A real-time positioning system and method for aerial cameras based on elevation data

Abstract

A real-time positioning system and method for aerial cameras based on elevation data, particularly for positioning devices and methods in situations where distance information cannot be obtained from aerial cameras. Utilizing a host computer's large-capacity database to store DEM data for the mission area, the approximate geographical location of the imaging area is estimated through rough positioning that is not based on distance information. The mission area that may be photographed is expanded outward with the estimated point as the center, and the DEM data for the area is requested from the host computer via a 10 Gigabit network. Based on the DEM data, data is iterated and accurately positioned from high points to low points. During the flight of the carrier aircraft, track estimation is used to pre-retrieve the data for the next mission area during the return phase of each photographic strip, and continuous high-precision positioning is achieved through repeated iterations. The positioning method involved in the present invention can achieve continuous high-precision target positioning of airborne reconnaissance cameras through track estimation and data interaction when distance information cannot be obtained.

Description

Technical Field

[0001] The present invention relates to a real-time positioning method for an aerial camera, belonging to the technical field of optoelectronic platform imaging control, and is particularly directed to a real-time positioning system and method when an aerial camera cannot obtain distance information of a carrier aircraft relative to a mission area. Background Art

[0002] During aerial camera missions, the actual latitude and longitude of the target in the image plays a significant role in guiding image intelligence analysis. During the actual photography process, positioning accuracy is significantly affected by ground elevation data. Conventionally, a typical height of the target area is used as an input parameter to calculate positioning results. This can introduce significant errors when the ground is undulating. Manually changing the ground height parameter by the operator is difficult to input continuously and results in significant lag. As a supplement, other reconnaissance methods can be used to obtain distance information to the target. This distance information, combined with the aircraft's position, attitude, and target pointing angle, can achieve higher positioning accuracy. However, without the support of other reconnaissance methods, it is difficult for aerial cameras to independently perform positioning functions.

[0003] In response to the above difficulties, when distance information cannot be obtained, the present invention solves the problem of manual input difficulties for operators by using the real-time interactive elevation data of the host computer. At the same time, with the help of the high-speed transmission of the 10 Gigabit network, the photo return interval, and the ping-pong data structure, continuous data update is achieved. At the same time, with the help of the elevation search method, high-precision real-time positioning under dynamic elevation conditions is achieved on the basis of the original positioning based on height or distance information. Summary of the Invention

[0004] Aiming at the demand for real-time, high-precision positioning of aerial cameras that is not based on distance information, the present invention is designed to use a host computer's large-capacity database to store global DEM data, interact with high-speed data in a 10 Gigabit network, and use the original positioning method to search for data to achieve high-precision, real-time positioning that is not based on distance information. This improves positioning accuracy over a wider range while being easy to operate and highly real-time.

[0005] The technical solution for achieving the purpose of the present invention is that the real-time positioning system of the aerial camera based on elevation data includes a host computer, an integrated control module, an image pre-processing module and a camera installed on the aircraft;

[0006] The host computer stores DEM data and serves as a control terminal. The host computer sends DEM data and control instructions to the integrated control module.

[0007] The integrated control module, the control instructions of the host computer are sent to the camera through the integrated control module, and the image data collected in real time by the camera and the DEM data of the host computer are output to the image preprocessing module through the integrated control module;

[0008] The image preprocessing module processes the image data and the DEM data and then outputs the positioning result and the processed image data to the host computer through the integrated control module.

[0009] A method for real-time positioning of an aerial camera based on elevation data comprises the following steps:

[0010] (1) Estimation preparation stage: Using the trajectory estimation method, the current position of the aircraft is A0, and the position A1 of the next period of time is estimated based on the aircraft's heading angle, flight speed and target pointing angle. The distance between A0 and A1 is S1. According to the trigonometric relationship, the relative height (estimated value) is divided by tan, which is the distance of the target area relative to A1. Expanding on the ground in the direction perpendicular to the heading, the position of the target area for photography B1 can be obtained.

[0011] (2) Target area data estimation: The aircraft requests the upper computer through the data channel of the integrated control module for the DEM data of the target area B1 corresponding to the area C1. The aircraft obtains the DEM data of the target area expanded by the N1 longitude and N2 latitude around B1, and uses the bubble method to obtain the highest and lowest point heights in the expanded target area.

[0012] (3) Image acquisition: When the aircraft moves from position A0 to position A1, the camera takes pictures in real time;

[0013] (4) Calculate the positioning. The image preprocessing module processes the image obtained in the third step, draws a navigation reference line with the aircraft position A0 as the starting point and position A1 as the end point, and uses the axis line perpendicular to the navigation reference line as the axis line. The axis line is projected to the ground, assuming the highest point is blocked, calculates the longitude and latitude of the ground projection line, finds the DEM data of the corresponding longitude and latitude, and compares the highest point of the corresponding longitude and latitude with the assumed highest point that is blocked. If they match, it is the corresponding position and the positioning information data is input into the host computer. If they do not match, it is the non-corresponding position and the non-positioning information data is input into the host computer. The host computer controls the aircraft to lower the altitude and re-acquire the image according to the third step, and repeats the fourth step. Before the altitude drops to the lowest point, a matching position will be found.

[0014] Furthermore, during the image acquisition process, the first and second steps are repeated to acquire data for the next area.

[0015] The advantage of the present invention is that positioning efficiency is improved by using a host computer to exchange elevation data in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Real-time positioning system for aerial cameras based on elevation data.

[0017] Figure 2 for Figure 1 Positioning data flow chart.

[0018] Figure 3 Positioning data update timing diagram.

[0019] Figure 4 Schematic diagram of the search principle of the positioning method.

[0020] Figure 5 Schematic diagram comparing the real-shot image and positioning results.

[0021] Description of the accompanying drawings: host computer 1, integrated control module 2, camera 3, image preprocessing module 4. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. 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 present invention.

[0023] The specific embodiments of the present invention are described in detail below with reference to the examples and drawings.

[0024] like Figure 1 、 2 In the invention, a real-time positioning system of an aerial camera based on elevation data includes a host computer 1, an integrated control module 2, an image preprocessing module 4 and a camera 3 provided on an aircraft;

[0025] The host computer 1 stores DEM data and serves as a control terminal. The host computer 1 sends DEM data and control instructions to the integrated control module 2. The instructions of the host computer 1 include instructions for adjusting the flight trajectory of the aircraft. Among them, the DEM data is elevation data. The DEM data jointly measured by the National Aeronautics and Space Administration (NASA) and the National Institute of Surveying, Mapping and Mapping (NIMA) of the Department of Defense is referred to as SRTM data. It can be downloaded from the website http: / / srtm.csi.cgiar.org / SELECTION / inputCoord.asp, and elevation data can be obtained from other channels.

[0026] The integrated control module 2, the control instructions of the host computer 1 are sent to the camera 3 through the integrated control module 2, and the image data collected in real time by the camera 3 and the DEM data of the host computer 1 are output to the image preprocessing module 4 through the integrated control module 2;

[0027] The image preprocessing module 4 processes the image data and the DEM data and then outputs the positioning result and the processed image data to the host computer 1 through the integrated control module 2 .

[0028] The proposed method for real-time positioning of aerial cameras based on elevation data is based on line-of-sight calculation. Given the known aircraft position and camera attitude, a projection is made onto the ground. Based on the target area's ground height or distance information, the target area's positioning information is calculated. However, the difficulty lies in the difficulty in obtaining ground height and distance information for the target area. Although DEM data is available, the data volume is too large for the camera's storage space, and the query and call cycles far exceed the requirements for real-time positioning.

[0029] A method for real-time positioning of an aerial camera based on elevation data comprises the following steps:

[0030] (1) Figure 3 As shown, in the estimation preparation stage: the data format is the original DAT data. The DAT data is stored according to 1 longitude by 1 latitude. There are 900 sampling points in each longitude and latitude area. The index file name is longitude and latitude point information. In the preparation stage, the camera 3 calls the track estimation program to estimate the future operation trajectory of the carrier aircraft. Using the track estimation method, the current position of the aircraft is A0, and the position A1 in the next period of time is estimated based on the aircraft's heading angle, flight speed and target pointing angle α. The distance between A0 and A1 is S1. According to the trigonometric relationship, the relative height (estimated value) is divided by tan(α), which is the distance of the target area relative to A1. Expand on the ground in the direction perpendicular to the heading to obtain the position B1 of the target area for photography;

[0031] (2) Target area data estimation: The aircraft requests the upper computer for the DEM data of the target area B1 corresponding to the area C1 through the data channel of the integrated control module. The DEM data of the target area expanded by the N1 longitude multiplied by the N2 latitude is obtained with B1 as the center point. The value of N1\N2 is generally 3, but can also be 4, 5, etc. The highest and lowest points in the expanded target area are obtained using the bubble method.

[0032] (3) Image acquisition: When the aircraft moves from position A0 to position A1, the camera takes pictures in real time and repeats the first and second steps to obtain the data of the next area;

[0033] (4) Calculate the positioning. The image preprocessing module processes the image obtained in the third step, draws a navigation reference line with the aircraft position A0 as the starting point and position A1 as the end point, and uses the axis line perpendicular to the navigation reference line as the line of sight. The axis line of sight is projected onto the ground. Assuming the highest point to be blocked (that is, assuming that the camera's visual axis points to the highest point in the area), calculate the longitude and latitude of the ground projection line (calculate a longitude and latitude point by the intersection of the camera's visual axis direction and the highest point Hmax in the area. After the calculation is completed, compare the actual DEM elevation information of the longitude and latitude. If the information matches, it is considered that the positioning point is the point). Find the DEM data of the corresponding longitude and latitude, and compare whether the highest point of the corresponding longitude and latitude matches the assumed blocked highest point. If they match, it is the corresponding position and the positioning information data is input into the host computer. If they do not match, it is the non-corresponding position and the non-positioning information data is input into the host computer. The host computer controls the aircraft to lower the altitude and re-acquire the image according to the third step, and repeats the fourth step. Before the altitude drops to the lowest point, a matching position will be found.

[0034] Specific press Figure 4 As shown, Hmax and Hmin are divided into fifteen intervals, H1 to H15. Using H1, a latitude and longitude are calculated again according to the Hmax method. After the calculation is completed, the actual DEM data elevation information of the latitude and longitude is compared. If the information matches, the positioning point is considered to be that point. If not, the elevation is lowered until it reaches Hmin. The latitude and longitude of the carrier aircraft are 109.481° East longitude and 34.8739° North latitude, the carrier aircraft flight altitude is 8289 meters, and the highest mission area is Hmax = 3238 and Hmin = 323. The latitude and longitude of the positioning points corresponding to H1 to H15 (repeat steps 3 and 4) and the corresponding elevation data are calculated in sequence (as shown in Table 1).

[0035] It should be noted that when using the above method, while taking pictures and calculating the position, camera 3 is unable to exchange data with the host computer 1. It is necessary to take advantage of the return segment of the swing scanning camera. When there is no data from the camera during the return phase, data is retrieved from the host computer 1. Taking into account the different speed-to-height ratios and different numbers of pictures taken by camera 1, the return time is different. Data is retrieved according to the shortest return time of 400ms. At the same time, a fixed delay is added after stopping shooting to avoid data backlog when the software just stops shooting, which causes camera data and DEM data to occupy the data bus.

[0036] Table 1

[0037]

[0038] (5) Compare the points on Google Earth software. The relationship between the positioning points and the points is as follows: Figure 5 As shown in the figure, it is verified that the positioning error of the DEM data is no more than 200 meters, and positioning can be achieved without elevation information.

[0039] (6) The verification results show that the real-time positioning method based on elevation data of the present invention can meet the positioning requirements of aerial cameras.

[0040] The contents not described in detail in the present invention regarding the calculation of the boresight pointing, expansion in the direction of the vertical heading, and the bubbling method are considered to be common knowledge for professionals in this field.

Claims

1. A real-time positioning method for an aerial camera based on elevation data, characterized in that: The following steps are involved: (1) Estimation preparation stage: Using the trajectory estimation method, the current position of the aircraft is A0, and the position A1 of the next period of time is estimated based on the aircraft's heading angle, flight speed and target pointing angle α. The distance between A0 and A1 is S1. According to the trigonometric relationship, the relative height is divided by tan(α), which is the distance of the target area relative to A1. Expanding on the ground in the direction perpendicular to the heading direction can obtain the position B1 of the target area for photography; (2) Target area data estimation: The aircraft requests the upper computer through the data channel of the integrated control module for the DEM data of the target area B1 corresponding to the area C1. The aircraft obtains the DEM data of the target area expanded by the N1 longitude and N2 latitude around B1, and uses the bubble method to obtain the highest and lowest point heights in the expanded target area. (3) Image acquisition: When the aircraft moves from position A0 to position A1, the camera takes pictures in real time; (4) Calculate the positioning. The image preprocessing module processes the image obtained in the third step, draws a navigation reference line with the aircraft position A0 as the starting point and position A1 as the end point, and uses the axis line perpendicular to the navigation reference line as the axis line. The axis line is projected to the ground, assuming the highest point is blocked, calculates the longitude and latitude of the ground projection line, finds the DEM data of the corresponding longitude and latitude, and compares the highest point of the corresponding longitude and latitude with the assumed highest point that is blocked. If they match, they are the corresponding positions, and the positioning information data is input into the host computer. If they do not match, they are the non-corresponding positions, and the non-positioning information data is input into the host computer. The host computer controls the aircraft to lower its altitude and re-acquire the image according to the third step, and repeats the fourth step. Before the altitude drops to the lowest point, a matching position will be found.

2. The real-time positioning method of an aerial camera based on elevation data according to claim 1, characterized in that: During the image acquisition process, the first and second steps are repeated to acquire data for the next area.

3. A real-time positioning system for aerial cameras based on elevation data, characterized in that: The method for real-time positioning of an aerial camera based on elevation data as described in any one of claims 1 to 2 is adopted; the system comprises a host computer, an integrated control module, an image preprocessing module and a camera mounted on an aircraft; The host computer stores DEM data and serves as a control terminal. The host computer sends DEM data and control instructions to the integrated control module. The integrated control module, the control instructions of the host computer are sent to the camera through the integrated control module, and the image data collected in real time by the camera and the DEM data of the host computer are output to the image preprocessing module through the integrated control module; The image preprocessing module processes the image data and the DEM data and then outputs the positioning result and the processed image data to the host computer through the integrated control module.

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