Photogrammetric Models Research Articles

A Non-parametric Discrete Fracture Network Model

A discrete fracture network (DFN) model based on non-parametric kernel density estimators (KDE) and directional-linear statistics is developed. The model provides a characterization of the fracture network with distributions of fracture orientation and size jointly. A solution to the Bertrand paradox is used for the calculation of disk sizes from trace lengths, the latter calculated from the intersection of disks and highwall faces by triangulation. A Poisson point process is applied for the generation of the model, with fractures assumed to be flat and circular in shape, the number of fractures per unit volume (P30) adjusted to match the experimental length of fractures per unit area (P21). Length censoring of traces due to the surface dimension is considered in the calculations by including semi-bounded traces, i.e., traces censored in one of their ends. Orientation and size biases are corrected with a weighting function in the random sampling. The truncation effect whereby no traces shorter than some cut-off length are recorded, is addressed by a randomized optimization algorithm. The joint fracture orientation-size distribution model developed is tested with trace maps of discontinuities measured from photogrammetric models of twelve highwall faces of quarry benches, with outstanding results. Computational advantages over traditional parametric fracture models are addressed.

A numerical simulation procedure for evaluating the accuracy of 3-dimensional photogrammetric models and its application to geometric parameters of discontinuities in rock masses

This study proposes a numerical simulation procedure to evaluate the accuracy of geometric parameters of 3-dimensional models reconstructed by photogrammetry based on the Open Graphics Library. As a technical mean to obtain photogrammetric photos and data, this method has achieved the goal of controlling the parameters in the photogrammetric process at will. The proposed method is validated by several physical model experiments using the unmanned aerial vehicle Phantom 4 Real-time kinematic (RTK). Through a series of numerical experiments, this study quantitatively analyzes the error of geometric parameters of discontinuities in rock masses caused by coordinate accuracy of camera positions and shooting distance, and some quantitative findings were obtained. These results conforming to common sense also validate the proposed simulation procedure. This numerical simulation procedure has a broad application prospect in guiding and optimization of photo acquisition of field outcrop balancing the accuracy and efficiency.

An Open-Source Photogrammetry Workflow for Reconstructing 3D Models.

Acquiring accurate 3D biological models efficiently and economically is important for morphological data collection and analysis in organismal biology. In recent years, structure-from-motion (SFM) photogrammetry has become increasingly popular in biological research due to its flexibility and being relatively low cost. SFM photogrammetry registers 2D images for reconstructing camera positions as the basis for 3D modeling and texturing. However, most studies of organismal biology still relied on commercial software to reconstruct the 3D model from photographs, which impeded the adoption of this workflow in our field due the blocking issues such as cost and affordability. Also, prior investigations in photogrammetry did not sufficiently assess the geometric accuracy of the models reconstructed. Consequently, this study has two goals. First, we presented an affordable and highly flexible SFM photogrammetry pipeline based on the open-source package OpenDroneMap (ODM) and its user interface WebODM. Second, we assessed the geometric accuracy of the photogrammetric models acquired from the ODM pipeline by comparing them to the models acquired via microCT scanning, the de facto method to image skeleton. Our sample comprised 15 Aplodontia rufa (mountain beaver) skulls. Using models derived from microCT scans of the samples as reference, our results showed that the geometry of the models derived from ODM was sufficiently accurate for gross metric and morphometric analysis as the measurement errors are usually around or below 2%, and morphometric analysis captured consistent patterns of shape variations in both modalities. However, subtle but distinct differences between the photogrammetric and microCT-derived 3D models could affect the landmark placement, which in return affected the downstream shape analysis, especially when the variance within a sample is relatively small. At the minimum, we strongly advise not combining 3D models derived from these two modalities for geometric morphometric analysis. Our findings can be indictive of similar issues in other SFM photogrammetry tools since the underlying pipelines are similar. We recommend that users run a pilot test of geometric accuracy before using photogrammetric models for morphometric analysis. For the research community, we provide detailed guidance on using our pipeline for building 3D models from photographs.

Three-Dimensional Modelling of A Bridge by Integrating Terrestrial and Aerial Photogrammetry Applying an Adapted Capture Method

Three-dimensional (3D) photogrammetric modelling is a contemporary remote sensing method for generating digital models with their specific appearance and texture, which are used in various areas of life. The modelling of complex geometry objects, such as masonry bridges, is not an easy task, because of their specific features (the presence of arches and various niches). This determines the choice of an adapted capture method according to the individual characteristics of the object. The paper presents research aimed at generating a highly accurate three-dimensional model of a bridge, by combining terrestrial and aerial photogrammetry. A low-cost unmanned aerial system (UAS) was used for capturing the upper side of the bridge. This significantly optimised capture time. But its capabilities do not allow to capture the bridge arches from the bottom upwards, nor to obtain an accurate model of the bridge railing. Because of this, a terrestrial survey was made with a digital camera, thus complementing the information required to generate a comprehensive model of the bridge. The integration of aerial and terrestrial capturing using low-cost cameras and systems, along with the application of modern algorithms for processing, allow to create precise, accurate, and detailed digital models. It is all very important for future conservation, restoration, adaptation, and socialisation of such type of objects which are monuments of culture.

Mesh Conflation of Oblique Photogrammetric Models Using Virtual Cameras and Truncated Signed Distance Field

Mesh Conflation of Oblique Photogrammetric Models Using Virtual Cameras and Truncated Signed Distance Field

A New Multi-Criteria Tie Point Filtering Approach to Increase the Accuracy of UAV Photogrammetry Models

Extracting accurate tie points plays an essential role in the accuracy of image orientation in Unmanned Aerial Vehicle (UAV) photogrammetry. In this study, a Multi-Criteria Decision Making (MCDM) automatic filtering method is presented. Based on the quality features of a photogrammetric model, the proposed method works at the level of sparse point cloud to remove low-quality tie points for refining the orientation results. In the proposed algorithm, different factors that affect the quality of tie points are identified. The quality measures are then aggregated by applying MCDM methods and a competency score for each 3D tie point. These scores are employed in an automatic filtering approach that selects a subset of high-quality points which are then used to repeat the bundle adjustment. To evaluate the proposed algorithm, various internal and external studies were conducted on different datasets. The findings suggest that our method is both effective and reliable. In addition, in comparison to the existing filtering techniques, the proposed strategy increases the accuracy of bundle adjustment and dense point cloud generation by about 40% and 70%, respectively.

Facies analysis, depositional activity, and internal structure of sieve deposits on an active alluvial fan

AbstractSieve lobes typically appear in gravel‐rich and matrix‐poor alluvial fans. Despite being extensively studied, the sieve‐lobe facies has been defined largely based on qualitative field observations without quantitative sedimentological analyses. Additionally, depositional activity of sieve lobes has not been monitored over extended periods (monthly to annually) and not directly associated with specific precipitation triggers. Furthermore, the internal geometry of sieve‐lobe built alluvial fans has not yet been imaged by subsurface methods. We performed a multi‐method analysis of sieve lobes in the Julian Alps (NW Slovenia) on an alpine alluvial fan composed of carbonate gravels. We performed a detailed textural and structural sedimentological analysis of 11 recent sieve lobes differing in size and age. A three‐year aerial survey of the alluvial fan surface with a small unmanned aircraft and photogrammetric modelling was used to detect active sieve‐lobe evolution. Detected sieve‐lobe formation events and volumetric surface changes were paired with triggering precipitation events. Ground‐penetrating radar (GPR) profiling depicted the geometry of the sieve‐lobe built alluvial fan. The sieve‐lobe facies consists of over 80% poorly sorted, open‐framework gravels and less than 2% mud. Lobes exhibit downward coarsening and increase in clast mean size. These textural and structural characteristics are present in all sieve lobes regardless of their age and size. Sieve lobes form with a sub‐annual frequency, usually following 24 h rainfall events exceeding 50 mm. Over 1000 m3 of sediment was deposited during these events. The GPR profiles confirm that the studied alluvial fan is formed predominantly by stacked sieve lobes. Quantitative sedimentary analysis of sieve lobes, monitoring of their recent evolution, and depiction of their subsurface geometry—demonstrated in this study—reinforce the challenged concept that sieve lobes are one of the main building blocks of alluvial fans. This work also demonstrates that, under specific conditions, sieving may become the dominant alluvial fan‐forming process.

3D LOW-COST MULTISPECTRAL UAV SYSTEMS: SURVEY AND ANALYSIS OF TORRESINO DA POLVERE OF SAN MARCO IN BERGAMO

Abstract. The Torresini da Polvere are special constructions built by the Venetian Republic between the 16th and 18th centuries. They are unique architectural structures, characterized by a pyramidal roof, for the preservation of the gunpowder. The torresino of San Marco in Bergamo is one of the best-preserved in the world and was then the subject of detailed research. The powder magazine was measured by professional, ground-based and airborne instruments. The paper shows a comparison between the existing structure and the photogrammetric model obtained by low-cost UAV systems to formulate an accurate estimate, including the pros and cons of different survey systems. It also aims to deepen the aspects associated with 3D reconstruction using multispectral imagery, from the investigation to data processing, to create models with NDVI mapping for the study of the building’s decay caused by biological agents.

SfM Photogrammetric Techniques Applied in the Building Archaeology Works of the Old Cloister of the Monastery of San Francisco from the 16th Century (Cazalla de la Sierra, Seville)

The cloister from the old monastery of San Francisco (Cazalla de la Sierra, Seville) has been suffering a series of remodeling transformations from its original construction in the 16th century to the current day. Thus, a study of building archaeology needed to be accomplished by using photogrammetric techniques by SfM (Structure from Motion) and laser scanning or TLS (Terrestrial Laser Scanning), which ensure the geometric exactitude and high resolution of the facings surveying. For that, over 500 images were taken for the 4 existing facings (about 78 lineal meters) from which a photogrammetric model was obtained of over 50 million polygons, as well as a cloud of over 40 million points from the laser scanning. It can be concluded that by using the techniques of SfM, the task of documenting, analyzing and studying the facings of the historical building in order to establish its evolutional process gains not only precision and exactitude but also opens the possibility to go further by obtaining products that are capable of helping us conserve, restore and protect the historical heritage, as well as generate the 3D virtualizations planned for the diffusion.

The topography of diet: Orientation patch count predicts diet in turtles.

Use of quantitative morphological methods in biology has increased with the availability of 3D digital data. Rotated orientation patch count (OPCr) leverages such data to quantify the complexity of an animal's feeding surface, and has previously been used to analyze how tooth complexity signals diet in squamates, crocodilians, and mammals. These studies show a strong correlation between dental complexity and diet. However, dietary prediction using this technique has not been tested on the feeding structures of edentulous (toothless) taxa. This study is the first to test the applicability of OPCr to the triturating surface morphology of a beaked clade. Fifty-five turtle specimens, 42 of which preserved both the skull and rhamphotheca, were categorized into dietary categories based on the food sources comprising 90% or 60% of their diets. Photogrammetric models of each specimen were read into molaR, producing OPCr results. Comparison of bone and rhamphotheca OPCr values shows no significant difference in complexity, implying that bone can suffice for predicting diet from morphology when keratin is absent. Carnivorous taxa have significantly lower OPCr values than herbivorous or omnivorous taxa, showing that feeding surface complexity in edentulous animals varies with diet similarly to tooth complexity in toothed taxa. Comparison of bone OPCr values by family shows that Testudinidae (tortoises) are more complex than Cheloniidae (sea turtles) and Chelydridae (snapping turtles), but that Cheloniidae and Chelydridae are not significantly different from each other. We therefore find that OPCr can be used to differentiate between carnivores and other dietary categories in edentulous taxa.

Augmented Reality Based on Apollo Lunar Imagery: Searching for Stars and Adding Virtual Objects

Abstract Based on photogrammetric models of the first three Apollo landing sites, we have created a method to project virtual objects onto photos taken on the lunar surface. We have applied this method to search for stars in high-resolution scans of Apollo lunar photos and to restore views of the starry sky in some iconic images. Our method can be used to incorporate computer-generated 3D graphics, such as constellation boundaries, and coordinate and contour lines, into lunar images. This research has several applications, including the visualization of digital terrain models, the creation of a virtual planetarium based on lunar photos, and demonstration of object motion in lunar gravity for educational purposes.

Assessment of Cranial Deformation Indices by Automatic Smartphone-Based Photogrammetric Modelling

This paper presents research carried out to assess the accuracy of a fully automatic smartphone-based photogrammetric solution (PhotoMeDAS) to obtain a cranial diagnostic based on the 3D head model. The rigorous propagation of the coordinate measurement uncertainty to the infant’s derived cranial deformation indices is demonstrated. The cranial anthropometric parameters and cranial deformation indices that PhotoMeDAS calculates automatically were analysed based on the estimated accuracy and uncertainty. To obtain both accuracy and uncertainty, a dummy head was measured 54 times under different conditions. The same head was measured with a top-of-the-line coordinate-measuring machine (CMM), and the results were used as ground-truth data. It is demonstrated that the PhotoMeDAS 3D models are an average of 1.01 times bigger than the corresponding ground truth, and the uncertainties are around 1 mm. Even assuming uncertainties in the coordinates of up to 1.5 mm, the error in the derived deformation index uncertainties is around 1%. In conclusion, the PhotoMeDAS solution improves the uncertainty obtained in an ordinary paediatric consultation and can be recommended as a tool for doctors to establish an adequate medical diagnosis based on comprehensive cranial deformation indices, which is much more precise and complete than the information obtained by existing analogue devices (measuring tapes and callipers) and easier to use and less expensive than radiological imaging (CT and MRI).

Photogrammetric Modelling of Street Conditions Using A Vehicle-mounted Non-metric Camera

Monitoring and modeling pavement distresses can employ either simple methods like direct measurements by tapes or straight edges, or more sophisticated approaches like laser scanners and stereoscopic cameras held at the ends of fixed poles. This study aims to detect pavement distress’s shape and position, such as cracks. For this purpose, overlapped images were collected for the distressed area to obtain complete coverage of the street conditions located in front of the College of Engineering /University of Duhok. Kurdistan Region, Iraq. A single non-metric camera attached to the side and the front of the vehicle is the approach employed as an image-collecting device. The camera shutter speed is selected to have a sequence of overlapped images to be processed, producing the pavement surface orthomosaic. The plane of the image in this study is inclined or obliquely relative to the pavement surface, so a gap is expected in the overlap area in the near range. To overcome this drawback and other problems, an indoor grid and tiles test was conducted to obtain the required parameters such as focal length, overlap percentage, camera shutter speed, and vehicle speed.   Ground control points (GCPs) and checkpoints for processing and accuracy checks were provided in each test and distributed evenly in the model area. The indoor parameter collecting tests revealed that the Root Mean Square Error (RMSE) for the (15) checkpoints was ±0.013m in X and ±0.016m in Y coordinates. Using a larger tilt angle and increasing camera height gave a root mean square error of ±0.009m in X and ±0.013m in Y, respectively. Image processing was conducted using Agisoft PhotoScan as it provided adequate accuracy and modeling tools in several previous papers

Accuracy Verification of Surface Models of Architectural Objects from the iPad LiDAR in the Context of Photogrammetry Methods

The creation of accurate three-dimensional models has been radically simplified in recent years by developing photogrammetric methods. However, the photogrammetric procedure requires complex data processing and does not provide an immediate 3D model, so its use during field (in situ) surveys is infeasible. This paper presents the mapping of fragments of built structures at different scales (finest detail, garden sculpture, architectural interior, building facade) by using a LiDAR sensor from the Apple iPad Pro mobile device. The resulting iPad LiDAR and photogrammetric models were compared with reference models derived from laser scanning and point measurements. For small objects with complex geometries acquired by iPad LiDAR, up to 50% of points were unaligned with the reference models, which is much more than for photogrammetric models. This was primarily due to much less frequent sampling and, consequently, a sparser grid. This simplification of object surfaces is highly beneficial in the case of walls and building facades as it smooths out their surfaces. The application potential of the IPad LiDAR Pro is severely constrained by its range cap being 5 m, which greatly limits the size of objects that can be recorded, and excludes most buildings.

A Photogrammetry-Assisted Methodology for the Documentation of Complex Stratigraphic Relationships

ABSTRACTAt Tell Yunatsite, a prehistoric settlement mound located in the Upper Thracian plain of Bulgaria, stratigraphic relationships between archaeological deposits are incredibly complex. Such complexity then prompted our exploration into developing a new methodology for the documentation of complex stratigraphic relationships. Here, we present the results of a new photogrammetry-assisted methodology that was developed to compensate for the shortcomings of currently utilized stratigraphic documentation methods, such as the Wheeler-Kenyon box grid and the Harris Matrix. First, using a UAV drone, we produce a high-resolution photogrammetric model of the entire site. Second, with structure from motion photogrammetry, we produce 2.5D models of excavation units in stratigraphic succession. Finally, utilizing GIS and Blender (a 3D computer graphics software application), we digitize the horizontal extents of each archaeological deposit and “fill” the space between their successive surfaces (from top to bottom) until a faithful 3D model of each deposit is generated. These deposit models are then combined and rendered simultaneously to form 3D block models of the excavation units that may, in turn, be cross-sectioned in any direction to view stratigraphic relationships in virtual profile.

Grain size of fluvial gravel bars from close-range UAV imagery – uncertainty in segmentation-based data

Abstract. Data on grain sizes of pebbles in gravel-bed rivers are of key importance for the understanding of river systems. To gather these data efficiently, low-cost UAV (uncrewed aerial vehicle) platforms have been used to collect images along rivers. Several methods to extract pebble size data from such UAV imagery have been proposed. Yet, despite the availability of information on the precision and accuracy of UAV surveys as well as knowledge of errors from image-based grain size measurements, open questions on how uncertainties influence the resulting grain size distributions still persist. Here we present the results of three close-range UAV surveys conducted along Swiss gravel-bed rivers with a consumer-grade UAV. We measure grain sizes on these images by segmenting grains, and we assess the dependency of the results and their uncertainties on the photogrammetric models. We employ a combined bootstrapping and Monte Carlo (MC) modeling approach to model percentile uncertainties while including uncertainty quantities from the photogrammetric model. Our results show that uncertainty in the grain size dataset is controlled by counting statistics, the selected processed image format, and the way the images are segmented. Therefore, our results highlight that grain size data are more precise and accurate, and largely independent of the quality of the photogrammetric model, if the data are extracted from single, undistorted nadir images in opposition to orthophoto mosaics. In addition, they reveal that environmental conditions (e.g., exposure to light), which control the quality of the photogrammetric model, also influence the detection of grains during image segmentation, which can lead to a higher uncertainty in the grain size dataset. Generally, these results indicate that even relatively imprecise and inaccurate UAV imagery can yield acceptable grain size data, under the conditions that the photogrammetric alignment was successful and that suitable image formats were selected (preferentially single, undistorted nadir images).

Lower Cretaceous dinosaur footprints from the Molfetta tracksite (Apulia, southern Italy)

The lower Albian track-bearing surface of the San Leonardo quarry (Molfetta, Apulia) is characterised by more than 800 footprints, produced by both quadrupedal and bipedal dinosaurs. Six well-preserved bipedal trackways, composed of tridactyl footprints are attributed to medium-to large-sized theropod dinosaurs. Only one clear but poorly preserved trackway and numerous isolated manus-pes couples have been attributed to quadrupedal dinosaurs. The tridactyl ichnoassemblage, analysed using both traditional methods and close-range photogrammetry, is represented by weakly mesaxonic and robust specimens. Morphological comparison with Upper Jurassic and Lower Cretaceous theropod tracks from surrounding areas, supported by morphometric analyses, points out a highest affinity with the specimens from Switzerland and North Africa. Nevertheless, a set of unique characters appears to justify the establishment of a new ichnospecies, Jurabrontes melphicticus. Additionally, the photogrammetric models of the quadrupedal trackway and four isolated manus-pes sets suggest they belong to the same morphotype, represented by asymmetrical tetradactyl pes and highly digitigrade tetra- or pentadactyl manus. These tracks share numerous morphological characters with both the ichnogenera Tetrapodosaurus and Metatetrapodus and thus can be attributed to a medium-sized ankylosaurian trackmaker.

Water Flows and Water Accumulations on Bedrock as a Structuring Element of Rock Art

The paper proposes a new method to quantify the flow of water and water accumulation zones on bedrock panels. This can be used to investigate how water influences the placement of rock art. The analysis is based on photogrammetric models on which water flows and accumulations were modelled using a NetLogo simulation and the SAGA hydrology package. To test the hypothesis that water was a structuring element in the creation of rock art, case studies of Bohus-granite panels from south-western Sweden were used. The described approach should be possible to use on most rock art placed on bedrock panels regardless of rock type, its state of cleaning, or present microfauna. The modelling of water flows and accumulations is a powerful tool to compare the image placement and image density in relation to water even on widely separated panels on which such observations cannot be made directly.

Depth and Dimension: Exploring the Problems and Potential of Photogrammetric Models for Ancient Coins

In numismatic collections, coins are typically documented and studied using 2D images of their obverse and reverse. While two photographs, under the correct lighting, provide adequate information for basic research, detailed numismatic study has generally required the physical handling of the items to capture the three-dimensional aspects of the coin. Recent advances in photogrammetry and digitisation provide new opportunities for numismatic research. Digitised, 3D models of ancient coins allow researchers and students to interact with these coins remotely, providing opportunities to study coins from collections that would otherwise be difficult to access. Ancient coins, however, can be challenging to digitise due to their small size, irregular shape, and reflectance. This study will explore and outline a methodology for creating 3D models of ancient coins that balances both expediency with quality. Three Roman Republican coins from the University of Auckland’s numismatic collection were digitised using photogrammetric methods to create 3D digital models for student use. Expedient capture relied primarily on the quality of the photogrammetry setup, as well as the use of macrophotography, to capture the detail of each coin effectively. While the digital models took longer to produce than traditional 2D images, it was possible to create high-quality digital 3D model coins in a relatively expedient manner. The balance between speed and increased data opens the door for a new era in numismatic cataloguing and qualitative research opportunities.

The Volumetric Wear Assessment of a Mining Conical Pick Using the Photogrammetric Approach.

The rapid wear of conical picks used in rock cutting heads in the mining industry has a significant economic impact in cost effectiveness for a given mineral extraction business. Any mining facility could benefit from decreasing the cost along with a substantial durability increase of a conical pick; thus, the hardfacing method of production and regeneration should be taken into account. In order to automatize the regeneration, the wear rate assessment is necessary. This paper presents a methodology used to create a 3D photogrammetric model of most of the commercially available tangential-rotary cutters in their before and after abrasive exploitation state. An experiment of three factors on two levels is carried out to indicate the proper setup of the scanning rig to obtain plausible results. Those factors are: light level, presence of polarizing filter and the distance from the scanned object. The 3D scan of the worn out specimen is compared to the master model via algorithm developed by the authors. This approach provides more detailed information about the wear mechanism and can help either in roadheader cutting head diagnostics or to develop a strategy and optimize the toolpath for the numerically controlled hardfacing machine.