Heritage Recording and 3D Modeling with Photogrammetry and 3D Scanning

A Performance Comparison of 3D Survey Instruments for Their Application in the Cultural Heritage Field

Thanks to the recent development of innovative instruments and software with high accuracy and resolution, 3D modelling provides useful insights in several sectors (from industrial metrology to cultural heritage). Moreover, the 3D reconstruction of objects of artistic interest is becoming mandatory, not only because of the risks to which works of art are increasingly exposed (e.g., wars and climatic disasters) but also because of the leading role that the virtual fruition of art is taking. In this work, we compared the performance of four 3D instruments based on different working principles and techniques (laser micro-profilometry, structured-light topography and the phase-shifting method) by measuring four samples of different sizes, dimensions and surface characteristics. We aimed to assess the capabilities and limitations of these instruments to verify their accuracy and the technical specifications given in the suppliers' data sheets. To this end, we calculated the point densities and extracted several profiles from the models to evaluate both their lateral (XY) and axial (Z) resolution. A comparison between the nominal resolution values and those calculated on samples representative of cultural artefacts was used to predict the performance of the instruments in real case studies. Overall, the purpose of this comparison is to provide a quantitative assessment of the performance of the instruments that allows for their correct application to works of art according to their specific characteristics.

Analysis of the Photogrammetric Use of 360-Degree Cameras in Complex Heritage-Related Scenes: Case of the Necropolis of Qubbet el-Hawa (Aswan Egypt)

This study shows the results of the analysis of the photogrammetric use of 360-degree cameras in complex heritage-related scenes. The goal is to take advantage of the large field of view provided by these sensors and reduce the number of images used to cover the entire scene compared to those needed using conventional cameras. We also try to minimize problems derived from camera geometry and lens characteristics. In this regard, we used a multi-sensor camera composed of six fisheye lenses, applying photogrammetric procedures to several funerary structures. The methodology includes the analysis of several types of spherical images obtained using different stitching techniques and the comparison of the results of image orientation processes considering these images and the original fisheye images. Subsequently, we analyze the possible use of the fisheye images to model complex scenes by reducing the use of ground control points, thus minimizing the need to apply surveying techniques to determine their coordinates. In this regard, we applied distance constraints based on a previous extrinsic calibration of the camera, obtaining results similar to those obtained using a traditional schema based on points. The results have allowed us to determine the advantages and disadvantages of each type of image and configuration, providing several recommendations regarding their use in complex scenes.

Development through Borders: Photogrammetry of a Moving Experience

Recognizing the variety of borders that gather and divide our world, such as geographical, temporal, social and psychological, the study highlights that the transit across these borders drives changes and continuities that contribute to human development. The research emphasizes the relevance of reviewing both the individual singularities and the shared aspects of border crossing experiences. The matching of these approaches allows building theoretical models referring to those experiences. Thus, this article aims to review borders crossing as a developmental and abductively generalizable process. Through the analogy between Abductive Generalization and photogrammetry, the study proposes an innovative way of representing these complex experiences. Three ways of border crossing - spatial displacement, imagination and social interactions - are explored in terms of their developmental potential. Using a case study of psychologists in a humanitarian non-governmental organization - NGO, an abductively generalized model is presented highlighting the spatial, cultural and psychological dimensions involved. In addition, the study proposes a three-dimensional helical model of development inspired by photogrammetry, incorporating principles of this technique to improve the understanding on the border crossing process. By recognizing mesogenetic influences, such as institutional and cultural dimensions, the article puts forward an interdisciplinary approach to understand development through border crossing. The models presented may potentially drive future research and interventions in Semiotic Cultural Psychology, enriching the promotion of human development in different border contexts. The study fosters the extension of this work by including several perspectives, methods and paradigms.

Multi-Level Optimization for Data-Driven Camera-LiDAR Calibration in Data Collection Vehicles

Accurately calibrating camera-LiDAR systems is crucial for achieving effective data fusion, particularly in data collection vehicles. Data-driven calibration methods have gained prominence over target-based methods due to their superior adaptability to diverse environments. However, current data-driven calibration methods are susceptible to suboptimal initialization parameters, which can significantly impact the accuracy and efficiency of the calibration process. In response to these challenges, this paper proposes a novel general model for the camera-LiDAR calibration that abstracts away the technical details in existing methods, introduces an improved objective function that effectively mitigates the issue of suboptimal parameter initialization, and develops a multi-level parameter optimization algorithm that strikes a balance between accuracy and efficiency during iterative optimization. The experimental results demonstrate that the proposed method effectively mitigates the effects of suboptimal initial calibration parameters, achieving highly accurate and efficient calibration results. The suggested technique exhibits versatility and adaptability to accommodate various sensor configurations, making it a notable advancement in the field of camera-LiDAR calibration, with potential applications in diverse fields including autonomous driving, robotics, and computer vision.

Cost-Effective Full-Color 3D Dental Imaging Based on Close-Range Photogrammetry

Dental imaging plays a crucial role in clinical dental practice. Conventional 2D dental imaging serves general-purpose tasks, such as patient documentation, while high-precision 3D dental scanning is tailored for specialized procedures, such as orthodontics and implant surgeries. In this study, we aimed to develop a cost-effective 3D imaging technique that could bridge the gap between conventional dental photography and high-precision 3D dental scanning, with the goal of improving patient dental care. We developed a 3D imaging technique based on close-range photogrammetry and termed it close-range photogrammetry-based dental imaging (CPDI). We evaluated this technique on both in vitro dental models and in vivo teeth. For dental models, we conducted a parametric study to examine the effects of the depth of field and specular reflection on reconstruction quality. We showed that the optimal results were achieved with an f/5.6 lens and without a circular polarizer for reflection suppression. This configuration generated 3D scans with 57.7 ± 3.2% and 82.4 ± 2.7% of reconstructed points falling within ±0.1 mm and ±0.2 mm error margins, respectively. With such accuracy, these 3D dental models can faithfully represent dental morphology and features. During in vivo imaging, we were able to reconstruct high-quality 3D models of the anterior arch, further demonstrating its clinical relevance. The reconstructed models carry both 3D shapes and detail full-color surface textures, which positions CPDI as a versatile imaging tool in different areas of clinical dental care.

A Collaborative Virtual Walkthrough of Matera's Sassi Using Photogrammetric Reconstruction and Hand Gesture Navigation

The COVID-19 pandemic has underscored the need for real-time, collaborative virtual tools to support remote activities across various domains, including education and cultural heritage. Virtual walkthroughs provide a potent means of exploring, learning about, and interacting with historical sites worldwide. Nonetheless, creating realistic and user-friendly applications poses a significant challenge. This study investigates the potential of collaborative virtual walkthroughs as an educational tool for cultural heritage sites, with a focus on the Sassi of Matera, a UNESCO World Heritage Site in Italy. The virtual walkthrough application, developed using RealityCapture and Unreal Engine, leveraged photogrammetric reconstruction and deep learning-based hand gesture recognition to offer an immersive and accessible experience, allowing users to interact with the virtual environment using intuitive gestures. A test with 36 participants resulted in positive feedback regarding the application's effectiveness, intuitiveness, and user-friendliness. The findings suggest that virtual walkthroughs can provide precise representations of complex historical locations, promoting tangible and intangible aspects of heritage. Future work should focus on expanding the reconstructed site, enhancing the performance, and assessing the impact on learning outcomes. Overall, this study highlights the potential of virtual walkthrough applications as a valuable resource for architecture, cultural heritage, and environmental education.

The efficacy of computed tomography scanning versus surface scanning in 3D finite element analysis

Finite element analysis (FEA) is a commonly used application in biomechanical studies of both extant and fossil taxa to assess stress and strain in solid structures such as bone. FEA can be performed on 3D structures that are generated using various methods, including computed tomography (CT) scans and surface scans. While previous palaeobiological studies have used both CT scanned models and surface scanned models, little research has evaluated to what degree FE results may vary when CT scans and surface scans of the same object are compared. Surface scans do not preserve the internal geometries of 3D structures, which are typically preserved in CT scans. Here, we created 3D models from CT scans and surface scans of the same specimens (crania and mandibles of a Nile crocodile, a green sea turtle, and a monitor lizard) and performed FEA under identical loading parameters. It was found that once surface scanned models are solidified, they output stress and strain distributions and model deformations comparable to their CT scanned counterparts, though differing by notable stress and strain magnitudes in some cases, depending on morphology of the specimen and the degree of reconstruction applied. Despite similarities in overall mechanical behaviour, surface scanned models can differ in exterior shape compared to CT scanned models due to inaccuracies that can occur during scanning and reconstruction, resulting in local differences in stress distribution. Solid-fill surface scanned models generally output lower stresses compared to CT scanned models due to their compact interiors, which must be accounted for in studies that use both types of scans.

Experimental Validation of Deflections of Temporary Excavation Support Plates with the Use of 3D Modelling

Almost every project is accompanied by earthworks, very often involving various types of excavation, and the work of people in the excavations. One of the most important tasks in earthworks is to ensure that the walls of the excavation are protected against sliding and that people working in and around the excavation are safe. Very often, in addition to criteria relating to safety and stability of the excavation, economic considerations are also an important criterion. This issue arises as early as the design stage and is related to the choice of construction and materials of which the shoring is to be made in such a way as to be able to withstand the pressure of the soil, ground loads resulting from stored excavated material and the operation of working machinery. Ongoing monitoring of the excavations and their reinforcement is also very important. The paper describes the unique results of experimental field tests, the purpose of which was to analyse the values of deflections of steel support plates of temporary excavation carried out on the object in 1:1 scale. The course of the experiment is presented for excavation support plates with a total depth of 6 m. Direct tests of the deflection arrow were carried out using two techniques, traditionally with a patch, and with laser scanning. Field tests were carried out for the designed situation without backfill load as well as for backfill load of 3.84, 15.36, 26.88 and 38.4 kN·m⁻², respectively, for two measurement stages. Stage-I of the study consisted in collecting the results for soil in intact condition, whereas Stage-II collected results for loosened soil. The research experiment was supported by numerical calculations performed using the finite difference method in variational approach. The measured maximum deflections ranged from 14.40 to 16 mm, and the calculated values were 14.95 and 14.99 mm. The comparison of calculation results and tests proved to be very consistent. The analysis of the values of deflections showed that backfill load does not have a significant effect on the deflection of the lower plate, but it does affect the deflection of the first plate up to a depth of 1.2 m. Based on the obtained results, it is recommended to assume the limit (maximum) deflection arrow for support plates of temporary excavations at least as w_gr = L/130, where L is the span of the plate. The calculation of deflection values was based on deflection values obtained experimentally and numerically for two steel variants: S235JR and S355JR. The w_gr indicator of the maximum deflection arrow proposed by the authors is not stipulated by the industry standards, but it can be very helpful for the designing of excavation reinforcement.

3D Modeling of Sculpture Nano-Ceramics under Sparse Image Sequence

To improve the analysis ability of point cloud 3D reconstruction of sparse images of nano-ceramic sculpture points, an automatic cloud 3D reconstruction method of nano-ceramic sculpture points based on sparse image sequence is proposed. Firstly, 3D angle detection and edge contour feature extraction methods are used to analyze 3D point cloud features of nano-ceramic sculpture point save image; secondly, the point cloud of the fuel economy image of nano-ceramic sculpture points is merged and the sloping action method is used to shape degradation to realize the information increase and fusion filtering of the fuel economy image of nano-ceramic sculpture points; finally, combined with the local mean denoising method, image is refined to improve the ability of sparse image outline structure of nano-ceramic sculpture points. The simulation results show that this method has high accuracy, good image matching ability, and high signal-to-noise ratio.

A Review of Mobile Mapping Systems: From Sensors to Applications

The evolution of mobile mapping systems (MMSs) has gained more attention in the past few decades. MMSs have been widely used to provide valuable assets in different applications. This has been facilitated by the wide availability of low-cost sensors, advances in computational resources, the maturity of mapping algorithms, and the need for accurate and on-demand geographic information system (GIS) data and digital maps. Many MMSs combine hybrid sensors to provide a more informative, robust, and stable solution by complementing each other. In this paper, we presented a comprehensive review of the modern MMSs by focusing on: (1) the types of sensors and platforms, discussing their capabilities and limitations and providing a comprehensive overview of recent MMS technologies available in the market; (2) highlighting the general workflow to process MMS data; (3) identifying different use cases of mobile mapping technology by reviewing some of the common applications; and (4) presenting a discussion on the benefits and challenges and sharing our views on potential research directions.

Multitechnique diagnostic analysis and 3D surveying prior to the restoration of St. Michael defeating Evil painting by Mattia Preti

In this study, a multimethodological analysis involving optical and physical/chemical diagnostic techniques and 3D photogrammetric survey was successfully applied, for the first time, on the large oil on canvas St. Michael defeating Evil painting by Mattia Preti, located inside the Church of the Immaculate Conception of Sarria (Floriana) in Malta. Pigmenting agents, binder media, and raw materials were first characterized, both at elemental and molecular scales, through X-ray fluorescence spectroscopy (XRF), optical stereo microscopy (SM), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FT-IR), and gas chromatography coupled with mass spectrometry (GC-MS). The main goal was to properly identify the execution technique of this famous painter, the artist's palette, and possible nondocumented interventions. The 3D photogrammetric survey, on the other side, allowed us to noninvasively evaluate the extension of the areas that experienced restorations, and to properly map the domains of the different canvasses observed. The joints between canvasses suggested that the painting was folded and rolled up. In addition, the employment of a thermal camera gave evidence of the different consolidating material injection points used during the restoration to strengthen the painting. The obtained results offer useful information for the development of optimized restoration and conservation strategies to be applied and provide, at the same time, answers to open questions related to provenance and dating of the investigated artwork.

WELDMAP: A Photogrammetric Suite Applied to the Inspection of Welds

This paper presents a new tool for external quality control in welds using close-range photogrammetry. The main contribution of the developed approach is the automatic assessment of welds based on 3D photogrammetric models, enabling objective and accurate analyses through an in-house tool that was developed, WELDMAP. As a result, inspectors can perform external quality control of welds in a simple and efficient way without requiring visual inspections or external tools, and thus avoiding the subjectivity and imprecisions of the classical protocol. The tool was validated with a large dataset in laboratory tests as well as in real scenarios.

3D Scanning/Printing: A Technological Stride in Sculpture

The creation of innovative tools, objects and artifacts that introduce abstract ideas in the real world is a necessary step for the evolution process and characterize the creative capacity of civilization. Sculpture is based on the available technology for its creation process and is strongly related to the level of technological sophistication of each era. This paper analyzes the evolution of basic sculpture techniques (carving, lost-wax casting and 3D scanning/printing), and their importance as a culture footprint. It also presents and evaluates the added creative capacities of each technological step and the different methods of 3D scanning/printing concerning sculpture. It is also an attempt to define the term “material poetics”, which is connected to sculpture artifacts. We conclude that 3D scanning/printing is an important sign of civilization, although artifacts lose a part of material poetics with additive manufacturing. Subsequently, there are various causes of the destruction of sculptures, leaving a hole in the history of art. Finally, this paper showcases the importance of 3D scanning/printing in salvaging cultural heritage, as it has radically altered the way we “backup” objects.

A dosimetric comparison of CT- and photogrammetry- generated 3D printed HDR brachytherapy surface applicators

In this study, we investigate whether an acceptable dosimetric plan can be obtained for a brachytherapy surface applicator designed using photogrammetry and compare the plan quality to a CT-derived applicator. The nose region of a RANDO anthropomorphic phantom was selected as the treatment site due to its high curvature. Photographs were captured using a Nikon D5600 DSLR camera and reconstructed using Agisoft Metashape while CT data was obtained using a Canon Aquillion scanner. Virtual surface applicators were designed in Blender and printed with PLA plastic. Treatment plans with a prescription dose of 3.85 Gy × 10 fractions with 100% dose to PTV on the bridge of the nose at 2 mm depth were generated separately using AcurosBV in the Varian BrachyVision TPS. PTV D_98%, D_90% and V_100%, and OAR D_0.1cc, D_2cc and V_50% dose metrics and dwell times were evaluated, with the applicator fit assessed by air-gap volume measurements. Both types of surface applicators were printed with minimal defects and visually fitted well to the target area. The measured air-gap volume between the photogrammetry applicator and phantom surface was 44% larger than the CT-designed applicator, with a mean air gap thickness of 3.24 and 2.88 mm, respectively. The largest difference in the dose metric observed for the PTV and OAR was the PTV V_100% of - 1.27% and skin D_0.1cc of - 0.28%. PTV D_98% and D_90% and OAR D_2cc and V_50% for the photogrammetry based plan were all within 0.5% of the CT based plan. Total dwell times were also within 5%. A 3D printed surface applicator for the nose was successfully constructed using photogrammetry techniques. Although it produced a larger air gap between the surface applicator and phantom surface, a clinically acceptable dose plan was created with similar PTV and OAR dose metrics to the CT-designed applicator. Additional future work is required to comprehensively evaluate its suitability in a clinically environment.

Conservation Challenges and Emerging Trends of Digital Preservation for UNESCO Architectural Heritage, Pakistan

Recent worldwide initiatives at world heritage forums, especially UNESCO, have increased the importance of architectural heritage. Architectural heritage includes built structures that are of outstanding value of natural and cultural identity and require conservation, preservation, presentation and transmission to the future generations. In this regard, UNESCO has enlisted six World Heritage Sites in Pakistan that need to be preserved. Moreover, the heritage sites are undergoing theft, vandalism, natural decay and other socio-cultural harms. One of the state-of-the-art methodologies is the digital preservation of the historic sites. Amongst the various available computer technologies, photogrammetry is the quickest and most cost-effective method that can be used for digital preservation. The research will focus on the digital preservation of UNESCO World Heritage Sites, which is an emerging trend in an architectural context. Developing countries have limited funds and resources and most historic sites are being neglected by the lack of financial resources. The paper suggests digital preservation as an emerging solution, identifies its challenges and suggests photogrammetry as a cost-effective solution to six UNESCO enlisted historic sites of Pakistan. It also suggests that once digitally recorded, information of historic sites can also be used in diverse applications to generate further finances.

Accuracy Assessment of Cultural Heritage Models Extracting 3D Point Cloud Geometric Features with RPAS SfM-MVS and TLS Techniques

A proper classification of 3D point clouds allows fully exploiting data potentiality in assessing and preserving cultural heritage. Point cloud classification workflow is commonly based on the selection and extraction of respective geometric features. Although several research activities have investigated the impact of geometric features on classification outcomes accuracy, only a few works focused on their accuracy and reliability. This paper investigates the accuracy of 3D point cloud geometric features through a statistical analysis based on their corresponding eigenvalues and covariance with the aim of exploiting their effectiveness for cultural heritage classification. The proposed approach was separately applied on two high-quality 3D point clouds of the All Saints’ Monastery of Cuti (Bari, Southern Italy), generated using two competing survey techniques: Remotely Piloted Aircraft System (RPAS) Structure from Motion (SfM) and Multi View Stereo (MVS) techniques and Terrestrial Laser Scanner (TLS). Point cloud compatibility was guaranteed through re-alignment and co-registration of data. The geometric features accuracy obtained by adopting the RPAS digital photogrammetric and TLS models was consequently analyzed and presented. Lastly, a discussion on convergences and divergences of these results is also provided.

Symmetry Detection and Analysis of Chinese Paifang Using 3D Point Clouds

The Chinese paifang is an essential constituent element for Chinese or many other oriental architectures. In this paper, a new method for detection and analysis of the reflection symmetry of the paifang based on 3D point clouds is proposed. The method invokes a new model to simultaneously fit two vertical planes of symmetry to the 3D point cloud of a paifang to support further symmetry analysis. Several simulated datasets were used to verify the proposed method. The results indicated that the proposed method was able to quantity the symmetry of a paifang in terms of the RMSE obtained from the ICP algorithm, with resistance to the presence of some random noise added to the simulated measurements. For real datasets, three old Chinese paifangs (with ages from 90 to 500 years) were scanned as point clouds to input into the proposed method. The method quantified the degree of symmetry for the three Chinese paifangs in terms of the RMSE, which ranged from 20 to 61 mm. One of the paifangs with apparent asymmetry had the highest RMSE (61 mm). Other than the quantification of the symmetry of the paifangs, the proposed method could also locate which portion of the paifang was relatively more symmetric. The proposed method can potentially be used for structural health inspection and cultural studies of the Chinese paifangs and some other similar architecture.

Generation of a Multi-Scale Historic BIM-GIS with Digital Recording Tools and Geospatial Information

This paper discusses the creation of an integrated historic BIM-GIS for the complex of San Pietro al Monte, an important Romanesque monument in Civate (Italy) inscribed in the UNESCO tentative list with other seven medieval Benedictine settlements. The reason behind the choice of an integrated H-BIM-GIS solution is motivated by the large extension of the considered area (about 30 km2) and the need for multi-scale digital information integrated into a 3D parametric environment. The model includes geospatial information at a territorial scale and in situ digital data capturing the complex at a higher level of detail. The work aims at exploring the pros and cons of a novel parametric 3D environment able to integrate both BIM and GIS data, methods, and processing tools in the case of historic buildings and sites.

A Parametric Scan-to-FEM Framework for the Digital Twin Generation of Historic Masonry Structures

Historic masonry buildings are characterised by uniqueness, which is intrinsically present in their building techniques, morphological features, architectural decorations, artworks, etc. From the modelling point of view, the degree of detail reached on transforming discrete digital representations of historic buildings, e.g., point clouds, into 3D objects and elements strongly depends on the final purpose of the project. For instance, structural engineers involved in the conservation process of built heritage aim to represent the structural system rigorously, neglecting architectural decorations and other details. Following this principle, the software industry is focusing on the definition of a parametric modelling approach, which allows performing the transition from half-raw survey data (point clouds) to geometrical entities in nearly no time. In this paper, a novel parametric Scan-to-FEM approach suitable for architectural heritage is presented. The proposed strategy uses the Generative Programming paradigm implementing a modelling framework into a visual programming environment. Such an approach starts from the 3D survey of the case-study structure and culminates with the definition of a detailed finite element model that can be exploited to predict future scenarios. This approach is appropriate for architectural heritage characterised by symmetries, repetition of modules and architectural orders, making the Scan-to-FEM transition fast and efficient. A Portuguese monument is adopted as a pilot case to validate the proposed procedure. In order to obtain a proper digital twin of this structure, the generated parametric model is imported into an FE environment and then calibrated via an inverse dynamic problem, using as reference metrics the modal properties identified from field acceleration data recorded before and after a retrofitting intervention. After assessing the effectiveness of the strengthening measures, the digital twin ability of reproducing past and future damage scenarios of the church is validated through nonlinear static analyses.

Close-Range Sensing and Data Fusion for Built Heritage Inspection and Monitoring—A Review

Built cultural heritage is under constant threat due to environmental pressures, anthropogenic damages, and interventions. Understanding the preservation state of monuments and historical structures, and the factors that alter their architectural and structural characteristics through time, is crucial for ensuring their protection. Therefore, inspection and monitoring techniques are essential for heritage preservation, as they enable knowledge about the altering factors that put built cultural heritage at risk, by recording their immediate effects on monuments and historic structures. Nondestructive evaluations with close-range sensing techniques play a crucial role in monitoring. However, data recorded by different sensors are frequently processed separately, which hinders integrated use, visualization, and interpretation. This article’s aim is twofold: i) to present an overview of close-range sensing techniques frequently applied to evaluate built heritage conditions, and ii) to review the progress made regarding the fusion of multi-sensor data recorded by them. Particular emphasis is given to the integration of data from metric surveying and from recording techniques that are traditionally non-metric. The article attempts to shed light on the problems of the individual and integrated use of image-based modeling, laser scanning, thermography, multispectral imaging, ground penetrating radar, and ultrasonic testing, giving heritage practitioners a point of reference for the successful implementation of multidisciplinary approaches for built cultural heritage scientific investigations.

A Multi-Analytical Study for the Enhancement and Accessibility of Archaeological Heritage: The Churches of San Nicola and San Basilio in Motta Sant’Agata (RC, Italy)

In the coming years, Italy will need to take on a great challenge concerning the digitization of its archaeological and architectural heritage, one of the richest and most problematic in the world. The aim is to improve the knowledge, conservation, enhancement and accessibility of cultural assets and to make them a resource for national and local development. In this process, the next generation of 3D survey methods (laser scanning and photogrammetry), in combination with diagnostic techniques (spectroscopy analyses) and GIS/BIM (Geographic Information System/Building Information Modeling) solutions, represent a valid support. This work, part of a broader intervention launched by the Municipality of Reggio Calabria for the requalification of some archaeological sites located within its urban and metropolitan area, is focused on the study case of Motta S. Agata. The ancient settlement is located 8 km from Reggio C. in a hilly area difficult to reach and preserves numerous structures in a state of ruin. Among these, two interesting medieval churches are proposed for examination: the church of San Nicola, characterized by five hypogeal funeral crypts, and the chapel of San Basilio, which preserves the traces of a wall painting. A multi-methodological approach including close-range photogrammetry, laser scanning and chemical and thermal analyses was adopted in order to fulfill different tasks: creating a topographic model of the hillfort, mapping the archaeological evidence, digitizing and returning 3D models of the churches, characterizing materials through chemical analyses and monitoring the surfaces with thermal imaging. These combined applications have contributed to reaching the planned goals, i.e., study, conservation, diagnostics, preparation for restoration interventions, development of digital media and dissemination. In this way, a type of interactive museum (made up of virtual tours and informative digital models) has been made available in order to improve the site’s accessibility and inclusivity as well as to test the effect of digitization in attracting tourists and local people toward a place located outside of the usual tourist circuits.

Symmetries of the Beijing Heping Temple Complex

Three-dimensional laser scanning technology has been more mature, and its application fields are expanding. It is being used in key projects and important work such as ancient building recording, restoration and reconstruction. In this paper, the technology is applied to the 3D scanning, data splicing and model simplification of Heping temple building complex in Beijing. After innovative research on ancient architecture, it is found that the group layout, single form and local components of Heping temple building complex in Beijing show symmetry everywhere, vividly reflecting the extensive and profound ancient architectural culture and order. This points out a new direction for the development and application of 3D laser scanning technology and opens up a new path for the in-depth study of the protection of ancient buildings in China.

Artificial Intelligence Based Structural Assessment for Regional Short- and Medium-Span Concrete Beam Bridges with Inspection Information

The functional and structural characteristics of civil engineering works, in particular bridges, influence the performance of transport infrastructure. Remote sensing technology and other advanced technologies could help bridge managers review structural conditions and deteriorations through bridge inspection. This paper proposes an artificial intelligence-based methodology to solve the condition assessment of regional bridges and optimize their maintenance schemes. It includes data integration, condition assessment, and maintenance optimization. Data from bridge inspection reports is the main source of this data-driven approach, which could provide a substantial amount og condition-related information to reveal the time-variant bridge condition deterioration and effect of maintenance behaviors. The regional bridge condition deterioration model is established by neural networks, and the impact of the maintenance scheme on the future condition of bridges is quantified. Given the need to manage limited resources and ensure safety and functionality, adequate maintenance schemes for regional bridges are optimized with genetic algorithms. The proposed data-driven methodology is applied to real regional highway bridges. The regional inspection information is obtained with the help of emerging technologies. The established structural deterioration models achieve up to 85% prediction accuracy. The obtained optimal maintenance schemes could be chosen according to actual structural conditions, maintenance requirements, and total budget. Data-driven decision support can substantially aid in smart and efficient maintenance planning of road bridges.

Heritage Sustainability of the Territory: Photogrammetric Survey of the Castle of Beas de Segura (Jaén, Spain)

Beas de Segura is an ancient village located in the valley of the Sierra de Segura, at the gateway to the Sierra de Cazorla, Segura y las Villas (Jaén, Spain). This territory has been inhabited by different cultures, from the Palaeolithic to the present day, giving rise to a complex urban fabric in which relevant architectural and archaeological elements still survive. The coexistence of these heritage structures with the inhabited domestic architecture has generated significant conflicts of coexistence, resulting in an accelerated process of physical and social deterioration of this increasingly impoverished area. Drawing, together with all the techniques that derive from it, is a necessary and precise source of knowledge and communication for understanding the territory, however complex it may be. This potential, applied to a heritage and social reality such as that of the Castle and Fortress of Beas de Segura (Jaén), allows for processes to be revealed, actions to be ordered, and interventions to be proposed. This article brings together the results of research carried out in this area of the Sierra de Segura, in which graphic expression, combined with the study of materials, has enabled us to identify original elements of the castle and medieval fortification. This system of knowledge discovery has been decisive in establishing a criterion for heritage intervention, seeking a sustainable balance between the development of life in this area of the city, the recovery of the collective memory of the surviving elements of the castle and fortress, and the conservation of the protected historical remains.

Deep Learning for LiDAR Point Clouds in Autonomous Driving: A Review

Recently, the advancement of deep learning (DL) in discriminative feature learning from 3-D LiDAR data has led to rapid development in the field of autonomous driving. However, automated processing uneven, unstructured, noisy, and massive 3-D point clouds are a challenging and tedious task. In this article, we provide a systematic review of existing compelling DL architectures applied in LiDAR point clouds, detailing for specific tasks in autonomous driving, such as segmentation, detection, and classification. Although several published research articles focus on specific topics in computer vision for autonomous vehicles, to date, no general survey on DL applied in LiDAR point clouds for autonomous vehicles exists. Thus, the goal of this article is to narrow the gap in this topic. More than 140 key contributions in the recent five years are summarized in this survey, including the milestone 3-D deep architectures, the remarkable DL applications in 3-D semantic segmentation, object detection, and classification; specific data sets, evaluation metrics, and the state-of-the-art performance. Finally, we conclude the remaining challenges and future researches.

Combining Multiband Imaging, Photogrammetric Techniques, and FOSS GIS for Affordable Degradation Mapping of Stone Monuments

The detailed documentation of degradation constitutes a fundamental step for weathering diagnosis and, consequently, for successful planning and implementation of conservation measures for stone heritage. Mapping the surface patterns of stone is a non-destructive procedure critical for the qualitative and quantitative rating of the preservation state. Furthermore, mapping is employed for the annotation of weathering categories and the calculation of damage indexes. However, it is often a time-consuming task, which is conducted manually. Thus, practical methods need to be developed to automatize degradation mapping without significantly increasing the diagnostic process’s cost for conservation specialists. This work aims to develop and evaluate a methodology based on affordable close-range sensing techniques, image processing, and free and open source software for the spatial description, annotation, qualitative analysis, and rating of stone weathering-induced damage. Low-cost cameras were used to record images in the visible, near-infrared, and thermal-infrared spectra. The application of photogrammetric techniques allowed for the generation of the necessary background, that was elaborated to extract thematic information. Digital image processing of the spatially and radiometrically corrected images and image mosaics enabled the straightforward transition to a spatial information environment simplifying the development of degradation maps. The digital thematic maps facilitated the rating of stone damage and the extraction of useful statistical data.

Developing a Virtual Museum: Experience from the Design and Creation Process

Virtual reality technology has grown significantly in recent years. The arrival of Head Mounted Displays (HDM) on the market for end-users has positioned these technologies as a new channel to promote new simulated or contextualized experiences. We have used the design and creation strategy to develop a virtual reality experience for the Oculus GO and Quest HDM. We digitized 30 pieces from nine local museums to provide an experience guided by a character that represents the main artisan work of the local region. A usability test was performed, showing that participants felt a high degree of immersion and realism. They were able to complete the assigned tasks, and results suggest that the software meets the main objective. Furthermore, the creation of this virtual reality (VR) experience has shown how important it is to make users a part of the creation process, as well as to develop a process to make the software useful to them and other users. Some recommendations are made based on the experience of the development, and comments are given on each step of the design and creation strategy.

Assessment of the Cultural Heritage Potential in Poland

Cultural heritage is a complex and multi-faceted concept, thus eluding a definition. Consequently, it is a daunting task to assess the cultural heritage potential of a country, region, or community unambiguously. The paper defines “cultural heritage potential” and presents an example of a synthetic assessment of the potential with Poland as an example. The assessment involved several normalised diagnostic variables grouped into four thematic fields. This way, cultural heritage potential could be represented by a “synthetic quality index”. The analysis yielded a ranked list of voivodeships (third-tier subdivision units) and their classification (typology) regarding cultural heritage potential. An in-depth analysis demonstrated that the cultural heritage potential rank of a voivodeship could be determined by values of selected diagnostic valuables, such as the number of heritage objects, number of food products of documented quality and particular cultural significance, and extensive cultural infrastructure. The typology can be a background for decision-making with the consequences of voivodeship classification depending on the context of a specific analysis. The proposed method for assessing cultural heritage potential is not related to the territorial extent of the area. Any quantifiable attribute of cultural heritage can be used in the assessment regardless of the unit of measure. Such an assessment can be useful for the identification of trouble areas, areas of concern, and model areas.

The Use of Virtual Reality to Promote Sustainable Tourism: A Case Study of Wooden Churches Historical Monuments from Romania

The accelerated development and expansion of cultural tourism in areas with unique tourist objectives, characterised by a high degree of risk in terms of their physical and chemical integrity, requires sustained efforts by all stakeholders to identify new methods, techniques, and procedures for their conservation, protection, and capitalisation, with respect to tourism. The aim of this study was to propose an optimal methodology for capitalising on tourism related to wooden churches, regarded as a structural item of tangible cultural heritage, with positive effects on the protection, conservation, information, and awareness of all stakeholders in tourism development. This involved the development of a web portal, in which were integrated the 3D models related to the analysed objects, the panoramic images inside them, the audio support, the photographs, and the accompanying text necessary to create and render a virtual reality (VR) production for purposes of virtual tourism (VT). The results obtained consisted of the creation of the website Bihor360°, which is freely navigable and whose content, including both textual and graphic information, can be easily accessed by all interested users. The aim involved was to release an online bridge for potential visitors to the fragile tourist attractions, facilitating the development of active knowledge and VR while raising awareness among the population and the local authorities about the role and the importance of the wooden churches in tourism and the local economy.

3D Reconstruction and Geostatic Analysis of an Early Medieval Cemetery (Olonne-sur-Mer, France)

A preventive excavation performed in 2018 prior to development work led to the discovery of more than 213 subjects buried from the 4th to the 11th centuries in the 1850 m2 dug area. This is a cemetery located in Olonne-sur-Mer in France (46.53723, −1.77603). The complex is limited to the south by a ditch. To the north, no limits were observed during the excavation and, to the west, ancient archaeological surveys suggest an extension of the burial area. Biological analysis of the skeletons reveals a demographic characterizing a natural community, with an under-representation of children under 5 and with subjects under 20 appearing to be grouped together in the center of the area. The place where the youngest are buried often testifies to a strategic position in Christian contexts (near church doors, under sub stillicidio gutters, etc.). Funeral practices are characterized by numerous skeletal alterations, especially in the western area of the site where their concentrations are particularly significant. These are not ossuaries but rather supernumerary bones present in the fills of graves of subjects in place or old tombs where no skeletons in place are preserved. These alterations mark the areas where burials are most frequent. The 3D reconstruction is coupled with geostatistical analyses (heatmap and Moran’s index), considering the digging of the land, the concentration of residual artefacts found in the graves, but also the biological characteristics of the sample and the funeral practices uncovered. From 2D entities generated with GIS software, the process of the elevation and sculpture of the volumes is innovative, because even if it is carried out by precise but classical computer graphics techniques, it is led by advanced taphonomical and anthropological reflections. This makes it possible to propose empty spaces, a potential gathering area for the village community and circulation paths. These elements are essential in order to go beyond the storytelling often proposed in archaeology and propose a vision based on the coherence of the observed facts. Even when the archaeological remains are only sunken (no preserved elevation), the integration of multisource archaeological data (biological anthropology, funerary, artefacts and pit size) allows relevant 3D reconstructions as a formidable tool for discussing past occupations. Three-dimensional technologies make it possible to recreate a lost environment to allow a better understanding of the site. They are didactic and help to share data between researchers and/or the public, especially when they are invisible such as the presence of empty space.

3D Reconstruction of Cultural Heritage Sites as an Educational Approach. The Sanctuary of Delphi

In the field of cultural heritage, three-dimensional (3D) reconstruction of monuments is a usual activity for many professionals. The aim in this paper focuses on the new technology educational application combining science, history, and archaeology. Being involved in almost all stages of implementation steps and assessing the level of participation, university students use tools of computer gaming platform and participate in ways of planning the virtual environment which improves their education through e-Learning. The virtual 3D environment is made with different imaging methods (helium-filled balloon, Structure for motion, 3D repository models) and a developmental plan has been designed for use in many future applications. Digital tools were used with 3D reconstructed buildings from the museum archive to Unity 3D for the design. The pilot study of Information Technology work has been employed to introduce cultural heritage and archaeology to university syllabuses. It included students with a questionnaire which has been evaluated accordingly. As a result, the university students were inspired to immerse themselves into the virtual lab, aiming to increasing the level of interaction. The results show a satisfactory learning outcome by an easy to use and real 3D environment, a step forward to fill in needs of contemporary online sustainable learning demands.

Evaluation of camera settings for photogrammetric reconstruction of humanoid phantoms for EBRT bolus and HDR surface brachytherapy applications

The fabrication of brachytherapy surface moulds is considered laborious and time consuming that often result in repeated attempts due to incorrect catheter positioning or the presence of air gaps. 3-dimensional printing using low-cost and reliable materials has allowed the rapid creation of patient-specific surface mould applicators to be achieved using patient imaging data obtained via CT scan. In this study we investigate whether an alternative approach using photogrammetry techniques can improve this process and how camera settings and object texture affect the reconstructions. Two humanoid phantoms, an anthropomorphic RANDO phantom and a Laerdal Little Anne CPR training manikin were used in this study. Both were imaged using a Nikon D5600 DSLR and Nokia 3.1 smartphone camera and reconstructed using Agisoft Metashape software. CT scans of both phantoms were taken as references for comparing the photogrammetry reconstructions. Models were reconstructed from different photo sets and assessed by distance to agreement with the CT models. Both phantoms were effectively reconstructed for most experiments. Increasing the number of photos used produced the better reconstructions while in general, reconstructions using video data were poor. The two phantoms were reconstructed at a similar quality. Background light that caused undesirable reflections significantly reduced reconstruction quality. Applying a non-reflective tape to the affected regions provided a suitable method for reducing their effects. Photogrammetry techniques were effectively able to reconstruct 3-dimensional models of both phantom. The camera settings and lighting did have a profound effect on the reconstruction quality and should be chosen appropriately depending on the scene.

Symmetry Analysis of Oriental Polygonal Pagodas Using 3D Point Clouds for Cultural Heritage

Ancient pagodas are usually parts of hot tourist spots in many oriental countries due to their unique historical backgrounds. They are usually polygonal structures comprised by multiple floors, which are separated by eaves. In this paper, we propose a new method to investigate both the rotational and reflectional symmetry of such polygonal pagodas through developing novel geometric models to fit to the 3D point clouds obtained from photogrammetric reconstruction. The geometric model consists of multiple polygonal pyramid/prism models but has a common central axis. The method was verified by four datasets collected by an unmanned aerial vehicle (UAV) and a hand-held digital camera. The results indicate that the models fit accurately to the pagodas’ point clouds. The symmetry was realized by rotating and reflecting the pagodas’ point clouds after a complete leveling of the point cloud was achieved using the estimated central axes. The results show that there are RMSEs of 5.04 cm and 5.20 cm deviated from the perfect (theoretical) rotational and reflectional symmetries, respectively. This concludes that the examined pagodas are highly symmetric, both rotationally and reflectionally. The concept presented in the paper not only work for polygonal pagodas, but it can also be readily transformed and implemented for other applications for other pagoda-like objects such as transmission towers.

Protocol Development for Point Clouds, Triangulated Meshes and Parametric Model Acquisition and Integration in an HBIM Workflow for Change Control and Management in a UNESCO's World Heritage Site

This article illustrates a data acquisition methodological process based on Structure from Motion (SfM) processing confronted with terrestrial laser scanner (TLS) and integrated into a Historic Building Information Model (HBIM) for architectural Heritage's management. This process was developed for the documentation of Cáceres' Almohad wall bordering areas, a UNESCO World Heritage Site. The case study's aim was the analysis, management and control of a large urban area where the urban growth had absorbed the wall, making it physically inaccessible. The methodology applied was the combination of: clouds and meshes obtained by SfM; with images acquired from Unmanned Aerial Vehicle (UAV) and Single Lens Reflex (SLR) and terrestrial photogrammetry; and finally, with clouds obtained by TLS. The outcome was a smart-high-quality three-dimensional study model of the inaccessible urban area. The final result was two-fold. On one side, there was a methodological result, a low cost and accurate smart work procedure to obtain a three-dimensional parametric HBIM model that integrates models obtained by remote sensing. On the other side, a patrimonial result involved the discovery of a XII century wall's section, that had supposedly been lost, that was hidden among the residential buildings. The article covers the survey campaign carried out by the research team and the techniques applied.

From the Semantic Point Cloud to Heritage-Building Information Modeling: A Semiautomatic Approach Exploiting Machine Learning

This work presents a semi-automatic approach to the 3D reconstruction of Heritage-Building Information Models from point clouds based on machine learning techniques. The use of digital information systems leveraging on three-dimensional (3D) representations in architectural heritage documentation and analysis is ever increasing. For the creation of such repositories, reality-based surveying techniques, such as photogrammetry and laser scanning, allow the fast collection of reliable digital replicas of the study objects in the form of point clouds. Besides, their output is raw and unstructured, and the transition to intelligible and semantic 3D representations is still a scarcely automated and time-consuming process requiring considerable human intervention. More refined methods for 3D data interpretation of heritage point clouds are therefore sought after. In tackling these issues, the proposed approach relies on (i) the application of machine learning techniques to semantically label 3D heritage data by identification of relevant geometric, radiometric and intensity features, and (ii) the use of the annotated data to streamline the construction of Heritage-Building Information Modeling (H-BIM) systems, where purely geometric information derived from surveying is associated with semantic descriptors on heritage documentation and management. The “Grand-Ducal Cloister” dataset, related to the emblematic case study of the Pisa Charterhouse, is discussed.

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 image-based 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.

Development and Validation of LiDAR Sensor Simulators Based on Parallel Raycasting

Three-dimensional (3D) imaging technologies have been increasingly explored in academia and the industrial sector, especially the ones yielding point clouds. However, obtaining these data can still be expensive and time-consuming, reducing the efficiency of procedures dependent on large datasets, such as the generation of data for machine learning training, forest canopy calculation, and subsea survey. A trending solution is developing simulators for imaging systems, performing the virtual scanning of the digital world, and generating synthetic point clouds from the targets. This work presents a guideline for the development of modular Light Detection and Ranging (LiDAR) system simulators based on parallel raycasting algorithms, with its sensor modeled by metrological parameters and error models. A procedure for calibrating the sensor is also presented, based on comparing with the measurements made by a commercial LiDAR sensor. The sensor simulator developed as a case study resulted in a robust generation of synthetic point clouds in different scenarios, enabling the creation of datasets for use in concept tests, combining real and virtual data, among other applications.

A Heritage Science Workflow to Preserve and Narrate a Rural Archeological Landscape Using Virtual Reality: The Cerro del Castillo of Belmez and Its Surrounding Environment (Cordoba, Spain)

The main aim of this article is to present a heritage action protocol based on the application of photogrammetric and LiDAR acquisitions, a catalogue of flora and fauna, archeological research, and 3D virtualization for the integrated recovery of a rural cultural heritage site located in the Alto Guadiato Valley of Cordoba, Spain. This joint multidisciplinary action focusing on a common heritage objective has resulted in a comprehensive and innovative action: the virtualization of an 800-hectare multitemporal archeological landscape. The results may be of interest to researchers, educators, and tourism agents, or for the dissemination of scientific knowledge, among other applications. The protocol of actions implemented in the framework of this project can be replicated in sites with similar characteristics, particularly rural areas with well-preserved landscapes that have not been investigated. The main result of the project is the preservation of geomorphological features using remote sensing technologies and the creation of a virtual lookout for this historical and natural landscape (GuadiatVR), which is a very uncommon outcome within the virtualization of historical landscapes. The lookout can be downloaded from Google Play on IOS.

Suitability Study of Structure-from-Motion for the Digitisation of Architectural (Heritage) Spaces to Apply Divergent Photograph Collection

The digitisation of architectural heritage has experienced a great development of low-cost and high-definition data capture technologies, thus enabling the accurate and effective modelling of complex heritage assets. Accordingly, research has identified the best methods to survey historic buildings, but the suitability of Structure-from-Motion/Multi-view-Stereo (SfM/MVS) for interior square symmetrical architectural spaces is unexplored. In contrast to the traditional SfM surveying for which the camera surrounds the object, the photograph collection approach is divergent in courtyards. This paper evaluates the accuracy of SfM point clouds against Terrestrial Laser Scanning (TLS) for these large architectural spaces with a symmetrical configuration, with the main courtyard of Casa de Pilatos in Seville, Spain, as a case study. Two different SfM surveys were conducted: (1) Without control points, and (2) referenced using a total station. The first survey yielded unacceptable results: A standard deviation of 0.0576 m was achieved in the northwest sector of the case study, mainly because of the difficulty of aligning the SfM and TLS data due to the way they are produced. This value could be admissible depending on the purpose of the photogrammetric model.

Color and Laser Data as a Complementary Approach for Heritage Documentation

Heritage recording has received much attention and benefits from recent developments in the field of range and imaging sensors. While these methods have often been viewed as two different methodologies, data integration can achieve different products, which are not always found in a single technique. Data integration in this paper can be divided into two levels: laser scanner data aided by photogrammetry and photogrammetry aided by scanner data. At the first level, superior radiometric information, mobility and accessibility of imagery can be actively used to add texture information and allow for new possibilities in terms of data interpretation and completeness of complex site documentation. In the second level, true orthophoto is generated based on laser data, the results are rectified images with a uniform scale representing all objects at their planimetric position. The proposed approaches enable flexible data fusion and allow images to be taken at an optimum time and position for radiometric information. Data fusion usually involves serious distortions in the form of a double mapping of occluded objects that affect the product quality. In order to enhance the efficiency of visibility analysis in complex structures, a proposed visibility algorithm is implemented into the developed methods of texture mapping and true orthophoto generation. The algorithm filters occluded areas based on a patch processing using a grid square unit set around the projected vertices. The depth of the mapped triangular vertices within the patch neighborhood is calculated to assign the visible one. In this contribution, experimental results from different historical sites in Jordan are presented as a validation of the proposed algorithms. Algorithms show satisfactory performance in terms of completeness and correctness of occlusion detection and spectral information mapping. The results indicate that hybrid methods could be used efficiently in the representation of heritage structures.

A Built Heritage Information System Based on Point Cloud Data: HIS-PC

The digital management of an archaeological site requires to store, organise, access and represent all the information that is collected on the field. Heritage building information modelling, archaeological or heritage information systems now tend to propose a common framework where all the materials are managed from a central database and visualised through a 3D representation. In this research, we offer the development of a built heritage information system prototype based on a high-resolution 3D point cloud data set. The particularity of the approach is to consider a user-centred development methodology while avoiding meshing/down-sampling operations. The proposed system is initiated by a close collaboration between multi-modal users (managers, visitors, curators) and a development team (designers, developers, architects). The developed heritage information system permits the management of spatial and temporal information, including a wide range of semantics using relational along with NoSQL databases. The semantics used to describe the artifacts are subject to conceptual modelling. Finally, the system proposes a bi-directional communication with a 3D interface able to stream massive point clouds, which is a big step forward to provide a comprehensive site representation for stakeholders while minimising modelling costs.

From the Point Cloud to BIM Methodology for the Ideal Reconstruction of a Lost Bastion of the Cáceres Wall

Thanks to the use of non-invasive techniques and remote sensing in a 19th century building, it was possible to demonstrate that said building is a lost part of the Cáceres wall. This wall was believed to maintain the straight line from a known section, but remote sensing makes it clear that at that point the wall makes a break creating a door of which there was no record. Once this premise was confirmed, an ideal reconstruction hypothesis was developed. For this, the work base was taken on the data collected in an exhaustive data collection process, which launched millions of control points and facilitated in theorizing the original state of this lost section. The HBIM methodology greatly facilitated the process, and will allow for possible modifications with an IFC file as advances are made in that area. Finally, the research proposes an architectural project path that takes into account the data obtained remotely, and that achieves the inclusion of this part of the city in cultural interest and, of course, in a protected and cataloged area.

Fusion of UAV and Terrestrial Photogrammetry with Laser Scanning for 3D Reconstruction of Historic Churches in Georgia

In September 2018, photogrammetric images and terrestrial laser scans were carried out as part of a measurement campaign for the three-dimensional recording of several historic churches in Tbilisi (Georgia). The aim was the complete spatial reconstruction with a spatial resolution and accuracy of approx. 1 cm under partly difficult external conditions, which required the use of different measurement techniques. The local measurement data were collected by two laser scanning campaigns (Leica BLK360 and Faro Focus 3D X330), several UAV flights and two terrestrial image sets. The photogrammetric point clouds were calculated with the image-based modelling programs AgiSoft and RealityCapture taking into account the control points from the laser scans. The mean residual errors from the registrations or photogrammetric evaluations are 4–16 mm, depending on the selected software, size and complexity of the monument and environmental conditions. The best completeness and quality of the resulting 3D model was achieved by using laser scan data and images simultaneously. The article presents recent results obtained with RealityCapture and gives a critical analysis of accuracy and modelling quality.

A Case Study on the Noncontact Inventory of the Oldest European Cast-iron Bridge Using Terrestrial Laser Scanning and Photogrammetric Techniques

Conventional measurement technologies of transportation infrastructures consist of discrete surveys which can be inconvenient in practice. Furthermore, data obtained using these methods are restricted to several points (or elements) placed on the observed structures. Modern survey techniques—for example, terrestrial laser scanning (TLS) and photogrammetric—allow for the surveying of quasi-continuous surfaces of examined structures. The examined object is an historic cast-iron suspension bridge in Ozimek (south of Poland). The bridge was constructed in 1825–1827 and constitutes the oldest European bridge of this type. The surveys were conducted using TLS and digital photogrammetric techniques. The data obtained were compared with traditional survey results (reference data) and the project. The achieved effects of the measurements show that the discrepancies between the applied techniques (TLS and photogrammetry) and reference methods varied only within several millimeters and can be regarded as satisfactory. Better compliance was obtained for TLS than photogrammetry. The main benefits of the applied techniques include reducing time in the field and obtaining a three-dimensional model of the structure that has satisfactory accuracy.

Initial User-Centered Design of a Virtual Reality Heritage System: Applications for Digital Tourism

Reality capture allows for the reconstruction, with a high accuracy, of the physical reality of cultural heritage sites. Obtained 3D models are often used for various applications such as promotional content creation, virtual tours, and immersive experiences. In this paper, we study new ways to interact with these high-quality 3D reconstructions in a real-world scenario. We propose a user-centric product design to create a virtual reality (VR) application specifically intended for multi-modal purposes. It is applied to the castle of Jehay (Belgium), which is under renovation, to permit multi-user digital immersive experiences. The article proposes a high-level view of multi-disciplinary processes, from a needs analysis to the 3D reality capture workflow and the creation of a VR environment incorporated into an immersive application. We provide several relevant VR parameters for the scene optimization, the locomotion system, and the multi-user environment definition that were tested in a heritage tourism context.

A Computational Workflow for Generating A Voxel-Based Design Approach Based on Subtractive Shading Envelopes and Attribute Information of Point Cloud Data

This study proposes a voxel-based design approach based on the subtractive mechanism of shading envelopes and attributes information of point cloud data in tropical climates. In particular, the proposed method evaluates a volumetric sample of new buildings based on predefined shading performance criteria. With the support of geometric and radiometric information stored in point cloud, such as position (XYZ), color (RGB), and reflection intensity (I), an integrated computational workflow between passive design strategy and 3D scanning technology is developed. It aims not only to compensate for some pertinent aspects of the current 3D site modeling, such as vegetation and surrounding buildings, but also to investigate surface characteristics of existing contexts, such as visible sun vectors and material properties. These aspects are relevant for conducting a comprehensively environmental simulation, while averting negative microclimatic impacts when locating the new building into the existing context. Ultimately, this study may support architects for taking decision-making in conceptual design stage based on the real contextual conditions.

A Real-Time Infrared Stereo Matching Algorithm for RGB-D Cameras’ Indoor 3D Perception

Low-cost, commercial RGB-D cameras have become one of the main sensors for indoor scene 3D perception and robot navigation and localization. In these studies, the Intel RealSense R200 sensor (R200) is popular among many researchers, but its integrated commercial stereo matching algorithm has a small detection range, short measurement distance and low depth map resolution, which severely restrict its usage scenarios and service life. For these problems, on the basis of the existing research, a novel infrared stereo matching algorithm that combines the idea of the semi-global method and sliding window is proposed in this paper. First, the R200 is calibrated. Then, through Gaussian filtering, the mutual information and correlation between the left and right stereo infrared images are enhanced. According to mutual information, the dynamic threshold selection in matching is realized, so the adaptability to different scenes is improved. Meanwhile, the robustness of the algorithm is improved by the Sobel operators in the cost calculation of the energy function. In addition, the accuracy and quality of disparity values are improved through a uniqueness test and sub-pixel interpolation. Finally, the BundleFusion algorithm is used to reconstruct indoor 3D surface models in different scenarios, which proved the effectiveness and superiority of the stereo matching algorithm proposed in this paper.

Machine Learning Generalisation across Different 3D Architectural Heritage

The use of machine learning techniques for point cloud classification has been investigated extensively in the last decade in the geospatial community, while in the cultural heritage field it has only recently started to be explored. The high complexity and heterogeneity of 3D heritage data, the diversity of the possible scenarios, and the different classification purposes that each case study might present, makes it difficult to realise a large training dataset for learning purposes. An important practical issue that has not been explored yet, is the application of a single machine learning model across large and different architectural datasets. This paper tackles this issue presenting a methodology able to successfully generalise to unseen scenarios a random forest model trained on a specific dataset. This is achieved looking for the best features suitable to identify the classes of interest (e.g., wall, windows, roof and columns).

Suitability of Automatic Photogrammetric Reconstruction Configurations for Small Archaeological Remains

Three-dimensional (3D) reconstruction is a useful technique for the documentation, characterization, and evaluation of small archeological objects. In this research, a comparison among different photogrammetric setups that use different lenses (macro and standard zoom) and dense point cloud generation calibration processes for real specific objects of archaeological interest with different textures, geometries, and materials is raised using an automated data collection. The data acquisition protocol is carried out from a platform with control points referenced with a metrology absolute arm to accurately define a common spatial reference system. The photogrammetric reconstruction is performed considering a camera pre-calibration as well as a self-calibration. The latter is common for most data acquisition situations in archaeology. The results for the different lenses and calibration processes are compared based on a robust statistical analysis, which entails the estimation of both standard Gaussian and non-parametric estimators, to assess the accuracy potential of different configurations. As a result, 95% of the reconstructed points show geometric discrepancies lower than 0.85 mm for the most unfavorable case and less than 0.35 mm for the other cases.