Dynamic Simulation Method of High-Speed Railway Engineering Construction Processes Based on Virtual Geographic Environment

International Journal of Geo-Information

Article Dynamic Simulation Method of High-Speed Railway Engineering Construction Processes Based on Virtual Geographic Environment

Xinwen Ning 1,2, Qing Zhu 1,*, Heng Zhang 2, Changjin Wang 2, Zujie Han 2, Junxiao Zhang 1 and Wen Zhao 2 1 Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 611756, China; [email protected] 2 China Railway Design Corporation, Tianjin 300251, China; [email protected] (X.N.); [email protected] (H.Z.); [email protected] (C.W.); [email protected] (Z.H.); [email protected] (W.Z.) * Correspondence: [email protected]; Tel.: +86-028-66367612

Received: 23 March 2020; Accepted: 22 April 2020; Published: 1 May 2020

Abstract: The spatial conflicts in the construction of high-speed railways not only reduce project efficiency, but also lead to serious accidents. To address these key issues, this paper presents a dynamic simulation method for constructions processes based on a virtual geographic environment. This approach can facilitate the identification of conflicts in the construction scheme through accurately expressing and analysing the intricate spatio-temporal relations among railway facility components, construction equipment and the surrounding environment. First, a high-precision virtual geographic scene in which the construction process and methods can be visualized and modelled intuitively is established with terrain, imagery, and engineering 3D models. Then, the overall construction processes can be accurately simulated by a sequential display of the railway components and the behaviour of construction equipment. To simulate the behaviour of construction equipment, the linkage relations between each joint of construction machinery are accurately modelled and animation control parameters are extracted. Finally, a construction simulation of a high-speed railway bridge was performed, and the experimental results show that the proposed method can provide a scientific basis for the optimization of complex engineering construction schemes, safety hazard assessments, and related full life cycle tasks.

Keywords: high-speed railway; construction process simulation; construction method simulation; virtual geographic environment

1. Introduction High-speed railway construction is a system-based project that includes many complex construction processes and usually requires a low-cost, high-quality, and short-duration construction period with adequate safety. Construction scheme development can be very difficult due to the complicated construction process and variability of methods, especially for specific geographical and geological conditions. Construction process simulation is very helpful for determining the best construction scheme by visualizing the construction process, presenting complex and dynamic spatiotemporal relationships among construction links, providing intuitive expressions and analyses of construction schemes, and effectively assessing the safety of the construction process. A good simulation can be the key to improving construction efficiency and construction quality. According to construction simulations, a real construction process can be simulated in the virtual world, and problems that can occur in actual construction can be discovered in advance [1].

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The existing construction simulation methods usually use three-dimensional surface models or BIMs (building information models) for the simple analysis and visualization of collision detection and virtual assembly [2–6]. Such methods only focus on the construction and assembly process of railway components and ignore the global relations among construction equipment and the surrounding geographical environment. The construction methods of railways are strongly influenced by environmental factors such as the terrain, geology, hydrology, weather, and traffic. Therefore, appropriately considering information associated with the surrounding environment and the spatio-temporal relations between actual construction processes and the surrounding area is the key to precise and scientific construction simulations. Three-dimensional geographic information system (3D GIS) has the characteristics of multi-source heterogeneous data fusion, mass quantity management and display, spatial analysis, etc., so it provides a very good basic platform for construction simulation [7,8]. Virtual geographic environments (VGEs) describe real geographic objects using dynamic spatio-temporal data, thereby enabling experiments and analyses in the virtual space with a true spatiotemporal context [9–16]. The construction environment [17], which is constructed in virtual geographic space, can not only reflect static objects such as construction sites and buildings but also reflect spatial information such as geographic locations and dynamic spatial relationships, including factors related to terrain filling, construction convenience, and construction processes. Currently, construction simulations in VGEs are mainly used to combine numerical simulations and scene simulations [18–20], and most methods focus on the visual display of the results of simulation models. Additionally, some studies have investigated the construction process based on real-time monitoring data [21,22]. This simulation method employs mathematical models and presents the data in terms of visualization; however, only technological processes and the guidance plan can be reflected, and the specific method used in the construction process is not considered. Hiam M. Khoury et al. [23–27] performed in-depth research on construction simulation, although most of the work was based on simulation software, and the impact of the geographical environment was rarely considered. In the field of railway engineering, simulations in VGEs are mainly applied for three-dimensional performance simulations of coupled system dynamics [28–30], line selection [27,31–33], run simulation [34] virtual driving [35], and similar processes; notably, few simulations have focused on railway construction or verified the effectiveness of the construction method to support construction scheme programming. Therefore, it is necessary to develop an accurate simulation method to simulate the dynamic construction process of complex engineering projects. This paper presents a dynamic construction simulation method in a VGE that can reflect the construction process of high-speed railways and depict the complex spatio-temporal relationships between construction elements and the surrounding environment. First, the three-dimensional models of a railway and construction equipment are decomposed at the component level, and then repositioned and assembled in the virtual scene. Then, a construction time sequence simulation is performed by changing the visibility of the model components according to the construction standards. A construction process video can be automatically generated, and the viewpoint can be adjusted according to the project progress. Finally, for a specific complex local construction process, a joint linkage mechanical model is developed to flexibly simulate the dynamic working process of construction machinery.

2. Methodology

2.1. Construction Process Simulation Framework Based on a Virtual Geographic Environment Figure1 illustrates a dynamic construction simulation framework based on VGEs, a dynamic 3D spatial information system that provides at uniﬁed digital framework of the whole railway environment, which is represented by both macro geographic and geological environments and micro railway facilities; this framework mainly includes the following three key technical components. ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 3 of 19

(DEM) data, digital orthophoto map (DOM) data, and three-dimensional model data. To dynamically simulate the construction process, a three-dimensional model must be decomposed according to the construction requirements, and then the decomposed model is reassembled in a virtual geographic scene. Models are organized and related in the scene based on semantic information. This process mainly includes the decomposition of railway work points and the construction of mechanical models. Model decomposition is the focus of process and engineering simulations. (2) Model components are displayed in chronological order for construction process simulation. Process simulations roughly show the overall flow of construction at the macro level. All the construction processes are decomposed into a plurality of subprocesses, and each subprocess is further disassembled into a plurality of construction steps. Each subprocess corresponds to a playlist, and each construction step corresponds to a key frame in the three-dimensional scene. In the playlist, the viewpoint parameters, the action parameters, and the model parameters are driven by time parameters so that the actions are shown sequentially in time. At this point, the simulation of construction processes is complete. (3) The construction method is simulated based on the joint linkage of construction machinery. A simulation is used to represent the construction method for local and complex work points. According to the construction method, local and complex work points are specifically displayed, and the user-oriented animation control parameters are mapped to mechanical joint activity parameters so that the operation of the construction machinery is effectively simulated. Moreover, the lifting object attachment parameters are added, and a work animation parameter file is jointly formed. At this point, the simulation of the construction method is complete. In addition, a work process simulation with a partial set of work points is usually integrated into the simulation process, and the ISPRSmethods Int. J. Geo-Inf.are combined2020, 9, 292 to complete the entire construction simulation process. 3 of 18

FigureFigure 1. 1.Dynamic Dynamic construction construction simulationsimulation framework based on on a a virtual virtual geographic geographic environment environment..

(1) A high-precision VGE is generated based on model decomposition and reassembly. The VGE provides a basic display environment and an information-bearing framework for construction simulation,2.2. Virtual andGeo-e itnvironment is formed Generation from the Based fusion On of Model multisource Decomposition data, suchand Reassembly as digital elevation model (DEM) data, digital orthophoto map (DOM) data, and three-dimensional model data. To dynamically simulate2.2.1. Model the construction component-level process, decomposition a three-dimensional model must be decomposed according to the constructionTo simulate requirements, the construction and then the process, decomposed the railway model work is reassembled point models in a virtual and construction geographic scene.mechanical Models models are organized need to be and broken related down in theinto scene components based onand semantic reassembled. information. This process This mainly process mainlyincludes includes decomposition the decomposition. Then, reassembly of railway can work be points completed and the only construction by determining of mechanical the adhesion models. Modelrelation decompositions among components. is the focus The of railway process engineering and engineering point model simulations. needs to recalculate the position (2) Model components are displayed in chronological order for construction process simulation. Process simulations roughly show the overall flow of construction at the macro level. All the construction processes are decomposed into a plurality of subprocesses, and each subprocess is further disassembled into a plurality of construction steps. Each subprocess corresponds to a playlist, and each construction step corresponds to a key frame in the three-dimensional scene. In the playlist, the viewpoint parameters, the action parameters, and the model parameters are driven by time parameters so that the actions are shown sequentially in time. At this point, the simulation of construction processes is complete. (3) The construction method is simulated based on the joint linkage of construction machinery. A simulation is used to represent the construction method for local and complex work points. According to the construction method, local and complex work points are specifically displayed, and the user-oriented animation control parameters are mapped to mechanical joint activity parameters so that the operation of the construction machinery is effectively simulated. Moreover, the lifting object attachment parameters are added, and a work animation parameter file is jointly formed. At this point, the simulation of the construction method is complete. In addition, a work process simulation with a partial set of work points is usually integrated into the simulation process, and the methods are combined to complete the entire construction simulation process.

2.2. Virtual Geo-Environment Generation Based on Model Decomposition and Reassembly

2.2.1. Model Component-Level Decomposition To simulate the construction process, the railway work point models and construction mechanical models need to be broken down into components and reassembled. This process mainly includes decomposition. Then, reassembly can be completed only by determining the adhesion relations ISPRS Int. J. Geo-Inf. 2020, 9, 292 4 of 18 ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 4 of 19 amonginformation components. for The each railway component engineering after decomposition point model needs to perform to recalculate reassembly the position in a three information-dimensional for eachscene. component after decomposition to perform reassembly in a three-dimensional scene. As shownAs shown in Figure in Figure2, each 2, modeleach model is traversed, is traversed, and eachand each leaf nodeleaf node element element in the in the model model can can be be extractedextracted as as a modela model component component object. object. Every model component component should should be be stored stored as as a single a single file and ﬁle andhas has a unique a unique coordinate coordinate system, system, and and the the transfer transfer variables variables are are recorded recorded inin the the transfer transfer table. table. In this In thisapproach approach,, the the decomposed decomposed model model file ﬁle can can be repositioned repositioned and and reassembledreassembled according according to to the the constructionconstruction process process in three-dimensionalin three-dimensional platform platform software. software. Thus, Thus, component-level component-level model model managementmanagement and display and display control control can be can achieved. be achieved.

Figure 2.FigureModel 2. decomposition Model decomposition and derivation. and derivation.

2.2.2.2.2.2. Model Model Reassembly reassembly WhenWhen the component the component model model is reassembled is reassembled and derived, and derived, the relative the relative position position relations relation betweens between the componentsthe component ands the and model the model origin origin under under the model the model coordinate coordinate system system are required. are required To achieve. To achieve accurateaccurate positioning, positioning, the insertion the insertion point point coordinates coordinates and attitude and attitude parameters parameters of the of model the model need toneed be to be speciﬁedspecified in a three-dimensional in a three-dimensional scene. scene. Therefore, Therefore, the relative the relative coordinates coordinates in the in model the model coordinate coordinate systemsystem need toneed be converted to be converted into absolute into absolute coordinates coordinates in the spatial in the coordinate spatial coordinate system. The system. main steps The main ofISPRS coordinate Int.steps J. Geo of- Inf.systemcoordinate 2020, 3 conversion, x FOR system PEER are REVIEWconversion shown in are the shown Figure 3in, andthe theFigure speciﬁc 3, and description the specific is asdescription follows.5 of 19 is as follows. (1) Model coordinate system to engineering coordinate system. Using the engineering coordinate system from the railway design and construction phase, the position and attitude of the body model in the engineering coordinate system can be obtained from the line design data and model geometry [27, 30-32]. According to the position and posture information associated with the body model in the engineering coordinate system and the relative position data in the assembled relation table, the reassembly coordinates of the subcomponents in the engineering coordinate system can be obtained through position translation and attitude rotation. (2) Engineering coordinate system to geographic coordinate system. The engineering coordinate system is typically a plane rectangular coordinate system after projection, and a geographic coordinate system needs to be used to display a railway three-dimensional scene that is long and has a large span. Reassembling the model in different projected coordinate systems requires calculating the model position, reprojecting, and calculating the projected azimuth correction value, that is, the meridian convergence angle correction. Notably, a Gaussian projection is for a vector, and components farther away from the central meridian show greater azimuth deviation. The calculation

method for the approximation of the deviation angle correction value is shown in Formula (1). Figure 3. Coordinate system conversion. Figure 3. Coordinate system conversion. 훾 = 훥퐿 ∗ 푠𝑖푛 퐵 (1) 2.2.3.(1) Virtual Model geographic coordinate environment system to engineering generation coordinate system. Using the engineering coordinate where γ is the meridian convergence angle correction value, ΔL is the longitudinal difference system from the railway design and construction phase, the position and attitude of the body Figurebetween 4 illustratesthe coordinate the generationposition point process and the of central a railway meridian, VGE, includingand B is the multimodal latitude of thespatio position.- model in the engineering coordinate system can be obtained from the line design data and model temporal dataIn railway fusion, data engineering, organization where, and the optimization. height difference Since the is notconstruction large, the method engineerings of railway coordinate geometry [27,30–32]. According to the position and posture information associated with the body model three-systemdimensional range scene is generallys are relatively less than mature 40 kilometre [12, 36s- 39and], onlythe azimuth a brief description deviation is is less given than here. 0.2 degrees. in the engineering coordinate system and the relative position data in the assembled relation table, (1) Multimodal spatio-temporal data fusion. A railway three-dimensional scene mainly involves themulti reassemblysource heterogeneous coordinates of data, the subcomponents such as DEM, in DOM the engineering, three-dimensional coordinate model, system line can vector,be obtained text throughannotation, position and attribute translation table and data. attitude Since rotation.a railway line is strip shaped, the terrain and features along the railway line use high-resolution data, and low-resolution data are used when the railway line is far away. The low-resolution below 1 meter DOM uses satellite images, the high-resolution above 0.5 meter DOM uses aviation photography images, the low-resolution below 20 meter DEM uses shuttle radar topography mission (SRTM) data, and the high-resolution below 0.5 meter DEM uses lidar data. To demonstrate the construction process, it is necessary to split the corresponding three- dimensional model, such as a body model (e.g., for a bridge) or mechanical model (e.g., for a tower crane), into many subcomponents. The line vector data record mileage information and can be used for rapid positioning according to the mileage data. The character annotations can be used to mark information in the three-dimensional scene, and the actions in the construction simulation process can be prompted. The attribute data record the model name, ID, spatial position, spatial pose, zoom, and other information. (2) Data organization and optimization. The three-dimensional scene data are multisource and multi-format data in large data sets, and the data need to be organized and optimized to improve the efficiency of data browsing and access. The DEM and DOM are organized in a tiled way and managed in layers. The three-dimensional model can be optimized by setting a maximum visible distance, a minimum visible distance, levels of detail (LOD), and other parameters. The three-dimensional models are organized and related in the scene based on semantic information which is extended and defined based on the international framework for dictionaries (IFD) standard issued by the buildingSMART organization. Semantic information is described, stored, and exchanged through metadata. Considering the decomposition of the three-dimensional model of a construction site, the body model is managed as a parent node, and each component model is managed as a child node in a three-dimensional scene. (3) Virtual geographic environment generation. The multimodal spatio-temporal data are unified to the same spatio-temporal reference, and the railway three-dimensional scene is generated. The three-dimensional model is loaded into the scene in the form of three-dimensional point symbols.

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(2) Engineering coordinate system to geographic coordinate system. The engineering coordinate system is typically a plane rectangular coordinate system after projection, and a geographic coordinate system needs to be used to display a railway three-dimensional scene that is long and has a large span. Reassembling the model in diﬀerent projected coordinate systems requires calculating the model position, reprojecting, and calculating the projected azimuth correction value, that is, the meridian convergence angle correction. Notably, a Gaussian projection is for a vector, and components farther away from the central meridian show greater azimuth deviation. The calculation method for the approximation of the deviation angle correction value is shown in Formula (1).

γ = ∆L sinB (1) × where γ is the meridian convergence angle correction value, ∆L is the longitudinal diﬀerence between the coordinate position point and the central meridian, and B is the latitude of the position. In railway engineering, where the height diﬀerence is not large, the engineering coordinate system range is generally less than 40 km and the azimuth deviation is less than 0.2 degrees.

2.2.3. Virtual Geographic Environment Generation Figure4 illustrates the generation process of a railway VGE, including multimodal spatio-temporal data fusion, data organization, and optimization. Since the construction methods of railway three-dimensional scenes are relatively mature [12,36–39], only a brief description is given here. (1) Multimodal spatio-temporal data fusion. A railway three-dimensional scene mainly involves multisource heterogeneous data, such as DEM, DOM, three-dimensional model, line vector, text annotation, and attribute table data. Since a railway line is strip shaped, the terrain and features along the railway line use high-resolution data, and low-resolution data are used when the railway line is far away. The low-resolution below 1 m DOM uses satellite images, the high-resolution above 0.5 m DOM uses aviation photography images, the low-resolution below 20 m DEM uses shuttle radar topography mission (SRTM) data, and the high-resolution below 0.5 m DEM uses lidar data. To demonstrate the construction process, it is necessary to split the corresponding three-dimensional model, such as a body model (e.g., for a bridge) or mechanical model (e.g., for a tower crane), into many subcomponents. The line vector data record mileage information and can be used for rapid positioning according to the mileage data. The character annotations can be used to mark information in the three-dimensional scene, and the actions in the construction simulation process can be prompted. The attribute data record the model name, ID, spatial position, spatial pose, zoom, and other information. (2) Data organization and optimization. The three-dimensional scene data are multisource and multi-format data in large data sets, and the data need to be organized and optimized to improve the efficiency of data browsing and access. The DEM and DOM are organized in a tiled way and managed in layers. The three-dimensional model can be optimized by setting a maximum visible distance, a minimum visible distance, levels of detail (LOD), and other parameters. The three-dimensional models are organized and related in the scene based on semantic information which is extended and defined based on the international framework for dictionaries (IFD) standard issued by the buildingSMART organization. Semantic information is described, stored, and exchanged through metadata. Considering the decomposition of the three-dimensional model of a construction site, the body model is managed as a parent node, and each component model is managed as a child node in a three-dimensional scene. (3) Virtual geographic environment generation. The multimodal spatio-temporal data are unified to the same spatio-temporal reference, and the railway three-dimensional scene is generated. The three-dimensional model is loaded into the scene in the form of three-dimensional point symbols. ISPRS Int. J. Geo-Inf. 2020, 9, 292 6 of 18 ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 6 of 19

Figure 4. Railway virtual geographic environment generation. Figure 4. Railway virtual geographic environment generation.

2.3.2.3. Construction Construction Process Process Simulation Simulation Based Based On on Model Model Component Component Timing Timing Display Display HighHigh-speed-speed railway railway construction construction technologies technologies and methods are and complicated. methods Three are-dimensional complicated. modelsThree-dimensional are disassembled models into small are disassembled parts, and the into processes small parts,used to and display the processesand hide small used parts to display are controlledand hide according small parts to different are controlled time points, according durations to different, and other time time points, information, durations, thus and simulating other time theinformation, construction thus process, simulating that is, the a construction construction process, process that simulation is, a construction based on process the time simulation series display based on of thethe timemodel series parts. display of the model parts.

2.3.1.2.3.1. Construction Construction process Process decomposition Decomposition In In the the construction construction process process simulation, simulation, the the ove overallrall construction construction process process is issplit split from from top top to to bottom,bottom, and and decomposed decomposed into into several several sub subprocesses;processes; then,then, eacheach subprocesssubprocess is is further further divided divided until until each eachdetailed detail actioned action is split. is split. In this In context, this context, the entire the processentire ofprocess bridge of construction bridge construction can be decomposed can be decomposedinto four parts: into four construction parts: construction preparation, preparation, lower structure lower construction, structure construction, beam structure beam construction, structure constructionand accessory, and structure accessory construction, structure construction, as shown in as Figure shown5. Eachin Figure part can5. Each be further part can divided be further into a dividednumber into of constructiona number of workconstruction steps, and work each steps, work and step each ultimately work step corresponds ultimately to acorresponds frame image to in a the framethree-dimensional image in the three scene.-dimensional For example, scene. the constructionFor example, preparation the construction stage preparation can be further stage divided can be into furtherground divided levelling, into pileground positioning, levelling machinery, pile position arrangement,ing, machinery and otherarrangement, tasks. and other tasks.

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Figure 5. Construction process decomposition.

FigureFigure 5. Construction5. Construction process process decomposition. decomposition. 2.3.2. Construction process simulation 2.3.2. Construction Process Simulation 2.3.2.Each Construction construction process process simulation is stored with a playlist. Because playlists can be nested, subprocesses Each construction process is stored with a playlist. Because playlists can be nested, subprocesses can can alsoEach be construction stored in playlists.process is Timestored information, with a playlist. viewpoint Because playlists information, can be browsing nested, subprocesses actions, and also be stored in playlists. Time information, viewpoint information, browsing actions, and model modelcan also states be are stored stored in playlists.in the sub Time-playlist information,s. The time viewpoint information information, is the most browsing important actions information, and states are stored in the sub-playlists. The time information is the most important information because becausemodel s ittates influences are stored the in duration the sub -ofplaylist a certains. The action time at information a certain point is the in most time. important Potential informationactions could it inﬂuences the duration of a certain action at a certain point in time. Potential actions could include includebecause moving it influences the viewpoint, the duration display of a certaining and action hiding at a certainparts of point the inmodel time.. PotentialThe information actions could in the moving the viewpoint, displaying and hiding parts of the model. The information in the playlist playlistinclude ismoving sequentially the viewpoint, processed display accordinging and to hiding the time par ts information, of the model and. The the information subprocess ines the are is sequentially processed according to the time information, and the subprocesses are implemented. implemented.playlist is sequentially When all sublistsprocessed have according been addressed to the time, the information,overall process and simulation the subprocess is formed,es are as Whenshownimplemented. all in sublistsFigure W 6. havehen all been sublists addressed, have been the overall addressed process, thesimulation overall process is formed, simulation as shown is formed, in Figure as 6. shown in Figure 6.

Figure 6. Construction process simulation. Figure 6. Construction process simulation. Figure 6. Construction process simulation. 2.4. Construction Method Simulation Based on Mechanical Joint Linkage 2.4. Construction Method Simulation Based On Mechanical Joint Linkage 2.4. MostConstruction construction Method methodsSimulation require Based On special Mechanical construction Joint Linkage machinery. The animated simulation Most construction methods require special construction machinery. The animated simulation of of constructionMost construction machinery methods is an require advanced special expression construction of virtualmachinery. construction, The animated and simulation the complete of construction process machinery can is be an simulated advanced directly expression to identify of virtual construction construction, diﬃculties and andthe priorities. complete constructionconstruction process machinery can isbe an simulated advanced directly expression to identify of virtual construction construction, difficulties and the and complete priorities. Mechanicalconstruction simulations process can of be construction simulated directly processes to identify involve construction complex mechanical difficulties joint and control priorities. and Mechanical simulations of construction processes involve complex mechanical joint control and linkageMechanical strategies, simulation the transfers of construction relationships processes among types involve of machinery, complex mechanical materials, and joint the control surrounding and linkage strategies, the transfer relationships among types of machinery, materials, and the environment,linkage strategies and the, the spatial transfer relationships relationships among among construction types of machinery. machinery A, jointmaterials, linkage and involves the surrounding environment, and the spatial relationships among construction machinery. A joint twosurrounding or more independent environment, jointsand the that spatial are simultaneously relationships among active inconstruction diﬀerent planes machinery to co-complete. A joint linkage involves two or more independent joints that are simultaneously active in different planes to anlinkage action. involves Through two or the more relative independent positioning joints ofthat model are simultaneous componentsly active (associated in different with planes a parent), to co-complete an action. Through the relative positioning of model components (associated with a afterco-complete multilevel an action.coordinate Through conversion, the relative the positioningposition and of attitude model components parameters (associated of the component with a parent), after multilevel coordinate conversion, the position and attitude parameters of the modelparent), in the after three-dimensional multilevel coordinate scene can conversion, be obtained, the and position component and attitudepositioning parameters and assembly of the can component model in the three-dimensional scene can be obtained, and component positioning and becomponent achieved. model Since thein the joints three are-dimens adjacentional to scene each other,can be when obtained, creating and acomponent joint animation, positioning the relative and assembly can be achieved. Since the joints are adjacent to each other, when creating a joint animation, relationshipassembly can between be achieved. the component Since the joints and the are parent adjacent may to be each considered other, when only creating with respect a joint to animation, the method ofthethe relative relative relative positioning. relationship relationship The betweenbetween following the component steps are used andand in thethe construction parent parent may may simulations be be considered considered based only only on with joint with re linkages. respectspect toto the the method method of of relative relative positioning.positioning. The followingfollowing stepssteps are are used used in in construction construction simulation simulations baseds based onon joint joint linkage linkagess..

2.4.12.4.1 Extraction Extraction of of mmechanicalechanical joint activity parameterparameterss

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2.4.1.ISPRS Extraction Int. J. Geo-Inf. of Mechanical2020, 3, x FOR JointPEER REVIEW Activity Parameters 8 of 19

AlthoughAlthough construction construction machinery machinery works works in in a avariety variety of of ways, ways, the the movement movement ofof eacheach jointjoint is is fixed.fixed. According According to to the the operation operation action actionss of ofconstruction construction machinery, machinery, the thecorresponding corresponding model model can be candecomposed be decomposed according according to the tojoints, the joints,and the and action the of action each joint of each is determined joint is determined to provide to a foundation provide a foundationfor the extraction for the of extraction mechanical of wo mechanicalrk parameters. work The parameters. joint splitting The of joint the splittingcrane model of the considering crane modeljoint considering activities yields joint activitiesthe bottom yields of the the crane bottom (no of action), the crane crane (no turnplate action), crane (yaw), turnplate first arm (yaw), (pitch), firstsecondary arm (pitch), arm secondary (z-direction arm translation), (z-direction translation),third arm (z third-direction arm (z-direction translation), translation), hoist cable hoist (z-direction cable (z-directionstretching stretching and pitch), and and pitch), oil andcylinder oil cylinder (pitch). (pitch). The bottom The bottom of the ofcrane the cranemoves moves with withthe crane the crane,, so it is so itfree is of free internal of internal parameters. parameters. The crane The turnplate crane turnplate mainly mainlyrotates rotatesin the horizontal in the horizontal direction direction around the aroundbottom the of bottom the crane of the and crane therefore and therefore has a translational has a translational parameter. parameter. AfterAfter the the model model joints joints are are decomposed, decomposed, the the level level of eachof each joint, joint, namely, namely, the the mutual mutual adhesion adhesion relationrelation associated associated with with two two joints, joints needs, needs to to be be determined determined accordingaccording toto the linkage linkage relation relationss in in the themodel. model. Since Since the the other other joints joints are are used used as as a final a final reference reference at atthe the bottom bottom of the of the crane, crane, the thebottom bottom of the of thecrane crane is a isprimary a primary joint. joint. The crane The craneturnplate turnplate is attached is attached to the tobottom the bottom of the crane of the and crane is a and secondary is a secondaryjoint. The joint. primary The primary arm and arm the and lifting the oil lifting cylinder oil cylinder are both are attached both attached to the tocrane the craneturnplate turnplate and are andtertiary are tertiary joints. joints. The secondary The secondary arm and arm the and oil the cylinder oil cylinder are four are fourth-levelth-level joints joints that thatare attached are attached below belowthe primary the primary arm. arm. The third The thirdarm is arm a fifth is a-level fifth-level joint that joint is thatattached is attached to the secondary to the secondary arm. The arm. hoist Thecable hoist is cable a six isth a- sixth-levellevel joint jointthat is that attached is attached to the to thethird third arm. arm. The The disassembly disassembly of ofthe the model model joint joints,s, the theaction action of of each each joint, joint, and and the the linkage linkagess among among joints joints are are shown shown in in F Figureigure 77..

third arm: five-level hoist cable: six-level joint parent: secondary arm parent: third arm action: z direction action: z direction stretch translation (DZ2) (ScaleZ), pitch (DPitch4) 0 secondary arm: four- level joint oil cylinder: four-level joint parent: primary arm parent: primary arm action: z direction action: pitch (DPitch3) translation (DZ1)

primary arm: three- lifting oil cylinder: three- level joint level joint parent: crane turnplate parent: crane turnplate action: pitch (DPitch1) action: pitch (DPitch2)

crane turnplate: secondary joint parent: crane truck bottom action: yaw (DYaw)

bottom of crane： first joint (no parameters)

Figure 7. Linkage relationships among crane joints. Figure 7. Linkage relationships among crane joints. The simulation mathematical model for the working state of a crane is as follows:

The simulation mathematical model for the working state of a crane is as follows: i M(R, L, S, H) = [R , L( ), S( ), H( ) (2) (dYaw) dPitch1, dPitch2, dPitch3, dPitch4 dZ1,dZ2... , dZn dZScale,dZ M(R, L,S,H）=[R(dYaw), L(dPitch1, dPitch2, dPitch3, dPitch4), S(dZ ,dZ … , dZ ), H(dZScale,dZ)] (2) R(dYaw) = dYaw 1 2 n (3)

푅(푑푌푎푤) = 푑푌푎푤 (3) 푠𝑖푛(푑푃𝑖푡푐ℎ1) ∗ 퐿 푑푃𝑖푡푐ℎ2 = 푎푟푐푡푎푛( ) 푐표푠(푑푃𝑖푡푐ℎ1) ∗ 퐿 − 퐿퐴퐵 퐿(푑푃𝑖푡푐ℎ1,푑푃𝑖푡푐ℎ2,푑푃𝑖푡푐ℎ3,푑푃𝑖푡푐ℎ4) = { 푑푃𝑖푡푐ℎ3 = 푑푃𝑖푡푐ℎ2 − 180 (4) 푑푃𝑖푡푐ℎ4 = −푑푃𝑖푡푐ℎ1

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푛

푆(푑푍1,푑푍2…,푑푍푛) = 퐿 + ∑ 푑푍푛 (5) ISPRS Int. J. Geo-Inf. 2020, 9, 292 1 9 of 18 퐿퐶 = 퐿푂퐶 ∗ 푑푍푆푐푎푙푒 퐻(푑푍푆푐푎푙푒,푑푍) = {  푑푍 = −퐿퐶 (6)  sin(dPitch1) L  dPitch2 = arctan ×  cos(dPitch1) L LAB L =  × − (4) (dPitch1, dPitch2, dPitch3, dPitch4)  dPitch3 = dPitch2 180 푅  푑푌푎푤− where (푑푌푎푤) is the lifting rotation state dPitch function4 = ; dPitch1 is a rotary yaw angle; 퐿(푑푃𝑖푡푐ℎ1,푑푃𝑖푡푐ℎ2,푑푃𝑖푡푐ℎ3,푑푃𝑖푡푐ℎ4) is the lifting state function of −the lifting arm; 푑푃𝑖푡푐ℎ1 is the pitch n angle of the lifting arm; 푑푃𝑖푡푐ℎ2 is the pitch angle ofX the oil cylinder body; 푑푃𝑖푡푐ℎ3 is the pitch S( ) = L + dZn (5) 푑푃𝑖푡푐dZ1,ℎdZ42 ..., dZn 퐿 angle of the lifting oil cylinder; is the pitch angle1 of the hoist cable; is the length of the first arm; 퐿퐴퐵 is the length between the first( arm and lifting arm; LC = LOC dZScale 푆(푑푍1,푑푍2…,푑푍푛) is the stretchingH state= function of the× arm; 푑푍푛 is the z-direction offset distance(6) (dZScale,dZ) dZ = L of the nth section of the arm; − C where 퐻(푑푍푆푐푎푙푒R(dYaw,푑푍) ) isis the the stretch lifting state rotation function state of the function; hoist cable;dYaw 푑푍푆푐푎푙푒is is a the rotary z-direction yaw stretching angle; L(dPitchratio1, dPitchof the2, dPitchhoist3, dPitchcable4;) is푑푍 the is liftingthe z-direction state function offset of distance the lifting of arm;the hoistdPitch cable1 is the; 퐿푂퐶 pitch is the angle original of thelength lifting arm;of thedPitch hoist2 cable;is the and pitch 퐿 angle퐶 is the of thestretching oil cylinder length body; of thedPitch hoist3 iscable. the pitch angle of the lifting oil cylinder; dPitch4 is the pitch angle of the hoist cable; L is the length of the first arm; LAB is the length between2.4.2. User the first-oriented arm and animation lifting arm; control parameters S is the stretching state function of the arm; dZ is the z-direction offset distance of (dZIn1, dZorder2..., dZ ton) control the mechanical motion, the followingn four animation control parameters are theabstracted nth section and of thethen arm; can be modified interactively as shown in Figure 8: A1, the rotation angle of the craneH(dZScale turnplate,dZ) is, the which stretch influences state function the plane of the rotation hoist cable; parameterdZScale DYawis the of z-direction the crane stretchingturnplate; ratio of the hoistA2, cable;the liftingdZ is angle the z-direction of the crane offset arm distance, which of influences the hoist cable;the pitchLOC angleis the of original the primary length ofarm, the the hoistlifting cable; oil and cylinder,LC is the the stretching oil cylinder length and the of the hoist hoist cable; cable. L1, the stretching length of the lifting arm, which influences the stretching lengths of the 2.4.2. User-Oriented Animation Control Parameters secondary arm DZ1 and the third arm DZ2; In orderL2, the to stretching control the length mechanical of the motion,lifting hook the following, which influences four animation the vertical control-direction parameters stretching are abstractedparameter and ScaleZ. then can be modified interactively as shown in Figure8: A1, the rotation angle of the crane turnplate, which influences the plane rotation parameter DYaw of the crane turnplate;

Stretching length of the lifting Stretching length of the arm: L1 lifting hook: L2 Correlation parameters: DZ1 and Correlation parameters: DZ2 ScaleZ

The lifting angle of the crane arm: A2 Correlation parameters: DPitch1, Rotation angle of the crane DPitch2 turnplate: A1 DPitch3, DPitch4 Correlation parameters: DYaw

Figure 8. Animation control parameter extraction oriented to the user. Figure 8. Animation control parameter extraction oriented to the user. A2, the lifting angle of the crane arm, which inﬂuences the pitch angle of the primary arm, 2.4.3. Mapping of animation control parameters to joint activity parameters the lifting oil cylinder, the oil cylinder and the hoist cable; L1,Animation the stretching control length parameters of the lifting are arm, oriented which to inﬂuences the user for the the stretching control of lengths virtual of construction, the secondary and armthe DZ1 joint and activity the third parameters arm DZ2; are used in the construction simulation to calculate the position and

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L2, the stretching length of the lifting hook, which inﬂuences the vertical-direction stretching parameter ScaleZ.

2.4.3. Mapping of Animation Control Parameters to Joint Activity Parameters Animation control parameters are oriented to the user for the control of virtual construction, and the joint activity parameters are used in the construction simulation to calculate the position and attitude of each joint. Thus, there is a need to establish mapping relationships for the animation controlISPRS parametersInt. J. Geo-Inf. 2020 to the, 3, x joint FOR activityPEER REVIEW parameters. The repositioning and assembly of the component10 of 19 model are performed in real time according to the joint parameters so that any control of mechanical animationmodel are based performed on the packagingin real time parameters according canto the be joint achieved, parameters as shown so that in Figure any control9. of mechanical animation based on the packaging parameters can be achieved, as shown in Figure 9.

Crane Body Position DPitch3 DZ2 Position

crane Turnplate DPitch1 DPitch4 DYaw Azimuth A1 Dpitch2 DZ1 ScaleZ Crane Arm Lifting Angle A2 Parameters driven joint activity parameters Crane Arm Stretch Length L1 Other fixed parameters(DX, DY, Lifting Hook DZ, DYaw, DPitch, DRoll) Stretching Length L2

Animation Control

Figure 9. Mapping of animation control parameters to joint activity parameters. Figure 9. Mapping of animation control parameters to joint activity parameters. 2.4.4. Attachment for Hoisting 2.4.4. Attachment for Hoisting After the joint actions of the construction machinery are simulated, it is necessary to simulate the action whenAfter thethe construction joint actions machinery of the construction lifts an object. machinery The object are issimulated, hoisted based it is onnecessary the movement to simulate of thethe machinery; action when for example, the construction the object rotates machinery with the lifts rotation an object. of the The arm. object As a result,is hoisted the hoisted based object on the needsmovement to be attached of the machinery to the construction; for example, machinery. the object When rotate analysings with the the rotation joint linkage of the arm relationships. As a result, ofthe crane,hoisted the object hoist needs cable tois a be sixth-level attached joint. to the When construction the crane machinery. is lifting, theWhen object analysing being hoisted the joint needslinkage to be relationship attached tos the of hoistthe crane, cable the and hoist becomes cable a is seventh-level a sixth-level joint. joint. Figure When 10 the illustrates crane is thelifting, joint the linkageobject relationships being hoisted after needs the to object be attac tohed be hoisted to the hoist is attached cable and to the becomes crane. a In seven the ﬁgure,th-level the joint. dashed Figure lines10 representillustrates the the transfer joint linkage of linkage relationships relationships, after i.e.,the theobject child to jointsbe hoisted will move is attached with the to movementthe crane. In ofthe parentfigure, joints,the dashed with the lines movements representmainly the transfer including of linkage rolling, relationships, rotation, translation, i.e., the andchild stretching. joints will move with the movement of the parent joints, with the movements mainly including rolling, rotation, translation, and stretching.

ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 11 of 19 ISPRS Int. J. Geo-Inf. 2020, 9, 292 11 of 18 ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 11 of 19 Bottom of Bottom of Primary Joint Crane Crane Bottom of Bottom of Primary Joint Crane Crane

Secondary Joint Crane Turnplate Crane Turnplate

Lifting Oil Lifting Oil Three-level Joints Primary Arm Primary Arm Cylinder Cylinder Lifting Oil Lifting Oil Three-level Joints Primary Arm Primary Arm Cylinder Cylinder

Four-level Joints Secondary Arm Oil Cylinder Secondary Arm Oil Cylinder

Five-level Joints Third Arm Yaw Third Arm Five-level Joints Third Arm Yaw Third Arm Pitch Six-level Joints Hoist Cable Hoist Cable Pitch Six-level Joints Hoist Cable Translation Hoist Cable Translation Seven-level Joints Scale Lift Object

Seven-level Joints Scale Lift Object Figure 10. Linkage relationships after crane attachment for lifting.

FigureFigure 10. 10.Linkage Linkage relationships relationship afters after crane crane attachment attachment for for lifting. lifting. 2.4.5. Work Animation Parameter Storage 2.4.5. Work animation parameter storage To save the work animation of construction machinery in a three-dimensional scene, an external 2.4.5. WorkTo save animation the work parameter animation softorage construction machinery in a three-dimensional scene, an external parameter script file is used. The parameter script file records the parameter information for the parameter script file is used. The parameter script file records the parameter information for the constructionTo save the machinery work animation in a key of operationconstruction step, machinery including in thea three yaw,-dimensional pitch, scale, scene, length, an duration,external construction machinery in a key operation step, including the yaw, pitch, scale, length, duration, parameternumber, etc., script and file linear is used.interpolation The parameter is performed script on file the records motion between the parameter the two information moments to for achieve the number, etc., and linear interpolation is performed on the motion between the two moments to constructiona smooth transition machinery between in a key actions operation and obtain step, anincluding animation. the Theyaw, yaw pitch, refers scale, to thelength, azimuth duration, angle achieve a smooth transition between actions and obtain an animation. The yaw refers to the azimuth number,of the crane etc., turntable,and linear pitch interpolation refers to the is armperformed lifting angle,on the scale motion refers between to the arm the two stretching moments length, to angle of the crane turntable, pitch refers to the arm lifting angle, scale refers to the arm stretching achievelength refersa smooth to the transition hoist cable between length, actions duration and refers obtain to the an timeanimation required. The for yaw the transition refers to the between azimuth two length, length refers to the hoist cable length, duration refers to the time required for the transition angleactions of orthe points crane in turntabl time, ande, pitch number refers is the to IDthe of arm the lifting hoisted angle, object. scale Figure refers 11 illustrates to the arm an stretching animation between two actions or points in time, and number is the ID of the hoisted object. Figure 11 illustrates length,parameter length script refers file, to wherein the hoist each cable row length, of data correspondsduration refers to a to key the frame time inrequired a three-dimensional for the transition scene. an animation parameter script file, wherein each row of data corresponds to a key frame in a three- betweenA user can two perform actions aor variety points of in construction time, and number operation is the animation ID of the simulations hoisted object. by editing Figure the11 illustrates parameter dimensional scene. A user can perform a variety of construction operation animation simulations by anscripts animation or real-time parameter control script parameters. file, wherein Based each row on theof data principle corresponds of parameter-driven to a key frame mechanicalin a three- editing the parameter scripts or real-time control parameters. Based on the principle of parameter- dimensionalanimation and scene the. A related user can computing perform a tools, variety the of animation construction script operation of a continuous animation operation simulation cans by be driven mechanical animation and the related computing tools, the animation script of a continuous editingedited bythe recording parameter the scrip statets parametersor real-time of control the machinery. parameters. Then, Based the complex on the principle animation of can parameter be edited- operation can be edited by recording the state parameters of the machinery. Then, the complex drivenand played mechanical for diff animationerent states and through the related the smooth computing transition tools, of the parameters. animation script of a continuous animation can be edited and played for different states through the smooth transition of parameters. operation can be edited by recording the state parameters of the machinery. Then, the complex animation can be edited and played for different states through the smooth transition of parameters.

FigureFigure 11. 11.Parameter Parameter ﬁle file generation generation for for work work animation. animation.

Figure 11. Parameter file generation for work animation.

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3. Experimental analysis 3. Experimental Analysis 3.1. Test Area Description 3.1. Test Area Description The construction of a high pier and the steep slope of a bridge on a high-speed railway line in ShanxiThe Province, construction China are of asimulated high pier based and theon a steep VGE slope. The bridge of a bridge adopts on a a(60+100+ high-speed 60) m railway continuous linein beamShanxi that Province, spans a main China river are simulated channel, and based a hanging on a VGE. basket The bridge cantilever adopts casting a (60 +method100 + 60) is adopted m continuous for construction.beam that spans The 19th a main pier river is located channel, on and a (60+100+60) a hanging basketm continuous cantilever beam casting brake method pier that is adopted spans a for river,construction. and the foundation The 19th pier is on is limestone located on rock a (60 of+ pressure100 + 60) on m a continuous dug foundati beamon. The brake base pier thickness that spans is a 7.5river, m, and and the the pier foundation has a round is on- limestoneend hollow rock-type of structure. pressure on The a dugheight foundation. of the pier The is 61.5 base m. thickness Due to is the7.5 large m, and span the pier of has continuous a round-end beams, hollow-type a well- structure.digging foundation The height of is the adopted pier is; 61.5 therefore, m. Due tothe the requirementlarge spans of for continuous linear control beams, and a well-diggingconstruction foundationimbalance are is adopted; very high. therefore, In addition, the requirements the 19th pier for is linearclose controlto the river and constructionside, the foundation imbalance top are is very higher high. than In addition,the design theed 19th water pier level is close of 8.2 to them, the river surroundingside, the foundation environment top is has higher a high than and the steep designed slope more water than level 40 of m 8.2 above m, the the surrounding top of the foundati environmenton, andhas the a high slope and is steep close slope to 45 more degrees. than The40 m construction above the top site of the is too foundation, narrow, and and the the slope construction is close to environment45 degrees. Theis so construction complicated site that is the too construction narrow, and the process construction has to be environment fully simulated is so complicatedbeforehand thatin a dynamicthe construction three-dimensional process has scene. to be fully simulated beforehand in a dynamic three-dimensional scene. BridgeBridge construction construction site site environment environment modelling modelling is is based based on on the the fusion of multisource data,data, suchsuch as assatellite satellite images, images, oblique oblique photography, photography and, and laser laser radar radar data. data According. According to to the the construction construction method method and andthe the construction construction performance performance requirements, requirements, the splitting the splitting and modelling and modelling schemes forschemes the engineering for the engineeringbody and relatedbody and auxiliary related auxiliary objects are objects determined. are determined. After all After kinds all of kinds objects of objects are modelled, are modelled models, modelsare positioned are positioned and integratedand integrated according according to the to relativethe relative spatial spatial relations relation ofs variousof various objects objects in in the theconstruction construction process. process. There There are a twore two methods methods for modelfor model positioning: positioning: absolute absolute positioning positioning and relative and relativepositioning. positioning. The absolute The positioning absolute positioning method is used method for calculating is used forthe placement calculating coordinates the placement and the coordinatesattitude of and the modelthe attitude in the of scene the model coordinate in the system scene coordinate and directly system positioning and directly the model. position Theing relative the model.positioning The relative method positioning is based on method another is model based that on another has completed model thethat absolute has completed positioning the absolute process as positioningthe parent, process the position as the o ﬀparent,set and the the position attitude offset oﬀset and of the the model attitude relative offset to of the the parent model are relative calculated; to thein parent this case, are the calculated positioning; in model this case, is converted the positioni throughng these model relative is converted relationships. through Figure the se12 illustratesrelative relationshipa three-dimensionals. Figure 12 scene illustrates of a construction a three-dimensional site. scene of a construction site.

FigureFigure 12. 12. ThreeThree-dimensional-dimensional scene scene of ofa construction a construction site site..

AccordingAccording to tothe the mathematical mathematical model model of ofthe the mechanical mechanical joint joint linkage linkage relationship relationships,s, a parameter a parameter controlcontrol panel panel for for crane crane operation operation animation animation is developeddeveloped basedbased on on a a three-dimensional three-dimensional platform platform so so that thatthe the work work state state of the of construction the construction machinery machinery is facilitated is facilitated by interactive by interactive operations and operation simulationss and in simulationa three-dimensionals in a three- scene,dimen assional shown scene, in Figure as shown 13. The in F userigure can 13. ﬂexibly The user modify can flexibly the animation modify control the animation control parameters through the panel, and based on the mapping relations between the

ISPRS Int. J. Geo-Inf. 2020, 9, 292 13 of 18

ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 13 of 19 parameters through the panel, and based on the mapping relations between the animation control animationparameters control and parameters the joint activityand the parameters, joint activity the parameters, assembly relationsthe assembly among relation the componentss among the of the componentcrane cans of be the determined crane can be in determined real time;therefore, in real time; the therefore, dynamic the operation dynamic of operation the crane of is the driven crane by the is drivenvarious by parameters.the various parameters. In addition, In the addition, control the panel control may panel also recordmay also data record for criticaldata for steps critical in crane stepsoperation, in crane operation, and these dataand these can be data used can to b generatee used to key generate frames. key Moreover, frames. Moreover, a mechanical a mechanical work animation workparameter animation ﬁle parameter can be createdfile can be by created exporting by exporting the parameters the parameters and data and for data all keyfor all steps. key steps. When the Whenparameter the parameter ﬁle is readfile is again, read theagain, motion the motion parameters parameters between between the key the operation key operation steps are steps interpolated are interpolatedso that a so continuous that a continuous operation operation animation animation of the construction of the construction machinery machinery can be can obtained. be obtained.

FigureFigure 13. Crane 13. Crane parameter parameter control control interface interface..

3.2. Construction Simulation

3.2. Construction3.2.1. Tower Simulation Crane Operation Simulation and Layout Scheme It is necessary to troubleshoot the relevant safety hazards during tower crane layout and operation 3.2.1.in Tower advance crane because operation the simulation example constructionand layout scheme site is steep and narrow. Therefore, the dynamic spatialIt is necessary relationships to troubleshoot involving the the tower relevant crane, safety the surrounding hazards during environment, tower crane and other layout construction and operationmachinery in advance must be because simulated the and example analysed. construction To determine site whether is steep tower and narrow. crane operations Therefore, at the diff erent dynamicheights spatial will colliderelationship withs the involving terrain, the the tower tower crane crane, modelthe surrounding is decomposed environment into a plurality, and other of tower constructioncrane assemblies machinery and must reassembled be simulated through and model analyse decompositiond. To determine and assembly, whether as shown tower in crane Figure 14. operationBefores at the different operation heights range will of thecollide tower with crane the terrain, is simulated, the tower an attachmentcrane model relation is decomposed between into the front a pluralityand rear of cantilevertower crane arms assemblies of the tower and cranereassembled needs to through be established model decomposition to ensure a suffi andcient assembly, spatial linkage as shownrelationship in Figure between 14. Before the cantilever the operation arms, range and theof the operation tower crane range is of simulated, the tower cranean attachment is analysed by relationrotating between the cantilever. the front and rear cantilever arms of the tower crane needs to be established to ensure a Figuresufficien 15t spatialillustrates linkage several relationship aspects between of tower the crane cantilever routing. arms, Scheme and the 1 showsoperation the range scheme of of theinitializing tower crane the is tower analyse craned by withrotating four the segments. cantilever. Since the working range of the tower crane does not meet the self-hoisting requirement, a subsequent section cannot be hoisted from the stool bridge. Scheme 2 shows the scheme of initializing the tower crane with five segments. Because the tower crane is raised, the chance of collision with steep slopes is reduced, and the working range of the tower crane meets the relevant requirements. However, in this case, the working range of the crane is close to the limit, and the installation process cannot be completed by the crane. Finally, Scheme 3 adopts a four-segment initial tower crane and the side slope of the tower crane is excavated so that the working range requirement of the tower crane and space requirement for the crane and the hoist can be met.

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ISPRS Int. J. Geo-Inf. 2020, 9, 292 14 of 18 ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 14 of 19

(a) (b)

Figure 14. Section view of the tower crane: (a) four segments; (b) five segments.

Figure 15 illustrates several aspects of tower crane routing. Scheme 1 shows the scheme of initializing the tower crane with four segments. Since the working range of the tower crane does not meet the self-hoisting requirement, a subsequent section cannot be hoisted from the stool bridge. Scheme 2 shows the scheme of initializing the tower crane with five segments. Because the tower crane is raised, the chance of collision with steep slopes is reduced, and the working range of the tower crane meets the relevant requirements. However, in this case, the working range of the crane is close to the limit, and the installation process cannot be completed by the crane. Finally, Scheme 3 adopts a four -segment initial (a) tower crane and the side slope of the tower(b) crane is excavated so that the working range requirement of the tower crane and space requirement for the crane and the hoist can be met. FigureFigure 14.14. Section view of the tower crane:crane: ((a)a) four segments; ((b)b) five ﬁve segments.

Figure 15 illustrates several aspects of tower crane routing. Scheme 1 shows the scheme of initializing the tower crane with four segments. Since the working range of the tower crane does not meet the self-hoisting requirement, a subsequent section cannot be hoisted from the stool bridge. Scheme 2 shows the scheme of initializing the tower crane with five segments. Because the tower crane is raised, the chance of collision with steep slopes is reduced, and the working range of the tower crane meets the relevant requirements. However, in this case, the working range of the crane is close to the limit, and the installation process cannot be completed by the crane. Finally, Scheme 3 adopts a four-segment initial tower crane and the side slope of the tower crane is excavated so that the working range requirement of the tower crane and space requirement for the crane and the hoist can be met.

FigureFigure 15.15. Comparison of towertower crane layoutlayout schemes.schemes

3.2.2. D Dynamicynamic crane Crane operation Operation simulation Simulation and and tower Tower crane Crane layout Layout simulation Simulation Crane operation simulations involve complex mechanical joint control and linkage linkages,s, as well as mechanical and and material material transfer transfer relationships. relationships. By By controlling controlling the the azimuth azimuth angle angle of the of theturntable, turntable, the thelifting lifting angle angle of the of thearm, arm, the the stretching stretching length length of ofthe the arm, arm, the the lifting lifting length length of of the the hoisting hoisting cable cable and and other factors, the ﬂexible operation of the construction machinery can be achieved. By attaching an object to the hoisting cable, a linkage between the object and the hoisting cable is achieved, and the construction machinery operation process can be ﬂexibly simulated. After the tower crane initialization scheme is determined, the installation process needs to be simulated in a three-dimensional scene for further troubleshooting. Figure 15. Comparison of tower crane layout schemes After the tower crane initialization scheme is determined, the installation process needs to be simulated in a three-dimensional scene to further assess the operation potential. Figure 16 illustrates 3.2.2. Dynamic crane operation simulation and tower crane layout simulation the process of installing the tower crane of the 19th pier using a crane during construction. Through the Crane operation simulations involve complex mechanical joint control and linkages, as well as mechanical and material transfer relationships. By controlling the azimuth angle of the turntable, the lifting angle of the arm, the stretching length of the arm, the lifting length of the hoisting cable and

ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 15 of 19

other factors, the flexible operation of the construction machinery can be achieved. By attaching an object to the hoisting cable, a linkage between the object and the hoisting cable is achieved, and the construction machinery operation process can be flexibly simulated. After the tower crane initialization scheme is determined, the installation process needs to be simulated in a three- dimensional scene for further troubleshooting. ISPRSAfter Int. J. Geo-Inf.the tower2020, 9crane, 292 initialization scheme is determined, the installation process needs15 to of be 18 simulated in a three-dimensional scene to further assess the operation potential. Figure 16 illustrates the process of installing the tower crane of the 19th pier using a crane during construction. Through processthe process of rotating of rotating the the crane crane base, base, stretching stretching the the arm, arm, hoisting hoisting the the hoisting hoisting cablecable andand other steps steps,, section assemblyassembly and large-cantileverlarge-cantilever splicingsplicing areare completedcompleted forfor thethe towertower crane.crane.

Figure 16. CContinuousontinuous a animationnimation of crane operation.operation. 3.2.3. Storage and Replaying of Construction Method Simulations 3.2.3. Storage and replaying of construction method simulations In a VGE, the user can control the crane operation in real time by adjusting parameters via the In a VGE, the user can control the crane operation in real time by adjusting parameters via the crane parameter control panel. When a scheme is reported and researched, the operation process is crane parameter control panel. When a scheme is reported and researched, the operation process is often not required to be controlled in real time, and the designed construction method needs to be often not required to be controlled in real time, and the designed construction method needs to be reproduced. Therefore, it is necessary to study the storage and reproduction methods of construction reproduced. Therefore, it is necessary to study the storage and reproduction methods of construction simulation processes. simulation processes. The user records the state parameters of each key operation step through the crane parameter The user records the state parameters of each key operation step through the crane parameter control panel, and the parameters are saved as an external parameter file for operation animation control panel, and the parameters are saved as an external parameter file for operation animation so so that the crane operation process is stored. Different parameters can be flexibly set with the crane that the crane operation process is stored. Different parameters can be flexibly set with the crane parameter control panel, and different parameter files can be generated. In addition, externally stored parameter control panel, and different parameter files can be generated. In addition, externally stored parameter files can also be manually modified. These different parameter files can be re-imported into parameter files can also be manually modified. These different parameter files can be re-imported the three-dimensional scene and analysed, and different construction processes can be reproduced in into the three-dimensional scene and analysed, and different construction processes can be the form of animations. Finally, the construction simulation process can be stored in the form of an reproduced in the form of animations. Finally, the construction simulation process can be stored in external parameter file. Figure 17 illustrates the storage and reproduction processes of a construction ISPRSthe form Int. J. of Geo an-Inf. external 2020, 3, x parameter FOR PEER REVIEW file. Figure 17 illustrates the storage and reproduction processes16 of 19of method simulation. a construction method simulation.

Figure 17. Figure 17. StorageStorage and and reproduction reproduction of construction method simulation simulation..

3.2.4. Simulation of the integral construction process for a bridge Construction process simulation cans be expressed in three-dimensional geographic environments by using an engineering body model, engineering auxiliary model and construction machinery, and construction animations can be generated through a small number of key frames. After the engineering body model and the engineering auxiliary model are decomposed and reassembled, a time period for displaying or hiding each component is set, and the display or hidden state of the model is added to the key frame. In these key frames, the position and attitude of the viewpoint can also be recorded to better observe the construction process. Moreover, actions such as flight and roaming can also be inserted between the key frames so that the construction conditions associated with different positions can be browsed. Finally, the key frames are played in sequence over time, and the key frame animation performance of the process is assessed. Figure 18 illustrates a bridge construction process in a three-dimensional scene that includes construction service roads, trestle construction, foundation pit filling, the construction platform layout, bridge pier construction, bridge beam construction, and closure. The construction service roads, the trestle and the foundation pit are simulated in engineering auxiliary models; the platform, the bridge pier, and the bridge beams are simulated in engineering body models; and all models and components are loaded into the three-dimensional scene in the form of graph layers. Construction process simulations provide a basis for construction machinery modelling and feasibility assessments of construction methods.

Figure 18. Construction process simulation.

ISPRS Int. J. Geo-Inf. 2020, 3, x FOR PEER REVIEW 16 of 19

ISPRS Int. J. Geo-Inf. 2020Figure, 9, 292 17. Storage and reproduction of construction method simulation. 16 of 18

3.2.4. Simulation of the integral construction process for a bridge 3.2.4. Simulation of the Integral Construction Process for a Bridge Construction process simulation cans be expressed in three-dimensional geographic Construction process simulation cans be expressed in three-dimensional geographic environments environments by using an engineering body model, engineering auxiliary model and construction by using an engineering body model, engineering auxiliary model and construction machinery, machinery, and construction animations can be generated through a small number of key frames. and construction animations can be generated through a small number of key frames. After the After the engineering body model and the engineering auxiliary model are decomposed and engineering body model and the engineering auxiliary model are decomposed and reassembled, a time reassembled, a time period for displaying or hiding each component is set, and the display or hidden period for displaying or hiding each component is set, and the display or hidden state of the model is state of the model is added to the key frame. In these key frames, the position and attitude of the added to the key frame. In these key frames, the position and attitude of the viewpoint can also be viewpoint can also be recorded to better observe the construction process. Moreover, actions such as recorded to better observe the construction process. Moreover, actions such as ﬂight and roaming can flight and roaming can also be inserted between the key frames so that the construction conditions also be inserted between the key frames so that the construction conditions associated with diﬀerent associated with different positions can be browsed. Finally, the key frames are played in sequence positions can be browsed. Finally, the key frames are played in sequence over time, and the key frame over time, and the key frame animation performance of the process is assessed. animation performance of the process is assessed. Figure 18 illustrates a bridge construction process in a three-dimensional scene that includes Figure 18 illustrates a bridge construction process in a three-dimensional scene that includes construction service roads, trestle construction, foundation pit filling, the construction platform construction service roads, trestle construction, foundation pit filling, the construction platform layout, layout, bridge pier construction, bridge beam construction, and closure. The construction service bridge pier construction, bridge beam construction, and closure. The construction service roads, the trestle roads, the trestle and the foundation pit are simulated in engineering auxiliary models; the platform, and the foundation pit are simulated in engineering auxiliary models; the platform, the bridge pier, the bridge pier, and the bridge beams are simulated in engineering body models; and all models and and the bridge beams are simulated in engineering body models; and all models and components are components are loaded into the three-dimensional scene in the form of graph layers. Construction loaded into the three-dimensional scene in the form of graph layers. Construction process simulations process simulations provide a basis for construction machinery modelling and feasibility assessments provide a basis for construction machinery modelling and feasibility assessments of construction methods. of construction methods.

Figure 18. Construction process simulation. Figure 18. Construction process simulation. 4. Conclusions

This paper introduces a dynamic 3D simulation method for complex high-speed railway engineering construction based on VGEs, and the following conclusions are summarized:

(1) Multiscale representation of railway environments and dynamic 3D simulations of construction process are achieved, and they greatly improve the overall and local precise control of project management. (2) The operation mode of construction machinery is converted into mechanical movement parameters for machinery, and further abstracted into user-oriented animation control parameters, which can optimize the dynamic operation process of complex construction machinery. (3) Dynamic 3D simulations of complex multi-specialty construction processes in a wide geographic area are generated in VGEs and provide an eﬀective method of optimizing construction plan designs, scientiﬁc management, hidden trouble investigations, accident rescue, etc. and also lays a foundation for the construction of digital twin railways. ISPRS Int. J. Geo-Inf. 2020, 9, 292 17 of 18

Next, we will focus on expanding the construction machinery library, and develop a variety of mechanical operation and control methods to achieve multi-mechanical collaborative construction simulation.

Author Contributions: All of the authors contributed to the research concepts and participated in discussing and writing the manuscript. Qing Zhu, Xinwen Ning and Junxiao Zhang conceived and designed the case study. Xinwen Ning performed the experiments and wrote the paper. Changjin Wang, Zujie Han, Heng Zhang and Wen Zhao revised the paper. Zujie Han, Xinwen Ning, Wen Zhao and Heng Zhang prepared and tested the datasets. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the National Natural Science Foundation of China (Grant No. 41941019), National Natural Science Foundation of China (Grant No. 2016YFC0803105). Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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