Accurate Digital Model Research Articles

Quasi-LPV system modeling and identification of a variable speed electro-mechanical and hydraulic MISO system

An accurate digital model is of great significance to system operation inversion and behavior prediction. The multi-energy domain coupling mechanism of the Electro-mechanical and Hydraulic (EMH) system is complex and has strong nonlinear characteristics. At present, the research mainly focuses on the mechanical-hydraulic coupling characteristics, while the research on the large operating range and the influence of electric motor and load characteristics on the nonlinear dynamics of the EMH system are less. Based on the first principle description, the nonlinear characteristics of the system components are described in this paper. Furthermore, the nonlinear dynamic model of the EMH system described in multi-state space is established based on the Quasi-LPV system. Combined with the experimental data, the structural and non-structural uncertain parameters of system are identified. Finally, the influence of the mechanical characteristics of electric motor, load on the nonlinear dynamics of the EMH system are discussed. Experiments show that the Quasi-LPV models proposed in this paper can accurately reproduce and predict system behavior. It provides technical support for rapid design, selection, and scheme optimization of hydraulic systems in general scenarios.

Automating Aircraft Scanning for Inspection or 3D Model Creation with a UAV and Optimal Path Planning

Visual inspections of aircraft exterior surfaces are required in aircraft maintenance routines for identifying possible defects such as dents, cracks, leaking, broken or missing parts, etc. This process is time-consuming and is also prone to error if performed manually. Therefore, it has become a trend to use mobile robots equipped with visual sensors to perform automated inspections. For such a robotic inspection, a digital model of the aircraft is usually required for planning the robot’s path, but a CAD model of the entire aircraft is usually inaccessible to most maintenance shops. It is very labor-intensive and time-consuming to generate an accurate digital model of an aircraft, or even a large portion of it, because the scanning work still must be performed manually or by a manually controlled robotic system. This paper presents a two-stage approach of automating aircraft scanning with an unmanned aerial vehicle (UAV) or autonomous drone equipped with a red–green–blue and depth (RGB-D) camera for detailed inspection or for reconstructing a digital replica of the aircraft when its original CAD model is unavailable. In the first stage, the UAV–camera system follows a predefined path far from the aircraft surface (for safety) to quickly scan the aircraft and generate a coarse model of the aircraft. Then, an optimal scanning path (much closer to the surface) in the sense of the shortest flying distance for full coverage is computed based on the coarse model. In the second stage, the UAV–camera system follows the computed path to closely inspect the surface for possible defects or scan the surface for generating a dense and precise model of the aircraft. We solved the coverage path planning (CPP) problem for the aircraft inspection or scanning using a Monte Carlo tree search (MCTS) algorithm. We also implemented the max–min ant system (MMAS) strategy to demonstrate the effectiveness of our approach. We carried out a digital experiment and the results showed that our approach can scan 70% of the aircraft surface within one hour, which is much more efficient than manual scanning.

English

BACKGROUND We intend to evaluate the accuracy of in vivo conventional and digital methods in generating complete-arch dental models for measuring tooth dimension. METHODS Search was conducted through an electronic database in Medline, Cochrane Library, ResearchGate, PubMed and Google Scholar using query terms such as intraoral scanning; digital impression; accuracy in vivo full arch digital impression; analog impression; accuracy conventional impression; in vivo intraoral scanning; alginate impression; accuracy of plaster models; digital models; and complete arch accuracy. The outcomes were the accuracy of teeth dimension measurements in plaster models in comparison to digitized and digital models in vivo. RESULTS Nine studies matched the inclusion criteria. Two papers compared teeth measurements through plaster models and direct digital models, four papers compared plaster models and digitized models, one paper compared plaster models, digitized and direct digital models, one paper compared four different methods of direct intraoral, plaster models, direct digital and digitized models and one study reported teeth measurements from directly measured intraoral, plaster models, and direct digital models. Neither digital nor plaster models could be considered to replicate exactly the dentition, however it was agreed by the authors that intraoral scanning could represent the intraoral situation more accurately on digital models due to the lesser procedural steps, hence fewer source of error. CONCLUSIONS According to the results of the present review, although there were slight differences in readings of the measurements made on all the methods, the differences were neither statistically nor clinically significant and it is acceptable in clinical application. This review was registered in PROSPERO at CRD42020208662. KEY WORDS Intraoral Scanning, Digital Impression, Analog Impression, Digitized Model, Digital Model, Digital Impression Accuracy, Stl files, Conventional Impression Accuracy, Tooth Dimension Accuracy, Digital Model Accuracy

An Accurate Digital Subsidence Model for Deformation Detection of Coal Mining Areas Using a UAV-Based LiDAR

Coal mine surface subsidence detection determines the damage degree of coal mining, which is of great importance for the mitigation of hazards and property loss. Therefore, it is very important to detect deformation during coal mining. Currently, there are many methods used to detect deformations in coal mining areas. However, with most of them, the accuracy is difficult to guarantee in mountainous areas, especially for shallow seam mining, which has the characteristics of active, rapid, and high-intensity surface subsidence. In response to these problems, we made a digital subsidence model (DSuM) for deformation detection in coal mining areas based on airborne light detection and ranging (LiDAR). First, the entire point cloud of the study area was obtained by coarse to fine registration. Second, noise points were removed by multi-scale morphological filtering, and the progressive triangulation filtering classification (PTFC) algorithm was used to obtain the ground point cloud. Third, the DEM was generated from the clean ground point cloud, and an accurate DSuM was obtained through multiple periods of DEM difference calculations. Then, data mining was conducted based on the DSuM to obtain parameters such as the maximum surface subsidence value, a subsidence contour map, the subsidence area, and the subsidence boundary angle. Finally, the accuracy of the DSuM was analyzed through a comparison with ground checkpoints (GCPs). The results show that the proposed method can achieve centimeter-level accuracy, which makes the data a good reference for mining safety considerations and subsequent restoration of the ecological environment.

3D simulation models for developing digital twins of heritage structures: challenges and strategies

Structural vulnerability assessment of heritage structures is a pivotal part of a risk mitigation strategy for preserving these valuable assets for the nations. For this purpose, developing digital twins has gained much attention lately to provide an accurate digital model for performing finite element (FE) analyses. Three-dimensional (3D) geometric documentation is the first step in developing the digital twin, and various equipment and methodologies have been developed to facilitate the procedure. Both aerial and terrestrial close-range photogrammetry can be combined with 3D laser scanning and geodetic methods for the accurate 3D geometric documentation. The data processing procedure in these cases mostly focuses on developing detailed, accurate 3D models that can be used for the FE modeling. The final 3D surface or volumes are produced mainly by combining the 3D point clouds obtained from the laser scanner and the photogrammetric methods. 3D FE models can be developed based on the geometries derived from the 3D models using FE software packages. As an alternative, developed 3D volumes provided in the previous step can be directly imported to some FE software packages. In this study, the challenges and strategies of each step are investigated by providing examples of surveyed heritage structures.

Visual Digital Forest Model Based on a Remote Sensing Data and Forest Inventory Data

This article discusses the process of creating a digital forest model based on remote sensing data, three-dimensional modeling, and forest inventory data. Remote sensing data of the Earth provide a fundamental tool for integrating subsequent objects into a digital forest model, enabling the creation of an accurate digital model of a selected forest quarter by using forest inventory data in educational and experimental forestry, and providing a valuable and extensive database of forest characteristics. The formalization and compilation of technologies for connecting forest inventory databases and remote sensing data with the construction of three-dimensional tree models for a dynamic display of changes in forests provide an additional source of data for obtaining new knowledge. The quality of forest resource management can be improved by obtaining the most accurate details of the current state of forests. Using machine learning and regression analysis methods as part of a digital model, it is possible to visually assess the course of planting growth, changes in species composition, and other morphological characteristics of forests. The goal of digital, interactive forest modeling is to create virtual simulations of the future status of forests using a combination of predictive forest inventory models and machine learning technology. The research findings provide a basic idea and technique for developing local digital forest models based on remote sensing and data integration technologies.

CSR-Net: Cross-Scale Residual Network for multi-objective scaphoid fracture segmentation.

The scaphoid is located in the carpals. Owing to the body structure and location of the scaphoid, scaphoid fractures are common and it is difficult to heal. Three-dimensional reconstruction of scaphoid fracture can accurately display the fracture surface and provide important support for the surgical plan involving screw placement. To achieve this goal, in this study, the cross-scale residual network (CSR-Net) is proposed for scaphoid fracture segmentation. In the CSR-Net, the features of different layers are used to achieve fusion through cross-scale residual connection, which realizes scale and channel conversions between the features of different layers. It can establish close connections between different scale features. The structures of the output layer and channel are designed to establish the CSR-Net as a multi-objective architecture, which can realize scaphoid fracture and hand bone segmentations synchronously. In this study, 65 computed tomography images of scaphoid fracture are tested. Quantitative metrics are used for assessment, and the results obtained show that the CSR-Net achieves higher performance in hand bone and scaphoid fracture segmentations. In the visually detailed display, the fracture surface is clearer and more intuitive than those obtained from other methods. Therefore, the CSR-Net can achieve accurate and rapid scaphoid fracture segmentation. Its multi-objective design provides not only an accurate digital model, but also a prerequisite for navigation in the hand bone.

Accuracy of digital dental models and three-dimensional printed dental models in linear measurements and Bolton analysis.

Background: Due to advances in digital technology, it is possible to obtain digital dental models through intraoral scanning. The stereolithographic data collected from the scanner can subsequently be printed into a three-dimensional dental model in resinic material. However, the accuracy between digital dental models and printed dental models needs to be evaluated since it might affect diagnosis and treatment planning in orthodontic treatment. This study aimed to evaluate the accuracy of digital models scanned by a Trios intraoral scanner and three-dimensional dental models printed using a Formlabs 2 3D printer in linear measurements and Bolton analysis. Methods: A total of 35 subjects were included in this study. All subjects were scanned using a Trios intraoral scanner to obtain digital study models. Stereolithographic data from previous scanning was printed using a Formlabs 2 3D printer to obtain printed study models. Mesiodistal, intercanine, intermolar, and Bolton analysis from all types of study models were measured. The intraclass correlation coefficient was used to assess intraobserver and interobserver reliability. All data were then statistically analyzed. Results: The reliability tests were high for both intraobserver and interobserver reliability, which demonstrates high reproducibility for all measurements on all model types. Most of the data compared between study models showed no statistically significant differences, though some data differed significantly. However, the differences are considered clinically insignificant. Conclusion: Digital dental models and three-dimensional printed dental models may be used interchangeably with plaster dental models for diagnostic and treatment planning purposes. Keywords: Accuracy, 3D printing, digital dental model, printed dental model.

Accurate Virtual Trial Assembly Method of Prefabricated Steel Components Using Terrestrial Laser Scanning

The comprehensive utilization of prefabricated components (PCs) is one of the features of industrial construction. Trial assembly is imperative for PCs used in high‐rise buildings and large bridges. Virtual trial assembly (VTA) is a preassembly process for PCs in a virtual environment that can avoid the time‐consuming and economic challenges in physical trial assembly. In this study, a general framework for VTA that is performed between a point cloud, a building information model (BIM), and the finite element method is proposed. In obtaining point clouds via terrestrial laser scanning, the registration accuracy of point clouds is the key to building an accurate digital model of PCs. Accordingly, an accurate registration method based on triangular pyramid markers is proposed. This method can enable the general registration accuracy of point clouds to reach the submillimeter scale. Two algorithms for curved members and bolt holes are developed for PCs with bolt assembly to reconstruct a precise BIM that can be used directly in finite element analysis. Furthermore, an efficient simulation method for accurately predicting the elastic deformation and initial stress caused by forced assembly is proposed and verified. The proposed VTA method is verified on a reduced‐scale steel pipe arch bridge. Experimental results show that the geometric prediction deviation of VTA is less than 1/1800 of the experimental bridge span, and the mean stress predicted via VTA is 90% of the measured mean stress. In general, this research may help improve the industrialization level of building construction.

Creation of a theoretical simulation model of orbital referencing of lunar objects’ optical observations taken by space lunar satellite to the selenocentric coordinate system

This paper aims at the creation of a selenocentric catalogue of lunar objects’ positions (SCLOP) and development of a theoretical simulation model of orbital referencing of lunar objects taken by space lunar satellite to the selenocentric coordinate system defined by SCLOP. The data produced by the modern space lunar missions serve as the basis for multi-parameter and highly accurate digital simulation model. The results obtained in the work are important and relevant for the development of navigation technologies on creation and orienting of coordinate systems and the study of celestial bodies’ figures. To solve the problems stated in this work, the following new results are produced: a) reliability of coordinate data in modern systems of coordinate and time support for lunar objects is investigated by the robust analysis; b) a method and a software complex for transforming selenographic coordinates (TSC) are developed; c) the software package is tested for work with navigation data and determining planetary parameters; d) a method of adaptive regression modeling (ARM) for transforming coordinate systems and assessing structures and parameters of the selenocentric system (SS) is created; e) an algorithm of multi-parameter identification of SS based on ARM-approach is developed to carry out works on expansion and estimation of the reference selenocentric system; f) a global dynamic selenocentric system is constructed on the basis of optical observations taken at “Clementine”, “LRO”, and “Apollo” missions; g) as a result, a simulation digital model of orbital referencing of lunar objects optical observations, taken by star sensors of lunar satellite and on-board laser interferometer, to the selenocentric coordinate system is developed.

Development and Verification of a Digital Twin Patient Model to Predict Specific Treatment Response During the First 24 Hours of Sepsis.

Directed acyclic graphs were used to define explicitly the causal relationship among organ systems and specific treatments used. A hybrid approach of agent-based modeling, discrete-event simulation, and Bayesian network was used to simulate treatment effect across multiple stages and interactions of major organ systems (cardiovascular, neurologic, renal, respiratory, gastrointestinal, inflammatory, and hematology). Organ systems were visualized using relevant clinical markers. The application was iteratively revised and debugged by clinical experts and engineers. Agreement statistics was used to test the performance of the model by comparing the observed patient response versus the expected response (primary and secondary) predicted by digital twin. Medical ICU of a large quaternary- care academic medical center in the United States. Adult (> 18 year yr old), medical ICU patients were included in the study. No additional interventions were made beyond the standard of care for this study. During the verification phase, model performance was prospectively tested on 145 observations in a convenience sample of 29 patients. Median age was 60 years (54-66 d) with a median Sequential Organ Failure Assessment score of 9.5 (interquartile range, 5.0-14.0). The most common source of sepsis was pneumonia, followed by hepatobiliary. The observations were made during the first 24 hours of the ICU admission with one-step interventions, comparing the output in the digital twin with the real patient response. The agreement between the observed versus and the expected response ranged from fair (kappa coefficient of 0.41) for primary response to good (kappa coefficient of 0.65) for secondary response to the intervention. The most common error detected was coding error in 50 observations (35%), followed by expert rule error in 29 observations (20%) and timing error in seven observations (5%). We confirmed the feasibility of development and prospective testing of causal artificial intelligence model to predict the response to treatment in early stages of critical illness. The availability of qualitative and quantitative data and a relatively short turnaround time makes the ICU an ideal environment for development and testing of digital twin patient models. An accurate digital twin model will allow the effect of an intervention to be tested in a virtual environment prior to use on real patients.

Development of the simulation model for Digital Twin applications in historical masonry buildings: The integration between numerical and experimental reality

The structural system integrity in historical masonry buildings is studied by developing the concept of the Digital Twin. The objectives are to develop a procedure for creating an accurate digital model, which integrates the experimental physical reality and to use it to study the structural response of the system, its preventive maintenance and strengthening operations.The key elements examined are the building of an accurate three-dimensional geometric model, the choice of material properties and, the consideration of construction stages along the history. The relation to structural surveys, in situ observation and measurements is explored, with particular attention to reproducing the damage observed. Non-Linear Finite Element modelling is adopted. The structural system is generated in a semi-automatic way, reducing time-consuming modelling tasks and reaching a good approximation of real geometry as well as having an efficient discretization in a finite element model.This procedure can be used to assess with high precision the present structural conditions of the system, study its future evolution for preventive maintenance or practical interventions as well as to understand past documented failures of structural members of the building.An application considered in Milan Cathedral demonstrates the applicability and advantages of the proposed procedure in complex buildings.

Evaluation of the Georeferencing Accuracy of a Photogrammetric Model Using a Quadrocopter with Onboard GNSS RTK.

Using a GNSS RTK (Global Navigation Satellite System Real Time Kinematic) -equipped unmanned aerial vehicle (UAV) could greatly simplify the construction of highly accurate digital models through SfM (Structure from Motion) photogrammetry, possibly even avoiding the need for ground control points (GCPs). As previous studies on this topic were mostly performed using fixed-wing UAVs, this study aimed to investigate the results achievable by a quadrocopter (DJI Phantom 4 RTK). Three image acquisition flights were performed for two sites of a different character (urban and rural) along with three calculation variants for each flight: georeferencing using ground-surveyed GCPs only, onboard GNSS RTK only, and a combination thereof. The combined and GNSS RTK methods provided the best results (at the expected level of accuracy of 1–2 GSD (Ground Sample Distance)) for both the vertical and horizontal components. The horizontal positioning was also accurate when georeferencing directly based on the onboard GNSS RTK; the vertical component, however, can be (especially where the terrain is difficult for SfM evaluation) burdened with relatively high systematic errors. This problem was caused by the incorrect identification of the interior orientation parameters calculated, as is customary for non-metric cameras, together with bundle adjustment. This problem could be resolved by using a small number of GCPs (at least one) or quality camera pre-calibration.

Linear Accuracy of Full-Arch Digital Models Using Four Different Scanning Methods: An In Vitro Study Using a Coordinate Measuring Machine

Improving the accuracy of the digital model is essential for the digitalization of the dental field. This study introduced a novel method of objective accuracy evaluation of digitized full dental arch model using coordinate measuring machine (CMM). To obtain a true linear measurement value using the CMM, 17 reference balls were attached to the typodont, and 12 measurements between balls on the X-(width), Y-(length), and Z-axes (height) were performed automatically. A rubber impression and a plaster cast replica of the typodont with balls were fabricated, and they were digitized with following methods: (a) true model intraoral scans; (b) impression cone-beam computed tomography (CBCT) scans; (c) cast CBCT scans; and (d) cast extraoral scans. Each scanning method was performed 20 times. Twelve linear measurements on the digitized models were automatically made using software. The one-sample t-test and one-way analysis of variance were used for measurement accuracy analysis. The cast extraoral scan was most accurate on X- and Y-axes, while impression CBCT was the most accurate on Z-axis. Over all axes, the intraoral scan resulted in the most deviation from the true model, and the reproducibility of each scan was also low. Extraoral scan shows high precision on width and length, and impression CBCT is advantageous for dental work where height factor is of importance.

Evaluation of the Accuracy of Digital Models Obtained Using Intraoral and Extraoral Scanners versus Gold Standard Plaster Model (Diagnostic Accuracy Study)

Introduction: Digital models showed promising results for orthodontic diagnosis and treatment planning. Digital models can be obtained from alginate impressions as well as direct intra-oral scanners. Studies assessing the accuracy of digital models have shown digital models to be valid, clinically acceptable, and more quickly obtainable. With the advent of new scanners with better scanning technology researches are necessary to evaluate their accuracy and reliability. Aim of Study: To evaluate the diagnostic accuracy of 3D digital models obtained through intraoral and extraoral scanning modalities to the reference gold standard plaster model. Material & Methods: Twenty-four adult male and female subjects were randomly selected for this study. The intraoral scanners evaluated in this study were Sirona (CEREC Omnicam) and 3 shape (TRIOS 3), while the laboratory scanners used were Sirona (inEos X5), and 3 shape (D850). Intra-oral scanning of the subjects and extra-oral scanning of their alginate impressions, plaster models of the alginate impression, rubber base impression, and plaster model of their rubber base impression were done. Linear dental measurements included intermolar width, interpremolar width, intercanine width, mesiodistal width of the 1st permanent molar, 1st premolar, canine and central incisor and arch width. All data were collected, tabulated and subjected to statistical analysis. Results: Small differences between the plaster and digital models were observed. Intra-observer reliability analysis for 14 out of the 16 measurements showed that all variables exhibited good to excellent reliability. Conclusions: There was no difference between the digitization using the intraoral scanner or the laboratory scanner. The most accurate digitization technique was the 3 Shape laboratory scanner of the cast of the alginate impression. The inEos X5 showed the highest error of digitization of the alginate and rubber base impressions.

Application and Development Prospect of Digital Twin Technology in Aerospace

Abstract The digital twin can be seen as the link between the physical and digital worlds, and has received widespread attention both at home and abroad. By establishing an accurate digital model of the physical entity and the communication relationship between the physical entity and the model, the digital model and the physical entity can be mapped in both directions, so that the twin model can be modified continuously using the data of the physical entity. The twin model, after diagnosing, predicting and evaluating, can output the simulation results to the controller for state control of the physical entity, thus achieving consistency between the twin and the physical entity. This paper first analyzes the relationship between the basic concepts of the digital twin. It then introduces the necessity of digital twin in aerospace applications, focusing on the existing applications of the digital twin in the aerospace field. Compared with traditional modelling simulations, the digital twin has the advantages of shorting design cycle, high reliability, less frequent overhaul and low maintenance cost. Finally, the outlook for the future development of the digital twin is discussed, focusing on the current situation of digital twin applications in aerospace.

Dimensional artefacts to achieve metrological traceability in advanced manufacturing

Dimensional measurements play a central role in enabling advanced manufacturing technologies, enhancing the quality of products and increasing productivity. This role becomes even more important in the context of Industry 4.0, where reliable and accurate digital models of products, processes and production systems are needed. To establish the traceability chain that links measurements in production to the length unit, dimensional artefacts – ranging from measurement standards to calibrated workpieces – are fundamental. The paper examines dimensional artefacts, discussing their characteristics, availability and role in supporting production by establishing metrological traceability, and provides guidelines for their selection, use and development.

Development of Digital Twin for Load Center on the Example of Distribution Network of an Urban District

The paper proposes a concept of building a digital twin based on the reinforcement learning method. This concept allows implementing an accurate digital model of an electrical network with bidirectional automatic data exchange, used for modeling, optimization, and control. The core of such a model is an agent (potential digital twin). The agent, while constantly interacting with a physical object (electrical grid), searches for an optimal strategy for active network management, which involves short-term strategies capable of controlling the power supplied by generators and/ or consumed by the load to avoid overload or voltage problems. Such an agent can verify its training with the initial default policy, which can be considered as a teacher’s advice. The effectiveness of this approach is demonstrated on a test 77-node scheme and a real 17-node network diagram of the Akademgorodok microdistrict (Irkutsk) according to the data from smart electricity meters.

Combined 3D Surveying and Raman Spectroscopy Techniques on Artifacts Preserved at Archaeological Museum of Lipari

Over the last years, the documentation of Heritage has been increasingly enriched with new forms of data representation and contents deriving from technological applications on artifacts and the progress of computer graphics: if, on the one hand, 3D survey has become an effective tool supplementing and supporting traditional study activities, as it can generate accurate and high-resolution digital models (available especially when physical access to materials is not possible, but also for enhancement or to formulate hypothetic reconstruction), on the other, archaeometry investigations can provide all that information (about composition, firing temperature of clay, etc.) that autopsy, comparison, formal, contextual, or bibliographic analysis cannot do on their own. This paper aims to show the potentialities of combined use of these non-destructive and non-contact approaches on the archaeological artifacts preserved at the Regional Museum of Lipari "L. Bernabò Brea" for the analysis, diagnostic, fruition, and forthcoming restoration purposes. Different methodologies, such as laser-based surveying, sfm digital photogrammetry, and Raman spectroscopy have been, respectively, adopted and combined to get reconstruction and characterize several clay masks and two figured calyx-kraters. The latter technique, in particular, has proved to be useful in compositional analysis of dyes and pigments contained in the clay.

Standard methods for creating digital skeletal models using structure-from-motion photogrammetry.

This article assesses best practices for producing 3D digital cranial models through structure-from-motion (SfM) photogrammetry, and whether the metric accuracy and overall presentation of photogrammetric models are comparable to physical crania. It is intended to present a user-friendly standard method of creating accurate digital skeletal models using Agisoft PhotoScan. Approximately 200 photographs were taken of three different crania, and were separated into series consisting of 50, 75, 100, 150, and approximately 200 photos. Forty-five cranial models were created using different photo series and a variety of PhotoScan settings. These models were assessed based on defined qualitative criteria, and model measurement estimates were compared with physical skeletal measurements using Bland-Altman plots. The majority of all models (37/45) produced measurement estimates with mean differences of 2 mm or less regardless of PhotoScan settings, and therefore demonstrated high levels of agreement with the physical measurements. Models created with 150 photographs and on "high" PhotoScan settings scored the highest in terms of qualitative appearance in the shortest amount of time. In PhotoScan, it is recommended to create cranial models using 150 photographs and "high" settings; this produces digital cranial models that are comparable to physical crania in both appearance and proportion. SfM photogrammetry is a convenient, noninvasive, and rapid 3D modeling tool that can be used in almost any setting to produce digital models, and following the guidelines established here will ensure that these models are metrically accurate.