Soil erosion gully depth monitoring method and system based on camera measurement

Abstract

The invention relates to the technical field of soil environment protection, in particular to a soil erosion gully depth monitoring method and system based on camera metrology, and the method comprises the steps: analyzing the length of an existing shadow through an orthoimage of a soil erosion gully, and converting the lengths of the existing shadow at different angles to obtain the vertical shadow length of the existing shadow; based on the vertical shadow length of the existing shadow, the change rate of the soil erosion gully is analyzed, and the virtual vertical shadow length of the parallel gully area is obtained; and obtaining the measurement depth of the soil erosion gully according to the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area. Through the method and the system, the problem that gully depth detection by utilizing the shadow length fails due to the fact that the soil erosion gully is parallel to the sunlight irradiation direction and cannot form an effective shadow is solved, the effective range of gully depth detection can be improved, and operability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of soil environmental protection, and in particular to a soil erosion gully depth monitoring method and system based on photogrammetry. Background Art

[0002] The erosion gullies of the hilly soil on the Loess Plateau have a serious destructive effect on the ecology. Monitoring the depth distribution of erosion gullies can provide a basis for soil and water conservation, evaluate ecological restoration, and ensure the development of social and economic production. Traditional methods for monitoring the depth of erosion gullies generally include manual measurement or measurement using equipment such as laser rangefinders. These methods are not only time-consuming and labor-intensive, but may not be able to measure accurately in complex terrain. Photogrammetry can quickly and accurately obtain the depth information of erosion gullies by taking photos of erosion gullies and then using image processing and three-dimensional reconstruction technology.

[0003] The existing publication number CN115060231B provides a rapid measurement method for soil erosion gully depth based on photogrammetry: first, use a drone to obtain images of the monitoring area and perform preprocessing, and record the drone flight time in real time; perform object-oriented classification on the drone images, identify the soil erosion gully boundary and the shadow area in the erosion gully, and use all pixel points on the soil erosion gully boundary in the image as target points, and then calculate the solar altitude angle and solar azimuth angle according to the location of the study area and the drone image acquisition time, and determine the shadow projection direction of each target point; calculate the shadow length projected by the edge of the erosion gully according to the shadow direction; calculate the relative height of all target points from the starting point of the projection shadow in turn, and measure the slope at the target point, and finally calculate the soil erosion gully depth in the target point area. The core technical point of this technical solution is: analyze the shadow length of the gully image obtained by the drone, and then use the shadow length as the basis for the final gully depth judgment. However, when the direction of the gully is consistent with the direction of sunlight, both sides of the gully can be fully illuminated by sunlight, and the characteristic of having a clear shadow on one side cannot be formed, and then the effective shadow length cannot be obtained, which leads to the failure of the gully depth monitoring method. Summary of the invention

[0004] In order to solve the above technical problems, the object of the present invention is to provide a soil erosion gully depth monitoring method and system based on photogrammetry.

[0005] According to a first aspect of an embodiment of the present invention, a soil erosion gully depth monitoring method based on photogrammetry is provided, and the technical solution adopted is specifically as follows: Obtain orthophotos of soil erosion gullies; Based on the orthophoto image, identifying the existing shadow, analyzing the length of the existing shadow, and converting the lengths of the existing shadows at different angles to obtain the vertical shadow length of the existing shadow; Based on the vertical shadow length of the existing shadow, the change rate of soil erosion gullies is analyzed to obtain the virtual vertical shadow length of the parallel gully area; The measured depth of the soil erosion gully is obtained based on the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area.

[0006] In some embodiments of the present invention, identifying existing shadows based on the orthoimage and analyzing the length of the existing shadows includes: Based on the orthophoto, a CNN neural network is used to obtain edge contours and identify existing shadows and light irradiation directions; Based on the edge contour, determining the direction of the existing shadow length; Analyze the number of alternations of black and white pixels in the length direction of the existing shadow to obtain the continuity of the existing shadow; The length of the existing shadow is obtained according to the continuity degree of the existing shadow and the number of black pixels in the length direction of the existing shadow.

[0007] In some embodiments of the present invention, the CNN neural network: The network architecture is convolution-pooling-classification output; The input is an orthophoto; The output is the segmented soil erosion gully outline and the shadow distribution within the soil erosion gully; The loss function is cross entropy loss; The training set consists of orthophotos and manually annotated images, where the manually annotated parts of the manually annotated images include the contours of soil erosion gullies, the shadow distribution within the soil erosion gullies, and the direction of light exposure.

[0008] In some embodiments of the present invention, converting the lengths of existing shadows at different angles to obtain the vertical shadow lengths of the existing shadows includes: Determining the angle of the edge profile according to the perpendicular direction between the edge profile and the light irradiation direction; The vertical shadow length of the existing shadow is obtained according to the angle of the edge contour and the length of the existing shadow.

[0009] In some embodiments of the present invention, the angle of the edge profile is determined, and then the step further includes: Set the angle threshold; Determine the relationship between the angle of the edge contour and the angle threshold; If the angle of the edge contour is greater than or equal to the angle threshold, the gully area corresponding to the edge contour is an existing shadow; Otherwise, the gully region corresponding to the edge contour is a parallel gully region.

[0010] In some embodiments of the present invention, determining the direction of the existing shadow length based on the edge contour includes: Combined with GIS system, determine the height of soil erosion gullies; From the higher end of the soil erosion gully to the lower end, the existing shadow length line is selected at intervals of 3 to 5 pixels, and the direction perpendicular to the edge contour line is the existing shadow length direction.

[0011] In some embodiments of the present invention, based on the vertical shadow length of the existing shadow, the change rate of the soil erosion gully is analyzed to obtain the virtual vertical shadow length of the parallel gully area, including: The vertical shadow lengths of all existing shadows are arranged in order from the higher end of the soil erosion gully to the lower end, and the virtual vertical shadow lengths distributed in the parallel gully area are processed by invalid data placeholders to obtain a vertical shadow length sequence; Analyze the distribution of vertical shadow length data and the invalid data in the vertical shadow length sequence to obtain the change rate of the soil erosion gully; According to the change rate and in combination with the vertical shadow length of the existing shadow, a virtual vertical shadow length of the parallel gully area is obtained.

[0012] In some embodiments of the present invention, obtaining an orthophoto image of soil erosion gullies includes: Use drones to capture images of soil erosion gullies from different perspectives; grayscale the soil erosion gully image to obtain a soil erosion gully grayscale image; Feature extraction and feature matching are performed on the soil erosion gully grayscale image to obtain an orthophoto image of the soil erosion gully.

[0013] According to a second aspect of an embodiment of the present invention, a soil erosion gully depth monitoring system based on photogrammetry is provided, comprising: a memory and a processor, wherein: The memory is used to store program code; The processor is used to read the program code stored in the memory and execute the method described in the first aspect of the embodiment of the present invention.

[0014] In some embodiments of the present invention, the processor comprises: Gully image acquisition module, used to obtain orthophoto images of soil erosion gullies; An existing shadow analysis module is used to identify the existing shadow based on the orthophoto image, analyze the length of the existing shadow, and convert the length of the existing shadow at different angles to obtain the vertical shadow length of the existing shadow; The parallel gully area analysis module is used to analyze the change rate of soil erosion gullies based on the vertical shadow length of the existing shadows and obtain the virtual vertical shadow length of the parallel gully area; The gully depth measurement module is used to obtain the measured depth of the soil erosion gully based on the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area.

[0015] Compared with the prior art, the soil erosion gully depth monitoring method and system based on photogrammetry provided by the present invention obtains the vertical shadow length of the existing shadow with the shadow feature part through the orthophoto image of the soil erosion gully; then, based on the vertical shadow length of the existing shadow, the change characteristics of the soil erosion gully are analyzed, and then the virtual vertical shadow length of the parallel gully area is obtained by using the change characteristics; finally, the measured depth of the soil erosion gully is obtained according to the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area. The method and system of the present invention solve the problem of failure of gully depth detection using shadow length due to the fact that the soil erosion gully is parallel to the direction of sunlight and cannot form an effective shadow, which can improve the effective range of gully depth detection and has operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A basic flow chart of a soil erosion gully depth monitoring method based on photogrammetry provided by an embodiment of the present invention; Figure 2 A schematic diagram of manually marking the internal shadows, edge contours and light irradiation directions of soil erosion gullies provided by an embodiment of the present invention; Figure 3 A schematic diagram of vertical shadow length provided by an embodiment of the present invention; Figure 4 A schematic diagram of the basic components of a soil erosion gully depth monitoring system based on photogrammetry provided by one embodiment of the present invention; The reference numerals in the figure are: 10. Memory; 20. Processor; 21. Gully image acquisition module; 22. Existing shadow analysis module; 23. Parallel gully area analysis module and 24. Gully depth measurement module. DETAILED DESCRIPTION

[0018] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the soil erosion gully depth monitoring method and system based on photogrammetry proposed by the present invention, its specific implementation method, structure, features and effects, in conjunction with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. Terms such as "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a circuit structure, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the article or device including the element.

[0020] A specific scheme of a soil erosion gully depth monitoring method based on photogrammetry provided by the present invention is described in detail below in conjunction with the accompanying drawings.

[0021] See also Figure 1 , which shows the basic process of a soil erosion gully depth monitoring method based on photogrammetry provided by an embodiment of the present invention.

[0022] like Figure 1 As shown, a soil erosion gully depth monitoring method based on photogrammetry is provided in one embodiment of the present invention, which specifically includes: S100: Obtain orthophoto images of soil erosion gullies.

[0023] In the hilly areas of the Loess Plateau, UAV formations or single UAVs are used to fly at the same altitude multiple times to capture soil erosion gully images from different perspectives based on the preset image scale. The soil erosion gully images are preprocessed, which includes: grayscale processing of the soil erosion gully images to obtain soil erosion gully grayscale images; and feature extraction and feature matching of the soil erosion gully grayscale images using the SIFT algorithm to obtain orthophoto images of the soil erosion gully.

[0024] So far, the orthophoto image of soil erosion gullies has been obtained. Next, the orthophoto image is used to analyze and calculate the depth of soil erosion gullies.

[0025] In the hilly areas of the Loess Plateau, soil erosion gullies are intricately distributed. When the orthophoto image is taken, the direction of light irradiation forms multiple angles with the soil erosion gullies. Therefore, there must be a situation where the direction of light irradiation is parallel to the direction of the soil erosion gullies. Both sides of these soil erosion gullies are affected by sunlight, so that in the image taken by the camera, the shadows on both sides are not obvious enough, resulting in the failure of the method of calculating the depth of the soil erosion gullies using the shadow length. However, in the hilly areas of the Loess Plateau, soil erosion gullies are caused by soil erosion, so the depth of the soil erosion gullies is continuously distributed, and the depth of the soil erosion gullies shows a characteristic of shallow to deep from the higher position to the lower position. In addition, soil erosion gullies are generally winding and tortuous, and there are gullies perpendicular to the direction of light irradiation, and there are also gullies parallel to the direction of light irradiation, so the depth of other parallel gullies without shadows can be calculated by using the gullies with shadows, combined with the trend of changes in the contours of all gullies in which they are located. Specifically, it includes steps S200 to S400.

[0026] S200: Based on the orthophoto image, identify the existing shadow, analyze the length of the existing shadow, and convert the length of the existing shadow at different angles to obtain the vertical shadow length of the existing shadow.

[0027] The depth of soil erosion gullies is related to the length of shadows created by sunlight. The longer the shadow, the deeper the soil erosion gullies. The two are positively correlated. However, due to the intricate distribution of soil erosion gullies and the difference in angle between the direction of soil erosion gullies and the direction of sunlight, the length of the existing shadow cannot be directly used as a basis for comparing the depth of soil erosion gullies. It is necessary to convert the length of existing shadows at different angles to obtain the shadow length at the same angle.

[0028] Therefore, the embodiment of the present invention identifies the existing shadows based on the orthophoto image, analyzes the lengths of the existing shadows, and converts the lengths of the existing shadows at different angles to obtain the vertical shadow lengths of the existing shadows.

[0029] Furthermore, based on the orthophoto, the existing shadows are identified and their lengths are analyzed, including: Firstly, based on the orthophoto image, the CNN neural network is used to obtain the edge contour and identify the existing shadows and the direction of light exposure. Furthermore, the network architecture of the CNN neural network is convolution-pooling-classification output, the input is the orthophoto image, the output is the segmented soil erosion gully contour and the shadow distribution in the soil erosion gully and the direction of light exposure, the loss function is the cross entropy loss, and the training set consists of the orthophoto image and the manually annotated image, such as Figure 2As shown in , the manually annotated parts of the manually annotated image include the edge contour of the soil erosion gully, the shadow distribution in the soil erosion gully, and the direction of light irradiation, where the direction of light irradiation is represented by the angle between the direction of light irradiation and the vertical direction of the orthophoto image, as shown in Figure 2 As shown, the light irradiation direction is 45 degrees.

[0030] For the convenience of subsequent calculations, after obtaining the light irradiation direction, the orthophoto image is rotated so that the light irradiation direction is the horizontal direction of the orthophoto image.

[0031] Then, based on the edge contour, the existing shadow length direction is determined. The specific operation method for determining the existing shadow length direction is: from one end of the soil erosion gully, select discontinuous shadow length lines along the edge contour line, and the direction perpendicular to the edge contour line is the existing shadow length direction. In addition, because the soil erosion gullies in the hills of the Loess Plateau are usually caused by soil erosion, in order to facilitate subsequent calculations, it is usually determined in combination with the GIS system to select the shadow length line from the higher end of the soil erosion gully to the lower end, that is, from the higher end of the soil erosion gully to the lower end, the existing shadow length line is selected at intervals of 3 to 5 pixels, and the direction perpendicular to the edge contour line is the existing shadow length direction.

[0032] Then, because there may be debris in the soil erosion gullies, the debris will affect the shadow of the soil erosion gullies, and the shadow is usually distributed continuously, so the effective existing shadow length can be determined according to the degree of shadow continuity along the length direction of the existing shadow. The degree of continuity of the shadow is related to the number of alternations of black and white pixels. The more frequent the alternation, the more debris there is in the shadow and the lower the degree of continuity. Therefore, the degree of continuity of the existing shadow can be obtained by analyzing the number of alternations of black and white pixels in the length direction of the existing shadow. The specific method for calculating the degree of continuity of the existing shadow is: ; In the formula, Indicates The degree of continuity of the existing shadow in the length direction of the existing shadow; Indicates The number of times black and white pixels alternate along the length of the existing shadow; represents the linear normalization function.

[0033] It should be noted that in order to ensure that the calculation results are meaningful, when performing fractional operations in the embodiments of the present invention, when the denominator is 0, it is necessary to add a parameter adjustment factor greater than 0 to the denominator to prevent the denominator from being 0. The value of the parameter adjustment factor is set by the implementer according to actual conditions, and this application does not impose any special restrictions.

[0034] The fewer times black and white pixels alternate in the length direction of the existing shadow, the higher the degree of continuity of the existing shadow.

[0035] Finally, according to the continuity of the existing shadow and the number of black pixels in the length direction of the existing shadow, the length of the existing shadow is obtained. The specific method for calculating the length of the existing shadow is: ; In the formula, Indicates The length of the existing shadow in the direction of the existing shadow length; Indicated in The number of black pixels in the length direction of the existing shadow; Indicates The degree of continuity of the existing shadow in the length direction of the existing shadow; Indicates that the data in brackets is rounded up.

[0036] The continuity of the existing shadow is used as a weight, combined with the number of black pixels in the length direction of the existing shadow to obtain the length of the existing shadow. The greater the continuity of the existing shadow and the more black pixels in the length direction of the existing shadow, the longer the corresponding length of the existing shadow.

[0037] At this point, the length of the existing shadow is obtained.

[0038] In order to compare the length of the existing shadow later, the length of the existing shadow is converted into the length in the vertical direction of the light. Therefore, by converting the length of the existing shadow at different angles, the vertical shadow length of the existing shadow is obtained. Further, according to the vertical direction of the edge contour and the light irradiation direction, the angle of the edge contour is determined; according to the angle of the edge contour, combined with the length of the existing shadow, the vertical shadow length of the existing shadow is obtained.

[0039] Specifically, the length direction of the existing shadow is perpendicular to the edge contour, so it is necessary to calculate the angle between the edge contour direction of the existing shadow position and the vertical direction of the light irradiation, and then obtain the vertical shadow length corresponding to the existing shadow. Figure 3 As shown, Figure 3 In the calculation, the angle between the shadow outline and the vertical line of the light irradiation direction can be calculated based on the local pixels of the shadow outline. Since the orthophoto image is rotated, the vertical direction of the orthophoto image is the vertical direction of the light irradiation. Therefore, the ratio of the ordinate to the abscissa of the local edge outline is the tangent value of the angle between the shadow outline and the vertical line of the light irradiation direction. The angle of the edge contour in the length direction of the existing shadow is the soil erosion gully. The angle between the edge contour in the direction of the existing shadow length and the perpendicular direction of the light irradiation direction, so the angle calculation formula for constructing the edge contour is: ; In the formula, Indicates The angle of the edge contour where the length direction of the existing shadow lies; Indicates The average of the pixel ordinates of the edge contour positions in the length direction of the existing shadows; Indicates The average of the horizontal coordinates of the pixels at the edge contour position in the direction of the existing shadow length; where the coordinate origin of the orthophoto image is located in the upper left corner of the image, and the right and downward directions are positive directions; Represents the inverse tangent function.

[0040] After calculating the angle of the edge contour, the larger the angle value, the more perpendicular the local gully is to the light irradiation direction; the smaller the angle value, the more parallel the local gully is to the light irradiation direction. When the angle is too small, the degree of parallelism is large, and the shadow will hardly reflect the depth of the gully.

[0041] Therefore, the angle of the edge contour is determined, and then the following steps are included: setting an angle threshold, which can be 30 degrees; judging the relationship between the angle of the edge contour and the angle threshold; if the angle of the edge contour is greater than or equal to the angle threshold, that is, , then the gully area corresponding to the edge contour is the existing shadow; otherwise, , the gully area corresponding to the edge contour is the parallel gully area.

[0042] for The vertical shadow length of the existing shadow is calculated by the formula: ; In the formula, Indicates The vertical projection length of the existing shadow in the direction of the existing shadow length; Indicates The length of the existing shadow in the direction of the existing shadow length; Indicates The angle of the edge contour where the length direction of the existing shadow lies; represents the cosine function; Indicates that the data in brackets is rounded up.

[0043] for The parallel gully area is the virtual vertical shadow length, which needs to be analyzed according to the change law of soil erosion gully depth.

[0044] S300: Analyze the change rate of the soil erosion gully based on the vertical shadow length of the existing shadow, and obtain the virtual vertical shadow length of the parallel gully area.

[0045] Soil erosion gullies in the hilly areas of the Loess Plateau are usually caused by water and soil loss, which erodes from the higher side to the other side. The soil erosion gullies in higher terrain are shallower, while the soil erosion gullies in lower terrain are deeper. Usually, the geographical environment of a soil erosion gully is consistent, so the erosion change rates of soil erosion gullies at different locations are relatively similar, so the change rate of soil erosion gullies at local locations can be used to replace the change rate of soil erosion gullies at other locations.

[0046] The depth of the soil erosion gully is reflected in the change of the shadow length. The longer the vertical shadow length is, the deeper the soil erosion gully is. Therefore, the change rate of the existing shadow length can be used as the erosion change rate of the entire soil erosion gully, and then the unknown vertical shadow length of other positions of the entire soil erosion gully can be obtained according to the continuous change of the shadow length. Since the shadow of the parallel gully area is small or non-existent, the shadow of this area is represented as a virtual shadow, and its corresponding vertical shadow length is represented as the virtual vertical shadow length.

[0047] Based on the above analysis, this embodiment analyzes the change rate of soil erosion gullies based on the vertical shadow length of the existing shadow, and obtains the virtual vertical shadow length of the parallel gully area. Further, it includes: First, the vertical shadow lengths of all existing shadows are arranged in order from the higher end to the lower end of the soil erosion gully, and the virtual vertical shadow lengths distributed in the parallel gully area are processed by invalid data placeholders to obtain a vertical shadow length sequence, for example: [45, -1, -1, 42, 40, 36, -1, -1, -1], where the virtual vertical shadow length is represented by -1.

[0048] Then, because the vertical shadow length sequence obtained above is arranged from high terrain to low terrain, there are points with smaller shadow contour angles, and some unknown data exists, which needs to be eliminated. Therefore, the distribution of vertical shadow length data and invalid data in the vertical shadow length sequence is analyzed to obtain the change rate of soil erosion gullies. The calculation method of the overall change rate of soil erosion gullies is: ; In the formula, Indicates the rate of change of soil erosion gullies; Indicates the number of existing shadows with vertical shadow length; Indicates the first existing shadows with vertical shadow length; Indicates The vertical projection length of the existing shadow in the direction of the existing shadow length; Indicates the number of invalid data between two vertical projection length data; express Indicates After the vertical projection length of the existing shadow in the direction of the existing shadow length, the interval Invalid data, There is a vertical shadow length.

[0049] The change rate of soil erosion gullies is obtained by calculating the mean of the difference between all two adjacent vertical projection lengths.

[0050] Finally, according to the change rate and the vertical shadow length of the existing shadow, the virtual vertical shadow length of the parallel gully area is obtained. The vertical shadow length of the first The corresponding virtual vertical shadow length, The vertical shadow length of each is known. Since the vertical shadow length sequence is sorted from high to low according to the terrain, if Greater than , indicating that the virtual vertical shadow length position is above the known vertical shadow length position. From the above analysis, we can see that the higher the soil erosion gully is, the shallower the depth of the soil erosion gully is, and the smaller the corresponding virtual vertical shadow length is. Less than , which means that the virtual vertical shadow length position is below the known vertical shadow length position. The deeper the soil erosion gully below is, the larger the virtual vertical shadow length is. The length of the virtual vertical shadow is: ; In the formula, Indicates The virtual vertical shadow length; Indicates The vertical projection length of the existing shadow in the direction of the existing shadow length; Indicates the sequence position corresponding to the vertical shadow length of the existing shadow in the vertical shadow length sequence; Indicates the sequence position corresponding to the virtual vertical shadow length in the vertical shadow length sequence; The interval between the position representing the vertical shadow length of the existing shadow and the position representing the virtual vertical shadow length; Represents the rate of change of soil erosion gullies.

[0051] When , it means that the virtual vertical shadow length position is above the known vertical shadow length position. The higher the position is above the soil erosion gully, the shallower the depth of the soil erosion gully is, and the smaller the corresponding virtual vertical shadow length is. Therefore, the virtual vertical shadow length is obtained by reducing a certain length on the basis of the vertical projection length of the existing shadow, where the reduced length amplitude is proportional to the change rate of the soil erosion gully and the interval between the position of the vertical shadow length of the existing shadow and the position of the virtual vertical shadow length. When , it means that the position of the virtual vertical shadow length is below the known vertical shadow length position. The depth of the soil erosion gully below is larger, and the virtual vertical shadow length is larger. Therefore, the virtual vertical shadow length is obtained by adding a certain length to the vertical projection length of the existing shadow, where the increased length is proportional to the change rate of the soil erosion gully and the interval between the position of the vertical shadow length of the existing shadow and the position of the virtual vertical shadow length.

[0052] At this point, the vertical shadow lengths of all positions are obtained, that is, a complete vertical shadow length sequence is obtained.

[0053] S400: Obtaining a measured depth of a soil erosion gully according to a vertical shadow length of an existing shadow and a virtual vertical shadow length of a parallel gully region.

[0054] The above process obtains the vertical shadow length sequence of different positions of the soil erosion gully, and then uses the existing method to obtain the measured depth of the soil erosion gully according to the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area. Among them, the existing method can adopt the rapid measurement method of soil erosion gully depth based on photogrammetry provided by publication number CN115060231B. The specific steps are as follows: A vertical shadow length sequence is formed according to the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area; According to the related method described in the rapid measurement method of soil erosion gully depth based on photogrammetry provided by the prior art CN115060231B, it is necessary to determine key parameters such as the sun's altitude, date, longitude and latitude, calculate the incident angle of the sun's rays, and obtain the relationship between the vertical shadow length and the actual soil erosion gully depth. For specific methods, please refer to the technology CN115060231B, which will not be repeated here; According to the above relationship, the vertical shadow length sequence is converted into the actual soil erosion gully depth sequence; The soil erosion gully depth sequence is used to correspond to the original soil erosion gullies to obtain the distribution of soil erosion gully depth; Finally, the current soil erosion gully depth distribution is compared with the historical soil erosion gully depth distribution, and the required monitoring indicators such as soil and water loss are obtained according to the soil erosion gully monitoring module.

[0055] Based on the same inventive concept as the above method, this embodiment also provides a soil erosion gully depth monitoring system based on photogrammetry.

[0056] See also Figure 4 , which shows the basic composition of a soil erosion gully depth monitoring system based on photogrammetry provided by an embodiment of the present invention.

[0057] like Figure 4 As shown, a soil erosion gully depth monitoring system based on photogrammetry includes: a memory 10 and a processor 20, wherein: A memory 10, used for storing program codes; The processor 20 is used to read the program code stored in the memory 10 and execute to obtain the orthophoto image of the soil erosion gully; based on the orthophoto image, identify the existing shadow, analyze the length of the existing shadow, and convert the length of the existing shadow at different angles to obtain the vertical shadow length of the existing shadow; based on the vertical shadow length of the existing shadow, analyze the change rate of the soil erosion gully to obtain the virtual vertical shadow length of the parallel gully area; according to the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area, obtain the measured depth of the soil erosion gully.

[0058] Furthermore, the processor 20 includes a gully image acquisition module 21, an existing shadow analysis module 22, a parallel gully region analysis module 23 and a gully depth measurement module 24. Among them: A gully image acquisition module 21 is used to obtain orthophoto images of soil erosion gullies; The existing shadow analysis module 22 is used to identify the existing shadow based on the orthophoto image, analyze the length of the existing shadow, and convert the length of the existing shadow at different angles to obtain the vertical shadow length of the existing shadow; A parallel gully region analysis module 23 is used to analyze the change rate of the soil erosion gully based on the vertical shadow length of the existing shadow, and obtain a virtual vertical shadow length of the parallel gully region; The gully depth measurement module 24 is used to obtain the measured depth of the soil erosion gully according to the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area.

[0059] It should be noted that the sequence of the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0060] Various embodiments in this specification are described in a progressive manner, and the same or similar parts between various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A soil erosion gully depth monitoring method based on photogrammetry, characterized in that: The method comprises: Obtain orthophotos of soil erosion gullies; Based on the orthophoto image, identifying the existing shadow, analyzing the length of the existing shadow, and converting the lengths of the existing shadows at different angles to obtain the vertical shadow length of the existing shadow; Based on the vertical shadow length of the existing shadow, the change rate of soil erosion gullies is analyzed to obtain the virtual vertical shadow length of the parallel gully area; The measured depth of the soil erosion gully is obtained based on the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area.

2. The method for monitoring soil erosion gully depth based on photogrammetry according to claim 1, characterized in that: Based on the orthophoto image, identifying existing shadows and analyzing the length of the existing shadows include: Based on the orthophoto, a CNN neural network is used to obtain edge contours and identify existing shadows and light irradiation directions; Based on the edge contour, determining the direction of the existing shadow length; Analyze the number of alternations of black and white pixels in the length direction of the existing shadow to obtain the continuity of the existing shadow; The length of the existing shadow is obtained according to the continuity degree of the existing shadow and the number of black pixels in the length direction of the existing shadow.

3. The soil erosion gully depth monitoring method based on photogrammetry according to claim 2 is characterized in that: The CNN neural network: The network architecture is convolution-pooling-classification output; The input is an orthophoto; The output is the segmented soil erosion gully outline and the shadow distribution within the soil erosion gully; The loss function is cross entropy loss; The training set consists of orthophotos and manually annotated images, where the manually annotated parts of the manually annotated images include the contours of soil erosion gullies, the shadow distribution within the soil erosion gullies, and the direction of light exposure.

4. The method for monitoring soil erosion gully depth based on photogrammetry according to claim 2, characterized in that: Convert the lengths of existing shadows at different angles to obtain the vertical shadow lengths of existing shadows, including: Determining the angle of the edge profile according to the perpendicular direction between the edge profile and the light irradiation direction; The vertical shadow length of the existing shadow is obtained according to the angle of the edge contour and the length of the existing shadow.

5. The method for monitoring soil erosion gully depth based on photogrammetry according to claim 4, characterized in that: Determining the angle of the edge profile, and then further comprising: Set the angle threshold; Determine the magnitude relationship between the angle of the edge contour and the angle threshold; If the angle of the edge contour is greater than or equal to the angle threshold, the gully area corresponding to the edge contour is an existing shadow; Otherwise, the gully region corresponding to the edge contour is a parallel gully region.

6. The method for monitoring soil erosion gully depth based on photogrammetry according to claim 2, characterized in that: Based on the edge contour, determining the direction of the existing shadow length includes: Combined with GIS system, determine the height of soil erosion gullies; From the higher end of the soil erosion gully to the lower end, the existing shadow length line is selected at intervals of 3 to 5 pixels, and the direction perpendicular to the edge contour line is the existing shadow length direction.

7. The method for monitoring soil erosion gully depth based on photogrammetry according to claim 6, characterized in that: Based on the vertical shadow length of the existing shadow, the change rate of soil erosion gullies is analyzed to obtain the virtual vertical shadow length of the parallel gully area, including: The vertical shadow lengths of all existing shadows are arranged in order from the higher end of the soil erosion gully to the lower end, and the virtual vertical shadow lengths distributed in the parallel gully area are processed by invalid data placeholders to obtain a vertical shadow length sequence; Analyze the distribution of vertical shadow length data and the invalid data in the vertical shadow length sequence to obtain the change rate of the soil erosion gully; According to the change rate and in combination with the vertical shadow length of the existing shadow, a virtual vertical shadow length of the parallel gully area is obtained.

8. The method for monitoring soil erosion gully depth based on photogrammetry according to claim 1, characterized in that: Obtain orthophotos of soil erosion gullies, including: Use drones to capture images of soil erosion gullies from different perspectives; grayscale the soil erosion gully image to obtain a soil erosion gully grayscale image; Feature extraction and feature matching are performed on the soil erosion gully grayscale image to obtain an orthophoto image of the soil erosion gully.

9. A soil erosion gully depth monitoring system based on photogrammetry, characterized in that: The system comprises: a memory and a processor, wherein: The memory is used to store program code; The processor is configured to read the program code stored in the memory and execute the method according to any one of claims 1 to 8.

10. The soil erosion gully depth monitoring system based on photogrammetry according to claim 9, characterized in that: The processor comprises: Gully image acquisition module, used to obtain orthophoto images of soil erosion gullies; An existing shadow analysis module is used to identify the existing shadow based on the orthophoto image, analyze the length of the existing shadow, and convert the length of the existing shadow at different angles to obtain the vertical shadow length of the existing shadow; The parallel gully area analysis module is used to analyze the change rate of soil erosion gullies based on the vertical shadow length of the existing shadows and obtain the virtual vertical shadow length of the parallel gully area; The gully depth measurement module is used to obtain the measured depth of the soil erosion gully according to the vertical shadow length of the existing shadow and the virtual vertical shadow length of the parallel gully area.

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