Methods for measuring the slope ratio of silt-retaining dams on the Loess Plateau

Abstract

This invention discloses a method for measuring the slope ratio of silt-retaining dams on the Loess Plateau, specifically implemented according to the following steps: Step 1, planning the UAV flight mission and constructing a geometric measurement model of the dam slope ratio; Step 2, acquiring images according to predetermined photographic positions and angles, and selecting images that meet the orthophoto requirements of the model; Step 3, extracting the UAV imaging altitude information from the images that meet the imaging requirements, extracting the model parameter information of feature targets in the images, and performing calculations. This invention achieves high-precision and high-efficiency measurement by constructing a mathematical measurement model of the silt-retaining dam slope ratio; by obtaining the scale relationship of the captured images through orthophoto recognition of silt-retaining dam feature indicators, an accurate spatial relationship between the UAV and the silt-retaining dam is established; and by employing a dual screening process of on-site interactive acquisition and image imaging analysis, the compliance of the acquired images is ensured, information extraction is completed quickly, and the needs of efficient thematic interpretation are met.

Description

Technical Field

[0001] This invention belongs to the field of silt-retention dam index measurement technology, and relates to a method for measuring the slope ratio information of silt-retention dams on the Loess Plateau. Background Technology

[0002] Soil erosion is a prominent problem on the Loess Plateau. A large number of silt-retaining dams have been built along the various levels of gullies to trap silt and create land. While these dams generate significant benefits, they also face major challenges in safe operation and management. During operation, the complex rainstorms, floods, and geological conditions of the watershed cause changes in some key indicators. Furthermore, the dam body is affected by various external conditions, causing changes in the mechanical parameters of the dam materials, directly impacting the stability of the dam slopes and potentially leading to landslides or even dam failure.

[0003] The dam slope ratio is not only a crucial parameter in the design of silt-retention dams, but also a vital basis for assessing the stability of the dam body during operation, and therefore must be accurately determined. Due to the age of some silt-retention dams and the incompleteness of design data, technical specifications are often incomplete, making dam slope ratio data reliant on on-site surveys. Influenced by micro-topographical conditions, the dam slope of silt-retention dams is not a uniform, single-gradient surface. On-site measurements require multiple personnel, resulting in low efficiency, time-consuming, and labor-intensive methods. Traditional measuring equipment, such as total stations and slope meters, requires manual measurement, involving walking back and forth along the upstream and downstream slopes of the dam. This approach has limitations in portability and operability, poor applicability in complex field environments, and measurement accuracy is significantly affected by micro-topographical conditions, incorporating estimation components and easily leading to deviations in the results. Summary of the Invention

[0004] The purpose of this invention is to provide a method for measuring the slope ratio of silt-retaining dams in the Loess Plateau, which solves the problems of low efficiency and low accuracy in existing silt-retaining dam slope ratio measurement technologies in the Loess Plateau.

[0005] The technical solution adopted in this invention is a method for measuring the slope ratio of silt-retaining dams on the Loess Plateau, which is implemented according to the following steps:

[0006] Step 1: Plan the drone flight mission and construct a geometric measurement model of the dam slope ratio;

[0007] Step 2: According to the planned drone flight mission, images are acquired at predetermined photography positions and angles, and images that meet the requirements of model orthophotography are selected.

[0008] Step 3: Extract the UAV imaging altitude information from the image that meets the imaging requirements, extract the model parameter information of the feature targets in the image, and perform calculations.

[0009] The invention is further characterized in that,

[0010] Step 1 is implemented in the following steps:

[0011] Step 1.1: Use an RTK drone to collect orthophotos of relevant technical indicators of silt-retention dams and obtain the actual distance between any two feature targets in the image;

[0012] Step 1.2: Determine the camera's field of view using the diameter of the visible area;

[0013] Step 1.3: Based on the feature target length measurement method and camera field of view theory, and combined with the acquisition of dam height index information of silt-retaining dams, a geometric measurement model of dam slope ratio is constructed.

[0014] Step 1.1 is as follows: The UAV takes off from any suitable position on the top of the dam, adjusts the gimbal camera to point vertically downwards, and climbs to a height that allows the entire appearance of the silt-retention dam's characteristic targets to be fully displayed on the flight control interface. The UAV stabilizes, takes photos, and transmits them back to the host computer or flight control equipment. The length of the silt-retention dam's characteristic targets is visually interpreted in the image processing and analysis software interface. The software detects the image pixel length of the silt-retention dam's characteristic targets and the diagonal pixel length of the transmitted image. The actual length of the silt-retention dam's characteristic targets can be obtained by multiplying the image pixel length of the characteristic targets by the ratio of the actual diagonal length to the diagonal pixel length.

[0015] Step 1.2 specifically involves: The camera field of view represents the geometric correspondence between the transmitted image and the framing range; where ∠θ is the camera field of view of the UAV, O and H represent the position and altitude of the UAV when shooting the feature target, respectively, O′ is the projection point on the ground when the UAV shoots the feature target, and the distance BO′ can be obtained according to the trigonometric function formula H*tan(1 / 2θ), thus obtaining the actual distance between AB;

[0016] The formula for calculating the actual length of the characteristic target of a silt-retaining dam is:

[0017] L=l'×(l / p) (1)

[0018] In the formula, L is the actual length of the silt-retention dam feature target, l′ is the pixel length of the silt-retention dam feature target, p is the pixel length of the diagonal of the returned image, p is a constant, and l is the actual length of the diagonal of the returned image; where the actual length l of the diagonal of the returned image is:

[0019] l=2×H×tan(1 / 2θ) (2)

[0020] In the formula, l is the actual length of the diagonal of the transmitted image, H is the drone's shooting height, and θ is the drone's field of view.

[0021] Step 1.3.1: When the dam height is known, obtain the dam height index information of the silt-retaining dam;

[0022] The dam slope ratio index includes the upstream and downstream dam slope ratios. Considering the possibility of siltation upstream of silt-retaining dams, the measurement model for the upstream and downstream dam slope ratios differs somewhat from the UAV flight mission. The specific flight mission planning and model construction are as follows:

[0023] When there is siltation upstream, the UAV flight mission for the upstream dam slope ratio measurement model is as follows:

[0024] The drone can take off from any suitable location in the middle of the dam crest and reach a certain altitude h. 1 Maintaining the current altitude, fly upstream while adjusting the aircraft via the flight control interface so that the gimbal camera is directly facing the silt-retaining dam, i.e., the horizontal reference line on the flight control interface is parallel to the dam crest. After completing this maneuver, adjust the gimbal camera vertically downwards, maintaining the current altitude and heading to continue flying until the boundary line between the upstream silt surface and the dam slope appears on the flight control interface, then hover. Next, fly downstream in the opposite direction until the boundary line disappears, denoted as p. 1 Stabilize the drone, then take a picture and transmit it back to the host computer or flight control equipment; after completing the maneuver, operate the drone to continue climbing, and mark the position before the dam crest line appears on the flight control interface as p. 2 The aircraft hovers and stabilizes, then takes a picture and transmits it back to the host computer or flight control equipment;

[0025] In actual flight missions, the drone hovers and takes photos in a straight line, but the position is not fixed. It depends on the length of the dam slope. When the dam slope is long enough, the position can be adjusted appropriately, but the drone must be in a position that meets the requirements of p. 1 The dam slope is visible on the flight control interface when the position is set, and it is in the p position. 2 The dam crest is not visible on the flight control interface when the drone is positioned, so that one long side of the orthophoto image is between the boundary between the dam slope and the silted ground and the dam crest.

[0026] Given the dam height and the presence of siltation, consider the upstream dam slope ratio measurement model. Let EF = x, EG = y, GH = a, GI = b, BE = c, and AE = d, where x, y, a, b, c, and d all represent lengths. Specifically: x and y are unknown; a and b can be calculated using the feature target length measurement method based on the returned images; c represents a length equal to the dam height h and the initial flight altitude h of the UAV. 1 The sum of the dam height h is directly obtained; d represents the length, which is equal to the dam height h and the final hovering photography height h of the drone. 2 sum;

[0027] c = h + h 1 (3)

[0028] d = h + h 2 (4)

[0029] According to the Pythagorean theorem:

[0030]

[0031] Since ΔEGF ~ ΔHGJ, by the similar triangle theorem, we know that:

[0032]

[0033] Since quadrilateral BEHJ ~ quadrilateral AEIK, we can obtain the following by the similar polygon theorem;

[0034]

[0035] According to trigonometric functions, we can obtain:

[0036]

[0037] Combining the above equations, we obtain x and y, which are the upstream dam slope ratios:

[0038]

[0039] When there is no siltation, the measurement model for the upstream and downstream dam slope ratio is as follows:

[0040] The drone can take off from any suitable location in the middle of the dam crest and reach a certain altitude h. 1 Maintain the current altitude and fly upstream or downstream of the silt-retention dam. Simultaneously, adjust the aircraft via the flight control interface so that the gimbal camera is directly facing the dam, meaning the horizontal reference line on the flight control interface is parallel to the dam crest. After completing this maneuver, adjust the gimbal camera vertically downwards, maintaining the current altitude and heading, and continue flying until the boundary line between the upstream or downstream dam slope and the riverbed appears on the flight control interface. Hover at this point, then fly in the opposite direction until the boundary line disappears. This point is recorded as p. 1 Hover and stabilize the drone, then take photos and transmit them back to the host computer or flight control equipment. After completing the above actions, return to base. If the boundary line cannot be determined, adjust the drone's position laterally along the direction parallel to the dam body so that the distance between the drone's projection point on the riverbed and the lowest point of the upstream or downstream dam slope is the shortest. This ensures that the lowest point of the upstream or downstream dam slope is located above the midpoint of the flight control interface, and this position is determined as the photography position. Similarly, the hovering photography position is not fixed and can be adjusted appropriately according to the length of the dam slope, but it must ensure that the dam slope is visible but the dam top is not visible on the flight control interface when the drone is in this position.

[0041] Given the dam height and without siltation, a model for measuring the upstream and downstream dam slope ratios is provided. Let EF = x, EG = e, GH = a, BE = c, where x, e, a, and c all represent lengths. Specifically: x is unknown; e and a can be calculated using a feature-based target length measurement method based on the returned images; c represents a length equal to the dam height h and the drone's hovering camera altitude h. 1The sum of these values, and the dam height h, are known and obtained from the design documents;

[0042]

[0043] Since ΔEGF ~ ΔHGJ, by the similar triangle theorem, we know that:

[0044]

[0045] Based on trigonometric functions, we can obtain the following formula:

[0046]

[0047] x can then be calculated, and from there, the slope ratio of the upstream or downstream dam can be obtained:

[0048]

[0049] Step 1.3.2: When the dam height is unknown, the dam height information cannot be directly obtained from the design documents. It is necessary to measure the dam height and the height difference from the upstream siltation surface to the dam crest. The measurement model for the upstream and downstream dam slope ratio is basically consistent with the UAV flight mission. The UAV is used to collect orthophotos of the characteristic targets of the silt-retaining dam. The specific flight mission planning and model construction are as follows:

[0050] Take off from any suitable location on the top of the dam using a drone, adjust the gimbal camera to point vertically downwards, and climb to a certain height h. 1 This allows the aircraft to stabilize itself while the entire dam structure is fully displayed on the flight control interface, enabling it to take photos and transmit them back to the host computer or flight control equipment.

[0051] Adjust the drone's orientation and maintain the current altitude to fly upstream or downstream of the silt-retention dam. Use the flight control interface to adjust the drone so that the gimbal camera is directly facing the dam, meaning the horizontal reference line on the flight control interface is parallel to the dam crest. After completing this maneuver, adjust the gimbal camera vertically downwards and continue flying at the current altitude and heading until the boundary line between the upstream dam slope and the silt-retention surface or the boundary line between the downstream dam slope and the riverbed appears on the flight control interface. Hover and stabilize the drone, take photos, and transmit them back to the host computer or flight control equipment. If the boundary line cannot be determined, adjust the drone's position laterally along a direction parallel to the dam body so that the distance between the drone's projection point on the riverbed and the lowest point of the downstream dam slope is minimized.

[0052] When the dam height is unknown, the slope ratio of a silt-retaining dam can be measured using a trigonometric function model, yielding the slope ratio tanα:

[0053]

[0054] in,

[0055] x = d / tan(1 / 2θ) - h 1 (15)

[0056] In the formula, h 1 θ is the take-off altitude of the UAV on the top of the dam, θ is the field of view angle of the UAV camera, d represents the shortest horizontal distance from the UAV hovering and photographing position on the upstream and downstream of the silt-retaining dam to the foot of the dam slope, and b represents the shortest horizontal distance from the foot of the dam slope to the top of the dam. Both d and b can be calculated using the feature target length measurement method based on the returned image to obtain the actual length corresponding to their pixel length.

[0057] When measuring the upstream dam slope ratio, x represents the height difference between the silt surface and the dam crest, and d represents the shortest distance from the UAV camera's projection point C on the silt surface to point D on the boundary line between the upstream silt surface and the dam slope, with CD perpendicular to the boundary line. When measuring the downstream dam slope ratio, x represents the downstream dam height h, and the measurement method is the same as that for measuring the height difference between the silt surface and the dam crest. d represents the shortest distance from the UAV camera's projection point on the riverbed to the boundary line between the downstream riverbed and the dam slope, or the lowest point of the dam slope.

[0058] In the actual measurement of the height difference between the silt surface and the dam crest, to reduce errors, the UAV can perform multiple flight missions and the average value can be taken; the UAV flight altitude is set to h. 1 h 2 …h n They arrived at their respective photography positions to carry out their tasks.

[0059] Or maintain the drone at the same altitude h 1 Moving laterally parallel to the dam crest, n photographic positions are selected for photographic work. All these positions are on the same horizontal straight line parallel to the aforementioned boundary line. The height difference x between the silt surface and the dam crest is expressed as:

[0060]

[0061] In the formula, x1, x2, x n The elevation difference between the silt surface and the dam crest was measured multiple times.

[0062] Step 2 is implemented in the following steps:

[0063] Step 2.1, On-site interactive data acquisition: Based on the dam slope ratio geometric measurement model constructed in Step 1 and the corresponding flight mission requirements, the image acquisition process is controlled in real time using the image transmission screen of the UAV flight control interface in a human-computer interaction manner. During the image acquisition process, the UAV is brought to the designated photography position according to the predetermined flight mission, and the image is acquired in a human-computer interaction manner using the image transmission screen of the UAV flight control interface according to the designated photography actions.

[0064] Step 2.2: Extract basic image information and UAV flight data, obtain UAV flight attitude information, perform image imaging analysis, and determine whether the imaging direction is perpendicular to the ground; for compliant images, obtain the corresponding UAV flight attitude information, gimbal camera parameters, camera imaging height and other parameters on the server device, and analyze whether the imaging direction meets the orthogonal requirements based on pitch angle and roll angle.

[0065] During step 2.1, when collecting data, check the following according to the flight mission requirements of the corresponding measurement model:

[0066] When using drones to collect images of the technical specifications of silt-retaining dams, check whether the images fully represent the overall features of the target.

[0067] When using drones to collect images of height-related technical indicators such as the height of the silt-retaining dam and the height difference between the silt surface and the dam crest, check whether the gimbal camera is facing the silt-retaining dam before taking the picture, and whether the boundary of the image transmission screen coincides with the boundary line between the upstream silt surface or the downstream riverbed and dam slope.

[0068] When using drones to collect images of technical indicators such as the slope of silt-retaining dams, the dam height is known. Before taking the picture, check whether the gimbal camera is facing the silt-retaining dam, and whether the boundary of the image transmission screen is between the boundary line between the dam slope and the silt-retaining ground and the dam crest.

[0069] The acquired images are initially screened, and images with blurry quality or poor exposure are removed on-site. Images that meet the requirements are then sent back to the host computer or flight control equipment.

[0070] In specific applications, step 2.2 involves using electronic devices such as PCs and servers to obtain EXIF ​​information through an EXIF ​​viewer; based on the pitch and roll angles, the imaging direction of the gimbal camera is determined. When the imaging direction is perpendicular to the ground, that is, theoretically the sum of the pitch angles of the UAV and the gimbal is equal to -90° and the sum of the roll angles of the UAV and the gimbal is equal to 0°, the transmitted image is considered qualified and stored; otherwise, a command is immediately sent to the flight control equipment to re-acquire the image.

[0071] Under the premise of meeting the accuracy of model calculation, set the threshold range for pitch angle and roll angle; the threshold range for the sum of pitch angles of UAV and gimbal is -85° to -95°, and the threshold range for the sum of roll angles of UAV and gimbal is -5° to 5°; if the pitch angle and roll angle are within the threshold range, the imaging direction can be regarded as perpendicular to the ground and the transmitted photos can be stored; otherwise, a command is immediately sent to the flight control equipment to re-acquire photos.

[0072] In step 3, the UAV imaging altitude information is extracted from the image that meets the imaging requirements, and the model parameter information of the feature targets in the image is extracted using the image processing software Digimizer; the length of the silt-retaining dam in the image is quickly interpreted visually, the pixel length of the feature targets is automatically detected, the length information of the selected targets is fed back through the measurement list, and the data is input into the model for calculation.

[0073] The beneficial effects of this invention are as follows: The method for measuring the slope ratio of silt-retaining dams on the Loess Plateau relies on RTK UAV high-precision positioning technology and camera field of view theory. By designing UAV flight missions and image acquisition schemes, a mathematical measurement model for the slope ratio of silt-retaining dams is constructed. The method provides reliable results for collecting slope ratio index information, with high measurement accuracy and controllable error range. The maximum error can be controlled below 3.5%, fully meeting the needs of field surveys and operation management of silt-retaining dams. It achieves efficient measurement of silt-retaining dam technical indicators, transforming the complex on-site measurement work of silt-retaining dam indicators into a simple geometric calculation process, significantly improving efficiency. Only one person and one UAV are needed to complete image acquisition on the dam top, supplemented by simple office work, to complete the measurement work. This method can meet the needs of efficient and accurate surveys of the technical indicators of tens of thousands of silt-retaining dams. Attached Figure Description

[0074] Figure 1 This is a flowchart of the method for measuring the slope ratio of silt-retaining dams on the Loess Plateau according to the present invention;

[0075] Figure 2 This is a schematic diagram of the camera field of view for the method of measuring the slope ratio of silt-retaining dams on the Loess Plateau according to the present invention;

[0076] Figure 3 This is a schematic diagram of the upstream dam slope ratio measurement model under the condition of known dam height and the presence of siltation, according to the present invention;

[0077] Figure 4 This is a schematic diagram of the upstream and downstream dam slope ratio measurement model under the condition of known dam height and no siltation.

[0078] Figure 5 This is a schematic diagram of the silt-retaining dam slope ratio measurement model under the condition of unknown dam height, according to the present invention. Detailed Implementation

[0079] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0080] This invention relates to a method for measuring the slope ratio information of silt-retaining dams on the Loess Plateau, such as... Figure 1 As shown, please follow these steps:

[0081] Step 1: Plan the drone flight mission and construct a geometric measurement model of the dam slope ratio;

[0082] Step 1.1: Use an RTK drone to collect orthophotos of relevant technical indicators of silt-retention dams and obtain the actual distance between any two feature targets in the image;

[0083] Step 1.1 is as follows: The UAV takes off from any suitable position on the top of the dam, adjusts the gimbal camera to point vertically downwards, and climbs to a height that allows the entire appearance of the silt-retention dam's characteristic targets to be fully displayed on the flight control interface. The UAV stabilizes, takes photos, and transmits them back to the host computer or flight control equipment. The length of the silt-retention dam's characteristic targets is visually interpreted in the image processing and analysis software interface. The software detects the image pixel length of the silt-retention dam's characteristic targets and the diagonal pixel length of the transmitted image. The actual length of the silt-retention dam's characteristic targets can be obtained by multiplying the image pixel length of the characteristic targets by the ratio of the actual diagonal length to the diagonal pixel length.

[0084] The drone's flight altitude represents relative altitude, specifically the vertical altitude relative to its takeoff position. In the model construction, the drone and gimbal camera can be approximated as a single point. In actual operation, due to inertia, it is difficult for the drone to directly remain or stabilize at the planned photography position; adjustments must be made based on the actual flight conditions, while still meeting the photography requirements specified in the mission plan. The planned flight maneuvers and operations in a drone mission are not the only way to achieve the drone's movement to the photography position and to capture images according to the specified requirements. Leveraging the high-precision positioning advantage of drones, and based on drone field-of-view theory, a geometric measurement model of the dam slope ratio is constructed using mathematical methods.

[0085] Step 1.2: Determine the camera's field of view using the diameter of the visible area;

[0086] Step 1.2 specifically involves: (e.g.) Figure 2 As shown, the camera field of view represents the geometric correspondence between the returned image (rectangular area in the figure) and the field of view (circular area in the figure); where ∠θ is the camera field of view of the UAV, O and H represent the position and altitude of the UAV when shooting the feature target, respectively, O′ is the projection point on the ground when the UAV shoots the feature target, and the distance BO′ can be obtained by the trigonometric function formula H*tan(1 / 2θ), thus obtaining the actual distance between AB;

[0087] The formula for calculating the actual length of the characteristic target of a silt-retaining dam is:

[0088] L=l'×(l / p) (1)

[0089] In the formula, L is the actual length of the silt-retention dam feature target, l′ is the pixel length of the silt-retention dam feature target, p is the pixel length of the diagonal of the returned image, p is a constant value, and l is the actual length of the diagonal of the returned image.

[0090] The actual length l of the diagonal of the returned image is:

[0091] l=2×H×tan(1 / 2θ) (2)

[0092] In the formula, l is the actual length of the diagonal of the transmitted image, H is the drone's shooting height, and θ is the drone's field of view.

[0093] Step 1.3: Based on the feature target length measurement method and camera field of view theory, and combined with the acquisition of dam height information of silt-retaining dams, a geometric measurement model for the dam slope ratio is constructed accordingly:

[0094] Step 1.3.1: When the dam height is known, obtain the dam height index information of the silt-retaining dam;

[0095] The dam slope ratio index includes the upstream and downstream dam slope ratios. Considering the possibility of siltation upstream of silt-retaining dams, the measurement model for the upstream and downstream dam slope ratios differs somewhat from the UAV flight mission. The specific flight mission planning and model construction are as follows:

[0096] When there is siltation upstream, the UAV flight mission for the upstream dam slope ratio measurement model is as follows:

[0097] The drone can take off from any suitable location in the middle of the dam crest and reach a certain altitude h. 1 Maintaining the current altitude, fly upstream while adjusting the aircraft via the flight control interface so that the gimbal camera is directly facing the silt-retaining dam, i.e., the horizontal reference line on the flight control interface is parallel to the dam crest. After completing this maneuver, adjust the gimbal camera vertically downwards, maintaining the current altitude and heading to continue flying until the boundary line between the upstream silt surface and the dam slope appears on the flight control interface, then hover. Next, fly downstream in the opposite direction until the boundary line disappears, denoted as p. 1 Stabilize the drone, then take a picture and transmit it back to the host computer or flight control equipment; after completing the maneuver, operate the drone to continue climbing from the above position. The position before the dam crest line appears on the flight control interface is denoted as p. 2 The aircraft hovers and stabilizes, then captures footage and transmits it back to the host computer or flight control equipment.

[0098] In actual flight missions, the hovering photography positions of the UAV are all on the same vertical line and are not fixed. They can be determined according to the length of the dam slope. When the dam slope is long enough, the positions can be adjusted appropriately, but the UAV must be in position p. 1 The dam slope is visible on the flight control interface when the position is set, and it is in the p position. 2 The dam crest is not visible on the flight control interface when the drone is positioned, so that one long side of the drone's orthophoto image is between the boundary between the dam slope and the silted ground and the dam crest.

[0099] Given the dam height, a model for measuring the upstream dam slope ratio when siltation is present, such as... Figure 3As shown, let EF = x, EG = y, GH = a, GI = b, BE = c, AE = d, where x, y, a, b, c, and d all represent lengths; where x and y are unknown; a and b can be calculated using the feature target length measurement method based on the returned image to obtain their actual pixel lengths; c represents a length equal to the dam height h and the initial flight altitude h of the UAV. 1 The sum of the dam height h is directly obtained; d represents the length, which is equal to the dam height h and the final hovering photography height h of the drone. 2 sum;

[0100] c = h + h 1 (3)

[0101] d = h + h 2 (4)

[0102] According to the Pythagorean theorem:

[0103]

[0104] Since ΔEGF ~ ΔHGJ, by the similar triangle theorem, we know that:

[0105]

[0106] Since quadrilateral BEHJ ~ quadrilateral AEIK, we can obtain the following by the similar polygon theorem;

[0107]

[0108] According to trigonometric functions, we can obtain:

[0109]

[0110] Combining the above equations, we obtain x and y, which are the upstream dam slope ratios:

[0111]

[0112] When there is no siltation, the UAV flight mission for the upstream and downstream dam slope ratio measurement model is as follows:

[0113] When there is no siltation upstream of the silt-retaining dam, the construction principle of the upstream and downstream dam slope ratio measurement model is basically the same. A drone is used to take off from any suitable location in the middle of the dam crest and reach a certain altitude h. 1 Maintain the current altitude and fly upstream (or downstream) of the silt-retention dam. Simultaneously, adjust the aircraft via the flight control interface so that the gimbal camera is directly facing the dam, meaning the horizontal reference line on the flight control interface is parallel to the dam crest. After completing this maneuver, adjust the gimbal camera vertically downwards, maintaining the current altitude and heading, until the boundary line between the upstream (or downstream) dam slope and the riverbed appears on the flight control interface. Hover at this point, then fly in the opposite direction until the boundary line disappears (denoted as p). 1Hover and stabilize the drone, then take photos and transmit them back to the host computer or flight control equipment. After completing these actions, return to base. If the boundary line cannot be determined, adjust the drone's position laterally along a direction parallel to the dam body so that the distance between the drone's projection point on the riverbed and the lowest point of the upstream (or downstream) dam slope is minimized (i.e., the lowest points of the upstream and downstream dam slopes are located above the midpoint of the flight control interface). This position is then determined as the photography position. Similarly, the above hovering photography position is not fixed and can be adjusted appropriately according to the length of the dam slope, but it must ensure that the dam slope is visible but the dam crest is not visible on the flight control interface when the drone is in this position.

[0114] Given the dam height and the absence of siltation, a model for measuring the upstream and downstream dam slope ratios is available, such as... Figure 4 As shown, let EF = x, EG = e, GH = a, BE = c, where x, e, a, and c all represent lengths; where: x is unknown; e and a can be calculated using the feature target length measurement method based on the returned image; c represents a length equal to the dam height h and the drone hovering photography height h. 1 The sum of these values, and the dam height h, are known and obtained from the design documents;

[0115] c = h + h 1 (10)

[0116] Since ΔEGF ~ ΔHGJ, by the similar triangle theorem, we know that:

[0117]

[0118] Based on trigonometric functions, we can obtain the following formula:

[0119]

[0120] x can then be calculated, and from there, the slope ratio of the upstream or downstream dam can be obtained:

[0121]

[0122] Step 1.3.2: When the dam height is unknown, the dam height information cannot be directly obtained from the design documents. It is necessary to measure the dam height and the height difference from the upstream siltation surface to the dam crest. The measurement model for the upstream and downstream dam slope ratio is basically consistent with the UAV flight mission. The UAV is used to collect orthophotos of the characteristic targets of the silt-retaining dam. The specific flight mission planning and model construction are as follows:

[0123] Take off from any suitable location on the top of the dam using a drone, adjust the gimbal camera to point vertically downwards, and climb to a certain height h. 1 This allows the aircraft to stabilize itself while the entire dam structure is fully displayed on the flight control interface, enabling it to take photographs and transmit them back to the host computer or flight control equipment.

[0124] Adjust the drone's orientation, maintaining the current altitude, and fly upstream (or downstream) of the silt-retention dam. Using the flight control interface, adjust the drone so that the gimbal camera is directly facing the dam, meaning the horizontal reference line on the flight control interface is parallel to the dam crest. After completing this maneuver, adjust the gimbal camera vertically downwards, maintaining the current altitude and heading, and continue flying until the boundary line between the upstream dam slope and the siltation surface, or the boundary line between the downstream dam slope and the riverbed, appears on the flight control interface. Hover and stabilize the drone, take photos, and transmit them back to the host computer or flight control equipment. If the boundary line cannot be determined, adjust the drone's position laterally along a direction parallel to the dam body, minimizing the distance between the drone's projection point on the riverbed and the lowest point of the downstream dam slope.

[0125] When the dam height is unknown, a model for measuring the slope ratio of a silt-retaining dam is provided, such as... Figure 5 As shown, based on trigonometric functions, the dam slope ratio tanα can be obtained:

[0126]

[0127] in,

[0128] x = d / tan(1 / 2θ) - h 1 (15)

[0129] In the formula, h 1 θ represents the takeoff altitude of the UAV at the top of the dam, θ represents the field of view angle of the UAV camera, d represents the shortest horizontal distance from the UAV's hovering photography position upstream and downstream of the silt-retaining dam to the toe of the dam slope, and b represents the shortest horizontal distance from the toe of the dam slope to the top of the dam. Both d and b can be calculated using the feature target length measurement method based on the returned images to obtain their actual pixel lengths.

[0130] When measuring the upstream dam slope ratio, x represents the height difference between the siltation surface and the dam crest, and d represents the shortest distance from the UAV camera's projection point C on the siltation surface to point D on the boundary line between the upstream siltation surface and the dam slope (CD is perpendicular to the boundary line). When measuring the downstream dam slope ratio, x represents the downstream dam height h, and the measurement method is the same as the method for measuring the height difference between the siltation surface and the dam crest. d represents the shortest distance from the UAV camera's projection point on the riverbed to the boundary line between the downstream riverbed and the dam slope (or the lowest point of the dam slope).

[0131] In the actual measurement of the height difference between the silt surface and the dam crest, to reduce errors, the UAV can perform multiple flight missions and the average value can be taken; the UAV flight altitude is set to h. 1 h 2 …h n They will proceed to the aforementioned photography locations to carry out their tasks.

[0132] Or maintain the drone at the same altitude h 1Moving laterally parallel to the dam crest, n photographic positions are selected for photographic operations. All these positions are on the same horizontal straight line parallel to the aforementioned boundary line. The height difference x between the silt surface and the dam crest is expressed as:

[0133]

[0134] In the formula, x1, x2, x n The elevation difference between the silt surface and the dam crest was measured multiple times.

[0135] Step 2: According to the planned drone flight mission, images are acquired at predetermined photography positions and angles, and images that meet the requirements of model orthophotography are selected.

[0136] Step 2.1, On-site Interactive Data Acquisition: Based on the dam slope ratio geometric measurement model constructed in Step 1 and the corresponding flight mission requirements, the image acquisition process is controlled in real time using the image transmission screen of the UAV flight control interface in a human-computer interaction manner to ensure the compliance of the acquired images. During the image acquisition process, according to the predetermined flight mission, the UAV reaches the designated photography position, and images are acquired using the image transmission screen of the UAV flight control interface in a human-computer interaction manner, following the specified photography actions.

[0137] During data collection, check the following according to the flight mission requirements of the corresponding measurement model:

[0138] When using drones to collect images of the technical specifications of silt-retaining dams, check whether the images fully represent the overall features of the target.

[0139] When using drones to collect images of height-related technical indicators such as the height of the silt-retaining dam and the height difference between the silt surface and the dam crest, check whether the gimbal camera is facing the silt-retaining dam before taking the picture, and whether the boundary of the image transmission screen coincides with the boundary line between the upstream silt surface (or the downstream riverbed) and the dam slope during the picture taking.

[0140] When using drones to collect images of technical indicators such as the slope of silt-retaining dams (with the dam height known), check whether the gimbal camera is facing the silt-retaining dam before taking the picture, and whether the boundary of the image transmission screen is between the boundary line between the dam slope and the silt-retaining ground and the dam crest during the picture taking.

[0141] The acquired images are initially screened, and images with blurry quality or poor exposure are removed on-site. Images that meet the requirements are then sent back to the host computer or flight control equipment.

[0142] Step 2.2: Extract basic image information and UAV flight data, obtain UAV flight attitude information, perform image imaging analysis, and determine whether the imaging direction is perpendicular to the ground;

[0143] For compliant images, the server-side device obtains the corresponding drone flight attitude information, gimbal camera parameters, camera imaging height, and other parameters. Based on the pitch and roll angles, it analyzes whether the imaging direction meets the orthophoto requirements.

[0144] The system receives images returned by the drone through flight control equipment or a host computer, and obtains drone flight attitude information, gimbal camera shooting parameters, geographic coordinates and corresponding flight altitude parameters corresponding to the images to be processed on server-side devices such as PCs and servers.

[0145] The flight attitude information of a UAV includes at least the flight pitch degree and the flight roll degree. The pitch degree is the angle between the aircraft's axis and the ground plane (horizontal plane), and the roll degree is the angle between the aircraft's plane of symmetry and the vertical plane passing through the aircraft's longitudinal axis. The shooting parameters of the gimbal camera include at least the gimbal pitch degree, the gimbal roll degree, the image size, and the gimbal camera's field of view. The geographic coordinates corresponding to the camera's imaging generally refer to latitude and longitude coordinates. The camera imaging altitude refers to the relative altitude, which is the altitude of the UAV relative to its takeoff position.

[0146] Because the shooting parameters, geographic coordinates, and altitude parameters corresponding to the drone camera imaging generally follow the EXIF ​​(Exchangeable Image File format) encoding standard.

[0147] In practical applications, electronic devices such as PCs and servers are used to obtain the information through image tools (such as EXIF ​​information viewers).

[0148] Based on the pitch and roll angles, the imaging direction of the gimbal camera is determined. When the imaging direction is perpendicular to the ground, that is, theoretically the sum of the pitch angles of the UAV and the gimbal is equal to -90° and the sum of the roll angles of the UAV and the gimbal is equal to 0°, the transmitted image is considered qualified and stored. Otherwise, a command is immediately sent to the flight control equipment to re-acquire the image.

[0149] In practical applications, the environment in which drones perform missions is quite complex. Affected by high-altitude airflow and wind speed, even when the drone is hovering, it cannot keep the fuselage absolutely stable at all times. Under the premise of meeting the accuracy of model calculation, the threshold range of pitch angle and roll angle is set.

[0150] Under normal circumstances, the threshold range for the sum of the pitch angles of the drone and the gimbal is -85° to -95°, and the threshold range for the sum of the roll angles of the drone and the gimbal is -5° to 5°. If the pitch angle and roll angle are within the threshold range, the imaging direction can be considered to be perpendicular to the ground and the transmitted photos can be stored. Otherwise, a command is immediately sent to the flight control equipment to re-acquire photos.

[0151] Step 3: Extract the UAV imaging altitude information from the image that meets the imaging requirements, extract the model parameter information of the feature targets in the image, and perform calculations.

[0152] During image feature target interpretation and data extraction, the UAV imaging altitude information is extracted from images that meet the imaging requirements, and the model parameter information of feature targets in the image is extracted using image processing software; the length of silt-retaining dams in the image is quickly interpreted visually, the pixel length of the feature targets is automatically detected, the length information of the selected targets is fed back through the measurement list, and calculation is performed.

[0153] The interpretation of feature targets and their pixel lengths are obtained using an electronic device through the image tool Digimizer. This tool allows for customizable units of measurement, enabling both precise manual and automatic measurements based on object features. It features automatic object recognition within images and automatically collects and stores measurement results, supporting data export to Excel spreadsheets. This meets the needs for feature target identification, measurement, and storage in silt-retention dams. In application, users select feature targets in an image using a preset measurement tool. The tool interprets and identifies the start and end positions and paths of the silt-retention dam feature target pixels, detects the pixel lengths and proportions of the feature targets, and, based on the field-of-view principle and feature target length calculation method, further obtains the actual distance between any two feature targets in the image.

[0154] Example

[0155] To verify the reliability of the method for measuring the slope ratio of silt-retaining dams on the Loess Plateau and to evaluate the accuracy of the model measurement, this embodiment selected three silt-retaining dams in the northern part of Yulin City, Shaanxi Province, for model example measurement verification. Through field surveys, based on the silt-retaining dam slope ratio measurement method given in this invention, the upstream and downstream slope ratios of the silt-retaining dams were measured through on-site collection and screening of feature images, interpretation and data extraction of technical indicators, and model calculation.

[0156] In this embodiment, the model accuracy is evaluated using absolute and relative errors. To eliminate the influence of subjective human factors on the model measurement accuracy, multiple sets of repeated measurements of the upstream and downstream dam slope ratios are performed using a slope meter. The mean value is used to calculate the average value as the agreed true value, and error analysis is conducted on the dam slope ratio model measurement results. The silt-retaining dam slope ratio measurement results and error statistics are shown in Table 1:

[0157] Table 1. Verification Measurement and Error Analysis of Silt-Resisting Dams

[0158]

[0159] Table 1 shows the slope meter verification results, which are the average values ​​of multiple repeated measurements. In this model example measurement, a DJI Phantom 4 RTK drone was used, and its flight positioning accuracy, camera parameters, and gimbal stability all met the technical requirements of this scheme. Empirical research shows that the overall error of the silt-retention dam slope ratio index model measurement results is relatively small, with the maximum error controllable below 3.5%. The maximum errors of the two technical schemes are 3.42% and 3.48%, respectively, fully meeting the needs of silt-retention dam field surveys and operation management.

[0160] It is evident that when the dam height is known, the dam slope ratio model is more complex to construct, but the model parameters in the scheme design are more inclusive, the drone photography positions are more flexible, and the overall measurement accuracy is relatively high. When the dam height is unknown, the model construction is simpler, but the requirements for model parameters are higher, the drone photography positions are relatively fixed, and precise control is required in actual operation, resulting in relatively lower overall measurement accuracy. However, both methods can meet the application requirements.

[0161] This invention presents a method for measuring the slope ratio of silt-retaining dams on the Loess Plateau. It designs a UAV flight mission and image acquisition scheme, constructs a mathematical measurement model for the slope ratio of silt-retaining dams, and achieves high-precision and high-efficiency measurement. By orthophotographing the characteristic features of the silt-retaining dams, it obtains the scale relationship of the captured images and uses the scale and UAV imaging height to obtain the actual length corresponding to the characteristic features of the silt-retaining dams. It establishes an accurate spatial relationship between the UAV and the silt-retaining dam, enabling the acquisition of pixel information for any characteristic feature, providing basic data for related model calculations. The method collects and filters characteristic images that meet the model measurement requirements. Through a dual-screening process of on-site interactive acquisition and image imaging analysis, it ensures the compliance of the collected images. This dual-screening process eliminates images from the UAV flight mission and image acquisition scheme that do not meet the designed accuracy requirements of the model measurement. The method extracts model parameter information of characteristic targets, quickly interprets the characteristic targets of the silt-retaining dams in the images visually, automatically detects their pixel lengths, and rapidly completes information extraction, meeting the needs of efficient thematic interpretation.

Claims

1. A method for measuring information of a dam slope ratio of a silt dam on the Loess Plateau, characterized in that, The method is implemented according to the following steps: Step 1, planning a UAV flight task, and constructing a dam slope ratio geometric measurement model; Step 2, collecting images according to the planned UAV flight task, at a given photographing position and angle, and screening images meeting the model orthographic photography requirements; Step 3, extracting UAV imaging height information from the images meeting the imaging requirements, extracting model parameter information of feature targets in the images, and performing calculation; The step 1 is implemented according to the following steps: Step 1.1, collecting a silt dam related technical index orthographic image by using an RTK UAV, and obtaining an actual distance of any two feature targets in the image; Step 1.2, determining a camera field of view angle according to a visual range diameter; Step 1.3, constructing a dam slope ratio geometric measurement model based on a feature target length measurement method and a camera field of view angle theory, and combining with an acquisition condition of dam height index information; The step 1.1 is specifically: the UAV takes off at an arbitrary suitable position on the dam top, adjusts a gimbal camera to be vertically downward, climbs to a height at which a complete view of the silt dam feature target is presented on a flight control interface, stabilizes the aircraft body, performs photography, and returns the image to an upper computer or a flight control device, visually interprets a silt dam length feature target on a software image processing and analysis interface, detects a silt dam feature target image pixel length and a return image diagonal line pixel length by using software, obtains an actual length of the silt dam feature target by multiplying the silt dam feature target image pixel length by a ratio of an actual length of the diagonal line to the diagonal line pixel length, The step 1.2 is specifically: the camera field of view angle represents the geometric correspondence between the returned image and the range of view; wherein, ∠ θ is the camera field of view angle of the unmanned aerial vehicle, O , H respectively represent the position and height of the unmanned aerial vehicle when shooting the feature target, O′ is the projection point on the ground when the unmanned aerial vehicle shoots the feature target, BO the distance between the unmanned aerial vehicle and the feature target is obtained according to the trigonometric function formula H * tan (1 / 2 θ ), so as to obtain the actual distance between AB . A silt dam feature target actual length calculation formula is: （1） wherein, L is the actual length of the feature target of the check dam, l′ is the pixel length of the feature target of the check dam, p is the pixel length of the diagonal line of the back image, p is a constant value, l is the actual length of the diagonal line of the back image; wherein the actual length of the diagonal line of the back image l is: （2） In the formula, l is the actual length of the diagonal of the returned image, H is the height of the UAV shooting, θ is the field of view angle of the UAV shooting; The step 1.3 specifically includes, Step 1.3.1, when the dam height is known, obtaining dam height index information of the silt dam; dam slope ratio indexes include upstream and downstream dam slope ratios; considering that there may be silt on the upstream of the silt dam, the measurement models of the upstream and downstream dam slope ratios and the UAV flight tasks have certain differences; specific flight task planning and model construction are as follows: When there is silt on the upstream, the UAV flight task of the upstream dam slope ratio measurement model is: The unmanned aerial vehicle is launched at an arbitrary suitable position in the middle of the dam top, reaches a certain height h 1 , maintains the current height and flies in the upstream direction, simultaneously adjusts the body through the flight control interface, so that the gimbal camera is directed at the silt dam, that is, the horizontal reference line of the flight control interface is parallel to the dam top, completes the action, adjusts the gimbal camera vertically downward, maintains the current height and heading and continues to fly, and stops when the upstream silt surface and the dam slope intersection line appears on the flight control interface, then flies in the opposite direction to the dam downstream until the intersection line disappears, which is recorded as p 1 , stabilizes the body, and then photographs and transmits to the upper computer or flight control equipment; after completing the action, the unmanned aerial vehicle continues to climb to a position before the dam top line appears on the flight control interface, which is recorded as p 2 , stops and stabilizes the body, and then photographs and transmits to the upper computer or flight control equipment; In actual flight task, the unmanned aerial vehicle hovering photography position is in the same vertical straight line, and is not a fixed position. The dam slope length is determined. When the dam slope is long enough, appropriate adjustment is made, but the unmanned aerial vehicle must be in p 1 The dam top is not visible in the flight control interface when the unmanned aerial vehicle is in p 2 The dam top is not visible in the flight control interface when the unmanned aerial vehicle is in Known dam height, there is a silt upstream dam slope ratio measurement model, let , x, y, a, b, c and d represent length; wherein: x, y unknown; a, b The pixel length corresponding to the actual length is calculated by using the back image based on the feature target length calculation method; c The representative length is equal to the dam height h And the initial flight height of the unmanned aerial vehicle h 1 The sum of the dam height h Is directly obtained; d The representative length is equal to the dam height h And the final hovering photography height of the unmanned aerial vehicle h 2 The sum; （3） （4） According to the Pythagorean theorem, we have: （5） Because From the similarity of triangles theorem, we have: ， ， （6） Again, because quadrilateral from the similar polygon theorem; （7） According to the trigonometric function, we have: （8） From the above equations, we have x , y， i.e. the slope ratio of the upstream dam （9）； When there is no silt, the upstream and downstream dam slope ratio measurement models are: The unmanned aerial vehicle is launched at an arbitrary suitable position in the middle of the dam top, reaches a certain height position h 1 , maintains the current height and flies in the upstream or downstream direction of the silt dam, simultaneously adjusts the body through the flight control interface so that the gimbal camera is directed to the silt dam, that is, the horizontal reference line of the flight control interface is parallel to the dam top, after the action is completed, the gimbal camera is adjusted to be vertically downward, the current height and heading are maintained, and flight is continued until the flight control interface appears the intersection line of the upstream or downstream dam slope and the riverbed, then the unmanned aerial vehicle is suspended, and then flies in the reverse direction to the position where the intersection line disappears, which is recorded as p 1 , the body is suspended and stabilized, then photography is performed and transmitted to the upper computer or the flight control device, after the above actions are completed, the unmanned aerial vehicle returns; if the intersection line cannot be determined, the position of the unmanned aerial vehicle is adjusted horizontally along the direction parallel to the dam body, so that the projection point of the unmanned aerial vehicle on the riverbed is closest to the line connecting the lowest points of the upstream and downstream dam slopes, that is, the lowest points of the upstream and downstream dam slopes are located above the midpoint of the flight control interface, and the position is determined as the photography position; similarly, the suspended photography position is not a fixed position, and the length of the dam slope slope can be appropriately adjusted, but the unmanned aerial vehicle must be located at the position so that the dam slope can be seen in the flight control interface and the dam top cannot be seen. Given dam height, no silt, upstream and downstream dam slope ratio measurement model, let , x, e, a and c all represent length; wherein: x is unknown; e, a Calculate the actual length corresponding to the pixel length of the back image based on the feature target length calculation method; c The length represented by represents the dam height h The height of the unmanned aerial vehicle hovering photography h 1 The sum of the dam height h Known, obtained from design documents; （10） Because From the similarity of triangles theorem, we have: （11） According to the trigonometric function, we have: （12） obtained x and then the slope ratio of the upstream or downstream dam slope is obtained: （13）； Step 1.3.2, when the dam height is unknown, dam height information of the silt dam cannot be directly obtained from design documents; it is necessary to measure the dam height and the height difference from the silt surface on the upstream to the dam top; the measurement models of the upstream and downstream dam slope ratios and the UAV flight tasks are basically the same; the UAV is used to collect silt dam feature target orthographic images; specific flight task planning and model construction are as follows: The UAV is launched at any suitable position on the dam top, a vertical downward gimbal camera is adjusted, and a certain height is climbed h 1 The dam body is completely presented on the flight control interface, the body is stabilized, photography is performed, and the image is returned to the upper computer or the flight control device. Adjust the direction of the fuselage, maintain the current height, and fly upstream or downstream of the silt dam, adjust the fuselage through the flight control interface so that the gimbal camera is perpendicular to the silt dam, that is, the horizontal reference line of the flight control interface is parallel to the dam top, after completing the action, adjust the gimbal camera vertically downward, maintain the current height and heading, and continue to fly until reaching the intersection line position of the upstream dam slope and the silt surface or the intersection line of the downstream dam slope and the riverbed, hover and stabilize the fuselage, take photos and transmit them to the upper computer or flight control equipment; if the intersection line cannot be determined, adjust the position of the unmanned aerial vehicle horizontally along the direction parallel to the dam body so that the projection point of the unmanned aerial vehicle on the riverbed is closest to the connecting line of the lowest point of the downstream dam slope; When the dam height is unknown, the dam slope ratio is obtained according to the trigonometric function tanα : （14） wherein, （15） In the formula, h 1 is the height of the dam top take-off for the UAV, θ is the camera field of view angle of the UAV, d represents the shortest horizontal distance from the dam slope toe to the dam top, b represents the shortest horizontal distance from the dam slope toe to the dam top, d , b Both use the back image to calculate the actual length corresponding to the pixel length based on the feature target length calculation method. When measuring the upstream dam slope ratio x The difference in elevation between the siltation surface and the dam crest. d The projection point of the drone photography position on the silt surface C Point at the boundary between the upstream siltation surface and the dam slope D The shortest distance, CD Perpendicular to the boundary line; when measuring the downstream dam slope ratio. x Indicates the downstream dam height h Its measurement method is the same as the method for measuring the difference in height between the silt surface and the dam crest. d This represents the shortest distance from the projection point of the drone's photographic location onto the riverbed to the downstream boundary between the riverbed and the dam slope, or the lowest point of the dam slope. In the actual measurement process of the difference between the silt surface and the dam top, the UAV performs multiple flight tasks to reduce errors and take the average value; the flight height of the UAV is set to h 1 、 h 2 … h n , respectively, to the photography position to perform the task operation; Or is the UAV maintained at the same height h 1 , parallel to the dam top direction transverse movement, select n Photography position photography work at this time, the photography position is in the same horizontal line parallel to the boundary line; the difference between the silt surface and the dam top x Is expressed as: （16） In the formula, x 1、 x 2、 x n The difference in height between the silt surface and the dam crest is measured several times. The step 2 is specifically implemented according to the following steps: Step 2.1, on-site interactive collection, according to the dam slope ratio geometric measurement model constructed in step 1 and the corresponding flight task requirements, the image acquisition process is real-time controlled by using the image transmission picture of the unmanned aerial vehicle flight control interface in a man-machine interactive manner, and in the image acquisition process, the unmanned aerial vehicle reaches the specified photography position according to the specified photography action, and the image is collected by using the image transmission picture of the unmanned aerial vehicle flight control interface in a man-machine interactive manner; Step 2.2, extracting image basic information and unmanned aerial vehicle flight data, obtaining unmanned aerial vehicle flight attitude information, and performing image imaging analysis to determine whether the imaging direction is perpendicular to the ground; for the compliant image, the corresponding unmanned aerial vehicle flight attitude information, gimbal camera parameters and camera imaging height parameters are obtained on the server equipment, and based on the pitch angle and roll angle, it is analyzed whether the imaging direction meets the orthographic requirement.

2. The loess plateau silt dam slope ratio information measuring method according to claim 1, characterized in that, When collecting in step 2.1, the following contents are checked according to the flight task requirements of the corresponding measurement model: When collecting the technical index image of the silt dam by using the unmanned aerial vehicle, it is checked whether the image completely presents the overall appearance of the feature target; When collecting the height type technical index image of the dam height, the height difference between the silt surface and the dam top of the silt dam by using the unmanned aerial vehicle, it is checked whether the gimbal camera is perpendicular to the silt dam before photography, and whether the boundary of the image transmission picture coincides with the intersection line of the upstream silt surface or the downstream riverbed and the dam slope during photography; When collecting the dam slope type technical index image of the silt dam by using the unmanned aerial vehicle, the dam height is known, it is checked whether the gimbal camera is perpendicular to the silt dam before photography, and whether the boundary of the image transmission picture is between the intersection line of the dam slope and the silt surface and the dam top during photography; The collected images are preliminarily screened, and the images with blurred quality and poor exposure are removed on site, and the images meeting the requirements are transmitted to the upper computer or flight control equipment.

3. The loess plateau silt dam slope ratio information measuring method according to claim 1, characterized in that, When the step 2.2 is applied, the EXIF information viewer is used to obtain the information by using a PC and a server electronic device; based on the pitch angle and the roll angle, the imaging direction of the gimbal camera is determined, when the imaging direction is perpendicular to the ground, that is, theoretically, the sum of the pitch angle of the unmanned aerial vehicle and the gimbal camera is equal to-90°, and the sum of the roll angle of the unmanned aerial vehicle and the gimbal camera is equal to 0°, the returned image is regarded as qualified and stored, otherwise an instruction is immediately sent to the flight control equipment to re-collect the photo. Under the premise of meeting the model calculation accuracy, set the pitch angle and roll angle threshold range; the threshold range of the sum of the pitch angle of the unmanned aerial vehicle and the gimbal is -85°~ -95°, and the threshold range of the sum of the roll angle of the unmanned aerial vehicle and the gimbal is -5°~5°; if the pitch angle and the roll angle are within the threshold range, it is considered that the imaging direction is perpendicular to the ground, and the returned photos are stored, otherwise an instruction is immediately sent to the flight control device to reacquire the photos.

4. The loess plateau silt dam slope ratio information measuring method according to claim 1, characterized in that, In step 3, the image satisfying the imaging requirement is extracted to obtain the unmanned aerial vehicle imaging height information, model parameter information of a feature target in the image is extracted by using an image processing software Digimizer; a length feature target of the earth dam in the image is quickly visually interpreted, pixel length of the feature target is automatically detected, length information of the selected target is fed back through a measurement list, and is brought into a model for calculation.

Images