A Laser Ranging Intersection Positioning Method Considering Atmospheric Refraction under the Geocentric Earth Fixed System

Abstract

The present invention discloses a laser ranging intersection positioning method considering atmospheric refraction under the Earth-centered Earth-fixed system, which relates to the field of photogrammetry. The method includes the following steps: correcting the laser ranging value by using the national distribution data of laser path difference; calculating the initial coordinates of the target by using the airborne POS navigation data; and calculating the accurate coordinates of the target under the Earth-centered Earth-fixed system by using multi-camera station data. The present invention takes into account the influence of atmospheric refraction on laser ranging, eliminates the influence of atmospheric refraction by using the laser path difference to correct the laser ranging value, and performs positioning under the Earth-centered Earth-fixed system to avoid the influence of the Earth's curvature and length deformation. Finally, the distance intersection positioning method is used to perform positioning, avoiding the influence of attitude errors on the positioning result, and solving the problem of high-precision positioning of the target by using an optoelectronic pod at a long distance.

Description

Technical Field

[0001] The present invention relates to the field of photogrammetry, and specifically to a laser ranging intersection positioning method considering atmospheric refraction in the Earth-Centered Earth-Fixed (ECEF) coordinate system. Background Art

[0002] The main equipment for an unmanned aerial vehicle (UAV) to implement ground target positioning is an airborne optoelectronic pod. The optoelectronic pod usually integrates a POS (Position and Orientation System), visible light imaging equipment, infrared imaging equipment, and laser ranging equipment, etc., and can achieve imaging of ground targets, measuring its own position and attitude using the integrated POS system, and measuring the distance to the target using the integrated laser ranging equipment, providing data sources for backend positioning.

[0003] Based on the optical images, POS information, and laser ranging information that the UAV optoelectronic pod can provide, there are multiple positioning methods that can be adopted, including:

[0004] 1) The ground target positioning method based on collinearity equations, which uses the carrier POS and optical images to achieve positioning based on collinearity equations and bundle adjustment.

[0005] 2) The slant range / azimuth positioning method, which uses the carrier POS and laser ranging to achieve ground target positioning.

[0006] 3) The reference map matching (end matching) method, which uses the automatic matching between the optoelectronic platform and reference data to achieve positioning.

[0007] Among them, method 1) requires an image processing process of the load, with low real-time performance; method 2) depends on the attitude measurement accuracy of the POS system, and the accuracy is significantly reduced under long-distance conditions; method 3) has high requirements for visible conditions and reference data production conditions. Therefore, these three methods are all insufficient in scenarios with high requirements for real-time performance and accuracy.

[0008] The positioning method based on distance intersection can achieve target positioning only relying on laser ranging, but the currently used distance intersection method usually ignores the laser ranging error introduced by atmospheric refraction; in addition, the current method usually completes target positioning in a certain type of national projection coordinate system, and at this time, factors such as the Earth's curvature and distance deformation make the positioning result unsatisfactory and cannot meet the high-precision positioning requirements. Therefore, targeted improvement measures need to be proposed for this method. Summary of the Invention

[0009] In view of the above problems, the present invention proposes a laser ranging intersection positioning method considering atmospheric refraction in the ECEF coordinate system. This method avoids the influence of the Earth's curvature and length deformation, avoids the influence of attitude errors on the positioning result, and solves the problem of implementing high-precision positioning of targets using an optoelectronic pod at long distances.

[0010] The technical solution adopted by the present invention is:

[0011] A laser ranging intersection positioning method taking into account atmospheric refraction in an earth-centered earth-fixed system comprises the following steps:

[0012] Step 1: Use the national distribution data of laser path difference to correct the laser distance measurement value. The specific method is as follows:

[0013] Step 1.1, using the onboard POS system to obtain the position of the camera station and the pitch angle of the laser at the time of measurement;

[0014] Step 1.2, use the position of the camera station and the elevation angle of the laser to find the laser path difference and correct the laser distance measurement value;

[0015] Step 2: Calculate the initial coordinates of the target using the position of the camera station and the pitch angle of the laser. The specific method is as follows:

[0016] Step 2.1, solve the exterior orientation elements using the position of the camera station and the pitch angle of the laser;

[0017] Step 2.2, using the exterior orientation elements of the first camera station and the corresponding corrected laser ranging values ​​to calculate the initial coordinates of the target;

[0018] Step 2.3: Convert the target initial coordinates to the Earth-centered Earth-fixed system;

[0019] Step 3: Use the data from multiple camera stations to calculate the precise coordinates of the target in the Earth-centered Earth-fixed system. The specific method is as follows:

[0020] Step 3.1, convert the geodetic coordinates of all the camera stations into the Earth-centered Earth-fixed coordinates;

[0021] Step 3.2, using the coordinates of each camera station, the corrected laser range value, and the initial coordinates of the target, establish the residual equation in the Earth-centered Earth-fixed system, combine all the residual equations, perform range intersection positioning, and solve the precise coordinates of the target;

[0022] Step 3.3, convert the precise coordinates of the target from the Earth-centered Earth-fixed system to the Earth coordinate system;

[0023] Complete target positioning.

[0024] Furthermore, in step 1.2, the calculation formula for correcting the laser ranging value is:

[0025]

[0026] Among them, L i is the laser ranging value of camera station i, ΔL i To find the laser path difference, The corrected laser ranging value for camera station i.

[0027] Further, in step 2.1, the calculation formula for solving the exterior orientation elements is:

[0028]

[0029] Where the subscript E represents the geocentric rectangular coordinate system, the subscript n represents the navigation coordinate system, the subscript b represents the inertial measurement unit coordinate system, and the subscript c represents the camera coordinate system. The rotation matrix constructed by the exterior orientation angular elements. The rotation matrix formed by the boresight offset angles (e x , e y , e z ) of the inertial measurement unit. The rotation matrix between the navigation coordinate system where the position (X IMU , Y IMU , Z IMU ) of the inertial measurement unit at the imaging moment is located and the geocentric rectangular coordinate system. The rotation matrix formed by the attitude angles (r, p, y) of the inertial measurement unit, and (A, α, κv) are the exterior orientation angular elements.

[0030] Further, in step 2.2, the method for calculating the initial coordinates of the target is:

[0031]

[0032] Where (X T , Y T , Z T ) are the coordinates of target T, (X S , Y S , Z S ) are the camera station coordinates obtained by POS measurement, A is the heading angle in the exterior orientation elements of the camera station, and α is the tilt angle in the exterior orientation elements of the camera station.

[0033] Further, the specific method of step 3.2 is:

[0034] (1) Establish a residual equation for each camera station; assume that the coordinates of the current camera station i in the geocentric earth-fixed coordinate system are The corrected laser ranging value is The current coordinates of target T are (X T , Y T , Z T ), then the residual equation of the current camera station i is:

[0035]

[0036] (2) Iteratively solve the residual equation using the least squares method to obtain the correction of the coordinates of target T.

[0037] (3) Add the correction to the coordinates of target T to obtain the new coordinates.

[0038] (4) Repeat steps (1) to (3) until the correction of the coordinates of target T is less than the threshold or the preset number of iterations is reached.

[0039] The beneficial effects of the present invention are as follows:

[0040] 1. The present invention corrects the laser ranging value using the national distribution data of laser path difference. On the premise of knowing the laser wavelength, laser pitch angle, and height, it searches for the laser path difference to correct the laser ranging error caused by atmospheric refraction.

[0041] 2. The present invention uses the distance intersection method to achieve the positioning of the target in the Earth-Centered Earth-Fixed (ECEF) coordinate system, avoiding the positioning errors caused by the Earth's curvature and length deformation during positioning in the projection coordinate system.

[0042] 3. The present invention only uses the POS attitude parameters when calculating the initial coordinates of the target, and uses the distance intersection method in the subsequent positioning process, avoiding the problem of significant reduction in positioning accuracy under long-distance conditions caused by relying on the POS attitude, and improving the positioning accuracy of the ground under long-distance conditions.

[0043] 4. The present invention takes into account the influence of atmospheric refraction on laser ranging, and interpolates the exterior orientation elements of each single-sided array image by introducing a model in which the interior and exterior orientation elements change with time, solving the problems of high-precision geometric processing and seamless stitching of the stepped array images. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram for calculating the initial value of the ground point coordinates using the position, attitude, and laser ranging values recorded by the POS system. DETAILED DESCRIPTION OF THE INVENTION

[0045] A laser ranging intersection positioning method considering atmospheric refraction in the Earth-Centered Earth-Fixed (ECEF) coordinate system. This method takes into account the influence of atmospheric refraction on laser ranging, and corrects the atmospheric refraction error and implements the positioning of the target in the ECEF coordinate system. This method first corrects the laser ranging value using the national distribution data of laser path difference to eliminate the laser ranging error caused by atmospheric refraction; secondly, calculates the initial coordinates of the target using the airborne POS navigation data; finally, calculates the accurate coordinates of the target in the ECEF coordinate system using multi-station data and the distance intersection positioning method.

[0046] The specific steps of this method are as follows:

[0047] Step 1. Correct the laser ranging value by using the national distribution data of laser path difference, including the following steps:

[0048] Step 1.1. Obtain the position of the camera station and the pitch angle of the laser at the measurement moment by using the airborne POS system.

[0049] Step 1.2. Search for the laser path difference by using the position and the laser pitch angle obtained in Step 1.1, and correct the laser ranging value. The specific method is as follows:

[0050] (1) Let the laser ranging value of camera station i be L i , and the searched laser path difference be ΔL i . Then the corrected laser ranging value of this camera station is:

[0051]

[0052] (2) Repeat the above process to correct the laser ranging values of all camera stations.

[0053] Step 2. If Figure 1 , calculate the initial coordinates of the target by using the position and the laser pitch angle obtained in Step 1.1, including the following steps:

[0054] Step 2.1. Solve the exterior orientation elements by using the position and the laser pitch angle. According to the relationship between the navigation coordinate system n and the Earth-centered Earth-fixed coordinate system E, first, the attitude angles (r, p, y) of the inertial measurement unit IMU can be converted into the exterior orientation angle elements (A, α, κv). The basic method is as follows:

[0055]

[0056] Among them, the subscript E represents the Earth-centered rectangular coordinate system, the subscript n represents the navigation coordinate system, the subscript b represents the IMU coordinate system, the subscript c represents the camera coordinate system, is the rotation matrix constructed by the exterior orientation angle elements, is the rotation matrix composed of the IMU optical axis eccentricity angles (e x , e y , e z ), is the rotation matrix composed of the inertial measurement unit attitude angles (r, p, y), is the rotation matrix between the navigation coordinate system n where the position (X IMU , Y IMU , Z IMU ) of the IMU at the imaging moment is located and the Earth-centered rectangular coordinate system E. Each rotation matrix can be determined by using the Earth-centered rectangular coordinates of the IMU center, the IMU attitude angles, and the IMU installation angles, and then the exterior orientation angle elements (A, α, κv) can be obtained.

[0057] Step 2.2, calculate the initial coordinates of the target using the exterior orientation elements of the first camera station and the corresponding laser ranging values:

[0058] According to the imaging geometry, the coordinates of the target point T (X T ,Y T ,Z T ) can be calculated by the following formula:

[0059]

[0060] Among them, (X S ,Y S ,Z S ) is the coordinate of the first camera station measured by POS, A is the heading angle in the external orientation element of the camera station, and α is the inclination angle in the external orientation element of the camera station.

[0061] Step 2.3, convert the target initial coordinates to the Earth-centered Earth-fixed system. This process can be calculated using formulas or open source software.

[0062] Step 3, using the multi-camera data to calculate the precise coordinates of the target in the Earth-centered Earth-fixed system, includes the following steps:

[0063] Step 3.1, convert the geodetic coordinates of all the camera stations into Earth-centered Earth-fixed coordinates. This process can be calculated using formulas or open source software.

[0064] Step 3.2, use the coordinates of each camera station, the corrected laser range value, and the initial coordinates of the target to establish the residual equation, and combine all the residual equations to perform range intersection positioning to solve the precise coordinates of the target. The specific method is:

[0065] (1) Establish the residual equation for each station; suppose the coordinates of the current station i in the Earth-centered Earth-fixed system are The corrected laser distance measurement value is The current coordinates of the target are (X T ,Y T ,Z T ), then the residual equation of the current camera station is:

[0066]

[0067] (2) Use the least squares method to iteratively solve the residual equation to obtain the correction number of the target coordinates;

[0068] (3) Add the correction number to the target coordinates to obtain the new coordinates;

[0069] (4) Repeat steps (1) to (3) until the correction number of the target coordinates is less than a certain threshold or reaches a certain number of iterations.

[0070] Step 3.4: Convert the target coordinates from the Earth-centered Earth-fixed (ECEF) coordinate system to the geodetic coordinate system, which can be calculated using formulas or open-source software.

[0071] Complete the target positioning.

[0072] In summary, this method utilizes the position of the camera station and the laser elevation angle. By finding the laser path difference and correcting the laser ranging value, it eliminates the laser ranging deviation caused by atmospheric refraction. It uses POS navigation data to solve the exterior orientation elements. On this basis, it calculates the initial target coordinates using the laser ranging value and converts them to the ECEF coordinate system. It converts the geodetic coordinates of all camera stations to ECEF coordinates, establishes a residual equation in the ECEF coordinate system, and solves for the high-precision coordinates of the target in the ECEF coordinate system through distance intersection positioning.

[0073] This invention takes into account the influence of atmospheric refraction on laser ranging. By using the laser path difference to correct the laser ranging value, it eliminates the influence of atmospheric refraction. It performs positioning in the ECEF coordinate system, avoiding the influence of the Earth's curvature and length deformation. Finally, it uses the distance intersection positioning method to perform positioning, avoiding the influence of attitude errors on the positioning result, and solves the problem of high-precision positioning of targets using an optoelectronic pod at long distances.

Claims

1. A laser ranging intersection positioning method taking into account atmospheric refraction in an earth-centered earth-fixed system, It is characterized in that The steps include: Step 1: Use the national distribution data of laser path difference to correct the laser distance measurement value. The specific method is as follows: Step 1.1, using the onboard POS system to obtain the position of the camera station and the pitch angle of the laser at the time of measurement; Step 1.2, use the position of the camera station and the pitch angle of the laser to find the laser path difference and correct the laser distance measurement value; Step 2: Calculate the initial coordinates of the target using the position of the camera station and the pitch angle of the laser. The specific method is as follows: Step 2.1, solve the exterior orientation elements using the position of the camera station and the pitch angle of the laser; Step 2.2, using the exterior orientation elements of the first camera station and the corresponding corrected laser ranging values ​​to calculate the initial coordinates of the target; Step 2.3: Convert the target initial coordinates to the Earth-centered Earth-fixed system; Step 3: Use the data from multiple camera stations to calculate the precise coordinates of the target in the Earth-fixed system. The specific method is as follows: Step 3.1, convert the geodetic coordinates of all the camera stations into the Earth-centered Earth-fixed coordinates; Step 3.2, using the coordinates of each camera station, the corrected laser range value, and the initial coordinates of the target, establish the residual equation in the Earth-centered Earth-fixed system, combine all the residual equations, perform range intersection positioning, and solve the precise coordinates of the target; Step 3.3, convert the precise coordinates of the target from the Earth-centered Earth-fixed system to the Earth coordinate system; Complete target positioning.

2. A laser ranging intersection positioning method taking into account atmospheric refraction in an earth-centered earth-fixed system as claimed in claim 1, It is characterized in that In step 1.2, the calculation formula for correcting the laser ranging value is: Among them, L i is the laser ranging value of camera station i, and ΔL i is the found laser path difference, is the corrected laser ranging value of camera station i.

3. A laser ranging intersection positioning method taking into account atmospheric refraction in an earth-centered earth-fixed system as claimed in claim 2, It is characterized in that In step 2.1, the calculation formula for solving the exterior orientation elements is: Among them, the subscript E represents the Earth-centered rectangular coordinate system, the subscript n represents the navigation coordinate system, the subscript b represents the inertial measurement unit coordinate system, and the subscript c represents the camera coordinate system. is the rotation matrix constructed by the exterior orientation angular elements. is the rotation matrix formed by the boresight eccentricity angles (e x , e y , e z ) of the inertial measurement unit. is the rotation matrix between the navigation coordinate system where the position (X IMU , Y IMU , Z IMU ) of the inertial measurement unit at the imaging moment is located and the Earth-centered rectangular coordinate system. is the rotation matrix formed by the attitude angles (r, p, y) of the inertial measurement unit, and (A, α, κv) are the exterior orientation angular elements.

4. A laser ranging intersection positioning method taking into account atmospheric refraction in an earth-centered earth-fixed system as claimed in claim 3, It is characterized in that In step 2.2, the method for calculating the initial coordinates of the target is: Among them, (X T , Y T , Z T ) are the coordinates of the target T, (X S , Y S , Z S ) are the camera coordinates obtained by POS measurement, A is the course angle in the external orientation elements of the camera, and α is the tilt angle in the external orientation elements of the camera.

5. The laser ranging intersection positioning method taking into account atmospheric refraction in an earth-centered earth-fixed system as claimed in claim 4, It is characterized in that The specific method of step 3.2 is: (1) Establish a residual equation for each camera station; let the coordinates of the current camera station \(i\) in the Earth-centered Earth-fixed coordinate system be The corrected laser ranging value is The current coordinates of the target \(T\) are \((X T , Y T , Z T ), then the residual equation of the current camera station \(i\) is: (2) Use the least squares method to iteratively solve the residual equation to obtain the correction value of the coordinates of the target T; (3) Add the correction number to the coordinates of the target T to obtain the new coordinates; (4) Repeat steps (1) to (3) until the correction number of the coordinates of the target T is less than the threshold or reaches the preset number of iterations.

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