Highway guardrail model lightweight method and device based on cesium

Abstract

A highway guardrail model lightweight method and device based on Cesium belong to the technical field of highway modeling. A guardrail BIM model is established based on the three-dimensional reference polyline, and a stand column BIM model is established based on the three-dimensional reference polyline feature point; a guardrail stand column primitive model is established for the guardrail BIM model and the stand column BIM model, a guardrail stand column lightweight model package is established based on the guardrail stand column primitive model; a guardrail dynamic modeling module is established based on Cesium; the guardrail stand column lightweight model package and the guardrail dynamic modeling module are called to construct a highway guardrail lightweight BIM+GIS application scene, and the guardrail stand column and the guardrail are subjected to lightweight processing. The method can reduce the processing data amount of the guardrail model, save network requests and memory consumption, improve the modeling system performance, reduce the processing time and improve the operation efficiency, and realizes model lightweight.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of highway modeling, and particularly relates to a highway guardrail model lightweight method and device based on Cesium. BACKGROUND

[0002] GIS technology lays the foundation for the digital development of traffic construction, and BIM technology brings rich construction information and accurate geometric information in the design, construction and operation stages of traffic infrastructure, so a virtual traffic model attached with a large amount of traffic information can be created based on BIM+GIS technology, and the BIM+GIS platform is the basis of intelligent traffic.

[0003] The original BIM model contains rich design attribute data and geometric data, and the data volume is huge, so lightweight processing is required before entering the GIS platform to support the smooth operation of various business systems and mobile terminals. Highway guardrails are different from road and bridge main BIM models, and the guardrails have the characteristics of long mileage, fine internal structure, single geometric shape and a large number of repetitions. The mainstream GIS products process the road and bridge main body and safety guardrail BIM models in the same way, that is, the BIM model is first converted into a Mesh surface, and then a 3dtiles (3D tile) service is published to realize BIM lightweight. Due to the huge volume of the guardrail model, the processing time of this conventional method for processing the guardrail BIM model is relatively long, which seriously affects the performance of the BIM+GIS platform and reduces the usability of the BIM model.

[0004] Taking a highway with a scale of 100 kilometers as an example, if only the left and right main lines are estimated, the highway guardrail line type volume reaches 400 kilometers. The guardrail unit length is calculated as 2m, each guardrail unit contains a railing and a column, and the Mesh triangular net of each guardrail unit is 50. Therefore, the number of Mesh triangular nets of the 100-kilometer highway guardrail is 400x1000÷2x50=10,000,000, which is far more than the road and bridge BIM data volume. The number of Mesh triangular nets of the conventional 100-kilometer highway and bridge BIM model is 30~80 million. When the conventional GIS platform processes and applies the highway BIM object, the network request and memory consumption increase significantly due to the huge volume of the guardrail BIM data, which reduces the system performance. Highway guardrail BIM model lightweight becomes a key technical problem that needs to be solved in BIM+GIS application. SUMMARY

[0005] In view of the above problems, the application provides a highway guardrail model lightweight method and device based on Cesium. The method can reduce the processing data volume of the guardrail model, reduce the processing time, and improve the performance of the modeling system.

[0006] The embodiment of the application provides a highway guardrail model lightweight method based on Cesium, which comprises the following steps:

[0007] Extracting a three-dimensional reference polyline and feature points of a highway guardrail, establishing a guardrail BIM model based on the three-dimensional reference polyline, and establishing a stand column BIM model based on the three-dimensional reference polyline feature points;

[0008] Establishing a guardrail stand column primitive model for the guardrail BIM model and the stand column BIM model, and establishing a guardrail stand column lightweight model package based on the guardrail stand column primitive model;

[0009] Converting the type of the three-dimensional reference polyline to obtain a GeoJSON file, and establishing a guardrail dynamic modeling module based on Cesium;

[0010] Calling the guardrail stand column lightweight model package and the guardrail dynamic modeling module, constructing a highway guardrail lightweight BIM+GIS application scene, and performing lightweight processing on the guardrail stand column and the guardrail;

[0011] The guardrail stand column primitive model is established for the guardrail BIM model and the stand column BIM model, and the guardrail stand column lightweight model package is established based on the guardrail stand column primitive model, which comprises the following steps:

[0012] Establishing a guardrail stand column primitive model, moving the guardrail stand column primitive model to the origin and converting the guardrail stand column primitive model into a gltf format file;

[0013] Importing a shp file basic primitive application instance model to generate a guardrail stand column lightweight model 3dtiles package through slicing;

[0014] The three-dimensional reference polyline is converted to obtain a GeoJSON file, and the guardrail dynamic modeling module is established based on Cesium, which comprises the following steps:

[0015] Splitting KML files of the three-dimensional reference polyline into single-line data, sharing the multi-line attributes of the KML files of the three-dimensional reference polyline with the split KML single-line, and exporting a GeoJSON file;

[0016] Constructing the spatial relationship between the rail profile control point coordinates and the reference line, and constraining the rail modeling position and direction;

[0017] The rail guide line is established through the guardrail reference line node offset, and the rail modeling position is constrained;

[0018] The offset reference line node coordinates and the guardrail profile feature point two-dimensional coordinate array are transmitted into a PolylineVolumeGeometry interface to generate a highway guardrail geometric object.

[0019] Further, the three-dimensional reference polyline and feature point of the highway guardrail are extracted, and a guardrail BIM model is established based on the three-dimensional reference polyline, including:

[0020] The three-dimensional reference polyline of the highway guardrail is extracted, and the guardrail BIM model is generated by regularly arraying or stretching the three-dimensional reference polyline of the guardrail along the three-dimensional reference polyline;

[0021] The positioning angle of the highway column in the guardrail BIM model is extracted, and the column BIM model is generated by arraying the column primitive according to the positioning angle;

[0022] The three-dimensional guide polyline feature points are extracted based on the three-dimensional reference polyline, and the three-dimensional guide polyline feature points are converted into shp format.

[0023] Further, the guardrail reference line node offset is used to establish a guide line for the guardrail, and the modeling position of the guardrail is constrained, including:

[0024] The reference line node is converted from the longitude and latitude high coordinates to the Cartesian3 coordinates in the Cartesian coordinate system;

[0025] The Cartesian3 coordinates of each node are converted into the geographic coordinates Cartographic based on the WGS84 ellipsoid, the height height of each node from the surface of the ellipsoid is obtained, the Cartesian3 coordinates of each node are updated and scaled and projected onto the ellipsoid surface;

[0026] The vector calculation is initialized, the remaining nodes are traversed, and the node forward direction is judged, and the inflection point offset processing is performed on the nodes with changed node direction.

[0027] Further, the inflection point offset processing is performed on the nodes with changed node direction, including:

[0028] When the node direction changes, the inflection point is added to increase the point density;

[0029] The cornerDirection vector is unitized, the reciprocal of the area enclosed by the cornerDirection vector and the backward is taken as the scaling ratio scalar, it is judged whether the projection angle of the forward and the backward on the ellipsoid tangent plane at the current position position is greater than or equal to π, and the deviation of the left vector is determined;

[0030] When the projection angle of the forward and the backward on the ellipsoid tangent plane at the current position position is greater than π, the left vector is determined to be outwardly deviated;

[0031] Determine the left vector inside when the projection angle of forward and backward on the tangent plane of the ellipsoid at the current position position is equal to π;

[0032] Calculate the coordinate start of the current position after offset according to the scaling scalar and the left offset.

[0033] Further, by offsetting the guardrail reference line node, a guide line for the guardrail is established to constrain the modeling position of the guardrail, and further comprising:

[0034] Calculate the reference frame change and offset;

[0035] Centered on the current input node position, construct a 4x4 transformation matrix transform from the east-north-up reference frame to the WGS84 ellipsoid;

[0036] Apply the unit vector negativeX in the negative x direction to the transform matrix, and convert the transform matrix to the west unit vector west in the world coordinate system by the multiplyByPointAsVector method;

[0037] Calculate the projection vectors Cartesian2 of the west and left vectors at the current position position tangent to the ellipsoid, and calculate the angle angle between the two projection vectors according to the positive and negative of the cross product of the west and left vectors;

[0038] By the multiplyByPoint method, based on the angle, the original height height of the current position point, and the horizontal and vertical offset distance coordinates calculated by the initialization vector, the scaled point is converted to the world coordinate system, and the coordinate array of the current position point after offset is returned.

[0039] Further, the three-dimensional reference polyline is type-converted to obtain a GeoJSON file, and a guardrail dynamic modeling module is established based on Cesium, and further comprising:

[0040] Use Cesium to pass the offset reference line node coordinates and the two-dimensional coordinate array of the guardrail profile feature points into the PolylineVolumeGeometry interface to generate a highway guardrail geometry object;

[0041] Call the highway guardrail geometry object, input the guardrail profile coordinates and the reference line, and establish a guardrail model.

[0042] Further, call the guardrail post lightweight model package and the guardrail dynamic modeling module to build a highway guardrail lightweight BIM+GIS application scene, and perform lightweight processing on the guardrail post and the guardrail, including:

[0043] The guardrail post lightweight model of the guardrail post instantiation model package is rendered by the Cesium API, so as to realize the post GPU instantiation rendering modeling;

[0044] The guardrail model is dynamically rendered by calling the inflection point offset guardrail dynamic modeling module in the BIM+GIS application platform, so as to realize the guardrail lightweight;

[0045] The model visible range is determined by the scene camera view frustum, the 3D Tiles clipping plane parameters are dynamically configured, and the model dynamic clipping and loading are realized.

[0046] Based on the same inventive concept, another aspect of the embodiments of the application further provides a Cesium-based highway guardrail model lightweight device, comprising:

[0047] The modeling unit is configured to extract a three-dimensional reference polyline and feature points of a highway guardrail, establish a guardrail BIM model based on the three-dimensional reference polyline, and establish a post BIM model based on the three-dimensional reference polyline feature points;

[0048] The model package unit is configured to establish a guardrail post primitive model for the guardrail BIM model and the post BIM model, and establish a guardrail post lightweight model package based on the guardrail post primitive model;

[0049] The guardrail post lightweight model package is established based on the guardrail post primitive model for the guardrail BIM model and the post BIM model, comprising:

[0050] The guardrail post primitive model is established, the guardrail post primitive model is moved to the origin and converted into a gltf format file;

[0051] The shp file basic primitive application instance model is imported to generate a guardrail post lightweight model 3dtiles package through slicing;

[0052] The dynamic modeling unit is configured to convert the three-dimensional reference polyline into a GeoJSON file and establish a guardrail dynamic modeling module based on Cesium;

[0053] The three-dimensional reference polyline is converted into a GeoJSON file, and a guardrail dynamic modeling module is established based on Cesium, comprising:

[0054] The KML file of the three-dimensional reference polyline is split into single-line type multi-line data, the split KML single line shares the multi-line properties of the KML file of the three-dimensional reference polyline, and a GeoJSON file is exported;

[0055] The spatial relationship between the railing profile control point coordinates and the reference line is constructed to constrain the railing modeling position and direction.

[0056] The railing guide line is established by offsetting the guardrail reference line node to constrain the railing modeling position.

[0057] The offset reference line node coordinates and the guardrail profile feature point two-dimensional coordinate array are transmitted into the PolylineVolumeGeometry interface to generate the highway guardrail geometric object.

[0058] The lightweight unit is used to call the guardrail post lightweight model package and the railing dynamic modeling module to construct the highway guardrail lightweight BIM+GIS application scene and perform lightweight processing on the guardrail post and the railing.

[0059] The beneficial effects of the present application are as follows: based on the above technical solution, the present application extracts the three-dimensional reference multi-segment line and the feature point of the highway guardrail, establishes the guardrail BIM model and the post BIM model based on the three-dimensional reference multi-segment line feature point, establishes the guardrail post graph model and then establishes the guardrail post lightweight model package for the guardrail BIM model and the post BIM model, performs lightweight processing on the BIM model data through the guardrail post lightweight model package, wherein the reference line in the model is identified and the coordinate direction is screened. The railing dynamic modeling module is established based on Cesium, the guardrail post lightweight model package and the railing dynamic modeling module are called, the highway guardrail lightweight BIM+GIS application scene is constructed, and the guardrail post and the railing are lightweight processed. Therefore, the processing data amount of the guardrail model can be reduced, the network request and the memory consumption can be saved, the modeling system performance can be improved, the processing time can be reduced, the running efficiency can be improved, and the model lightweight is realized.

[0060] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the structures indicated in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without any creative labor.

[0062] Figure 1 A flow chart of a highway guardrail model lightweight method based on Cesium is shown;

[0063] Figure 2 Fig. 1 shows a schematic diagram of the relationship between the highway guardrail structure and components of the present application and the reference line;

[0064] Figure 3 Fig. 2 shows a schematic diagram of the relationship between the highway guardrail structure and components of the present application and the reference line;

[0065] Figure 4 Fig. 3 shows a schematic diagram of the post model structure of the present application;

[0066] Figure 5 Fig. 4 shows a schematic diagram of the guardrail model structure of the present application;

[0067] Figure 6 Fig. 5 shows a schematic diagram of the guardrail profile and control point relationship of the present application;

[0068] Figure 7 Fig. 6 shows a schematic diagram of the scene of the highway guardrail model of the present application;

[0069] Figure 8 Fig. 7 shows a schematic diagram of a Cesium-based highway guardrail model lightweight system of the present application.

[0070] In the figure: 1 - guardrail, 2 - guardrail post, 3 - guardrail reference line, 4 - guardrail guide line. DETAILED DESCRIPTION

[0071] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0072] It should be noted that the terms "first", "second", etc. in the present application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so as to implement the embodiments of the present application described herein. In the present application, the terms "up", "down", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings.

[0073] The embodiments of the present application provide a Cesium-based highway guardrail model lightweight method, as shown in Figure 1 , comprising:

[0074] S101: Extract the three-dimensional reference polyline and feature points of the highway guardrail, establish a guardrail BIM model based on the three-dimensional reference polyline, and establish a column BIM model based on the three-dimensional reference polyline feature points;

[0075] S102: Establish a guardrail column primitive model for the guardrail BIM model and the column BIM model, and establish a guardrail column lightweight model package based on the guardrail column primitive model;

[0076] S103: Type conversion is performed on the three-dimensional reference polyline to obtain a GeoJSON file, and a railing dynamic modeling module is established based on Cesium;

[0077] S104: Call the guardrail column lightweight model package and the railing dynamic modeling module to construct a highway guardrail lightweight BIM+GIS application scenario, and perform lightweight processing on the guardrail column and the railing.

[0078] It should be noted that the Cesium-based highway guardrail model lightweight method in the embodiments of the present specification is generally applied in a server, which can be a cloud server and a local server. The server can be an electronic device such as a notebook computer, a desktop computer, a tablet computer, and an all-in-one machine.

[0079] Specifically, the extraction of the three-dimensional reference polyline and the feature points of the highway guardrail, and the establishment of the guardrail BIM model based on the three-dimensional reference polyline include:

[0080] Extracting the three-dimensional reference polyline of the highway guardrail, and generating a guardrail BIM model by regularly arraying or stretching the three-dimensional reference polyline of the guardrail along the three-dimensional reference polyline;

[0081] Extracting the positioning angle of the highway column in the guardrail BIM model, and generating a column BIM model by arraying column primitives according to the positioning angle;

[0082] Extracting three-dimensional guide polyline feature points based on the three-dimensional reference polyline, and converting the three-dimensional guide polyline feature points into shp format.

[0083] Specifically, referring to Figure 2 and Figure 3 , step S1: Extract the highway guardrail reference line and feature points using BIM software to guide the modeling of the guardrail.

[0084] It includes S1.1: Extracting the guardrail reference line to guide the modeling of the column and the railing.

[0085] As shown in Figure 2 and Figure 3 , the BIM software is applied to extract the three-dimensional reference polyline of the highway guardrail and convert it into KML format.

[0086] It should be noted that the Bentley BIM software establishes the guardrail BIM model by applying a three-dimensional reference polyline, that is, the guardrail BIM model is generated in a regular array or stretched guardrail primitive along the three-dimensional reference polyline, the column model is generated from the column primitive array according to its positioning angle attribute, and the guardrail rail model is generated by stretching the primitive section, and the reference line data can be converted into a three-dimensional linear kml format based on the WGS84 coordinate reference according to the coordinate setting.

[0087] S1.2: Extract the reference line feature point coordinates, and guide the guardrail column instantiation rendering.

[0088] The GIS software extracts the three-dimensional guide polyline feature points according to 2 meters or other standard guardrail lengths, and exports them in shp file format.

[0089] It should be noted that the three-dimensional guide polyline is imported into the GIS software, the longitude and latitude coordinates and rotation angle attributes of the feature points are extracted through the specified length extraction point function, and are exported in shp file format, and the optional operation: the corresponding attributes of design, construction and operation and maintenance can be added by adding attribute fields to the specified points, which can enrich the application scenarios.

[0090] In some specific embodiments, the guardrail column primitive model is established for the guardrail BIM model and the column BIM model, and the guardrail column lightweight model package is established based on the guardrail column primitive model, including:

[0091] The guardrail column primitive model is established, the guardrail column primitive model is moved to the origin and converted into a gltf format file;

[0092] The shp file basic primitive application instance model is imported to generate the guardrail column lightweight model 3dtiles package.

[0093] Specifically, S2: the GIS software is used to construct the guardrail column lightweight model package, and the guardrail column lightweight is realized.

[0094] S2.1: Establish a three-dimensional column model, and construct a column instantiation rendering basic primitive.

[0095] As shown in Figure 4 , the BIM software is applied to establish the guardrail column primitive gltf format file.

[0096] Specifically, the BIM software establishes the guardrail column primitive model, and moves it to the origin, and converts it into a gltf format file through the BIM software.

[0097] S2.2: Configure the guardrail column instantiation model package, and construct the LOD rendering rule.

[0098] AsFigure 5 As shown, the Cesiumlab software is applied to import the shp file basic primitive, the instance model slicing function is applied and the parameters are set, the guardrail post lightweight model 3dtiles package is generated, and the format is i3dm.

[0099] It should be noted that the 3dtiles data is mainly in b3dm and i3dm formats, and the lightweight model data is transmitted through an Internet streaming service transmission model. Among them, b3dm is based on slicing rules to directly convert model Mesh into small model slices, generate a series of spatial position index files and small model files, and when rendering, the corresponding position model slice file is obtained from the server according to the viewport position, and is rendered independently. Only by limiting the memory usage can the model loading performance be controlled, and loading fine models in a small scene can easily cause lag; i3dm is an instantiation model based on the rendering characteristics of GPU. In the GPU card, only the Mesh data amount of one model primitive is occupied, and the model rendering batch copy is realized based on the position, rotation angle, scale and other parameters of other instances, instead of independent rendering of each object. Compared with the b3dm format, for specific large quantities of the same models such as guardrail posts and manhole covers, the GPU pressure can be significantly reduced, thereby improving the performance of the modeling system.

[0100] S2.2.1: Configure the LOD model package. Modify the meta.json file in the LOD model template folder. The model LOD is divided into 11 levels in total, the first level is set to 2 pixels, and the second to eleventh levels are set to gltf files in the meta.json file directory.

[0101] S2.2.2: Generate instance model package. Apply cesiumlab software for instance slicing, input file selection S1.2 shp file, LOD model selection S2.2.1 LOD model package, angle setting shp file angle attribute field, scale setting 1:1, elevation setting shp file Z elevation attribute field, after setting, generate guardrail post 3dtiles data package.

[0102] In some specific embodiments, the type conversion of the three-dimensional reference polyline obtains a GeoJSON file, and a guardrail dynamic modeling module is established based on Cesium, including:

[0103] The KML file of the three-dimensional reference polyline is split into single-line type multi-line data, the split KML single line shares the multi-line attributes of the KML file of the three-dimensional reference polyline, and a GeoJSON file is exported.

[0104] The method further comprises:

[0105] The spatial relationship between the guardrail profile control point coordinates and the reference line is constructed to constrain the position and direction of the guardrail modeling.

[0106] wherein a rail guide line is established by guardrail reference line node offset, to constrain the rail modeling position;

[0107] The reference line node is converted from the latitude-longitude-height coordinate into a Cartesian3 coordinate in the Cartesian coordinate system;

[0108] The Cartesian3 coordinate of each node is converted into a Cartographic geographic coordinate based on the WGS84 ellipsoid, the height of each node from the surface of the ellipsoid is obtained, the Cartesian3 coordinate of each node is updated and scaled to project onto the ellipsoid surface;

[0109] Initialize vector calculation, iterate through the remaining nodes and determine the node forward direction, and perform inflection point offset processing for the nodes with changed node direction.

[0110] When the node direction changes, add an inflection point to increase the point density;

[0111] Unitize the cornerDirection vector, and determine whether the projection angle of forward and backward on the ellipsoid tangent plane at the current position position is greater than or equal to π according to the reciprocal of the area enclosed by the cornerDirection vector and backward as the scaling ratio scalar, to determine the bias of the left vector;

[0112] When the projection angle of forward and backward on the ellipsoid tangent plane at the current position position is greater than π, it is determined that the left vector is outwardly biased;

[0113] When the projection angle of forward and backward on the ellipsoid tangent plane at the current position position is equal to π, it is determined that the left vector is inwardly biased;

[0114] According to the scaling ratio scalar and the left offset, the coordinate start after the offset of the current position is calculated.

[0115] Calculate the reference frame change and offset;

[0116] With the current input node position as the center, a 4x4 transformation matrix transform from the east-north-up reference frame to the WGS84 ellipsoid is constructed;

[0117] Apply the unit vector negativeX in the negative x direction to the transform matrix, and convert the transform matrix into the west unit vector west in the world coordinate system by the multiplyByPointAsVector method;

[0118] Calculate the projection vectors Cartesian2 of the west and left vectors at the current position position, and the angle angle between the two projection vectors according to the positive and negative of the cross product value of the west and left vectors;

[0119] Through the multiplyByPoint method, based on the angle, the original height height of the current position point, and the horizontal and vertical offset distance coordinates calculated by the initialization vector, the scaled point is converted to the world coordinate system, and the coordinate array of the offset current position point is returned.

[0120] The offset reference line node coordinates and the two-dimensional coordinate array of the guardrail profile feature points are input into the PolylineVolumeGeometry interface to generate a highway guardrail geometric object.

[0121] The highway guardrail geometric object is called to input the rail profile coordinates and the reference line to establish a rail model.

[0122] Specifically, S3: develop a Cesium-based rail dynamic modeling module to achieve lightweight guardrail modeling.

[0123] S3.1: Convert the reference line to a single line to provide guardrail modeling direction and coordinate data.

[0124] Apply GIS software to convert the KML three-dimensional reference multi-segment line to a line segment type and export it as a GeoJSON file.

[0125] It should be noted that guardrail reconstruction requires calculation of reference line forward direction, inflection point and offset direction, and requires continuous and uninterrupted line segments. The reference line file may contain multi-line data composed of multiple single lines, which may cause reconstruction to be interrupted. To ensure that each data represents only one continuous reference line, the calculation of the reference line is a basic data acquisition method in this modeling and is not described in detail in this application.

[0126] Import the KML file obtained in S1.1 into GIS software, split the multi-line data into single-line type, and the split single line shares the original multi-line attribute, and export it as a GeoJSON file.

[0127] S3.2: Build the spatial relationship between the rail profile control point coordinates and the reference line to constrain the rail modeling position and direction.

[0128] As shown in Figure 6 , the guardrail section control point coordinates are extracted, and the stand column origin, i.e., the offset relationship between the reference line and the feature point envelope rectangle bottom midpoint, is determined.

[0129] It should be noted that the guardrail profile polygon is imported into the CAD software, and under the premise of keeping the shape of the guardrail profile unchanged, the number of profile connection feature points is reduced as much as possible to reduce the calculation complexity of the guardrail model reconstruction in the Cesium platform, and the two-dimensional coordinates of each feature point in the tangent plane projection are obtained and exported. Since the guardrail reference line is extracted based on the bottom origin of the column, not the actual layout position of the guardrail, in order to ensure the reconstruction accuracy of the guardrail in space, the reference line path nodes need to be offset adjusted, and the horizontal and vertical offset amounts between the bottom midpoint of the feature point envelope rectangle and the column origin are calculated to determine the final offset value [x, y] of each node.

[0130] S3.3: Establishing a guardrail guide line by offsetting the guardrail reference line nodes to constrain the modeling position of the guardrail.

[0131] As shown in Figure 3 , by applying Cesium geometric objects, coordinate conversion, etc. API, through the vector operation, projection conversion, coordinate conversion and matrix transformation interfaces provided by Cesium, the overall offset of the guardrail reference line is realized.

[0132] Taking one piece of data in the GeoJSON file generated in S3.1 as an example, the node offset processing flow is described in detail.

[0133] S3.3.1: Coordinate conversion.

[0134] Convert the reference line nodes from longitude, latitude, and height coordinates (longitude, latitude, height) to Cartesian3 coordinates (x, y, z) in the Cartesian coordinate system.

[0135] S3.3.2: Fit the ellipsoid surface.

[0136] Convert the Cartesian3 coordinates of each node to geographic coordinates (Cartographic) based on the WGS84 ellipsoid, and obtain the height of each node from the ellipsoid surface.

[0137] Update the Cartesian3 coordinates of each node to scale and project them onto the ellipsoid surface.

[0138] S3.3.3: Initialize vector calculation.

[0139] Let the first node be the current position position and the second node be the next position nextPosition.

[0140] Compute the forward direction unit vector forward (from position to nextPosition), the backward vector (the opposite direction of forward), the unit normal to the tangent plane of the WGS84 ellipsoid at the current position surfaceNormal, and the left vector (the cross product of forward and surfaceNormal).

[0141] Record the current node height h0 and the next node height h1, copy position to previousPosition, and update position to nextPosition.

[0142] S3.3.4: Traverse the remaining nodes.

[0143] From the second node to the second last node, execute steps S3.3.5 to S3.3.9.

[0144] S3.3.5: Determine the forward direction.

[0145] Update nextPosition to the next node of the current node.

[0146] If position and nextPosition coordinates are the same, skip the current node and re-execute step S3.3.5 from the next node.

[0147] Recalculate the forward and surfaceNormal vectors, and compute the corner direction unit vector cornerDirection (the sum of forward and backward vectors).

[0148] Compute the unit projection vectors of forward and backward vectors on the tangent plane normal (surfaceNormal), and determine whether it is a corner.

[0149] If the absolute value of the dot product of the two vectors is not 1, it indicates that the node direction changes, and a corner needs to be added, execute step S3.3.6; otherwise, it indicates that the node advances along a straight line, execute step S3.3.8.

[0150] S3.3.6: Handle corner offset.

[0151] When the node direction changes, in order to ensure the natural transition of the guardrail, a corner needs to be added to increase the point density.

[0152] Unitize the cornerDirection vector, and determine whether the angle between the projections of forward and backward on the tangent plane at the current position position on the ellipsoid is greater than or equal to π, according to the reciprocal of the area enclosed by cornerDirection and backward as a scaling factor scalar, to determine whether the left vector is outward or inward.

[0153] When the angle between the projections of forward and backward on the tangent plane at the current position position on the ellipsoid is greater than π, determine that the left vector is outward;

[0154] When the angle between the projections of forward and backward on the tangent plane at the current position position on the ellipsoid is equal to π, determine that the left vector is inward;

[0155] According to the scaling factor scalar and the left offset, calculate the coordinates of the current position after the offset start.

[0156] S3.3.7: Update the back-to-head vector.

[0157] Take previousPosition and its corresponding height h0, current offset position start and the corresponding height h1 of the current position as input data, and execute the steps of S3.3.8 in turn, and update the left and backward vectors after the calculation is completed.

[0158] Use the new left and scaling factor scalar to update the calculation of the back-to-head position offset coordinates previousPosition.

[0159] S3.3.8: Calculate the reference frame transformation and offset.

[0160] Centered on the current input node position, construct a 4x4 transformation matrix transform from the East-North-Up (ENU) reference frame to the WGS84 ellipsoid.

[0161] Apply the negative x direction unit vector negativeX (-1, 0, 0) to the transform matrix, and convert it to the west unit vector west in the world coordinate system by the multiplyByPointAsVector method.

[0162] Calculate the projection vectors Cartesian2 of west and left vectors on the tangent plane at the current position position, and the angle angle between the two projection vectors according to the positive and negative of the cross product of west and left vectors.

[0163] Using the multiplyByPoint method, convert the scaled point to the world coordinate system based on the angle, the original height of the current position point, and the horizontal and vertical offset distance coordinates (x, 0, y) obtained in S3.3.3, and return the coordinate array of the current position point after offset.

[0164] If called by S3.3.7, S3.3.10, do not perform the update of copying the current position coordinates to the previous position.

[0165] S3.3.9: Update node position.

[0166] Update the position to the nextPosition coordinates, and also update the height h0 and h1 backward by one bit.

[0167] If the current node index is less than the second last node, return to S3.3.5 for further processing.

[0168] S3.3.10: Output node offset result.

[0169] After repeating the steps of S3.3.8 for the last node position and the corresponding height h1, output the Cartesian3 coordinate array of all the offset processed guardrail reference line nodes.

[0170] S3.4: Apply Cesium modeling API to build the fence model.

[0171] Pass the offset reference line node coordinates and the two-dimensional coordinate array of the fence profile feature points into the PolylineVolumeGeometry interface to generate the highway guardrail geometry object.

[0172] S3.4.1: Call the modeling API and input the fence profile coordinates and reference line to build the fence model.

[0173] Use the PolylineVolumeGeometry interface to create the guardrail geometry object, pass the reference line offset nodes (Cartesian3 coordinate array) obtained in S3.3 into the polylinePositions attribute to define the center path of the geometry object; adjust the two-dimensional projection coordinates of the fence profile feature points extracted in S3.2, translate the envelope rectangle center point to (0, 0), and pass the adjusted coordinate array into the shapePositions attribute as the fence profile shape description.

[0174] S3.4.2: Configure corner transition parameters to ensure natural transition.

[0175] The default Rounded round corner style is selected by the cornerType property to ensure that the guardrail naturally transitions at the corner.

[0176] S3.5: Optimize the guardrail modeling process to improve modeling performance. Apply the Cesium geometry instance API to define geometry objects and combine the view frustum visibility to asynchronously and dynamically add the guardrail reconstruction.

[0177] The camera's view range is rendered, and the out-of-range is not rendered.

[0178] It should be noted that the Primitive primitive API is the key to guardrail reconstruction. By configuring the material and display condition attribute values through the GeometryInstance instance, the rendering effect can be optimized. Directly loading 100-kilometer baseline data for guardrail reconstruction will consume a large amount of CPU resources, causing the map rendering to lag. To improve performance, use the camera frustum to dynamically calculate the required guardrail, and set the asynchronous attribute to implement asynchronous reconstruction in the background. By processing data in batches and asynchronously, multiple Webworker processes are enabled for parallel computing, which can improve the speed of guardrail reconstruction calculation and the smoothness of display. At the same time, modular functions are used to encapsulate the reconstruction process, which can improve efficiency and flexibility, and facilitate reuse in different scenarios.

[0179] S3.5.1: Configure the viewport camera distance parameter to dynamically control the guardrail rendering quality and reduce GPU overhead.

[0180] Specifically, use the GeometryInstance API provided by Cesium to create and pass the guardrail geometry object generated in S3.4 into the geometry attribute; in the attributes, set the color and transparency of the guardrail through the color attribute to achieve custom material effects; use the distanceDisplayCondition attribute to control the visibility range of the guardrail to ensure that the instance is only rendered within the specified distance to reduce GPU rendering overhead.

[0181] S3.5.2: Configure the camera frustum parameters to dynamically control the guardrail rendering range and further reduce GPU overhead.

[0182] Specifically, calculate the boundary sphere corresponding to each baseline obtained in S3.3, obtain the current camera frustum parameters, keep the near plane, left plane, and upper and lower planes default settings, adjust the distance between the far plane and the camera to 5000 meters, and construct a custom frustum to limit the guardrail rendering reconstruction range.

[0183] Based on the computeVisibility parameter of the cullingVolume, the relationship between the bounding sphere and the view cone space is calculated: when the bounding sphere is in the intersection or contains the view cone range and is not loaded, the corresponding guardrail reference line is executed S3.5.3; when the bounding sphere is completely outside the view cone and has been loaded, the scene performs an unloading operation, removes the corresponding primitive object and releases the resource.

[0184] S3.5.3: Start multi-batch asynchronous execution, optimize guardrail modeling sequence according to viewport range and distance, and reduce memory overhead.

[0185] Specifically, the geometry instances obtained in the view cone range are transmitted into the Primitive primitive geometry instance collection in batches. The appearance parameter is set to determine the shader description, and the material rendering mode of the geometry instance is determined. The core is to set the asynchronous attribute to true, so that Cesium will execute the guardrail reconstruction task according to the size of each instance array, so as to perform calculation in the background and avoid blocking the main thread. Optional operation: set the releaseGeometryInstances attribute to true, which will release the memory occupied by the geometry instance after loading, reducing the memory occupation.

[0186] S3.6: Encapsulate the guardrail modeling module parameters to improve ease of use.

[0187] The guardrail offset distance, reference line data, maximum visible distance range of the guardrail, and two-dimensional coordinates of the feature points are taken as input parameters, and the PrimitiveCollection primitive data collection is taken as output data. The guardrail reconstruction function is encapsulated, which is easy to call and simplifies the data processing process.

[0188] In some specific embodiments, the guardrail post lightweight model package and the guardrail dynamic modeling module are called to build a highway guardrail lightweight BIM+GIS application scene, and the guardrail post and the guardrail are subjected to lightweight processing, including:

[0189] The guardrail post lightweight model of the guardrail post instantiation model package is rendered and configured through the Cesium API to realize the post GPU instantiation rendering modeling;

[0190] The guardrail dynamic modeling module is called in the BIM+GIS application platform to dynamically render the guardrail model, thereby realizing the lightweight of the guardrail;

[0191] The model visible range is determined through the scene camera view cone, the 3D Tiles clipping plane parameters are dynamically configured, and the model dynamic clipping and loading are realized.

[0192] Based on the same inventive concept, another aspect of the embodiment of the present application also provides a Cesium-based highway guardrail model lightweight device, referring to Figure 8 , comprising:

[0193] The modeling unit 201 is configured to extract a three-dimensional reference polyline and feature points of a highway guardrail, establish a guardrail BIM model based on the three-dimensional reference polyline, and establish a column BIM model based on the three-dimensional reference polyline feature points;

[0194] The model package unit 202 is configured to establish a guardrail column primitive model for the guardrail BIM model and the column BIM model, and establish a guardrail column lightweight model package based on the guardrail column primitive model;

[0195] Establishing a guardrail column primitive model for the guardrail BIM model and the column BIM model, and establishing a guardrail column lightweight model package based on the guardrail column primitive model, comprises:

[0196] Establishing a guardrail column primitive model, moving the guardrail column primitive model to the origin, and converting the guardrail column primitive model into a gltf format file;

[0197] Importing a shp file basic primitive application instance model to generate a guardrail column lightweight model 3dtiles package through slicing;

[0198] The dynamic modeling unit 203 is configured to perform type conversion on the three-dimensional reference polyline to obtain a GeoJSON file, and establish a guardrail dynamic modeling module based on Cesium;

[0199] Performing type conversion on the three-dimensional reference polyline to obtain a GeoJSON file, and establishing a guardrail dynamic modeling module based on Cesium, comprises:

[0200] Splitting a KML file of the three-dimensional reference polyline into single-line type multi-line data, sharing multi-line attributes of a KML file of the three-dimensional reference polyline by the split KML single line, and exporting a GeoJSON file;

[0201] Establishing a spatial relationship between a guardrail profile control point coordinate and a reference line, and constraining a guardrail modeling position and direction;

[0202] The guardrail guide line is established by offsetting a guardrail reference line node to constrain the guardrail modeling position;

[0203] The offset reference line node coordinate and the guardrail profile feature point two-dimensional coordinate array are transmitted into a PolylineVolumeGeometry interface to generate a highway guardrail geometric object;

[0204] The lightweight unit 204 is configured to call the guardrail post lightweight model package and the guardrail dynamic modeling module, construct a highway guardrail lightweight BIM+GIS application scene, and perform lightweight processing on the guardrail post and the guardrail.

[0205] The effect verification achieved by the highway guardrail model lightweight method in the present application is described in detail below.

[0206] For example, referring to Figure 7 , 10 complex highway BIM+GIS scenes are rendered, including roadbed and pavement, bridges, and highway guardrail BIM models. In the scenes, the conventional method of full-volume b3dm slicing and the method of the present application are used to load the guardrail through guardrail post GPU instantiation rendering and guardrail GIS dynamic modeling. The rendering indicators of the two loading methods are compared and tested comprehensively, including the number of requests, resource occupation, request completion time, GPU existing occupation, and rendering frame rate.

[0207] The resource consumption of the conventional method and the method of the present application in different scenes is shown in Table 1. The total size of the guardrail model loaded by the method of the present application is much smaller than that of the conventional method in all scenes, and the data resource size is reduced by more than 98%. Small data volume not only effectively reduces the bandwidth pressure of the server, but also significantly improves the transmission efficiency, especially suitable for low network bandwidth or high concurrency demand application scenarios.

[0208] Table 1

[0209]

[0210] In terms of data request completion time, the method of the present application performs better than the conventional method in all scenes.

[0211] Although in some scenes (such as scenes 1, 4, 5, and 7), the number of requests of the method of the present application is slightly higher than that of the conventional method, the data resource size of a single request is greatly reduced, which shows the advantage of granularity optimization. In other scenes (such as scenes 9 and 10), the number of requests is roughly the same, but due to its smaller resource size and shorter completion time, the increase in the number of requests is reasonable and acceptable. If the weight of the number of requests, the size of the requested resources, and the completion time in the calculation of the optimization rate is 0.05, 0.5, and 0.45, respectively, the average optimization rate of the 10 scenes is 84%.

[0212] Based on the above 10 scene perspectives, three-dimensional terrain and orthographic image data, and other related BIM models of highway engineering (pavement, bridges, tunnels, and slopes) are loaded simultaneously to evaluate the video memory occupation in real use scenarios. The specific test data of each scene is shown in Table 2. The average video memory occupation of the guardrail is reduced from 785 Mb to 147.2 Mb, and the average video memory overhead is reduced by 72%.

[0213] Table 2

[0214]

[0215] In a standard test environment, the above-mentioned 10 complex highway scenes are still selected, and the frustum culling technique is used to optimize the loading and rendering of remote 3D Tiles data, ensuring that only the necessary data within the view range is loaded, and avoiding additional burden on rendering performance from irrelevant areas. Test results show that in ordinary screens with a refresh rate of 90Hz or below, the frame rate (FPS) of the optimized web rendering can reach the maximum allowed by the device.

[0216] To further verify the optimization effect, a screen supporting a high refresh rate of 190Hz is selected for performance testing. The display frame rate is tested in the same 10 scenes, unit: FPS, and the evaluation results are shown in Table 3. The average frame rate of "ordinary slicing" is 143.1FPS, and that of "the method of the present application" is increased to 183.6FPS after optimization, an increase of 40.5FPS, and the frame rate smoothness is improved by about 28.3%.

[0217] Table 3

[0218]

[0219] The present application generates a lightweight model of the highway guardrail by combining the advantages of i3dm instantiation technology and Cesium GIS modeling API technology. Compared with the mainstream GIS product, which slices the highway guardrail as a common BIM model, the present application can significantly reduce GPU memory overhead and graphics card pressure, while reducing network requests.

[0220] In the example, a certain 100-kilometer highway is taken as an example: the guardrail model 3D Tiles data package is reduced from the original 6.5GB to 345MB under "the method of the present application", of which the column model data package is 338MB and the guardrail benchmark line GeoJSON data is 7MB. The "ordinary slicing" generates a b3dm model that takes 12 hours, while the "method of the present application" generates an i3dm column that takes only 20 minutes. The number of files increases from 786 of "ordinary slicing" to 181901 of "the method of the present application", further refining the data granularity and reusing degree.

[0221] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions described in the foregoing embodiments, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A lightweight method for highway guardrail models based on Cesium, characterized in that, include: Extract the three-dimensional reference polyline and feature points of the highway guardrail, establish a guardrail BIM model based on the three-dimensional reference polyline, and establish a column BIM model based on the feature points of the three-dimensional reference polyline. A guardrail column primitive model is established for the guardrail BIM model and the column BIM model, and a lightweight guardrail column model package is established based on the guardrail column primitive model; The three-dimensional reference polyline is converted to obtain a GeoJSON file, and a dynamic modeling module for the railing is built based on Cesium; The lightweight model package for guardrail posts and the dynamic modeling module for railings are called to construct a lightweight BIM+GIS application scenario for highway guardrails, and to perform lightweight processing on guardrail posts and railings. The process involves establishing a guardrail column primitive model based on the guardrail BIM model and the column BIM model, and then creating a lightweight guardrail column model package based on the guardrail column primitive model, including: Create a guardrail post graphic model, move the guardrail post graphic model to the origin, and convert it into a gltf format file; Import the basic primitives of the shapefile, apply the example model, slice it to generate a lightweight 3dtiles package of guardrail posts; The process of converting the three-dimensional reference polyline to obtain a GeoJSON file and establishing a dynamic railing modeling module based on Cesium includes: The KML file of the 3D reference polyline is split into single-line data. The split KML single lines share the multi-line attributes of the LML file of the 3D reference polyline and are exported as GeoJSON files. Establish the spatial relationship between the control point coordinates of the railing section and the baseline, and constrain the position and orientation of the railing model; Among them, by offsetting the guardrail baseline nodes, a guardrail guide line is established to constrain the guardrail modeling position; The offset baseline node coordinates and the two-dimensional coordinate array of guardrail profile feature points are passed to the PolylineVolumeGeometry interface to generate a highway guardrail geometry object.

2. The method according to claim 1, characterized in that, The process of extracting the three-dimensional reference polyline and feature points of the highway guardrail, and establishing a BIM model of the guardrail based on the three-dimensional reference polyline, includes: Extract the 3D reference polyline of the highway guardrail, and generate a guardrail BIM model by arraying or stretching the 3D reference polyline primitives according to rules. Extract the positioning angle of the highway posts in the guardrail BIM model, and generate a column BIM model by arraying the post elements according to the positioning angle. Based on the three-dimensional reference polyline, feature points of the three-dimensional guiding polyline are extracted, and the feature points of the three-dimensional guiding polyline are converted into shp format.

3. The method according to claim 1, characterized in that, By offsetting the baseline nodes of the guardrail, guide lines are established to constrain the modeling position of the guardrail, including: Convert the baseline nodes from latitude, longitude, and height coordinates to Cartesian 3 coordinates in the Cartesian coordinate system; Convert the Cartesian3 coordinates of each node to Cartographic coordinates based on the WGS84 ellipsoid, obtain the height of each node from the surface of the ellipsoid, update the Cartesian3 coordinates of each node and scale the projection onto the ellipsoid. Initialize the vector calculation, traverse the remaining nodes and determine the node's forward direction, and perform inflection point offset processing for nodes whose direction changes.

4. The method according to claim 3, characterized in that, The inflection point offset processing for nodes whose orientation changes includes: When the node direction changes, inflection points are added to increase the node density; Normalize the cornerDirection vector, and use the reciprocal of the area enclosed by the cornerDirection vector and the backward vector as the scaling factor (scalar). Determine whether the angle between the projections of the forward and backward vectors onto the tangent plane of the current position ellipsoid is greater than or equal to π, and thus determine the bias of the left vector. When the angle between the projections of forward and backward onto the tangent plane of the current position ellipsoid is greater than π, the left vector is determined to be externally biased. When the angle between the projections of forward and backward onto the tangent plane of the current position ellipsoid is equal to π, the inward bias of the left vector is determined. Calculate the coordinates start after the current position is offset, based on the scaling factor scalar and the left offset.

5. The method according to claim 3, characterized in that, By offsetting the baseline nodes of the guardrail, guide lines are established to constrain the modeling position of the guardrail. This also includes: Calculate the changes and shifts in the reference frame; Using the current input node position as the center, construct a 4x4 transformation matrix transform from the East-North-Upper reference frame to the WGS84 ellipsoid; Apply the negative x-direction unit vector negativeX to the transform matrix, and use the multiplyByPointAsVector method to convert the transform matrix into the western unit vector west in the world coordinate system; Calculate the projection vector Cartesian2 of the west and left vectors at the current position and the tangent plane of the ellipsoid, and calculate the sign of the angle between the two projection vectors based on the sign of the cross product of the west and left vectors. The `multiplyByPoint` method converts the scaled point to the world coordinate system based on the angle, the original height of the current position point, and the horizontal and vertical offset coordinates calculated from the initial vector, and returns an array of offset coordinates of the current position point.

6. The method according to claim 1, characterized in that, The three-dimensional reference polyline is converted to a GeoJSON file. A dynamic railing modeling module based on Cesium is established, which also includes: Using Cesium, the offset baseline node coordinates and the two-dimensional coordinate array of guardrail profile feature points are passed into the PolylineVolumeGeometry interface to generate a highway guardrail geometry object. The highway guardrail geometry object is invoked, and the guardrail section coordinates and baselines are input to establish the guardrail model.

7. The method according to claim 1, characterized in that, The lightweight model package for guardrail posts and the dynamic modeling module for railings are used to construct a lightweight BIM+GIS application scenario for highway guardrails, performing lightweight processing on the guardrail posts and railings, including: The lightweight model of the guardrail post is rendered using the Cesium API to configure the guardrail post instantiation model package, thereby achieving GPU instantiation rendering modeling of the posts. By calling the dynamic modeling module for inflection point offset guardrails within the BIM+GIS application platform, the guardrail model is dynamically rendered to achieve lightweight guardrails. The visible range of the model is determined by the view frustum of the scene camera, and the clipping plane parameters of 3D Tiles are dynamically configured to achieve dynamic clipping and loading of the model.

8. A lightweight device for highway guardrail models based on Cesium, characterized in that, include: The modeling unit is used to extract the three-dimensional reference polyline and feature points of the highway guardrail, establish a guardrail BIM model based on the three-dimensional reference polyline, and establish a column BIM model based on the feature points of the three-dimensional reference polyline. The model package unit is used to create a guardrail column primitive model for the guardrail BIM model and the column BIM model, and to create a lightweight guardrail column model package based on the guardrail column primitive model. For the aforementioned guardrail BIM model and column BIM model, a guardrail column primitive model is established. Based on the guardrail column primitive model, a lightweight guardrail column model package is established, including: Create a guardrail post graphic model, move the guardrail post graphic model to the origin, and convert it into a gltf format file; Import the basic primitives of the shapefile, apply the example model, slice it to generate a lightweight 3dtiles package of guardrail posts; The dynamic modeling unit performs type conversion on the three-dimensional reference polyline to obtain a GeoJSON file, and establishes a railing dynamic modeling module based on Cesium. The three-dimensional reference polyline is type-converted to obtain a GeoJSON file. A dynamic railing modeling module is built based on Cesium, including: The KML file of the 3D reference polyline is split into single-line data. The split KML single lines share the multi-line attributes of the LML file of the 3D reference polyline and are exported as GeoJSON files. Establish the spatial relationship between the control point coordinates of the railing section and the baseline, and constrain the position and orientation of the railing model; Among them, by offsetting the guardrail baseline nodes, a guardrail guide line is established to constrain the guardrail modeling position; The offset baseline node coordinates and the two-dimensional coordinate array of guardrail profile feature points are passed into the PolylineVolumeGeometry interface to generate a highway guardrail geometry object. The lightweight unit is used to call the lightweight model package for guardrail posts and the dynamic modeling module for railings to build a lightweight BIM+GIS application scenario for highway guardrails and to perform lightweight processing on guardrail posts and railings.

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