Coastal mud flat elevation measurement method based on orthographic reconstruction technology

Abstract

The invention discloses a coastal tidal flat elevation measurement method based on an orthographic reconstruction technology, and the method comprises the following steps: laying image control points in a target monitoring area of a muddy tidal flat, and then measuring the elevation information of each image control point; an unmanned aerial vehicle is adopted to collect aerial photos of the area according to the planned flight route; an RTK base station is erected in the area to collect static POS data; obtaining static POS data and airborne POS data to calculate flight POS data; flight POS data and aerial photos are obtained, modeling is carried out in combination with elevation information of an image control point, and point cloud data and an orthoimage of the area are generated; and identifying a ponding area from the orthoimage, removing the ponding area from the point cloud data, and establishing a digital elevation model of the area to obtain tidal flat elevation information of the area. Therefore, the problem that large-range tidal flat elevation measurement cannot be carried out due to the limitation of the tidal falling time of the muddy tidal flat in the traditional artificial beach running is solved.

Description

Technical Field

[0001] The present invention relates to a coastal tidal flat elevation measurement method based on orthographic reconstruction technology, belonging to the technical field of geological surveying. Background Art

[0002] The muddy tidal flat is broad, flat, and has a small water depth. Horizontally on the muddy tidal flat, the bottom sediments such as mud, silt, and sand are significantly sorted, and the sediment movement law changes greatly. Therefore, a reliable on-site topographic survey method is needed to obtain the tidal flat topography, which has important practical guiding significance for mastering the evolution law of the coastal tidal flat, the development, utilization, and protection of coastal zone resources. However, it is difficult to obtain tidal flat elevation as important basic data for scientific research.

[0003] Currently, the measurement methods for the topography of the muddy tidal flat mainly include traditional manual beach walking, shipborne sounding instruments, satellite remote sensing measurement, etc. Due to the muddy and easily sinkable nature of the muddy tidal flat and the crisscrossing tidal channels, it is difficult for personnel to reach some areas. Traditional manual beach walking not only has low measurement efficiency but also has safety risks for personnel and equipment; shipborne sounding instrument measurement has a high cost, and the spatial resolution and inversion accuracy of satellite remote sensing measurement often cannot meet the actual research needs. Summary of the Invention

[0004] The purpose of the present invention is to provide a coastal tidal flat elevation measurement method based on orthographic reconstruction technology, which can realize the monitoring of the coastal geomorphic evolution process quickly, with a moderate spatial resolution and low cost through the photogrammetry of an unmanned aerial vehicle (UAV), and solves the problem that the traditional manual beach walking cannot carry out a large-scale tidal flat elevation measurement due to the limitation of the ebb tide time on the muddy tidal flat.

[0005] To achieve the above technical purpose, the present invention will adopt the following technical solutions:

[0006] A coastal tidal flat elevation measurement method based on orthographic reconstruction technology includes the following steps:

[0007] After arranging image control points in the target monitoring area of the muddy tidal flat, measure the elevation information of each image control point, denoted as the image control point elevation information;

[0008] In the target monitoring area of the muddy tidal flat, use an unmanned aerial vehicle to collect aerial photography photos according to the planned flight route, and set up an RTK reference station to collect static POS data;

[0009] Obtain the static POS data and the onboard POS data on the unmanned aerial vehicle and perform calculation to obtain the flight POS data;

[0010] Obtain the flight POS data and the aerial photography photos collected by the unmanned aerial vehicle, and combine with the image control point elevation information to perform modeling, then the point cloud data and orthophoto of the target monitoring area can be generated;

[0011] Identify the waterlogging area from the orthophoto, and remove the point cloud data corresponding to the waterlogging area from the point cloud data corresponding to the target monitoring area. Then, establish a digital elevation model of the target monitoring area through modeling software to obtain the tidal flat elevation information of this area.

[0012] Preferably, the image control points are arranged around and at the center point of the target monitoring area.

[0013] Preferably, generating the point cloud data and orthophoto of the target monitoring area specifically includes the following steps:

[0014] Perform the first pass of spatial triangulation on the aerial photos and flight POS data collected by the unmanned aerial vehicle in the first modeling software to achieve absolute spatial orientation, then conduct image control point piercing, and execute the second pass of spatial triangulation to generate the point cloud data and orthophoto of the target monitoring area.

[0015] Preferably, identifying the waterlogging area from the orthophoto and removing the point cloud data corresponding to the waterlogging area from the point cloud data corresponding to the target monitoring area are specifically completed in the aerial survey software.

[0016] Preferably, verification points are also arranged in the target monitoring area of the muddy tidal flat, and the elevation information of each verification point is measured, denoted as the verification point elevation information;

[0017] Use the root mean square error between the obtained tidal flat elevation information of the target monitoring area and the verification point elevation information to verify the error of the obtained tidal flat elevation information of the target monitoring area.

[0018] Preferably, the measurement of the elevation information of the image control points and verification points is all achieved by connecting to the JScors system using a dual-frequency GPS-RTK positioning system.

[0019] Preferably, the image control points and verification points are arranged using image control cloth.

[0020] Preferably, by periodically monitoring the same target monitoring area, the topographic elevation information of the muddy tidal flat at different times is obtained, and then the erosion and deposition evolution of this area is monitored.

[0021] Preferably, when planning the flight route of the unmanned aerial vehicle, the Z-shaped route coverage strategy is adopted, and it is ensured that the overlap rate of adjacent flight strips ≥ 85%.

[0022] Another technical object of the present invention is to provide an electronic device, including a memory, a processor, and a computer program stored on the memory and running on the processor. This computer program runs to execute the above-mentioned coastal tidal flat elevation measurement method based on orthophoto reconstruction technology.

[0023] Based on the above technical objectives, the present invention has the following advantages over the prior art:

[0024] The coastal tidal flat elevation measurement method based on orthophoto reconstruction technology described in the present invention has an elevation accuracy of centimeter level in topography measurement, which greatly improves the efficiency of tidal flat topography measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1. It is a flow chart of the coastal mudflat elevation measurement method based on orthophoto reconstruction technology according to the present invention;

[0026] Figure 2 It shows a top view of image control points and verification points used in the field observation of a muddy tidal flat by a drone according to the present invention;

[0027] Figure 3 The main view of the base station for on-site observation of muddy tidal flats using a drone is shown. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way serves as any limitation on the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention. Unless otherwise specified, the relative arrangement of components and steps, expressions and numerical values described in these embodiments do not limit the scope of the present invention. Technologies, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the technologies, methods and equipment should be considered part of the specification. In all examples shown and discussed here, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of the exemplary embodiments may have different values.

[0029] Generally, the tidal action of coastal muddy tidal flats is strong. Affected by the tidal action, the effective measurement time window within a single tidal cycle is often less than 3 hours. The traditional artificial beach measurement method is difficult to achieve large-scale terrain data collection within a single tidal cycle. In addition, the terrain of coastal muddy tidal flats is complex, making large-scale terrain measurement difficult. Therefore, the present invention has developed a coastal muddy flat elevation measurement method based on orthophoto reconstruction technology, which can achieve a single flight of 5km within a single tidal cycle window. 2For topographic surveys of the above areas, the measurement resolution can reach the centimeter level. Considering the relatively flat terrain and fine surface texture of the muddy tidal flats, the aerial survey operation process was optimized. During the operation, a Z-shaped flight path coverage strategy was designed, and at the same time, the overlap rate of adjacent flight strips was increased to ≥85% (the overlap rate for land topographic surveys is generally 70%).

[0030] Therefore, the present invention can quickly and efficiently achieve topographic surveys of tidal flat areas within a single tidal cycle for the characteristics of muddy tidal flats. At the same time, the operation process was optimized, and the topographic changes of tidal flats can be reflected in real time through continuous observations, thus realizing the analysis of erosion and deposition evolution of muddy tidal flats.

[0031] Example 1

[0032] As Figure 1 shown, the method for coastal tidal flat elevation measurement based on orthographic reconstruction technology of the present invention includes the following steps:

[0033] Step 1: Determine the scope of monitoring the topography of the muddy tidal flat and the scope of monitoring time;

[0034] In this step, the scope of monitoring the topography of the muddy tidal flat (hereinafter referred to as the monitoring scope) is the area with more developed tidal creeks and clearer beach surface texture; the monitoring time is selected during the ebb tide period (to obtain good measurement results, rainy and foggy weather should be avoided).

[0035] Step 2: Set up image control points and a certain number of verification points around the perimeter and at the center point within the scope of monitoring the topography of the muddy tidal flat. Use a dual-frequency GPS-RTK positioning system to connect to the JScors system to measure the elevations of the image control points and verification points. The image control points and verification points are arranged using an image control layout of 50cm * 50cm, and specific reference can be made to the appendix Figure 2 ;

[0036] In this step, the image control points are generally arranged around the perimeter and at the center point of the measurement area. If it is difficult for humans to reach and set them up, they can also be arranged in the nearby surrounding area. The verification points can be randomly arranged within the monitoring scope.

[0037] Step 3: Set up an RTK reference station to collect static data: Select some control points within the monitoring scope to set up an RTK reference station to collect static POS data, with a sampling interval of 1s; the specific structure of the RTK reference station can be referred to in the appendix Figure 3 。

[0038] Step 4: Plan the flight path of the unmanned aerial vehicle within the monitoring area, and use the unmanned aerial vehicle to collect aerial photography photos of the area according to the planned flight path of the unmanned aerial vehicle within the monitoring area;

[0039] In this step, a Z-shaped flight path coverage strategy is adopted when planning the flight path of the unmanned aerial vehicle, and it is ensured that the overlap rate of adjacent flight strips is ≥85%.

[0040] Step 5: Export the airborne POS data and static POS data, perform PPK calculation to obtain the flight POS data;

[0041] Step 6: Import the flight POS data and the photos taken by the UAV into the modeling software (such as PiX4D 3D modeling software), perform spatial triangulation calculation to achieve spatial absolute orientation, then conduct image control point measurement, and perform the second round of spatial triangulation calculation to generate the point cloud data and orthophoto of the monitoring area; Since the water accumulation area will affect the tidal flat digital elevation model, an aerial survey software (such as HiData software) is used to identify the water accumulation area from the orthophoto, and the point cloud data corresponding to the water accumulation area is removed from the point cloud data corresponding to the monitoring area; After removing the water accumulation area, use the modeling software (such as PiX4D 3D modeling software) to establish the digital elevation model of the monitoring area, and the tidal flat elevation information of the monitoring area can be obtained.

[0042] Step 7: Verify the model error: Calculate the root mean square error between the elevation values of the verification points collected by JScors and the tidal flat elevation information obtained in Step 6 to verify the error of the tidal flat elevation information and evaluate the accuracy of the generated digital elevation model.

[0043] Specifically, use the elevation values and plane values of the verification points collected by JScors as the inspection true values, and the corresponding tidal flat elevation information obtained in Step 6 as the observed values for comparative analysis to calculate the mean square error.

[0044] Obtain the mean square errors of the observed values in the X, Y, and H directions through the mean square error calculation formula, and then evaluate the data accuracy according to the provisions of CH / T 9015—2012 "Specification for 3D Geographic Information Model Data Products".

[0045] The mean square error formulas are shown in Formulas (1), (2), and (3):

[0046]

[0047] In the formula, ΔL = L - Li (i = 1, 2,..., n), where: ΔL represents the error ΔX of the observed value in the X direction, the error ΔY of the observed value in the Y direction, or the error ΔH of the observed value in the H direction; L is the inspection true value; Li is the observed value; n is the number of verification points. m x represents the mean square error of the observed value in the X direction, m y represents the mean square error of the observed value in the Y direction, m h represents the mean square error of the observed value in the H direction.

[0048] According to the mean square errors in the X and Y directions, the plane mean square error m of the observed value can be calculated, and the calculation formula is shown in Formula (4):

[0049]

[0050] Select measurement models #1 and #2 for accuracy verification. The field measurement and model measurement verification points are shown in Tables 1 and 2. The evaluation of the model positioning accuracy is shown in Tables 3 and 4.

[0051] Table 1 Accuracy Verification Points of Aerial Survey Model for Section #1

[0052]

[0053] Table 2 Accuracy Verification Points of Aerial Survey Model for Section #2

[0054]

[0055]

[0056] Table 3 Evaluation of Absolute Positioning Accuracy of Aerial Survey Model for Section #1 Unit: m

[0057]

[0058] As can be seen from Table 3, in the model of Section #1, the maximum error in the X direction is 0.104 m, the mean error is 0.057 m, the maximum error in the Y direction is 0.118 m, the mean error is 0.067 m, the maximum error in the H direction is 0.107 m, and the mean error is 0.057 m.

[0059] Table 4 Evaluation of Absolute Positioning Accuracy of Aerial Survey Model for Section #2 Unit: m

[0060]

[0061] As can be seen from Table 4, in the model of Section #2, the maximum error in the X direction is 0.092 m, the mean error is 0.055 m, the maximum error in the Y direction is 0.109 m, the mean error is 0.055 m, the maximum error in the H direction is 0.098 m, and the mean error is 0.066 m.

[0062] In summary, the accuracy evaluation results of the verification point data of the models of Sections #1 and #2 both meet the accuracy requirements of the model specification in CH / T 9015—2012 Specification for 3D Geographic Information Model Data Products, where the planar mean error is better than 0.3 m and the elevation mean error is better than 0.5 m.

[0063] Step 8: Perform periodic monitoring and modeling on the same area to obtain the topographic elevation information of the muddy tidal flat at different times, and thus monitor the erosion and deposition evolution of the area.

[0064] In this step, overlay analysis can be performed on the images to reflect the changes in the tidal flat topography.

[0065] Example 2

[0066] The present invention also provides a storage medium. When the program stored in the storage medium runs, it executes the above-mentioned coastal intertidal elevation measurement method based on orthographic reconstruction technology.

[0067] Embodiment 3

[0068] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. The processor executes the above-mentioned coastal intertidal elevation measurement method based on orthographic reconstruction technology through the operation of the computer program.

[0069] The serial numbers of the above-mentioned embodiments of the present invention are only for description and do not represent the superiority or inferiority of the embodiments.

[0070] In the above-mentioned embodiments of the present invention, the descriptions of each embodiment have their own emphases. For the parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0071] In several embodiments provided by the present application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only illustrative. For example, the division of the units can be a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect couplings or communication connections of units or modules can be in electrical or other forms.

[0072] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place, or can be distributed to multiple units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0073] In addition, the functional units in each embodiment of the present invention can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0074] When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, read-only memories (ROMs), random access memories (RAMs), mobile hard disks, magnetic disks, or optical discs that can store program codes.

[0075] 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 form. Any technical solutions obtained by using equivalent replacements or equivalent transformations fall within the protection scope of the present invention.

Claims

1. A coastal tidal flat elevation measurement method based on orthographic reconstruction technology, characterized in that, It includes the following steps: After setting out image control points in the target monitoring area of the muddy tidal flat, measure the elevation information of each image control point, denoted as the elevation information of the image control point; In the target monitoring area of the muddy tidal flat, use a drone to collect aerial photos according to the planned flight route, and set up an RTK reference station to collect static POS data; Obtain the static POS data and the on-board POS data on the drone and perform calculations to obtain the flight POS data; Obtain the flight POS data and the aerial photos collected by the drone, and combine the elevation information of the image control points to perform modeling, then the point cloud data and orthophoto of the target monitoring area can be generated; Identify the water accumulation area from the orthophoto, and remove the point cloud data corresponding to the water accumulation area from the point cloud data corresponding to the target monitoring area, and then establish the digital elevation model of the target monitoring area through modeling software to obtain the tidal flat elevation information of this area.

2. The coastal tidal flat elevation measurement method based on orthographic projection reconstruction technology according to claim 1, characterized in that The image control points are set out around and at the center of the target monitoring area.

3. The coastal tidal flat elevation measurement method based on orthographic projection reconstruction technology according to claim 1, wherein Generating the point cloud data and orthophoto of the target monitoring area specifically includes the following steps: Perform the first pass of spatial triangulation on the aerial photos collected by the drone and the flight POS data in the first modeling software to achieve spatial absolute orientation, then perform image control point piercing, and perform the second pass of spatial triangulation to generate the point cloud data and orthophoto of the target monitoring area.

4. The coastal intertidal elevation measurement method based on orthographic reconstruction technology according to claim 1, characterized in that, Identifying the water accumulation area from the orthophoto and removing the point cloud data corresponding to the water accumulation area from the point cloud data corresponding to the target monitoring area is specifically completed in the aerial survey software.

5. The coastal tidal flat elevation measurement method based on orthographic reconstruction technology according to claim 1, characterized in that Verification points are also set out in the target monitoring area of the muddy tidal flat, and the elevation information of each verification point is measured, denoted as the elevation information of the verification point; Perform the root mean square error between the obtained tidal flat elevation information of the target monitoring area and the elevation information of the verification points to verify the error of the obtained tidal flat elevation information of the target monitoring area.

6. The method for measuring the elevation of coastal tidal flats based on the orthographic projection reconstruction technology according to claim 5, wherein, The measurement of the elevation information of the image control points and verification points is all achieved by using a dual-frequency GPS-RTK positioning system connected to the JScors system.

7. The method for measuring the elevation of coastal tidal flats based on the orthographic projection reconstruction technology according to claim 6, wherein, The image control points and verification points are set out using image control cloth.

8. The method for measuring the elevation of coastal tidal flats based on the orthographic projection reconstruction technology according to claim 1, characterized in that, By performing periodic monitoring on the same target monitoring area, the topographic elevation information of the muddy tidal flat at different times can be obtained, and then the erosion and deposition evolution of this area can be monitored.

9. The coastal tidal flat elevation measurement method based on orthographic reconstruction technology according to claim 1, characterized in that When planning the drone flight route, adopt the Z-shaped route coverage strategy and ensure that the overlap rate of adjacent flight strips is ≥85%.

10. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and running on the processor, characterized in that, This computer program runs to execute the coastal tidal flat elevation measurement method based on orthophoto reconstruction technology described in any one of claims 1 to 8.

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