Aerial automatic refueling taper sleeve positioning method based on solar blind ultraviolet imaging

Abstract

The invention discloses an aerial automatic refueling taper sleeve positioning system and method based on solar-blind ultraviolet imaging, aims to solve the problems of low positioning precision, easy environmental interference and the like in a complex environment in the prior art, and provides a faster, more accurate and more reliable taper sleeve positioning solution for aerial refueling operation. The system comprises an oiling machine and an oil receiving machine, a taper sleeve on the oiling machine is provided with a plurality of ultraviolet lamps which are asymmetrically installed, and an oiling probe of the oil receiving machine is provided with a solar blind ultraviolet camera which is used for capturing images of the ultraviolet lamps for positioning. The method comprises the following steps: continuously acquiring image data; the image is processed, and light spots contained in the image are distinguished and recognized; the coverage area of each light spot is calculated, and the barycentric coordinates of the light spots with the areas reaching the standard are obtained; light spots on the taper sleeve are screened out, and the position relation of the camera relative to the taper sleeve is obtained through calculation; and the pose state of the taper sleeve is calculated according to the light spot information, and information support is provided for butt joint of an oil receiver and an oiling machine.

Description

Technical Field

[0001] The invention relates to the technical field of ultraviolet imaging, and in particular to an aerial automatic refueling drogue positioning method based on solar-blind ultraviolet imaging. Background Art

[0002] The present invention focuses on the application of ultraviolet imaging and visual detection technology in aerial refueling technology, especially the drogue positioning system during aerial refueling. As a key technology in the field of modern aviation, aerial refueling technology is of great significance for enhancing the combat radius of aircraft and improving endurance. In the hose-drogue aerial refueling system, the precise positioning of the refueling drogue is a key step in achieving successful docking between the two aircraft, and its accuracy and reliability are directly related to the success of the refueling operation.

[0003] Traditional positioning methods, such as 3D laser scanning, special optical markers (such as LED cursors) and color recognition, have met the positioning needs to a certain extent, but they still have many limitations. Although the 3D laser scanning method is accurate, the equipment is complex, the cost is high, and it is easily affected by the environment; although the special optical marking method is simple, it is easily affected by noise in complex backgrounds, resulting in reduced positioning accuracy. To solve these problems, researchers are constantly exploring more advanced and efficient positioning technologies. Among them, solar-blind ultraviolet imaging technology has gradually attracted attention due to its unique advantages.

[0004] Solar-blind ultraviolet imaging technology is only sensitive to ultraviolet light in the 200nm to 300nm band, where there is almost no natural light source in the near-Earth atmosphere. Therefore, it can significantly reduce background interference, is not affected by day or night environments, and improves the accuracy of target detection.

[0005] The present invention is based on the above advantages of solar-blind ultraviolet imaging technology and proposes a new aerial automatic refueling drogue positioning system and method.

[0006] Among the existing technical solutions for positioning the aerial automatic refueling cone sleeve, common positioning methods include the use of three-dimensional laser scanning, special optical markers (such as LED cursors), color recognition, etc.

[0007] For example, in patent CN116379921A "Refueling Dredger Positioning Method", a refueling drogue positioning method is proposed, which realizes the positioning of the refueling drogue by acquiring three-dimensional laser point cloud data of the target area and performing segmentation, clustering, fitting and other steps; Another example is patent CN114543664B "A method and device for positioning a refueling cone sleeve based on laser scanning", which describes a method and device for positioning a refueling cone sleeve based on laser scanning. This method determines the center position of the cone sleeve by obtaining four coordinate points on the circular ring at the end of the cone sleeve; As described in the document "Research Progress and Key Issues of Automatic Aerial Refueling Technology", there are some refueling cone sleeve positioning methods based on visible light visual detection, which use LED cursors or special color marks as visual features for positioning.

[0008] Among them: Although the method in patent CN116379921A "Refueling Dredger Positioning Method" improves the positioning efficiency to a certain extent, the laser scanning and point cloud processing process is relatively complicated, has high hardware requirements, and is more sensitive to interference and noise in specific environments, which may lead to a decrease in positioning accuracy; The method in patent CN114543664B "A method and device for positioning a refueling drogue based on laser scanning" relies on accurate laser scanning and angle calculation. Its positioning accuracy and robustness may be affected for fast-moving refueling drogues or complex and changing flight environments. Although the refueling cone sleeve positioning method based on visible light vision detection simplifies the positioning process to a certain extent, the LED cursor and other optical markers are easily affected by background interference and noise, especially in complex backgrounds, which may lead to reduced positioning accuracy.

[0009] In summary, the existing technical solutions have made certain progress in the positioning of the refueling cone sleeve, but there are still some shortcomings. Therefore, it is particularly important to develop a more advanced, efficient and reliable refueling cone sleeve positioning system.

[0010] In view of the shortcomings of the existing technology, the present invention proposes an aerial automatic refueling drogue positioning system and method based on day-blind ultraviolet imaging, aiming to solve the problems of low positioning accuracy and susceptibility to environmental interference in complex environments in the existing technical solutions, and provide a faster, more accurate and reliable drogue positioning solution for aerial refueling operations. Summary of the invention

[0011] The purpose of the present invention is to provide an aerial automatic refueling drogue positioning method based on solar-blind ultraviolet imaging to overcome the deficiencies in the prior art.

[0012] To achieve the above object, the present invention provides the following technical solutions: The present application discloses an aerial automatic refueling drogue positioning method based on solar-blind ultraviolet imaging, comprising a refueling aircraft and a receiving aircraft, wherein the refueling aircraft is provided with a drogue, and the drogue is provided with a plurality of asymmetrically installed ultraviolet lamps, and the solar-blind ultraviolet camera is arranged at the refueling probe of the receiving aircraft, and the solar-blind ultraviolet camera captures the imaging of the ultraviolet lamp for positioning; the method comprises the following sub-steps: S1: Continuously acquire image data through a UV camera; S2: Processing the image data to distinguish and identify the light spots contained in the image; S3: Calculate the coverage area of ​​each light spot, and for the light spots that meet the area requirements, calculate and obtain the coordinates of their center of gravity; S4: Filter out the light spot on the cone sleeve, and calculate and obtain the position relationship of the camera relative to the cone sleeve; S5: The position and posture state of the drogue is calculated based on the light spot information to provide information support for the docking of the receiving aircraft and the refueling aircraft.

[0013] Preferably, the number of the ultraviolet lamps is 8, which are installed at 0°, 30°, 66°, 106°, 152°, 202°, ​​257° and 317° in a counterclockwise order.

[0014] Preferably, S1 includes the following contents: a first-in-first-out image cache queue mechanism is used to manage image data; the ultraviolet camera acquires image data and establishes a queue to store the image data; the newly acquired image data automatically replaces the earliest acquired image data, and the queue length is kept constant during the storage process.

[0015] Preferably, S2 includes the following sub-steps: S21: Binarize the image to generate a binary image; S22: performing connected domain analysis according to the ultraviolet light spot in the binary image, identifying and marking all connected pixel regions; S23: traverse each pixel in the image, mark the unvisited white pixels, assign the same label to the pixels in the same connected domain, and then distinguish the ultraviolet spots contained in the image.

[0016] Preferably, the S21 comprises the following steps: S211: Segment the image into foreground and background, where the foreground includes the light spot; S212: Calculate the grayscale histogram of the image and count the pixel distribution of each grayscale level; S213: setting a number of segmentation thresholds, and calculating the inter-class variance of the foreground and the background under each segmentation threshold; S214: Selecting the segmentation threshold when the inter-class variance is the largest as the segmentation standard to generate a binary image.

[0017] Preferably, S3 comprises the following sub-steps: S31: Calculate the coverage area of ​​each identified light spot; S32: Screen the light spots by coverage area to remove interference from image noise; S33: Calculate the average value of the pixel coordinates of each light spot to obtain the initial coordinates of the center of gravity; S34: Perform distortion correction on the initial coordinates of the center of gravity to obtain the non-distorted coordinates of the center of gravity of the light spot.

[0018] Preferably, S4 includes the following contents: when several ultraviolet lamps cannot be distinguished in the image acquired by the ultraviolet camera and appear as a large light spot, the positional relationship between the camera and the cone sleeve is calculated through the relative position of the center of gravity of the large light spot in the image, so as to provide information support to guide the receiving aircraft to approach the refueling machine.

[0019] Preferably, S4 includes the following content: when a plurality of ultraviolet lamps appear as a plurality of independent light spots in the image acquired by the ultraviolet camera: S41: Check the light spots, remove redundant and erroneous light spots, and avoid interference caused by misidentification; S42: Screen the remaining light spots, eliminate interference factors, and screen out the light spots on the cone sleeve.

[0020] Preferably, the S4 includes checking the light spots, removing redundant and erroneous light spots, and avoiding interference caused by misidentification, including the following sub-steps: S411: measuring the average distance from each point on the light spot profile to the centroid coordinates, and estimating the radius representing the light spot; S412: Preset a tolerance value, select two light spots in the image, and check the distance between their centers of gravity. If the distance is less than the sum of the estimated radius of the two light spots and the tolerance value, the two light spots are determined to be incorrect, and the light spot with a smaller area is deleted, while the light spot with a larger area is retained.

[0021] Preferably, the step S4 includes performing ellipse detection on the light spot to screen out the light spot on the cone sleeve, including the following sub-steps: S421: Randomly select the centroid coordinates of a number of light spots from the centroid coordinates of the light spots to be detected; S422: Calculate the ellipse parameters corresponding to the centroid coordinates of the light spot in the ellipse parameter space; S423: Selecting ellipse parameters that meet the conditions from the ellipse parameters through ellipse determination conditions and peak value detection, thereby determining the light spot that actually belongs to the cone sleeve.

[0022] Preferably, S4 includes the following contents: matching the light spot with the ultraviolet lamp, obtaining the transformation matrix of the cone sleeve relative to the camera by solving the n-point perspective problem, and then calculating the distance, posture and angle of the cone sleeve relative to the camera.

[0023] The present application also discloses an automatic aerial refueling cone sleeve positioning device based on day-blind ultraviolet imaging, including a memory and one or more processors, wherein the memory stores executable code, and when the one or more processors execute the executable code, they are used to implement the above-mentioned automatic aerial refueling cone sleeve positioning method based on day-blind ultraviolet imaging.

[0024] The present application also discloses a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, the above-mentioned method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging is implemented.

[0025] Beneficial effects of the present invention: (1) The solar-blind ultraviolet camera in the present invention adopts a photon counting imaging detection method with high detection sensitivity. It can detect extremely weak signals. The camera can detect signals when the distance between the camera and the fuel dispenser cone sleeve is far (more than 1.5 km), which greatly improves the detection distance. Moreover, the solar-blind ultraviolet camera is not affected by the day and night environment, and the detected image background is clean, which is much greater than the effective detection distance of the visible light camera. (2) Compared with the traditional refueling drogue positioning method based on visible light visual detection, the solar-blind ultraviolet imaging technology adopted by the present invention can greatly reduce background interference, thereby significantly improving the accuracy and robustness of target detection; this technical advantage enables high-precision positioning even in a changing and complex environment, ensuring the stability and reliability of positioning; (3) Through the asymmetric layout of the UV lamp design, the system can not only accurately identify the position of each beacon, but also effectively estimate the roll angle of the drogue. The system adaptability has been comprehensively enhanced; this innovative design greatly enhances the system's adaptability to different flight attitudes, allowing the system to maintain excellent performance under various flight conditions; (4) Compared with traditional 3D laser scanning and other methods, the present invention does not need to rely on complex equipment and has low cost, which not only simplifies the operation and maintenance of the system, but also facilitates the widespread promotion and application of the system, especially in scenarios with limited resources; (5) Although the traditional Hough transform is effective in processing shape detection, it is computationally intensive and time-consuming when processing large amounts of data. The improved algorithm of the present invention only requires five ultraviolet lamps to accurately locate the cone sleeve, which not only significantly reduces the amount of calculation and improves the processing speed, but also ensures the accuracy of positioning when part of the ultraviolet lamp is blocked. This innovation makes the system more flexible and reliable in practical applications. (6) For the pixel coordinates of the centroid of the UV light spot detected in the image and the three-dimensional coordinates of the UV light in the world coordinate system, an accurate matching relationship is obtained by calculating the minimum reprojection error. Even if the cone sleeve is partially blocked, the cone sleeve posture can be calculated through the correct matching relationship.

[0026] The features and advantages of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is a schematic diagram of the steps of a method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to the present invention; Figure 2 It is a schematic diagram of the layout of the ultraviolet lamp of the present invention; Figure 3 It is a composition diagram of the ultraviolet lamp camera of the present invention; Figure 4 It is a schematic diagram of calculating the angle between the ultraviolet light and the camera at a long distance of the present invention; Figure 5 It is a schematic diagram of the ultraviolet light spot of the present invention; Figure 6 It is a schematic diagram of ellipse parameters of the present invention; Figure 7 is the ultraviolet lamp ellipse detection result of the present invention; Figure 8 It is a schematic diagram of the device of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0029] See also Figure 1 The embodiment of the present invention provides a method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging, including the following contents: The present invention selects day-blind ultraviolet light in the 254 nanometer band as a signal source, and installs eight ultraviolet lamps on the cone sleeve in an asymmetric manner through a fixing ring. The installation angles of the ultraviolet lamps are all limited to the range of 0° to 360°, and are set to 0°, 30°, 66°, 106°, 152°, 202°, ​​257° and 317° in a counterclockwise direction, starting from a certain specific reference point. The logic of the angle value is: under the premise of satisfying the continuous coverage of the entire circumference, the obvious distinction between the ultraviolet lamps is achieved by adopting non-uniform angular intervals (based on 30°, 36°, 40°, 46°, 50°, 55°, 60° and other incremental strategies), and the angular interval is controlled between 30° and 60° to ensure that there is enough spacing between the ultraviolet lamps, thereby effectively improving the recognition accuracy of the relative positions of the ultraviolet lamps during visual detection, and providing a strong basis for the accurate estimation of the roll angle of the cone sleeve.

[0030] The solar-blind UV camera is installed at a fixed position on the refueling probe of the receiving aircraft, and the imaging of the UV lamp on the drogue is captured by the solar-blind UV camera. To ensure the high efficiency and real-time performance of image processing, the present invention adopts a first-in-first-out (FIFO) image cache queue mechanism to manage the image data continuously acquired by the UV camera, achieving an effective balance between image capture and algorithm processing time.

[0031] When the queue reaches its capacity limit, new images will automatically replace the oldest stored images to maintain a constant queue length.

[0032] Subsequently, the images in the queue are binarized, which involves segmenting the images into foreground (i.e., light spots) and background.

[0033] First, the grayscale histogram of the image is calculated and the pixel distribution of each grayscale level is counted.

[0034] Next, by traversing all potential thresholds, calculating the inter-class variance between the foreground and the background under each threshold, the threshold that maximizes the inter-class variance is selected as the final segmentation criterion to achieve the best threshold segmentation. The method is as follows: After calculating the grayscale histogram of the image, the inter-class variance is calculated according to the following formula: in, is the candidate threshold, and are the pixel ratios of foreground and background, respectively. and are the average grayscale values ​​of the foreground and background respectively. Traverse and find The maximum threshold is used as the final segmentation threshold.

[0035] For example, the grayscale histogram of a certain frame of image shows that the grayscale values ​​of the foreground light spot are mainly concentrated between 200 and 255, and the grayscale values ​​of the background are mainly concentrated between 0 and 100. By calculating the inter-class variance, it is found that when the threshold is set to 150, the inter-class variance reaches the maximum value. Therefore, 150 is selected as the segmentation threshold.

[0036] Based on this, in the generated binary image, the foreground pixels (light spots) are assigned a value of 255 (white) and the background pixels are assigned a value of 0 (black).

[0037] Furthermore, a connected domain analysis is performed on the binary image to identify and mark all connected pixel regions, each of which corresponds to an independent UV light spot. By traversing each pixel in the image and starting the labeling process for unvisited white pixels, it is ensured that the pixels in the same connected region are assigned the same label, thereby achieving effective differentiation of light spots.

[0038] For each identified light spot, calculate its coverage area and ignore the light spots with too small area (for example, the light spots with less than 10 pixels) because they may be caused by image noise. For the light spots with the required area, calculate the average value of all its pixel coordinates to determine the centroid pixel coordinates of the light spot, and obtain the non-distorted centroid pixel coordinates of the light spot after distortion correction.

[0039] The solar-blind UV camera in the present invention adopts a photon counting imaging detection method with high detection sensitivity, and can detect extremely weak signals. When the distance between the camera and the tanker cone sleeve is far (more than 1.5 km), the eight UV lamps cannot be clearly distinguished in the image, but appear as a large overall light spot. In this case, there is no need to accurately calculate the specific positional relationship between the camera and the cone sleeve. The angular relationship of the camera relative to the cone sleeve can be calculated through the relative position of the center of gravity of this large light spot in the image. This angular relationship plays an important auxiliary role in guiding the receiving aircraft to approach the tanker.

[0040] When the distance between the camera and the cone sleeve is close (within 20m), the eight UV lamps can be clearly presented as eight independent light spots in the image. At this time, by measuring the average distance from each point on the light spot profile to the center of gravity, the "radius" representing the light spot size can be estimated.

[0041] In order to eliminate the misidentification of light spots caused by image overlap or errors, the present invention checks the distance between the centers of gravity of each pair of light spots. If the distance between the two light spots is less than the sum of their "radii" plus a preset small tolerance value, they are judged to be too close. At this time, the light spot with a larger area is retained, and the one with a smaller area is eliminated.

[0042] Subsequently, it is necessary to further screen out the light spots that actually belong to the cone sleeve to effectively eliminate the interference of environmental noise (such as background noise, environmental reflection, etc.), so as to ensure the accuracy and reliability of the positioning system.

[0043] The mathematical equation of an ellipse can describe the projection of a circle on an image. The present invention uses an ellipse curve formed by judging whether there is a light spot in the image to determine whether the cone target is in the field of view. The traditional Hough transform ellipse detection algorithm has too much calculation. The positions of the feature points in this system are not adjacent, and a continuous ellipse contour cannot be obtained. Therefore, it is necessary to improve the Hough transform ellipse detection algorithm to realize the detection of the cone target. The core idea is to transform the curve detection problem in the image space into the peak detection problem in the ellipse parameter space.

[0044] The five-parameter model of the ellipse (center point coordinates ( , ), rotation angle , semi-major axis and the minor semiaxis ) requires at least five independent points to be uniquely determined. Five points are sufficient to determine the parameters of an ellipse. At the same time, compared with sampling of more points, it can reduce the computational complexity and improve the efficiency of the algorithm. During the ellipse detection process, five light spot centroid points are randomly sampled each time, and the corresponding ellipse parameters in the ellipse parameter space are calculated. If the parameter meets the ellipse judgment condition, the corresponding counter is accumulated. Finally, the true ellipse parameters are extracted through peak detection to complete the ellipse detection and determine the light spot that truly belongs to the cone sleeve. Next, the ultraviolet imaging point is matched with each ultraviolet lamp. By solving the n-point perspective (PnP) problem, the transformation matrix of the cone sleeve relative to the camera is obtained. Then the distance and angle of the cone sleeve relative to the camera can be calculated.

[0045] For all the remaining spots, they are all located on an ellipse, sorted by area, and retaining up to eight points with the largest area. Then, these points are sorted counterclockwise and pushed into the two-dimensional vector points2Ds. At the same time, the three-dimensional coordinates of the ultraviolet lamp in the world coordinate system are sorted counterclockwise and pushed into the three-dimensional vector points3Ds. At this point, we have obtained two vectors, but their matching relationship has not yet been determined. The present invention adopts a traversal matching method to determine the correct sorting.

[0046] For each matching relationship, solve the transformation matrix and compare the reprojection error. The rotation matrix R and translation vector T with the minimum reprojection error can be obtained. If this minimum reprojection error meets the preset limit requirements, then the corresponding matching relationship is correct, and the corresponding R and T are the cone sleeve posture we expect.

[0047] If the requirements are not met, the result is discarded and a new image is obtained for processing.

[0048] For solving the n-point perspective (PnP) problem, the present invention can obtain relatively stable calculation results by identifying more than 4 ultraviolet lamps. According to the mathematical principle of the PnP problem, when the points in the 3D space and the corresponding points in the 2D image are known, the posture of the target object can be estimated by solving the PnP problem. In practical applications, the P3P method is a special case of the PnP problem, which can be solved with only 3 points, but this method may have multiple solutions in some cases and has high requirements for initial conditions. Therefore, in order to ensure the stability and reliability of the calculation, the present invention uses at least 4 ultraviolet lamps as a minimum. In the present invention, even if part of the ultraviolet lamp is shielded for some reason, the posture of the cone sleeve can be calculated by calculating the correct matching relationship between the ultraviolet light spot and the ultraviolet lamp.

[0049] Example like Figure 2As shown in the figure, 8 UV lamps are installed on the cone sleeve in an asymmetrical manner through a fixing ring, and the fixing ring with 8 UV lamps is called a UV lamp ring. The UV lamp on the far right of the figure is marked as No. 0. As the starting point, the installation angles of the other 8 UV lamps are set to 0°, 30°, 66°, 106°, 152°, 202°, ​​257° and 317° in a counterclockwise direction compared to the No. 0 UV lamp. This layout design not only helps to accurately identify the position of each UV lamp, but also provides a basis for the subsequent calculation of the roll angle of the camera relative to the cone sleeve.

[0050] like Figure 3 As shown, the UV lamp ring is installed on the cone sleeve, and the solar-blind UV camera is installed at a fixed position of the refueling probe of the receiving aircraft. In this system, the camera is installed at the lower end of the probe.

[0051] A solar-blind UV camera is used to continuously capture the image of the UV lamp on the cone sleeve. To ensure the real-time and efficient image processing, we use a first-in-first-out (FIFO) image cache queue mechanism to manage these image data. When the queue reaches the preset capacity limit, the new image will automatically replace the oldest stored image to keep the queue length constant.

[0052] Subsequently, the images in the queue are binarized and connected domains are analyzed to achieve effective differentiation of light spots. For each identified light spot, its coverage area is calculated, and light spots with too small an area are ignored. For light spots with an area that meets the standard, the average value of all its pixel coordinates is calculated to determine the centroid pixel coordinates of the light spot, and the non-distorted centroid pixel coordinates of the light spot are obtained after distortion correction.

[0053] When the distance between the camera and the cone is far (e.g. more than 1.5 km), the eight UV lamps appear as a large overall light spot in the image, and this light spot is regarded as an overall target. Figure 4 As shown, at this time, the angle of the target relative to the camera can be calculated by the pixel coordinates of the overall large light spot on the image.

[0054] When the distance between the camera and the cone is close (within 20m), the eight UV lamps can be clearly presented as eight independent light spots in the image. Figure 5 As shown, interference signals and some noise signals caused by environmental reflections can also be observed in the figure.

[0055] At this time, by measuring the average distance from each point on the spot profile to the center of gravity, the "radius" that characterizes the spot size can be estimated. Check the distance between the centers of gravity of each pair of spots. If the distance between the two spots is less than the sum of their "radii" plus a preset small tolerance value, they are judged to be too close. At this time, the larger spot is retained and the smaller one is eliminated.

[0056] Subsequently, the improved Hough transform is used to detect the UV lamp located on the cone sleeve. The mathematical equation of an ellipse can describe the projection of a circle on an image. In a digital image, an ellipse can be described by the following parameters: the coordinates of the center point ( ), rotation angle , semi-major axis and the minor semiaxis ,like Figure 6 shown.

[0057] In a two-dimensional coordinate system, the standard expression of an elliptic curve is: By simplifying formula (1), we can get the general expression of elliptic curve: In formula (2), A, B, C, D, E, and F are the coefficients of the elliptic curve. A, B, C, D, and E constitute the elliptic parameter unit. The elliptic curve must meet the following conditions: For all the light spots to be detected, 5 light spots are randomly sampled to calculate the ellipse parameters, thereby detecting the ellipse. The algorithm process is as follows: 1. The pixel coordinate point set of all the light spot centroids to be detected is , is the ellipse parameter unit set; 2. Randomly sample 5 points from the feature point set D , substituting into equation (2) we can get a linear equation system consisting of 5 parametric equations; 3. If the above system of equations has a solution And satisfying formula (3), then find the ellipse parameter unit set Does the parameter unit exist? , so that ( is the allowable error), if it does not exist, then Insert a new parameter unit in , The counter is set to 1; otherwise, the parameter unit The counter is incremented by 1 and updated ; 4. If the parameter unit The counter value is greater than the specified threshold (In this system, N is selected as 3), then The corresponding ellipse is the candidate ellipse; 5. Determine whether the candidate ellipse is a true ellipse by the ratio of the number of points falling on the candidate ellipse to its perimeter. This ratio reflects the density of the light spots inside the ellipse. If the ratio is higher than a preset threshold, the candidate ellipse is considered to be true, that is, it is formed by the ultraviolet light spots on the cone sleeve. This usually means that there are enough light spots inside the ellipse to support it as a true ellipse. For the judgment result, if the candidate ellipse is considered to be true, the points falling on the ellipse are removed from the feature point set. Remove it from the memory occupied by the ellipse parameter unit set, go to step 6; otherwise, Remove the parameter unit corresponding to the ellipse and go to step 2 to continue detection.

[0058] 6. Determine whether the number of detected ellipses meets the requirements. If so, end the process; otherwise, go to step 2 and continue detection.

[0059] If multiple ellipse parameters are detected, the parameter with the largest counter value is used as the final parameter to complete the ellipse detection and determine the UV light spot that actually belongs to the cone sleeve. In this system, there is only one ellipse that needs to be determined, so there is no problem of excessive calculation caused by too many ellipses.

[0060] like Figure 7 As shown, all UV lamps on the cone sleeve are finally detected through ellipse detection.

[0061] Next, the UV imaging points are matched with each UV lamp. The transformation matrix of the cone sleeve relative to the camera is obtained by solving the n-point perspective (PnP) problem.

[0062] Then the distance and angle of the cone sleeve relative to the camera can be calculated.

[0063] The algorithm process is as follows: 1. All remaining light spots are located on the same ellipse. All light spots are sorted by area, and up to eight points with the largest area are retained.

[0064] 2. If N (5≤N≤8) UV spots are identified in the UV image, they correspond to the actual N UV lamps. Select N UV lamps from the 8 UV lamps in a counterclockwise direction. The first UV lamp selected is marked as 0, and the subsequent UV lamps are marked as 1 to (N-1) in sequence. The 3D coordinates of the selected UV lamps are pushed into the 3D vector points3D in the order of the serial numbers. Selection method.

[0065] 3. Mark one of the spots in the UV image as 0, and mark the other spots as 1 to (N-1) in a counterclockwise direction, and push the pixel coordinates of the center of gravity of the spots into the two-dimensional vector points2Ds in order of sequence. There are N ways of sorting.

[0066] 4. Match the UV lamp in the world 3D coordinates with the 2D coordinates of the centroid pixel of the UV spot in the image by serial number (for example, UV lamp No. 0 corresponds to UV spot No. 0). For each matching relationship, solve the transformation matrix separately and compare the reprojection error. The rotation matrix R and translation vector T with the minimum reprojection error can be obtained. If this minimum reprojection error meets the preset limit requirements, then the corresponding matching relationship is correct, and the corresponding R and T are the cone sleeve posture we expect. If it does not meet the requirements, the result is discarded and a new image is obtained for processing.

[0067] Finally, R and T calculated by solving the n-point perspective (PnP) problem are the posture of the cone sleeve relative to the UV camera.

[0068] An embodiment of the automatic aerial refueling cone sleeve positioning device based on day-blind ultraviolet imaging of the present invention can be applied to any device with data processing capabilities, and the any device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented through software, or through hardware or a combination of software and hardware. Taking software implementation as an example, as a device in a logical sense, it is formed by the processor of any device with data processing capabilities in which it is located reading the corresponding computer program instructions in the non-volatile memory into the internal memory for execution. From a hardware perspective, if Figure 8 As shown in the figure, it is a hardware structure diagram of any device with data processing capability where the aerial automatic refueling drogue positioning device based on solar-blind ultraviolet imaging of the present invention is located, except Figure 8 In addition to the processor, memory, network interface, and non-volatile memory shown, any device with data processing capabilities in the embodiment of the device may also include other hardware according to the actual function of the device with data processing capabilities, which will not be described in detail. The implementation process of the functions and effects of each unit in the above device is specifically detailed in the implementation process of the corresponding steps in the above method, which will not be described in detail here.

[0069] For the device embodiment, since it basically corresponds to the method embodiment, the relevant parts can refer to the partial description of the method embodiment. The device embodiment described above is only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of the present invention. Ordinary technicians in this field can understand and implement it without paying creative work.

[0070] An embodiment of the present invention further provides a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, an aerial automatic refueling drogue positioning device based on solar-blind ultraviolet imaging in the above embodiment is implemented.

[0071] The computer-readable storage medium may be an internal storage unit of any device with data processing capability described in any of the aforementioned embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be an external storage device of any device with data processing capability, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), an SD card, a flash card (Flash Card), etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit and an external storage device of any device with data processing capability. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capability, and may also be used to temporarily store data that has been output or is to be output.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging, characterized in that: The invention comprises a refueling machine and a receiving machine, wherein the refueling machine is provided with a cone sleeve, and the cone sleeve is provided with a plurality of asymmetrically installed ultraviolet lamps, and the day-blind ultraviolet camera is arranged at the refueling probe of the receiving machine, and the day-blind ultraviolet camera captures the imaging of the ultraviolet lamp for positioning; the method comprises the following sub-steps: S1: Continuously acquire image data through a UV camera; S2: Processing the image data to distinguish and identify the light spots contained in the image; S3: Calculate the coverage area of ​​each light spot, and for the light spots that meet the area requirements, calculate and obtain the coordinates of their center of gravity; S4: Filter out the light spot on the cone sleeve, and calculate and obtain the position relationship of the camera relative to the cone sleeve; S5: The position and posture state of the cone sleeve is calculated based on the light spot information to provide information support for the docking of the receiving aircraft and the refueling aircraft.

2. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: The number of the ultraviolet lamps is 8, which are installed in a counterclockwise order at 0°, 30°, 66°, 106°, 152°, 202°, ​​257° and 317°.

3. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: The S1 includes the following contents: a first-in-first-out image cache queue mechanism is used to manage image data; the ultraviolet camera acquires image data and establishes a queue to store the image data; the newly acquired image data automatically replaces the earliest acquired image data, and the queue length is kept constant during the storage process.

4. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: The S2 includes the following sub-steps: S21: Binarize the image to generate a binary image; S22: performing connected domain analysis according to the ultraviolet light spot in the binary image, identifying and marking all connected pixel regions; S23: traverse each pixel in the image, mark the unvisited white pixels, assign the same label to the pixels in the same connected domain, and then distinguish the ultraviolet spots contained in the image.

5. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: The S3 comprises the following sub-steps: S31: Calculate the coverage area of ​​each identified light spot; S32: Screen the light spots by coverage area to remove interference from image noise; S33: Calculate the average value of the pixel coordinates of each light spot to obtain the initial coordinates of the center of gravity; S34: Perform distortion correction on the initial coordinates of the center of gravity to obtain the non-distorted coordinates of the center of gravity of the light spot.

6. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: The S4 includes the following contents: when several ultraviolet lamps cannot be distinguished in the image acquired by the ultraviolet camera and appear as a large light spot, the positional relationship between the camera and the cone sleeve is calculated through the relative position of the center of gravity of the large light spot in the image, and information support is provided to guide the receiving aircraft to approach the refueling machine.

7. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: S4 includes the following content: when a plurality of ultraviolet lamps appear as a plurality of independent light spots in the image acquired by the ultraviolet camera: S41: Check the light spots, remove redundant and erroneous light spots, and avoid interference caused by misidentification; S42: Screen the remaining light spots, eliminate interference factors, and screen out the light spots on the cone sleeve.

8. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: S4 includes checking the light spots, removing redundant and erroneous light spots, and avoiding interference caused by misidentification, including the following sub-steps: S411: measuring the average distance from each point on the light spot profile to the centroid coordinates, and estimating the radius representing the light spot; S412: Preset a tolerance value, select two light spots in the image, and check the distance between their centers of gravity. If the distance is less than the sum of the estimated radius of the two light spots and the tolerance value, the two light spots are determined to be incorrect, and the light spot with a smaller area is deleted, while the light spot with a larger area is retained.

9. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: The step S4 includes performing ellipse detection on the light spot to select the light spot on the cone sleeve, including the following sub-steps: S421: Randomly select the centroid coordinates of a number of light spots from the centroid coordinates of the light spots to be detected; S422: Calculate the ellipse parameters corresponding to the centroid coordinates of the light spot in the ellipse parameter space; S423: Selecting ellipse parameters that meet the conditions from the ellipse parameters through ellipse determination conditions and peak value detection, thereby determining the light spot that actually belongs to the cone sleeve.

10. The method for positioning an automatic aerial refueling drogue based on solar-blind ultraviolet imaging according to claim 1, characterized in that: The S4 includes the following contents: matching the light spot with the ultraviolet lamp, obtaining the transformation matrix of the cone sleeve relative to the camera by solving the n-point perspective problem, and then calculating the distance, posture and angle of the cone sleeve relative to the camera.

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