Photogrammetric Models Research Articles

Digitalization of the Workflow for Drone-Assisted Inspection and Automated Assessment of Industrial Buildings for Effective Maintenance Management

Industrial buildings are a key element in the industrial fabric, and their maintenance is essential to ensure their proper functioning and avoid disruptions and costly economic losses. Continuous maintenance based on an accurate diagnosis makes it possible to meet the challenges of aging infrastructures, which demands a reliable data-based assessment for maintenance management implementing corrective and preventive actions, according to the damage criticality. This paper researches an innovative digitalized process for the inspection and diagnosis of industrial buildings, which leads to categorizing and prioritizing maintenance actions in an objective and cost-effective way from the inspection data. The process integrates some technical developments carried out in this work, aimed to automate the workflow: the drone-based inspection, the building condition assessment from the definition of a standardized construction pathology library, and a visual analysis of pathology evolution based on photogrammetry. The use of drones for digitalized inspection involves some challenges related to the positioning of the drone for damage localization, which has been herein overcome by developing a geo-annotation system for image acquisition. This system has also enabled the capture of geo-located images intended to generate 3D photogrammetric models for quantifying the pathological process evolution. Moreover, the assessment procedure outlined through multi-criteria decision-making methodology MIVES establishes a single criterion to automatically weight the relative importance of the damage defined in the library. As a result, this procedure yields the so-called Intervention Urgency Index (IUI), which allows prioritizing the maintenance actions associated with the damage while also considering economic criteria. In such a way, the overall process aims to increase reliability and consistency in the results of inspection and diagnosis needed for the effective maintenance management of industrial buildings.

Quantitative Neuroanatomical measurement on Photogrammetric model: Validation study.

To scrutinize and compare the accuracy of measurements obtained from photogrammetric models against direct measurements taken on dry skulls, with the aim to verify the feasibility of photogrammetry for quantitative analysis in microsurgical neuroanatomy. Two dry human skulls were used. Each was scanned using the dual camera system of a smartphone The selected photos were separately processed two different software to create 3D models. Subsequently, 41 anatomical measures (both linear and curvilinear) based on common anatomical landmarks, were taken both directly on dry skulls and on photogrammetric models and compared. Analyzed factors included measurement error, intra- and inter-rater reliability and, the intermodality agreement. Four photogrammetric models were created. Our analysis revealed similar errors when comparing the photogrammetric and direct measurements. Measurements from digital models exhibited robust reliability among repeated measures and different observers, supported by very high Intraclass Correlation Coefficient (ICC) values. Mean measurement difference between Agisoft Metashape software-generated models and direct measurement was 0.01 cm with no systematic bias observed. Conversely, the Metascan app-derived models showed a mean measurement difference of -0.35 cm compared to direct measurement, displaying good agreement for smaller measurements and a systematic proportional bias with increasing measurement size. The role of two photogrammetric models is validated as quantitative analysis technique for laboratory neuroanatomical studies showing acceptable measurement error, high intra- and inter-rater reliability as well as good to very good agreement compared to direct measurement on dry skulls, replacing the expensive and time-consuming methods like CT scans and neuronavigation system.

The carved monuments of La Milpa, Belize: Results of photogrammetric and epigraphic documentation

Abstract La Milpa, situated in northern Belize, stands out as one of the region's largest archaeological sites, having served as the capital of an ancient Maya city-state. Its significance is indicated by extensive monumental architecture, with the epicenter covering approximately 8.8 ha. The site's corpus of monuments, comprising 23 stelae and several altars, underscores its prominence in northern Belize, rivaling the corpora of sites such as Nim li Punit and Caracol. Despite its remote location, La Milpa has garnered the attention of researchers, particularly since the first modern survey of the site in 1988. Subsequent studies—in particular, that by Nikolai Grube in the 1990s—has provided detailed analyses of the site's corpus of carved monuments. Recent efforts, including epigraphic documentation in 2019, serve to enhance our understanding of La Milpa's dynastic history through traditional epigraphic and computational photographic methods. Utilizing field observations, raking light photography, and 3D photogrammetric models, we have refined previous analyses and provide new insights into the iconography and textual segments of the monuments. Here, we present the results of these recent efforts as well as our new analyses of a selection of monuments.

An Integrated Approach to Riverbed Morphodynamic Modeling Using Remote Sensing Data

River inlets, deltas, and estuaries represent delicate ecosystems highly susceptible to climate change impacts. While significant progress has been made in understanding the morphodynamics of these environments in recent decades, the development of models still requires thorough testing and data integration. In this context, remote sensing emerges as a potent tool, providing crucial data and the ability to monitor temporal changes. In this paper, an integrated approach combining remote sensing and morphodynamic modeling is proposed to assess river systems comprehensively. By utilizing multispectral or RGB optical imagery from satellites or UAVs for river classification and remotely derived bathymetry, echo sounder data for ground truth, and photogrammetric modeling of emerged areas, we outline a procedure to create an integrated and continuous digital terrain model (DTM) of a riverbed, paying particular attention to the wet–dry interface. This method enables us to identify the river centerline, its width, and its slope variations. Additionally, by applying a linear morphodynamic model that considers the spatial variability of river morphology commonly found in estuarine environments, it is possible to predict the wavelength and migration rate of sediment bars. This approach has been successfully applied to recreate the DTM and monitor the morphodynamics of the seaward reach of the Roya River (Italy).

A Drone-Based Structure from Motion Survey, Topographic Data, and Terrestrial Laser Scanning Acquisitions for the Floodgate Gaps Deformation Monitoring of the Modulo Sperimentale Elettromeccanico System (Venice, Italy)

The structural deformation monitoring of civil infrastructures can be performed using different geomatic techniques: topographic measurements with total stations and levels, TLS (terrestrial laser scanning) acquisitions, and drone-based SfM (structure from motion) photogrammetric surveys, among others, can be applied. In this work, these techniques are used for the floodgate gaps and the rubber joints deformation monitoring of the MOSE system (Modulo Sperimentale Elettromeccanico), the civil infrastructure that protects Venice and its lagoon (Italy) from high waters. Since the floodgates are submerged most of the time and cannot be directly measured and monitored using high-precision data, topographic surveys were performed in accessible underwater tunnels. In this way, after the calculation of the coordinates of some reference points, the coordinates of the floodgate corners were estimated knowing the geometric characteristics of the system. A specific activity required the acquisition of the TLS scans of the stairwells in the shoulder structures of the Treporti barrier because many of the reference points fixed on the structures were lost during the placement of elements on the seabed. They were replaced with new points whose coordinates in the project/as-built reference system were calculated by applying the Procrustean algorithm by means of homologous points. The procedure allowed the estimation of the transformation parameters with maximum residuals of less than 2.5 cm, a value in agreement with the approximation of the real concrete structures built. Using the obtained parameters, the coordinates of the new reference points were calculated in the project reference system. Once the 3D orientation of all caissons in the barrier was reconstructed, the widths of the floodgate gaps were estimated and compared with the designed values and over time. The obtained values were validated in the Treporti barrier using a drone-based SfM photogrammetric survey of the eight raised floodgates, starting from the east shoulder caisson. The comparison between floodgate gaps estimated from topographic and TLS surveys, and those obtained from measurements on the 3D photogrammetric model, provided a maximum difference of 1.6 cm.

Erosion anisotropy analysis of construction materials as a key tool for strengthening preventive conservation strategies in built heritage

In this paper, we present an innovative Erosion Anisotropy Analysis as a pioneering tool to discern the most harmful hydrometerological agents and their predominant directions of impact on built heritage. The proposed Erosion Anisotropy Analysis includes: 1) the analysis of weathering, bio-weathering and erosion processes affecting the building materials; 2) analysis of climatic series identifying preferential directionality of hydrometeorological agents; 3) erosion quantification using photogrammetric models; and 4) comparative analysis between both erosion and climatic anisotropy models.The proposed analysis is applied to the Cerrillos Tower (Almería, Spain), which is considered a paradigmatic case study due to their location and exposure conditions. Results determinate the primary vulnerability directions against hydrometeorological agents (N200–330°E) and highlight solar radiation, wind and wind-driven rain as the most damaging factors. Moreover, the Erosion Anisotropy Analysis describes the erosion patterns developed as well as their anisotropic distribution in the Tower.The proposed methodology is a benchmark for designing and dimensioning effective preventive measures to mitigate their impact under current climatic conditions as well as to prevent future scenarios within the global framework of climate change.

Neuroanatomical photogrammetric models using smartphones: a comparison of apps

ObjectivesA deep knowledge of the surgical anatomy of the target area is mandatory for a successful operative procedure. For this purpose, over the years, many teaching and learning methods have been described, from the most ancient cadaveric dissection to the most recent virtual reality, each with their respective pros and cons. Photogrammetry, an emergent technique, allows for the creation of three-dimensional (3D) models and reconstructions. Thanks to the spreading of photogrammetry nowadays it is possible to generate these models using professional software or even smartphone apps. This study aims to compare the neuroanatomical photogrammetric models generated by the two most utilized smartphone applications in this domain, Metascan and 3D-Scanner, through quantitative analysis.MethodsTwo human head specimens (four sides) were examined. Anatomical dissection was segmented into five stages to systematically expose well-defined structures. After each stage, a photogrammetric model was generated using two prominent smartphone applications. These models were then subjected to both quantitative and qualitative analysis, with a specific focus on comparing the mesh density as a measure of model resolution and accuracy. Appropriate consent was obtained for the publication of the cadaver's image.ResultsThe quantitative analysis revealed that the models generated by Metascan app consistently demonstrated superior mesh density compared to those from 3D-Scanner, indicating a higher level of detail and potential for precise anatomical representation.ConclusionEnabling depth perception, capturing high-quality images, offering flexibility in viewpoints: photogrammetry provides researchers with unprecedented opportunities to explore and understand the intricate and magnificent structure of the brain. However, it is of paramount importance to develop and apply rigorous quality control systems to ensure data integrity and reliability of findings in neurological research. This study has demonstrated the superiority of Metascan in processing photogrammetric models for neuroanatomical studies.

Unveiling Stage Zero Conditions in the New Forest National Park: A UAV‐Based Structure‐From‐Motion Photogrammetry and LiDAR Approach for Reconstructing an Anastomosing Wet Woodland at the Avon Water

ABSTRACTIn recent years, there have been significant technological advances in uncrewed aerial vehicles (UAVs) and in particular the use of lightweight consumer‐grade ‘drones’. This combined with the development of structure‐from‐motion (SfM) technology has provided river restoration practitioners with a new tool that can be used to give an affordable, repeatable and objective assessment of river restoration projects. In this study, a combined SfM photogrammetry and LiDAR approach is utilised on a section of the Avon water, a small watercourse in the New Forest National Park. Victorian‐era straightening and channelisation has significantly altered the ecological and morphological state of the river system, but recent river restoration projects aim to reverse these effects. Whilst historic maps may be used as a guide to reveal the former alignment, changes in river planform occurred much earlier and these maps may not represent the natural course of the river. High‐resolution orthophotos and 3D photogrammetric models of the site are created that reveal a palaeolandscape consisting of a mosaic of anabranching channels. These are interpreted to represent a former anastomosing wet woodland and ‘Stage Zero’ of the river system. It is inferred that early human habitation and associated land clearance altered hydrological and hydrogeological conditions, reducing floodplain connectivity and promoting single‐threaded planform configurations. This was then followed by the most recent Victorian‐era straightening. The palaeolandscape revealed by the study provides a guide for future Stage Zero river restoration in the New Forest and elsewhere, demonstrating an application of low cost, UAV‐derived photogrammetry in river restoration research.

Navigating the Intersection Between the Orbit and the Skull Base: The "Mirror" McCarty Keyhole During Transorbital Approach: An Anatomic Study With Surgical Implications.

McCarty keyhole (MCK) is the most important entry point during orbitocranial and cranio-orbital approaches; nevertheless, its anatomic coordinates have never been detailedly described from transorbital perspective. To provide the spatial coordinates for intraorbital projection of the "mirror" MCK by using the well-established main anatomic-surgical bony landmarks met along transorbital corridor. MCK was identified in 15 adult dry skulls (30 sides) on exocranial surface of pterional region based on the well-defined external bony landmarks: on the frontosphenoid suture, 5 to 6 mm behind the joining point (JP) of frontozygomatic suture (FZS), frontosphenoid suture (FSS), and sphenozygomatic suture (SZS). A 1-mm burr hole was performed and progressively enlarged to identify the intracranial and intraorbital compartments. Exit site of the intraorbital part of burr hole was referenced to the FZS on the orbital rim, the superior orbital fissure, and the inferior orbital fissure and to the JP of FZS, FSS, and SZS. To electronically validate the results, 3-dimensional photorealistic and interactive models were reconstructed with photogrammetry. Finally, for a further validation, McCarty mirror keyhole was also exposed, based on results achieved, through endoscopic transorbital approach in 10 head specimens (20 sides). Intraorbital projection of MCK was identified on the FSS on intraorbital surface, 1.5 ± 0.5 mm posterior to JP, 11.5 ± 1.1 mm posterior to the FZS on orbital rim following the suture, 13.0 ± 1.2 mm from most anterior end of superior orbital fissure, 15.5 ± 1.4 mm from the most anterior end of the inferior orbital fissure in vertical line, on measurements under direct macroscopic visualization (mean ± SD). These values were electronically confirmed on the photogrammetric models with mean difference within 1 mm. To be aware of exact position of intraorbital projection of MCK during an early stage of transorbital approaches provides several surgical, clinical, and aesthetic advantages.

Performance of steel protective structure for historical masonry aqueducts against rockfall: Numerical and field studies

This study investigates the design and impact performance of novel steel protection system intended to safeguard historical masonry aqueducts from damage caused by hazardous rocks. The historical aqueduct under consideration is located on the Sumela Monastery campus. To achieve this, we developed a three-dimensional (3D) photogrammetric model of the study area and identified all risky blocks along with their real positions. Subsequently, we conducted 3200 probabilistic rockfall analyses in eight critical trajectories with four different rock sizes to calculate the velocity, kinetic energy, and run-out distance of fallen blocks. In the second part of the study, finite element models of the steel protective structure were created using Abaqus software. A nonlinear dynamic impact analysis method was applied to analyze nine rockfall scenarios with two different geometries and four different sizes. Based on the rockfall and impact analyses, sections of the protection structure were designed using plastic design criteria. The steel protection structure for aqueducts demonstrated high effectiveness against rockfall, with a risk index (Ir) ranging from 0.93 to 1.00 (except for the upper end of the column–beam connection impacts). Even in these scenarios, the structure provided protection by reducing rock energy and altering its trajectory. In the third part, a steel structure was constructed in the field, and a rock cleaning process was carried out. During rock cleaning, punctures occurred while breaking sharp rocks. To mitigate this risk, a parametric study was conducted using a steel angle stopper. The proposed simple steel angle stopper effectively reduced rockfall damage to historical structures by blocking rock passages and rapidly reducing kinetic energy. Ultimately, during the removal of 5000 m³ of hazardous rocks, no damage was inflicted on the historical structure. The protection system showed a near 100 % success rate in safeguarding the aqueduct. This temporary structure can be employed to protect historical structures from rockfall hazards.

Interpreting environments of deposition from facies analysis of outcrop versus seismic reflection data: A cautionary tale from the Mount Messenger Formation, Taranaki Basin (New Zealand)

The lower part of the Mount Messenger Formation, which crops out along the North Taranaki coast (North Island, New Zealand), is widely regarded to display classic examples of exhumed basin floor fan strata. This interpretation is supported by numerous publications on the sedimentary facies and depositional environments inferred for these strata, which are exposed in coastal cliff exposures about 20 m high with limited lateral extent. Consequently, for almost three decades, this succession has served as an analogue and training ground for geoscientists investigating the features of basin floor fan deposits and their reservoir characteristics. Here, we bring together seismic stratigraphy and seismic geomorphology of 2D and 3D seismic reflection datasets, as well as photogrammetric models based on images collected using uncrewed aerial vehicle (UAV) drones from selected locations along the outcrop belt to challenge this paradigm. We analyzed seismic reflection data in an area immediately offshore and down-dip of the strata exposed in the coastal outcrop and found no objective criteria for submarine fan depositional elements based on accepted seismic stratigraphic criteria. Furthermore, mapping of seismic reflectors revealed large submarine channel systems (up to 3 km wide and up to 200 m deep) within the lower part of the Mount Messenger Formation. Submarine channel depositional elements (less than 250 m wide and 25 m thick) are also observed to incise through the outcrops, but they are generally below seismic resolution. In the context of the regional geology, we conclude that the lower Mount Messenger Formation accumulated as continental slope sediments cross-cut by channels rather than as basin floor fans. This study issues a cautionary tale about applying facies analysis to outcrop with limited 3D exposure to interpret sedimentary environments. The spatial distribution of facies and architectural elements viewed in seismic data are invaluable for testing the veracity of facies interpretations.

Three-Dimensional Reconstruction of the Early Christian Temples of the Roman Fortress of Pitiunt

Since 2018, the authors have been working on reconstructing the exterior of the Great Pitiunt Roman fortress in 3D. This article presents the results of the visualization of the exterior and interior of the temple complex. During the study, the dimensions and plans of the site were analyzed, revealing discrepancies in various sources. To clarify the complex’s dimensions, aerial photography using UAV was conducted, and photogrammetric models, orthophoto, and digital surface models were created. The research also uncovered previously unrecorded architectural features. During the reconstruction of the temples, much attention was paid to the structural design of the buildings, connections and load distribution. Engineering calculations have been carried out for the clarification of the structural solutions. The article presents the results of a detailed reconstruction of the exterior, interior and structural features of Temple Nos. 1–4, based on preserved archaeological evidence, excavation results, contemporaneous Early Christian sites, and an analysis of the materials and technologies used at the time. The reconstruction of the mosaic floor of Temple No. 2 allowed a realistic visualization of the interior.

Accuracy of Photogrammetric Models for 3D printed Wrist-hand Orthoses

Accuracy of Photogrammetric Models for 3D printed Wrist-hand Orthoses

A photogrammetric approach for real‐time visual SLAM applied to an omnidirectional system

AbstractThe problem of sequential estimation of the exterior orientation of imaging sensors and the three‐dimensional environment reconstruction in real time is commonly known as visual simultaneous localisation and mapping (vSLAM). Omnidirectional optical sensors have been increasingly used in vSLAM solutions, mainly for providing a wider view of the scene, allowing the extraction of more features. However, dealing with unmodelled points in the hyperhemispherical field poses challenges, mainly due to the complex lens geometry entailed in the image formation process. To address these challenges, the use of rigorous photogrammetric models that appropriately handle the geometry of fisheye lens cameras can overcome these challenges. Thus, this study presents a real‐time vSLAM approach for omnidirectional systems adapting ORB‐SLAM with a rigorous projection model (equisolid‐angle). The implementation was conducted on the Nvidia Jetson TX2 board, and the approach was evaluated using hyperhemispherical images captured by a dual‐fisheye camera (Ricoh Theta S) embedded into a mobile backpack platform. The trajectory covered a distance of 140 m, with the approach demonstrating accuracy better than 0.12 m at the beginning and achieving metre‐level accuracy at the end of the trajectory. Additionally, we compared the performance of our proposed approach with a generic model for fisheye lens cameras.

Drone photogrammetry as a tool for modern conflict archaeology: a case study of a Second World War armament bunker in Bavaria

ABSTRACT Within this paper, a case study on the application of drone photogrammetry at the Second World War armament bunker Weingut I is presented. The aim of the project was the mapping of the preserved remains in advance to the installation of a memorial site. In particular, the preserved concrete arch and one of the ventilation shafts were mapped by this method in high quality. Therefore, even small details of the building structure as well as several damage spots needing remediation became visible. One important advantage of drone prospecting is an enhanced occupational safety and a cost and time reduction as no further manual resources are necessary. In areas without finalized clearing for Unexploded Ordnance, other manual survey method would be especially dangerous. By comparing the photogrammetric model of the bunker Weingut I with corresponding ALS Digital Surface Models (DSM) of varying resolution, the increase in information is shown.

Paleo-valley infills record landscape response to late-Quaternary glacial/interglacial climate oscillations in the French western Alps

Reconstructing mountainous landscape evolution throughout the Quaternary is challenging because of the poor long-term preservation of geomorphic records in a context of rapid surface dynamics and topographic rejuvenation. The Quaternary geomorphic evolution of the western European Alps has been strongly controlled by climatic oscillations between glacial and interglacial periods. Significant erosion and sediment remobilization during these glacial/interglacial cycles have left very few sedimentary archives to quantify the surface dynamics and paleo-environmental conditions within the mountain belt over the last hundreds of thousands of years. Alpine valleys within the periglacial zone are potential candidates to target long-term geological archives, since they may contain alluvial deposits that have been preserved from subsequent glaciations. In the Drac valley (French western Alps), three generations of paleo-valleys are preserved, each of which was filled with alluvial and lacustrine sediments in response to glacial damming downstream. The valleys were incised during subsequent times of glacial retreat, leading to the formation of epigenetic valleys. Detailed 3D mapping of the paleo-valleys was carried out using photogrammetric models to constrain their geometry. Mapping was combined with luminescence dating of alluvial deposits to reconstruct the temporal evolution of the Drac valley. This chronological framework, together with additional data from the literature, allowed us to quantitatively constrain the complex alluvial dynamics along the Drac river during the last ca. 230 ka. Poly-phased alluvial deposition occurred in the most recent paleo-valley between ca. 90 and 20 ka (i.e., from late MIS 5 to MIS 2) in a context of global climate cooling and major Alpine glaciation. Sediment infilling of the intermediate paleo-valley is dated at around 130 ka; i.e., during the late-glacial phase of the penultimate glaciation, at the abrupt warming transition between MIS 6 and MIS 5. Finally, the oldest paleo-valley was filled around 230 ka (during a sub-stage of MIS 7) probably in a cooling and glacial context. The overall alluviation pattern and chronology of the study area highlight the asynchronous and partially contrasting glacial dynamics between the different glacier systems (i.e., Drac, Bonne and Romanche/Isère glaciers) within the Ecrins-Pelvoux massif of the French western Alps.

The Course of the Trochlear Nerve Presented via a 3-Dimensional Photorealistic Anatomic Model

Several factors contribute to the anatomical complexity of the trochlear nerve, including small diameter, complex and longest intracranial course, deep location, and numerous neurovascular relationships. A 3-dimensional (3D) photorealistic model of the cranial nerves provides a detailed and immersive representation of the anatomy, enabling one to improve surgical planning, advanced surgical research, and training. The purpose of this work is to present a 3D photogrammetric study for a more intuitive and interactive way to explore and describe the entire course of trochlear nerve. Two injected-fixed head human specimens (4 sides) were examined. The dissection protocol was divided into the following steps: 1) brain hemisphere exposure; 2) hemispherectomy dissecting all cranial nerves and partial removal of the free edge of the tentorium; 3) middle fossa and lateral wall of cavernous sinus exposure; and 4) orbital exposure. A detailed 3D photogrammetric model was generated for each dissection step. Four main volumetric models were generated during a step-by-step layered dissection of the entire nerve pathway highlighting its different segments. Finally, a full and integrated model of the entire course of the nerve was created. The models are available for visualization on monoscopic display, virtual, and augmented reality environment. The present photogrammetric model provides a more comprehensive understanding of the nerve's anatomy in its different segments, allows for customizable views thus simulating different perspectives, and can be a valuable alternative to traditional dissections. It is an advanced tool for surgical planning and surgical simulation as well as virtual reality representation of the anatomy.

A Method for Reconstruction of Size Distributions from 3D Drone Image Analysis: A Case Study

AbstractThis paper describes a novel procedure to assess fragmentation from automatic analysis of 3D photogrammetric models with a commercial software. The muckpiles from 12 blasts were photographed with a conventional drone to build 3D photogrammetric models; the flights were made with a relatively constant ground sampling distance (GSD) of 6.2 sd 0.92 mm (mean and standard deviation, respectively). A comparison with already published mass-based size distributions from 11 of these blasts, shows a good performance of automatic 3D-fragmentation measurements in the coarse range (P ≥ 60%), while deviations between mass-based and 3D model fragmentation analysis grow towards the central-fines range. As a solution, the Swebrec function is fitted to the reliable part of the size distributions, well above the GSD, and then is extended towards the fines, down to a percentage passing of 5–10%. The suitable fitting range is obtained iteratively from the mass-based fragmentation data; the lower fragment size considered is independent of the model’s resolution (i.e. GSD) with mean of 357 mm (equivalent to a passing in the range 66–86%, and well above the GSD of our models). The resulting distributions match properly mass-based size distributions with relative errors in percentile sizes of 15.5 sd 3.4%, and they can be represented with the simplest form of the fragmentation-energy-fan. As a guideline for reconstruction of size distributions and fines assessment when mass-based data is not available, the lower-fitting limit of 357 mm yields reasonable results (mean errors in pass in the range 5–36%) for the present case. The errors are limited enough to keep a sound description of the variation of fragmentation with change in blast design.

FLATTENING COMPLEX ARCHITECTURAL SURFACES: PHOTOGRAMMETRIC 3D MODELS CONVERTED INTO 2D MAPS

Abstract. The paper describes a workflow to flatten 3D photogrammetric models of undevelopable surfaces into unfragmented 2D texture maps. The aim is to create a texture map with reduced fragmentation compared to typical photogrammetric texture files associated with 3D models. Geometric reformatting of the mesh is required to achieve an unfragmented final texture image with enough visual quality to allow for its use in 2D editing software (e.g., Photoshop, Illustrator, etc.). With a lighter model and defragmented texture, graphic documentation of conditions, treatments, or other relevant information can be performed directly. The approach considers both simple and complex architectural surfaces, with particular attention to elements that cannot be developed without introducing distortions. In the case of historic buildings, such surfaces constitute the majority, especially in the case of decorative elements and irregular vaulted systems. The approach extends to full 3D models, particularly those where orthomosaics would result in stretched details. We will discuss two methods: the first is particularly suitable when the photogrammetric project (oriented images) is still available, and the second applies to generic 3D models without the availability of the original images.

Evaluation of the Applicability of Digital Photogrammetry-Based Initial Imperfections on NLFEM Ultimate Strength Analysis of Ship- Type Stiffened Plates

In this study, the effects of initial imperfections on the ultimate strength values of ship-type stiffened plate structures are discussed and analysed from the point of view of how the initial imperfection forms are obtained. Ship stiffened panels are subjected to complex loading conditions during their operational lifespan. Accurate prediction of their strength and failure modes necessitates a thorough understanding of the effects of various imperfections on their behavior. Two primary sources of initial imperfections are considered: the buckling mode shapes resulting from linear eigenvalue buckling analysis and measurements based on digital photogrammetry. Buckling mode shapes, arising from the manufacturing process are extracted using linear static structural analysis. Digital photogrammetry is employed to capture and quantify imperfections by analysing high-resolution images of the physical structure. Numerical investigation is conducted by incorporating these two types of initial imperfections into non-linear finite element method (NLFEM) calculations. The buckling mode imperfections are applied as geometric perturbations, while the photogrammetry-based imperfections are incorporated as statistically representative deviations from the ideal geometry. Stiffened panel's structural response is analysed under longitudinal uniaxial compression. A new NLFEM project schematic has been utilized instead of the procedure outlined in the technical circular S.P 01/19 by Türk Loydu, which has been discontinued after ANSYS® Workbench™V.2019R2. This is proven by two validation case studies in ANSYS® Workbench™2022R2 version for considering buckling mode initial imperfections. A case study is then conducted using a 3D model of a stiffened plate panel, which is fabricated in a shipyard located in Trabzon, created by Photomodeler V. 2023.3.0.238 employing the digital photogrammetry method.NLFEM analysis is carried out for both initially deflected model after eigenvalue buckling analysis and naturally deflected model after welding operations. The comparative ultimate strength results are quite consistent, and this shows that the digital photogrammetric modelling method can be used in the analysis of ship structural elements.