Spherical target point cloud correction method and device for pulsed laser scanning

Abstract

The present invention discloses a spherical target point cloud correction method and device for pulsed laser scanning. Based on the intensity distribution of the laser spot and the geometric distribution characteristics of the laser spot on the spherical target attachment surface, a spherical target point cloud correction model is established, and correction is achieved according to the spherical target point cloud correction model. When establishing the spherical target point cloud correction model, according to the pulsed laser measurement principle, the distribution characteristics of the laser on the target surface are analyzed, and the spatial geometric relationship between the laser spot and the spherical target is constructed. The two-dimensional rasterization method of the spot is set to rasterize the spot into multiple sub-spots at equal angles in the radial and annular directions, and a unified ranging equation for the sub-spot is established accordingly, and a weight that satisfies the two-dimensional Gaussian distribution characteristics is assigned to each sub-spot ranging value, and a correction model is established in an integral accumulation manner. The present invention performs position correction on the point cloud on the surface of the spherical target, and then obtains more accurate point cloud coordinates, so as to facilitate high-precision fitting of the center of the spherical target.

Description

Technical Field

[0001] The present invention relates to the technical field of high-precision spherical target point cloud acquisition, and in particular to a spherical target point cloud correction technical solution for pulsed laser scanning. Background Art

[0002] Terrestrial 3D laser measurement is an advanced high-precision stereo measurement technology, also known as real-scene reproduction technology. It is widely used in tasks such as cultural relics protection, disaster monitoring, 3D reconstruction, and large-scale engineering measurement. The raw data measured is called point cloud, which is a collection of many discrete measurement points on the surface of the measured object. Terrestrial 3D laser scanners can be divided into phase type and pulse type according to their measurement principles. Pulse laser scanners use pulsed laser sources and use pulse flight time difference to measure distance. They are suitable for automatic measurement of large scenes, in which the confirmation of the pulsed laser echo signal time directly determines the accuracy of laser measurement. Existing studies have confirmed that both the target shape and the laser spot size will affect the laser echo signal. In the ranging of pulsed laser radar, traditional ranging methods include leading edge discrimination (LED), constant fraction discrimination (CFD), and peak discrimination (PD). Gaussian fitting method and centroid method are the most commonly used peak discrimination methods, which are widely used to confirm the echo peak moment of terrestrial 3D laser scanners. However, the geometric characteristics of the target surface will cause changes in waveform amplitude and width, thus affecting the actual ranging results.

[0003] A spherical target is a special target. Because it is rotationally invariant and does not require reorientation, it can obtain higher feature point accuracy and is often used as a feature primitive for high-precision registration of large scene point clouds. The laser scanning target obtains a point cloud on the surface of the spherical target, and the coordinates of the target center are solved as features using a spherical fitting algorithm. At present, the least squares method (LS), RANSAC, eSphere and other methods are commonly used to solve the spherical parameters (center coordinates and radius). However, in actual measurements, the target surface point cloud not only contains gross errors, but the target point cloud itself has measurement errors. These measurement errors are jointly affected by the laser echo time measurement method, the spot energy distribution, and the geometric characteristics of the target surface.

[0004] In summary, previous studies have mainly focused on the fitting method of existing target point clouds, and the original point cloud of the target also has certain measurement errors. In addition, the geometric characteristics of the target and the laser energy distribution will jointly affect the echo. Therefore, the present invention proposes a spherical target point cloud correction technology solution for pulsed laser scanning. Establishing an effective target point cloud three-dimensional correction model is the key to high-precision fitting of the target center. Summary of the invention

[0005] In view of the above problems, the present invention proposes a spherical target point cloud correction method for pulsed laser scanning, aiming to correct the position of the point cloud on the surface of the spherical target, obtain an accurate target point cloud, and then fit a more accurate target center to improve the registration accuracy between large scene point clouds.

[0006] In order to achieve the above-mentioned purpose, the technical solution proposed in the present invention provides a spherical target point cloud correction method for pulsed laser scanning, based on the intensity distribution of the laser spot and the geometric distribution characteristics of the laser spot on the attachment surface of the spherical target, a spherical target point cloud correction model is established, and correction is achieved according to the spherical target point cloud correction model; when establishing the spherical target point cloud correction model, according to the principle of pulsed laser measurement, the distribution characteristics of the laser on the target surface are analyzed, and the spatial geometric relationship between the laser spot and the spherical target is constructed, and the two-dimensional rasterization method of the spot is set to rasterize the spot into multiple sub-spots at equal angles in radial and circumferential directions, and a unified ranging equation for the sub-spot is established accordingly, and a weight satisfying the two-dimensional Gaussian distribution characteristics is assigned to the ranging value of each sub-spot, and the spherical target point cloud correction model is established in an integral accumulation manner.

[0007] Moreover, when the correction is implemented according to the spherical target point cloud correction model, the implementation process includes the following processing,

[0008] Preprocessing, including calculating the distance and azimuth of the target center in the scanning coordinate system by the target point cloud computing; taking the angle between the vector of the target edge and the vector of the target center in the scanning coordinate system as the limit measurement angle;

[0009] A single laser point in the target point cloud is selected for processing. First, the three Euler angles between the spot coordinate system and the scanning coordinate system are calculated, and the spot is rasterized, including dividing a laser beam into multiple sub-spots along the radial and circumferential directions, calculating the angle between the sub-spot and the laser measurement distance TC, and subtracting the angle from the limit measurement angle. If it is less than 0, the sub-spot participates in the calculation, otherwise it does not participate in the calculation; the weight of each sub-spot is calculated according to the energy distribution characteristics of the laser, and then the theoretical ranging value of the laser beam is calculated; then the ranging value of the laser center is calculated, and the ranging correction number of the laser point is calculated. If the ranging correction number is negative, the point is retained, otherwise it is deleted; then, the actual ranging value is corrected to obtain the corrected laser point coordinates;

[0010] The above processing is performed on all laser points on the target surface, and a new target point cloud set is output.

[0011] Moreover, during preprocessing, the average value of the azimuths of all points is taken as the azimuth of the target center, and the sum of the minimum value of the point cloud ranging value and the design radius of the target is taken as the distance of the target center in the scanning coordinate system.

[0012] Furthermore, let the position of any point P in the spot be expressed as (α, β), where β∈[0,360°], is the half divergence angle, and the following Gaussian distribution function is used to calculate the weight of each sub-spot according to the energy distribution characteristics of the laser:

[0013]

[0014] Among them, p(α,β) is the relative energy weight function of the sub-spot.

[0015] Moreover, let the laser emission point be T, the center of the sphere be O, the line connecting the laser emission point and the center of the sphere intersects the sphere at C, the intersection point of the laser spot center and the target is S, P is any point on the target surface within the spot, the radius of the target is R, the length of the laser measurement distance TC is l, the angle between ST and CT is θ, and the angle between PT and CT is θ P , the angle between SO and CO is ω, let ST = d s , calculate the distance value of the laser center according to the following formula,

[0016]

[0017] Furthermore, the theoretical distance measurement value of the laser beam is calculated according to the following correction model:

[0018]

[0019] Among them, D s is the theoretical laser distance measurement value.

[0020] Furthermore, the ranging correction for this point is calculated by the following formula:

[0021] d=d r +(d s -D s )

[0022] Among them, d is the corrected distance value, d r is the actual distance measured by the laser.

[0023] On the other hand, the present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the spherical target point cloud correction method for pulsed laser scanning as described above is implemented.

[0024] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for correcting a spherical target point cloud for pulsed laser scanning as described above is implemented.

[0025] On the other hand, the present invention also provides a computer program product, comprising a computer program, which, when executed by a processor, implements the spherical target point cloud correction method for pulsed laser scanning as described above.

[0026] Compared with the prior art, the present invention has the following differences and beneficial effects:

[0027] 1. The influence of the surface geometric characteristics of the spherical target on the point cloud measurement accuracy is theoretically analyzed, and the influence mechanism of the geometric characteristics of the target and the spot distribution on the ranging error is intuitively understood;

[0028] 2. A method of dividing a single laser spot into multiple sub-spots by two-dimensional rasterization is proposed, and the specific expression of the unified ranging equation for each sub-spot is derived. The correction equation of the actual measured point cloud on the surface of the spherical target is established by using the integral accumulation method;

[0029] 3. A spherical target point cloud correction method for pulsed laser scanning is proposed. The ranging correction value of the point cloud is calculated according to the distribution characteristics of each spot on the target surface and the orientation in the scanning coordinate system to obtain a more accurate target point cloud. This method establishes a correction model for the target point cloud by geometric deduction, improves the accuracy of the target point cloud, and facilitates fitting a more accurate target center.

[0030] The solution of the present invention is simple and convenient to implement, has strong practicality, solves the problems of low practicality and inconvenience in actual application existing in related technologies, can improve user experience, and has important market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the geometric relationship between the light spot and the target according to an embodiment of the present invention.

[0032] Figure 2 FIG. 4 is a schematic diagram of light spot rasterization according to an embodiment of the present invention.

[0033] Figure 3 Schematic diagram of the geometric relationship between the sub-spot and the laser beam in the measurement coordinate system in the unified ranging model of an embodiment of the present invention.

[0034] Figure 4 Schematic diagram of the position of sub-spots in the spot plane in the unified ranging model of an embodiment of the present invention.

[0035] Figure 5 A schematic diagram of energy distribution characteristics of a light spot provided by an embodiment of the present invention.

[0036] Figure 6 A flowchart provided for an embodiment of the present invention.

[0037] Figure 7A schematic diagram of the physical structure of an electronic device provided by an embodiment of the present invention.

[0038] Figure 8 It is a schematic diagram comparing the effects of the method of the embodiment of the present invention and the prior art method, wherein part (a) is the error of the fitting radius, part (b) is the mean error of the fitting sphere, and part (c) is the difference between the target spacing and the actual target baseline. DETAILED DESCRIPTION

[0039] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0040] The embodiment of the present invention provides a spherical target point cloud correction method for pulsed laser scanning, and the correction principle is as follows:

[0041] The target surface point cloud correction model is established, taking into account the intensity distribution of the laser spot and the geometric distribution characteristics of the spot on the attachment surface of the spherical target, so as to improve the fitting accuracy of the spherical target center, and realize the correction according to the spherical target point cloud correction model. In the process of establishing the target surface point cloud correction model, according to the principle of pulsed laser measurement, the distribution characteristics of the laser on the target surface are analyzed, and the spatial geometric relationship between the laser center and the spherical target is analyzed, and the two-dimensional rasterization method of the spot is set (the spot is rasterized into multiple sub-spots at equal angles in the radial and annular directions); a unified ranging equation for the sub-spot is established, and an energy weight function of a two-dimensional Gaussian distribution is established. The ranging value of each sub-spot is assigned a weight that satisfies the characteristics of the two-dimensional Gaussian distribution, and the theoretical laser ranging value is obtained by weighted averaging, and then a spherical target point cloud correction model is established. When correcting, the difference between the theoretical laser ranging value and the laser center ranging value is used as the ranging compensation value of the target surface point. The present invention overcomes the error existing in the target point cloud for determining the echo time based on the Gaussian method and the center of gravity method, performs position correction on the point cloud on the surface of the spherical target, and then obtains more accurate point cloud coordinates, so as to facilitate high-precision fitting of the center of the spherical target.

[0042] For the convenience of implementation reference, the following part of the specific correction implementation process of the embodiment is provided:

[0043] Ⅰ) Spatial geometric relationship between laser and spherical target.

[0044] Figure 1The geometric relationship of the light spot attached to the surface of the spherical target is shown. The laser emission point is T, the center of the sphere is O, the line connecting the laser emission point and the center of the sphere intersects the sphere at C, the intersection of the center of the laser spot and the target is S, and P is any point on the target surface within the spot. The radius of the target is R, the length of the laser measurement distance TC is l, the angle between ST and CT is θ, and the angle between PT and CT is θ P , the angle between SO and CO is ω. Let ST = d s , which can be obtained by solving formula (1).

[0045]

[0046] II) Gridding of light spots. The distance measurement value obtained by echo measurement can be equivalent to the integration of the distance measurement values ​​of multiple sub-spots inside the laser. The present invention proposes to grid the light spot in both radial and annular directions, and define the light spot of each grid unit as a sub-spot, such as Figure 2 This rasterization method can accurately refine and quantitatively describe the impact of the ranging values ​​of different areas of the laser spot on the overall ranging value of the laser.

[0047] In the embodiment, first, the light spot is divided into n concentric apertures along the radial direction of the light spot with a step size of Δα (n can be any positive integer, and n is preferably set to 15 in this embodiment), which are recorded as Δα1, Δα2, ... Δα n After that, each concentric aperture is divided into m area blocks along the annular direction with a step size of Δβ (m can be any positive integer, and m is preferably set to 36 in this embodiment), which are recorded as Δβ1, Δβ2, … Δβ m The position of any point P in the spot can be expressed as (α, β), where β∈[0,360°], is the half divergence angle. Therefore, the light spot can be gridded into n×m sub-spots.

[0048] III) Unified ranging equation of sub-spots. The unified ranging equation is the key to establishing the three-dimensional correction model of the target point cloud. First, the spatial geometric characteristics of the sub-spot P are analyzed to quantitatively describe the vector TP in the scanner coordinate system. Figure 3 Describes the geometric relationship between the laser beam and the sub-spot P in the scanner coordinate system. The vector TS of the laser center S in the scanning coordinate system o-xyz can be expressed as (X s ,Y s ,Z s). Vector TP can be represented by TS and SP, that is, TP = TS + SP. However, it is very difficult to directly represent the direction vector of SP in o-xyz. To this end, the present invention proposes to establish a spot coordinate system Sx′y′z′, where the center S of the laser beam is the origin of the coordinate, along TS is the positive direction of the x′ axis, the z′ axis is perpendicular to the upward direction, and the y′ axis is perpendicular to the surface Sx′z′. The coordinate system Sx′y′z′ is a right-handed system, such as Figure 4 .

[0049] In Sx′y′z′, the angle between SP and the y′ axis is β, and the direction vector of TS is (1,0,0). The three Euler angles between Sx′y′z′ and o-xyz are defined as ε1, ε2, and ε3. ε1, ε2, and ε3 are obtained by solving formula (2).

[0050]

[0051] In the formula, are the rotation matrices around the z′ axis, x′ axis, and y′ axis respectively. SP can be expressed as SP=(0, sinαcosβ, sinαsinβ) in Sx′y′z′. Therefore, SP in o-xyz can be described by formula (3).

[0052]

[0053] Where Δx, Δy, Δz are the components of SP on the three coordinate axes o-xyz. α is the angle between TP and TS. β=[0,360°]. Formula (3) is satisfied for any sub-spot P. Therefore, the coordinate of TP in o-xyz is TP=TS+SP=(X S +Δx,Y S +Δy,Z S +Δz). Therefore, the angle between the arbitrary sub-spot vector TP and TO (the vector of the target center in the scanner coordinate system) is θ p .

[0054]

[0055] Among them, ||TO|| is the modulus of vector TO, and ||TP|| is the modulus of vector TP.

[0056] refer to Figure 1 , when the sub-spot P is attached to the target surface, the distance between P and the laser emission point T is d′. In the triangle TPO, d′ can be solved by formula (5).

[0057]

[0058] Wherein, γ is the angle between OP and TP. After arrangement, the unified ranging equation of any sub-spot proposed by the present invention can be expressed by formula (6).

[0059]

[0060] IV) Two-dimensional Gaussian weight function. The energy of the laser spot is a two-dimensional Gaussian distribution function from the center to the surroundings, such as Figure 5 As shown. Therefore, when calculating the theoretical laser ranging value, the influence of the sub-spot energy on the sub-spot ranging value in the laser beam ranging should be taken into account. The present invention proposes to use the relative energy of the sub-spot as the weight of the sub-spot ranging value. The present invention proposes to construct the relative energy weight function p(α, β) of the sub-spot based on the distribution characteristics of the laser energy as shown in formula (7).

[0061]

[0062] V) Correction model. The correction model proposed in the present invention is the theoretical laser distance value D s It is the integral of the product of the sub-spot and the energy weight in the whole spot domain, as shown in formula (8).

[0063]

[0064] Therefore, D s Distance value d relative to the center of the light spot s The difference is the distance correction number Δd, and exp() is an exponential function. The actual laser distance value d is obtained by formula (9): r Correction is performed to obtain the corrected distance measurement value d, and then the new target point cloud coordinates are obtained.

[0065] d=d r +(d s -D s ) (9)

[0066] The correction process of the spherical target point cloud is to return the actual measurement point to the laser center measurement point. Assume that the input spherical target point cloud is N is the number of laser points in the point cloud, i is the laser point number, (x i ,y i ,z i ) is the coordinate of the ith laser point. The correction process mainly includes two steps: spot rasterization processing and ranging correction number calculation.

[0067] The embodiment provides a spherical target point cloud correction method for pulsed laser scanning, and the specific correction implementation process is as follows: Figure 6 , including the following steps:

[0068] Ⅰ) Preprocessing: After inputting the initial target point cloud, the target point cloud calculates the distance and azimuth of the target center in the scanning coordinate system.

[0069] The present invention proposes to use the average value of the azimuth angles of all points as the azimuth angle of the target center, and the sum of the minimum value of the point cloud distance measurement value and the design radius of the target as the distance of the target center in the scanning coordinate system. On this basis, the angle between the vector of the target edge and the vector of the target center in the scanning coordinate system is used as the limit measurement angle.

[0070] In the embodiment, the distance l and the azimuth (A) of the target surface center in the scanning coordinate system are calculated by the target point cloud computing. c ,H c ). The average value of all point cloud azimuths is taken as (A c ,H c ), the minimum value of the distance measurement value in the point cloud is taken as the surface center measurement distance l. At this measurement distance, the angle ang between the straight line from the scanning center to the edge of the target and the straight line TC to the center of the target in the scanner coordinate system is calculated.

[0071] II) Select a single laser point in the target point cloud for processing. First, for a single laser point, use formula (2) to calculate the three rotation angles of coordinate transformation, that is, the three Euler angles between the spot coordinate system and the scanning coordinate system.

[0072] In the embodiment, for a single laser point, three rotation angles ε1, ε2, ε3 of coordinate transformation are calculated using formula (2).

[0073] Then the light spot is rasterized: the light spot is rasterized and the ranging value of the sub-spot is calculated.

[0074] The present invention proposes to divide a laser beam into multiple sub-spots along the radial and circumferential directions, calculate the angle between the sub-spot and the vector TC by formula (4), and make a difference between the angle and the limit measurement angle. If the angle is less than 0, the sub-spot participates in the calculation; otherwise, it does not participate in the calculation. Then, the weight of each sub-spot is calculated by the Gaussian distribution function of formula (7), and then the theoretical distance measurement value of the laser beam is calculated according to formula (8).

[0075] In the embodiment, a laser beam is divided into n×m sub-spots along the radial and circumferential directions. The ranging value d′ of each sub-spot is calculated. The angle angl between the sub-spot and TC is calculated. By judging the relationship between ang and angl, it is determined whether the sub-spot participates in the calculation. If angl is less than ang, the sub-spot participates in the calculation, otherwise, it does not participate in the calculation. Afterwards, the weight of each sub-spot is calculated by the Gaussian distribution weight function of formula (7). The weight of each sub-spot is accumulated to obtain Sum1. The product of the weight of each sub-spot and the ranging value is accumulated to obtain Sum2.

[0076] III) Calculate the measurement correction Δd: Calculate the ranging correction of the current laser point based on integral accumulation and correct the coordinates of the point.

[0077] The present invention proposes to calculate the distance measurement value of the laser center according to formula (1), and then calculate the distance measurement correction number of the point according to formula (9). Whether the point is retained is determined by the positive or negative sign of the distance measurement correction number. If the distance measurement correction number is negative, the point is retained; otherwise, the point is deleted. After that, the actual distance measurement value is corrected to obtain the corrected laser point coordinates.

[0078] In the embodiment, the theoretical distance measurement value D of the laser is calculated by Sum1 and Sum2. S . Using geometric relationships, the distance value of the laser center is calculated as d s . By d s and D S Calculate the measurement correction Δd of the point. The sign of Δd determines whether the point is retained. If Δd is negative, the point is retained, otherwise, it is deleted. r Correction is performed, and then the corrected point coordinates x are calculated i ′,y i ′,z i ′.

[0079] IV) Update all point clouds: Determine whether all point clouds have been calibrated. If not, return and take the next laser point to execute steps II) and III). If yes, stop iteration and output the calibrated target point cloud.

[0080] In the embodiment, steps II) and III) are performed on all point clouds on the target surface to obtain a new target point cloud set. M is the number of target point clouds after processing, and u is the number of laser point labels after processing.

[0081] Figure 7 An example of a physical structure diagram of an electronic device is shown in FIG. Figure 7 As shown, the electronic device may include: a processor, a communications interface, a memory, and a communications bus, wherein the processor, the communications interface, and the memory communicate with each other via the communications bus. The processor may call logic instructions in the memory to execute a spherical target point cloud correction method for pulsed laser scanning.

[0082] In addition, the logic instructions in the above-mentioned memory can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0083] On the other hand, the present invention also provides a computer program product, which includes a computer program. The computer program can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the spherical target point cloud correction method for pulsed laser scanning provided by the above-mentioned methods.

[0084] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to execute the spherical target point cloud correction method for pulsed laser scanning provided by the above-mentioned methods.

[0085] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0086] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0087] In order to understand the technical effect of the present invention, Leica RTC360 3D laser measurement is used to obtain target point clouds at different distances. The correction effect of the point cloud correction model on the actual measured target point cloud is quantitatively evaluated to illustrate the feasibility of the model. The distance between the target and the scanner is 40m / 45m / 50m / 55m / 65m. The target point cloud scanned by RTC 360 at a measurement distance of 2m is fitted to the center of the sphere, and the distance between the corresponding target centers is calculated. For the point cloud at a measurement distance of 2m at 5 stations, the average distance between the centers of the two targets is used as the baseline between the two targets. The production radius is the actual radius of the target. Now use e r 、m p 、e d As the error parameter for quantitatively evaluating the target point cloud fitting sphere. r Indicates the error between the radius of the point cloud fitting sphere and the production radius. m p It represents the root mean square error RMSE of the point cloud fitting sphere, e d Represents the error between the distance of the fitted target center and the target baseline. The method of the embodiment of the present invention is to fit the target center after correcting the target point cloud through the spherical target point cloud correction model. The target center is fitted using the method of the embodiment of the present invention and the least squares method, RANSAC method and eSphere method. The fitting results are shown in Figure 8 As shown in , part (a) is the error of the fitting radius, part (b) is the mean error of the fitting sphere, and part (c) is the difference between the target spacing and the actual target baseline. Obviously, the accuracy results of the technical solution of the present invention are better than those of the other three prior art methods.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A spherical target point cloud correction method for pulsed laser scanning, characterized in that: Based on the intensity distribution of the laser spot and the geometric distribution characteristics of the laser spot on the attachment surface of the spherical target, a spherical target point cloud correction model is established, and correction is performed according to the spherical target point cloud correction model; when establishing the spherical target point cloud correction model, according to the principle of pulsed laser measurement, the distribution characteristics of the laser on the target surface are analyzed, and the spatial geometric relationship between the laser spot and the spherical target is constructed. The two-dimensional rasterization method of the spot is set to rasterize the spot into multiple sub-spots at equal angles in the radial and circumferential directions, and a unified ranging equation for the sub-spots is established accordingly, and the ranging value of each sub-spot is assigned a weight that satisfies the two-dimensional Gaussian distribution characteristics, and the spherical target point cloud correction model is established in an integral accumulation manner; Assume that the position of any point P in the spot is represented by (α, β), where β∈[0,360°], is the half divergence angle, and the following Gaussian distribution function is used to calculate the weight of each sub-spot according to the energy distribution characteristics of the laser: Among them, p(α,β) is the relative energy weight function of the sub-spot; The laser emission point is T, the center of the sphere is O, the line connecting the laser emission point and the center of the sphere intersects the sphere at C, the intersection of the laser spot center and the target is S, P is any point on the target surface within the spot, the radius of the target is R, the length of the laser measurement distance TC is l, the angle between ST and CT is θ, and the angle between PT and CT is θ P , the angle between SO and CO is ω, let ST = d s , calculate the distance value of the laser center according to the following formula, The theoretical distance measurement value of the laser beam is calculated according to the following correction model: Among them, D s is the theoretical laser ranging value; The ranging correction number of this point is calculated by the following formula: d=d r +(d s -D s ) Among them, d is the corrected distance value, d r is the actual distance measured by the laser.

2. The spherical target point cloud correction method for pulsed laser scanning according to claim 1, characterized in that: When the correction is implemented according to the spherical target point cloud correction model, the implementation process includes the following processing: Preprocessing, including calculating the distance and azimuth of the target center in the scanning coordinate system by the target point cloud computing; taking the angle between the vector of the target edge and the vector of the target center in the scanning coordinate system as the limit measurement angle; A single laser point in the target point cloud is selected for processing. First, the three Euler angles between the spot coordinate system and the scanning coordinate system are calculated, and the spot is rasterized, including dividing a laser beam into multiple sub-spots along the radial and circumferential directions, calculating the angle between the sub-spot and the laser measurement distance TC, and subtracting the angle from the limit measurement angle. If it is less than 0, the sub-spot participates in the calculation, otherwise it does not participate in the calculation; the weight of each sub-spot is calculated according to the energy distribution characteristics of the laser, and then the theoretical ranging value of the laser beam is calculated; then the ranging value of the laser center is calculated, and the ranging correction number of the laser point is calculated. If the ranging correction number is negative, the point is retained, otherwise it is deleted; then, the actual ranging value is corrected to obtain the corrected laser point coordinates; The above processing is performed on all laser points on the target surface, and a new target point cloud set is output.

3. The spherical target point cloud correction method for pulsed laser scanning according to claim 2, characterized in that: During preprocessing, the average value of the azimuths of all points is taken as the azimuth of the target center, and the sum of the minimum value of the point cloud ranging value and the design radius of the target is taken as the distance of the target center in the scanning coordinate system.

4. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the spherical target point cloud correction method for pulsed laser scanning as described in any one of claims 1 to 3 is implemented.

5. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for correcting a spherical target point cloud for pulsed laser scanning according to any one of claims 1 to 3 is implemented.

6. A computer program product, comprising a computer program, characterized in that: When the computer program is executed by a processor, the method for correcting a spherical target point cloud for pulsed laser scanning according to any one of claims 1 to 3 is implemented.

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