3D Modeling Method Research Articles

Validity and reliability of three-dimensional modeling of orthodontic dental casts using smartphone-based photogrammetric technology

The development of intraoral scanning technology has effectively enhanced the digital documentation of orthodontic dental casts. Albeit, the expense of this technology is the main limitation. The purpose of the present study was to assess the validity and reliability of virtual three-dimensional (3D) models of orthodontic dental casts, which were constructed using smartphone-based 3D photogrammetry. A smartphone was used to capture a set of two-dimensional images for 30 orthodontic dental casts. The captured images were processed to construct 3D virtual images using Agisoft and 3DF Zephyr software programs. To evaluate the accuracy of the virtual 3D models obtained by the two software programs, the virtual 3D models were compared with cone-beam computed tomography scans of the 30 dental casts. Colored maps were used to express the absolute distances between the points of each compared two surfaces; then, the means of the 100%, 95th, and 90th of the absolute distances were calculated. A Wilcoxon signed-rank test was applied to detect any significant differences. The differences between the constructed 3D images and the cone-beam computed tomography scans were not statistically significant and were accepted clinically. The deviations were mostly in the interproximal areas and in the occlusal details (sharp cusps and deep pits and fissures). This study found that smartphone-based stereophotogrammetry is an accurate and reliable method for 3D modeling of orthodontic dental casts, with errors less than the accepted clinically detectable error of 0.5 mm. Smartphone photogrammetry succeeded in presenting occlusal details, but it was difficult to accurately reproduce interproximal areas.

Three-dimensional modeling of loose layers based on stratum development law

Abstract Loose layers are the locus of human activities. The high-quality 3D modeling of loose layers has essential research significance and applicability in engineering geology, hydraulic and hydroelectric engineering, and urban underground space design. To address the shortcomings of traditional 3D loose-layer modeling based on borehole data, such as the lack of bedrock surface constraints, simple strata pinch-out processing, and the higher fitting error of the strata surface, a 3D loose-layer modeling method based on the stratum development law is proposed. The method mainly uses three different virtual boreholes, bedrock-boundary virtual boreholes, pinch-out virtual boreholes, and densified virtual boreholes, to control the stratigraphic distribution. Case studies demonstrate the effectiveness of this 3D loose-layer modeling method in the Qinhuai District of Nanjing and Hangkonggang District of Zhengzhou. Compared to the previous methods that interpolated stratigraphic surfaces with elevation information, the method proposed in this article interpolates the stratum thickness based on stacking, which could improve the interpolation accuracy. In the area where the loose layers and exposed bedrock are alternately distributed, stratigraphic thickness errors’ mean and standard deviation decreased by 2.11 and 2.13 m. In the pure loose-layer area, they dropped by 0.96 and 0.33 m. In addition, the proposed approach allows us to infer the different stratigraphic distribution patterns accurately and complete 3D loose-layer model construction with higher accuracy and a good visualization effect.

Hydrogeological model for underground oil storage in rock caverns

For underground engineering, hydrogeological conditions of the engineering site are usually complicated, and a fine hydrogeological model is the basis for the accurate analysis of groundwater flow fields. A 3D fine hydrogeological modeling method applicable to large underground engineering was proposed in this study, which was mainly composed of data preprocessing, initial model establishment and model calibration. The modeling method adequately considers the complexity of geometric parameters and the non-uniformity of the spatial distribution of physical parameters in the geological zone. The boundaries of the model were determined based on independent hydrogeological units. The hydrogeological model is calibrated based on the monitoring data and supplementary investigation information. The 3D fine hydrogeological modeling method has been successfully applied to a large underground water-sealed oil storage engineering under construction. The groundwater level, water inflow and flow directions in four typical construction stages were used as the calibration information. Based on the fine hydrogeological model, the flow analysis was conducted to assess the containment properties of the oil storage caverns during operation. The feedback analyses of the buried depth of underground engineering and the permeability reduction ratio of the grouted zone of caverns were carried out. Through flow analyses, the complex geological conditions had obvious influence on the groundwater flow field, and the hydraulic connection between the oil storage and the river boundaries was obtained. The permeability reduction ratio of the grouted zone of caverns in this engineering was from 18% to 45%. The analysis results showed that the oil storages met the requirements of containment properties during operation. The 3D fine hydrogeological model is helpful to accurately analyze the groundwater flow field for underground engineering, and can provide scientific guidance to the design, construction and operation of underground water-sealed oil storage engineering.

Study of the Mechanical Behavior of Steel-Hybrid Composite Beams Constructed by Suspension Bracing Method

The construction process of steel–concrete composite girders was simulated using a 3D finite-element model and suspension-bracing method. The influences of multiple factors such as self-weight of suspension bracket, wind load, longitudinal spacing of suspension points, concrete deck slab thickness, concrete casting process, and suspension bracket removal on the mechanical properties of the main steel girder and the composite girder were analyzed. The mechanical behavior of the steel–concrete composite girders during the construction process using the suspension-bracing method was revealed. The results show that (1) the normal stress and displacement of the steel girder increases with the increase of the weight of the suspension bracket, and they have a relatively large impact on the increase. (2) The wind load during the construction process will produce large transverse displacement of the main steel girder, the transverse wind load should be considered in the load combination analysis, and necessary measures should be taken to limit the transverse displacement of the main steel girder during the deck casting process. (3) The displacement and stress of the main steel girder will show a parabolic change with the change of the longitudinal spacing of the suspension points, so the optimal value of the longitudinal spacing of the suspension points is recommended to be 4 m. (4) The maximum midspan displacement and stress of the main steel girder increase with the increase of the deck slab thickness, and the weight of the deck slab occupies the main position in the whole system force. (5) In the process of casting deck slabs with the suspension-bracing method, the stress and deformation of the main steel girder increase with the concrete construction stage of the deck slabs. To ensure that the geometric shape of the bridge at each stage is consistent with the theory result, the design elevation of each section should be preraised during the construction process according to the vertical displacement and deformation of the main steel girder caused by the construction of each casting stage. In addition, the upward rebound of the main steel girder caused by the removal of the suspension bracket must be fully considered when setting the prearch of the steel–concrete composite girder.

Contributions to Increasing the Efficiency of Studying the Subject “Engineering Graphics”

The article approaches the problem of increasing the efficiency of studying the subject of Engineering Graphics within the limits of the hours stipulated in the curriculum. The transition to the widespread use of IT tools makes it necessary to combine the paper format with the electronic one. The student’s task usually consists in creating flat drawings after intuitive axonometric drawings. Based on the experience in teaching the discipline, the authors considered opportune to use the spatial models of the individual task created by the students themselves. A staggered teaching method of 3D modeling was elaborated with the selection of a minimum set of commands necessary to realize the proposed model at each of the practical occupations. Students can see the relationship between real objects and their projections, get acquainted with spatial modeling and develop spatial imagination.

Development of Suppositories Silicone Molds Using Additive Technologies

Introduction. In modern practice, suppositories are prepared by hand rolling method or fusion. 3D printing can overcome the disadvantages of traditional suppository manufacturing methods and solve the problems of personalization. 3D printing makes it possible to manufacture drug-loaded suppositories without the use of molds or other physical support. The current studies have a number of limitations, and the printing of one suppository requires a long time. This report proposes a method of 3D modeling and 3D printing to produce personalized suppositories by fusion.Aim. Various sizes and shapes suppositories silicone molds development by molding method from hydrophilic, lipophilic and amphiphilic bases.Materials and methods. Suppository bases: cocoa butter (Luker, Colombia), polyethylene glycol (PEG) 1500 (Merck KGaA, Germany), PEG-400 (Merck KGaA, Germany), Witepsol H-15 (Chimmed Group, Russia); pharmaceutical substance: paracetamol (Hebei Jiheng (Group) Pharmaceutical Co. Ltd, China); filaments for 3D printing: polyethylene terephthalate (PET-G natural, LLC "PrintProdakt", Russia); silicone two-component platinum, hardness Shore 30A (China); solvents: Acetonitrile Grade HPLC (Merck KGaA, Germany). The design of the both casting and master molds of suppositories was carried out using the KOMPAS-3D version 17.1. Master molds were printed by Picaso PRO 250 and Picaso X Pro 3D printers. Mold segments were obtained by filling master molds with a mixture of two-component silicone. Suppositories were obtained by molding method. Their average weight and standard deviation were determined. Paracetamol concentration in suppositories was carried out by UV spectrophotometry on a UV-1240 mini spectrophotometer (Shimadzu, Япония). Silicone molds were soaked and washed in hot water with surfactants. Washouts from the molds were taken by soaking the mold.Results and discussion. The torpedo-shaped form was chosen as the model form of suppositories. For the chosen form, three volumes of suppositories were designed: 3.32 ml; 1.5 ml and 0.25 ml. Silicone molds were designed and manufactured for all volumes. The cast suppositories were examined for compliance with the regulatory documentation for the dosage form, the average weight and mass uniformity were evaluated. Suppositories with paracetamol were made. A procedure for cleaning the obtained silicone molds has been developed.Conclusion. The resulting silicone molds make it possible to obtain suppositories in accordance with the regulatory documentation for the suppositories. Silicone molds have significant advantages compared to analogues of metal or polymeric molds.

Modeling and deformation simulation of weft knitted fabric at yarn level

This study proposes a method for 3D modeling of weft knitted fabric and simulating its deformation behavior. A geometric model of the fabric was established using a loop-mesh unit, and the surface of the yarn was calculated using a reference frame. The patterns of the fabrics were represented by bitmap images. To simulate the deformation behavior of the fabric, a physical model was built based on a dynamic spline that included stretching and bending of the yarn. To simplify the collisions between continuous yarns, collisions were detected using a discrete sphere-spring model. The Euler-Lagrange theorem was introduced to achieve the energy balance of the system, and a stable shape was obtained by solving the Euler-Lagrange equation explicitly according to the convergence conditions. Rendering and deformation of the model were implemented using a simulator program via C++ and OpenGL. The simulation displayed the 3D appearance of the weft knitted fabric. The deformed shapes of fabrics were accurately predicted by the proposed method.

A digital hologram-based encryption and compression method for 3D models

This study proposes a novel method to compress and decompress the 3D models for safe transmission and storage. The 3D models are first extracted to become 3D point clouds, which would be classified by the K-means algorithm. Then, these nearby 3D point clouds are converted into a computer-generated hologram (CGH) by calculating the point distribution on the hologram plane using the optical wavefront propagation method. The computer-generated hologram (CGH) contains the spatial coordinate information on point clouds, which can be decompressed using the convolutional neural network (CNN) method. The decompression accuracy of 3D point clouds is quantitatively assessed by normalized correlation coefficients (NCCs), reflecting the correlation between two points and influenced by the hologram resolution, the convolution kernel, and the diffraction distance. Numerical simulations have shown that the novel method can reconstruct a high-quality 3D point cloud with an accuracy of 0.1 mm.

An Automatic Geometric Registration Method for Multi Temporal 3D Models

The application research of ground change detection based on multi-temporal 3D models is attracting more and more attention. However, the conventional methods of using UAV GPS-supported bundle adjustment or measuring ground control points before each data collection are not only economically costly, but also have insufficient geometric accuracy. In this paper, an automatic geometric-registration method for multi-temporal 3D models is proposed. First, feature points are extracted from the highest resolution texture image of the 3D model, and their corresponding spatial location information is obtained based on the triangular mesh of the 3D model, which is then converted into 3D spatial-feature points. Second, the transformation model parameters of the 3D model to be registered relative to the base 3D model are estimated by the spatial-feature points with the outliers removed, and all the vertex positions of the model to be registered are updated to the coordinate system of the base 3D model. The experimental results show that the position measurement error of the ground object is less than 0.01 m for the multi-temporal 3D models obtained by the method of this paper. Since the method does not require the measurement of a large number of ground control points for each data acquisition, its application to long-period, high-precision ground monitoring projects has great economic and geometric accuracy advantages.

Growth of oriented orthotropic structures with reaction/diffusion

Lattice structures can present advantageous mechanical properties while remaining remarkably lightweight. Precise lattice design can however be tricky to set up with classical 3D modeling methods as it involves very fine details. Interestingly, natural porous structures can present such lattice-like or membrane-like features which motivates to seek for more bio-inspired approaches to microstructure design. In this paper, we present a novel method to grow lattice-like and membrane-like structures within an arbitrary shape and aligned along an oriented field. Our method relies on the use of a dedicated anisotropic reaction–diffusion system guided by an orthotropic diffusion tensor field. Assuming for instance the diffusion tensor to be related to the stress analysis of a given shape allows to generate emerging stripes patterns aligned along each one of the principal stress directions independently. A globally coherent mechanical model conforming to the initial shape boundary and infilled with oriented microstructures can therefore be synthesized. Further, we demonstrate the capability of this approach to handle other types of oriented fields such as obtained through optimization of material directions in scenarios with multiple load cases. Our approach relies on spatially and temporally local operations allowing for efficient parallelization. This permits user-interaction and automated adaptation of the design, even for fine meshes over large volumes. For instance, a designer can locally erase or “draw” over the structure and let it regrow and adapt as well as enforce regions to be deliberately full or empty. The proposed approach yields smooth and conformal oriented anisotropic geometrical patterns. This is related to recent effort in the structural optimization community on the topic of optimized oriented infills and microstructure de-homogenization. One of the resulting designs is validated by means of a full scale general non-linear analysis showcasing the advantageous properties of oriented microstructures for stability and robustness to buckling.

INDOOR AND OUTDOOR STRUCTURED MONOMER RECONSTRUCTION OF CITY 3D REAL SCENE BASED ON NONLINEAR OPTIMIZATION AND INTEGRATION OF MULTI-SOURCE AND MULTI-MODAL DATA

Abstract. 3D Real Scene is an important part of new infrastructure construction, which provides a unified spatial base for economic and social development and informatization of various departments. According to the demand of real 3D Real Scene digital construction, this paper aims to study the method of indoor and outdoor structured monomer reconstruction of city 3D Real Scene, develop digital twin platform, and strive to lead the development of 3D Real Scene. The main research contents of this paper are as follows: 1) Spatio-temporal-spectral-angular remote sensing observation system and data fusion model; 2) Rapid construction method of vector monomer 3D model of indoor and outdoor entity object; 3) 3D structural reconstruction technology of urban component level based on vector images; 4) A universal digital twins platform, LuojiaDT. The technologies we have developed have been widely used in the national 3D Real Scene construction of China, including smart city, smart transportation, cultural heritage protection, public security and police, urban underground pipe network, indoor and outdoor location service. This research will promote the continuous development of digital twins technology.

The Application of 3D Virtual Technology in the Teaching of Clinical Medicine

The booming development of 3D virtual technology provides the basis for the innovation of teaching mode of clinical medicine. Integrating 3D virtual technology into the clinical education teaching of medical students can help medical students learn clinical expertise more intuitively, enrich practical experience, improve hands-on ability, and make up for the shortcomings of traditional medical teaching. However, the traditional 3D modeling method has the problems of sparse and insufficient accuracy of output results, which greatly limits the specific application of 3D virtual technology in clinical teaching. Therefore, this paper addresses the shortcomings of previous 3D virtual technology in 3D modeling of organs, introduces deep learning, and then proposes a pyramidal shape perception network with the ability to generate samples on point clouds. Experimental results show that the proposed model not only has a large improvement in accuracy but also shows a high degree of confidence in providing real-time feedback of local image attributes.

Individual navigation templates for pedicle screw placement in spine surgery: a systematic review

The literature review presents data from world studies on the use of individual navigation templates in spine surgery and analyzes the published results of the application of individual navigation templates on different parts of the spine. The accuracy and safety of fixed transpedicular screws were evaluated using the templates. The main stages of template creation were highlighted, including the visualization methods for 3D modeling, 3D printing methods, available materials, as well as the time and costs associated with 3D printing were determined. For information analysis 23 publications were selected, 8 of them relate to the cervical spine, 10 — to the thoracic, and 5 — to the lumbar spine. The data of 460 patients in whom 3,294 screws had been fixed using the templates were analyzed, and the analysis has revealed that out of 3,294 screws, 3,059 (92.8%) have the highest level of safe fixation.

Individual navigation templates for pedicle screw placement in spine surgery: a systematic review

The literature review presents data from world studies on the use of individual navigation templates in spine surgery and analyzes the published results of the application of individual navigation templates on different parts of the spine. The accuracy and safety of fixed transpedicular screws were evaluated using the templates. The main stages of template creation were highlighted, including the visualization methods for 3D modeling, 3D printing methods, available materials, as well as the time and costs associated with 3D printing were determined. For information analysis 23 publications were selected, 8 of them relate to the cervical spine, 10 — to the thoracic, and 5 — to the lumbar spine. The data of 460 patients in whom 3,294 screws had been fixed using the templates were analyzed, and the analysis has revealed that out of 3,294 screws, 3,059 (92.8%) have the highest level of safe fixation.

A New Reading of the Inscriptions on the Handles of the Nominal Knives Found on the Sims Bay Shores

Purpose. The article presents a new reading of the inscriptions on two nominal knives found on the coast of Sims Bay in the Laptev Sea. The results of the reading are differs from the readings of paleographers and researchers published earlier. It was possible to give a correct reading of these inscriptions due to the use of the non-contact 3D modeling method developed by the RSSDA Laboratory and used in the Code of Russian Inscriptions (CRI).Results. The reading of the inscriptions on the nominal knives proposed by the authors of this article made it possible to establish their belonging to Gury (baptismal name) – Akaky (prayer? name) Ivanov's son Karzyaev, the likely head of the commercial and industrial expedition in the 20s of the 17th century. The site of polar sailors of the 17th century in the Sims Bay is located in 70 km to the west from the Thaddeus the North island, where in 1940 members of the hydrographic detachment of the East Taimyr hydrographic expedition found similar finds, including 8 other knives. Unfortunately, these knives have only partially preserved handles, and most turned out to be represented only by blades. Inscriptions filled with Slavic script could be found only on two knives from a hut in Sims Bay.Conclusion. According to the official version, both finds belong to the members of the Russian trade and industrial expedition in the 17th century. The rich composition of the archaeological artifacts collected at these two locations makes this site of Russian culture of the 17th century unique.

A Fast Scheduling Method for Massive Oblique Photography 3D Models

In view of the large amount of oblique photography 3D model data and the fact that high-performance hardware devices cannot load and render massive oblique photography 3D models at one time, this paper provides a fast scheduling method for massive oblique photography 3D models: get the tile radius, side length, scheduling range, and other parameters from the original data, normalize the original tile to a hundred grid, use a regular grid + quadtree + hexadecimal tree to build a tile spatial index, resample the tile data at each level to generate the elevation model DEM and the real radiographic image TDOM, and use the DEM+TDOM method to reconstruct the layered and block top-level 3D model to achieve rapid scheduling and rendering of massive oblique photography 3D models. Experiments show that the method is efficient and feasible and can meet the visualization and real-time interaction requirements of massive urban 3D models.

Prediction of the Structural Properties of Powder Materials by 3D Modeling Methods

This article examines the main problems of modelling spherical (circular) particles. The main method of the initial process of filling lobules using the Cauchy and Reynolds problem is substantiated. An image of an object-oriented complex of free fall of a spherical particle and their many non-collision spheres is presented. Based on the obtained research results, the main parameters of the process of filling particles of heterogeneous materials. An example of visualization of the developed software product for filling material particles is given, taking into account a number of cross-sections of a cylindrical hopper in height. A histogram of the distribution of material particles from porosity over the volume of a cylindrical hopper is also constructed.

3D geological implicit modeling method of regular voxel splitting based on layered interpolation data

In view of the problems in traditional geological modeling methods, such as the insufficient utilization of geological survey data, the inaccurate expression of a stratigraphic model, and the large amount of model data, a 3D geological model cannot be smoothly loaded and rendered on the web end. In this paper, a 3D geological implicit modeling method of regular voxel splitting based on hierarchical interpolation data is proposed. This method first uses the boreholes and geological section data from a geological survey for data conversion and fusion, compares the applicability of different interpolation algorithms through cross-validation research, and uses the best fitting algorithm to interpolate and encrypt discrete points in the formation. Then, it constructs the regular voxels, designs five different regular voxel split types, and divides the voxels. In addition, the data structure design of the voxel split model is implemented, and the irregular voxel metadata structure is analyzed and displayed through Three.js. Using this method, based on the survey data of an area in Zhengzhou, the global workflow from data processing to model construction and visualization is demonstrated. The experimental results show that the model can integrate multisource hierarchical interpolation data; express different stratum structures accurately and smoothly, and can realize the rendering, spatial query and analysis of the internal information of a geological body in a browser.

A new method of 3D direct current resistivity modelling using a long electrode source for forward probing in tunnels

ABSTRACTThe direct current resistivity method has been widely used for the prediction of water‐bearing structures in subway tunnels and mine tunnels. The traditional direct current resistivity uses point electrode sources in tunnels to excite the electric field; potential electrodes are arranged on the back of the tunnel face to measure the position of the anomaly using the apparent resistivity sounding curve. Due to the dimension limitations of the tunnel cavity, the maximum distance of potential electrodes is often restricted. Thus, the exploration depth often cannot cover the target appropriately. Additionally, owing to the inaccessibility of point electrode sources on the tunnel face, point electrode sources can only be set near the tunnel face, so the electric signal excited by point electrode sources cannot be coupled with the water‐bearing anomaly at a large depth. As such the traditional point electrode method for forward probing in tunnels has a shortcoming of small detection depth. To overcome this problem by increasing the detection depth, a horizontal drilling copper casing is first used as a new long electrode source array, which (as far as the authors are aware) has never been reported in forward probing in tunnels. We developed a new method of 3D direct current resistivity modelling with a long electrode source for forward probing in tunnels using the finite‐element method. The long electrode current source was used to replace the conventional point electrode current source, and the observed potential electrodes were respectively arranged in the tunnel floor, tunnel face and horizontal drilling. Theoretical formulas for the long electrode source for the whole‐space direct current method are first applied in forward probing in tunnels. An analytical test for a whole‐space model with the long electrode source has been used to validate the accuracy of the 3D algorithm. Three synthetic geological models for the long electrode source were used to examine the applicability by investigating the detection capability to predict the anomaly. The observed signal of apparent resistivity excited by the long electrode source is stronger than that of the point electrode source because the long electrode source is closer to the anomaly. This new method using the long electrode source greatly improves the resolution of the anomaly, which is of great significance for the safety of the tunnel construction.

A 3D Face Modeling and Recognition Method Based on Binocular Stereo Vision and Depth-Sensing Detection

The human face is an important channel for human interaction and is the most expressive part of the human body with personalized and diverse characteristics. To improve the modeling speed as well as recognition speed and accuracy of 3D faces, this paper proposes a laser scanning binocular stereo vision imaging method based on binocular stereo vision and depth-sensing detection method. Existing matching methods have a weak anti-interference capability, cannot identify the spacing of objects quickly and efficiently, and have too large errors. Using the technique mentioned in this paper can remedy these shortcomings by mainly using the laser lines scanned onto the object as strong feature cues for left and right views for binocular vision matching and thus for depth measurement perception of the object. The experiments in this paper first explore the effect of parameter variation of the laser scanning binocular vision imaging system on the accuracy of object measurement depth values in an indoor environment; the experimental data are selected from 68 face feature points for modeling, cameras that photograph faces, stereo calibration of the cameras using calibration methods to obtain the parameters of the binocular vision imaging system, and after stereo correction of the left and right camera images, the laser line scan light is used as a pixel matching strong features for binocular camera matching, which can achieve fast recognition and high accuracy and then select the system parameters with the highest accuracy to perform 3D reconstruction experiments on actual target objects in the indoor environment to achieve faster recognition.