An internal error step calibration method and device for an oval scanning airborne bathymetric laser radar

Abstract

The application provides an egg-shaped scanning airborne depth laser radar internal error step calibration method and device. By step-by-step calibration of laser ranging error, collimation axis error and driving motor rotation angle error, the complexity of error calibration is reduced, the influence of multi-factor interference on overall calibration accuracy is avoided, and the laser radar internal error value can be effectively calibrated. The error value can be used to evaluate the instrument quality during the instrument processing and assembly stage, and the system error can be corrected in the subsequent calculation, so as to avoid the precision decline caused by the laser radar self-measurement data error, thereby improving the acquisition precision of laser three-dimensional point cloud data.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of airborne laser bathymetry, and particularly relates to an internal error step-by-step calibration method and device for an oviform scanning airborne bathymetric laser radar. BACKGROUND

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

[0003] The core goal of airborne bathymetric laser radar is to accurately obtain the three-dimensional coordinates of laser foot points. As a highly integrated complex system, the measurement accuracy of airborne bathymetric laser radar is affected by various system errors and random errors. In order to obtain high-precision laser three-dimensional point cloud data, airborne bathymetric laser radar must be calibrated to eliminate measurement errors and improve measurement accuracy. The errors affecting the measurement accuracy include integrated errors and internal errors. The system integrated error is mainly the installation angle error, i.e. the error caused by the non-parallelism between the laser scanning system coordinate axis and the inertial platform coordinate axis, which is usually corrected by flight dynamic calibration. The internal error refers to the error existing in the laser scanning system itself, mainly including ranging error and structural error, which cannot be eliminated by flight dynamic calibration and must be calibrated before flight. Calibrating the internal error of airborne bathymetric laser radar not only can evaluate the equipment quality at the instrument processing and assembly stage, but also can correct the system error in subsequent calculation, thereby avoiding the measurement data error of the laser radar itself and maximizing the measurement accuracy.

[0004] The documents "Research on Self-calibration Method of Domestic Spiral Scanning Laser Radar System" (Yang Shujuan et al., 2018, Journal of Electronics and Information), "Calibration Method of Light and Small Unmanned Aerial Vehicle Laser Radar Measurement System" (Tian Lulin et al., 2024, Journal of University of Information Engineering), the book "Airborne Laser Radar Measurement Technology Theory and Method" (Zhang Xiaohong, 2007, Wuhan University Press), the invention patent "Geometric Correction Method and Device for Placement Error of Unmanned Aerial Vehicle Radar" (CN114859326A, 2022), "Placement Angle Error Correction Method Based on Airborne Laser Depth Measurement System" (CN116299369A, 2023) calibrate the system placement angle error of the airborne laser radar, but do not calibrate the internal error. The documents "Calibration Model and Simulation Analysis of Circular Scanning Airborne Laser Depth Measurement System" (Shen Erhua et al., 2016, Journal of Surveying and Mapping), "Research on Structural Error and Positioning Accuracy of Airborne Dual-frequency Laser Radar" (Lü Deliang et al., 2018, Laser and Optoelectronics Progress), "Positioning Model and Collimation Axis Error Influence Analysis of Airborne Laser Radar Depth Measurement System" (Yu Jiayong et al., 2019, Infrared and Laser Engineering), the book "Airborne LiDAR Data Error Processing Theory and Method" (Wang Liying, 2013, Surveying and Mapping Press) simulate the influence of internal error on measurement accuracy, but mainly focus on the calibration of system placement angle error, and do not provide a calibration scheme for internal error. The invention patent "Scanning Platform Coordinate System Error Correction Method Based on Airborne Laser Radar System" (CN116990787A, 2023) corrects the scanning coordinates through a correction equation, and corrects and compensates the overall influence caused by the structural error, but does not explicitly calibrate each internal error value. The invention patents "Calibration Method for Ranging Accuracy of Airborne Laser Radar Based on Circular Scanning" (CN111123245A, 2020) and "Test Method for Maximum Ranging Capability and Angle Measurement Accuracy of Airborne Laser Radar Based on Circular Scanning" (CN111123246A, 2020) calibrate the ranging error value and the angle measurement error value respectively, but they are for circular scanning airborne laser radars and are not applicable to oval scanning airborne laser radars.

[0005] In summary, in the currently disclosed airborne laser radar calibration patent documents, most of them calibrate the system placement angle error, few of them calibrate 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. SUMMARY

[0006] The purpose of the present application is to provide an oval scanning airborne depth laser radar internal error step-by-step calibration method and device to solve the problem of calibrating the internal error value of the oval scanning airborne laser radar, in view of the shortcomings of the prior art.

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

[0008] The airborne depth laser radar is placed on a tripod, the laser radar mirror transceiver and scanning device are turned on, and a complete laser scanning track is irradiated on a flat wall surface;

[0009] The prism-free total station is placed on a tripod and leveled;

[0010] The laser ranging error is calibrated;

[0011] The collimation axis error is calibrated;

[0012] The driving motor rotation angle error is calibrated.

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

[0014] The center point of the laser radar mirror is marked as P, the center point, long axis top point and short axis top point of the laser scanning track are marked as O, A, C, B and D, the laser foot point scanning sequence is A-B-C-D, and the center point of the total station is marked as G;

[0015] The laser radar transceiver and mirror scanning device are turned off, the mirror is manually rotated, the transceiver is turned on every 30°, waveform data is collected and waveform detection is performed to obtain a calculated distance value, and the total station is used to measure an observed distance value from the mirror center to the laser foot point on the wall surface;

[0016] Let the calculated distance value s = [s1, s2,..., s 12 ] T , and the corresponding observed distance value be S' = [S1', S2',..., S 12 ' T ;

[0017] The calculation formula of the calculated distance value is:

[0018] s = cΔt / 2;

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

[0020] A constant K is added to the above formula:

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

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

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

[0024]

[0025] The above formula is written in matrix form:

[0026] V = BX - L;

[0027] Wherein, X = ΔK;

[0028] There are 12 laser foot points, so

[0029]

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

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

[0032] B T BX = B T L;

[0033] Solving the above formula gives:

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

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

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

[0037] K + ΔK → K;

[0038] According to the updated error plus constant K, recalculate S, 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 ΔK, and then update the error correction K again. Repeat this step until |ΔK| < 0.001;

[0039] Considering the error, the distance value calculated by the laser radar is:

[0040] S = cΔt / 2 + K.

[0041] In the internal error step calibration method of the egg-shaped scanning airborne depth laser radar, the calibration collimation axis error comprises:

[0042] The boresight error includes an error of an angle between the mirror normal and the rotation axis of the driving motor and an error of an angle between the incident light and the rotation axis of the driving motor.

[0043] A laser scanning reference coordinate system O-XYZ is established with the mirror center as the origin, the X-axis direction is the reverse 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-hand system, the driving motor rotation angle is defined as θ, the angle between the mirror normal and the rotation axis of the driving motor is defined as α, the angle between the incident light and the rotation axis of the driving motor is defined as β, and the direction vector of the mirror normal in the O-XYZ coordinate system is:

[0044]

[0045] From the above formula, the angles between the projections of the reflected light in the XZ and YZ planes and the Z-axis are respectively:

[0046]

[0047] The angle between the reflected light and the vertical downward direction is defined as the scanning angle, and the scanning angle is calculated 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, and when the line connecting the center of the laser scanning track and the center of the mirror is perpendicular to the target plane, the azimuth angle Ψ is calculated according to the angles between the projections of the reflected light in the XZ and YZ planes and the Z-axis.

[0050]

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

[0052]

[0053] The laser radar transceiver device and the rotating mirror scanning device are turned off, the mirror is manually rotated, the laser foot point falls on points A, B, C and D in turn, the transceiver device is turned on, waveform data is collected, and after waveform detection, the laser ranging error is eliminated to obtain the distance value S calculated in turn A , S B , S C , S D, the driving motor rotation angle is 0°, 90°, 180°, 270° respectively, the calculated distance value and the driving motor rotation angle are substituted into the above formula in turn to obtain the coordinates of A, B, C, D points in the laser scanning reference coordinate system respectively as [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 two-point distance formula according to the two-point coordinates is:

[0055]

[0056] Wherein, the initial values of α and β are respectively the designed angle between the mirror normal and the driving motor rotation shaft and the designed angle between the incident light and the driving motor rotation shaft;

[0057] Substitute the A, B point coordinates, the A, C point coordinates, the A, D point coordinates, the B, C point coordinates, the B, D point coordinates, and the C, D point coordinates into the above formula in turn to obtain the AB distance H AB , the AC distance H AC , the AD distance H AD , the BC distance H BC , the BD distance H BD , and the CD distance H CD ;

[0058] The AB distance H′ AB , the AC distance H′ AC , the AD distance H′ AD , the BC distance H′ BC , the BD distance H′ BD , and the CD distance H′ CD are measured by the total station;

[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 error equation is established by linearizing the distance calculation formula:

[0061]

[0062] The above formula is written in matrix form:

[0063] V=BX-L;

[0064] Wherein, X=[ΔαΔβ] T ;

[0065] There are 6 laser foot points, so

[0066]

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

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

[0069] B T BX=B T L;

[0070] Solving the above formula gives:

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

[0072] The correction numbers Δα and Δβ of α and β are calculated by substituting H and H' into the above formula;

[0073] According to Δα and Δβ, the angle between the mirror normal and the driving motor shaft and the angle between the incident light and the driving motor shaft are updated:

[0074] α+Δα→α;

[0075] β+Δβ→β;

[0076] According to the updated mirror normal and the drive motor shaft angle α and the incident light and the drive motor shaft angle β re-calculate H, and then re-calculate B and L, and then based on the least squares indirect adjustment principle to solve the error equation of the normal equation to obtain the correction Δα and Δβ, and then update α and β again, repeat the step, until |Δα| < 0.001 and |Δβ| < 0.001;

[0077] According to the design value and the measured value, the mirror normal and the drive motor shaft angle error value is calculated:

[0078] Δα = α - 5°;

[0079] Wherein, α is the final calculation of the mirror normal and the drive motor shaft angle;

[0080] According to the design value and the measured value, the mirror normal and the drive motor shaft angle error value is calculated:

[0081] Δβ = β - 45°;

[0082] Wherein, β is the final calculation of the mirror normal and the drive motor shaft angle.

[0083] In the internal error step calibration method of the oval scanning airborne depth laser radar, the calibration of the drive motor angle error comprises:

[0084] Adjust the position of the laser radar, so that the line OP between the center of the laser scanning track and the center of the mirror is perpendicular to the wall surface, and the steps of calibrating the drive motor angle error are as follows:

[0085] Close the laser radar mirror scanning device, open the transceiver device, at this time the drive motor is at zero position, mark the reflected laser on the wall laser foot point as E;

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

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

[0088] According to the azimuth angle calculation formula, the mirror normal and the drive motor shaft angle α is known, the azimuth angle calculation formula is expressed as:

[0089]

[0090] The actual driving motor rotation angle θ when the laser foot point falls on the E point is obtained by substituting the measured azimuth angle Ψ into the above formula, when the E point is in the counterclockwise direction of the A point, the error value Δθ of the driving motor rotation angle is θ, when the E point is in the clockwise direction of the A point, the error value Δθ of the driving motor rotation angle is θ-360°;

[0091] The above step is repeated 5 times to obtain 5 groups of driving motor rotation angle error values, and the average of the driving motor rotation angle error values is obtained:

[0092]

[0093] Wherein, Δθ i is the error value of the driving motor rotation angle obtained by the ith measurement;

[0094] Considering the error, the actual driving motor rotation angle is:

[0095]

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

[0097] The application also provides an internal error step-by-step calibration device for an egg-shaped scanning airborne depth-finding laser radar, comprising:

[0098] A first layout module is configured to layout the airborne depth-finding laser radar and the total station in a calibration field.

[0099] A first acquisition module is configured to acquire a distance solution value of a wall surface laser foot point based on the laser radar.

[0100] A second acquisition module is configured to acquire a distance observation value between two points and an included angle formed by three connected points based on the total station.

[0101] A first calculation module is configured to calculate a laser ranging error.

[0102] A second calculation module is configured to calculate a collimation axis error.

[0103] A third calculation module is configured to calculate a driving motor rotation angle error.

[0104] The application has the following beneficial effects:

[0105] The error calibration method and device disclosed by the application are suitable for calibrating internal error values of an oval scanning airborne depth laser radar, and through step-by-step calibration of laser ranging error, collimation axis error and driving motor rotation angle error, the complexity of error calibration is reduced, the influence of multi-factor interference on overall calibration accuracy is avoided, the internal error values of the laser radar can be effectively calibrated, the error values can be used for evaluating instrument quality in the instrument processing and assembly stage, and system error can be corrected in subsequent calculation, so that the precision of laser three-dimensional point cloud data acquisition is improved. BRIEF DESCRIPTION OF DRAWINGS

[0106] Figure 1 The method technical flowchart of the application is shown in the figure.

[0107] Figure 2 The calibration test field schematic diagram is shown in the figure.

[0108] Figure 3 The laser ranging error correction result diagram is shown in the figure.

[0109] Figure 4 The laser scanning reference coordinate system schematic diagram is shown in the figure.

[0110] Figure 5 The azimuth angle change diagram with driving motor rotation angle is shown in the figure.

[0111] Figure 6 The device schematic diagram of the application is shown in the figure. DETAILED DESCRIPTION

[0112] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the application is further described in detail below in combination with specific embodiments and with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0113] The internal errors of the airborne depth laser radar mainly include ranging error and structural error, wherein the structural error is composed of collimation axis error and driving motor rotation angle error. The collimation axis error includes the error of the angle between the mirror normal and the driving motor rotation shaft and the error of the angle between the incident light and the driving motor rotation shaft. These errors are coupled with each other and are difficult to calibrate uniformly. In view of the problem, a step-by-step calibration method and device for internal errors of an oval scanning airborne depth laser radar are provided, through step-by-step calibration of each internal error, the mutual interference between different error sources is reduced, and accurate calibration of the internal error values of the laser radar is realized.

[0114] Embodiment 1

[0115] In combination with Figure 1The application provides an internal error step calibration method and technical process for an egg-shaped scanning airborne depth laser radar, and the method comprises the following steps:

[0116] S1: placing the airborne depth laser radar on a tripod, turning on a laser radar mirror transceiver and a scanning device, and irradiating a complete laser scanning track on a flat wall surface;

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

[0118] S3: calibrating laser ranging error;

[0119] S4: calibrating a collimation axis error;

[0120] S5: calibrating a driving motor rotation angle error.

[0121] S1 specifically comprises the following steps:

[0122] In combination with Figure 2 It is specified that a calibration test field is placed on a horizontal ground, the airborne depth laser radar is placed on the tripod, the laser radar mirror transceiver and the scanning device are turned on, and a complete laser scanning track is irradiated on a flat wall surface.

[0123] The scanning mode of the laser radar is egg-shaped scanning, the incident light and the driving motor rotation shaft are in the same plane and form a 45° angle, the normal line of the reflector is inconsistent with the direction of the driving motor rotation shaft, when the reflector rotates at high speed under the driving of the driving motor, the normal line of the reflector forms a circular cone in space, the horizontally incident laser beam is reflected by the reflector and is shot in different directions, and an egg-shaped laser foot point is formed on a target plane.

[0124] S2 specifically comprises the following steps:

[0125] The prism-free total station is placed on the tripod and leveled, and the total station is ensured to be in sight with the center of the reflector and the wall laser foot point.

[0126] S3 specifically comprises the following steps:

[0127] As shown in Figure 2 The center point of the laser radar reflector is marked as P, the center point, the long axis top point and the short axis top point of the laser scanning track are marked as O, A, C, B and D respectively, the laser foot point scanning sequence is A-B-C-D, and the center point of the total station is marked as G.

[0128] The laser radar transceiver and the mirror scanning device are turned off, the reflector is manually rotated, the transceiver is turned on every 30°, waveform data is collected and waveform detection is performed to obtain a calculated distance value, and the observation distance value of the reflector center to the wall laser foot point is measured by using the total station.

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

[0130] Table 1 (unit: m)

[0131]

[0132] Let the calculated distance value s = [s1, s2,..., s 12 ] T , and the corresponding observed distance value S' = [S1', S2',..., S 12 ' T .

[0133] The calculation formula of the calculated distance value is:

[0134] s = cΔt / 2;

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

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

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

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

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

[0140] Table 2 (unit: m)

[0141]

[0142] Linearize the above formula to establish an error equation:

[0143]

[0144] Write the above formula in matrix form:

[0145] V = BX - L;

[0146] Wherein, X = ΔK.

[0147] There are 12 laser foot points, so

[0148]

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

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

[0151] B T BX = B T L.

[0152] Solving the above formula gives:

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

[0154] Substitute S and S' into the above formula to calculate the correction ΔK of K.

[0155] For example, substitute S' (the observed distance value) and S in Table 1 and Table 2 into the above formula to calculate ΔK = 0.052 m;

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

[0157] K + ΔK → K.

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

[0159] 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 square indirect adjustment principle to obtain the correction ΔK, and then update the error correction K again. Repeat this step until |ΔK| < 0.001.

[0160] For example, this embodiment iteratively calculates 1 time, and the error plus constant K finally calculated is K = -0.948 m.

[0161] Considering the error, the laser radar calculated distance value is:

[0162] S = cΔt / 2 + K.

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

[0164] S4 specifically includes:

[0165] Combined with Figure 4The laser scanning reference coordinate system is illustrated, and a laser scanning reference coordinate system O-XYZ is established with the center of the mirror 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 and Y axes form a right-hand system, the driving motor rotation angle is defined as θ, the angle between the mirror normal and the driving motor rotation axis is defined as α, the angle between the incident light and the driving motor rotation axis is defined as β, and the direction vector of the mirror normal in the O-XYZ coordinate system is:

[0166]

[0167] From the above formula, the angles between the projections of the reflected light in the XZ and YZ planes and the Z-axis are respectively:

[0168]

[0169] The scanning angle between the reflected light and the vertical downward direction is defined, and the scanning angle is calculated according to the above formula

[0170]

[0171] The azimuth angle between the line connecting the laser foot point and the center point of the laser scanning trajectory and the X-axis positive direction is defined, and when the line connecting the center of the laser scanning trajectory and the center of the mirror is perpendicular to the target plane, the azimuth angle Ψ is calculated according to the angles between the projections of the reflected light in the XZ and YZ planes and the Z-axis.

[0172]

[0173] According to the distance value S calculated by the laser radar, the projections of the reflected light in the XZ and YZ planes The scanning angle The coordinates of the laser foot point in the laser scanning reference coordinate system are calculated:

[0174]

[0175] The laser radar transceiver device and the rotating mirror scanning device are turned off, the mirror is manually rotated, the laser foot point falls on points A, B, C and D in turn, the transceiver device is turned on, waveform data is collected, and after waveform detection, the laser ranging error is eliminated to obtain the distance value S A , S B , S C , S D , the driving motor rotation angles are 0°, 90°, 180° and 270° respectively, and the calculated distance values and the driving motor rotation angles are substituted into the above formula to obtain the coordinates of points A, B, C and D in the laser scanning reference coordinate system respectively as [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 according to two-point coordinates is:

[0177]

[0178] The initial values of α and β are set as the designed angle between the mirror normal and the driving motor shaft and the designed angle between the incident light and the driving motor shaft, respectively.

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

[0180] The AB distance H′ AB , the AC distance H′ AC , the AD distance H′ AD , the BC distance H′ BC , the BD distance H′ BD , and the CD distance H′ CD are measured by the total station.

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

[0182] For example, the embodiment adopts the mirror normal of the laser radar and the shaft angle of the driving motor to be designed as 5°, and the incident light and the shaft angle of the driving motor to be designed as 45°, so the initial values of α and β are set as 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, and the coordinates in Table 3 are substituted into the distance calculation formula to calculate H, and the results are shown in Table 4.

[0183] Table 3 (unit: m)

[0184]

[0185] Table 4 (unit: m)

[0186]

[0187] The error equation is established by linearizing the distance calculation formula:

[0188]

[0189] The above formula is written in matrix form:

[0190] V = BX - L;

[0191] Wherein, X = [Δα Δβ] T .

[0192] There are 6 laser foot points, so

[0193]

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

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

[0196] B T BX = B T L.

[0197] Solving the above formula gives:

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

[0199] The correction numbers Δα and Δβ of α and β are calculated by substituting H and H' into the above formula.

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

[0201] According to Δα and Δβ, the mirror normal and the driving motor rotation axis angle and the incident light and the driving motor rotation axis angle are updated as follows:

[0202] α + Δα → α;

[0203] β + Δβ → β.

[0204] For example, the mirror normal and the driving motor rotation axis angle α and the incident light and the driving motor rotation axis angle β are designed as 5° and 45° respectively, and after updating, α = 4.022° and β = 44.792°.

[0205] According to the updated mirror normal and the driving motor rotation axis angle α and the incident light and the driving motor rotation axis angle β, H is recalculated, and then B and L are recalculated, and the normal equation of the error equation is solved based on the least square indirect adjustment principle to obtain the correction Δα and Δβ, and then α and β are updated again, and the step is repeated until |Δα| < 0.001 and |Δβ| < 0.001.

[0206] For example, the mirror normal and the driving motor rotation axis angle α = 4.024° and the incident light and the driving motor rotation axis angle β = 44.743° are obtained after 2 times of iterative calculation.

[0207] According to the design value and the measured value, the mirror normal and the driving motor rotation axis angle error value is calculated as follows:

[0208] Δα = α - 5°;

[0209] Wherein, α is the final calculated mirror normal and the driving motor rotation axis angle.

[0210] For example, the mirror normal and the driving motor rotation axis angle error value of the embodiment is -0.976°.

[0211] According to the design value and the measured value, the incident light and the driving motor rotation axis angle error value is calculated as follows:

[0212] Δβ = β - 45°;

[0213] Wherein, β is the final calculated incident light and the driving motor rotation axis angle.

[0214] For example, the incident light and the driving motor rotation axis angle error value of the embodiment is -0.266°.

[0215] S5 specifically comprises:

[0216] The drive motor rotation angle error is generally composed of zero setting error and angle measurement error. Since the drive motor rotation angle of the laser radar is usually measured by an angle encoder, the angle measurement error is very high and can be ignored, and the present application only considers the zero setting error.

[0217] In order to calculate the drive motor rotation angle by using the azimuth angle, the laser radar position is first adjusted to make the PA distance equal to the PC distance and the PB distance 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 surface, and then the drive motor rotation angle error is calibrated. The drive motor rotation angle error calibration steps are as follows:

[0218] The laser radar mirror scanning device is turned off and the transceiver device is turned on, at this time the drive motor is at zero position, the reflected laser on the wall laser foot point is marked as E, and the angle ∠AOE between OA and OE is measured by using the total station instrument. When the E point is in the counterclockwise direction of the A point, the azimuth angle Ψ = ∠AOE, and when the E point is in the clockwise direction of the A point, the azimuth angle Ψ = 360°-∠AOE.

[0219] For example, the present embodiment collects ∠AOE = 2.085°, and the E point is in the clockwise direction of the A point, so the azimuth angle Ψ = 357.915°.

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

[0221]

[0222] Combining Figure 5 The change of the azimuth angle with the drive motor rotation angle is illustrated, the azimuth angle and the drive motor rotation angle are positively correlated, and the domain and the value domain are one-to-one corresponding. The actual drive motor rotation angle θ when the laser foot point falls to the E point is obtained by substituting the measured azimuth angle Ψ into the above formula. When the E point is in the counterclockwise direction of the A point, the error value Δθ of the drive motor rotation angle is θ, and when the E point is in the clockwise direction of the A point, the error value Δθ of the drive motor rotation angle is θ-360°.

[0223] For example, the actual drive motor rotation angle θ = 358.422° is obtained by substituting the normal line of the reflector and the drive motor rotation shaft angle α = 4.024° and the azimuth angle Ψ = 357.915° into the above formula, and since the E point is in the clockwise direction of the A point, the error value Δθ of the drive motor rotation angle is -1.578°.

[0224] The above steps are repeated 5 times to obtain 5 groups of drive motor rotation angle error values, and the average of the 5 groups of drive motor rotation angle error values is taken to obtain the error value Δθ of the drive motor rotation angle:

[0225]

[0226] Wherein, Δθ iThe error value of the driving motor rotation angle obtained for the ith measurement.

[0227] For example, Table 5 is five groups of driving motor rotation angle error values collected in the embodiment, and the error value of the driving motor rotation angle is calculated by substituting the data in Table 5 into the above formula: Δθ = -1.586°.

[0228] Table 5

[0229]

[0230] Considering the error, the actual driving motor rotation angle is:

[0231]

[0232] wherein θ is the driving motor rotation angle measured by the laser radar angle encoder, is the error-corrected driving motor rotation angle, when , when ,

[0233] Embodiment 2:

[0234] In combination with Figure 6 a kind of egg-shaped scanning type airborne depth-finding laser radar internal error step calibration device provided by the present application, comprising:

[0235] M1: laying module, for laying airborne depth-finding laser radar and total station in calibration field;

[0236] M2: first acquisition module, for obtaining the distance solution value of wall surface laser foot point based on laser radar;

[0237] M3: second acquisition module, for obtaining the distance observation value between two points and the included angle formed by three point lines based on total station;

[0238] M4: first calculation module, for calculating laser ranging error;

[0239] M5: second calculation module, for calculating collimation axis error;

[0240] M6: third calculation module, for calculating driving motor rotation angle error.

[0241] The above-described specific embodiments further detail the purposes, technical solutions and beneficial effects of the present application. It should be understood that the above-described specific embodiments are merely examples of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application.

Claims

1. A step-by-step calibration method for internal errors of an oval-shaped scanning airborne depth sounding lidar, characterized in that, The method includes: The airborne depth-sounding lidar is mounted on a tripod, and the lidar's rotating mirror transceiver and scanning device are turned on to illuminate a complete laser scanning trajectory on a flat wall surface. Set up the prism-free total station on the tripod and level it; Calibrate laser ranging error, including: The center point of the lidar 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 sequence is: ABCD, and the center point of the total station is marked as G. Turn off the lidar transceiver and rotating mirror scanning device, manually rotate the reflector, turn on the transceiver every 30°, collect waveform data and perform waveform detection to obtain the calculated distance value, and at the same time use the total station to measure the observation distance from the center of the reflector to the laser foot point on the wall. Let the calculated distance value s = [s1, s2, ... , s 12 ] T The corresponding observation distance value is S′ = [S1′,S2′, ... , S 12 ′] T ; The formula for calculating the distance value is: ； Where c is the speed of laser propagation in air, and ∆t is the propagation time of laser in air obtained by waveform detection; right Add error and constant K: ； The initial value of the error constant K is set as the negative of the internal optical path design length of the lidar. Linearize the above equation to establish the error equation: ； Rewrite the above equation in matrix form: ； in, ; There are a total of 12 laser feet, then ； For each laser foot point ; Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed: ； Solving the above equation, we get: ； Substitute S and S′ into The correction ΔK to K is calculated. Update the error plus constant based on ΔK: ； Recalculate S based on 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 ΔK. Then update the error correction K again, and repeat this process until... ; Taking into account errors, the distance value calculated by the lidar is: ； Calibrate the line of sight error; Calibrate the rotation angle error of the drive motor.

2. The method for step-by-step calibration of internal errors of an oval-shaped scanning airborne depth-sounding lidar as described in claim 1, characterized in that, The calibration line-of-sight error includes: The line-of-sight error includes the angle error between the mirror normal and the drive motor shaft and the angle error between the incident ray and the drive motor shaft; A laser scanning reference coordinate system O-XYZ is established with the center of the reflector as the origin. The X-axis is the opposite direction of the incident light ray, the Y-axis is the flight direction, and the Z-axis forms a right-handed system with the X and Y axes. The rotation angle of the drive motor is defined as θ, the angle between the normal of the reflector and the axis of the drive motor is defined as α, the angle between the incident light ray and the axis of the drive motor is defined as β, and the direction vector of the normal of the reflector in the O-XYZ coordinate system is: ； From the above formula, the angles between the projections of the reflected rays on the XZ and YZ planes and the Z-axis are respectively: ； ； Define the angle between the reflected ray and the vertically downward direction as the scanning angle, and calculate the scanning angle according to the above formula. : ； The azimuth angle is defined as the angle between the line connecting the laser foot point and the center point of the laser scanning trajectory and the positive X-axis. When the line connecting the center of the laser scanning trajectory and the center of the reflector is perpendicular to the target plane, the azimuth angle is calculated based on the angle between the projection of the reflected light rays onto the XZ and YZ planes and the Z-axis. : ； Based on the distance value S calculated by the laser radar, the projection of the reflected light onto 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 lidar transceiver and rotating mirror scanning device, manually rotate the reflector to make the laser endpoints fall sequentially at points A, B, C, and D, turn on the transceiver, collect waveform data, and after waveform detection, eliminate laser ranging errors to obtain the calculated distance value S. A S B S C S D The drive motor rotation angles are 0°, 90°, 180°, and 270°. Substituting the calculated distance value and the drive motor rotation angle into the above formula, the coordinates of points A, B, C, and D in the laser scanning reference coordinate system are obtained as [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 of the reflector and the shaft of the drive motor is designed to be 5°, and the angle between the incident ray and the shaft of the drive motor is designed to be 45°. Therefore, 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 following table in sequence. The distance H between AB is calculated separately. 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 was measured using the total station. AB AC is far from H′ AC AD is far from H′ AD BC is far from H′ BC BD is far from H′ BD CD is far from 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}; Linearize the distance calculation formula to establish an error equation: ； Rewrite the above equation in matrix form: ； in, ; There are a total of 6 laser feet, then ； For each laser foot point ; Based on the principle of least squares indirect adjustment, the normal equation of the error equation is listed: ； Solving the above equation, we get: ； Substitute H and H′ into The corrections Δα and Δβ for α and β are calculated. Based on Δα and Δβ, update the angle between the mirror normal and the drive motor axis and the angle between the incident ray and the drive motor axis: ； ； Based on the updated angle α between the mirror normal and the drive motor shaft and the angle β between the incident ray and the drive motor shaft, H is recalculated, then B and L are recalculated. Then, based on the least squares indirect adjustment principle, the normal equation of the error equation is solved to obtain the corrections Δα and Δβ. α and β are then updated again, and this process is repeated until... and ; Calculate the angle error between the normal of the reflector and the shaft of the drive motor based on the design and measurement values: ； Wherein, α is the angle between the mirror normal and the drive motor shaft, which is calculated in the final step; Calculate the angle error between the incident ray and the drive motor shaft based on the design and measurement values: ； Wherein, β is the angle between the incident ray and the drive motor shaft, which is calculated in the final step.

3. The method for step-by-step calibration of internal errors of an oval-shaped scanning airborne depth-sounding lidar as described in claim 1, characterized in that... The calibration drive motor angle error includes: The steps for adjusting the position of the lidar so that the line OP connecting the center of the laser scanning trajectory and the center of the reflector is perpendicular to the wall, and calibrating the rotational error of the drive motor are as follows: The lidar rotating mirror scanning device is turned off, and the transceiver device is turned on. At this time, the drive motor is in the zero position, and the reflected laser is marked as E on the laser foot point on the wall. The angle between OA and OE was measured using the total station. ; When point E is counterclockwise from point A, the azimuth angle When point E is clockwise from point A, the azimuth angle is... ; According to the azimuth angle calculation formula, given the angle α between the normal of the reflector and the shaft of the drive motor, the azimuth angle calculation formula is expressed as follows: ； The measured azimuth angle Substituting into the above formula, we obtain the actual drive motor rotation angle θ when the laser foot point lands at point E. When point E is counterclockwise from point A, the error value of the drive motor rotation angle is... When point E is clockwise from point A, the error value of the drive motor's rotation angle is... ; 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. : ； in, This represents the error value of the drive motor rotation angle obtained from the i-th measurement; Taking into account the error, the actual rotation angle of the drive motor is: ； Where θ is the drive motor rotation angle measured by the lidar angle encoder. The angle of the drive motor after error correction, when hour, ,when hour, .

4. An oval-shaped scanning airborne depth sounding lidar internal error step-by-step calibration device, used to implement the error step-by-step calibration method as described in any one of claims 1-3, characterized in that, The device includes: The first deployment module is used to deploy airborne depth-sounding lidar and total station within the calibration field; The first acquisition module is used to acquire the distance calculation value of the laser foot point on the wall based on the lidar; The second acquisition module is used to acquire the distance observation value between two points and the included angle formed by the line connecting the three points based on the total station; The first calculation module is used to calculate the laser ranging error; The second calculation module is used to calculate the line-of-sight error; The third calculation module is used to calculate the rotational angle error of the drive motor.

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