An antenna profile precision measurement method based on unmanned aerial vehicle photogrammetry

Abstract

The application provides an antenna profile precision measurement method based on unmanned aerial vehicle photogrammetry. Firstly, flight and photogrammetry parameters of the unmanned aerial vehicle used for antenna profile precision measurement are preliminarily planned according to antenna parameters. Then, the light incidence angle, the frequency of being photographed and the intersection angle of the to-be-measured points on the main reflector of the antenna are calculated according to the antenna equation and the camera station position. The shooting effect of the unmanned aerial vehicle photogrammetry is evaluated according to the frequency of being photographed and the intersection angle of all the to-be-measured points on the main reflector of the antenna. Then, the camera shooting angle at the camera station coordinate position is planned based on the obtained each unmanned aerial vehicle camera station coordinate. The final obtained camera station position and shooting angle of the unmanned aerial vehicle photogrammetry are converted into a path planning file executable by the unmanned aerial vehicle, and the photogrammetry is automatically performed by the unmanned aerial vehicle photogrammetry system. The application can quickly plan the unmanned aerial vehicle shooting position and shooting angle under the premise of ensuring the measurement precision.

Description

Technical Field

[0001] This invention relates to the field of antenna profile accuracy measurement technology, specifically to a method for measuring antenna profile accuracy based on UAV photogrammetry. Background Technology

[0002] With the deepening development of aerospace engineering and deep space exploration, ground tracking antennas, as key equipment for receiving information from spacecraft, are increasingly larger in aperture and higher in operating frequency bands. The antenna's reflector is a crucial structure for transmitting and receiving electromagnetic signals; its accuracy directly determines its performance and observation efficiency. Especially in high-frequency observations, even small surface errors can cause significant gain loss. For large antennas, traditional industrial photogrammetry requires engineering machinery, which is time-consuming. Environmental factors (temperature, wind load, etc.) cause uneven changes in the antenna structure, which are coupled into the measurement results, ultimately leading to poor antenna reflector accuracy and insufficient electrical performance to meet technical requirements. Therefore, how to quickly and accurately measure the antenna's main reflector during antenna installation has become a critical issue that urgently needs to be addressed in antenna system construction. In recent years, with the rapid development of UAV technology, UAV photogrammetry, with its advantages of high automation, high efficiency, and low cost, has been gradually applied to the surface accuracy measurement of antenna main reflectors. When using UAV photogrammetry, multiple stereo pairs of images of the measured points on the antenna reflector are obtained by photographing the antenna reflector from different positions above the antenna, thus forming a multi-view stereo vision. UAV photogrammetry is well-suited for measuring and adjusting the profile accuracy of the main reflector of large, high-precision antennas, which can greatly reduce operating costs and risks. At the same time, UAV photogrammetry can measure the profile accuracy of antennas at any pitch angle, providing basic data such as gravity deformation for subsequent real-time measurement and adjustment of large antennas. It is one of the main development directions for antenna profile accuracy measurement in the future. Summary of the Invention

[0003] The technical problem to be solved:

[0004] During the actual measurement process, the applicant discovered that the current method of using drones to conduct photogrammetry of antenna arrays still has the following problems:

[0005] First, the measurement accuracy is low: For planar antennas, UAV photogrammetry mostly adopts aerial photogrammetry, which involves reciprocating flight and fixed shooting angles, resulting in low measurement accuracy that cannot meet the surface accuracy measurement requirements of high-precision antennas.

[0006] Secondly, for complex antenna surfaces, such as parabolic antennas, since the normal vector directions at different positions of the curved surface are different, when planning the shooting path and shooting angle, it is necessary to take into account the influence of the camera's light incident angle, the frequency of shooting of the point to be measured, and the intersection angle, and quickly generate UAV path planning and shooting angle planning suitable for antenna surface accuracy measurement to improve measurement efficiency and accuracy.

[0007] Third, there is no corresponding evaluation method for drone photogrammetry shooting effects. Currently, the shooting effect is evaluated based on the solution results of the captured images after shooting is completed, which often requires secondary shooting and results in low measurement efficiency.

[0008] To address the problems existing in the prior art and improve the measurement accuracy and efficiency of antenna profiles, this invention proposes an antenna profile accuracy measurement method based on UAV photogrammetry. By calculating the intersection of the points to be measured on the antenna reflector, the UAV's camera station position and shooting angle are planned, and the shooting measurement effect can be evaluated in a timely manner, thereby improving measurement efficiency and accuracy. This method can be used to guide the measurement of antenna profile accuracy at the working angle in practical engineering.

[0009] The technical solution of this invention is as follows:

[0010] A method for measuring antenna profile accuracy based on UAV photogrammetry includes the following steps:

[0011] Step 1: Establish a Cartesian coordinate system with the center of the antenna reflector, and make preliminary plans for the flight and photogrammetry parameters of the UAV used for antenna profile accuracy measurement based on the antenna parameters;

[0012] Step 2: Based on the antenna equation and the camera station location, calculate the incident angle of the light rays at the point to be measured on the main reflector of the antenna, the frequency of the image being captured, and the intersection angle.

[0013] Step 3: Evaluate the UAV photogrammetry shooting effect based on the shooting frequency and intersection angle of all test points on the antenna main reflector: If the shooting frequency of all test points is greater than the set value, and the intersection angle of all test points is within the set range, then the UAV photogrammetry shooting effect is considered to meet the requirements, thus obtaining the final UAV camera station coordinates that meet the photogrammetry requirements. Otherwise, optimize the flight radius, altitude, number of flight circles, and number of shots per circle until the requirements are met;

[0014] Step 4: Based on the coordinates of each drone camera station obtained in Step 3, plan the camera shooting angle at that camera station coordinate position;

[0015] Step 5: When the antenna is actually working, adjust the coordinates of the camera station position and the camera shooting angle according to the elevation angle of the antenna. Based on the latitude, longitude and altitude of the center of the antenna parabolic surface, convert the camera station position into the position in the geodetic coordinate system to obtain the camera station position and shooting angle of the UAV photogrammetry.

[0016] Step 6: Convert the final camera station positions and shooting angles obtained from the UAV photogrammetry into a path planning file that can be executed by the UAV, and then the UAV photogrammetry system will automatically perform the photogrammetry.

[0017] In a further preferred embodiment, the antenna parameters in step 1 include the antenna aperture. Depth of the main reflector Information such as camera frame size, lens focal length, and size of the coded marker and reflector, etc., are included. The flight and photogrammetry parameters include the UAV's flight radius, altitude, number of flight orbits, and number of shots per orbit.

[0018] A further preferred approach involves, in step 1, initially planning the flight and photogrammetry parameters of the UAV, specifically defining the feasible range of these parameters:

[0019] The drone is required to fly at least two laps, with at least four camera stations captured per lap.

[0020] Flight radius The scope requirement is

[0021]

[0022] According to the formula

[0023]

[0024] Determine the effective shooting height The range, of which For camera focal length, and For camera frame, The number of coded labels in a single photo. The surface area of ​​the antenna's main reflector. The total number of coded targets, For the size of the reflector and the code mark, This refers to the size of the camera's CMOS sensor pixels.

[0025] A further optimized approach, in step 2, is to measure the point... The angle of incidence, frequency of photography, and angle of intersection are calculated through the following process:

[0026] (1) Based on the point to be measured Heshe Station Given the coordinates, calculate the distance between the two. ;

[0027] (2) Calculate the incident angle of the light rays when the camera is taken at the point to be measured, based on the antenna equation. Obtain the normal vector of the point to be measured. Calculate the points to be measured With the camera station Vector of the connection With normal vector The included angle As the angle of incidence of light;

[0028] (3) When l≤ and When the angle is ≤60°, it means that the camera station has captured the image of the point to be measured. Count the number of camera stations that meet the criteria. That is, the point to be measured The frequency of being photographed is determined, and the camera stations that meet the conditions are included in the camera station set {S};

[0029] (4) Based on the selected set of camera stations {S}, establish the points to be measured. The vector connecting the points to each camera station in the camera station set {S} is used. Then, the angle between any two vectors is calculated, and the angles are sorted from largest to smallest. The average of the first ten intersection angles is taken as the point to be measured. The intersection angle B.

[0030] A further preferred embodiment, in step 2, is the point to be measured. The selection can be made in the following way: select multiple busbars on the main reflector surface of the antenna, and select several test points on each busbar.

[0031] Further optimization in step 3 involves: first, increasing the number of cameras in each ring; if the optimization effect after increasing the number of cameras is not significant, then adjusting the radius and height of the outer ring cameras until the requirements are met.

[0032] A further optimized approach, the specific process of planning the camera shooting angle in step 4 is as follows:

[0033] The camera station is located above the X-axis of the coordinate system. Establish a system of equations

[0034]

[0035] In the formula, Let be a point on the antenna reflector surface, ( This is the normal vector of the plane containing the azimuth angle of the UAV gimbal;

[0036] Solving the system of equations yields the farthest shooting point of the camera on the antenna reflector at different gimbal azimuth angles of the UAV camera station. coordinate ;

[0037] Based on the solution, the farthest shooting point of the camera The coordinates are used to determine the maximum pitch angle of the camera gimbal. Based on the obtained maximum pitch angle With camera field of view Based on the relationship, the camera shooting angle is determined as follows:

[0038]

[0039] In this case, the camera's vertical downward angle is considered as 0° of pitch. Divide the orientation equally; .

[0040] Further preferred solutions, if If the camera is located within the range of the antenna's main reflector, then the maximum pitch angle of the camera gimbal in each direction is:

[0041]

[0042] This refers to the camera's field of view.

[0043] like If the antenna is located outside the range of the main reflector, then the maximum elevation angle is:

[0044] When the azimuth angle of the gimbal When it is 0:

[0045]

[0046] When the azimuth angle of the gimbal When it is π:

[0047]

[0048] When the azimuth angle of the gimbal For other angles:

[0049]

[0050]

[0051] Beneficial effects

[0052] The present invention proposes an antenna profile accuracy measurement method based on UAV photogrammetry, which can quickly plan the UAV shooting position and shooting angle while ensuring measurement accuracy, thereby shortening the measurement time, improving the measurement accuracy, saving a lot of manpower and material resources, and ensuring that the antenna system has high electromagnetic wave radiation characteristics.

[0053] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0054] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0055] Figure 1 : Flowchart of the present invention;

[0056] Figure 2 : A schematic diagram illustrating the planning of the number of UAV photogrammetry stations in this invention;

[0057] Figure 3 : Diagram showing camera shooting angle planning;

[0058] Figure 4 : A schematic diagram showing the camera's furthest shooting point inside the antenna;

[0059] Figure 5 : A diagram showing the camera's furthest shooting point outside the antenna;

[0060] Figure 6 A map showing the location of the UAV and all measurement points on the antenna reflector surface in the photogrammetry system software;

[0061] Figure 7 Electromagnetic wave test of antenna system in the S-band;

[0062] Figure 8 : Electromagnetic wave test of antenna system X-band radiation pattern;

[0063] Figure 9 Electromagnetic wave test pattern of antenna system in the Ku band. Detailed Implementation

[0064] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0065] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0066] In this embodiment, UAV photography was used to measure the reflector of a 40 m aperture antenna receiving S / X / Ku bands. Through multiple measurements and adjustments, the surface accuracy of the main reflector was finally better than ±0.3 mm (rms), and the electrical performance test of the antenna system met the requirements.

[0067] Figure 1 The diagram shown is the overall flowchart of the antenna profile accuracy measurement method based on UAV photogrammetry in this embodiment, which includes the following steps:

[0068] Step 1: Establish a Cartesian coordinate system with the center of the antenna reflector. Based on the antenna parameters, make preliminary plans for the flight and photogrammetry parameters of the UAV used for antenna profile accuracy measurement, that is, set the feasible range of the flight and photogrammetry parameters.

[0069] The antenna parameters include antenna aperture. Depth of the main reflector Information such as camera frame size, lens focal length, and size of the coded marker and reflector, etc., are included. The flight and photogrammetry parameters include the UAV's flight radius, altitude, number of flight orbits, and number of shots per orbit.

[0070] In this embodiment, the drone is set to fly at least two laps, with at least four camera stations captured per lap. Flight radius The scope requirement is

[0071]

[0072] According to the formula

[0073]

[0074] Determine the effective shooting height The range, of which For camera focal length, and For camera frame, The number of coded labels in a single photo. The surface area of ​​the antenna's main reflector. The total number of coded targets, For the size of the reflector and the code mark, This refers to the size of the camera's CMOS sensor pixels.

[0075] Step 2: Based on the antenna equation and the camera station location, calculate the incident angle of the light rays at the point to be measured on the main reflector of the antenna, the frequency of the image being captured, and the intersection angle.

[0076] In this embodiment, three busbars are selected on the main reflector surface of the antenna, namely radial lines from the center of the antenna reflector surface to the edge of the antenna reflector surface, and several test points are selected on each busbar.

[0077] For the point to be measured The angle of incidence, frequency of photography, and angle of intersection are calculated through the following process:

[0078] (1) Based on the point to be measured Heshe Station The coordinates of the camera station are the coordinates of the camera in the drone in the Cartesian coordinate system. The distance between the two is calculated. ;

[0079] (2) Calculate the incident angle of the light rays when the camera is taken at the point to be measured, based on the antenna equation. Obtain the normal vector of the point to be measured. Calculate the points to be measured With the camera station Vector of the connection With normal vector The included angle As the angle of incidence of light;

[0080] (3) When l≤ and When the angle is ≤60°, it means that the camera station has captured the image of the point to be measured. Count the number of camera stations that meet the criteria. That is, the point to be measured. The frequency of being photographed is determined, and the camera stations that meet the conditions are included in the camera station set {S}.

[0081] (4) Based on the selected set of camera stations {S}, establish the points to be measured. The vector connecting the points to each camera station in the camera station set {S} is used. Then, the angle between any two vectors is calculated, and the angles are sorted from largest to smallest. The average of the first ten intersection angles is taken as the point to be measured. The intersection angle B.

[0082] Step 3: According to the principles of photogrammetry, the coordinates of the points to be measured can be determined by using four or more camera stations at different locations. The accuracy of stereoscopic measurement is significantly affected by the intersection angle. The measurement accuracy is best when the intersection angle is 90°; the smaller or larger the intersection angle, the lower the accuracy. Based on this, the photogrammetric effect of the UAV is evaluated according to the frequency of photography of all points to be measured on the antenna's main reflector and the intersection angle: if the frequency of photography of all points to be measured is greater than a set value (10 in this embodiment), and the intersection angle of all points to be measured is within a set range (60°~120° in this embodiment), then the photogrammetric effect of the UAV is considered to meet the requirements, thus obtaining the final UAV camera station coordinates that meet the photogrammetric requirements. Otherwise, the flight radius, altitude, number of flight circles, and number of shots per circle are optimized until the requirements are met. Since the shooting frequency and intersection angle of edge points are poor, in this embodiment, the optimization direction is as follows: first, try increasing the number of camera stations in each circle; if increasing the number of camera stations has no significant effect, then adjust the radius and altitude of the outer circle camera stations until the requirements are met.

[0083] Step 4: When photographing a large antenna, the pan and tilt angles are rotated multiple times to expand the acquisition range of the camera station, effectively improving the measurement accuracy of the points to be measured. Figure 3 As shown, the gimbal azimuth angle is divided into equal angles around the circumference. Furthermore, since each ring of camera stations and antennas is centrally symmetrical, the shooting angles of camera stations at different positions within each ring are the same. Therefore, for each UAV camera station coordinate obtained in step 3, the camera shooting angle at that coordinate position is planned using the following process:

[0084] The camera station is located above the X-axis of the coordinate system. Establish a system of equations

[0085]

[0086] In the formula, Let be a point on the antenna reflector surface, ( This is the normal vector of the plane containing the azimuth angle of the UAV gimbal.

[0087] Solving the system of equations will yield the farthest shooting point of the camera on the antenna reflector at different gimbal azimuth angles of the UAV camera station. coordinate .

[0088] Based on the solution, the farthest shooting point of the camera The coordinates, if Located within the range of the antenna's main reflector, such as Figure 4 As shown, the maximum pitch angle of the gimbal in each direction is...

[0089]

[0090] This is the camera's field of view.

[0091] like Located outside the range of the antenna's main reflector, such as Figure 5 As shown, the maximum pitch angle is:

[0092] When the azimuth angle of the gimbal When it is 0:

[0093]

[0094] When the azimuth angle of the gimbal When it is π:

[0095]

[0096] When the azimuth angle of the gimbal For other angles:

[0097]

[0098]

[0099] The maximum pitch angle of the camera station in each position was derived. Then, through judgment With camera field of view The size of the image is used to determine the corresponding pitch angle of the gimbal in each direction. Since each camera station has a field of view of [missing information]... An orthophoto, with the camera's field of view half-angle being... ,when At that time, if according to If only one photograph is taken, there will be a missed area between that photograph and the orthophoto taken at that azimuth and angle. The range of the missed angle is... Therefore, it is necessary to refine and discretize the pitch shooting angle. Here, the pitch angle is set to... , ;when At that time, then according to The image can be taken to capture the entire area in that direction, similar to an orthophoto. The maximum elevation angle is then used to determine the optimal angle. With camera field of view Based on the relationship, the camera shooting angle is determined as follows:

[0100]

[0101] In this case, the camera's vertical downward angle is considered as 0° of pitch. For azimuth division, 6 / 8 / 12 are generally used. .

[0102] Step 5: Since steps 3 and 4 are based on the antenna's main reflector being vertically upward, during actual antenna operation, the camera station's position coordinates and camera shooting angle are adjusted according to the antenna's elevation angle. Then, based on the latitude, longitude, and altitude of the antenna's parabolic center, the camera station's position is converted to a geodetic coordinate system, yielding the UAV photogrammetric camera station position and shooting angle. .

[0103] Step 6: Convert the final camera station positions and shooting angles obtained from the UAV photogrammetry into a path planning file that can be executed by the UAV, and then the UAV photogrammetry system will automatically perform the photogrammetry.

[0104] After processing the photogrammetric image, the coordinates of the point to be tested on the antenna are obtained and compared with the theoretical model to determine the accuracy of the antenna's main reflector. Once the accuracy of the antenna's main reflector meets the technical requirements after adjustment, electrical performance testing is performed. Figures 7-9 The electromagnetic wave test pattern of the antenna system shows that the antenna performance is excellent.

[0105] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for measuring antenna profile accuracy based on unmanned aerial photogrammetry, characterized in that: Includes the following steps: Step 1: Establish a Cartesian coordinate system with the center of the antenna reflector, and make preliminary plans for the flight and photogrammetry parameters of the UAV used for antenna profile accuracy measurement based on the antenna parameters; Step 2: Based on the antenna equation and the camera station location, calculate the incident angle of the light rays at the point to be measured on the main reflector of the antenna, the frequency of the image being captured, and the intersection angle. Step 3: Evaluate the UAV photogrammetry shooting effect based on the shooting frequency and intersection angle of all test points on the antenna main reflector: If the shooting frequency of all test points is greater than the set value, and the intersection angle of all test points is within the set range, then the UAV photogrammetry shooting effect is considered to meet the requirements, thus obtaining the final UAV camera station coordinates that meet the photogrammetry requirements. Otherwise, optimize the flight radius, altitude, number of flight circles, and number of shots per circle until the requirements are met; Step 4: Based on the coordinates of each drone camera station obtained in Step 3, plan the camera shooting angle at that camera station coordinate position; the specific process is as follows: The camera station is located above the X-axis of the coordinate system. Establish a system of equations In the formula, Let be a point on the antenna reflector surface, ( This is the normal vector of the plane containing the azimuth angle of the UAV gimbal; Solving the system of equations yields the farthest shooting point of the camera on the antenna reflector at different gimbal azimuth angles of the UAV camera station. coordinate ; For camera focal length, For the size of the reflector and the code mark, The size of the camera's CMOS pixel; Based on the solution, the farthest shooting point of the camera The coordinates are used to determine the maximum pitch angle of the camera gimbal. Based on the obtained maximum pitch angle With camera field of view Based on the relationship, the camera shooting angle is determined as follows: In this case, the camera's vertical downward angle is considered as 0° of pitch. Divide the orientation equally; ; like If the camera is located within the range of the antenna's main reflector, then the maximum pitch angle of the camera gimbal in each direction is: This refers to the camera's field of view. like If the antenna is located outside the range of the main reflector, then the maximum elevation angle is: When the azimuth angle of the gimbal When it is 0: When the azimuth angle of the gimbal When it is π: When the azimuth angle of the gimbal For other angles: in Antenna aperture, Depth of the main reflective surface; Step 5: When the antenna is actually working, adjust the coordinates of the camera station position and the camera shooting angle according to the elevation angle of the antenna. Based on the latitude, longitude and altitude of the center of the antenna parabolic surface, convert the camera station position into the position in the geodetic coordinate system to obtain the camera station position and shooting angle of the UAV photogrammetry. Step 6: Convert the final camera station positions and shooting angles obtained from the UAV photogrammetry into a path planning file that can be executed by the UAV, and then the UAV photogrammetry system will automatically perform the photogrammetry.

2. The antenna profile accuracy measurement method based on UAV photogrammetry according to claim 1, characterized in that: The antenna parameters mentioned in step 1 include the antenna aperture. Depth of the main reflector Information such as camera frame size, lens focal length, and size of the coded marker and reflector, etc., are included. The flight and photogrammetry parameters include the UAV's flight radius, altitude, number of flight orbits, and number of shots per orbit.

3. The antenna profile accuracy measurement method based on UAV photogrammetry according to claim 2, characterized in that: Step 1 involves preliminary planning of the UAV's flight and photogrammetry parameters, which means setting the feasible range of the flight and photogrammetry parameters: The drone is required to fly at least two laps, with at least four camera stations captured per lap. Flight radius The scope requirement is According to the formula Determine the effective shooting height The range, of which For camera focal length, and For camera frame, The number of coded labels in a single photo. The surface area of ​​the antenna's main reflector. The total number of coded targets, For the size of the reflector and the code mark, This refers to the size of the camera's CMOS sensor pixels.

4. The antenna profile accuracy measurement method based on UAV photogrammetry according to claim 1, characterized in that: In step 2, for the point to be measured The angle of incidence, frequency of photography, and angle of intersection are calculated through the following process: (1) Based on the point to be measured Heshe Station Given the coordinates, calculate the distance between the two. ; (2) Calculate the incident angle of the light rays when the camera is taken at the point to be measured, based on the antenna equation. Obtain the normal vector of the point to be measured. Calculate the points to be measured With the camera station Vector of the connection With normal vector The included angle As the angle of incidence of light; (3) When l≤ and At that time, it indicates that the camera station has captured images of the point to be measured. Count the number of camera stations that meet the criteria. That is, the point to be measured The frequency of being photographed is determined, and the camera stations that meet the conditions are included in the camera station set {S}; (4) Based on the selected set of camera stations {S}, establish the points to be measured. The vector connecting the points to each camera station in the camera station set {S} is used. Then, the angle between any two vectors is calculated, and the angles are sorted from largest to smallest. The average of the first ten intersection angles is taken as the point to be measured. The intersection angle B.

5. The antenna profile accuracy measurement method based on UAV photogrammetry according to claim 4, characterized in that: In step 2, the point to be measured The selection can be made in the following way: select multiple busbars on the main reflector surface of the antenna, and select several test points on each busbar.

6. The antenna profile accuracy measurement method based on UAV photogrammetry according to claim 1, characterized in that: In step 3, the optimization direction is: first, increase the number of each perimeter camera station; If increasing the number of camera stations does not significantly improve performance, adjust the radius and height of the outer camera stations until the requirements are met.

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