Method for Solving Multiple Echoes in the Air by Lidar Based on Distance and Reflectivity Constraints

Abstract

The present invention discloses a method for resolving multiple echoes in the air of a lidar based on distance and reflectivity constraints. Geometric calibration equations and radiation calibration equations of a mapping lidar are respectively established to correct the distance measurement indication value, angle measurement indication value, amplitude, and relative reflectivity of each echo. The time-of-flight principle is used to determine the time interval of the farthest laser echo. According to the laser emission repetition frequency, the number of main laser emission waves existing within the time interval of the farthest laser echo is determined. Then, adjacent consecutive scanning points in the pitch and azimuth directions are respectively determined according to the scanning pitch angle and azimuth angle. Finally, the continuity of the main emission wave is judged, and based on the geometric and radiation continuity between adjacent consecutive scanning points, the continuity noise energy is calculated using the ranging result and relative reflectivity result of each echo, and the continuity noise function corresponding to each MTA is obtained. A robust non-linear optimization model is constructed and optimized to solve. The present invention can achieve accurate calculation of the MTA time.

Description

Technical Field

[0001] The present invention belongs to the field of three-dimensional lidar point cloud acquisition, and particularly relates to a method for resolving multi-echo in the air of a lidar based on distance and reflectivity constraints. Background Art

[0002] Multi-Time-Around (MTA) in lidar measurement is defined as the echo received after the time delay exceeds a multiple of the pulse repetition interval. As the effective range of mapping lidar becomes farther and the laser emission repetition frequency becomes higher, the consistency of high-density three-dimensional point clouds is a basic requirement for data quality in high-precision mapping. The long distance and high repetition frequency bring the inevitable problem of time ambiguity caused by multi-echo in the air during lidar measurement, that is, within the laser flight time corresponding to the range, the lidar has emitted multiple main waves, and there are multiple echoes in the air, resulting in time ambiguity where the echo cannot be directly corresponded to the main wave, leading to the loss of consistency in the distribution of target three-dimensional point clouds within the same scan line and between adjacent scan lines. Only by determining the emitted main wave corresponding to each echo can the laser flight time of this measurement be resolved and the target distance be accurately measured.

[0003] The MTA problem is actually the ranging problem of lidar. The laser pulls the points in the distance to the near wrongly, resulting in the point clouds in the distance becoming noise in the near point clouds. The MTA problem will bring great difficulties to subsequent data processing, target automatic detection and recognition, map making and other technological processes, leading to errors in recognition and manual processes.

[0004] In the real world, most objects, whether natural objects such as vegetation and soil or artificial objects such as roads, signs, and buildings, have surface continuity, and generally there will be no drastic changes in distance, texture, and reflectivity in the adjacent areas.

[0005] Currently, when solving the time ambiguity problem of multi-echo in the air of lidar, most methods are based on spatial continuity and do not consider the inherent measurement deviation of the instrument. The accuracy and robustness during lidar mapping for longer distances, higher laser emission repetition frequencies, and denser point clouds are affected. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides a method for resolving multi-echo in the air of a lidar based on distance and reflectivity constraints. On the basic premise of the surface continuity of the scanned target, the inherent measurement error of the lidar instrument itself will be calibrated before resolving MTA, including:

[0007] (1) Geometric calibration, establishing a calibration model of distance and angle during lidar scanning measurement to improve the geometric accuracy of each measurement;

[0008] (2) Radiation calibration to establish a calibration model for the measured amplitude and reflectivity of the lidar, improving the radiation accuracy of each measurement;

[0009] (3) Use the geometric and radiation continuity of the target surface to perform MTA calculation.

[0010] The object of the present invention is achieved by the following technical solutions:

[0011] A lidar multi-echo resolution method in the air based on distance and reflectivity constraints, the method comprising the following steps:

[0012] S1: Establish a geometric calibration equation for the mapping lidar to correct the distance measurement indication value and angle measurement indication value of each echo;

[0013] S2: Establish a radiation calibration equation for the mapping lidar to correct the amplitude and relative reflectivity of each echo;

[0014] S3: According to the corrected distance measurement indication value of each echo of the mapping lidar, use the time-of-flight principle to determine the time interval of the farthest laser echo;

[0015] S4: According to the laser emission repetition frequency of the mapping lidar, determine the number of main laser emission waves existing within the time interval of the farthest laser echo;

[0016] S5: Determine adjacent consecutive scan points in the pitch direction according to the scan pitch angle; determine adjacent consecutive scan points in the azimuth direction according to the scan azimuth angle;

[0017] S6: According to the adjacent consecutive scan points in the pitch direction and azimuth direction, judge the continuity of the main emission wave. When the main emission wave is a continuous main wave, use the ranging result and relative reflectivity result of each echo of the mapping lidar, based on the geometric and radiation continuity between adjacent consecutive scan points, calculate the continuity noise energy, obtain the continuity noise function corresponding to each multi-echo in the air, construct a robust non-linear optimization model and perform optimization and solution to complete the solution of the multi-echo problem in the air.

[0018] Further, the specific content of S1 includes:

[0019] According to the ranging principle of the mapping lidar, referring to the distance correction technology of the laser rangefinder, establish a lidar distance measurement correction equation and calculate the corrected distance measurement indication value R m :

[0020] R m = R 0 + a R ·R 0 + b R

[0021] In the formula, R 0 is the distance from the original measurement indication value, a R is the ranging multiplication constant, and b R is the ranging addition constant; by referring to the distance calibration technology of the electro-optical distance measuring instrument for ranging indication calibration, a R and b R are obtained;

[0022] According to the scanning angle measurement principle of the surveying and mapping lidar, referring to the angle correction technologies of the theodolite and total station, a lidar angle measurement correction equation is established, including the pitch angle correction equation and the azimuth angle correction mathematical equation, and the corrected pitch angle and azimuth angle are calculated:

[0023] θ m = θ 0 + a θ ·θ 0 + b θ

[0024] In the formula, θ m is the original measurement indication value of the pitch angle, a θ is the pitch angle multiplication constant, and b θ is the pitch angle addition constant; by referring to the pitch angle calibration technology of the electro-optical goniometer for pitch angle measurement indication calibration, a θ and b θ are obtained;

[0025]

[0026] In the formula, is the original measurement indication value of the azimuth angle, is the collimation axis correction constant of the azimuth angle, is the trunnion correction constant of the azimuth angle; by referring to the azimuth angle calibration technology of the electro-optical goniometer for azimuth angle measurement indication calibration, and

[0027] Furthermore, the S2 specifically includes:

[0028] According to the detection response principle of the surveying and mapping lidar, referring to the photoelectric sensing detection technology, a lidar echo amplitude correction equation is established, and the corrected echo amplitude is calculated:

[0029]

[0030] In the formula, P echo is the echo response power, and P DL is the minimum detectable power of the surveying and mapping lidar system;

[0031] According to the detection response principle of the surveying and mapping lidar, based on the relationship between the detection response amplitude of the laser detection system and the relative reflectivity, a calibrated standard diffuse reflection whiteboard is used as the traceability reference for the relative reflectivity standard of the lidar, and the relative reflectivity correction equation of the lidar echo is established:

[0032] ρ rel =A mp_echo -A mp_ref (R m )

[0033] In the formula, A mp_echo is the echo amplitude, and A mp_ref (R m ) is the echo amplitude of the reference diffuse reflection whiteboard at the distance R m .

[0034] Furthermore, the calculation formula for the time interval ΔT max of the farthest laser echo is as follows:

[0035]

[0036] where c is the speed of light.

[0037] Furthermore, the calculation formula for the number N of the main laser emission waves existing within the time interval of the farthest laser echo in the S4 is as follows:

[0038] N = ΔT max ·PRR

[0039] In the formula, PRR is the laser emission repetition frequency.

[0040] Furthermore, the S5 specifically includes:

[0041] Continuity judgment is performed through the corrected pitch angle measurement indication value θ m to obtain the spatially adjacent points within a scan line. If |θ m,i -θ m,i-1 | = θ m,res , it is judged as the adjacent points continuous in the pitch direction, where θ m,res is the pitch angle measurement resolution of the lidar;

[0042] Continuity judgment is performed through the corrected azimuth angle measurement indication value to obtain the spatially continuous points between adjacent scan lines. If then it is judged as the adjacent points continuous in the azimuth direction, where, is the azimuth angle measurement resolution of the surveying and mapping lidar.

[0043] Furthermore, the S6 specifically includes:

[0044] S6.1: Based on the obtained number N of the main laser emission waves, construct the corrected distance vectors R corresponding to the possible multiple echoes in the air for each echo m_MTA,j and the relative reflectivity vectors ρ rel_MTA,j :

[0045] R m_MTA,j =[R m_1 R m_2 ...R m_N

[0046] ρ rel_MTA,j =[ρ rel_1 ρ rel_2 ...ρ rel_N

[0047] In the formula, j corresponds to the number of multiple echoes in the air obtained by calculating S4, and j ≤ N;

[0048] S6.2: Construct the distance continuity noise vector ΔR m_MTA,J and the relative reflectivity continuity noise vector Δρ rel_MTA,J :

[0049] ΔR m_MTA,J =[R m_2 -R m_1 R m_3 -R m_2 ...R m_N -R m_N-1

[0050] Δρ rel_MTA,J =[ρ 2 -ρ 1 ρ 3 -ρ 2 ...ρ N -ρ N-1

[0051] S6.3: Use the elements in the distance continuity noise vector ΔR m_MTA,J as the weight factors of the non-linear weighting function to construct the distance non-linear weighting kernel function Use the elements in the relative reflectivity continuity noise vector Δρ rel_MTA,J as the weight factors of the non-linear weighting function to construct the relative reflectivity non-linear weighting kernel function

[0052]

[0053] In the formula, a 1 , b 1 , c 1 are the coefficients of the distance non-linear weighting kernel function, a 2 , b​​​​2 , c 2 is the coefficient of the relative reflectivity non - linear weighted kernel function, where i ≤ N - 1.

[0054] S6.4: Use the distance non - linear weighted kernel function as the weight to calculate the distance continuity noise energy model Use the relative reflectivity non - linear weighted kernel function as the weight to calculate the reflectivity continuity noise energy model

[0055]

[0056] In the formula, l is the size of the neighborhood calculation block, and k is the number of neighborhoods divided according to l;

[0057] S6.5: According to the characteristics of the maximum laser emission repetition rate PRR and high scanning density of the mapping lidar, there is a similarity between the distance and the reflectivity among spatially adjacent scanning points. When the continuity noise energy is the smallest, the MTA solution result is obtained and

[0058] S6.6: Judge and Are they equal:

[0059] If and are equal, the solution is completed, and the multiple echoes in the air corresponding to the laser echo are the results obtained in S6.5;

[0060] If and are not equal, adjust the coefficients of the distance non - linear weighted kernel function and the relative reflectivity non - linear weighted kernel function in S6.3, and return to S6.4.

[0061] A lidar air multiple - echo solution device based on distance and reflectivity constraints, characterized in that it includes one or more processors for implementing the lidar air multiple - echo solution method based on distance and reflectivity constraints.

[0062] An electronic device, including:

[0063] One or more processors;

[0064] A storage device for storing one or more programs, which when executed by the electronic device, enable the electronic device to implement the lidar air multiple - echo solution method based on distance and reflectivity constraints.

[0065] A computer - readable storage medium, on which a program is stored, and when the program is executed by a processor, it implements the lidar air multiple - echo solution method based on distance and reflectivity constraints.

[0066] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0067] The multi-echo resolution method for airborne lidar based on distance and reflectivity constraints of the present invention constructs spatial continuity noise based on dual constraints of distance and reflectivity, and uses a non-linear weighting function to non-linearly amplify the influence of the continuity noise, greatly improving the sensitivity of the weighting function to slight changes in the continuity noise; calibrates and corrects the lidar distance, angle, and reflectivity, improves the measurement consistency of the original data from the aspect of basic data attributes, and ensures the calculation accuracy and robustness after final non-linear weighting, thereby achieving high-precision resolution of the multi-echo time in the air of the mapping lidar at long operating distances and high laser emission repetition frequencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is a flowchart of the multi-echo resolution method for airborne lidar based on distance and reflectivity constraints of the present invention.

[0069] Figure 2 is a schematic diagram of MTA at a constant laser emission repetition frequency.

[0070] Figure 3 is a schematic diagram of the scanning pitch direction of the lidar and each spatial continuous point.

[0071] Figure 4 is a schematic diagram of the distance continuity of adjacent points on the scanned surface.

[0072] Figure 5 is a schematic diagram of the specific implementation process of step S6.

[0073] Figure 6 is a schematic diagram of the neighborhood block size and the number of blocks during MTA resolution. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] In order to further illustrate the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following is a description of the implementation manner in conjunction with the accompanying drawings.

[0075] The foregoing and other technical contents, features, and effects of the present invention can be clearly presented in the following detailed description of the specific implementation manner in conjunction with the accompanying drawings. Through the description of the specific implementation manner, a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose can be obtained. However, the accompanying drawings are only for reference and illustration, and are not used to limit the technical solution of the present invention.

[0076] The multi-echo resolution method for airborne lidar based on distance and reflectivity constraints in this embodiment has a flowchart as shown in Figure 1As shown below: First, perform measurement indication corrections related to the target set and radiation properties, including distance, angle, amplitude, and relative reflectivity, ensuring the consistency and accuracy of the measurement results; perform neighborhood division to determine adjacent laser scanning points; calculate the statistical weights of the feature parameters of adjacent points for different MTAs. The feature parameters include distance and reflectivity; determine the true MTA according to the results of the weight function. Specifically, it includes the following steps:

[0077] S1: Establish a geometric calibration equation for the mapping lidar, and correct the distance measurement indication and angle measurement indication of each echo;

[0078] Specifically, S1 includes:

[0079] According to the ranging principle of the mapping lidar, referring to the existing distance correction technology of laser rangefinders, establish a mathematical model for correcting the measured distance of the lidar;

[0080] And calculate the corrected distance measurement indication R m :

[0081] R m = R 0 + a R ·R 0 + b R

[0082] In the formula, R 0 is the original distance measurement indication, a R is the ranging multiplication constant, b R is the ranging addition constant; calibrate the ranging indication by referring to the distance calibration technology of electro-optical rangefinders to obtain a R and b R ;

[0083] According to the scanning angle measurement principle of the mapping lidar, referring to the angle correction technologies of the theodolite and total station, establish an angle measurement correction equation for the lidar, including the pitch angle correction equation and the azimuth angle correction mathematical equation, and calculate the corrected pitch angle and azimuth angle:

[0084] θ m = θ 0 + a θ ·θ 0 + b θ

[0085] In the formula, θ m is the original pitch angle measurement indication, a θ is the pitch angle multiplication constant, b θ is the pitch angle addition constant; calibrate the pitch angle measurement indication by referring to the pitch angle calibration technology of electro-optical goniometers to obtain a θ and b θ ;

[0086]

[0087] Wherein, is the original measured value of the azimuth angle, is the collimation axis correction constant of the azimuth angle, is the trunnion correction constant of the azimuth angle; by referring to the azimuth angle calibration technology of the optoelectronic theodolite, the calibration of the measured value of the azimuth angle is carried out to obtain and

[0088] S2: Establish a radiation calibration equation for the mapping lidar, and correct the amplitude and relative reflectivity of each echo.

[0089] Specifically, S2 includes:

[0090] According to the detection response principle of the mapping lidar, referring to the existing optoelectronic sensing detection technology, establish an echo amplitude correction equation for the lidar, and calculate the corrected echo amplitude:

[0091]

[0092] Wherein, P echo is the echo response power, and P DL is the minimum detectable power of the mapping lidar system;

[0093] According to the detection response principle of the mapping lidar, based on the relationship between the detection response amplitude and the relative reflectivity of the laser detection system, use a calibrated standard diffuse reflection whiteboard as the traceability reference for the relative reflectivity standard of the lidar, and establish a relative reflectivity correction equation for the lidar echo:

[0094] ρ rel = A mp_echo - A mp_ref (R m )

[0095] Wherein, A mp_ref (R m ) is the echo amplitude of the reference diffuse reflection whiteboard at a distance R m .

[0096] S3: According to the corrected distance measurement value of each echo of the mapping lidar, use the time-of-flight principle to determine the time interval ΔT max :

[0097]

[0098] where c is the speed of light.

[0099] S4: Determine the number N of main laser emission waves present within the time interval ΔT of the farthest laser echo according to the pulse repetition rate PRR of the mapping lidar. max Therein:

[0100] N = ΔT max ·PRR

[0101] Figure 2 A schematic is given in, where i represents the main emission wave, j represents the echo, τ is the emission repetition period, and T m,MTA1 , T m-1,MTA2 , T m-2,MTA3 , T m-2,MTA4 are respectively the times of four different MTAs corresponding to the echo j. N is the number of main laser emission waves and is also the number of multiple echoes (MTA) in the air.

[0102] S5: Determine adjacent consecutive scan points in the pitch direction according to the scan pitch angle; determine adjacent consecutive scan points in the azimuth direction according to the scan azimuth angle.

[0103] Figure 3 A schematic of adjacent consecutive scan points in the pitch direction is given in, and the determination method specifically includes:

[0104] Perform continuity judgment through the corrected pitch angle measurement indication value θ m to obtain spatially adjacent points within a scan line. If |θ m,i -θ m,i-1 | = θ m,res , then it is judged as adjacent consecutive points in the pitch direction, where θ m,res is the pitch angle measurement resolution of the lidar, which is a fixed parameter of the mapping lidar system.

[0105] Figure 4 A schematic of adjacent consecutive scan points in the azimuth direction is given in, and the determination method specifically includes:

[0106] Perform continuity judgment through the corrected azimuth angle measurement indication value to obtain spatially continuous points within adjacent scan lines. If then it is judged as adjacent consecutive points in the azimuth direction, where is the azimuth angle measurement resolution of the mapping lidar, which is a fixed parameter of the mapping lidar system.

[0107] S6: Based on adjacent consecutive scan points in the pitch direction and azimuth direction, perform continuity judgment on the transmitted main wave. When the transmitted main wave is a continuous main wave, use the ranging result and relative reflectivity result of each echo of the mapping lidar. Based on the geometric and radiation continuity between adjacent consecutive scan points, calculate the continuity noise energy, obtain the continuity noise function corresponding to each multi-echo in the air, construct a robust non-linear optimization model and perform optimization and solution to complete the solution of the multi-echo problem in the air.

[0108] As Figure 2 shown, determine Figure 2 that the transmitted main wave in Figure 4 is a continuous main wave.

[0109] Specifically, as Figure 5 shown, S6 includes:

[0110] S6.1: According to the obtained number N of laser transmitted main waves, respectively construct the corrected distance vector R m_MTA,j and relative reflectivity vector ρ rel_MTA,j corresponding to each possible MTA of each echo:

[0111] R m_MTA,j = [R m_1 R m_2 ... R m_N

[0112] ρ rel_MTA,j = [ρ rel_1 ρ rel_2 ... ρ rel_N

[0113] In the formula, j corresponds to the number of multi-echoes (MTA) in the air calculated in S4, and j ≤ N.

[0114] S6.2: According to S6.1, respectively construct the distance continuity noise vector ΔR m_MTA,J and relative reflectivity continuity noise vector Δρ rel_MTA,J :

[0115] ΔR m_MTA,J = [R m_2 - R m_1 R m_3 - R m_2 ... R m_N - R m_N-1

[0116] Δρ rel_MTA,J = [ρ 2 - ρ 1 ρ 3 - ρ 2 ... ρN -ρ N-1

[0117] S6.3: Use the elements in the distance continuity noise vector ΔR m_MTA,J as the weight factors of the non - linear weighting function to construct the distance non - linear weighted kernel function Use the elements in the relative reflectivity continuity noise vector Δρ rel_MTA,J as the weight factors of the non - linear weighting function to construct the relative reflectivity non - linear weighted kernel function

[0118]

[0119] where a 1 、b 1 、c 1 are the coefficients of the distance non - linear weighted kernel function, and a 2 、b 2 、c 2 are the coefficients of the relative reflectivity non - linear weighted kernel function, i ≤ N - 1.

[0120] S6.4: Use the distance non - linear weighted kernel function as the weight to calculate the distance continuity noise energy Use the relative reflectivity non - linear weighted kernel function as the weight to calculate the reflectivity continuity noise energy

[0121]

[0122] where l is the size of the neighborhood calculation block, k is the number of neighborhoods divided according to l, and the schematic diagrams of l and k are as shown in Figure 6 shown.

[0123] S6.5: According to the characteristics of the maximum laser emission repetition rate PRR and high scanning density of the mapping lidar, there is a similarity between the distance and reflectivity among spatially adjacent scanning points. When the continuity noise energy is the smallest, the MTA solution result is obtained and

[0124] S6.6: Judge and whether they are equal:

[0125] If and are equal, the solution is completed, and the MTA corresponding to the laser echo is the result obtained in S115;

[0126] If and ​If they are not equal, adjust the distance non - linear weighted kernel function coefficient and the relative reflectivity non - linear weighted kernel function coefficient in S6.3, and return to S6.4.

[0127] It should be noted that the reference technologies adopted in the present invention, including the distance correction technology of electro - optical rangefinders, the angle correction technology of electro - optical goniometers, the lidar detection equation, and the reflectivity calibration technology of electro - optical detection systems, are all mature methods in the prior art, and the specific steps will not be elaborated here.

[0128] The multi - echo resolution method of mapping lidar in the air in this embodiment establishes a method for constructing spatial continuity noise based on double constraints of distance and reflectivity. Using the non - linear weighted function, the influence of continuity noise is non - linearly amplified, greatly improving the sensitivity of the weighted function to slight changes in continuity noise. The lidar distance, angle, and reflectivity are all calibrated and corrected, improving the measurement consistency of the original data from the aspect of basic data attributes, ensuring the final non - linear weighted resolution accuracy and robustness, and thus realizing the high - precision resolution of the multi - echo time of mapping lidar in the air at long working distances and high laser emission repetition frequencies.

[0129] Corresponding to the foregoing embodiment of the lidar multi - echo resolution method in the air based on distance and reflectivity constraints, the present invention also provides an embodiment of a lidar multi - echo resolution device based on distance and reflectivity constraints.

[0130] The lidar multi - echo resolution device based on distance and reflectivity constraints provided by the embodiment of the present invention includes one or more processors for implementing the lidar multi - echo resolution method based on distance and reflectivity constraints in the above - mentioned embodiment.

[0131] The embodiment of the lidar multi - echo resolution device based on distance and reflectivity constraints of the present invention can be applied to any device with data - processing capabilities, and this any device with data - processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented by software, or by hardware, or by a combination of software and hardware. Taking software implementation as an example, as a logically meaningful device, it is formed by the processor of any device with data - processing capabilities reading the corresponding computer program instructions in the non - volatile memory into the memory for operation. From the hardware level, in addition to the processor, memory, network interface, and non - volatile memory, any device with data - processing capabilities where the device in the embodiment is located usually also includes other hardware according to the actual functions of this any device with data - processing capabilities, which will not be elaborated here.

[0132] The implementation processes of the functions and roles of each unit in the above - mentioned device are specifically described in the implementation processes of the corresponding steps in the above - mentioned method, which will not be elaborated here.

[0133] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial descriptions of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the present invention. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0134] The embodiments of the present invention also provide a computer-readable storage medium, on which a program is stored. When the program is executed by a processor, the method for resolving multiple echoes in the air of a lidar based on distance and reflectivity constraints in the above embodiments is implemented.

[0135] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the foregoing embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be an external storage device, such as a plug-in hard disk, a SmartMedia card (SMC), an SD card, a Flash card, etc. equipped on the device. Further, the computer-readable storage medium may also include both an internal storage unit of any device with data processing capabilities and an external storage device. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and can also be used to temporarily store the data that has been output or will be output.

[0136] Those of ordinary skill in the art can understand that the above are only preferred examples of the invention and are not used to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, for those skilled in the art, they can still modify the technical solutions described in the foregoing examples or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, etc. made within the spirit and principle of the invention shall be included in the protection scope of the invention.

Claims

1. A method for solving multi-echoes in the air of a laser radar based on distance and reflectivity constraints, characterized in that: The method comprises the following steps: S1: Establish the geometric calibration equation of the surveying laser radar to correct the distance measurement indication and angle measurement indication of each echo; S2: Establish the mapping lidar radiation calibration equation to correct the amplitude and relative reflectivity of each echo; S3: Based on the distance measurement indication corrected by each echo of the mapping laser radar, the time interval of the farthest laser echo is determined using the time flight principle; S4: determining the number of laser emission main waves existing in the time interval of the farthest laser echo according to the laser emission repetition frequency of the surveying and mapping laser radar; S5: determining adjacent continuous scanning points in the pitch direction according to the scanning pitch angle; determining adjacent continuous scanning points in the azimuth direction according to the scanning azimuth angle; S6: According to the adjacent continuous scanning points in the pitch direction and azimuth direction, the continuity of the transmitted main wave is judged. When the transmitted main wave is a continuous main wave, the continuous noise energy is calculated based on the geometric and radiation continuity between the adjacent continuous scanning points using the ranging results and relative reflectivity results of each echo of the mapping laser radar, and the continuous noise function corresponding to each multi-echo in the air is obtained. A robust nonlinear optimization model is constructed and optimized to solve the multi-echo problem in the air. The S6 specifically includes: S6.1: Based on the number of laser emission main waves N, construct the corrected distance vector R corresponding to each possible multiple echo in the air m_MTA，j and the relative reflectivity vector ρ rel_MTA，j : R m_MTA，j =[R m_1 R m_2 … R m_N ]; r rel_MTA ,j=[ρ rel_1 r rel_2 … r rel_N ]; Where, j corresponds to the number of multi-echoes in the air obtained by calculating S4, and j≤N; S6.2: Construct the distance continuity noise vector ΔR respectively m_MTA，J and the relative reflectivity continuity noise vector Δρ rel_MTA,J : ΔR m_MTA,J =[R m_2 -R m_1 R m_3 -R m_2 … R m_N -R m_N-1 ]; Dr. rel_MTA,J =[ρ rel_2 -r rel_1 r rel_3 -r rel_2 … r rel_N -r rel_N-1 ]; S6.3: The distance continuity noise vector ΔR m_MAT,J The elements in are used as weight factors of the nonlinear weighted function to construct the distance nonlinear weighted kernel function The relative reflectivity continuity noise vector Δρ rel_MTA,J The elements in are used as weight factors of the nonlinear weighting function to construct the relative reflectivity nonlinear weighted kernel function Where a1, b1, c1 are the coefficients of the nonlinear weighted kernel function of distance, a2, b2, c2 are the coefficients of the nonlinear weighted kernel function of relative reflectivity, i≤N-1; S6.4: Using the distance nonlinear weighted kernel function as the weight to calculate the distance continuity noise energy model The nonlinear weighted kernel function of relative reflectivity is used as the weight to calculate the reflectivity continuity noise energy model In the formula, l is the size of the neighborhood calculation block, and k is the number of neighborhoods divided according to l; S6.5: Based on the characteristics of the maximum laser emission repetition frequency PRR and high scanning density of the mapping laser radar, there is a similarity between the distance and reflectivity between adjacent scanning points in space. When the continuous noise energy is minimized, the MTA solution result is obtained. and S6.6: Judgment and Are they equal? like and If they are equal, the solution is completed, and the multi-echo in the air corresponding to the laser echo is the result obtained by S6.5; like and If they are not equal, adjust the coefficients of the distance nonlinear weighted kernel function and the relative reflectivity nonlinear weighted kernel function in S6.3, and return to S6.

4.

2. The method for solving multi-echo aerial laser radar based on distance and reflectivity constraints according to claim 1 is characterized in that: The S1 specifically includes: According to the distance measurement principle of surveying laser radar, referring to the distance correction technology of laser rangefinder, the laser radar distance measurement correction equation is established, and the corrected distance measurement indication R is calculated. m : R m =R0+a R ·R0+b R ; Where R0 is the original measured value of the distance, a R is the distance multiplication constant, b R is the distance measurement constant; by referring to the distance calibration technology of the photoelectric rangefinder, the distance indication is calibrated to obtain a R and b R ; According to the scanning angle measurement principle of surveying laser radar, referring to the angle correction technology of theodolite and total station, the laser radar angle measurement correction equation is established, including the pitch angle correction equation and the azimuth angle correction mathematical equation, and the corrected pitch angle and azimuth angle are calculated: i m =θ0+a θ ·θ0+b θ ; Where θ0 is the original measured value of the pitch angle, a θ is the pitch angle multiplied by a constant, b θ is the pitch angle constant; the pitch angle measurement indication is calibrated by referring to the pitch angle calibration technology of the photoelectric goniometer, and a is obtained θ and b θ ; In the formula, is the original measurement indication of azimuth, is the azimuth collimation axis correction constant, is the azimuth trunnion correction constant; the azimuth measurement indication is calibrated by referring to the azimuth calibration technology of the photoelectric goniometer, and the and 3. The method for solving multi-echo in air of laser radar based on distance and reflectivity constraints according to claim 2 is characterized in that: The S2 specifically includes: According to the detection response principle of surveying and mapping laser radar, referring to the photoelectric sensing detection technology, the laser radar echo amplitude correction equation is established, and the corrected echo amplitude is calculated: Where P echo is the echo response power, P DL It is the minimum detectable power of the mapping lidar system; According to the detection response principle of surveying and mapping laser radar, based on the relationship between the detection response amplitude of the laser detection system and the relative reflectivity, a standard diffuse reflection whiteboard that has been calibrated by metrology is used as the traceability reference of the laser radar relative reflectivity standard, and the laser radar echo relative reflectivity correction equation is established: r rel =A mp_echo -A mp_ref (R m ); In the formula, A mp_echo is the corrected echo amplitude, A mp_ref (R m ) is the reference diffuse reflection white plate at a distance R m The echo amplitude at .

4. The method for solving multi-echo aerial laser radar based on distance and reflectivity constraints according to claim 3 is characterized in that: The time interval ΔT of the farthest laser echo max The calculation formula is as follows: Where c is the speed of light.

5. The method for solving multi-echo aerial laser radar based on distance and reflectivity constraints according to claim 4 is characterized in that: The calculation formula for the number N of laser emission main waves existing in the time interval of the farthest laser echo in S4 is as follows: N=ΔT max ·PRR; Where PRR is the laser emission repetition frequency.

6. The method for solving multi-echo aerial laser radar based on distance and reflectivity constraints according to claim 5 is characterized in that: The S5 specifically includes: By modifying the positive pitch angle measurement indication θ m Continuity judgment is performed to obtain the spatial proximity points within a scan line. If |θ m，i -θ m，i-1 |=θ m，res , then it is judged as a continuous adjacent point in the pitch direction, where θ m,res is the LiDAR elevation angle measurement resolution; The azimuth measurement indication is corrected Perform continuity judgment to obtain spatial continuous points between adjacent scan lines. If It is judged as a continuous adjacent point in the azimuth direction, where Azimuth measurement resolution for mapping lidar.

7. A laser radar aerial multi-echo solution device based on distance and reflectivity constraints, characterized in that: It comprises one or more processors for implementing the laser radar aerial multi-echo solution method based on distance and reflectivity constraints as described in any one of claims 1 to 6.

8. An electronic device, characterized in that: include: one or more processors; A storage device for storing one or more programs, which, when executed by the electronic device, enables the electronic device to implement the laser radar aerial multi-echo solution method based on distance and reflectivity constraints as described in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that: A program is stored thereon, and when the program is executed by a processor, the method for solving multi-echo aerial laser radar based on distance and reflectivity constraints as described in any one of claims 1 to 6 is implemented.

Images