A Method for Calibrating the Installation Angle of Roadside Millimeter-Wave Radar Based on Trajectory Points

Abstract

The present invention discloses a method for calibrating the installation angle of a roadside millimeter-wave radar based on trajectory points. The method calibrates the functional relationship of a curve on the road, allows a target to move along the curve, and allows the radar to continuously observe the target to obtain the target's trajectory points. Through these trajectory points and the calibrated curve, the angle between the radar normal and the true north direction can be calculated. The present invention does not require the target to move in a straight line within the radar detection domain, can utilize existing lane lines on the road, and is suitable for complex road conditions such as curved roads. In addition, after the subsequent radar installation position adjustment, the present invention only needs to perform a translation transformation on the curve calibrated in the early stage in the new coordinate system, and there is no need to perform complex calibration on the curve again. In the scenario of vehicle-road collaborative unmanned driving, the functional relationship between the lane line / curve to be calibrated can also be obtained through a high-precision map, which can effectively reduce the complexity of the curve calibration process.

Description

Technical Field

[0001] The present invention belongs to the technical field of millimeter wave radar installation and calibration, and in particular to a method for calibrating the installation angle of a roadside millimeter wave radar based on trajectory points. Background Art

[0002] Millimeter-wave radar, as a sensing device for autonomous vehicles or roadsides, is widely used in the smart transportation sector to measure moving vehicles, pedestrians, and other targets. Millimeter-wave radar boasts high cost-effectiveness, long detection range, weather resistance, and 24 / 7 operation. However, compared to video detectors and lidar, millimeter-wave radar struggles to detect stationary targets. Furthermore, millimeter-wave radar cannot capture the target's appearance, which doesn't directly correspond to human perception. These factors pose challenges to millimeter-wave radar calibration, specifically determining the conversion between the radar coordinate system and the world coordinate system. The most critical aspect of millimeter-wave radar calibration is the radar's mounting angle, specifically the angle between the radar normal and true north. Current methods for calibrating millimeter-wave radar mounting angles typically require specialized equipment or devices, or impose significant limitations on the calibration scenario. For example, targets within the detection area must move along a specified straight line. Current calibration methods are unsuitable for common curved roads, as it's impossible to force targets to move along a specified straight line. Summary of the Invention

[0003] The purpose of the present invention is to address the shortcomings of the existing technology and provide a millimeter-wave radar installation angle calibration method that has low dependence on the calibration scene, does not require special equipment or devices, and does not require the target to move along a specified straight line.

[0004] The technical solution to achieve the purpose of the present invention is: a method for calibrating the installation angle of a roadside millimeter-wave radar based on trajectory points, the method comprising the following steps:

[0005] Step 1: Establish a polar coordinate system (R, θ) with the radar installation location as the origin, the north direction as the polar axis, and the counterclockwise direction as the positive angle direction, denoted as polar coordinate system I, where R is the polar diameter and θ is the polar angle;

[0006] Step 2: calibrate the motion curve, mark points on the curve, and fit the functional relationship between the polar angle and the polar diameter of the curve in the polar coordinate system I as θ = f(R);

[0007] Step 3: Make a target move along the motion curve, and the radar continuously measures the position of the target in its own coordinate system (R i , α i ), the self-coordinate system is recorded as polar coordinate system II, R i Indicates the target distance observed by the radar in the i-th frame, α iis the target azimuth observed by the radar in the i-th frame, that is, the angle between the line connecting the radar to the target and the radar normal, and the angle is positive in the counterclockwise direction;

[0008] Step 4: According to the function relationship θ = f(R) and the position of the target observed by the radar in multiple frames (R i , α i ), calculate the angle between the radar normal and the north direction.

[0009] Furthermore, the fitting method in step 2 uses polynomial fitting, spline curve fitting, or neural network fitting. Since lane lines are common on roads, in step 3 of this invention, the target can be moved along the lane lines. The corresponding lane lines can be marked in step 2, without the need to draw other curves on the road. For convenience, the motion curve in step 2 can be a lane line or a lane centerline.

[0010] Furthermore, the specific fitting process of the curve in step 2 is:

[0011] Step 2-1: Mark the longitude and latitude coordinates (E0, N0) of the radar installation location, where E0 represents longitude and N0 represents latitude.

[0012] Step 2-2, select M points on the curve in sequence, and mark them to obtain the longitude and latitude coordinates of these points (E j , N j ), where j = 1, 2…M represents the jth point on the curve;

[0013] Step 2-3, get the distance R between the radar and the jth point j :

[0014]

[0015] Where Re is the radius of the Earth;

[0016] Get the angle θ between the line connecting the radar to the jth point on the curve and the north direction i :

[0017]

[0018] Steps 2-4, use an M-1 order polynomial fit (R j ,θ j ), we can get the functional relationship of the curve θ=f(R).

[0019] Furthermore, the polar coordinate system II in step 3 is a polar coordinate system with its own position as the origin, the normal as the polar axis, and the counterclockwise direction as the positive direction.

[0020] Furthermore, the specific process of step 4 includes:

[0021] The target position detected by the radar (R i , α i ), use the curve function relationship calibrated in step 2 to calculate its polar angle in polar coordinate system I:

[0022] θ i =f(R i )

[0023] For single-frame measurement data, α i is the angle between the line connecting the radar to the target and the radar normal, θ i is the angle between the line connecting the radar to the target and the north direction, then θ i -α i It is the angle between the radar normal and the true north direction;

[0024] The average value of multiple frames of measurement data is used as the angle β between the calibrated radar normal and the true north direction:

[0025]

[0026] Where N is the number of frames of measurement data.

[0027] Compared with the prior art, the present invention has the following significant advantages:

[0028] 1) No special equipment or devices are required, and the target does not need to move in a straight line within the radar detection field. It can utilize existing lane lines on the road and is suitable for complex road conditions such as curved roads.

[0029] 2) Because polar coordinate system I modeling depends solely on the radar's installation position, not its orientation, subsequent adjustments to the radar's installation position require only a translation transformation of the previously calibrated curves in the new coordinate system, eliminating the need for complex recalibration. This is particularly true in vehicle-road collaborative autonomous driving scenarios, where the functional relationship between lane lines and the curves to be calibrated can be obtained from high-precision maps, effectively reducing the complexity of the curve calibration process.

[0030] The present invention is further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Flowchart of the roadside millimeter-wave radar installation angle calibration method based on trajectory points.

[0032] Figure 2 Schematic diagram of the establishment of the polar coordinate system I and the calibration of the curve function relationship θ=f(R).

[0033] Figure 3 is the target position detected by the millimeter-wave radar when the target moves along the curve (R i , α i) schematic diagram.

[0034] Figure 4 To calculate the target position (R i , α i ) corresponds to the polar angle θ in the polar coordinate system I i Schematic diagram. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0036] It should be noted that if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0037] In one embodiment, combined Figure 1 This paper provides a trajectory point-based roadside millimeter-wave radar installation angle calibration method. This method can measure the angle between the normal direction of the roadside millimeter-wave radar and the true north direction on curved roads. This method includes the establishment of a coordinate system and the calibration of motion curves, as well as the millimeter-wave radar detection of moving targets, coordinate conversion, and calculation of the radar normal angle. The specific steps are as follows:

[0038] Step 1: Establish a polar coordinate system (R, θ) with the radar installation location as the origin, the north direction as the polar axis, and the counterclockwise direction as the positive angle direction, denoted as polar coordinate system I, where R is the polar diameter and θ is the polar angle;

[0039] Step 2: Draw a feasible motion curve on the road within the detection domain, and record the longitude and latitude coordinates by continuously marking points on the curve to calibrate the functional relationship between the polar angle and the polar diameter of the curve in the polar coordinate system I, θ = f(R), as shown in the following example: Figure 2 As shown in;

[0040] Here, the specific fitting calibration method of the curve is:

[0041] Step 2-1: Mark the longitude and latitude coordinates (E0, N0) of the radar installation location, where E0 represents longitude and N0 represents latitude.

[0042] Step 2-2, select M points on the curve in sequence, and mark them to obtain the longitude and latitude coordinates of these points (E j , N j ), where j = 1, 2…M represents the jth point on the curve;

[0043] Step 2-3, get the distance R between the radar and the jth point j :

[0044]

[0045] Where Re is the radius of the Earth;

[0046] Get the angle θ between the line connecting the radar to the jth point on the curve and the north direction i :

[0047]

[0048] Steps 2-4, use an M-1 order polynomial fit (R j ,θ j ), we can get the functional relationship of the curve θ=f(R).

[0049] Step 3: Make a target move along the motion curve, and the radar continuously measures the position of the target in its own coordinate system (R i , α i ),like Figure 3 As shown, the local coordinate system is recorded as polar coordinate system II, R i Indicates the target distance observed by the radar in the i-th frame, α i is the target azimuth observed by the radar in the i-th frame, that is, the angle between the line connecting the radar to the target and the radar normal, and the angle is positive in the counterclockwise direction;

[0050] Step 4: According to the function relationship θ = f(R) and the position of the target observed by the radar in multiple frames (R i , α i ), calculate the angle between the radar normal and the true north direction, specifically including:

[0051] The target position detected by the radar (R i , α i ), use the curve function relationship calibrated in step 2 to calculate its polar angle in polar coordinate system I:

[0052] θ i =f(R i )

[0053] For single-frame measurement data, α i is the angle between the line connecting the radar to the target and the radar normal, θ iis the angle between the line connecting the radar to the target and the north direction, then θ i -α i It is the angle between the radar normal and the true north direction;

[0054] The average value of multiple frames of measurement data is used as the angle β between the calibrated radar normal and the true north direction:

[0055]

[0056] Where N is the number of frames of measurement data.

[0057] In one embodiment, a track point-based roadside millimeter-wave radar installation angle calibration system is provided, the system comprising:

[0058] The first module is used to establish a polar coordinate system (R, θ) with the radar installation location as the origin, the north direction as the polar axis, and the counterclockwise direction as the positive angle direction, denoted as polar coordinate system I, where R is the polar diameter and θ is the polar angle;

[0059] The second module is used to calibrate the motion curve, mark points on the curve, and fit the functional relationship between the polar angle and the polar diameter of the curve in the polar coordinate system I: θ = f(R);

[0060] The third module is used to make a target move along the motion curve, and the radar continuously measures the position of the target in its own coordinate system (R i , α i ), the self-coordinate system is recorded as polar coordinate system II, R i Indicates the target distance observed by the radar in the i-th frame, α i is the target azimuth observed by the radar in the i-th frame, that is, the angle between the line connecting the radar to the target and the radar normal, and the angle is positive in the counterclockwise direction;

[0061] The fourth module is used to calculate the position of the target (R) according to the function relationship θ = f(R) and the position of the target observed by the radar in multiple frames. i , α i ), calculate the angle between the radar normal and the north direction.

[0062] Regarding the specific limitations of the roadside millimeter-wave radar installation angle calibration system based on trajectory points, please refer to the limitations of the roadside millimeter-wave radar installation angle calibration method based on trajectory points above, which will not be repeated here. The various modules in the above-mentioned roadside millimeter-wave radar installation angle calibration system based on trajectory points can be implemented in whole or in part through software, hardware, and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0063] In one embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the following steps are performed:

[0064] Step 1: Establish a polar coordinate system (R, θ) with the radar installation location as the origin, the north direction as the polar axis, and the counterclockwise direction as the positive angle direction, denoted as polar coordinate system I, where R is the polar diameter and θ is the polar angle;

[0065] Step 2: calibrate the motion curve, mark points on the curve, and fit the functional relationship between the polar angle and the polar diameter of the curve in the polar coordinate system I as θ = f(R);

[0066] Step 3: Make a target move along the motion curve, and the radar continuously measures the position of the target in its own coordinate system (R i , α i ), the self-coordinate system is recorded as polar coordinate system II, R i Indicates the target distance observed by the radar in the i-th frame, α i is the target azimuth observed by the radar in the i-th frame, that is, the angle between the line connecting the radar to the target and the radar normal, and the angle is positive in the counterclockwise direction;

[0067] Step 4: According to the function relationship θ = f(R) and the position of the target observed by the radar in multiple frames (R i , α i ), calculate the angle between the radar normal and the north direction.

[0068] For the specific limitations of each step, please refer to the limitations of the roadside millimeter-wave radar installation angle calibration method based on trajectory points above, which will not be repeated here.

[0069] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the following steps are implemented:

[0070] Step 1: Establish a polar coordinate system (R, θ) with the radar installation location as the origin, the north direction as the polar axis, and the counterclockwise direction as the positive angle direction, denoted as polar coordinate system I, where R is the polar diameter and θ is the polar angle;

[0071] Step 2: calibrate the motion curve, mark points on the curve, and fit the functional relationship between the polar angle and the polar diameter of the curve in the polar coordinate system I as θ = f(R);

[0072] Step 3: Make a target move along the motion curve, and the radar continuously measures the position of the target in its own coordinate system (R i , α i ), the self-coordinate system is recorded as polar coordinate system II, R iIndicates the target distance observed by the radar in the i-th frame, α i is the target azimuth observed by the radar in the i-th frame, that is, the angle between the line connecting the radar to the target and the radar normal, and the angle is positive in the counterclockwise direction;

[0073] Step 4: According to the function relationship θ = f(R) and the position of the target observed by the radar in multiple frames (R i , α i ), calculate the angle between the radar normal and the north direction.

[0074] For the specific limitations of each step, please refer to the limitations of the roadside millimeter-wave radar installation angle calibration method based on trajectory points above, which will not be repeated here.

[0075] The present invention does not require special equipment or devices, does not require the target to move in a straight line within the radar detection domain, can utilize existing lane lines on the road, and is suitable for complex road conditions such as curved roads. In addition, since the modeling of the polar coordinate system I depends only on the radar installation position and does not depend on the radar direction, after the subsequent adjustment of the radar installation position, the previously calibrated curve only needs to be translated in the new coordinate system, and there is no need to perform complex calibration of the curve again. Especially in the scenario of vehicle-road collaborative unmanned driving, the functional relationship between the lane line / curve to be calibrated can also be obtained through high-precision maps, which can effectively reduce the complexity of the curve calibration process.

[0076] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for calibrating the installation angle of a roadside millimeter-wave radar based on trajectory points, characterized in that: The method comprises the following steps: Step 1: Establish a polar coordinate system (R, θ) with the radar installation location as the origin, the north direction as the polar axis, and the counterclockwise direction as the positive angle direction, denoted as polar coordinate system I, where R is the polar diameter and θ is the polar angle; Step 2: calibrate the motion curve, mark points on the curve, and fit the functional relationship between the polar angle and the polar diameter of the curve in the polar coordinate system I as θ = f(R); Step 3: Make a target move along the motion curve, and the radar continuously measures the position of the target in its own coordinate system (R i ,α i ), the self-coordinate system is recorded as polar coordinate system II, R i Indicates the target distance observed by the radar in the i-th frame, α i is the target azimuth observed by the radar in the i-th frame, that is, the angle between the line connecting the radar to the target and the radar normal, and the angle is positive in the counterclockwise direction; Step 4: According to the function relationship θ = f(R) and the position of the target observed by the radar in multiple frames (R i ,α i ), calculate the angle between the radar normal and the true north direction; The specific process of step 4 includes: The target position detected by the radar (R i ,α i ), use the curve function relationship calibrated in step 2 to calculate its polar angle in polar coordinate system I: i i =f(R i ) For single-frame measurement data, α i is the angle between the line connecting the radar to the target and the radar normal, θ i is the angle between the line connecting the radar to the target and the north direction, then θ i -α i It is the angle between the radar normal and the true north direction; The average value of multiple frames of measurement data is used as the angle β between the calibrated radar normal and the true north direction: Where N is the number of frames of measurement data.

2. The method for calibrating the installation angle of a roadside millimeter-wave radar based on trajectory points according to claim 1, characterized in that: The motion curve in step 2 is the lane line or the lane center line.

3. The method for calibrating the installation angle of a roadside millimeter-wave radar based on trajectory points according to claim 1, characterized in that: The fitting method in step 2 adopts polynomial fitting, spline curve fitting or neural network fitting.

4. The method for calibrating the installation angle of a roadside millimeter-wave radar based on trajectory points according to claim 1, characterized in that: The specific fitting process of the curve in step 2 is: Step 2-1: Mark the longitude and latitude coordinates (E0, N0) of the radar installation location, where E0 represents longitude and N0 represents latitude. Step 2-2, select M points on the curve in sequence, and mark them to obtain the longitude and latitude coordinates of these points (E j ,N j ), where j = 1, 2…M represents the jth point on the curve; Step 2-3, get the distance R between the radar and the jth point j : Where Re is the radius of the Earth; Get the angle θ between the line connecting the radar to the jth point on the curve and the north direction i : Steps 2-4, use an M-1 order polynomial fit (R j ,θ j ), we can get the functional relationship of the curve θ=f(R).

5. The method for calibrating the installation angle of a roadside millimeter-wave radar based on trajectory points according to claim 1, characterized in that: In step 3, the polar coordinate system II is a polar coordinate system with its own position as the origin, the normal as the polar axis, and the counterclockwise direction as the positive direction.

6. A track point-based roadside millimeter-wave radar installation angle calibration system based on the method according to any one of claims 1 to 5, characterized in that: The system comprises: The first module is used to establish a polar coordinate system (R, θ) with the radar installation location as the origin, the north direction as the polar axis, and the counterclockwise direction as the positive angle direction, denoted as polar coordinate system I, where R is the polar diameter and θ is the polar angle; The second module is used to calibrate the motion curve, mark points on the curve, and fit the functional relationship between the polar angle and the polar diameter of the curve in the polar coordinate system I: θ = f(R); The third module is used to make a target move along the motion curve, and the radar continuously measures the position of the target in its own coordinate system (R i ,α i ), the self-coordinate system is recorded as polar coordinate system II, R i Indicates the target distance observed by the radar in the i-th frame, α i is the target azimuth observed by the radar in the i-th frame, that is, the angle between the line connecting the radar to the target and the radar normal, and the angle is positive in the counterclockwise direction; The fourth module is used to calculate the position of the target (R) according to the function relationship θ = f(R) and the position of the target observed by the radar in multiple frames. i ,α i ), calculate the angle between the radar normal and the north direction.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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