Hydraulic engineering digital design method based on digital twinning

Abstract

The invention discloses a hydraulic engineering digital design method based on digital twinning, and relates to the technical field of hydraulic engineering, and the method comprises the steps: collecting the three-dimensional point cloud data of a hydraulic engineering through an industrial camera; constructing a building information model based on the three-dimensional point cloud data of the water conservancy project; performing model lightweight processing on the building information model of the water conservancy project by utilizing an optimized edge folding algorithm; hydraulic engineering dense matching point cloud data are collected through an image sensor carried by an unmanned aerial vehicle by using an oblique photography technology; performing three-dimensional modeling on the water conservancy project; carrying out filtering processing on the digital surface model by utilizing a cloth simulation filtering algorithm; and performing data fusion integration on the building information twinborn model and the digital surface twinborn model to establish a hydraulic engineering digital twinborn model fusion maturity evaluation index system. The building information model data and the digital surface model data are fused and integrated, multi-source data fusion management is carried out, and the informatization level of the water conservancy project is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water conservancy projects, and in particular to a digital design method for water conservancy projects based on digital twins. Background Art

[0002] Building information modeling technology is the most widely used information technology in the field of smart cities and engineering construction. It has become an important information technology that the government focuses on and the industry actively explores and researches. The introduction of building information modeling technology can serve as a technical support for the intelligent construction and operation management of water conservancy projects. It integrates multi-dimensional information such as progress, cost, and quality by establishing a high-precision 3D information model. It is applied to the planning, design, construction, operation and maintenance of water conservancy projects throughout the entire life cycle, and conducts construction site layout, progress control, model collision inspection, operation and maintenance, etc., to achieve multi-professional collaborative design and three-dimensional visual management. However, with the in-depth development of engineering digital informatization, the limitations of building information modeling technology have also been gradually magnified. It lacks external space information and is separated from the real space, making it difficult to carry out collaborative and integrated management.

[0003] Compared with building information modeling technology, the biggest advantage of digital surface modeling technology is that it can collect, store and manage information data in geographic space and has powerful spatial analysis capabilities. At present, digital surface models are considered to be the pillar industry of the 21st century and an important part of the information industry. With the growing demand for the development of water conservancy engineering informatization, the application scope of geographic information system technology in the field of water conservancy continues to expand and deepen. Based on oblique photography technology, three-dimensional digital products can be quickly obtained, which reduces the production cost and time cycle of three-dimensional data and becomes an important data source for three-dimensional digital surface models. Applying it to the field of water conservancy projects can be used for planning and site selection, flood simulation and visual management of water conservancy projects, and quickly collect and construct digital terrain and geological products to promote the informatization development of the water conservancy industry. Promoting the construction of smart water conservancy is one of the important paths to achieve high-quality development of water conservancy in the new stage. At present, the research on the application of digital twins in the water conservancy industry started late, and various technologies are still immature. How to establish a high-precision multi-fusion data base, synchronize simulation operation with the physical basin, and virtual-real interaction is the key issue of current research. Summary of the invention

[0004] In order to solve the above technical problems, a digital design method for water conservancy projects based on digital twins is provided. This technical solution solves the problems raised in the above background technology.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is: A digital design method for water conservancy projects based on digital twins, comprising: Collect 3D point cloud data of water conservancy projects through industrial cameras; Construct building information models based on 3D point cloud data of water conservancy projects; The optimized edge collapse algorithm is used to lightweight the building information model of the water conservancy project to obtain the building information twin model; Using oblique photography technology and image sensors carried by drones, dense matching point cloud data of water conservancy projects is collected; Based on the dense matching point cloud data of the water conservancy project, the water conservancy project is 3D modeled to obtain a digital surface model; The digital surface model is filtered using a cloth simulation filtering algorithm to obtain a digital surface twin model of the water conservancy project ground. The building information twin model and the digital surface twin model are integrated to obtain the digital twin model of the water conservancy project. Establish an evaluation index system for the fusion maturity of the digital twin model of water conservancy projects, and obtain the model fusion maturity of the building information twin model and the digital surface twin model; Determine whether the model fusion maturity is lower than the preset threshold. If so, rebuild the digital twin model of the water conservancy project. If not, do not output it.

[0006] Preferably, the construction of a building information model based on the three-dimensional point cloud data of the water conservancy project specifically includes: Divide the three-dimensional space into at least one small cube of the same volume, each small cube containing at least one data point in the three-dimensional point cloud data; Preset isosurface threshold; Traverse each voxel and determine whether the function value at its vertex crosses the given isosurface threshold. If so, calculate the intersection of the isosurface and the voxel edge. If not, do not output. Set all intersection points as vertices of the isosurface mesh; Connect the isosurfaces in adjacent voxels to form a continuous triangular mesh; Smooth the generated triangular mesh to optimize the mesh visual effect.

[0007] Preferably, the method of using the optimized edge collapse algorithm to perform model lightweight processing on the building information model of the water conservancy project to obtain the building information twin model specifically includes: S101: using an average area formula, calculating the average area of ​​all adjacent triangles at each vertex in the building information model of the water conservancy project; S102: Select any one of the triangular meshes in the building information model, and calculate the unit normal vector of the triangular mesh using a unit normal vector formula; S103: Calculate the normal vector of each vertex based on the unit normal vectors of all adjacent triangular meshes of each vertex in the building information model; S104: Calculate the curvature of each vertex using a curvature formula; S105: Obtain constraint factors; S106: Calculate the folding cost of each vertex by multiplying the constraint factor by the curvature of each vertex; S107: performing a folding operation on the vertex with the minimum folding cost, and updating the building information model; S108: determining whether the number of unfolded points at this time is less than a preset lightweight threshold, if so, outputting the building information model at this time as a building information twin model, if not, returning to step S101; The average area formula is:

[0008] In the formula, is the average area of ​​all triangles adjacent to vertex v, is the perimeter of the i-th triangle adjacent to vertex v, , , are the lengths of the three sides of the i-th triangle adjacent to vertex v, is the total number of triangles adjacent to vertex v; The unit normal vector formula is:

[0009] In the formula, , , Respectively The vector formed by the vertex and the origin of the vertex in the same triangle mesh, is the unit normal vector of the triangle mesh; The normal vector of each vertex is:

[0010] In the formula, for The normal vector of the vertex, For The average area of ​​all triangles with adjacent vertices; The curvature formula is:

[0011] In the formula, for The curvature of the vertex, for Vector and The magnitude of the angle between the vectors.

[0012] Preferably, the method of collecting dense matching point cloud data of water conservancy projects by using an image sensor carried by a drone using oblique photography technology specifically includes: Obtaining image sensor related parameters, including focal length and pixel size; Calculate the relative altitude of the UAV using the relative altitude formula; Based on the relative altitude, five image sensors are mounted on the drone, and the drone adopts a five-direction flight mode to simultaneously collect dense matching point cloud data of water conservancy projects from five angles, including one vertical angle and four side angles; The relative altitude formula is:

[0013] In the formula, is the relative altitude of the UAV, is the preset image resolution, is the sensor focal length, is the sensor pixel size.

[0014] Preferably, the three-dimensional modeling of the water conservancy project based on the dense matching point cloud data of the water conservancy project to obtain the digital surface model specifically includes: Determine the geometric relationship between the images collected by the five image sensors; Extract route connection points from densely matched point cloud data of water conservancy projects; Using the extracted route connection points, the relative positions and attitudes between the images collected by the five image sensors are calculated using the collinearity condition equation through the least squares method; Connect the same-name points in different images to form a complete three-dimensional model; The collinearity condition equation is:

[0015] In the formula, is the image point coordinate, is the image principal point coordinate, is the ground point coordinate, is the image sensor coordinate, , , is the image sensor attitude parameter.

[0016] Preferably, the filtering process of the digital surface model by using a cloth simulation filtering algorithm to obtain a digital surface twin model of the water conservancy project ground specifically includes: Modify the vertical coordinates of all points in the digital surface model to the opposite of the original vertical coordinates; Construct a water conservancy project cloth particle model, and place the cloth particle model above the maximum point of the vertical coordinate of the modified digital surface model; Project the modified digital surface model and the cloth particle model in a top view, obtain the point in the modified digital surface model that is closest to each cloth mesh particle, and record it as the nearest point, and record the vertical coordinate value of the nearest point as the height of the nearest point; Allow the movable cloth particles to fall naturally under the influence of gravity only, and record the vertical coordinate of the position when the cloth particles finally stop falling, which is recorded as the position height of the cloth particles; Determine whether the position height of the cloth particle is greater than the height of the nearest point. If so, set the position height of the cloth particle to the height of the nearest point and set the cloth particle as an immovable particle. If not, do nothing. Using the relationship formula between position and force, calculate the displacement of each cloth particle affected by the interaction force, select two adjacent particles, and make them move the same distance in opposite directions. The immovable particles will not move. Calculate the height difference between the modified digital surface model and the cloth particles, and determine whether the height difference is less than the set threshold. If so, output it as ground point information; if not, output it as non-ground point information; Aggregate ground point information and output it as a digital surface twin model; The cloth particle model is composed of grid-distributed particles with a certain mass and no size, and each particle is connected to surrounding particles through a set inter-particle interaction force; The relationship between position and force is:

[0017] In the formula, is the mass of the cloth particles, is the position function of the cloth particle at time t, is the gravity acting on the cloth particles, is the inter-particle interaction force on the cloth particles, for right The partial derivative of .

[0018] Preferably, the data fusion and integration of the building information twin model and the digital surface twin model to obtain the water conservancy project digital twin model specifically includes: Convert the IFC format of the building information twin model data into the CityGML format that can be recognized by the digital surface twin model data; The local coordinate system of the building information twin model data is converted to the WGS-84 coordinate system of the digital surface twin model data. Based on the seven-parameter coordinate conversion formula, the point cloud data of the building information twin model is converted to the global coordinates of the WGS-84 reference ellipsoid. The converted building information twin model data and digital surface twin model data are integrated through data fusion; The seven-parameter coordinate transformation formula is:

[0019] Where X, Y, and Z are the coordinates of the point cloud data of the building information twin model. , , is the coordinate of the converted building information twin model data, Dx, Dy, Dz are translation parameters, Rx, Ry are rotation parameters, Sx, Sz are scale difference parameters; The coordinate origin of the WGS-84 coordinate system is the center of mass of the earth. The Z axis of its geocentric space rectangular coordinate system points to the direction of the line connecting the north and south poles of the earth, the X axis points to the intersection of the zero meridian plane and the equator, and the Y axis is perpendicular to the X axis and the Z axis to form a right-handed coordinate system.

[0020] Preferably, the establishment of a water conservancy project digital twin model fusion maturity evaluation index system to obtain the model fusion maturity of the building information twin model and the digital surface twin model specifically includes: The evaluation dimensions are determined to be data integration, model consistency, functional interoperability, application effect and system stability; Through the expert scoring method, the digital twin model of the water conservancy project is analyzed and scored from the five evaluation dimensions; Get the corresponding score weights of the five evaluation dimensions; Based on the expert scores and score weights, the model fusion maturity of the building information twin model and the digital surface twin model is calculated using the scoring formula; The scoring formula is:

[0021] In the formula, The model fusion maturity of building information twin model and digital surface twin model, is the expert rating of the i-th rating dimension, is the score weight of the i-th scoring dimension.

[0022] Compared with the prior art, the present invention has the following beneficial effects: Integrate the building information model data and the digital surface model data, conduct multi-source data fusion management, form data support, improve the informatization level of water conservancy projects, conduct a maturity evaluation of the data fusion of the building information model data and the digital surface model data, provide a reference direction for deeper integration in the future, establish a refined, interactively shareable digital twin base plate data, and realize information management. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of the digital design method of water conservancy projects based on digital twins of the present invention; Figure 2 A flow chart of a method for constructing a building information model according to the present invention; Figure 3 This is a flow chart of the model lightweight processing method of the present invention; Figure 4 This is a flow chart of the method for collecting dense matching point cloud data of water conservancy projects of the present invention; Figure 5 A flow chart of a method for three-dimensional modeling of a water conservancy project according to the present invention; Figure 6 It is a flow chart of the cloth simulation filtering algorithm method of the present invention; Figure 7 It is a flow chart of the data fusion integration method of the present invention; Figure 8 This is a flow chart of the method for establishing a fusion maturity evaluation index system for a digital twin model of a water conservancy project according to the present invention. DETAILED DESCRIPTION

[0024] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art may think of other obvious variations.

[0025] Reference Figure 1 As shown in the figure, a digital design method for water conservancy projects based on digital twins includes: Collect 3D point cloud data of water conservancy projects through industrial cameras; Construct building information models based on 3D point cloud data of water conservancy projects; The optimized edge collapse algorithm is used to lightweight the building information model of the water conservancy project to obtain the building information twin model; Using oblique photography technology and image sensors carried by drones, dense matching point cloud data of water conservancy projects is collected; Based on the dense matching point cloud data of the water conservancy project, the water conservancy project is 3D modeled to obtain a digital surface model; The digital surface model is filtered using a cloth simulation filtering algorithm to obtain a digital surface twin model of the water conservancy project ground. The building information twin model and the digital surface twin model are integrated to obtain the digital twin model of the water conservancy project. Establish an evaluation index system for the fusion maturity of the digital twin model of water conservancy projects, and obtain the model fusion maturity of the building information twin model and the digital surface twin model; Determine whether the model fusion maturity is lower than the preset threshold. If so, rebuild the digital twin model of the water conservancy project. If not, do not output it.

[0026] Reference Figure 2 As shown in the figure, based on the 3D point cloud data of the water conservancy project, the construction of the building information model specifically includes: Divide the three-dimensional space into at least one small cube of the same volume, each small cube containing at least one data point in the three-dimensional point cloud data; Preset isosurface threshold; Traverse each voxel and determine whether the function value at its vertex crosses the given isosurface threshold. If so, calculate the intersection of the isosurface and the voxel edge. If not, do not output. Set all intersection points as vertices of the isosurface mesh; Connect the isosurfaces in adjacent voxels to form a continuous triangular mesh; Smooth the generated triangular mesh to optimize the mesh visual effect.

[0027] The purpose of surface reconstruction is to convert disordered three-dimensional point cloud data into a surface model with a clear geometric shape and topological structure. There are many surface reconstruction algorithms, including implicit function-based reconstruction, polygonal mesh-based reconstruction, and voxel-based reconstruction. The choice of algorithm depends on specific application requirements, data characteristics, computing resources and other factors.

[0028] Reference Figure 3 As shown in the figure, the optimized edge collapse algorithm is used to lightweight the building information model of the water conservancy project, and the building information twin model obtained specifically includes: S101: Calculate the average area of ​​all adjacent triangles at each vertex in the building information model of the water conservancy project using the average area formula; S102: Select any one of the triangular meshes in the building information model, and calculate the unit normal vector of the triangular mesh using a unit normal vector formula; S103: Calculate the normal vector of each vertex based on the unit normal vectors of all adjacent triangular meshes of each vertex in the building information model; S104: Calculate the curvature of each vertex using a curvature formula; S105: Obtain constraint factors; S106: Calculate the folding cost of each vertex by multiplying the constraint factor by the curvature of each vertex; S107: performing a folding operation on the vertex with the minimum folding cost, and updating the building information model; S108: determining whether the number of unfolded points at this time is less than a preset lightweight threshold, if so, outputting the building information model at this time as a building information twin model, if not, returning to step S101; The average area formula is:

[0029] In the formula, is the average area of ​​all triangles adjacent to vertex v, is the perimeter of the i-th triangle adjacent to vertex v, , , are the lengths of the three sides of the i-th triangle adjacent to vertex v, is the total number of triangles adjacent to vertex v; The unit normal vector formula is:

[0030] In the formula, , , Respectively The vector formed by the vertex and the origin of the vertex in the same triangle mesh, is the unit normal vector of the triangle mesh; The normal vector of each vertex is:

[0031] In the formula, for The normal vector of the vertex, For The average area of ​​all triangles with adjacent vertices; The curvature formula is:

[0032] In the formula, for The curvature of the vertex, for Vector and The magnitude of the angle between the vectors.

[0033] In order to better reduce the deformation of the model, the folding cost is sorted during the simplification process. The relatively flat surface area has a smaller folding cost, while the area with more surface curves and larger curvature has a larger folding cost. They are optimized and sorted, giving priority to areas with smaller folding costs, that is, areas with unclear surface features and relatively flat areas, to fully retain the surface boundary features of the model and the texture details of the model.

[0034] Reference Figure 4As shown in the figure, using oblique photography technology through the image sensor carried by the drone, the dense matching point cloud data of water conservancy projects is collected, including: Obtaining image sensor related parameters, including focal length and pixel size; Calculate the relative altitude of the UAV using the relative altitude formula; Based on the relative altitude, five image sensors are mounted on the drone, and the drone adopts a five-direction flight mode to simultaneously collect dense matching point cloud data of water conservancy projects from five angles, including one vertical angle and four side angles; The relative altitude formula is:

[0035] In the formula, is the relative altitude of the UAV, is the preset image resolution, is the sensor focal length, is the sensor pixel size.

[0036] By using drone oblique photography technology and synchronously collecting images from different perspectives, a high-resolution oblique photography model of the water conservancy project is constructed to truly reflect the ground conditions and generate a simulated digital surface model of the water conservancy project.

[0037] Reference Figure 5 As shown in the figure, based on the dense matching point cloud data of the water conservancy project, the water conservancy project is 3D modeled, and the digital surface model obtained specifically includes: Determine the geometric relationship between the images collected by the five image sensors; Extract route connection points from densely matched point cloud data of water conservancy projects; Using the extracted route connection points, the relative positions and attitudes between the images collected by the five image sensors are calculated using the collinearity condition equation through the least squares method; Connect the same-name points in different images to form a complete three-dimensional model; The collinearity condition equation is:

[0038] In the formula, is the image point coordinate, is the image principal point coordinate, is the ground point coordinate, is the image sensor coordinate, , , is the image sensor attitude parameter.

[0039] The collinearity condition equation is a mathematical equation that describes the geometric relationship between image points and ground points in photogrammetry. Under ideal circumstances, that is, when no errors or distortions are considered, the image point, the projection center and the corresponding ground point should be located on the same straight line, that is, they satisfy the collinearity condition. This condition can be expressed as a mathematical equation, namely the collinearity condition equation.

[0040] Reference Figure 6 As shown in the figure, the digital surface model is filtered using the cloth simulation filtering algorithm to obtain the digital surface twin model of the water conservancy project ground, which specifically includes: Modify the vertical coordinates of all points in the digital surface model to the opposite of the original vertical coordinates; Construct a water conservancy project cloth particle model, and place the cloth particle model above the maximum point of the vertical coordinate of the modified digital surface model; Project the modified digital surface model and the cloth particle model in a top view, obtain the point in the modified digital surface model that is closest to each cloth mesh particle, and record it as the nearest point, and record the vertical coordinate value of the nearest point as the height of the nearest point; Allow the movable cloth particles to fall naturally under the influence of gravity only, and record the vertical coordinate of the position when the cloth particles finally stop falling, which is recorded as the position height of the cloth particles; Determine whether the position height of the cloth particle is greater than the height of the nearest point. If so, set the position height of the cloth particle to the height of the nearest point and set the cloth particle as an immovable particle. If not, do nothing. Using the relationship formula between position and force, calculate the displacement of each cloth particle affected by the interaction force, select two adjacent particles, and make them move the same distance in opposite directions. The immovable particles will not move. Calculate the height difference between the modified digital surface model and the cloth particles, and determine whether the height difference is less than the set threshold. If so, output it as ground point information; if not, output it as non-ground point information; Aggregate ground point information and output it as a digital surface twin model; The cloth particle model is composed of grid-distributed particles with a certain mass and no size, and each particle is connected to surrounding particles through a set inter-particle interaction force; The relationship between position and force is:

[0041] In the formula, is the mass of the cloth particles, is the position function of the cloth particle at time t, is the gravity acting on the cloth particles, is the inter-particle interaction force on the cloth particles, for right The partial derivative of .

[0042] As a point cloud filtering algorithm, the cloth algorithm has the advantages of simple model and high filtering efficiency. It has high filtering accuracy for flat areas such as roads.

[0043] Reference Figure 7 As shown in the figure, the building information twin model and the digital surface twin model are integrated to obtain the water conservancy project digital twin model, which specifically includes: Convert the IFC format of the building information twin model data into the CityGML format that can be recognized by the digital surface twin model data; The local coordinate system of the building information twin model data is converted to the WGS-84 coordinate system of the digital surface twin model data. Based on the seven-parameter coordinate conversion formula, the point cloud data of the building information twin model is converted to the global coordinates of the WGS-84 reference ellipsoid. The converted building information twin model data and digital surface twin model data are integrated through data fusion; The seven-parameter coordinate transformation formula is:

[0044] Where X, Y, and Z are the coordinates of the point cloud data of the building information twin model. , , is the coordinate of the converted building information twin model data, Dx, Dy, Dz are translation parameters, Rx, Ry are rotation parameters, Sx, Sz are scale difference parameters; The coordinate origin of the WGS-84 coordinate system is the center of mass of the earth. The Z axis of its geocentric space rectangular coordinate system points to the direction of the line connecting the north and south poles of the earth, the X axis points to the intersection of the zero meridian plane and the equator, and the Y axis is perpendicular to the X axis and the Z axis to form a right-handed coordinate system.

[0045] The translation parameter is in meters, the rotation parameter is in angular seconds, and the scale difference parameter is in parts per million. During the conversion process, attention should be paid to the unification of coordinate units and precision control to ensure the accuracy and reliability of the conversion results.

[0046] Reference Figure 8 As shown in the figure, a fusion maturity evaluation index system for the digital twin model of water conservancy projects is established, and the model fusion maturity of the building information twin model and the digital surface twin model is obtained, including: The evaluation dimensions are determined to be data integration, model consistency, functional interoperability, application effect and system stability; Through the expert scoring method, the digital twin model of the water conservancy project is analyzed and scored from the five evaluation dimensions; Get the corresponding score weights of the five evaluation dimensions; Based on the expert scores and score weights, the model fusion maturity of the building information twin model and the digital surface twin model is calculated using the scoring formula; The scoring formula is:

[0047] In the formula, The model fusion maturity of building information twin model and digital surface twin model, is the expert rating of the i-th rating dimension, is the score weight of the i-th scoring dimension.

[0048] This is a complex but systematic process that involves multiple dimensions and indicators, aiming to comprehensively reflect the level, quality and effect of the integration of building information twin models and digital surface twin models. Furthermore, the present solution also proposes a computer-readable storage medium, on which a computer-readable program is stored. When the computer-readable program is called, the above-mentioned digital design method of water conservancy projects based on digital twins is executed.

[0049] It is understandable that the storage medium may be a magnetic medium, such as a floppy disk, a hard disk, or a magnetic tape; an optical medium, such as a DVD; or a semiconductor medium, such as a solid state drive (SSD).

[0050] To sum up, the advantages of the present invention are: integrating building information model data and digital surface model data, conducting multi-source data fusion management, forming data support, improving the informatization level of water conservancy projects, conducting maturity evaluation of the data fusion of building information model data and digital surface model data, providing reference direction for deeper integration in the future, establishing a refined, interactively shareable digital twin base plate data, and realizing informatization management.

[0051] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A digital design method for water conservancy projects based on digital twins, characterized in that: include: Collect 3D point cloud data of water conservancy projects through industrial cameras; Construct building information models based on 3D point cloud data of water conservancy projects; The optimized edge collapse algorithm is used to lightweight the building information model of the water conservancy project to obtain the building information twin model; Using oblique photography technology and image sensors carried by drones, dense matching point cloud data of water conservancy projects is collected; Based on the dense matching point cloud data of the water conservancy project, the water conservancy project is 3D modeled to obtain a digital surface model; The digital surface model is filtered using a cloth simulation filtering algorithm to obtain a digital surface twin model of the water conservancy project ground. The building information twin model and the digital surface twin model are integrated to obtain the digital twin model of the water conservancy project. Establish an evaluation index system for the fusion maturity of the digital twin model of water conservancy projects, and obtain the model fusion maturity of the building information twin model and the digital surface twin model; Determine whether the model fusion maturity is lower than the preset threshold. If so, rebuild the digital twin model of the water conservancy project. If not, do not output it.

2. According to claim 1, a digital design method for water conservancy projects based on digital twins is characterized in that: The construction of the building information model based on the three-dimensional point cloud data of the water conservancy project specifically includes: Divide the three-dimensional space into at least one small cube of the same volume, each small cube containing at least one data point in the three-dimensional point cloud data; Preset isosurface threshold; Traverse each voxel and determine whether the function value at its vertex crosses the given isosurface threshold. If so, calculate the intersection of the isosurface and the voxel edge. If not, do not output. Set all intersection points as vertices of the isosurface mesh; Connect the isosurfaces in adjacent voxels to form a continuous triangular mesh; Smooth the generated triangular mesh to optimize the mesh visual effect.

3. A digital design method for water conservancy projects based on digital twins according to claim 2, characterized in that: The method of using the optimized edge collapse algorithm to perform model lightweight processing on the building information model of the water conservancy project to obtain the building information twin model specifically includes: S101: using an average area formula, calculating the average area of ​​all adjacent triangles at each vertex in the building information model of the water conservancy project; S102: Select any one of the triangular meshes in the building information model, and calculate the unit normal vector of the triangular mesh using a unit normal vector formula; S103: Calculate the normal vector of each vertex based on the unit normal vectors of all adjacent triangular meshes of each vertex in the building information model; S104: Calculate the curvature of each vertex using a curvature formula; S105: Obtain constraint factors; S106: Calculate the folding cost of each vertex by multiplying the constraint factor by the curvature of each vertex; S107: performing a folding operation on the vertex with the minimum folding cost, and updating the building information model; S108: determining whether the number of unfolded points at this time is less than a preset lightweight threshold, if so, outputting the building information model at this time as a building information twin model, if not, returning to step S101; The average area formula is: In the formula, is the average area of ​​all triangles adjacent to vertex v, is the perimeter of the i-th triangle adjacent to vertex v, , , are the lengths of the three sides of the i-th triangle adjacent to vertex v, is the total number of triangles adjacent to vertex v; The unit normal vector formula is: In the formula, , , Respectively The vector formed by the vertex and the origin of the vertex in the same triangle mesh, is the unit normal vector of the triangle mesh; The normal vector of each vertex is: In the formula, for The normal vector of the vertex, For The average area of ​​all triangles with adjacent vertices; The curvature formula is: In the formula, for The curvature of the vertex, for Vector and The magnitude of the angle between the vectors.

4. A digital design method for water conservancy projects based on digital twins according to claim 3, characterized in that: The method of collecting dense matching point cloud data of water conservancy projects by using the image sensor carried by the drone using the oblique photography technology specifically includes: Obtaining image sensor related parameters, including focal length and pixel size; Calculate the relative altitude of the UAV using the relative altitude formula; Based on the relative altitude, five image sensors are mounted on the drone, and the drone adopts a five-direction flight mode to simultaneously collect dense matching point cloud data of water conservancy projects from five angles, including one vertical angle and four side angles; The relative altitude formula is: In the formula, is the relative altitude of the UAV, is the preset image resolution, is the sensor focal length, is the sensor pixel size.

5. A digital design method for water conservancy projects based on digital twins according to claim 4, characterized in that: The three-dimensional modeling of the water conservancy project based on the dense matching point cloud data of the water conservancy project to obtain the digital surface model specifically includes: Determine the geometric relationship between the images collected by the five image sensors; Extract route connection points from densely matched point cloud data of water conservancy projects; Using the extracted route connection points, the relative positions and attitudes between the images collected by the five image sensors are calculated using the collinearity condition equation through the least squares method; Connect the same-name points in different images to form a complete three-dimensional model; The collinearity condition equation is: In the formula, is the image point coordinate, is the image principal point coordinate, is the ground point coordinate, is the image sensor coordinate, , , is the image sensor attitude parameter.

6. A digital design method for water conservancy projects based on digital twins according to claim 5, characterized in that: The method of filtering the digital surface model using the cloth simulation filtering algorithm to obtain the digital surface twin model of the water conservancy project ground specifically includes: Modify the vertical coordinates of all points in the digital surface model to the opposite of the original vertical coordinates; Construct a water conservancy project cloth particle model, and place the cloth particle model above the maximum point of the vertical coordinate of the modified digital surface model; Project the modified digital surface model and the cloth particle model in a top view, obtain the point in the modified digital surface model that is closest to each cloth mesh particle, and record it as the nearest point, and record the vertical coordinate value of the nearest point as the height of the nearest point; Allow the movable cloth particles to fall naturally under the influence of gravity only, and record the vertical coordinate of the position when the cloth particles finally stop falling, which is recorded as the position height of the cloth particles; Determine whether the position height of the cloth particle is greater than the height of the nearest point. If so, set the position height of the cloth particle to the height of the nearest point and set the cloth particle as an immovable particle. If not, do nothing. Using the relationship formula between position and force, calculate the displacement of each cloth particle affected by the interaction force, select two adjacent particles, and make them move the same distance in opposite directions. The immovable particles will not move. Calculate the height difference between the modified digital surface model and the cloth particles, and determine whether the height difference is less than the set threshold. If so, output it as ground point information; if not, output it as non-ground point information; Aggregate ground point information and output it as a digital surface twin model; The cloth particle model is composed of grid-distributed particles with a certain mass and no size, and each particle is connected to surrounding particles through a set inter-particle interaction force; The relationship between position and force is: In the formula, is the mass of the cloth particles, is the position function of the cloth particle at time t, is the gravity acting on the cloth particles, is the inter-particle interaction force on the cloth particles, for right The partial derivative of .

7. A digital design method for water conservancy projects based on digital twins according to claim 6, characterized in that: The data fusion and integration of the building information twin model and the digital surface twin model to obtain the water conservancy project digital twin model specifically includes: Convert the IFC format of the building information twin model data into the CityGML format that can be recognized by the digital surface twin model data; The local coordinate system of the building information twin model data is converted to the WGS-84 coordinate system of the digital surface twin model data. Based on the seven-parameter coordinate conversion formula, the point cloud data of the building information twin model is converted to the global coordinates of the WGS-84 reference ellipsoid. The converted building information twin model data and digital surface twin model data are integrated through data fusion; The seven-parameter coordinate transformation formula is: Where X, Y, and Z are the coordinates of the point cloud data of the building information twin model. , , is the coordinate of the converted building information twin model data, Dx, Dy, Dz are translation parameters, Rx, Ry are rotation parameters, Sx, Sz are scale difference parameters; The coordinate origin of the WGS-84 coordinate system is the center of mass of the earth. The Z axis of its geocentric space rectangular coordinate system points to the direction of the line connecting the north and south poles of the earth, the X axis points to the intersection of the zero meridian plane and the equator, and the Y axis is perpendicular to the X axis and the Z axis to form a right-handed coordinate system.

8. The digital design method for water conservancy projects based on digital twins according to claim 7 is characterized in that: The establishment of a water conservancy project digital twin model fusion maturity evaluation index system to obtain the model fusion maturity of the building information twin model and the digital surface twin model specifically includes: The evaluation dimensions are determined to be data integration, model consistency, functional interoperability, application effect and system stability; Through the expert scoring method, the digital twin model of the water conservancy project is analyzed and scored from the five evaluation dimensions; Get the corresponding score weights of the five evaluation dimensions; Based on the expert scores and score weights, the model fusion maturity of the building information twin model and the digital surface twin model is calculated using the scoring formula; The scoring formula is: In the formula, The model fusion maturity of building information twin model and digital surface twin model, is the expert rating of the i-th rating dimension, is the score weight of the i-th scoring dimension.

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