A water surface image three-dimensional coordinate calibration method and device based on laser positioning

Abstract

The application discloses a water surface image three-dimensional coordinate calibration method and device based on laser positioning, and utilizes surveying equipment to obtain water level height and lens focal point coordinates; a plurality of laser spot center calibration point pixel coordinates formed by a plurality of laser emitters in a video field of view range and close to a boundary are obtained; actual coordinates or horizontal and vertical overturn angles of the laser spot center calibration points measured at a plurality of different elevations are obtained, and actual geodetic projection coordinates corresponding to the laser spot center calibration point pixel coordinates are determined; two-dimensional affine transformation is carried out according to the laser spot center calibration point pixel coordinates and the actual geodetic projection coordinates, so that actual longitude and latitude projection coordinates of pixel points in a video flow measurement image are obtained; three-dimensional calibration is carried out according to the water level height, the lens focal point coordinates and the actual longitude and latitude projection coordinates, so that actual longitude and latitude and elevation coordinates of any pixel point in the video flow measurement image at any water level are obtained, and millimeter-level accurate calibration of a water surface image without a shore base is realized.

Description

Technical Field

[0001] This application relates to the field of video flow measurement technology, specifically to a method and apparatus for three-dimensional coordinate calibration of water surface images based on laser positioning. Background Technology

[0002] Video flow measurement technology is an emerging non-contact method for monitoring water flow. Its basic principle is to calculate water flow velocity by analyzing the surface texture features of water flow (such as ripples, bubbles, and floating debris particles) in video images. This method uses image recognition algorithms to calculate the pixel displacement velocity of surface textures or particles, i.e., the number of pixels tracked by the surface texture or particles per unit time. Therefore, to calculate the actual movement velocity of surface textures or particles, the precise coordinates of each pixel within the video range are required.

[0003] Given a fixed camera orientation, there have been many methods for calibrating video pixel coordinates in the past. The most common method is shore-based calibration, which involves calibrating solid feature points (or positioning targets) on both sides of the river within the video field of view. By establishing the relationship between the pixel coordinates of the feature points and their actual latitude and longitude coordinates, the conversion relationship from pixel coordinates to actual coordinates is obtained, thereby determining the actual coordinates of the pixels on the river surface.

[0004] However, with the gradual promotion and application of video flow measurement methods, it has been found that the shore-based calibration method cannot be applied to situations with larger river widths. When the river width is greater than 200m, video flow measurement often cannot simultaneously take into account both the large field of view and the identification of river surface texture. In order to ensure the interpretability of video images, full-section monitoring can only be abandoned, that is, only a part of the river width can be monitored (for example, only the main channel area can be monitored). At this time, the entire video field of view will be the surface of the river flow, without any land surface, and there are no solid feature points that can be used for calibration within the field of view.

[0005] To achieve shore-based video pixel calibration, various methods have been used in the past, such as hovering drones, docking unmanned vessels, channel buoys, and floating tracer particles, as fixed-point positioning targets. However, due to the impact and fluctuation of water flow on the water surface, the positioning targets cannot be completely fixed, resulting in poor positioning accuracy and errors that can even reach tens to hundreds of centimeters. Summary of the Invention

[0006] Therefore, this application provides a method and apparatus for three-dimensional coordinate calibration of water surface images based on laser positioning, in order to solve the problem of poor positioning accuracy in existing shore-based video pixel calibration methods.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] Firstly, a method for three-dimensional coordinate calibration of water surface images based on laser positioning includes:

[0009] Step 1: Use surveying equipment to obtain the water level height and lens focus coordinates;

[0010] Step 2: Obtain the pixel coordinates of the center calibration points of multiple laser spots formed by multiple laser emitters within the video field of view and near the boundary;

[0011] Step 3: Obtain the actual coordinates or horizontal and vertical flip angles of the center calibration point of each laser spot measured by the total station on multiple shore bases at different elevations;

[0012] Step 4: Determine the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points based on the actual coordinates of the laser spot center calibration points or the horizontal and vertical flip angles.

[0013] Step 5: Perform a two-dimensional affine transformation based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates to obtain the actual latitude and longitude projection coordinates of any pixel in the video flow measurement image;

[0014] Step 6: Perform three-dimensional calibration based on water level, lens focus coordinates, and actual latitude and longitude projection coordinates to obtain the actual latitude, longitude, and elevation coordinates of any pixel in the video flow measurement image at any water level.

[0015] Preferably, in step 1, the lens focus coordinates are determined by identifying multiple feature points on the outer packaging surface of the video flow measurement lens based on the relationship between the focal length, the position of the lens center point, and the focus. The relative displacement between the feature points and the focus is measured, and then the actual coordinates of the feature points are measured using a total station. The accurate coordinates of the lens focus are calculated based on the actual coordinates and relative displacement of the feature points.

[0016] Preferably, step 4 specifically includes: calculating the average measurement error of each laser spot center calibration point, and determining whether the average error is within the allowable error range; if it is within the allowable error range, then using the measured coordinates of the laser spot center calibration point as the corresponding actual geodetic projection coordinates; if it is not within the allowable error range, then calculating the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points based on the horizontal and vertical flip angles.

[0017] Preferably, when calculating the actual geodetic projection coordinates corresponding to the pixel coordinates of the center calibration points of multiple laser spots based on the horizontal and vertical flip angles, the specific steps are as follows:

[0018] Choose any two shore bases from multiple shore bases with different elevations; determine two straight lines based on the latitude, longitude and elevation of the shore bases, and the horizontal and vertical flip angles of the laser spot center calibration point to be calculated, and calculate the midpoint of the common perpendicular of the two three-dimensional spatial straight lines as the intersection point. The intersection point is the actual geodetic projection coordinate of the laser spot center calibration point to be calculated.

[0019] Preferably, if the two lines are skew lines, then calculate the point that is closest to and equal to the two lines.

[0020] As a preferred option, step 5 specifically involves:

[0021] The overdetermined equations are obtained based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates, and the optimal solution of the overdetermined equations is calculated. The unknowns of the two-dimensional affine transformation are determined based on the optimal solution of the overdetermined equations, and the affine transformation formula is obtained. The actual latitude and longitude projection coordinates of any pixel in the video flow measurement image are calculated based on the affine transformation formula.

[0022] Preferably, the affine transformation formula is:

[0023]

[0024] Where m and n represent the row and column of the pixel, respectively, a, b, c, d, e, and f represent the optimal solutions of the overdetermined system of equations, and x and y represent the actual latitude and longitude coordinates of the pixel in the video flow measurement image.

[0025] Preferably, step 6 specifically includes:

[0026] A straight line is determined based on the lens focus coordinates and the actual latitude and longitude projected coordinates of the pixels in the calculated video flow measurement image:

[0027]

[0028]

[0029] Where x, y, and z represent the actual latitude, longitude, and elevation coordinates of a pixel in the video flow measurement image, and z = H represents the actual water level, and O represents the obtained water level. x O y O z Represents the lens focus coordinates, t represents a unique parameter, and F... x F y , This represents the actual latitude and longitude projected coordinates of a pixel in a video flow measurement image.

[0030] Secondly, a laser-based water surface image three-dimensional coordinate calibration device is provided, wherein the laser-based water surface image three-dimensional coordinate calibration device is used to implement the laser-based water surface image three-dimensional coordinate calibration method, including:

[0031] The calibration data acquisition module is used to obtain water level height and lens focus coordinates using surveying equipment;

[0032] The laser calibration point data acquisition module is used to acquire the pixel coordinates of the center calibration points of multiple laser spots formed by multiple laser emitters within the video field of view and near the boundary;

[0033] The total station measurement data acquisition module is used to acquire the actual coordinates or horizontal and vertical flip angles of the center calibration point of each laser spot measured by the total station on multiple shore bases at different elevations;

[0034] The actual geodetic projection coordinate calculation module is used to determine the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points based on the actual coordinates of the laser spot center calibration points or the horizontal and vertical flip angles.

[0035] The two-dimensional affine transformation module is used to perform two-dimensional affine transformation based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates, thereby obtaining the actual latitude and longitude projection coordinates of any pixel in the video flow measurement image.

[0036] The 3D affine transformation module is used to perform 3D calibration based on water level, lens focus coordinates, and actual latitude and longitude projection coordinates, so as to obtain the actual latitude, longitude, and elevation coordinates of any pixel in the video flow measurement image at any water level.

[0037] Compared with the prior art, this application has at least the following beneficial effects:

[0038] This application provides a method and apparatus for three-dimensional coordinate calibration of water surface images based on laser positioning. The method utilizes surveying equipment to obtain water level height and lens focus coordinates; acquires pixel coordinates of multiple laser spot center calibration points formed by multiple laser emitters within the video field of view and near the boundary; acquires the actual coordinates or horizontal and vertical flip angles of each laser spot center calibration point measured by a total station on multiple shorelines at different elevations; determines the actual geodetic projection coordinates corresponding to the pixel coordinates of the multiple laser spot center calibration points based on the actual coordinates or horizontal and vertical flip angles; performs a two-dimensional affine transformation based on the pixel coordinates of the multiple laser spot center calibration points and the actual geodetic projection coordinates to obtain the actual latitude and longitude projection coordinates of any pixel in the video flow measurement image; and performs three-dimensional calibration based on the water level height, lens focus coordinates, and actual latitude and longitude projection coordinates to obtain the actual latitude, longitude, and elevation coordinates of any pixel in the video flow measurement image at any water level. This application uses high-power lasers to achieve laser positioning on the water surface, and combines it with a multi-angle total station's distance-free positioning algorithm to achieve millimeter-level accurate calibration of water surface images without shoreline support. Attached Figure Description

[0039] To more intuitively illustrate the prior art and this application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concept disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, size ratios, etc. of certain units (components).

[0040] Figure 1 A flowchart of a method for three-dimensional coordinate calibration of water surface images based on laser positioning is provided in Embodiment 1 of this application;

[0041] Figure 2 This is a schematic diagram of the measurement setup for a three-dimensional coordinate calibration method for water surface images based on laser positioning, provided in Embodiment 1 of this application. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] In the description of this application: unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," etc., in this application are intended to distinguish the objects referred to and do not have any special meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "including," "comprising," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0044] The terms used in this application, such as "upper," "lower," "left," "right," and "middle," are generally used to indicate the general relative positional relationship for the purpose of intuitive understanding by referring to the accompanying drawings, and are not absolute limitations on the positional relationship in the actual product.

[0045] Example 1

[0046] Please see Figure 1 and Figure 2 This embodiment provides a method for three-dimensional coordinate calibration of water surface images based on laser positioning, including:

[0047] S1: Use surveying equipment to obtain water level height and lens focus coordinates;

[0048] Specifically, before using surveying equipment to obtain water level height and lens focus coordinates, it is necessary to investigate the water level of rivers and lakes, and to start the calibration work on a cloudy day or at night when the water level is relatively stable and the natural light is weak.

[0049] During calibration, the surveying equipment needs to be installed and fixed, ensuring a consistent video field of view. Then, the surveying equipment is used to obtain the water level height H and the lens focus coordinates C. Since the lens focus coordinates C are generally difficult to measure directly, it is necessary to first determine several feature points on the outer surface of the video flow measurement lens based on the relationship between the focal length, the lens center point, and the focus. The relative displacement between these feature points and the focus is then measured. After installation, a total station is used to measure the actual coordinates of the feature points, and the accurate focus coordinates are then calculated. In this embodiment, the camera used in the experiment has 5 megapixels and a focal length of 50mm.

[0050] S2: Obtain the pixel coordinates of the center calibration points of multiple laser spots formed by multiple laser emitters within the video field of view and near the boundary;

[0051] Specifically, this step requires four (or more) high-power, small-spot laser emitters. Turn on the laser emitters, align them with points near the edge of the video field of view, and fix them in place. Record the pixel coordinates of the laser spot's center calibration point, denoted as pixel coordinates S1-S4. The laser emitter power should be above 30W, the spot diameter at 30m should be less than 8cm, the angle between the laser path and the water surface should be greater than 30°, and the emission distance should be less than 100m.

[0052] S3: Obtain the actual coordinates or horizontal and vertical flip angles of the center calibration point of each laser spot measured by the total station on multiple shorelines at different elevations;

[0053] Specifically, approximately 5-7 total station points at different elevations are selected on the shore. The precise latitude, longitude, and elevation of each station are determined by transect surveying. The center calibration point of the laser spot on the water surface is measured, and the direct measurement results (i.e., actual coordinates) and horizontal and vertical flip angles are recorded. The total station points on the shore are recorded as P1-P7, the direct measurement results are C11-C74 (a total of 28 points), and the horizontal and vertical flip angles are La11-La74 and Ha11-Ha74 (28 points each). The laser emitter should be turned on when aiming and focusing, and turned off during measurement.

[0054] S4: Determine the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points based on the actual coordinates of the laser spot center calibration points or the horizontal and vertical flip angles.

[0055] Specifically, the actual geodetic projection coordinates corresponding to the pixel coordinates S1-S4 of the laser calibration spot center calibration point can be directly measured by a total station (i.e., the actual coordinates measured in step S3) if conditions permit. The average error of the measurement results from seven different stations can be used to determine the coordinates; if the error is less than the allowable error, it can be used directly. If it cannot be directly measured, it needs to be determined by calculating the horizontal and vertical flip angles La11-La74 and Ha11-Ha74. The calculation process is as follows:

[0056] Suppose the precise coordinates of the total station lens at the seven measured stations are P1-P7, and the horizontal and vertical flip angles are La11-La74 and Ha11-Ha74, respectively. Then, the actual coordinates of S1-S4 can be calculated from any two stations. Taking the calculation of S1 as an example, using stations P1 and P2, with horizontal and vertical flip angles of La11, Ha11, La21, and Ha21, respectively, the straight line passing through point P1 with horizontal and vertical flip angles of La11 and Ha11 can be represented as:

[0057] (1)

[0058] In equation (1), (x1, y1, z1) represent the latitude, longitude, and elevation of P1, in meters; t represents the linear parameter, which can be rewritten as a vector parameter:

[0059] (2)

[0060] Similarly, the straight line passing through point P2 with horizontal and vertical flip angles of La21 and Ha21 respectively can be represented as:

[0061] (3)

[0062] Under ideal conditions, if no error exists, then the straight line and If the two lines must intersect at point S1, then finding the intersection point of the two lines will give the actual coordinates of S1. However, due to objective errors in measurement, ... and Since the lines are skew, we need to find a point in space that is closest to and equidistant from both lines. This point is actually the midpoint of the common perpendicular of the two lines in three-dimensional space. The common perpendicular is perpendicular to the lines. and Then its direction is:

[0063] (4)

[0064] The intersection point of the common perpendicular with the two lines can be obtained by solving the following system of equations:

[0065] (5)

[0066] This system of equations has three unknowns: t, s, and u. The vector equations are three-dimensional, and the values ​​of t, s, and u can be obtained directly by solving them. Therefore, the intersection points of the two common perpendiculars with the two lines are:

[0067] (6)

[0068] (7)

[0069] set up for and The midpoint, then That is, the actual coordinates of the desired point S1. and The distance represents the solution error. Similarly, from the seven total station stations, any two stations can be chosen to calculate the actual coordinates of point S1, resulting in a total of 21 calculation results. Comparing the elevation values ​​of each calculation result with the water surface elevation value, eliminating items with large errors, and averaging the remaining items yields the final calculated result for the actual coordinates of point S1. The range of calculation error can be determined through the error terms and the sample variance of each calculation result. The actual coordinates of points S2-S4 can be calculated using the same process.

[0070] It should be noted that in this step, when calculating the actual coordinates of each pixel, the actual geodetic projection coordinates of the center points S1-S4 of the laser calibration spot are first calculated, and then the correspondence between the pixel coordinates and the actual coordinates is calculated. Since the water surface has a weak ability to reflect laser light, it may be necessary to adjust the parameters of the laser rangefinder or total station to enhance the signal reception capability. If direct measurement results cannot be obtained due to reasons such as long distance, water ripples, or low reflectivity, it is necessary to calculate the horizontal and vertical flip angles of S1-S4 based on multiple stations.

[0071] S5: Perform a two-dimensional affine transformation based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates to obtain the actual latitude and longitude projection coordinates of any pixel in the video flow measurement image.

[0072] Specifically, after obtaining the actual coordinates of S1-S4, a two-dimensional affine transformation is performed to obtain the actual latitude and longitude projection coordinates of any pixel.

[0073] Let the pixel coordinates of S1-S4 be (m1, n1), (m2, n2), (m3, n3), and (m4, n4), respectively. Then the corresponding actual latitude and longitude coordinates are (x1, y1), (x2, y2), (x3, y3), and (x4, y4), respectively. The affine transformation to be solved is:

[0074] (8)

[0075] Where m and n represent the row and column of the pixel, respectively, with rows from bottom to top and columns from left to right. The affine transformation in Equation 8 requires solving for 6 unknowns. For each known pixel and its corresponding coordinates, two equations can be established. Therefore, for a two-dimensional coordinate affine transformation, at least three known points are needed to form a system of linear equations for solving. Based on the four known points S1-S4 in this embodiment, the system of equations is as follows:

[0076] (9)

[0077] Equation 9 is an overdetermined system of equations. Solving the optimal solution of this system of equations will yield the affine transformation parameters of Equation 8. Thus, for any pixel, given the row and column where the pixel is located, its actual projected coordinates can be obtained.

[0078] S6: Perform three-dimensional calibration based on water level, lens focus coordinates, and actual latitude and longitude projection coordinates to obtain the actual latitude, longitude, and elevation coordinates of any pixel in the video flow measurement image at any water level.

[0079] In practice, the fluctuation of the measured water surface elevation also needs to be considered. When the water level rises or falls, the actual three-dimensional coordinates represented by each pixel will change accordingly. Assume the measured water surface is approximately horizontal, and that any point on the plane has the same elevation. Let the three-dimensional spatial coordinates of the lens focus be C(O). x O y O z If the current stable water surface elevation is H, then for any pixel coordinate F(m, n), its actual projected coordinate F(m, n) can be obtained according to Equation 8. x , F y , Given two points C and F in three-dimensional space, a unique straight line can be determined through these two points:

[0080] (10)

[0081] In the formula, t is the only parameter. When the future water level of the measured water surface changes... At that time, it can be Substituting into equation 10, we can solve for the parameter t, i.e.:

[0082] (11)

[0083] Substituting t into Equation 10, we can solve for the position of any pixel at the water level. The latitude and longitude x and y coordinates of any pixel in the video flow measurement image at any water level are obtained by using these coordinates.

[0084] This embodiment provides a laser-based method for 3D coordinate calibration of water surface images. It utilizes a high-power laser to achieve laser positioning on the water surface. Compared to previous positioning methods such as UAV hovering, unmanned vessel mooring, channel buoys, and floating tracer particles, this method is unaffected by water flow impacts or fluctuations in water or air fluids. Combined with a multi-angle total station's distance-free positioning algorithm, it achieves millimeter-level accurate calibration of water surface images without a shoreline. This solves the problem of accurate calibration of actual coordinates in shoreline-free video flow measurement images, and is of great significance for expanding the application of video flow measurement methods in wide rivers and improving the accuracy of video flow measurement interpretation.

[0085] Example 2

[0086] This embodiment provides a laser-based three-dimensional coordinate calibration device for water surface images. This device is used to implement the laser-based three-dimensional coordinate calibration method for water surface images described in Embodiment 1, including:

[0087] The calibration data acquisition module is used to obtain water level height and lens focus coordinates using surveying equipment;

[0088] The laser calibration point data acquisition module is used to acquire the pixel coordinates of the center calibration points of multiple laser spots formed by multiple laser emitters within the video field of view and near the boundary;

[0089] The total station measurement data acquisition module is used to acquire the actual coordinates or horizontal and vertical flip angles of the center calibration point of each laser spot measured by the total station on multiple shore bases at different elevations;

[0090] The actual geodetic projection coordinate calculation module is used to determine the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points based on the actual coordinates of the laser spot center calibration points or the horizontal and vertical flip angles.

[0091] The two-dimensional affine transformation module is used to perform two-dimensional affine transformation based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates, thereby obtaining the actual latitude and longitude projection coordinates of any pixel in the video flow measurement image.

[0092] The 3D affine transformation module is used to perform 3D calibration based on water level, lens focus coordinates, and actual latitude and longitude projection coordinates, so as to obtain the actual latitude, longitude, and elevation coordinates of any pixel in the video flow measurement image at any water level.

[0093] For details on the implementation of each module in a laser-based water surface image three-dimensional coordinate calibration device, please refer to the above description of the limitations of a laser-based water surface image three-dimensional coordinate calibration method, which will not be repeated here.

[0094] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

Claims

1. A method for three-dimensional coordinate calibration of water surface images based on laser positioning, characterized in that, include: Step 1: Use surveying equipment to obtain the water level height and lens focus coordinates; Step 2: Obtain the pixel coordinates of the center calibration points of multiple laser spots formed by multiple laser emitters within the video field of view and near the boundary; Step 3: Obtain the actual coordinates or horizontal and vertical flip angles of the center calibration point of each laser spot measured by the total station on multiple shore bases at different elevations; Step 4: Determine the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points based on the actual coordinates of the laser spot center calibration points or the horizontal and vertical flip angles. Step 5: Perform a two-dimensional affine transformation based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates to obtain the actual latitude and longitude projection coordinates of any pixel in the video flow measurement image; Step 6: Perform three-dimensional calibration based on water level height, lens focus coordinates, and actual latitude and longitude projection coordinates to obtain the actual latitude, longitude, and elevation coordinates of any pixel in the video flow measurement image at any water level; Step 4 specifically includes: calculating the average measurement error of each laser spot center calibration point, and determining whether the average error is within the allowable error range; If it is within the allowable error, the measured coordinates of the laser spot center calibration point are used as the corresponding actual geodetic projection coordinates; if it is not within the allowable error, the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points are calculated based on the horizontal and vertical flip angles. The calculation of the actual geodetic projection coordinates corresponding to the pixel coordinates of the center calibration points of multiple laser spots based on the horizontal and vertical flip angles is specifically as follows: Choose any two shore bases from multiple shore bases with different elevations; determine two straight lines based on the latitude, longitude and elevation of the shore bases, and the horizontal and vertical flip angles of the laser spot center calibration point to be calculated, and calculate the midpoint of the common perpendicular of the two three-dimensional spatial straight lines as the intersection point. The intersection point is the actual geodetic projection coordinate of the laser spot center calibration point to be calculated.

2. The method for three-dimensional coordinate calibration of water surface images based on laser positioning according to claim 1, characterized in that, In step 1, the lens focus coordinates are determined by identifying multiple feature points on the outer surface of the video flow measurement lens based on the relationship between the focal length, the position of the lens center point, and the focus. The relative displacement between the feature points and the focus is measured, and then the actual coordinates of the feature points are measured using a total station. The accurate coordinates of the lens focus are calculated based on the actual coordinates and relative displacement of the feature points.

3. The method for three-dimensional coordinate calibration of water surface images based on laser positioning according to claim 1, characterized in that, If two lines are skew lines, then calculate the point that is closest to and equal to the two lines.

4. The method for three-dimensional coordinate calibration of water surface images based on laser positioning according to claim 1, characterized in that, Step 5 specifically involves: The overdetermined equations are obtained based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates, and the optimal solution of the overdetermined equations is calculated. The unknowns of the two-dimensional affine transformation are determined based on the optimal solution of the overdetermined equations, and the affine transformation formula is obtained. The actual latitude and longitude projection coordinates of any pixel in the video flow measurement image are calculated based on the affine transformation formula.

5. The method for three-dimensional coordinate calibration of water surface images based on laser positioning according to claim 4, characterized in that, The affine transformation formula is: ， Where m and n represent the row and column of the pixel, respectively, a, b, c, d, e, and f represent the optimal solutions of the overdetermined system of equations, and x and y represent the actual latitude and longitude coordinates of the pixel in the video flow measurement image.

6. The method for three-dimensional coordinate calibration of water surface images based on laser positioning according to claim 1, characterized in that, Step 6 specifically includes: A straight line is determined based on the lens focus coordinates and the actual latitude and longitude projected coordinates of the pixels in the calculated video flow measurement image: ， ， Where x, y, and z represent the actual latitude, longitude, and elevation coordinates of a pixel in the video flow measurement image, and z = H represents the actual water level, and O represents the obtained water level. x O y O z Represents the lens focus coordinates, t represents a unique parameter, and F... x F y , This represents the actual latitude and longitude projected coordinates of a pixel in a video flow measurement image.

7. A three-dimensional coordinate calibration device for water surface images based on laser positioning, characterized in that, The laser-based water surface image three-dimensional coordinate calibration device is used to implement the laser-based water surface image three-dimensional coordinate calibration method according to any one of claims 1-6, including: The calibration data acquisition module is used to obtain water level height and lens focus coordinates using surveying equipment; The laser calibration point data acquisition module is used to acquire the pixel coordinates of the center calibration points of multiple laser spots formed by multiple laser emitters within the video field of view and near the boundary; The total station measurement data acquisition module is used to acquire the actual coordinates or horizontal and vertical flip angles of the center calibration point of each laser spot measured by the total station on multiple shore bases at different elevations; The actual geodetic projection coordinate calculation module is used to determine the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points based on the actual coordinates of the laser spot center calibration points or the horizontal and vertical flip angles. The two-dimensional affine transformation module is used to perform two-dimensional affine transformation based on the pixel coordinates of multiple laser spot center calibration points and the actual geodetic projection coordinates, thereby obtaining the actual latitude and longitude projection coordinates of any pixel in the video flow measurement image. The 3D affine transformation module is used to perform 3D calibration based on water level, lens focus coordinates and actual latitude and longitude projection coordinates, so as to obtain the actual latitude, longitude and elevation coordinates of any pixel in the video flow measurement image at any water level. The actual geodetic projection coordinate calculation module is specifically used to: calculate the average measurement error of each laser spot center calibration point, and determine whether the average error is within the allowable error range; if it is within the allowable error range, then the measured coordinates of the laser spot center calibration point are used as the corresponding actual geodetic projection coordinates; if it is not within the allowable error range, then the actual geodetic projection coordinates corresponding to the pixel coordinates of multiple laser spot center calibration points are calculated based on the horizontal and vertical flip angles. The calculation of the actual geodetic projection coordinates corresponding to the pixel coordinates of the center calibration points of multiple laser spots based on the horizontal and vertical flip angles is specifically as follows: Choose any two shore bases from multiple shore bases with different elevations; determine two straight lines based on the latitude, longitude and elevation of the shore bases, and the horizontal and vertical flip angles of the laser spot center calibration point to be calculated, and calculate the midpoint of the common perpendicular of the two three-dimensional spatial straight lines as the intersection point. The intersection point is the actual geodetic projection coordinate of the laser spot center calibration point to be calculated.

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