optimisation of the photogrammetric procedures.</p></li><li><p>Following this strategy, the possibility of performing a multiclass semantic segmentation (on the 2D images and, consequently, on the 3D point cloud) is also discussed, considering the accuracy of the obtainable results.</p></li></ul>

A bit closer to the past: the three-dimensionalization of an Inca ceremony in the north Calchaquí Valley (Salta, Argentina)

<p>Like other expansive polities, the expansion of the Inca empire across the highlands and lowlands of South America is not only a history of trade and warfare, but also of mesmerizing public performances that yielded new and memorable experiences. During highly ritualized public celebratory events, the local polities gained first-hand access to the imperial liturgy, which was vital to promote and legitimate the Inca cosmology across the newly acquired lands. Especially in the last 20 years, new technologies, an ever-growing corpus of archaeological data, as well as increasing hardware capacity and software development, make it possible to emulate the scenes that people got to witness during the Inca public events, at a home computer scale and without complex and expensive equipment. Furthermore, it prompts us to test and apply new tools and academic dissemination techniques, perhaps more suitable to current technologies and means of knowledge storage and circulation. This article presents the process of building a three-dimensional (3D) model that, on the one hand, combines historical, ethnographic, and archaeological data with Geographic Information System (GIS) datasets; on the other hand, it uses detailed architectural analysis and astronomical measurements. The objective is to yield renders that accurately display the atmospheric and lighting conditions prevailing when the site was inhabited. We will offer a detailed description of all methods, techniques, equipment, and software used to create the model and the parameters for rendering the images. The authors intend to exemplify how 3D modelling goes well beyond the 3D model as a product in itself; it becomes a fundamental tool that encouraged us to test new variables and discuss new interpretations about this settlement. Results indicate that its builders designed these settlement's Inca compounds to show off the imperial capabilities and constructive proficiency, to convey exceptional, memorable experiences to its residents and visitors, and to stage explicit links between the imperial representatives and some fundamental procreative components of the Andean cosmos. In doing so, Guitián's plaza served to stage and communicate the privileged role the imperial representatives claimed to have in a broader cosmological scheme.</p><p>Highlights:</p><ul><li><p>Inca public performances were finely choreographed so that objects, places, people, landscape, and skyscape features interacted according to the main principles of imperial cosmology.</p></li><li><p>Current mid-range hardware and specialized yet reasonably user-friendly software are suitable to create accurate three-dimensional (3D) models combining historical, archaeological, and astronomical data.</p></li><li><p>Creating such a detailed 3D model contributes to cultural heritage and academic dissemination and prompted us to revise and broaden our interpretations.</p></li></ul>

Espacios agrarios, asentamientos prehispánicos y tecnología LiDAR en el área costera central del Ecuador

<p class="VARAbstract">The use of Light Detection and Ranging (LiDAR) technology has revolutionised pre-Hispanic archaeology in large tracts of Central America (Canuto et. al. 2018; Fisher et al. 2016; Garrison et al. 2019; Chase &amp; Weishampel, 2016). This contribution is particularly significant in areas in which jungles and a complex orography had precluded the implementation of large-scale landscape archaeology studies.</p><p class="VARAbstract">Although this technology has not been used in South America as intensively as in Central America (Mexico, Guatemala and Honduras, among others), LiDAR is beginning to be used to answer questions concerning the interaction between the landscape, pre-Hispanic societies and their economic exploitation strategies (Amazonia, Peru) (Van Valkenburg et al., 2020). This work analyses one of the most important archaeological areas in central Ecuador, Cerros de Hojas-Jaboncillo (Figs. 1 &amp; 2), which has traditionally been identified as a major centre of the Manteña culture. This culture spanned the current provinces of Manabí, Santa Elena and Guayas between the 8^th and 15^th centuries AD.</p><p class="VARAbstract">Although the site was discovered in the early 20th century (Saville, 1907 &amp; 1910; Estrada, 1957) on the slopes and summits of the Chongón-Colonche and Balzar hills range (formerly called Sierra de Bálsamo), it has not been until recent moments that the characterization of its extension, its spatial conformation, as well as the main geoarchaeological characteristics of the site have begun to be possible (López, 2008; Delgado, 2009; Tobar, 2012; Lunniss, 2012; Veintimilla-Bustamante, 2012). The limitations of previous studies were largely due to the prevalence of thick sub-tropical forests, whose trees are sometimes 14 m tall.</p><p class="VARNormal">In 2016, a large-scale LiDAR flight covering 147.78 km² at a density of 9 ppm² has revealed the main features of the archaeological complex, including various sites that illustrate a multi-nuclear settlement pattern (Figs. 5, 8 &amp; 10). The study suggests that settlements, between 0.5 and 3 ha in size (Fig. 8), followed a common pattern, standing on small long hilltop plateaus. The complexes were visually connected and were linked by a road network.</p><p class="VARNormal">There is little doubt that one of the most important discoveries concerns the relationship between archaeological sites and complex agrarian systems, which point to the exploitation of wide areas. These had irrigation systems that involved rainwater retention and water resources maximisation (Figs. 6 &amp; 8). The system made intensive rainwater use during the humid season (December-May); it also took advantage of the coastal mists that ensure precipitations on the hilltops.</p><p class="VARNormal">At the same time, the LiDAR survey has established differences between the settlement pattern in the north-eastern sector, in which the interaction between settlements and the agro-system is not so obvious, and the south-western sector, whose settlements are clearly related to wide terraced systems.</p><p class="VARNormal">These results will allow for comparisons between Cerros de Hojas-Jaboncillo and other known Manteño sites, such as Japotó (Bouchard, 2010), Agua Blanca (McEwan &amp; Silva, 1992) and Ligüiqui. All of them point to the continued occupation of the same areas, and the continuity of some sites at least between the Guangala period (500 BC.-600 AD) and the late Manteño period (12^th-15^th centuries), as seen in Salango and its territory (Béarez, Gay &amp; Lunniss, 2012).</p><p class="VARNormal">Most research in the 20^th century has argued for an increase in social complexity during the classic Manteño period (8^th-11^th centuries), following a diffusionist explanatory pattern (Estrada, 1957). However, the LiDAR analysis of the Cerros de Hojas-Jaboncillo site points to prolonged periods of stable management of the environment, a response to the need to make use of the available resources. Archaeology, through large-scale landscape studies and the in-depth characterisation of sites through wide-ranging sampling methodologies can contribute to answering the question as to whether environmental management led to the formation of a “Manteño state” or whether this society can be better defined as a chiefdom (Touchard-Houlbert, 2010).</p><p class="VARNormal"><strong>Highlights:</strong></p><ul><li><p>The study focused on the LiDAR research of the Cerro de Hojas-Jaboncillo, the most important pre-Hispanic site in the Manabi province (Ecuador).</p></li><li><p>LiDAR technology has allowed users to identify an intense occupation in a forest area, where until now, it was impossible to detect archaeological structures.</p></li><li><p>The study has established the close relationship between the pre-Hispanic occupation model and the use of complex irrigation systems.</p></li></ul>

Modelling the last of the “Movies”: discussion and digital survey of the Eothen formerly ML286

<p class="VARAbstract">The research presented here puts together different direct and/or physical operations all aimed to enhance the knowledge and produce advanced dissemination of the very last ship from the “Mosquitos’ Fleet” which operated during the World War I and in some operations even during the World War II. The exploration of the valuable remains along the Thames River in London, the intervention with archaeology strategy, the use of digital survey procedures, the investigation of the references about the fleet, the digital modelling and drawing and the final online sharing of the 3D model, brought together to a specific digital heritage creation of an element with a high risk of getting lost. An international team worked together on the poor shipwreck of the Eothen (the last name assigned to this ship by its last owner). The intervention was operated in very odd operative conditions, with the hull invaded by the mud, the very wet environment and the daily flood of the area, such a mix of difficult conditions were a special challenge for the survey operations, which were optimized and accurately planned to allow the best and efficient result in terms of coverage and level of details. The following post-processing aimed to the production of a classic set of 2D drawings and an interactive 3D model, accessible in a real-time visualization from the sketchfab.com platform creates an excellent base for a possible following restoration/musealisation intervention, or, at least, allow digital preservation of a rich dataset of the remains of this interesting piece from the naval history of the first half of the 20th century.</p><p>Highlights:</p><ul><li><p>The “mosquito fleet” has a specific page in the WWI naval wars. Based on a specific ship, it is missing detailed documentation, the survey of the last one can highlight that episode.</p></li><li><p>The digital survey of the Eothen has a strategy aimed to allow the full documentation of the shipwreck in a very difficult environment, managing floods, mud, vegetation and reflections.</p></li><li><p>The drawings and the 3D model, accessible from a free platform allow complete access to this ruined ship, a contribution to knowledge and a base for possible intervention hypothesis.</p></li></ul>

Transfer learning and performance enhancement techniques for deep semantic segmentation of built heritage point clouds

<p class="VARAbstract">The growing availability of three-dimensional (3D) data, such as point clouds, coming from Light Detection and Ranging (LiDAR), Mobile Mapping Systems (MMSs) or Unmanned Aerial Vehicles (UAVs), provides the opportunity to rapidly generate 3D models to support the restoration, conservation, and safeguarding activities of cultural heritage (CH). The so-called scan-to-BIM process can, in fact, benefit from such data, and they can themselves be a source for further analyses or activities on the archaeological and built heritage. There are several ways to exploit this type of data, such as Historic Building Information Modelling (HBIM), mesh creation, rasterisation, classification, and semantic segmentation. The latter, referring to point clouds, is a trending topic not only in the CH domain but also in other fields like autonomous navigation, medicine or retail. Precisely in these sectors, the task of semantic segmentation has been mainly exploited and developed with artificial intelligence techniques. In particular, machine learning (ML) algorithms, and their deep learning (DL) subset, are increasingly applied and have established a solid state-of-the-art in the last half-decade. However, applications of DL techniques on heritage point clouds are still scarce; therefore, we propose to tackle this framework within the built heritage field. Starting from some previous tests with the Dynamic Graph Convolutional Neural Network (DGCNN), in this contribution close attention is paid to: i) the investigation of fine-tuned models, used as a transfer learning technique, ii) the combination of external classifiers, such as Random Forest (RF), with the artificial neural network, and iii) the evaluation of the data augmentation results for the domain-specific ArCH dataset. Finally, after taking into account the main advantages and criticalities, considerations are made on the possibility to profit by this methodology also for non-programming or domain experts.</p><p>Highlights:</p><ul><li><p>Semantic segmentation of built heritage point clouds through deep neural networks can provide performances comparable to those of more consolidated state-of-the-art ML classifiers.</p></li><li><p>Transfer learning approaches, as fine-tuning, can considerably reduce computational time also for CH domain-specific datasets, as well as improve metrics for some challenging categories (i.e. windows or mouldings).</p></li><li><p>Data augmentation techniques do not significantly improve overall performances.</p></li></ul>