Internal error step-by-step calibration method and device for oval scanning type airborne depth sounding laser radar

Abstract

The invention provides a step-by-step calibration method and a step-by-step calibration device for internal errors of an oval scanning type airborne sounding laser radar. By gradually calibrating the laser ranging error, the collimation axis error and the driving motor rotation angle error, the complexity of error calibration is reduced, the influence of multi-factor interference on the overall calibration precision is avoided, and the internal error value of the laser radar can be effectively calibrated. The error value can be used for evaluating the instrument quality in the instrument processing and assembling stages, and correcting the system error in the subsequent calculation, thereby preventing the precision reduction caused by the error of the measurement data of the laser radar, and improving the obtaining precision of the laser three-dimensional point cloud data.

Description

Technical Field

[0001] The invention belongs to the technical field of airborne laser depth sounding, and in particular relates to a step-by-step calibration method and device for internal errors of an oval scanning airborne depth sounding laser radar. Background Art

[0002] Airborne laser bathymetry is an advanced shallow water measurement technology that integrates multiple measurement sensors such as laser scanning systems, global navigation satellite systems and inertial navigation systems. By emitting blue-green band laser pulses and receiving echo signals, it can achieve full coverage and high-resolution measurement of the three-dimensional space of land and sea, and has the advantages of high efficiency, flexibility, economy and safety. Compared with traditional shipborne sonar measurement methods, airborne laser bathymetry technology is not restricted by terrain, has high measurement efficiency and dense measurement points. It is currently the most effective means for high-efficiency water depth measurement and has broad application and development prospects.

[0003] The core goal of airborne depth-sounding laser radar is to accurately obtain the three-dimensional coordinates of the laser foot points. As a highly integrated complex system, the measurement accuracy of airborne depth-sounding laser radar is affected by various system errors and random errors. In order to obtain high-precision laser three-dimensional point cloud data, the airborne depth-sounding laser radar must be calibrated to eliminate measurement errors and improve measurement accuracy. Errors that affect measurement accuracy include integration errors and internal errors. System integration errors are mainly installation angle errors, that is, errors caused by the non-parallelism between the coordinate axes of the laser scanning system and the coordinate axes of the inertial platform, which are usually corrected by flight dynamic calibration. Internal errors refer to errors in the laser scanning system itself, mainly including ranging errors and structural errors, which cannot be eliminated by flight dynamic calibration and must be calibrated before flight. Calibrating the internal errors of airborne depth-sounding laser radar can not only evaluate the quality of the equipment during the instrument processing and assembly stages, but also correct system errors in subsequent solutions, thereby avoiding errors in the laser radar's own measurement data and maximizing measurement accuracy.

[0004] The literature "Research on Self-calibration Method of Domestic Spiral Scanning LiDAR System" (Yang Shujuan et al., 2018, Journal of Electronics and Information Technology), "Calibration Method of Light and Small Unmanned Aerial Vehicle LiDAR Measurement System" (Tian Lulin et al., 2024, Journal of Information Engineering University), the book "Theory and Method of Airborne LiDAR Measurement Technology" (Zhang Xiaohong, 2007, Wuhan University Press), the invention patent "Geometric Correction Method and Device for Unmanned Aerial Vehicle Radar Installation Error" (CN114859326A, 2022), and "A Method for Correcting Installation Angle Error Based on Airborne Laser Depth Sounding System" (CN116299369A, 2023) calibrated the system installation angle error of airborne laser radar, but did not calibrate the internal error. Although the literature "Calibration Model and Simulation Analysis of Circular Scanning Airborne Laser Bathymetry System" (Shen Erhua et al., 2016, Acta Geodaetica et Cartographica Sinica), "Study on Structural Error and Positioning Accuracy of Airborne Dual-frequency LiDAR" (Lv Deliang et al., 2018, Progress in Laser and Optoelectronics), "Positioning Model of Airborne LiDAR Bathymetry System and Analysis of the Influence of Line of Sight Axis Error" (Yu Jiayong et al., 2019, Infrared and Laser Engineering), and the book "Theory and Method of Airborne LiDAR Data Error Processing" (Wang Liying, 2013, Geodesy and Cartography Press) analyzed the influence of internal errors on measurement accuracy through simulation, they mainly focused on the calibration of system installation angle errors and did not provide calibration solutions for internal errors. The invention patent "Coordinate System Error Correction Method for Scanning Platform Based on Airborne LiDAR System" (CN116990787A, 2023) corrected the scanning coordinates through the correction equation and compensated for the overall impact caused by the structural error, but did not clearly calibrate the values ​​of various internal errors. The invention patents "A method for calibrating the ranging accuracy of airborne laser radar based on circular scanning" (CN111123245A, 2020) and "A method for testing the maximum ranging capability and angular measurement accuracy of airborne laser radar based on circular scanning" (CN111123246A, 2020) calibrated the ranging error value and angular measurement error value respectively, but they are aimed at circular scanning airborne laser radars and are not suitable for oval scanning airborne laser radars.

[0005] In summary, among the currently disclosed patent documents on airborne laser radar calibration, most of them calibrate the system installation angle error, and rarely involve the calibration of the internal error of the laser radar, especially the calibration of the internal error value of the oval scanning airborne laser radar, and no effective solution has been proposed yet. Summary of the invention

[0006] The purpose of the present invention is to provide a method and device for step-by-step calibration of the internal errors of an oval scanning airborne depth-finding laser radar in order to solve the problem of calibrating the internal error values ​​of an oval scanning airborne laser radar in view of the deficiencies in the above-mentioned prior art.

[0007] In order to achieve the above object, according to a first aspect of the present invention, the present invention provides a step-by-step calibration method for internal errors of an oval scanning airborne depth-sounding laser radar, comprising:

[0008] Place the airborne depth-sounding laser radar on a tripod, turn on the laser radar rotating mirror transceiver and scanning device, and illuminate a complete laser scanning track on the flat wall;

[0009] Place the reflectorless total station on a tripod and level it;

[0010] Calibrate laser ranging error;

[0011] Calibrate the sight axis error;

[0012] Calibrate the drive motor angle error.

[0013] In the step-by-step calibration method for the internal error of an oval scanning airborne depth-measuring laser radar, the calibration of the laser ranging error includes:

[0014] The center point of the laser radar reflector is marked as P, the center point, the long axis vertex and the short axis vertex of the laser scanning trajectory are O, A, C, B, and D respectively, the laser foot point scanning sequence is: ABCD, and the center point of the total station is marked as G;

[0015] Turn off the laser radar transceiver and the rotating mirror scanning device, manually rotate the reflector, open the transceiver every 30°, collect waveform data and perform waveform detection to obtain the calculated distance value, and use the total station to measure the observed distance value from the center of the reflector to the wall laser foot point;

[0016] Let the calculated distance value s = [s1, s2, ..., s 12 ] T , the corresponding observed distance value is S′=[S1′,S2′,...,S 12 ′] T ;

[0017] The calculation formula for the distance value is:

[0018] s = cΔt / 2;

[0019] Where c is the propagation speed of the laser in the air, and Δt is the propagation time of the laser in the air obtained by waveform detection;

[0020] Add the error plus constant K to the above formula:

[0021] S=f(K)=s+K=[S1,S2,...,S 12 ] T ;

[0022] The initial value of the error plus constant K is set to the design length of the internal optical path of the laser radar;

[0023] The error equation is established by linearizing the above equation:

[0024]

[0025] Write the above formula in matrix form:

[0026] V = BX-L;

[0027] Where, X = ΔK;

[0028] There are 12 laser foot points in total.

[0029]

[0030] For each laser foot point, L i =[S′ i -S i ];

[0031] Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed:

[0032] B T BX=B T L;

[0033] Solving the above formula we get:

[0034] X=(B T B) -1 B T L;

[0035] Substitute S and S′ into the above formula to calculate the correction factor ΔK of K;

[0036] According to ΔK, update the error plus constant:

[0037] K+ΔK→K;

[0038] Recalculate S according to the updated error plus constant K, then recalculate L, and then solve the normal equation of the error equation based on the least squares indirect adjustment principle to obtain the correction number ΔK, then update the error correction amount K again, and repeat this step until |ΔK|<0.001;

[0039] Taking the error into account, the distance calculated by the laser radar is:

[0040] S=cΔt / 2+K.

[0041] In the step-by-step calibration method for the internal error of an oval scanning airborne depth-sounding laser radar, the calibration of the sight axis error includes:

[0042] The collimation axis error includes the angle error between the normal line of the reflector and the rotating shaft of the drive motor and the angle error between the incident light and the rotating shaft of the drive motor;

[0043] A laser scanning reference coordinate system O-XYZ is established with the center of the reflector as the origin, the X-axis direction is the opposite direction of the incident light, the Y-axis is the flight direction, the Z-axis and the X-axis and the Y-axis form a right-handed system, the driving motor angle is defined as θ, the angle between the normal line of the reflector and the driving motor shaft is α, the angle between the incident light and the driving motor shaft is β, and the direction vector of the normal line of the reflector in the O-XYZ coordinate system is:

[0044]

[0045] From the above formula, we can get the angles between the projection of the reflected light on the XZ and YZ planes and the Z axis respectively:

[0046]

[0047] Define the angle between the reflected light and the vertical downward direction as the scanning angle, and calculate the scanning angle according to the above formula:

[0048]

[0049] The angle between the line connecting the laser foot point and the center point of the laser scanning track and the positive direction of the X-axis is defined as the azimuth angle. When the line connecting the center of the laser scanning track and the center of the reflector is perpendicular to the target plane, the azimuth angle Ψ is calculated according to the angle between the projection of the reflected light on the XZ and YZ planes and the Z axis:

[0050]

[0051] According to the distance value S calculated by the laser radar, the projection of the reflected light on the XZ and YZ planes The scanning angle Calculate the coordinates of the laser foot point in the laser scanning reference coordinate system:

[0052]

[0053] Turn off the laser radar transceiver and the rotating mirror scanning device, manually rotate the reflector, so that the laser foot points fall on points A, B, C, and D in turn, turn on the transceiver, collect waveform data, and eliminate the laser ranging error after waveform detection to obtain the calculated distance value S in turn. A , S B , S C , S D, the driving motor rotation angles are 0°, 90°, 180°, and 270° respectively. Substituting the calculated distance value and the driving motor rotation angle into the above formula in turn, the coordinates of points A, B, C, and D in the laser scanning reference coordinate system are [x A (α,β,0°),y A (α,β,0°),z A (α,β,0°)] T ,[x B (α,β,90°),y B (α,β,90°),z B (α,β,90°)] T ,[x C (α,β,180°),y C (α,β,180°),z C (α,β,180°)] T ,[x D (α,β,270°),y D (α,β,270°),z D (α,β,270°)] T ;

[0054] The formula for calculating the distance between two points based on their coordinates is:

[0055]

[0056] The initial values ​​of α and β are respectively set to the design angle between the normal line of the reflector and the rotating shaft of the drive motor and the design angle between the incident light and the rotating shaft of the drive motor;

[0057] Substitute the coordinates of points A and B, A and C, A and D, B and C, B and D, and C and D into the above formula to obtain the distance H between AB and AB 、AC distance H AC , AD distance H AD , BC distance H BC , BD distance H BD 、CD distance H CD ;

[0058] The distance H′ between AB is measured by the total station. AB , AC distance H′ AC , AD distance H′ AD , BC is at a distance of H′ BC , BD distance H′ BD , CD distance H′ CD ;

[0059] Let H = {H AB ,HAC ,H AD ,H BC ,H BD ,H CD}, H′={H′ AB ,H′ AC ,H′ AD ,H′ BC ,H′ BD ,H′ CD};

[0060] The distance calculation formula is linearized to establish an error equation:

[0061]

[0062] Write the above formula in matrix form:

[0063] V = BX-L;

[0064] Where X = [ΔαΔβ] T ;

[0065] There are 6 laser foot points in total.

[0066]

[0067] For each laser foot point, L i =[H i -H i ];

[0068] Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed:

[0069] B T BX=B T L;

[0070] Solving the above formula we get:

[0071] X=(B T B) -1 B T L;

[0072] Substituting H and H′ into the above formula, we can calculate the corrections Δα and Δβ of α and β;

[0073] According to Δα and Δβ, the angle between the normal line of the reflector and the rotating shaft of the drive motor and the angle between the incident light and the rotating shaft of the drive motor are updated:

[0074] α+Δα→α;

[0075] β+Δβ→β;

[0076] Recalculate H according to the updated angle α between the normal line of the reflector and the shaft of the drive motor and the angle β between the incident light and the shaft of the drive motor, then recalculate B and L, and then solve the normal equation of the error equation based on the least squares indirect adjustment principle to obtain the correction numbers Δα and Δβ, and then update α and β again, and repeat this step until |Δα|<0.001 and |Δβ|<0.001;

[0077] The angle error between the normal line of the reflector and the shaft of the drive motor is calculated based on the design value and the measured value:

[0078] Δα=α-5°;

[0079] Wherein, α is the angle between the normal line of the reflector and the rotating shaft of the driving motor obtained by final calculation;

[0080] The angle error between the incident light and the drive motor shaft is calculated based on the design value and the measured value:

[0081] Δβ=β-45°;

[0082] Wherein, β is the angle between the incident light and the shaft of the driving motor obtained by final calculation.

[0083] In the step-by-step calibration method for the internal error of an oval scanning airborne depth-measuring laser radar, the calibration of the driving motor rotation angle error includes:

[0084] Adjust the position of the laser radar so that the line OP connecting the center of the laser scanning track and the center of the reflector is perpendicular to the wall. The steps of calibrating the rotation angle error of the drive motor are as follows:

[0085] Turn off the laser radar rotating mirror scanning device and turn on the transceiver. At this time, the drive motor is at zero position, and the reflected laser is marked as E on the wall laser foot point;

[0086] The angle ∠AOE between OA and OE is measured by the total station;

[0087] When point E is counterclockwise from point A, the azimuth angle Ψ=∠AOE, and when point E is clockwise from point A, the azimuth angle Ψ=360°-∠AOE;

[0088] According to the azimuth angle calculation formula, the angle α between the normal line of the reflector and the shaft of the drive motor is known. The azimuth angle calculation formula is expressed as:

[0089]

[0090] Substitute the measured azimuth angle Ψ into the above formula to obtain the actual driving motor rotation angle θ when the laser foot point falls on point E. When point E is counterclockwise from point A, the error value of the driving motor rotation angle Δθ=θ; when point E is clockwise from point A, the error value of the driving motor rotation angle Δθ=θ-360°;

[0091] Repeat the above steps 5 times to obtain 5 sets of the driving motor rotation angle error values, and average them to obtain the driving motor rotation angle error value Δθ:

[0092]

[0093] Among them, Δθ i is the error value of the driving motor angle obtained by the i-th measurement;

[0094] Taking the error into account, the actual rotation angle of the driving motor is:

[0095]

[0096] Where θ is the driving motor angle measured by the laser radar angle encoder, is the driving motor angle after error correction, when hour, when hour,

[0097] The present invention also provides a step-by-step calibration device for internal errors of an oval scanning airborne depth-measuring laser radar, comprising:

[0098] The first deployment module is used to deploy the airborne bathymetric laser radar and total station in the calibration field;

[0099] A first acquisition module, used for acquiring a distance solution value of a wall laser foot point based on the laser radar;

[0100] A second acquisition module is used to acquire the distance observation value between two points and the angle formed by the line connecting three points based on the total station;

[0101] A first calculation module, used for calculating the laser ranging error;

[0102] The second calculation module is used to calculate the sight axis error;

[0103] The third calculation module is used to calculate the rotation angle error of the driving motor.

[0104] The beneficial effects of the present invention are:

[0105] The error calibration method and device disclosed in the present invention are suitable for calibrating the internal error value of an oval scanning airborne depth-finding laser radar. By gradually calibrating the laser ranging error, the sighting axis error and the driving motor angle error, the complexity of the error calibration is reduced, and the influence of multiple factors on the overall calibration accuracy is avoided. The internal error value of the laser radar can be effectively calibrated. The error value can be used to evaluate the quality of the instrument during the instrument processing and assembly stages, and the system error can be corrected in the subsequent solution to avoid the decrease in accuracy caused by the laser radar's own measurement data errors, thereby improving the acquisition accuracy of the laser three-dimensional point cloud data. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 It is a technical flow chart of the method of the present invention;

[0107] Figure 2 This is a schematic diagram of the calibration test site;

[0108] Figure 3 This is the result diagram of laser ranging error correction;

[0109] Figure 4 This is a schematic diagram of the laser scanning reference coordinate system;

[0110] Figure 5 is the diagram of the change of azimuth angle with the rotation angle of the driving motor;

[0111] Figure 6 It is a schematic diagram of the device of the present invention. DETAILED DESCRIPTION

[0112] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0113] The internal errors of airborne depth-finding laser radar mainly include ranging error and structural error, among which the structural error is composed of the sight axis error and the drive motor angle error. The sight axis error also includes the angle error between the normal of the reflector and the drive motor shaft and the angle error between the incident light and the drive motor shaft. These errors are mutually coupled and difficult to calibrate uniformly. To address this problem, a method and device for step-by-step calibration of the internal errors of an oval scanning airborne depth-finding laser radar was proposed. By calibrating each internal error step by step, the mutual interference between different error sources was reduced, and the accurate calibration of the internal error value of the laser radar was achieved.

[0114] Embodiment 1:

[0115] Combination Figure 1The technical process of the step-by-step calibration method for the internal error of an oval scanning airborne depth-sounding laser radar provided by the present invention is described, including:

[0116] S1: Place the airborne depth-sounding laser radar on a tripod, turn on the laser radar rotating mirror transceiver and scanning device, and illuminate a complete laser scanning track on the flat wall;

[0117] S2: Place the prism-free total station on a tripod and level it;

[0118] S3: Calibrate laser ranging error;

[0119] S4: Calibrate the sight axis error;

[0120] S5: Calibrate the driving motor angle error.

[0121] S1 specifically includes:

[0122] Combination Figure 2 Describe the calibration test site, place a tripod on the horizontal ground, install the airborne depth-sounding lidar on the tripod, turn on the lidar rotating mirror transceiver and scanning device, and illuminate a complete laser scanning track on the flat wall.

[0123] The laser radar scans in an oval shape. The incident light and the drive motor shaft are in the same plane and form an angle of 45°. The normal of the reflector is inconsistent with the direction of the drive motor shaft. When the reflector rotates at high speed driven by the drive motor, the normal of the reflector forms a cone in space. The horizontally incident laser beam is reflected by the reflector in different directions, forming an oval laser footprint on the target plane.

[0124] S2 specifically includes:

[0125] Place the prism-free total station on a tripod and level it, ensuring that the total station has line of sight with the center of the reflector and the laser foot point on the wall.

[0126] S3 specifically includes:

[0127] like Figure 2 As shown, the center point of the laser radar reflector is marked as P, the center point, major axis vertex and minor axis vertex of the laser scanning trajectory are O, A, C, B, and D respectively, the laser foot point scanning order is: ABCD, and the center point of the total station is marked as G.

[0128] Turn off the laser radar transceiver and the rotating mirror scanning device, rotate the reflector manually, open the transceiver every 30°, collect waveform data and perform waveform detection to obtain the solved distance value, and use the total station to measure the observed distance value from the center of the reflector to the laser foot point on the wall.

[0129] For example, Table 1 shows the calculated distance values ​​and observed distance values ​​of 12 wall laser foot points collected in this embodiment.

[0130] Table 1 (Unit: m)

[0131]

[0132] Let the distance value s=[s1,s2,...,s 12 ] T , and its corresponding observed distance value is S′=[S1′,S2′,...,S 12 ′] T ;

[0133] The calculation formula for solving the distance value is:

[0134] s = cΔt / 2;

[0135] Wherein, c is the propagation speed of the laser in the air, and Δt is the propagation time of the laser in the air obtained by waveform detection.

[0136] Add the error plus constant K to the above formula:

[0137] S=f(K)=s+K=[S1,S2,...,S 12 ] T ;

[0138] Among them, the initial value of the error plus constant K is set to the negative value of the design length of the internal optical path of the laser radar;

[0139] For example, in this embodiment, the internal optical path design length of the laser radar is 1m, so the initial value of K is -1m. The solved distance value in Table 1 is substituted into the above formula to calculate S, and the results are shown in Table 2.

[0140] Table 2 (unit: m)

[0141]

[0142] The error equation is established by linearizing the above equation:

[0143]

[0144] Write the above formula in matrix form:

[0145] V = BX-L;

[0146] Where X = ΔK.

[0147] There are 12 laser foot points in total.

[0148]

[0149] For each laser foot point, Li =[S′ i -S i ].

[0150] Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed:

[0151] B T BX=B T L.

[0152] Solving the above formula we get:

[0153] X=(B T B) -1 B T L.

[0154] Substituting S and S′ into the above formula, we can calculate the correction value ΔK of K.

[0155] For example, substituting S′ (observation distance value) and S in Table 1 and Table 2 into the above formula, we can calculate ΔK = 0.052 m;

[0156] According to ΔK, update the error plus a constant:

[0157] K+ΔK→K.

[0158] For example, the initial value of the error plus constant K in this embodiment is -1m, and after updating, K=-0.948m.

[0159] Recalculate S based on the updated error plus the constant K, then recalculate L, and then solve the normal equation of the error equation based on the least squares indirect adjustment principle to obtain the correction number ΔK. Then update the error correction K again, and repeat this step until |ΔK|<0.001.

[0160] For example, in this embodiment, the iterative calculation is performed once, and the final calculated error plus the constant K=-0.948m.

[0161] Taking the error into account, the distance calculated by the laser radar is:

[0162] S=cΔt / 2+K.

[0163] For example, combined with Figure 3 It shows the result of laser ranging error correction. After ranging error correction, the calculated distance value is close to the observed distance value.

[0164] S4 specifically includes:

[0165] Combination Figure 4The laser scanning reference coordinate system is explained. The laser scanning reference coordinate system O-XYZ is established with the center of the reflector as the origin. The X-axis direction is the opposite direction of the incident light, the Y-axis is the flight direction, and the Z-axis, X-axis, and Y-axis form a right-handed system. The driving motor angle is defined as θ, the angle between the normal line of the reflector and the driving motor shaft is α, and the angle between the incident light and the driving motor shaft is β. The direction vector of the normal line of the reflector in the O-XYZ coordinate system is:

[0166]

[0167] From the above formula, we can get the angles between the projection of the reflected light on the XZ and YZ planes and the Z axis respectively:

[0168]

[0169] Define the angle between the reflected light and the vertical downward direction as the scanning angle, and calculate the scanning angle according to the above formula

[0170]

[0171] The angle between the line connecting the laser foot point and the center point of the laser scanning track and the positive direction of the X-axis is defined as the azimuth angle. When the line connecting the center of the laser scanning track and the center of the reflector is perpendicular to the target plane, the azimuth angle Ψ is calculated based on the angle between the projection of the reflected light on the XZ and YZ planes and the Z axis:

[0172]

[0173] According to the distance value S calculated by the laser radar, the projection of the reflected light on the XZ and YZ planes Scan Angle Calculate the coordinates of the laser foot point in the laser scanning reference coordinate system:

[0174]

[0175] Turn off the laser radar transceiver and the rotating mirror scanning device, manually rotate the reflector to make the laser foot point fall to points A, B, C, and D in turn, turn on the transceiver, collect waveform data, and eliminate the laser ranging error after waveform detection to obtain the calculated distance value S in turn. A , S B , S C , S D , the driving motor angles are 0°, 90°, 180°, and 270° respectively. Substituting the calculated distance value and the driving motor angle into the above formula in turn, the coordinates of points A, B, C, and D in the laser scanning reference coordinate system are [x A (α,β,0°),y A (α,β,0°),z A (α,β,0°)] T,[x B (α,β,90°),y B (α,β,90°),z B (α,β,90°)] T ,[x C (α,β,180°),y C (α,β,180°),z C (α,β,180°)] T ,[x D (α,β,270°),y D (α,β,270°),z D (α,β,270°)] T .

[0176] The formula for calculating the distance between two points based on their coordinates is:

[0177]

[0178] The initial values ​​of α and β are respectively set to the design angle between the normal line of the reflector and the rotating shaft of the driving motor and the design angle between the incident light and the rotating shaft of the driving motor.

[0179] Substitute the coordinates of points A and B, A and C, A and D, B and C, B and D, and C and D into the above formula to obtain the distance H between AB and AB 、AC distance H AC , AD distance H AD , BC distance H BC , BD distance H BD 、CD distance H CD .

[0180] The distance H′ between AB is measured by total station. AB , AC distance H′ AC , AD distance H′ AD , BC is at a distance of H′ BC , BD distance H′ BD , CD distance H′ CD .

[0181] Let H = {H AB ,H AC ,H AD ,H BC ,H BD ,H CD}, H′={H′ AB ,H′ AC ,H′ AD ,H′ BC ,H′ BD ,H′ CD}.

[0182] For example, in this embodiment, the angle between the normal line of the reflector of the laser radar and the shaft of the drive motor is designed to be 5°, and the angle between the incident light and the shaft of the drive motor is designed to be 45°, so the initial values ​​of α and β are set to 5° and 45° respectively. The coordinates of points A, B, C, and D in the laser scanning reference coordinate system are shown in Table 3. Substituting the coordinates in Table 3 into the distance calculation formula to calculate H, the results are shown in Table 4.

[0183] Table 3 (Unit: m)

[0184]

[0185] Table 4 (Unit: m)

[0186]

[0187] Linearize the distance calculation formula to establish the error equation:

[0188]

[0189] Write the above formula in matrix form:

[0190] V = BX-L;

[0191] Where X = [ΔαΔβ] T .

[0192] There are 6 laser foot points in total.

[0193]

[0194] For each laser foot point, L i =[H i -H i ].

[0195] Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed:

[0196] B T BX=B T L.

[0197] Solving the above formula we get:

[0198] X=(B T B) -1 B T L.

[0199] Substituting H and H′ into the above formula, we can obtain the correction values ​​Δα and Δβ of α and β.

[0200] For example, substituting H and H′ in Table 4 into the above formula, Δα=-0.978° and Δβ=-0.208° are calculated.

[0201] According to Δα and Δβ, update the angle between the normal line of the reflector and the shaft of the drive motor and the angle between the incident light and the shaft of the drive motor:

[0202] α+Δα→α;

[0203] β+Δβ→β.

[0204] For example, in this embodiment, the angle α between the normal line of the reflector and the rotating shaft of the driving motor and the angle β between the incident light and the rotating shaft of the driving motor are designed to be 5° and 45° respectively. After updating, α=4.022° and β=44.792°.

[0205] Recalculate H according to the updated angle α between the normal line of the reflector and the shaft of the drive motor and the angle β between the incident light and the shaft of the drive motor, and then recalculate B and L. Then, solve the normal equation of the error equation based on the principle of least squares indirect adjustment to obtain the correction numbers Δα and Δβ, and then update α and β again. Repeat this step until Δα|<0.001 and |Δβ|<0.001.

[0206] For example, the present embodiment performs iterative calculations twice, and finally calculates that the included angle α between the normal line of the reflector and the rotating shaft of the drive motor is 4.024°, and the included angle β between the incident light and the rotating shaft of the drive motor is 44.743°.

[0207] Calculate the angle error between the normal line of the reflector and the drive motor shaft based on the design value and the measured value:

[0208] Δα=α-5°;

[0209] Among them, α is the angle between the normal line of the reflector and the shaft of the driving motor obtained by final calculation.

[0210] For example, the error value of the angle between the normal line of the reflector and the shaft of the drive motor calculated in this embodiment is -0.976°.

[0211] Calculate the angle error between the incident light and the drive motor shaft based on the design value and the measured value:

[0212] Δβ=β-45°;

[0213] Among them, β is the angle between the incident light and the shaft of the driving motor obtained by final calculation.

[0214] For example, the angle error between the incident light and the shaft of the driving motor calculated in this embodiment is -0.266°.

[0215] S5 specifically includes:

[0216] The driving motor angle error is generally composed of two parts: zeroing error and angle measurement error. Since the driving motor angle of the laser radar is usually measured by an angle encoder with high angle measurement accuracy, the angle measurement error can be ignored. The present invention only considers the zeroing error.

[0217] In order to use the azimuth angle to calculate the drive motor angle, first adjust the laser radar position so that the PA distance is equal to the PC distance, and the PB distance is equal to the PD distance, so that the line OP connecting the center of the laser scanning track and the center of the reflector is perpendicular to the wall, and then calibrate the drive motor angle error. The drive motor angle error calibration steps are as follows:

[0218] Turn off the laser radar mirror scanning device, turn on the transceiver, and the drive motor is at zero position. Mark the reflected laser on the wall laser foot point as E, and use the total station to measure the angle ∠AOE between OA and OE. When point E is counterclockwise from point A, the azimuth angle Ψ = ∠AOE, and when point E is clockwise from point A, the azimuth angle Ψ = 360°-∠AOE.

[0219] For example, in this embodiment, ∠AOE=2.085° is collected. When point E is in the clockwise direction of point A, the azimuth angle Ψ=357.915°.

[0220] According to the azimuth angle calculation formula, the angle α between the normal line of the reflector and the shaft of the drive motor is known. The azimuth angle calculation formula is expressed as:

[0221]

[0222] Combination Figure 5 It shows that the azimuth angle changes with the rotation angle of the drive motor. The azimuth angle and the rotation angle of the drive motor are in a positive correlation function relationship, and the definition domain and the value range correspond one to one. Substitute the measured azimuth angle Ψ into the above formula to obtain the actual rotation angle θ of the drive motor when the laser foot point falls on point E. When point E is counterclockwise from point A, the error value of the drive motor rotation angle Δθ=θ, and when point E is clockwise from point A, the error value of the drive motor rotation angle Δθ=θ-360°.

[0223] For example, substituting the angle α=4.024° between the normal line of the reflector and the rotation axis of the drive motor and the azimuth angle Ψ=357.915° into the above formula, the actual rotation angle θ=358.422° of the drive motor can be obtained. Since point E is clockwise from point A, the error value of the rotation angle of the drive motor Δθ=-1.578°.

[0224] Repeat the above steps 5 times to obtain 5 sets of drive motor angle error values, and average them to obtain the drive motor angle error value Δθ:

[0225]

[0226] Among them, Δθ iis the error value of the driving motor angle obtained by the i-th measurement.

[0227] For example, Table 5 shows 5 groups of drive motor rotation angle error values ​​collected in this embodiment. Substituting the data in Table 5 into the above formula, the error value of the drive motor rotation angle Δθ=-1.586° is obtained.

[0228] Table 5

[0229]

[0230] Taking the error into account, the actual rotation angle of the drive motor is:

[0231]

[0232] Where θ is the driving motor angle measured by the laser radar angle encoder, is the driving motor angle after error correction, when hour, when hour,

[0233] Embodiment 2:

[0234] Combination Figure 6 The present invention provides an oval scanning airborne depth-measuring laser radar internal error step-by-step calibration device, comprising:

[0235] M1: Deployment module, used to deploy airborne bathymetric lidar and total station in the calibration field;

[0236] M2: The first acquisition module is used to obtain the distance solution value of the wall laser foot point based on the laser radar;

[0237] M3: The second acquisition module is used to obtain the distance observation value between two points and the angle formed by the line connecting three points based on the total station;

[0238] M4: the first calculation module, used to calculate the laser ranging error;

[0239] M5: The second calculation module is used to calculate the collimation axis error;

[0240] M6: The third calculation module is used to calculate the rotation angle error of the drive motor.

[0241] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in this application should be included in the protection scope of the present invention.

Claims

1. A step-by-step calibration method for internal errors of an oval scanning airborne depth-sounding laser radar, characterized in that: The method comprises: Place the airborne depth-sounding laser radar on a tripod, turn on the laser radar rotating mirror transceiver and scanning device, and illuminate a complete laser scanning track on the flat wall; Place the reflectorless total station on a tripod and level it; Calibrate laser ranging error; Calibrate the sight axis error; Calibrate the drive motor angle error.

2. The method for calibrating the internal error of an oval scanning airborne depth-sounding laser radar according to claim 1, characterized in that: The calibration laser ranging error includes: The center point of the laser radar reflector is marked as P, the center point, the long axis vertex and the short axis vertex of the laser scanning trajectory are O, A, C, B, and D respectively, the laser foot point scanning sequence is: ABCD, and the center point of the total station is marked as G; Turn off the laser radar transceiver and the rotating mirror scanning device, manually rotate the reflector, open the transceiver every 30°, collect waveform data and perform waveform detection to obtain the calculated distance value, and use the total station to measure the observed distance value from the center of the reflector to the wall laser foot point; Let the calculated distance value s = [s1, s2, ..., s 12 ] T , the corresponding observed distance value is S′=[S1′,S2′,...,S 12 ′] T ; The calculation formula for the distance value is: s = cΔt / 2; Where c is the propagation speed of the laser in the air, and Δt is the propagation time of the laser in the air obtained by waveform detection; Add the error plus constant K to the above formula: S=f(K)=s+K=[S1,S2,...,S 12 ] T ; The initial value of the error plus constant K is set to the negative value of the design length of the internal optical path of the laser radar; The error equation is established by linearizing the above equation: Write the above formula in matrix form: V = BX-L; Where, X = ΔK; There are 12 laser foot points in total. For each laser foot point, L i =[S' i -S i ]; Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed: B T BX=B T L; Solving the above formula we get: X=(B T B) -1 B T L; Substitute S and S′ into the above formula to calculate the correction factor ΔK of K; According to ΔK, update the error plus constant: K+ΔK→K; Recalculate S according to the updated error plus constant K, then recalculate L, and then solve the normal equation of the error equation based on the least squares indirect adjustment principle to obtain the correction number ΔK, then update the error correction amount K again, and repeat this step until |ΔK|<0.001; Taking the error into account, the distance calculated by the laser radar is: S=cΔt / 2+K.

3. The step-by-step calibration method for internal errors of an oval scanning airborne depth-sounding laser radar according to claim 1, characterized in that: The calibration sight axis error includes: The collimation axis error includes the angle error between the normal line of the reflector and the rotating shaft of the drive motor and the angle error between the incident light and the rotating shaft of the drive motor; A laser scanning reference coordinate system O-XYZ is established with the center of the reflector as the origin, the X-axis direction is the opposite direction of the incident light, the Y-axis is the flight direction, the Z-axis and the X-axis and the Y-axis form a right-handed system, the driving motor angle is defined as θ, the angle between the normal line of the reflector and the driving motor shaft is α, the angle between the incident light and the driving motor shaft is β, and the direction vector of the normal line of the reflector in the O-XYZ coordinate system is: From the above formula, we can get the angles between the projection of the reflected light on the XZ and YZ planes and the Z axis respectively: Define the angle between the reflected light and the vertical downward direction as the scanning angle, and calculate the scanning angle according to the above formula: The angle between the line connecting the laser foot point and the center point of the laser scanning track and the positive direction of the X-axis is defined as the azimuth angle. When the line connecting the center of the laser scanning track and the center of the reflector is perpendicular to the target plane, the azimuth angle Ψ is calculated according to the angle between the projection of the reflected light on the XZ and YZ planes and the Z axis: According to the distance value S calculated by the laser radar, the projection of the reflected light on the XZ and YZ planes The scanning angle Calculate the coordinates of the laser foot point in the laser scanning reference coordinate system: Turn off the laser radar transceiver and the rotating mirror scanning device, manually rotate the reflector, so that the laser foot points fall on points A, B, C, and D in turn, turn on the transceiver, collect waveform data, and eliminate the laser ranging error after waveform detection to obtain the calculated distance value S in turn. A , S B , S C , S D , the driving motor rotation angles are 0°, 90°, 180°, and 270° respectively. Substituting the calculated distance value and the driving motor rotation angle into the above formula in turn, the coordinates of points A, B, C, and D in the laser scanning reference coordinate system are [x A (α,β,0°),y A (α,β,0°),z A (α,β,0°)] T ,[x B (α,β,90°),y B (α,β,90°),z B (α,β,90°)] T ,[x C (α,β,180°),y C (α,β,180°),z C (α,β,180°)] T ,[x D (α,β,270°),y D (α,β,270°),z D (α,β,270°)] T ; The formula for calculating the distance between two points based on their coordinates is: The angle between the normal line of the reflector and the rotating shaft of the drive motor is designed to be 5°, and the angle between the incident light and the rotating shaft of the drive motor is designed to be 45°, so the initial values ​​of α and β are set to 5° and 45° respectively; Substitute the coordinates of points A and B, A and C, A and D, B and C, B and D, and C and D into the above formula to obtain the distance H between AB and AB 、AC distance H AC , AD distance H AD , BC distance H BC , BD distance H BD 、CD distance H CD ; The distance H′ between AB is measured by the total station. AB , AC distance H′ AC , AD distance H′ AD , BC is at a distance of H′ BC , BD distance H′ BD , CD distance H′ CD ; Let H = {H AB , H AC , H AD , H BC , H BD , H CD}, H' = {H' AB , H' AC , H' AD , H' BC , H' BD , H' CD}; The distance calculation formula is linearized to establish an error equation: Write the above formula in matrix form: V = BX-L; Where, X=[ΔaΔb] T ; There are 6 laser foot points in total. For each laser foot point, L i =[H′ i -H i ]; Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed: B T BX=B T L; Solving the above formula we get: X=(B T B) -1 B T L; Substituting H and H′ into the above formula, we can calculate the corrections Δα and Δβ of α and β; According to Δα and Δβ, the angle between the normal line of the reflector and the rotating shaft of the drive motor and the angle between the incident light and the rotating shaft of the drive motor are updated: α+Δα→α; β+Δβ→β; Recalculate H according to the updated angle α between the normal line of the reflector and the shaft of the drive motor and the angle β between the incident light and the shaft of the drive motor, then recalculate B and L, and then solve the normal equation of the error equation based on the least squares indirect adjustment principle to obtain the correction numbers Δα and Δβ, and then update α and β again, and repeat this step until |Δα|<0.001 and |Δβ|<0.001; The angle error between the normal line of the reflector and the shaft of the drive motor is calculated based on the design value and the measured value: Δα=α-5°; Wherein, α is the angle between the normal line of the reflector and the rotating shaft of the driving motor obtained by final calculation; The angle error between the incident light and the drive motor shaft is calculated based on the design value and the measured value: Δβ=β-45°; Wherein, β is the angle between the incident light and the shaft of the driving motor obtained by final calculation.

4. The method for calibrating the internal error of an oval scanning airborne depth-sounding laser radar according to claim 1, characterized in that: The calibrating the driving motor rotation angle error comprises: Adjust the position of the laser radar so that the line OP connecting the center of the laser scanning track and the center of the reflector is perpendicular to the wall. The steps of calibrating the rotation angle error of the drive motor are as follows: Turn off the laser radar rotating mirror scanning device and turn on the transceiver. At this time, the drive motor is at zero position, and the reflected laser is marked as E on the wall laser foot point; The angle ∠AOE between OA and OE is measured by the total station; When point E is counterclockwise from point A, the azimuth angle Ψ=∠AOE, and when point E is clockwise from point A, the azimuth angle Ψ=360°-∠AOE; According to the azimuth angle calculation formula, the angle α between the normal line of the reflector and the shaft of the drive motor is known, and the azimuth angle calculation formula is expressed as: Substitute the measured azimuth angle Ψ into the above formula to obtain the actual driving motor rotation angle θ when the laser foot point falls on point E. When point E is counterclockwise from point A, the error value of the driving motor rotation angle Δθ=θ; when point E is clockwise from point A, the error value of the driving motor rotation angle Δθ=θ-360°; Repeat the above steps 5 times to obtain 5 sets of the driving motor rotation angle error values, and average them to obtain the driving motor rotation angle error value Δθ: Among them, Δθ i is the error value of the driving motor angle obtained by the i-th measurement; Taking the error into account, the actual rotation angle of the driving motor is: Where θ is the driving motor angle measured by the laser radar angle encoder, is the driving motor angle after error correction, when hour, when hour, 5. A step-by-step calibration device for internal errors of an oval scanning airborne depth-measuring laser radar, characterized in that: The device comprises: The first deployment module is used to deploy the airborne bathymetric laser radar and total station in the calibration field; A first acquisition module, used for acquiring a distance solution value of a wall laser foot point based on the laser radar; A second acquisition module is used to acquire the distance observation value between two points and the angle formed by the line connecting three points based on the total station; A first calculation module, used for calculating the laser ranging error; The second calculation module is used to calculate the sight axis error; The third calculation module is used to calculate the rotation angle error of the driving motor.

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