A method for generating hydrodynamic river grid terrain based on cross-sectional measurement data

Abstract

The present invention provides a method for generating hydrodynamic river channel grid terrain based on cross-section measurement data, comprising drawing grid subdivision control lines by combining cross-section, image, shoreline and other data; generating a quadrilateral unstructured grid based on the control lines; traversing the grid to calculate the normal direction angles of the grid unit edges; continuously tracing from the starting unit edge, and determining the upstream and downstream, left and right bank relationships of the grid by comparing the degree of collinearity of the normals, that is, determining a two-dimensional index number; using structured numbers, calculating the mileage of each grid center point, the distance from the left bank, and the length of the horizontal and vertical lines where the grid center point is located; continuously segmenting by elevation low points, and establishing an upstream and downstream one-to-one correspondence between key element points of the upstream and downstream sections; using the corresponding cross-section point data of the upstream and downstream, based on the mileage and considering the change in cross-section width, interpolating at the cross-section line to generate a new section; using the structured numbers to traverse the grid, and assigning the elevation attributes of the intersecting grid center points based on the new section data.

Description

Technical Field

[0001] The invention relates to the technical field of water conservancy project planning, in particular to a method for generating hydrodynamic river channel grid terrain based on cross-section measurement data. Background Art

[0002] In the practice of flood prevention and disaster reduction in the water conservancy industry, with the continuous improvement of computing power, flood risk management in the new era has become increasingly intelligent and refined. The construction of the "four predictions" platform for flood prevention based on digital twin technology has put forward higher requirements for "simulation and rehearsal". For the simulation of the evolution of river floods, most of the previous methods were based on one-dimensional river models based on the "river section-section" structure. The cross-sectional process elements (water level, flow, etc.) output by the model are difficult to fully support the rehearsal function of the river flood evolution process. For this reason, it is necessary to build a two-dimensional shallow water model covering the river range. The typical result of river topography measurement is the river cross section. How to generate river topography data suitable for two-dimensional hydrodynamic calculations based on the existing river section data is a problem in the existing technology.

[0003] In two-dimensional hydrodynamic models, the most important role of terrain data is to assign elevation values ​​to the grid. In this sense, the ultimate goal of research on river channel terrain generation methods is to obtain a set of high-quality grid data with accurate elevation attribute values. Unlike general two-dimensional hydrodynamic calculation scenarios, two-dimensional river channel hydrodynamic models have their own unique characteristics: water flow is generally confined to a narrow and long channel and flows along the river. Given this characteristic, two-dimensional river channel hydrodynamic models should preferably use a body-fitting grid generated with the river bank as the longitudinal control line as the computational grid. Clearly, existing river channel terrain generation technologies have shortcomings in their applicability to two-dimensional river channel hydrodynamic models and fail to fully consider cross-sectional morphological variations, especially underwater terrain.

[0004] The invention patent application with application publication number CN111681316A discloses a high-precision river channel topography interpolation method, comprising: 1. classifying the cross-section type of the measured river channel and determining the number of longitudinal control lines of the measured river channel; 2. overlaying the cross-section control lines of the river channel with a satellite image of the measured river channel as a base map to draw the longitudinal control lines of the river channel; 3. interpolating the elevation values ​​at the intersection of the cross-section lines and the longitudinal control lines based on the river channel cross-section elevation data, and interpolating the longitudinal control lines into a three-dimensional curve; 4. converting the cross-section control lines of the river channel into three-dimensional lines, and generating the basic data of a three-dimensional terrain model together with the interpolated three-dimensional longitudinal control lines, using the Delaunay method to triangulate the interpolation area, and using a two-dimensional linear interpolation method to determine the elevation of the triangulated mesh vertices, thereby generating the three-dimensional terrain model. This method only adds control lines for the above-water terrain and does not fully consider the accuracy improvement of the underwater terrain. Furthermore, when only the river channel cross-section data is available, the interpolation effect is not ideal and cannot meet the terrain data requirements of the two-dimensional hydrodynamic model.

[0005] The invention patent application with application publication number CN109960838A discloses a method for automatically generating river channel topography that reflects the basic characteristics of a river. This method combines measured river channel cross-sectional data with high-resolution remote sensing images or existing river channel vector data to extract the left and right bank (embankment) lines and the river channel thalassemia line that reflect the basic characteristics of the river. By encrypting the middle line between the left and right bank (embankment) lines and the thalassemia line of the river channel and intersecting it with the measured river channel cross-sectional line, a directional interpolation line segment of the river channel is formed. Further directional interpolation is performed to generate river channel elevation points that reflect the basic characteristics of the three lines of the river, thereby realizing the automatic generation of river channel topography. This method requires the known location of the river channel thalassemia line, which is generally located in the underwater part. When the measurement section spacing is large and the river channel morphology is more complex, the location of the thalassemia line cannot be directly determined. Summary of the Invention

[0006] In order to solve the above-mentioned technical problems, the present invention proposes a method for generating hydrodynamic river channel grid terrain based on cross-sectional measurement data. Based on the existing cross-sectional measurement data, the method fully considers the key morphological elements of the upstream and downstream sections in the spatial interpolation, assigns values ​​to the elevation attributes of the two-dimensional body-fitting grid of the river channel, and thus obtains grid terrain data suitable for two-dimensional hydrodynamic calculations of the river channel.

[0007] The present invention aims to provide a method for generating hydrodynamic river channel grid terrain based on cross-sectional measurement data, comprising obtaining the location of the measurement cross-sectional data, high-resolution remote sensing images, and shoreline or levee data, and further comprising the following steps:

[0008] Step 1: Based on the acquired data, draw the grid division control lines, including longitudinal control lines and transverse control lines;

[0009] Step 2: For each river section, generate the same number of control points on the longitudinal control line and the transverse control line to generate a quadrilateral grid, where the quadrilateral grid is an unstructured grid;

[0010] Step 3: traverse the unstructured grid and calculate the normal direction angle α of each grid cell edge, that is, the angle between the normal and the x-axis direction;

[0011] Step 4: Structuring the topological relationship of the unstructured grid, and converting the grid number into a two-dimensional index number with the longitudinal direction and the transverse direction of the river channel as the axis direction;

[0012] Step 5: Using the horizontal starting edge as the reference edge, traverse the other unit edges in the grid where it is located, compare the collinearity of the normals of the current unit edge and the reference edge, and find the unit edge with the largest collinearity;

[0013] Step 6: Take each grid in the upstream of the river as the starting grid, and the edge of the grid cell at the most upstream of the river as the starting edge. By continuously tracing the edge of the cell with the largest degree of collinearity of normals downstream, the 2D index numbers of the passed grids are determined in sequence to achieve the structuring of all grid numbers.

[0014] Step 7: Define the line connecting the center points of the grids with the same vertical number and the center points of the outermost unit edges on the left and right banks as the horizontal line, and define the line connecting the center points of the grids with the same horizontal number and the center points of the outermost unit edges on the upstream and downstream sides as the vertical line;

[0015] Step 8: Establish a one-to-one correspondence between the key cross-section points of the upstream and downstream sections;

[0016] Step 9: Based on the corresponding relationship and the position of the transverse line, linear interpolation is performed according to the distance while taking into account the change in cross-section width;

[0017] Step 10: Use a structured numbering system to traverse all grids, interpolate the cross-section data at the transverse line where the grid is located, and assign the elevation attribute of the grid center point.

[0018] Preferably, the longitudinal control lines are the left and right bank lines, and the transverse control lines include the upstream and downstream cross sections and the internal control lines perpendicular to the flow direction of the river.

[0019] In any of the above schemes, it is preferred that the transverse control lines divide the river channel into N sections, and each river section is surrounded by two transverse control lines and two longitudinal control lines.

[0020] In any of the above solutions, preferably, the normal direction of the grid unit edge is from the unit with a larger number to the unit with a smaller number by default, wherein the normal direction of the grid unit edge located at the boundary is directed outward by default.

[0021] In any of the above solutions, preferably, the coordinates of the two endpoints of the grid unit edge are (x1, y1) and (x2, y2), and the normal direction angle calculation formula of the unit edge is:

[0022]

[0023] In any of the above schemes, it is preferred to take the positive direction of the longitudinal direction of the river channel from upstream to downstream, and take the positive direction of the transverse direction of the river channel from left bank to right bank.

[0024] In any of the above schemes, preferably, step 5 also includes setting the upstream left bank grid point as the coordinate origin, taking the grid where this point is located as the starting grid, numbering it as (1,1), and selecting the left bank unit edge of the grid as the horizontal starting edge, and the upstream unit edge of the grid as the vertical starting edge.

[0025] In any of the above solutions, preferably, step 5 includes the following sub-steps:

[0026] Step 51: traverse other unit edges of the starting grid, compare the collinearity of the normals of the current unit edge and the reference edge, and find the unit edge with the largest collinearity as the target edge;

[0027] Step 52: adding 1 to the horizontal number of the two-dimensional index number of another grid other than the used grid that shares the same edge with the target edge;

[0028] Step 53: Use the target edge as the new reference edge, traverse other unit edges, compare the collinearity of the normals of the current unit edge and the reference edge, and find the unit edge with the largest collinearity;

[0029] Step 54: Repeat steps 52-53 until you reach the right bank.

[0030] In any of the above solutions, it is preferred that the degree of collinearity of the normals is expressed as the deviation angle d a To express it, the calculation formula is

[0031]

[0032] Among them, α b , α c They are the normal direction angles of the base edge and the current edge respectively.

[0033] In any of the above schemes, preferably, step 7 also includes using a structured numbering system to traverse all grids, calculate the mileage of each grid center point from the respective longitudinal starting unit edge and the lateral distance from the respective left bank unit edge, as well as the length of the lateral line and the longitudinal line.

[0034] In any of the above solutions, preferably, step 8 includes the following sub-steps:

[0035] Step 81: Establishing a corresponding relationship between the upstream and downstream sections;

[0036] Step 82: Segment the upstream and downstream sections by their respective lowest elevation points, and continue segmenting the latest two groups of left and right section points by their respective lowest elevation points;

[0037] Step 83: Repeat steps 81-82 until no further segmentation is possible.

[0038] In any of the above solutions, preferably, the linear interpolation formula is

[0039]

[0040] Among them, y represents the distance from the left bank, z represents the elevation, u and d represent upstream and downstream respectively, i represents the sequence number of the corresponding upstream and downstream section points in the correspondence table, ω is the weight coefficient, and c is the width scaling coefficient.

[0041] In any of the above solutions, preferably, the calculation formula of the width scaling factor c is:

[0042]

[0043] Among them, B, B u 、B d They are the width of the current transverse line, the upstream section width and the downstream section width respectively.

[0044] In any of the above solutions, it is preferred that the calculation formula for the elevation z is:

[0045]

[0046] Among them, z k Indicates the elevation of the kth section point, y k Indicates the distance between the kth section point and the left bank. The subscripts k and k+1 indicate the section point numbers generated by interpolation at the transverse line. k <y<y k+1 Indicates that the current grid center point is between two consecutive section points generated by interpolation at the transverse line.

[0047] The present invention proposes a method for generating hydrodynamic river channel grid terrain based on cross-section measurement data. The method can fully consider the key morphological elements of the cross section and their changes, especially the underwater part, and directly assign elevation attributes based on the unstructured body-fitting grid. The results are more suitable for the calculation of two-dimensional hydrodynamic models of rivers. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The flowchart is a preferred embodiment of the method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to the present invention.

[0049] Figure 2 The flowchart is another preferred embodiment of the method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to the present invention.

[0050] Figure 3 A schematic diagram of control lines for drawing grid subdivision according to an embodiment of the method for generating hydrodynamic river grid terrain based on cross-sectional measurement data of the present invention.

[0051] Figure 4 The figure is a schematic diagram of an embodiment of an unstructured grid at a certain resolution according to the method for generating hydrodynamic river grid terrain based on cross-sectional measurement data of the present invention.

[0052] Figure 5 The figure is a schematic diagram of an embodiment of the unit edge normal direction angle of the method for generating hydrodynamic river grid terrain based on cross-section measurement data according to the present invention.

[0053] Figure 6 The figure is a schematic diagram of an embodiment of the starting grid and starting unit edges of the method for generating hydrodynamic river grid terrain based on cross-section measurement data according to the present invention.

[0054] Figure 7 It is a partial schematic diagram of an embodiment of the structured two-dimensional index numbering of the method for generating hydrodynamic river grid terrain based on cross-section measurement data according to the present invention.

[0055] Figure 8 A partial schematic diagram of a method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to the present invention using red horizontal lines and blue vertical lines according to an embodiment of the present invention.

[0056] Figure 9 It is a schematic diagram of an embodiment of the correspondence between upstream and downstream cross-section points in a method for generating hydrodynamic river grid terrain based on cross-section measurement data according to the present invention.

[0057] Figure 10 The figure is a result diagram of an embodiment of a river channel topography generated by a method for generating a hydrodynamic river channel grid topography based on cross-section measurement data according to the present invention. DETAILED DESCRIPTION

[0058] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0059] Example 1

[0060] like Figure 1 As shown, a method for generating hydrodynamic river grid terrain based on cross-section measurement data is performed, step 1000 is executed to obtain the location of the measurement cross-section data, high-resolution remote sensing images, and shoreline or levee data.

[0061] Execute step 1010, and draw grid subdivision control lines based on the acquired data, including longitudinal control lines and transverse control lines. The longitudinal control lines are the left and right bank lines, and the transverse control lines include upstream and downstream cross sections and internal control lines perpendicular to the river flow direction. The transverse control lines divide the river into N sections, and each river section is surrounded by two transverse control lines and two longitudinal control lines.

[0062] Execute step 1020 to generate the same number of control points on the longitudinal control line and the transverse control line for each river section, and generate a quadrilateral grid, where the quadrilateral grid is an unstructured grid.

[0063] Execute step 1030, traverse the unstructured grid, and calculate the normal direction angle α of each grid cell edge, that is, the angle between the normal and the x-axis. The normal direction of the grid cell edge is from the cell with the larger number to the cell with the smaller number by default. The normal direction of the grid cell edge at the boundary is pointed outward by default. The coordinates of the two endpoints of the grid cell edge are (x1, y1) and (x2, y2) respectively. The calculation formula of the normal direction angle of the cell edge is:

[0064]

[0065] Execute step 1040 to structure the topological relationship of the unstructured grid, convert the grid number into a two-dimensional index number with the longitudinal and transverse directions of the river channel as the axis directions, and use the direction from upstream to downstream as the positive direction of the longitudinal direction of the river channel, and the direction from left bank to right bank as the positive direction of the transverse direction of the river channel.

[0066] Execute step 1050, using the horizontal starting edge as the reference edge, traverse the other unit edges of the grid in which it is located, compare the degree of collinearity of the normals of the current unit edge and the reference edge, find the unit edge with the largest degree of collinearity, set the upstream left bank grid point as the coordinate origin, and use the grid where this point is located as the starting grid, numbering it as (1,1), and select the left bank unit edge of the grid as the horizontal starting edge, and the upstream unit edge of the grid as the vertical starting edge. The following sub-steps are included:

[0067] Execute step 1051, traverse the other unit edges of the starting grid, compare the collinearity of the normals of the current unit edge and the reference edge, find the unit edge with the largest collinearity, and use it as the target edge. The collinearity of the normals is expressed as the deviation angle d. a To express it, the calculation formula is

[0068]

[0069] Among them, α b , α c They are the normal direction angles of the base edge and the current edge respectively.

[0070] Execute step 1052 to increase the horizontal number of the two-dimensional index number of another grid other than the used grid that shares the same edge with the target edge by 1.

[0071] Execute step 1053, take the target edge as the new reference edge, traverse other unit edges, compare the collinearity of the normals of the current unit edge and the reference edge, and find the unit edge with the largest collinearity.

[0072] Execute step 1054 and repeat steps 1052-1053 until reaching the right bank.

[0073] Execute step 1060, taking each grid upstream of the river channel as the starting grid and the grid cell edge upstream of the river channel as the starting edge, and continuously tracing the cell edge with the largest degree of collinearity of normals downstream, and sequentially determining the two-dimensional index numbers of the passed grids to achieve structuring of all grid numbers.

[0074] Execute step 1070, define the line connecting the center points of the grids with the same longitudinal number and the center points of the transverse outer unit edges as transverse lines, and define the line connecting the center points of the grids with the same transverse number and the center points of the longitudinal outermost unit edges as longitudinal lines. Use the structured numbering system to traverse all grids and calculate the distance of each grid center point from its respective longitudinal starting unit edge and the transverse distance from its respective left bank unit edge, as well as the length of the transverse and longitudinal lines.

[0075] Execute step 1080 to establish a one-to-one correspondence between the key cross-section points of the upstream and downstream cross-sections, including the following sub-steps:

[0076] Execute step 1080 to establish a corresponding relationship between the upstream and downstream sections;

[0077] Execute step 1080 to segment the upstream and downstream sections based on their respective lowest elevation points, and continue segmenting the latest two groups of left and right section points based on their respective lowest elevation points.

[0078] Execute step 1080 and repeat steps 1081-1082 until no further segmentation is possible.

[0079] Execute step 1090, and perform linear interpolation based on the corresponding relationship and the position of the transverse line, taking into account the change in cross-sectional width according to the distance. The linear interpolation formula is:

[0080]

[0081] Among them, y represents the distance from the left bank, z represents the elevation, u and d represent the upstream and downstream respectively, i represents the order number of the corresponding cross-section points in the corresponding relationship table, ω is the weight coefficient, and c is the width scaling coefficient. The calculation formula is:

[0082]

[0083] Among them, B, B u 、B d They are the width of the current transverse line, the upstream section width and the downstream section width respectively.

[0084] Execute step 1100, use the structured numbering system to traverse all grids, use the interpolated cross-section data at the horizontal line where the grid is located, and assign the elevation attribute of the grid center point. The calculation formula of the elevation z is

[0085]

[0086] Among them, z k Indicates the elevation of the kth section point, y k Indicates the distance between the kth section point and the left bank. The subscripts k and k+1 indicate the section point numbers generated by interpolation at the transverse line. k <y<y k+1 Indicates that the current grid center point is between two consecutive section points generated by interpolation at the transverse line.

[0087] Example 2

[0088] The present invention provides a method for generating a two-dimensional hydrodynamic river grid terrain based on cross-sectional measurement data. The specific technical solution is as follows:

[0089] like Figure 2 As shown, a method for generating a two-dimensional hydrodynamic river grid terrain based on cross-section measurement data includes the following steps:

[0090] Step 1: Based on the location of the measured cross-section data, high-resolution remote sensing imagery, and shoreline or levee data, draw grid control lines, including longitudinal and transverse control lines. Longitudinal control lines primarily refer to the left and right shorelines, while transverse control lines include upstream and downstream cross-sections and internal control lines perpendicular to the river flow. In particular, increasing the number of transverse control lines is necessary to improve grid quality at river bends. Transverse control lines divide the river into several sections, with each section surrounded by two transverse and two longitudinal control lines.

[0091] Step 2: For each river section, generate the same number of control points on the horizontal and vertical control lines, and then generate a quadrilateral mesh. The quadrilateral mesh generated in this step is an unstructured mesh, that is, the topological relationship is unstructured.

[0092] Step 3: Traverse the above unstructured grid and calculate the normal direction angle α of each grid cell edge, that is, the angle between the normal and the x-axis, in the range of (-π,π]. The normal direction of the cell edge is from the cell with a larger number to the cell with a smaller number by default. The normal direction of the cell edge at the boundary is pointed outward by default. Assume that the coordinates of the two endpoints of the cell edge are (x1, y1) and (x2, y2) respectively. The formula for calculating the normal direction angle of the cell edge is:

[0093]

[0094] Step 4: To clarify the relative positional relationships of each grid, the topological relationship of the unstructured grid is structured. This means that the grid number (hereinafter referred to as the global number for ease of description) is converted into a two-dimensional index number with the longitudinal direction of the river (positive direction from upstream to downstream) and the transverse direction (positive direction from left bank to right bank) as the axis direction. The upstream left bank grid point is set as the coordinate origin, and the grid containing this point is set as the starting grid, numbered (1,1). The left bank unit edge of this grid is selected as the transverse starting edge, and the upstream unit edge of this grid is selected as the longitudinal starting edge.

[0095] Step 5: Take the horizontal starting edge as the reference edge (located on the left bank), traverse the other unit edges of the grid where it is located (that is, the starting grid with the two-dimensional index number (1,1)), compare the collinearity of the normal of the current unit edge and the reference edge, and find the unit edge with the largest collinearity. For the sake of convenience, the unit edge with the largest collinearity is called the target edge. At this time, add 1 to the horizontal number in the two-dimensional index number of another grid other than the starting grid that shares the same edge with the target edge, that is, the number is (2,1). Use the target edge as the new reference edge and repeat step 5 until you reach the right bank. At this point, the row of grids upstream of the river completes the structured numbering. Among them, the degree of collinearity of the normal is expressed by the deviation angle d α To express it, the calculation formula is

[0096]

[0097] Where, α b , α c They are the normal direction angles of the base edge and the current edge respectively.

[0098] Step 6: Similar to Step 5, starting with each grid at the farthest upstream of the river and the edge of the grid cell at the farthest upstream, the 2D index numbers of each grid are determined sequentially by tracing the edge of the cell with the highest degree of collinearity of normals downstream, thus structuring all grid numbers. At this point, each grid, in addition to its original global number, also has a 2D index number that indicates its relative position within the entire grid set. For example, the 2D index number of the grid with global number 235 is (4,34), indicating that it is located in the 34th row from the upstream section and the 4th column from the left bank.

[0099] Step 7: Define the lines connecting the center points of the grids with the same longitudinal number and the center points of the outermost horizontal edge (left and right banks) as transverse lines. Define the lines connecting the center points of the grids with the same transverse number and the center points of the outermost vertical edge (upstream and downstream sections) as longitudinal lines. Using the structured numbering system, traverse all grids and calculate the distance from each grid center point to the respective longitudinal starting edge of the unit and the transverse distance from the respective left bank edge of the unit, as well as the lengths of the transverse and longitudinal lines.

[0100] Step 8: Establish a one-to-one correspondence between the key cross-section points of the upstream and downstream sections for subsequent interpolation calculations. The left and right bank cross-section points are key elements, and a correspondence is first established between the upstream and downstream sections. Furthermore, while establishing the upstream and downstream correspondence at the lowest elevation point, the upstream and downstream sections are segmented at their respective lowest elevation points. The newly segmented left and right sets of cross-section points are further segmented at their respective lowest elevation points. While establishing the upstream and downstream correspondence at the newly obtained lowest elevation point, the segmentation and correspondence process is repeated until no further segmentation is possible.

[0101] Step 9: Based on the correspondence between the upstream and downstream section points established in step 8, perform linear interpolation at the position of the transverse line obtained in step 7 according to the distance while taking into account the change in section width.

[0102]

[0103] Where y represents the distance from the left bank; z represents the elevation; superscripts u and d represent upstream and downstream, respectively; subscript i represents the corresponding cross-section points upstream and downstream; ω is the weight coefficient, which is equal to the mileage of the transverse line to be interpolated (the distance from the upstream section) and the mileage between the upstream and downstream sections; c is the width scaling coefficient, which is calculated as follows:

[0104]

[0105] Where, B, B u 、B d They are the width of the current transverse line, the upstream section width and the downstream section width respectively.

[0106] Step 10: Using the structured numbering system, traverse all grids and use the interpolated cross-section data (generated in step 9) at the transverse line where the grid is located to assign the elevation attribute of the grid center point. The calculation formula is:

[0107]

[0108] Where, subscripts k and k+1 represent the interpolation points on the transverse line (numbered starting from the left bank), y k <y<y k+1 Indicates that the current grid center point is between two consecutive section points generated by interpolation at the transverse line.

[0109] By adopting the above technical solution, the characteristics of the present invention are mainly reflected in the following aspects:

[0110] (1) The basic grid adopts the unstructured grid topology that is more commonly used in practice. By structuring it, the relative position of each grid space can be determined, which is more compatible with the existing cross-section data structure (based on mileage-distance-left bank distance-elevation) and facilitates subsequent interpolation.

[0111] (2) In terms of spatial interpolation, between the key elements of adjacent upstream and downstream sections, such as the left and right banks, the lowest point, the second lowest point, the second lowest point, and so on, the corresponding interpolation relationship is automatically established to fully consider the key information of the cross section.

[0112] Based on the above characteristics, compared with the existing river terrain generation technology, the technical method proposed in this patent can fully consider the key morphological elements of the cross section and their changes, especially the underwater part, and directly assign elevation attributes based on the unstructured body-fitting grid. The results are more suitable for the calculation of two-dimensional hydrodynamic models of rivers.

[0113] Example 3

[0114] A method for generating two-dimensional hydrodynamic river channel grid terrain based on cross-sectional measurement data is implemented as follows:

[0115] Step 1: Between the upstream and downstream measurement sections, such as Figure 2 As shown, the vertical and horizontal control lines of the grid are drawn in combination with high-resolution remote sensing imagery. At river bends, the number of horizontal control lines is increased to improve grid quality. In this embodiment, the river section is divided into nine sections by horizontal control lines, each surrounded by two horizontal control lines and two vertical control lines. Tables 1 and 2 respectively show the measurement data for the given upstream and downstream sections. The first row in the table shows the distance from the left bank, and the second row shows the elevation, both in meters.

[0116] Table 1 Upstream section measurement data

[0117] y 0.0 2.6 2.6 5.2 54.2 56.8 59.4 59.4 61.9 69.7 72.3 72.3 74.8 74.8 77.4 80.0 z 8.1 7.1 6.1 5.1 4.1 4.1 3.1 2.1 1.1 1.1 2.1 3.1 4.1 5.1 7.1 8.1

[0118] Table 2 Downstream section measurement data

[0119] y 0.0 2.9 2.9 5.9 5.9 8.8 8.8 11.7 20.5 23.5 23.5 26.4 29.3 32.3 85.0 88.0 88.0 90.9 z 7.2 6.2 5.2 4.2 3.2 2.2 1.2 0.2 0.2 1.2 2.2 3.2 3.2 3.9 4.2 5.2 6.2 7.2

[0120] Step 2: For each river section, set an equal number of control points on the horizontal and vertical control lines, and then generate a quadrilateral grid, such as Figure 3 Partial display of river section ④ in the middle. Figure 4 is an unstructured grid at a certain resolution of this embodiment.

[0121] Step 3: Traverse all grids and calculate the direction angle α of the normal line of each grid cell edge (from the cell with a larger number to the cell with a smaller number), such as Figure 5 shown.

[0122] Step 4: Set the left bank grid point on the uppermost stream as the coordinate origin, and the grid where this point is located as the starting grid, number it as (1,1), and select the left bank unit edge of the grid as the horizontal starting edge, and the upstream unit edge of the grid as the vertical starting edge, as shown in the following example: Figure 6shown.

[0123] Step 5: Using the starting horizontal edge as the reference edge, traverse the other cell edges in the grid where it resides (i.e., the starting grid with the 2D index number (1,1)). Compare the collinearity of the normals of the current cell edge with the reference edge. Find the cell edge with the greatest collinearity, defining it as the target edge. Increase the horizontal index of the 2D index of the grid other than the starting grid that shares a common edge with the target edge by 1, resulting in a new index number (2,1). Using the target edge as the new reference edge, repeat Step 5 until you reach the right bank. This completes the structural numbering of the upstream row of grids in the river channel.

[0124] Step 6: Compare to step 5, take each grid in the upper reaches of the river as the starting grid, take the grid cell edge in the upper reaches of the river as the starting edge, and continuously trace the cell edge with the largest degree of collinearity of normal lines downstream, and set the two-dimensional index number of the passed grids in sequence to achieve the structured numbering of all grids. After steps 5 and 6, the local example of grid structured numbering is as follows Figure 7 shown.

[0125] Step 7: If Figure 8 As shown in the figure, the lines connecting the center points of the grids with the same longitudinal number and the center points of the outermost horizontal edge (left and right banks) are defined as transverse lines, and the lines connecting the center points of the grids with the same transverse number and the center points of the outermost vertical edge (upstream and downstream sections) are defined as longitudinal lines. Using the structured numbering system, all grids are traversed, and the distance from each grid center point to the respective longitudinal starting element edge and the transverse distance from the respective left bank element edge, as well as the length of the transverse and longitudinal lines, are calculated to prepare for subsequent cross-section interpolation calculations.

[0126] Step 8: The left and right bank section points are used as key elements, and a corresponding relationship is first established between the upstream and downstream sections. In addition, while establishing the upstream and downstream corresponding relationship at the lowest elevation point, the upstream and downstream sections are segmented at their respective lowest elevation points, and the latest left and right groups of section points segmented are further segmented at their respective lowest elevation points. While establishing the upstream and downstream corresponding relationship at the newly obtained lowest elevation point, the above segmentation and corresponding relationship establishment process is repeated until no further segmentation is possible. In this embodiment, the upstream and downstream corresponding relationship of the section points is shown in Table 3 and Figure 9 shown.

[0127] Table 3 One-to-one correspondence between upstream and downstream sections

[0128]

[0129]

[0130] Step 9: Based on the correspondence between the upstream and downstream section points established in step 8, linear interpolation is performed at the position of the transverse line obtained in step 7 according to the distance and taking into account the change in section width to obtain the cross-sectional shape data at the transverse line.

[0131] Step 10: Using the structured numbering system, traverse all grids, use the cross-sectional shape data (generated by step 9) at the transverse line where the grid is located to interpolate the elevation attributes of the grid center point through spatial interpolation. The interpolation results are as follows: Figure 10 shown.

[0132] In order to better understand the present invention, the above is described in detail in conjunction with the specific embodiments of the present invention, but it is not intended to limit the present invention. Any simple modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention. Each embodiment in this specification focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the system embodiment, since it basically corresponds to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

Claims

1. A method for generating hydrodynamic river channel grid terrain based on cross-sectional measurement data, comprising obtaining the location of the measurement cross-sectional data, high-resolution remote sensing images, and shoreline or levee data, and further comprising the following steps: Step 1: Based on the acquired data, draw the grid division control lines, including longitudinal control lines and transverse control lines; Step 2: For each river section, generate the same number of control points on the longitudinal control line and the transverse control line to generate a quadrilateral grid, where the quadrilateral grid is an unstructured grid; Step 3: traverse the unstructured grid and calculate the normal direction angle α of each grid cell edge, that is, the angle between the normal and the x-axis direction; Step 4: Structuring the topological relationship of the unstructured grid, and converting the grid number into a two-dimensional index number with the longitudinal direction and the transverse direction of the river channel as the axis direction; Step 5: Using the horizontal starting edge as the reference edge, traverse the other unit edges in the grid where it is located, compare the collinearity of the normals of the current unit edge and the reference edge, and find the unit edge with the largest collinearity; Step 6: Take each grid in the upstream of the river as the starting grid, and the edge of the grid cell at the most upstream of the river as the starting edge. By continuously tracing the edge of the cell with the largest degree of collinearity of normals downstream, the 2D index numbers of the passed grids are determined in sequence to achieve the structuring of all grid numbers. Step 7: Define the line connecting the center points of the grids with the same vertical number and the center points of the outermost unit edges on the left and right banks as the horizontal line, and define the line connecting the center points of the grids with the same horizontal number and the center points of the outermost unit edges on the upstream and downstream sides as the vertical line; Step 8: Establish a one-to-one correspondence between the key cross-section points of the upstream and downstream sections; Step 9: Based on the corresponding relationship and the position of the transverse line, linear interpolation is performed according to the distance while taking into account the change in cross-section width; Step 10: Use a structured numbering system to traverse all grids, interpolate the cross-section data at the transverse line where the grid is located, and assign the elevation attribute of the grid center point.

2. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 1, characterized in that: The longitudinal control lines are the left and right bank lines, and the transverse control lines include the upstream and downstream cross sections and the internal control lines perpendicular to the flow direction of the river. The transverse control lines divide the river into N sections, and each river section is surrounded by two transverse control lines and two longitudinal control lines.

3. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 2, characterized in that: The normal direction of the grid unit edge is from the unit with a larger number to the unit with a smaller number by default, wherein the normal direction of the grid unit edge at the boundary is outward by default.

4. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 3, characterized in that: The coordinates of the two endpoints of the grid cell edge are (x1, y1) and (x2, y2), and the normal direction angle of the cell edge is calculated as follows:

5. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 4, characterized in that: The step 5 also includes setting the upstream left bank grid point as the coordinate origin, taking the grid where this point is located as the starting grid, numbering it as (1,1), and selecting the left bank unit edge of the grid as the horizontal starting edge and the upstream unit edge of the grid as the vertical starting edge.

6. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 5, characterized in that: The step 5 includes the following sub-steps: Step 51: traverse other unit edges of the starting grid, compare the collinearity of the normals of the current unit edge and the reference edge, and find the unit edge with the largest collinearity as the target edge; Step 52: adding 1 to the horizontal number of the two-dimensional index number of another grid other than the used grid that shares the same edge with the target edge; Step 53: Use the target edge as the new reference edge, traverse other unit edges, compare the collinearity of the normals of the current unit edge and the reference edge, and find the unit edge with the largest collinearity; Step 54: Repeat steps 52-53 until you reach the right bank.

7. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 6, characterized in that: The degree of collinearity of normals is expressed as the deviation angle d a To express it, the calculation formula is Among them, α b , α c They are the normal direction angles of the base edge and the current edge respectively.

8. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 7, characterized in that: The step 7 also includes using a structured numbering system to traverse all grids, calculate the distance between each grid center point and its respective longitudinal starting unit edge and the lateral distance from its respective left bank unit edge, and the length of the lateral and longitudinal lines.

9. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 8, characterized in that: The step 8 includes the following sub-steps: Step 81: Establishing a corresponding relationship between the upstream and downstream sections; Step 82: Segment the upstream and downstream sections by their respective lowest elevation points, and continue segmenting the latest two groups of left and right section points by their respective lowest elevation points; Step 83: Repeat steps 81-82 until no further segmentation is possible.

10. The method for generating hydrodynamic river grid terrain based on cross-sectional measurement data according to claim 9, characterized in that: The linear interpolation formula is Among them, y represents the distance from the left bank, z represents the elevation, u and d represent the upstream and downstream respectively, i represents the order number of the corresponding cross-section points in the corresponding relationship table, ω is the weight coefficient, and c is the width scaling coefficient. Among them, B, B u 、B d They are the width of the current transverse line, the upstream section width and the downstream section width respectively.

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