Method for measuring river bank line and river level height based on three-dimensional laser point cloud

Abstract

The application discloses a kind of river bank line and river level height measurement method based on three-dimensional laser point cloud, comprising the following steps: erecting laser radar on river, collecting the point cloud in target area, clustering extraction river bank line point cloud, obtaining the two-dimensional projection point cloud of river bank line point cloud, based on concave hull algorithm obtains the point cloud coordinate of river bank profile, creates water surface elevation table;The water surface elevation table created in, horizontal table header indicates the position of river bank profile in river, vertical table header indicates the x coordinate, z coordinate of corresponding position.The application can not only measure the horizontal position of river bank line compared with traditional method, but also obtain its relative height, further fit accurate river water level equation on this basis, provide information support for hydrological measurement and ship overheight early warning system.

Description

Technical Field

[0001] This invention relates to a method for measuring riverbank lines and river level height based on three-dimensional laser point clouds, belonging to the field of river hydrological mapping. Technical field. Background Technology

[0002] Real-time measurement of riverbanks and river level is crucial for obtaining hydrological information and plays a vital role in flood control, vessel height warning, and bridge protection. Previously, river level measurements were often conducted manually, such as with manual water gauges. To handle large-scale water level fluctuations, multiple water gauges were typically deployed in a group to ensure both high and low water levels could be measured. Indirect observation methods, primarily using various level gauges such as float gauges, pressure gauges, and ultrasonic gauges, were also employed. However, these methods are complex. In addition, research has been conducted on riverbank extraction methods based on two-dimensional images. Edge detection methods used include the Sobel operator, Canny operator, Roberts operator, and Prewitt operator. The basic principle is to calculate pixel step changes using differential operators, analyze grayscale transitions to determine edges in the image, and ultimately extract the riverbank. However, image recognition is easily affected by ambient light and cannot work at night. Reflection of light from the river surface also affects riverbank extraction. More importantly, due to dimensional mapping, the riverbank extracted from two-dimensional images lacks height information, rendering the extracted riverbank contour meaningless in some situations. For example, in a vessel over-height early warning system, it cannot provide a benchmark for real-time calculation of changes in the vessel's height on the horizontal plane.

[0003] With the development and widespread adoption of LiDAR in recent years, acquiring 3D point cloud information of objects has become increasingly convenient, and research on point clouds has become a hot topic in the field of computer vision technology. The 3D point cloud output by LiDAR has many advantages over 2D images: it can obtain accurate 3D geometric information of the target, avoid data loss caused by dimension transformation, and is less affected by changes in external lighting and imaging distance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method for measuring riverbank lines and river level height based on three-dimensional laser point clouds. Compared with traditional methods, this method can not only measure the horizontal position of the riverbank line but also obtain its relative height. Based on this, an accurate equation for the river level is further fitted, providing information support for hydrological surveys and ship over-altitude early warning systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for measuring riverbank line and river level height based on three-dimensional laser point clouds includes the following steps:

[0007] Step 1: Install lidar on the river channel;

[0008] Step 2: Collect point cloud data within the target area: Use the lidar system set up in Step 1 to collect point cloud data within the target area;

[0009] Step 3: Clustering and extracting point cloud of the riverbank: Using the Euclidean clustering principle, extract the point cloud clusters near the riverbank to obtain the riverbank point cloud;

[0010] Step 4: Obtain the two-dimensional projection point cloud of the riverbank point cloud: Project the riverbank point cloud obtained in Step 3 one by one into the vertical plane XOZ perpendicular to the river surface, thereby obtaining the corresponding two-dimensional projection point cloud of the riverbank.

[0011] Step 5: Obtain the point cloud coordinates of the riverbank contour based on the concave hull algorithm: The concave hull algorithm is used to process the two-dimensional projection point cloud of the riverbank to create the concave hull of the two-dimensional projection point cloud of the riverbank, thereby obtaining the point cloud coordinates of the riverbank contour.

[0012] Step 6: Create a water surface elevation table: Based on the point cloud coordinates of the riverbank outline obtained in Step 5, create a water surface elevation table; in the created water surface elevation table, the horizontal header represents the position of the riverbank outline in the river channel, and the vertical header represents the x and z coordinates of the corresponding position.

[0013] Preferably, the step one of setting up a lidar on the river channel specifically includes: setting up a lidar at the middle position of the river bridge, and establishing an XYZ three-dimensional coordinate system in the three-dimensional space where the lidar is located, wherein: the origin O of the XYZ three-dimensional coordinate system is set on the lidar body, the X direction is the vertical direction of the river water surface, the Y direction is the horizontal direction of the river water surface, and the Z direction is the direction perpendicular to the river water surface.

[0014] Preferably, in step two, after acquiring the point cloud within the target area using the lidar, the point cloud is divided into two parts: a left point cloud and a right point cloud, based on the sign of the y-coordinate value output by the lidar.

[0015] Preferably, in step three, when performing clustering and extraction of point cloud clusters near the riverbank, the left and right point clouds need to be processed separately to obtain the corresponding left and right riverbank point clouds.

[0016] Preferably, in step four, when performing the two-dimensional projection of the riverbank point cloud, the left and right riverbank point clouds need to be projected onto the XOZ vertical plane respectively, so as to obtain the two-dimensional projection point cloud of the three-dimensional point cloud of the left and right riverbank on the XOZ vertical plane.

[0017] Preferably, in step five, when using the concave hull algorithm to process the two-dimensional projected point cloud of the riverbank, it is necessary to create concave hull lines for the two-dimensional projected point clouds of the left and right riverbanks respectively, so as to obtain the point cloud coordinates of the left and right riverbanks.

[0018] Preferably, in step six, the created water surface elevation table includes a left water surface elevation table for the left side of the river and a right water surface elevation table for the right side of the river.

[0019] Preferably, after completing the creation of the water surface elevation table described in step six, the method further includes step I: ship over-limit warning, which specifically includes the following steps:

[0020] Step I-1: Generate the equations of the left and right riverbank outlines.

[0021] The equation of the straight line of the left riverbank profile satisfies:

[0022]

[0023] The equation of the right riverbank profile straight line satisfies:

[0024]

[0025] In the formula: , , The constant is obtained by fitting the coordinates of four point clouds of the riverbank outline in the left-side water surface elevation table described in step six.

[0026] , , The constant is obtained by fitting the coordinates of four point clouds of the riverbank outline in the right-hand water surface elevation table described in step six.

[0027] Step I-2: Calculate the distance d from the ship's hull to the left and right riverbanks.

[0028] Calculate the distances of the ship's hull relative to the left and right riverbanks respectively. , To determine the proximity of the ship's hull to the left and right riverbanks;

[0029] Distance of the hull relative to the left bank satisfy:

[0030]

[0031] Distance of the hull relative to the right bank satisfy:

[0032]

[0033] In the formula: (x0, y0) represents the position of the centroid of the point cloud of the ship's hull;

[0034] Step I-3: Calculate the height of the water surface at the location of the ship.

[0035] Calculate the height of the water surface at the location of the ship. First, select the appropriate water level table based on the ship's proximity to the left and right riverbanks: when the ship is closer to the left riverbank, calculate the water level at the ship's location. Select the left-hand water surface elevation table when the water surface is at an angle, and vice versa;

[0036] The height of the water surface at the location of the ship Calculated using the following formula:

[0037]

[0038] In the formula: (x1, z1) and (x2, z2) are the coordinates of two points on the riverbank outline in the selected water surface elevation table;

[0039] Step I-4: Predict the increase in water level when the ship reaches the bridge.

[0040]

[0041] In the formula: This indicates the distance of the lidar relative to the water surface below its installation location;

[0042] Step I-5: Over-limit alarm judgment

[0043] After calculating the expected height h of the ship under the bridge, the expected height h is compared with a preset threshold to determine whether to issue an alarm; the formula for calculating the expected height h of the ship under the bridge is:

[0044]

[0045] In the formula: This represents the largest z-coordinate value in the current hull point cloud cluster.

[0046] Preferably, after completing the creation of the water surface elevation table described in step six, the method further includes step II, creating the horizontal plane equation of the river water:

[0047]

[0048] The equation of the river's horizontal surface passes through the normal vector of the river's horizontal surface. And the coordinates (x0, y0, z0) of a single point on the river's horizontal surface are used to determine this, where:

[0049]

[0050] normal vector The coordinates (x0, y0, z0) of a single point on the river's horizontal surface are obtained through the following steps:

[0051] Step II-1: Calculate the average pitch angle of the river surface and the coordinates of a single point on the river surface.

[0052] The average pitch angle of the river surface is The calculation formula is:

[0053]

[0054] In the formula: The angle of inclination of the vertical drop line of the left riverbank. The angle of inclination of the vertical drop line of the right riverbank;

[0055] The coordinates of a single point on the river's horizontal surface are (x0, y0, z0), where:

[0056]

[0057]

[0058]

[0059] In the formula: ( ) represents the coordinates of a single point on the vertical drop line of the left riverbank. () represents the coordinates of a single point on the vertical drop line of the right riverbank.

[0060] Step II-2: Calculate the normal vector and vector angle of the river's horizontal plane.

[0061] The vector angle of the normal vector to the river surface is (α+90°). ○ ), Calculation formula:

[0062]

[0063] Step II-3: Calculate the coefficients of the equation for the river surface.

[0064] Apply the vector angle of the normal vector of the river surface obtained in step II-2 to the normal vector of the river surface. From this, the coefficients A, B, and C can be calculated: A = -tg(α), B = 0, C = 1, which clearly satisfies: .

[0065] By applying the coordinates (x0, y0, z0) of a single point on the river's horizontal surface obtained in step II-1 to the equation of the river's horizontal surface, the coefficient D can be solved: .

[0066] Furthermore, in step II-1, the equation of the vertical drop line of the left bank of the river channel is:

[0067]

[0068] The equation of the vertical drop line of the right bank of the river is:

[0069]

[0070] In the formula, ( ) represents the coordinates of the farthest endpoint of the left bank of the river detected by the lidar. () represents the coordinates of the nearest endpoint of the left bank of the river detected by the lidar; ) represents the coordinates of the farthest endpoint of the right riverbank detected by the lidar. () represents the coordinates of the nearest endpoint of the right riverbank detected by the lidar;

[0071] The coordinates of a single point on the vertical drop line of the left riverbank are ( );

[0072] The coordinates of a single point on the vertical drop line of the right riverbank are ( );

[0073] , .

[0074] Based on the above-mentioned technical objectives, the present invention has the following advantages compared with the prior art:

[0075] This invention can more accurately extract the position coordinates of the riverbank outline, unaffected by external light. Based on this, it can predict whether the height of a ship reaching the bridge exceeds the limit, and can also fit an accurate equation of the river level to know the water level difference at various points within 100 meters of the bridge. Attached Figure Description

[0076] Figure 1 This is a flowchart of the measurement method described in this invention.

[0077] Figure 2 This is a schematic diagram of the lidar coordinate system and imaging.

[0078] Figure 3 The figure shows the point clouds of the left and right riverbanks separated by the positive and negative y-coordinates. In the figure: (a) represents the point cloud of the left riverbank and (b) represents the point cloud of the right riverbank.

[0079] Figure 4 The diagram shows the left riverbank point cloud cluster obtained after clustering. In the figure, (a) represents the front view of the left riverbank point cloud cluster, and (b) represents the side view of the left riverbank point cloud cluster.

[0080] Figure 5 The diagram shows the right riverbank point cloud cluster obtained after clustering. In the figure: (a) is the front view of the right riverbank point cloud cluster, and (b) is the side view of the right riverbank point cloud cluster.

[0081] Figure 6 The projection of the point clouds of the left and right riverbanks onto the XOZ plane and the envelopes extracted by the concave hull algorithm are shown in the figure. In the figure, (a) represents the envelope of the point cloud of the left riverbank and (b) represents the envelope of the point cloud of the right riverbank.

[0082] Figure 7 This demonstrates the principle for calculating the average tilt angle α of the river surface. Detailed Implementation

[0083] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specifically stated, the relative arrangement, expressions, and values ​​of components and steps set forth in these embodiments do not limit the scope of the present invention. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0084] like Figure 1 As shown, the method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to the present invention includes the following steps:

[0085] Step 1: Install lidar on the river channel;

[0086] Specifically, such as Figure 2 As shown, a lidar is installed in the middle of the river bridge, and a three-dimensional XYZ coordinate system is established based on the three-dimensional space where the lidar is located. The origin O of the XYZ coordinate system is set on the lidar body (it can be set on the laser transmitter head), and the X-axis represents the vertical direction of the river surface (i.e., the vertical direction of the water surface). Figure 2 (in the forward and backward direction), Y direction is the transverse direction of the river surface (i.e., the attached direction). Figure 2 (The left and right directions in the middle), Z direction is the direction perpendicular to the river surface (i.e., the attached direction). Figure 2 (the vertical direction in the middle).

[0087] The device installed in the middle of the bridge in the picture is the RoboSense RS-LiDAR-M1 laser radar.

[0088] Step 2: Collect point cloud data within the target area: Use the lidar system set up in Step 1 to collect point cloud data within the target area; after collecting the point cloud data using the lidar, divide the point cloud into two parts—left and right—based on the sign of the y-coordinate value output by the lidar. The result is as follows: Figure 3 As shown.

[0089] The point cloud obtained during data collection contains all data on trees, roads, vehicles, etc., within a 30-50 meter range on both sides of the riverbank. However, only the point cloud clusters of the riverbank area are needed to extract the riverbanks. Therefore, it is necessary to use the Euclidean clustering principle to further extract the point cloud clusters near the left and right riverbanks. The specific steps are shown in step three.

[0090] Step 3: Clustering and Extracting Riverbank Point Clouds: Using Euclidean clustering, point cloud clusters near the riverbank are extracted to obtain the riverbank point cloud. In this invention, when clustering and extracting point cloud clusters near the riverbank, the left and right point clouds need to be processed separately to obtain the corresponding left and right riverbank point clouds. The maximum number of cluster points is set to 35,000, the minimum number of cluster points is set to 2,500, and the nearest neighbor search radius is set to 5 meters. The results are as follows... Figure 4 As shown.

[0091] The process of a known Euclidean clustering algorithm is as follows:

[0092] Step 1: Find a point p in space 11 Use a KD-Tree to find the n nearest points to it, and determine the distance from these n points to p. 11 The distance. Points p whose distance is less than the threshold r. 12 , p 13 , p 14 ...place it in class Q;

[0093] Step 2, in Q(p) 11 ) found a little bit of p in it 12 Repeat step 1;

[0094] Step 3, in Q(p) 11 , p 12 Find a point, repeat step 1, and find p. 22 , p 23 , p 24 ...put them all into QQ;

[0095] Step 4: When no more points can be added to Q, the search is complete.

[0096] Step 4: Obtain the 2D projection point cloud of the riverbank point cloud: Project the riverbank point cloud obtained in Step 3 one by one into the vertical plane XOZ perpendicular to the river surface, thereby obtaining the corresponding 2D projection point cloud of the riverbank.

[0097] In this invention, when performing a two-dimensional projection of the riverbank point cloud, the left and right riverbank point clouds need to be projected onto the XOZ vertical plane respectively to obtain the two-dimensional projection point clouds of the three-dimensional point clouds of the left and right riverbanks onto the XOZ vertical plane. The result is as follows: Figure 5 As shown.

[0098] Step 5: Obtain the point cloud coordinates of the riverbank contour based on the concave hull algorithm: The concave hull algorithm is used to process the two-dimensional projection point cloud of the riverbank to create the concave hull of the two-dimensional projection point cloud of the riverbank, thereby obtaining the point cloud coordinates of the riverbank contour.

[0099] In this invention, when using the concave hull algorithm to process the two-dimensional projected point cloud of the riverbank, it is necessary to create concave hull lines for the two-dimensional projected point clouds of the left and right riverbanks respectively, so as to obtain the point cloud coordinates of the left and right riverbanks.

[0100] Specifically, the two-dimensional projection point clouds of the left and right riverbanks are used to create concave envelopes using a concave hull algorithm. Then, the lower half of the envelope is extracted based on the changing trends of the x and z coordinates, and this lower half is used as the riverbank contour. In the program, these contour points on the concave envelope are stored in an array arranged clockwise. Therefore, the points whose x-coordinates continuously increase are extracted to form the point cloud of the riverbank contour. Figure 6 As shown.

[0101] The idea behind a known algorithm for solving concave envelopes based on Delaunay triangulation is as follows:

[0102] Step 1: Obtain the Delaunay triangulation M for the point set S. The triangulation is represented in standard Mesh form.

[0103] Step 2: Initialize all Edge objects for M, and calculate the length of the Edge and the set of adjacent triangles. Edges with two adjacent triangles are internal edges, edges with one adjacent triangle are boundary edges, and edges with zero adjacent triangles are edges that will degenerate during the calculation.

[0104] Step 3: Add all boundary edges with a length greater than R to the queue, and repeat the following process while the queue is not empty:

[0105] (1) Take out an edge E from the queue to obtain the unique adjacent triangle T of E.

[0106] (2) Find the other two edges E1 and E2 in T and remove their adjacent triangle set from T.

[0107] (3) Add the newly formed boundary edges in E1 and E2 with a length greater than R to the queue.

[0108] (4) Mark E as invalid. If E1 or E2 is degenerate, mark it as invalid as well.

[0109] Step 4: Collect all valid boundary edges, form an edge list, and output it.

[0110] Step 6: Create a water surface elevation table: Based on the point cloud coordinates of the riverbank outline obtained in Step 5, create a water surface elevation table; in the created water surface elevation table, the horizontal header represents the position of the riverbank outline in the river channel, and the vertical header represents the x and z coordinates of the corresponding position.

[0111] In this invention, the created water surface elevation table includes a left water surface elevation table for the left side of the river and a right water surface elevation table for the right side of the river.

[0112] During creation, for a point (x, y, z) on the river surface, its water level z is assumed to be the same as the height z of a point with the same x coordinate on the riverbank. Therefore, based on the point cloud coordinates of the left and right riverbank contours in the XOZ plane obtained in step three, left and right river surface elevation tables are created (which can be represented by a structure array or a two-dimensional array in the program), as shown in Tables 1 and 2 below:

[0113] Table 1. Examples of water surface elevation on the left side.

[0114] River location Point 1 Point 2 Point 3 Point 4 5 points … x-coordinate 25.77 meters 27.54 meters 27.81 meters 30.30 meters 32.08 meters … z-coordinate -4.67 meters -6.23 meters -6.33 meters -7.40 meters -7.98 meters …

[0115] Table 2 Example of water surface elevation on the right side

[0116] River location Point 1 Point 2 Point 3 Point 4 5 points … x-coordinate 30.51 meters 30.83 meters 31.87 meters 34.61 meters 34.96 meters … z-coordinate -5.80 meters -5.95 meters -6.36 meters -7.48 meters -7.63 meters …

[0117] In the table, the x-coordinate represents the horizontal forward distance from each point on the riverbank outline to the radar (transmitter), and the z-coordinate represents the vertical distance from each point on the riverbank outline to the radar (transmitter). Knowing this data allows for prediction of whether ships will exceed their height and collide with the bridge when they pass underneath, and also allows for the fitting of a mathematical equation to the river's horizontal plane, revealing the change in the river's height over a given distance (approximately 0-100 meters).

[0118] Based on the aforementioned water surface elevation table, this invention proposes two applications: one is for constructing a method for early warning of ship over-limit conditions, and the other is for constructing a horizontal equation for river water.

[0119] The aforementioned ship over-limit early warning method, as shown in step I, specifically includes the following steps:

[0120] Step I-1: Generate the equations of the left and right riverbank outlines.

[0121] The equation of the straight line of the left riverbank profile satisfies:

[0122]

[0123] The equation of the right riverbank profile straight line satisfies:

[0124]

[0125] In the formula: , , The constant is obtained by fitting the coordinates of four point clouds of the riverbank outline in the left-side water surface elevation table described in step six.

[0126] , , The constant is obtained by fitting the coordinates of four point clouds of the riverbank outline in the right-hand water surface elevation table described in step six.

[0127] Step I-2: Calculate the distance d from the ship's hull to the left and right riverbanks.

[0128] Calculate the distances of the ship's hull relative to the left and right riverbanks respectively. , To determine the proximity of the ship's hull to the left and right riverbanks;

[0129] Distance of the hull relative to the left bank satisfy:

[0130]

[0131] Distance of the hull relative to the right bank satisfy:

[0132]

[0133] In the formula: (x0, y0) represents the position of the centroid of the point cloud of the ship's hull;

[0134] Distance between the left and right riverbanks , The calculation results are as follows Figure 7 As shown.

[0135] Step I-3: Calculate the height of the water surface at the location of the ship.

[0136] Calculate the height of the water surface at the location of the ship. First, select the appropriate water level table based on the ship's proximity to the left and right riverbanks: when the ship is closer to the left riverbank, calculate the water level at the ship's location. Select the left-hand water surface elevation table when the water surface is at an angle, and vice versa;

[0137] The height of the water surface at the location of the ship Calculated using the following formula:

[0138]

[0139] In the formula: (x1, z1) and (x2, z2) are the coordinates of two points on the riverbank outline in the selected water surface elevation table;

[0140] Furthermore, in this invention, when calculating height... At that time, it was assumed that points on the river surface with the same longitudinal distance (x-coordinate value) from the radar had the same water surface height (z-coordinate).

[0141] Step I-4: Predict the increase in water level when the ship reaches the bridge.

[0142]

[0143] In the formula: This indicates the distance of the lidar relative to the water surface below its installation location. The distance between the lidar and the water surface (transmitter head) under the bridge is measured using surveying instruments such as total stations, laser rangefinders, and RTK receivers.

[0144] Step I-5: Over-limit alarm judgment

[0145] After calculating the expected height h of the ship under the bridge, the expected height h is compared with a preset threshold to determine whether to issue an alarm; the expected height h of the ship under the bridge satisfies:

[0146]

[0147] In the formula: This represents the largest z-coordinate value in the current hull point cloud cluster.

[0148] The system issues an alarm when the expected height h exceeds the allowed threshold.

[0149] The method for constructing the equation of the river's horizontal surface is shown in step II. The created equation of the river's horizontal surface is as follows:

[0150]

[0151] The equation of the river's horizontal surface passes through the normal vector of the river's horizontal surface. And the coordinates (x0, y0, z0) of a single point on the river's horizontal surface are used to determine this, where:

[0152]

[0153] normal vector The coordinates (x0, y0, z0) of a single point on the river's horizontal surface are obtained through the following steps:

[0154] Step II-1: Calculate the average pitch angle of the river surface and the coordinates of a single point on the river surface.

[0155] like Figure 7 As shown, the average pitch angle of the river surface is The calculation formula is:

[0156]

[0157] In the formula: The angle of inclination of the vertical drop line of the left riverbank. The angle of inclination of the vertical drop line of the right riverbank;

[0158] The coordinates of a single point on the river's horizontal surface are (x0, y0, z0), where:

[0159]

[0160]

[0161]

[0162] In the formula: ( ) represents the coordinates of a single point on the vertical drop line of the left riverbank. () represents the coordinates of a single point on the vertical drop line of the right riverbank.

[0163] The equation for the vertical drop line of the left bank of the river is:

[0164]

[0165] The equation of the vertical drop line of the right bank of the river is:

[0166]

[0167] In the formula, ( ) represents the coordinates of the farthest endpoint of the left bank of the river detected by the lidar. () represents the coordinates of the nearest endpoint of the left bank of the river detected by the lidar; ) represents the coordinates of the farthest endpoint of the right riverbank detected by the lidar. () represents the coordinates of the nearest endpoint of the right riverbank detected by the lidar;

[0168] The coordinates of a single point on the vertical drop line of the left riverbank are ( );

[0169] The coordinates of a single point on the vertical drop line of the right riverbank are ( );

[0170] , .

[0171] Step II-2: Calculate the normal vector and vector angle of the river's horizontal plane.

[0172] The vector angle of the normal vector to the river surface is (α+90°). ○ ), Calculation formula:

[0173]

[0174] Step II-3: Calculate the coefficients of the equation for the river surface.

[0175] Apply the vector angle of the normal vector of the river surface obtained in step II-2 to the normal vector of the river surface. From this, the coefficients A, B, and C can be calculated;

[0176] By applying the coordinates (x0, y0, z0) of a single point on the river's horizontal surface obtained in step II-1 to the equation of the river's horizontal surface, the coefficient D can be solved: .

[0177] Based on the water surface elevation tables on the left and right sides under the bridge in Tables 1 and 2, the equation of the river level is calculated as follows: .

[0178] In summary, due to the advantages of 3D point clouds over 2D images—namely, the ability to directly and accurately obtain the 3D geometric shape information of the target, avoiding data loss caused by dimensional transformation, and less susceptibility to changes in external lighting and imaging distance—the method of this invention can accurately obtain the point cloud coordinates of the riverbank contour and the river's elevation. It is unaffected by external light and data loss due to dimensionality. Therefore, the invented riverbank point cloud contour extraction method and river level extraction method are highly suitable for projects related to river channel and hydrological mapping.

[0179] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for measuring riverbank line and river level height based on three-dimensional laser point clouds, characterized in that, Includes the following steps: Step 1: Install lidar on the river channel; Step 2: Collect point cloud data within the target area: Use the lidar system set up in Step 1 to collect point cloud data within the target area; Step 3: Clustering and extracting point cloud of the riverbank: Using the Euclidean clustering principle, extract the point cloud clusters near the riverbank to obtain the riverbank point cloud; Step 4: Obtain the two-dimensional projection point cloud of the riverbank point cloud: Project the riverbank point cloud obtained in Step 3 one by one into the vertical plane XOZ perpendicular to the river surface, thereby obtaining the corresponding two-dimensional projection point cloud of the riverbank. Step 5: Obtain the point cloud coordinates of the riverbank contour based on the concave hull algorithm: The concave hull algorithm is used to process the two-dimensional projection point cloud of the riverbank to create the concave hull of the two-dimensional projection point cloud of the riverbank, thereby obtaining the point cloud coordinates of the riverbank contour. Step 6: Create a water surface elevation table: Based on the point cloud coordinates of the riverbank outline obtained in Step 5, create a water surface elevation table; in the created water surface elevation table, the horizontal header indicates the position of the riverbank outline in the river channel, and the vertical header indicates the x and z coordinates at the corresponding positions; the created water surface elevation table includes a left water surface elevation table for the left side of the river and a right water surface elevation table for the right side of the river; After completing the creation of the water surface elevation table described in step six, the process also includes step I: ship over-limit warning, which specifically includes the following steps: Step I-1: Generate the equations of the left and right riverbank outlines: The equation of the straight line of the left riverbank profile satisfies: ； The equation of the right riverbank profile straight line satisfies: ； In the formula: , , The constant is obtained by fitting the coordinates of four point clouds of the riverbank outline in the left-side water surface elevation table described in step six. , , The constant is obtained by fitting the coordinates of four point clouds of the riverbank outline in the right-hand water surface elevation table described in step six. Step I-2: Calculate the distance d from the ship's hull to the left and right riverbanks: Calculate the distances of the ship's hull relative to the left and right riverbanks respectively. , To determine the proximity of the ship's hull to the left and right riverbanks; Distance of the hull relative to the left bank satisfy: ； Distance of the hull relative to the right bank satisfy: ； In the formula: ( , () indicates the position of the centroid of the point cloud on the ship's hull; Step I-3: Calculate the water level height at the location of the ship: Calculate the height of the water surface at the location of the ship. First, select the appropriate water level table based on the ship's proximity to the left and right riverbanks: when the ship is closer to the left riverbank, calculate the water level at the ship's location. Select the left-hand water surface elevation table when the water surface is at an angle, and vice versa; The height of the water surface at the location of the ship Calculated using the following formula: ； In the formula: (x1, z1) and (x2, z2) are the coordinates of two points on the riverbank outline in the selected water surface elevation table; Indicates the longitudinal distance from the lidar; Step I-4: Predict the increase in water level when the ship reaches the bridge: ； In the formula: h0 represents the distance between the lidar and the water surface below its installation location, where h0 > 0; Step I-5: Over-limit alarm judgment: After calculating the expected height h of the ship under the bridge, the expected height h is compared with a preset threshold to determine whether to issue an alarm; the expected height h of the ship under the bridge is: ； In the formula: This represents the largest z-coordinate value in the current hull point cloud cluster.

2. The method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to claim 1, characterized in that, The specific steps of setting up a lidar on the river in step one include: setting up a lidar in the middle of the river bridge, and establishing an XYZ three-dimensional coordinate system in the three-dimensional space where the lidar is located. The origin O of the XYZ three-dimensional coordinate system is set on the lidar body, the X direction is the vertical direction of the river surface, the Y direction is the horizontal direction of the river surface, and the Z direction is the direction perpendicular to the river surface.

3. The method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to claim 2, characterized in that, Step 2: After acquiring the point cloud within the target area using the lidar, the point cloud is divided into two parts: the left point cloud and the right point cloud, based on the sign of the y-coordinate value output by the lidar.

4. The method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to claim 3, characterized in that, In step three, when clustering and extracting point cloud clusters near the riverbank, the left and right point clouds need to be processed separately to obtain the corresponding left and right riverbank point clouds.

5. The method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to claim 4, characterized in that, In step four, when performing the two-dimensional projection of the riverbank point cloud, the left and right riverbank point clouds need to be projected onto the XOZ vertical plane respectively to obtain the two-dimensional projection point clouds of the three-dimensional point clouds of the left and right riverbanks on the XOZ vertical plane.

6. The method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to claim 5, characterized in that, In step five, when using the concave hull algorithm to process the two-dimensional projected point cloud of the riverbank, it is necessary to create concave hull lines for the two-dimensional projected point clouds of the left and right riverbanks respectively, so as to obtain the point cloud coordinates of the left and right riverbanks.

7. The method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to claim 1, characterized in that, After completing step six in creating the water surface elevation table, step two is also included: creating the horizontal plane equation of the river water. ； The equation of the river's horizontal surface passes through the normal vector of the river's horizontal surface. And the coordinates (x0, y0, z0) of a single point on the river's horizontal surface are used to determine this, where: ； normal vector The coordinates (x0, y0, z0) of a single point on the river's horizontal surface are obtained through the following steps: Step II-1: Calculate the average pitch angle of the river surface and the coordinates of a single point on the river surface. The average pitch angle of the river surface is The calculation formula is: ； In the formula: The angle of inclination of the vertical drop line of the left riverbank. The angle of inclination of the vertical drop line of the right riverbank; The coordinates of a single point on the river's horizontal surface are (x0, y0, z0), where: ； ； ； In the formula: ( ) represents the coordinates of a single point on the vertical drop line of the left riverbank. () represents the coordinates of a single point on the vertical drop line of the right riverbank; Step II-2: Calculate the normal vector angle of the river's horizontal plane. The vector angle of the normal vector to the river surface is (α+90°). ○ ), then tg(α+90) ○ The direction of the normal vector is denoted as ; the calculation formula is: ； Step II-3: Calculate the coefficients of the equation for the river's horizontal surface: Apply the vector angle of the normal vector of the river surface obtained in step II-2 to the normal vector of the river surface. From this, the coefficients A, B, and C can be calculated: A = -tg(α), B = 0, C = 1, which clearly satisfies: ; By applying the coordinates (x0, y0, z0) of a single point on the river's horizontal surface obtained in step II-1 to the equation of the river's horizontal surface, the coefficient D can be solved: .

8. The method for measuring riverbank line and river level height based on three-dimensional laser point clouds according to claim 7, characterized in that, In step II-1, the equation of the vertical drop line of the left bank of the river is: ； The equation of the vertical drop line of the right bank of the river is: ； In the formula, , The X and Z coordinates represent the vertical drop line of the left bank of the river, respectively. These represent the X and Z coordinates of the farthest point of the left bank detected by the lidar, respectively. These represent the X and Z coordinates of the nearest endpoint of the left bank detected by the lidar, respectively. , The X and Z coordinates of the vertical drop line of the right bank of the river channel are respectively represented. These represent the X and Z coordinates of the farthest point of the right riverbank detected by the lidar, respectively. These represent the X and Z coordinates of the nearest endpoint of the right riverbank detected by the lidar, respectively. The coordinates of a single point on the vertical drop line of the left riverbank are ( ); The coordinates of a single point on the vertical drop line of the right riverbank are ( ); ， 。

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