A radar calibration method based on ellipse centroid method

Abstract

The present invention provides a radar calibration method based on the ellipse centroid method, step 1: obtaining the geodetic coordinate data of the ellipse track of the measured object and the polar coordinate data of the ellipse track of the measured object measured by radar; step 2: unifying the data coordinate system; step 3: extracting the true value data of the measured object and the component data of the x and y components of the measured data, and using them to calculate the deviation between the true value azimuth and the measured value azimuth to obtain the azimuth calibration value; step 4: repeating steps 1 to 4, the number of repetitions M is not less than three times; averaging the obtained azimuth calibration values ​​to obtain the final azimuth calibration value; averaging the obtained elevation calibration values ​​to obtain the final elevation calibration value. The present invention only needs to analyze the track data to obtain the radar calibration data, has strong geographical adaptability, low cost, and convenient testing.

Description

Technical Field

[0001] The invention belongs to the field of radar and relates to a radar calibration method based on an ellipse centroid method. Background Art

[0002] With the increasing maturity of radar technology, radar is widely used in the fields of national defense, meteorology, measurement and control, air traffic control, water conservancy, emergency rescue and disaster relief, and is indispensable in modernization construction. The basic principle of radar is relatively simple, but it is not easy to implement in different occasions. It works by radiating electromagnetic energy and detecting the echo reflected by the target, and obtains relevant information about the target by analyzing the characteristics of the echo signal and the signal of the positioning system. As a measurement system, each measurement is based on the reference point to obtain the value. Through system calibration, the measurement value is corrected once, and finally the true physical quantity value of the measurement target is obtained.

[0003] Traditional calibration methods usually require metrology professionals to operate special metrology equipment to complete equipment calibration. This process is highly specialized and has high calibration accuracy, but resources are limited and implementation is inconvenient. During equipment operation, the original calibration results of the equipment are always unable to apply to the new equipment status due to factors such as fault maintenance and position changes, and recalibration is required to restore normal detection. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a radar calibration method based on the ellipse centroid method, comprising the following steps:

[0005] Step 1: Obtain geodetic coordinate data of the elliptical track of the object to be measured and polar coordinate data of the elliptical track of the object to be measured by radar;

[0006] Step 2: Unify the data coordinate system: convert the geodetic coordinate data of the elliptical track of the measured object into the rectangular coordinate data of the station center to obtain the true value data of the measured object, and convert the polar coordinate data of the elliptical track of the measured object measured by radar into the rectangular coordinate data of the station center to obtain the measurement data of the measured object;

[0007] Step 3: extract the component data of the x and y components of the true value data and the measured data of the measured object, and use them to calculate the deviation between the true value azimuth and the measured value azimuth to obtain the azimuth calibration value; extract the component data of the x and z components of the true value data and the measured data of the measured object, and use them to calculate the deviation between the true value elevation angle and the measured elevation angle to obtain the elevation calibration value; the calculation method of the deviation between the true value azimuth and the measured value azimuth is the same as the calculation method of the deviation between the true value elevation angle and the measured elevation angle; in the station center rectangular coordinate system xOyOz, the positive direction of the x-axis points to due east, the positive direction of the y-axis points to due north, and the positive direction of the z-axis points to due up;

[0008] Step 4: Repeat steps 1 to 4, with the number of repetitions M being no less than three times; average the obtained azimuth calibration values ​​to obtain the final azimuth calibration value; average the obtained elevation angle calibration values ​​to obtain the final elevation angle calibration value.

[0009] Furthermore, the specific process of calculating the azimuth calibration value is:

[0010] Step 3.1: Use median filtering to perform data preprocessing on the component data of the true value data of the measured object, remove abnormal points, and obtain a first data sample set;

[0011] Step 3.2: Randomly select points to perform ellipse fitting, further remove noise points, determine the optimal data point trace of the ellipse, and obtain the second data sample set;

[0012] Step 3.3: Fit an ellipse to the second data sample set using a least square curve fitting algorithm, calculate the coordinates of the ellipse centroid, convert the ellipse centroid coordinate data into polar coordinate data, and calculate the true value orientation of the true value data;

[0013] Repeat steps 3.1-3.3 to obtain the measured value orientation of the measured data of the measured object, and the orientation calibration value is obtained by subtracting the true value orientation from the measured value orientation.

[0014] Furthermore, the specific process of obtaining the second sample data set is:

[0015] Define the geometric distance threshold T from the ellipse to the culling threshold point r , the minimum threshold of effective points percentage T minp , the maximum threshold of effective points percentage T maxp and the maximum number of iterations N; divide the first sample data set into six regions in order, randomly select one point in each region, a total of six points, and substitute the following unknown ellipse equation into it:

[0016] T1x 2 +T2xy+T3y 2 +T4x+T5y+T6=0

[0017] Form a system of equations, solve the ellipse equation coefficients (T1, T2, T3, T4, T5, T6), and bring the solved ellipse equation coefficients back to the above equation to obtain the ellipse equation T1x 2 +T2xy+T3y 2 +T4x+T5y+T6;

[0018] Substitute all sample points into the ellipse equation T1x in turn 2 +T2xy+T3y 2 +T4x+T5y+T6, if the value is greater than the threshold value T rThen discard the point, and finally calculate the percentage of valid points and total points. If the percentage is greater than the threshold T minp , then save the result; repeat the above process until the proportion of valid points is greater than the threshold T maxp Or the number of iterations exceeds N, and a second sample data set is obtained.

[0019] Furthermore, the specific process of finding the centroid of the ellipse is:

[0020] For the objective function

[0021]

[0022] Find the partial derivative and satisfy the condition Get a linear equation system, use the elimination method to solve the equation, and get the coefficient of the equation (a 11 , a 12 , a 22 , a1, a2, a3), so that the objective function value is minimized and the ellipse equation is obtained;

[0023] According to the coefficient of equation (a 11 , a 12 , a 22 , a1, a2, a3) to solve the centroid coordinates of the ellipse (x0, y0), the calculation formula is:

[0024]

[0025] According to the following conversion formula from the station center rectangular coordinate system to the polar coordinate system, the true value azimuth value α of the true value data is obtained:

[0026]

[0027] Furthermore, the process of converting the geodetic coordinate data into the station center rectangular coordinate data is as follows:

[0028]

[0029] in is the radius of curvature of the y-axis; a is the major semi-axis of the ellipsoid, b is the minor semi-axis of the ellipsoid; the geodetic rectangular coordinates of the station center are (X0, Y0, Z0); B is the latitude of the geodetic coordinates, L is the longitude of the geodetic coordinates, H is the altitude of the geodetic coordinates, and (X, Y, Z) represents a point in the geodetic rectangular coordinate system;

[0030] The specific formula for converting polar coordinate data into station center rectangular coordinate data is as follows:

[0031]

[0032] Among them, (x, y, z) represents a point in the station-centered rectangular coordinate system, and (R, A, E) represents a point in the polar coordinate system.

[0033] Compared with the prior art, the present invention has the following technical effects:

[0034] (1) The present invention can obtain radar calibration data by only analyzing the track data, has strong geographical adaptability, low cost, and convenient testing.

[0035] (2) It is suitable for quickly completing calibration and resuming duty after system adjustment. It can also be used for daily operation, integrating a real-time processing system to monitor the effectiveness of system target measurement in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the process of the present invention according to an embodiment of the present invention.

[0037] Figure 2 Schematic diagram of X and Y component projection according to an embodiment of the present invention.

[0038] Figure 3 Schematic diagram of X and Z component projection according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention processes the geodetic coordinate track data of the track of a specific shape of the target and the radar measurement track data by using an analysis method based on curve fitting to obtain the difference of the characteristic points of the two curves, and completes the radar calibration accordingly.

[0040] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] like Figure 1 As shown, the embodiment of the present invention specifically includes the following steps:

[0042] Step 1: Obtain the geodetic coordinate data of the elliptical track of the object being measured and the polar coordinate data of the corresponding radar measurement.

[0043] Step 2: Unify the data coordinate system. Convert the geodetic coordinate data of the elliptical track of the measured object into the rectangular coordinate data of the station center to obtain the true value data of the measured object, and convert the polar coordinate data of the elliptical track of the measured object measured by radar into the rectangular coordinate data of the station center to obtain the measurement data of the measured object.

[0044] The conversion from geodetic coordinates to station center rectangular coordinates must go through the process from geodetic coordinate system to geodetic rectangular coordinate system and from geodetic rectangular coordinate system to station center rectangular coordinate system. The specific formula is as follows:

[0045] B is the latitude of the geodetic coordinates, L is the longitude of the geodetic coordinates, H is the altitude of the geodetic coordinates, (X, Y, Z) represents a point in the geodetic rectangular coordinate system; (x, y, z) represents a point in the station center rectangular coordinate system, and (R, A, E) represents a point in the polar coordinate system. The geodetic rectangular coordinates of the station center are (X0, Y0, Z0). The formulas involved are as follows:

[0046]

[0047] in is the radius of curvature of the y-axis; a is the major semi-axis of the ellipsoid, and b is the minor semi-axis of the ellipsoid.

[0048]

[0049] The specific formula for converting polar coordinates to station center rectangular coordinates is as follows:

[0050]

[0051] In the rectangular coordinate system of the station center, the positive direction of the x-axis points to the east, the positive direction of the y-axis points to the north, and the positive direction of the y-axis points to the top.

[0052] Step 3: Extract the x and y components to calculate the deviation of the azimuth α; extract the x and z components to calculate the deviation of the elevation angle β. The calculation process of the two branches is the same, and the following will take the first branch as an example to illustrate. The schematic diagram of the X and Y component projection of this embodiment is as follows Figure 2 As shown, the X and Z component projection schematic diagram of this embodiment is as shown Figure 3 shown.

[0053] Step 4: Use median filtering to preprocess the extracted component data, remove abnormal points, and obtain the first data sample set.

[0054] Step 5: Randomly select points to perform ellipse fitting, further eliminate noise points, determine the optimal data point trace of the ellipse, and obtain the second data sample set.

[0055] Define the geometric distance threshold T from the ellipse to the culling threshold point according to the required accuracy r , the minimum threshold of effective points percentage T minp , the maximum threshold of effective points percentage T maxp , the maximum number of iterations N. The first sample data set is divided into six regions in order, and a point is randomly selected from each region, a total of six points, and the following ellipse equation with unknown parameters is substituted into it:

[0056] T1x 2 +T2xy+T3y 2 +T4x+T5y+T6=0

[0057] Form a system of equations, solve the system of equations, and obtain a set of ellipse equation coefficients (T1, T2, T3, T4, T5, T6). Substitute the above equation to obtain the ellipse equation. Substitute all sample points into the ellipse equation T1x in turn. 2 +T2xy+T3y 2 +T4x+T5y+T6, if the value is greater than the threshold value T r Then discard the point, and finally calculate the percentage of valid points and total points, which is greater than the threshold T minp , then save the result. Repeat the above process until the proportion of valid points is greater than the threshold T maxp Or the number of iterations exceeds N.

[0058] Step 6: Use the least squares curve fitting algorithm to fit an ellipse to the second data sample set and calculate the centroid (center) of the ellipse.

[0059] For the second data sample set, the least squares method is used to fit the ellipse:

[0060] For the objective function

[0061]

[0062] Find the partial derivative, satisfying the following conditions

[0063]

[0064] You can get a linear equation system, and use the elimination method to solve the equation to get a set of equation coefficients (a 11 , a 12 , a 22 , a1, a2, a3), so that the objective function value is minimized, and the equation of the ellipse is obtained.

[0065] Step 7: Solve the coordinates of the ellipse's centroid (center), and convert the ellipse's centroid (center) coordinate data into polar coordinate data.

[0066] The coefficient of the equation obtained in the previous step (a 11 , a 12 , a 22 , a1, a2, a3) into the following formula to obtain the centroid (center) coordinates (x0, y0) of the ellipse.

[0067]

[0068] The azimuth α is obtained by using the following conversion formula from the station center rectangular coordinate system to the polar coordinate system.

[0069]

[0070] Step 8: Solve for the deviation of orientation α.

[0071] According to the methods of steps 4 to 7, the true value data and the measured data are processed to obtain the true value azimuth α1 and the measured value azimuth α2 respectively, and the difference between the two is the azimuth calibration value Δ α .

[0072] Δ α =α1-α2

[0073] Step 9: Process the extracted x and z components according to steps 4 to 8 to solve the calibration value Δ of the elevation angle β β .

[0074] Step 10: Repeat steps 1 to 9, with the number of repetitions M being no less than three times; average the obtained azimuth calibration values ​​to obtain the final azimuth, and average the obtained elevation calibration values ​​to obtain the final elevation calibration value.

[0075] This embodiment also gives the actual application process of the algorithm. The algorithm can be packaged into a self-contained module, providing data input and output interfaces, integrated with other real-time systems or analysis software, and expanding the calibration function. The specific main development process is as follows:

[0076] Step 1: Determine the input geodetic coordinate data format and the polar coordinate data format of radar measurement; define the median filter parameter interface; define the geometric distance threshold T from the point to the ellipse r , the minimum threshold of effective points percentage T minp , the maximum threshold of effective points percentage T maxp , maximum number of iterations N, average number M, convergence of calibration values ​​(in azimuth and elevation), etc. Use geodetic coordinate data as the true value and use this data as the standard to calibrate the polar coordinate data measured by radar;

[0077] Step 2: Develop a data parsing program module according to the defined input geodetic coordinate data format and the polar coordinate data format of radar measurement to parse the imported data; develop the parameter input interface of step 1 and input the parameters; open up auxiliary memory space for subsequent processing.

[0078] Step 3: Use the above coordinate conversion formula to convert the data of the geodetic coordinate system into the rectangular coordinate system data of the station center, and convert the polar coordinate data into the rectangular coordinate system data of the station center;

[0079] Step 4: From the rectangular coordinate system of the station center, extract the x and y components and store them in two buffers for backup, and then extract the x and z components and store them in another two buffers for backup.

[0080] Step 5: Perform median filtering on the data in the four buffers to remove outliers and transfer the data to another four buffers.

[0081] Step 6: Divide the data in each buffer into six equal parts and save the partition points.

[0082] Step 7: Randomly select a point in each partition and store it in an array. Use these six points to obtain a set of ellipse parameters and the ellipse equation. Then substitute each point in the corresponding buffer into the ellipse equation. If the value is greater than the threshold T r , then remove the point. Solve the effective point ratio, which is greater than the minimum threshold T minp , then save the result. When the proportion is greater than the threshold T maxp Or when the number of processing times is greater than N, the processing ends. Each partition is processed according to this method to obtain a new data set.

[0083] Step 8: Use the least squares method mentioned above to fit an ellipse to the new data set, use the ellipse centroid (center) coordinate calculation formula to obtain the coordinates of the four ellipse centroids (centers), and then use the station center coordinate system to station center polar coordinate system conversion formula to obtain the true azimuth, measured azimuth, true elevation angle, and measured elevation angle.

[0084] Step 9: Use the method in the technical solution to make a difference, obtain the azimuth calibration value and the elevation calibration value, and store them;

[0085] Step 10: Repeat the process from step 2 to step 9 for 3 times to obtain 3 sets of calibration values;

[0086] Step 11: Calculate the arithmetic mean of the three sets of calibration values ​​and output the final calibration value.

[0087] The radar calibration method based on the ellipse centroid method described in the present invention can obtain radar calibration data by only analyzing the track data, has strong geographical adaptability, low cost, and convenient testing. It is suitable for quickly completing calibration and resuming duty after system adjustment; it can also be used in daily operation, integrating a real-time processing system, and real-time monitoring of the effectiveness of system target measurement.

[0088] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0089] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0090] In the several embodiments provided in the present application, it should be understood that the disclosed systems and devices can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0091] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0092] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0093] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name in English: Read-Only Memory, English abbreviation: ROM), random access memory (full name in English: Random Access Memory, English abbreviation: RAM), disk or optical disk and other media that can store program codes.

[0094] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A radar calibration method based on the ellipse centroid method, characterized in that: The method comprises the following steps: Step 1: Obtain geodetic coordinate data of the elliptical track of the object to be measured and polar coordinate data of the elliptical track of the object to be measured by radar; Step 2: Unify the data coordinate system: convert the geodetic coordinate data of the elliptical track of the measured object into the rectangular coordinate data of the station center to obtain the true value data of the measured object, and convert the polar coordinate data of the elliptical track of the measured object measured by radar into the rectangular coordinate data of the station center to obtain the measurement data of the measured object; Step 3: extract the component data of the x and y components of the true value data and the measured data of the measured object, and use them to calculate the deviation between the true value azimuth and the measured value azimuth to obtain the azimuth calibration value; extract the component data of the x and z components of the true value data and the measured data of the measured object, and use them to calculate the deviation between the true value elevation angle and the measured elevation angle to obtain the elevation calibration value; the calculation method of the deviation between the true value azimuth and the measured value azimuth is the same as the calculation method of the deviation between the true value elevation angle and the measured elevation angle; in the station center rectangular coordinate system xOyOz, the positive direction of the x-axis points to due east, the positive direction of the y-axis points to due north, and the positive direction of the z-axis points to due up; Step 4: Repeat steps 1 to 3, with the number of repetitions M being no less than three times; average the obtained azimuth calibration values ​​to obtain the final azimuth calibration value; average the obtained elevation calibration values ​​to obtain the final elevation calibration value; The specific process of calculating the azimuth calibration value is: Step 3.1: Use median filtering to perform data preprocessing on the component data of the true value data of the measured object, remove abnormal points, and obtain a first data sample set; Step 3.2: Randomly select points to perform ellipse fitting, further remove noise points, determine the optimal data point trace of the ellipse, and obtain the second data sample set; Step 3.3: Fit an ellipse to the second data sample set using a least square curve fitting algorithm, calculate the coordinates of the ellipse centroid, convert the ellipse centroid coordinate data into polar coordinate data, and calculate the true value orientation of the true value data; Repeat steps 3.1-3.3 to obtain the measured value orientation of the measured data of the measured object, and the orientation calibration value is obtained by subtracting the true value orientation from the measured value orientation.

2. The radar calibration method based on the ellipse centroid method according to claim 1, characterized in that: The specific process of obtaining the second sample data set is: Define the geometric distance threshold from the ellipse to the culling threshold point , Minimum threshold of effective points ratio 、 Maximum threshold of effective points ratio and the maximum number of iterations N; divide the first sample data set into six regions in order, randomly select one point in each region, a total of six points, and substitute the following unknown ellipse equation into it: Form a system of equations and solve the coefficients of the elliptic equation ( , , , , , ), bring the solved elliptic equation coefficients back into the above equation to obtain the elliptic equation ; Substitute all sample points into the ellipse equation in turn If the value is greater than the threshold Then discard the point, and finally calculate the percentage of valid points and total points. If the percentage is greater than the threshold , then save the result; repeat the above process until the proportion of valid points is greater than the threshold Or the number of iterations exceeds N, and a second sample data set is obtained.

3. The radar calibration method based on the ellipse centroid method according to claim 2, characterized in that: The specific process of finding the centroid of an ellipse is: For the objective function Find the partial derivative and satisfy the condition Get a linear equation system, solve the equation using elimination method, and get the coefficient of the equation , so that the objective function value is minimized and the ellipse equation is obtained; According to the coefficients of the equation Solve for the coordinates of the center of mass of the ellipse ( , ), the calculation formula is: According to the following conversion formula from the station center rectangular coordinate system to the polar coordinate system, the true value of the true value data is obtained. : 。 4. The radar calibration method based on the ellipse centroid method according to claim 3 is characterized in that: The process of converting geodetic coordinate data into station center rectangular coordinate data is as follows: in is the radius of curvature of the y-axis; , is the semi-major axis of the ellipsoid, is the minor semi-axis of the ellipsoid; the geodetic rectangular coordinates of the station center are (X0, Y0, Z0); B is the latitude of the geodetic coordinates, L is the longitude of the geodetic coordinates, H is the height of the geodetic coordinates, and (X, Y, Z) represents a point in the geodetic rectangular coordinate system; The specific formula for converting polar coordinate data into station center rectangular coordinate data is as follows: Among them, (x, y, z) represents a point in the station-centered rectangular coordinate system, and (R, A, E) represents a point in the polar coordinate system.

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