CN106597470A - A device and method for acquiring 3D point cloud data using a 2D laser scanner - Google Patents

Abstract

The invention discloses a three-dimensional point cloud data acquisition device and method by using a two-dimensional laser scanner, and provides a method for converting two-dimensional to three-dimensional coordinates of laser point cloud data. The influence of factors such as the difference of the working modes of the sensors, the hardware process level and the like on the conversion process is analyzed, and a corresponding solution is provided: approximating the true speed of the turntable by Kalman filtering; the acquisition time of serial port data is corrected; the angle variation of the laser spot in one period is compensated; and calculating the angle and position deviation of the laser scanner on the horizontal axis and the vertical axis. Experiments show that when the rotating platform is used for static three-dimensional laser scanning, a three-dimensional point cloud structure of a space can be accurately obtained. When the mobile scanning is carried out, the volume is relatively light, so that the position of the mobile platform can be obtained through the registration of data while the three-dimensional data is obtained, and the synchronous acquisition and positioning of the map are realized.

Description

A device and method for acquiring 3D point cloud data using a 2D laser scanner

technical field

The invention relates to the technical field of 3D mapping realized by a 2D laser ranging sensor, in particular to a device and method for acquiring 3D point cloud data using a 2D laser scanner.

Background technique

Three-dimensional laser scanners can obtain data information in the entire three-dimensional space. However, three-dimensional laser scanners are generally expensive and relatively large in size. Such as velodyne HDL-64E (priced at about 300,000 RMB), ibeo Scala laser (priced at about 200,000 RMB).

When performing 3D laser scanning, it is often a "stop and go" type of scanning and must be scanned at a pre-set location. However, in some special environments, such as mines or caves, more convenient and smart hand-held laser mapping equipment is often required [1-2]. The realization of 3D mapping based on 2D laser ranging sensor is a low-cost 3D mapping solution, and it is also the best solution that can realize 360-degree omni-directional 3D mapping. High practical significance and commercial value. Therefore, the industry urgently needs to develop a method that can change the limitations of 2D radar in such applications, and transform 2D lidar into a lidar capable of mobile 3D scanning.

At present, there are mainly two motion modes for 3D mapping based on 2D laser ranging sensors, one is a 180-degree swing mode, and the other is a continuous rotation mode. The purpose of both modes is to rotate the 2D measurement surface to obtain a 3D measurement space.

The first mode, the 180-degree swing mode, requires the laser to be mounted on a device that can swing left and right within a range of 180 degrees, at a frequency of 1 Hz. This movement mode is simple and easy to realize, but the acceleration and deceleration movement of the two end points causes the overall rotation speed to be uneven, which affects the coordinate transformation relationship from 2D to 3D, and the inertial oscillation of the swing will damage the laser to a certain extent, reducing the use of the equipment life.

The second mode, the continuous rotation mode, is to install the laser on a device that can rotate continuously in one direction, and the rotation speed remains constant, which is beneficial to calculate and interpolate the precise positional relationship, so as to obtain a more accurate 2D to 3D transformation relationship. And the inertial direction of continuous rotation is constant, and there is no vibration damage to the laser.

Zhang Ji et al. realized the laser scanning technology of the above two modes, and disclosed the relevant codes for 3D map construction using laser point cloud data [3]. M. Bosse et al. designed a device that uses spring force for swing scanning, called Zebedee, which integrates a two-dimensional laser scanner and an inertial navigation device [4]. Germany's 3D LASERSCAN company also realized the above two modes, and Based on this technology, the commercialization of the product has been realized [5]. However, none of their literatures introduced the 2D to 3D coordinate transformation method of laser point cloud data before registration and composition.

[1] M.Kaess, H.Johannsson, R.Roberts, V.Ila, J.Leonard, and F.Dellaert, "iSAM2: Incremental smoothing and mapping using the bayes tree," The International Journal of Robotics Research, vol.31 , pp.217–236, 2012.

[2]R.Zlot and M.Bosse, "Efficient large-scale 3D mobile mapping and surface reconstruction of an underground mine," in The 7th International Conference on Field and Service Robots, Matsushima, Japan, July 2012.

[3] J. Zhang and S. Singh. LOAM: Lidar Odometry and Mapping in Real-time. Robotics: Science and Systems Conference (RSS). Berkeley, CA, July 2014.

[4] M.Bosse, R.Zlot, and P.Flick, "Zebedee: Design of a spring-mounted 3-Drange sensor with application to mobile mapping," vol.28, no.5, pp.1104–1119, 2012.

[5] http://www.3d-scanner.net/faq.html.

Contents of the invention

In view of the above technical problems, the present invention provides a device and method for acquiring 3D point cloud data using a 2D laser scanner, which can accurately acquire a spatial 3D point cloud structure.

In order to realize the above-mentioned purpose of the invention, the present invention adopts following technical scheme:

A three-dimensional point cloud data acquisition device utilizing a two-dimensional laser scanner, comprising a two-dimensional laser scanner, a rotating shaft, a transmission wheel, an encoder, a multi-channel conductive slip ring, a drive motor, a tray, and a transmission bearing; the two-dimensional laser The scanner is fixed on the tray, and the lower end of the tray is connected to the transmission wheel through the transmission bearing; the transmission wheel is connected to the drive motor, and the drive motor drives it to rotate, thereby driving the tray to rotate, and the tray drives the two-dimensional laser scanner to rotate; the encoder is set on the shaft , to calculate the rotation angle of the rotating shaft; the multi-channel conductive slip ring is set on the rotating shaft; the encoder is connected to the serial port of the computer through the multi-channel conductive slip ring, and the acquired data is read out through the serial port of the computer; the laser on the two-dimensional laser scanner The data interface is connected to the network port of the computer through a multi-channel conductive slip ring, and the laser scanning data of the two-dimensional laser scanner is read through the network port of the computer.

A method for converting coordinates of three-dimensional point cloud data based on the device according to claim 1, comprising the steps of:

Step a: Assume that the time point of obtaining laser scanning data from the computer network port is T _l , at this time the rotation angle of the device read from the computer serial port is θ ₀ , the time point is T _s , and the time difference between the two is T _d = T _s -T _l , the angle error caused by the time difference is ω*T _d , correcting this error to obtain the actual rotation angle of the device at T _l time is θ ₁ =θ ₀ -ω*T _d , where ω represents the angular velocity of the device;

Step a.1: calculating the angular velocity ω of the device;

Assuming that the two adjacent rotation angles read from the serial port are α ₁ and α ₂ respectively, and the corresponding times are T ₁ and T ₂ respectively, then the instantaneous angular velocity of the device is:

ω=(α ₁ -α ₂ )/(T ₁ -T ₂ ) (1)

Step a.2: Correction of serial port data acquisition time:

If there is a rotation angle in the first piece of data read through the serial port, keep T _s at this time unchanged; if there is no rotation angle in the first piece of data, the rotation angle is obtained from the second piece of data in the serial port, then At this time, the actual acquisition time point of the rotation angle should be T _s '=T _s -0.01;

Step b: Take the laser scanning center in one laser scanning cycle as the origin, the horizontal direction as the x-axis, and the vertical direction as the y-axis to establish a coordinate system; set the x and y coordinates of the laser point P as P[0], P[ 1], then its rotation angle in the laser scanning cycle is a tan2(P[1], P[0]), in the laser scanning cycle, the device rotates ω*t degree, t is the laser scanning Period, so the offset of laser point P in this period is:

θ ₂ ＝[αtan 2(P[1],P[0]+λ]/(2π×ω×t)

Where λ is the scanning angle of the two-dimensional laser scanner;

For each laser point data, the corrected rotation angle is θ ₃ =θ ₁ +θ ₂ ;

Step c: Obtain the angle difference θ ₄ between the laser scanner and the horizontal plane, and the relative distance r between the laser scanning center and the rotating shaft center of the device;

Step d: Construct rotation matrices M ₁ , M ₂ , where

M ₁ corrects the horizontal position deviation of the laser scanner, and M ₂ corrects the position deviation between the laser scanning center and the rotating shaft center of the device and the deviation caused by the rotation angle error of the laser point.

Step e: For each laser point, make the following conversion:

P _out ＝M ₂ *M ₁ *P _in

P _in is the rotation angle of the device read through the computer serial port, and P _out is the rotation angle of the device after coordinate transformation.

Further, in the step a, the rotation angular velocity ω is filtered through the Kalman filter algorithm; the specific design is as follows:

State vector: X=[ω], measurement vector: Z=[ω], the state equation is X _k+1 ＝X _k +W _k , k=0,1,2...n, W is the system noise;

The observation equation is obtained by formula (1), the dynamic noise Q=0.0001, the initial value is X ₀ =360°, the estimated variance of the state vector P ₀ =(5°) ² , the measurement noise R is obtained from the mean square error of the observation vector, and the calculation result R = 4.03°.

Further, in the step c, the angle difference θ between the laser scanner and the horizontal plane is measured by a high _- precision inclinometer; the relative distance r between the laser scanning center and the center of the rotating shaft of the device is measured by a vernier caliper.

The beneficial effects of the present invention are: 1. When the device provided by the present invention is used for static three-dimensional laser scanning, the three-dimensional point cloud structure of the space can be accurately obtained; 2. When the device provided by the present invention is used for mobile scanning, due to its relatively large volume Portable, while obtaining three-dimensional data, the position of the mobile platform can be obtained through data registration, which realizes the simultaneous acquisition and positioning of the map; 3. The invention provides a coordinate conversion method for laser point cloud data from two-dimensional to three-dimensional ;Analyzed the influence of factors such as the difference in sensor working mode and hardware technology level on the conversion process, and gave a corresponding solution: approach the real speed of the turntable through Kalman filtering; correct the acquisition time of serial port data; compensate a The angle variation of the laser point within the period; calculate the angle and position deviation of the laser scanner on the horizontal axis and the vertical axis.

Description of drawings

Fig. 1 is a structural diagram of the device of the present invention; Fig. 2 is the angular velocity after Kalman filtering; Fig. 3 is the angular velocity error comparison after Kalman filtering; Fig. 4 is a serial port data diagram; Fig. 5 is the angular variation of laser data points in a rotation cycle; Figure 6 is the angle deviation θ ₄ of the laser on the horizontal axis; Figure 7 is the distance deviation r between the laser scanning center and the center of the rotating shaft; Figure 8 is the scanning result after Kalman filter correction; Figure 9 is the scanning result before Kalman filter correction; Figure 10 is the error map caused by θ ₄ (enlarged to 2.6 degrees); Figure 11 is the error caused by r (enlarged to 0.14 meters); Figure 12 is the two-dimensional laser plane; Figure 13 is the slow speed scanning result; Figure 14 is normal Speed scan results.

detailed description

The present invention will be further described below in conjunction with the embodiments and the accompanying drawings.

1, mechanical principle of the present invention:

The laser scanner used in this embodiment is the 30LX laser radar of HOKUYO Company, which can realize two-dimensional 270° plane scanning and detect obstacles up to 30m away. The pulsed laser is emitted in all directions in the plane by rotating the mirror and the reflected light is received by the laser receiver. The distance between the obstacle and the radar is measured by calculating the time difference between reflection and reception. In this way, the information of one or more points of the obstacle in the scanning plane is obtained. Using this information, the distance (depth) and width information of obstacles can be obtained, but without knowing the height information, it is impossible to accurately identify obstacles and perceive the three-dimensional environment.

The difficulty in realizing the uniform rotation of the HOKUYO-30LX radar is to keep the connection between the network cable and the power cable at the same time, and the speed should be as stable as possible, such as one rotation per second, the speed error is less than 1%, and the angle of laser rotation can be recorded in real time. The accuracy requirement is 0.25 degrees, and the angle output frequency is 100HZ. At the same time provide control port (RS232), power port (12V/3A), laser data interface (100Mbps Ethernet). The serial port adopts RS232 protocol, the baud rate is 115200, and the serial port is connected with the computer, which is used to read the swing angle data and issue control commands.

In order to achieve the above object, the structure of the present invention is shown in Figure 1, consisting of a two-dimensional laser scanner 1, a rotating shaft 2, a transmission wheel 3, an encoder 4, a multi-channel conductive slip ring 5, a drive motor 7, a tray 8, and a transmission bearing 6 composition. The two-dimensional laser scanner 1 is fixed on the tray 8, and the tray 8 and the transmission wheel 3 are connected through the rotating bearing 6. The drive motor 7 drives the rotation of the tray 8 by controlling the rotation of the transmission wheel 3 . Its rotation angle is calculated by an encoder 4 fixed on the rotating shaft 2 . During the rotation process, the connection between the network cable and the power supply line is solved by the multi-channel conductive slip ring 5 . The multi-channel conductive slip ring 5 is arranged on the rotating shaft 2; the encoder 4 is connected to the serial port of the computer through the multi-channel conductive slip ring 5, and the data obtained by it is read out through the serial port of the computer; the laser data interface on the two-dimensional laser scanner 1 is connected through the multi-channel The conductive slip ring 5 is connected to the network port of the computer, and the laser scanning data of the two-dimensional laser scanner 1 is read through the network port of the computer. The axis of the rotating bearing 6 and the central point emitted by the radar laser beam of the two-dimensional laser scanner 1 are on a vertical line as far as possible. The rotation center of the tray is consistent with the rotation center of the laser beam, reducing the complexity of coordinate conversion calculations.

2. Coordinate transformation:

For 2D radar, all it obtains are coordinates relative to the scan center as the origin. In order to achieve data registration, it is necessary to transform the point coordinates on these planes into three-dimensional space. Ideally, after obtaining the rotation angle of the laser data points, a coordinate transformation is performed on each data point to achieve this transformation. However, due to the influence of factors such as the level of hardware technology and differences in sensor working modes, it is difficult to obtain accurate position changes of the laser point during the rotation process. The three main error sources and the final conversion method of the laser point in the coordinate conversion process are discussed below.

2.1 The difference between laser scanning and serial port operating frequency

The frequency of the laser scanning is 40HZ, and the working frequency of the serial port is 100HZ. Assume that the time point of obtaining the laser scanning is T _l , and then immediately read the angle value of the current rotating platform from the serial port, which is recorded as θ ₀ , and its time is recorded as T _s . The time difference between the two is T _d =T _s -T _l , the angle error of the device caused by the time difference is ω*T _d , and the actual rotation angle of the device when the laser data is obtained is θ ₁ =θ ₀ -ω* after correcting the error T _d , where ω represents the angular velocity of the rotating device.

1) Acquisition of the angular velocity of the rotating device

The default speed of the rotating device is 360 degrees per second. However, due to the lack of such high precision in the hardware technology and PID program, the rotation angle of the turntable will fluctuate around 360 degrees, or even change drastically. Assuming that the angles of the swinging device corresponding to the two adjacent acquisitions of laser data are α ₁ and α ₂ respectively; the corresponding times are T ₁ and T ₂ respectively, then the instantaneous angular velocity of the rotating device is:

ω=(α ₁ -α ₂ )/(T ₁ -T ₂ ) (1)

We sampled 13,400 measured values of angular velocities, and after filtering out outliers, we retained points with angular velocities between 355 and 365 degrees per second.

In order to obtain the rotation angle of the device more accurately, the angular velocity of the device is filtered by Kalman filtering. The specific design is as follows:

State vector: X=[ω], measurement vector: Z=[ω].

The state equation is: X _k+1 =X _k +W _k , k=0,1,2,3...,n.

The observation equation is obtained by formula (1), dynamic noise Q=0.0001, the initial value is X ₀ =360, the state vector estimation variance P ₀ =(5 ^° ) ² , the measurement noise R is obtained from the mean square error of the observation vector, and the calculation result is R = 4.03°.

It can be seen from Figure 2 that the angular velocity of the rotating device is mostly between 350 and 370 degrees. The angular velocity after Kalman filtering is relatively smoother, basically oscillating between 358 and 362 degrees, and the average error is also smaller, as shown in Figure 3 and Table 1.

Table 1 Rotary platform angle/angular velocity error table

2) Serial port data acquisition time problem

The rotation angle of the code disc data recording device is read from the serial port, the data format is as shown in the figure, and the angle accuracy reaches 0.05 degrees.

Table 2 Serial port angle data format

Since the frequency of the rotating device is inconsistent with that of the radar data, when we obtain the radar data, we immediately query the swing angle, and there will be a time difference of at most 0.02 seconds. Because in order to ensure that there is a complete angle record in the read data, one more data should be read in actual operation. 0.02 seconds includes 0.01 seconds waiting for the arrival of serial port data and 0.01 seconds waiting for the second piece of data to be read. But this 0.02 seconds may also cause a huge deviation in point cloud registration. Assuming that the turntable swings 360 degrees per second, the error of 0.02 seconds is 7.2 degrees.

Therefore, the time T _s for the arrival of the serial port data is corrected as follows. If the angle data can be obtained from the first serial port data read, keep T _s unchanged; if the angle data can be obtained in the second serial port data read Obtained from the data, it actually shows that the angle data has been sent in the first article, but the data is cut off due to the frequency of the serial port data, so the real data acquisition time should be T′ _s = T _s -0.01.

2.2 The acquisition time of the data points within one rotation cycle (0.025 seconds) of the laser scanning data is different

HOKUYO laser scanning data has about 1080 points in one scanning cycle, its angular resolution is 0.25 degrees, and the scanning range is 270 degrees. There is a certain time difference in the acquisition of 1080 points, while the laser prism rotates, the scanner itself rotates with the rotating device, resulting in a slight deviation in the angle of the 1080 points, although it is small, when the distance of the scanned object At greater distances, small angular errors can also cause large offsets. In addition, when the prism inside the laser rotates and scans, its scanning period needs 0.025 seconds. In this time segment, since the laser is in a rotating state of 360 degrees per second, in theory, the first scanned point of the laser is the same as the last scanned point. The point difference is 9 degrees, and since the effective scanning range of the laser is 270 degrees, the value is about 6.75 degrees. Fig. 5 shows the corresponding angles of 1080 points in one scanning cycle when the rotating device is turned to 160.35 degrees instantaneously.

A coordinate system is established with the laser scanning center within one laser scanning cycle as the origin, the horizontal direction as the x-axis, and the vertical direction as the y-axis. Let the x and y coordinates of the laser point P be P[0], P[1], then its rotation angle in this cycle is a tan2(P[1],P[0]), and the laser prism rotates once The rotating device rotates ω*0.025 degrees within a period of time, so the offset of this point in this period is θ ₂ =[a tan2(P[1],P[0])+3/4π]/2π* ω*0.025, for each laser point data, the corrected rotation angle is θ ₃ =θ ₁ +θ ₂ .

2.3 Hardware process factors

The laser scanner is fixed on the rotating platform by four screws. Due to the limitations of the hardware process, it is difficult to ensure that the laser scanner is completely level. Let the angle difference between it and the horizontal plane be θ ₄ , which is difficult to identify or measure with the naked eye. Comes through program debugging. In addition, the center axis of the laser scanning center and the rotating platform is not strictly on a straight line, and the relative distance between the centers is set as r, which can also be obtained through program debugging.

In this embodiment, the _θ4 value is measured by a high-precision inclinometer; the r value is measured by a vernier caliper.

2.4 Coordinate transformation method

The coordinate transformation method mainly has the following three steps:

Step 1. Calculate θ ₀ , θ ₁ , θ ₂ , θ ₃ , θ ₄ each time the laser data is read

Step 2, construct rotation matrices M ₁ , M ₂ , where

M ₁ corrects the horizontal position deviation of the laser scanner, and M ₂ corrects the position deviation between the center of the laser scanner and the center of the rotating shaft of the device and the deviation caused by the point cloud rotation angle error.

Step 3, for each laser point, do the following conversion:

P _out ＝M ₂ *M ₁ *P _in

P _in is the rotation angle of the rotating platform read through the serial port of the computer, and P _out is the rotation angle of the rotating device after conversion.

3. Experiment

3.1 Static scanning

The rotating scanning device is fixedly placed in the center of the room. After the angular velocity of the rotating platform is filtered by Kalman, the velocity change is relatively more stable and the error is relatively small, so that more accurate point cloud space coordinates can be obtained, as can be clearly seen in Figure 8 The line on the ceiling of the house and the incandescent lamp in the point cloud data; while the angular velocity error of the original rotating platform is relatively large, the obtained point cloud space coordinate error is relatively large, which makes the spatial outline of the house relatively rough, as shown in Figure 9.

Figure 10 and Figure 11 are the distortions of the scanning results caused by the angle and position deviation of the laser scanner on the horizontal axis and the vertical axis. In order to highlight this error, the angle error of the horizontal axis is enlarged to 2.6 degrees (actually 0.6 degrees). At this time, it is difficult to see the edge outline of the house, because there are many points with coordinate errors accumulated on the edge; the center of the vertical axis The position deviation r is enlarged to 0.14 meters (actually 0.04 meters). At this time, it will be found that the point cloud data of the room has shifted as a whole. This is the result that the center of the scanned data and the rotation center axis are not on the same vertical axis.

3.2 Dynamic scanning

We put the laser rotating platform on top of the mobile robot. First, use 2D laser scanning (rotate the tray and keep the laser data level on the ground), and use the HECTOR MAPPING algorithm to scan out the shape of the corridor on the 5th floor, as shown in Figure 12. When the pallet rotates, the 3D point cloud data in the environment is obtained by using the LOAM program. When the mobile robot moves in a straight line or the rotation angle is small, 3D scanning can accurately obtain the 3D space point cloud data of the scanned space; and when the mobile robot rotates at a large angle, the rotation angular velocity cannot be too large. During the experiment, the angular velocity is controlled to not exceed 40 degrees per second, and accurate 3D point cloud data of the environment can be obtained, as shown in Figure 13; otherwise, the excessively fast rotational angular velocity will reduce the common point data between adjacent point clouds and cause registration Errors occur in the algorithm, which leads to deviations in the 3D point cloud map, as shown in Figure 14.

4 Conclusion

The present invention obtains the three-dimensional data of the whole space by accurately calculating the rotation angle of the rotating platform, and performing coordinate conversion of the corresponding laser point data. This kind of 3D scanning using a rotating platform is not only more cost-effective than 3D laser scanners, but also has a relatively light volume. It can obtain 3D data while obtaining the position of the scanner through data registration, which solves the problem of synchronous map acquisition. and positioning technology. The main questions to be addressed in the next step are:

1) To obtain a more stable and accurate rotation angle, it is necessary to further improve the level of hardware design and optimize the error compensation algorithm.

2) Obtaining the accurate motion trajectory of the mobile platform can be assisted by the IMU, and at the same time use the graph optimization algorithm to optimize the registration results of the obtained point cloud data as a whole.

Claims (4)

1. a kind of three dimensional point cloud acquisition device of utilization two dimensional laser scanning instrument, it is characterised in that sweep including two-dimensional laser Retouch instrument (1), rotating shaft (2), drive (3), encoder (4), multi-path conducting slip ring (5), motor (7), pallet (8), biography Dynamic bearing (6)；The two dimensional laser scanning instrument (1) is fixed on pallet (8), and pallet (8) lower end is by drive bearing (6) and biography Driving wheel (3) is connected；Drive (3) connection motor (7), drives it to rotate, so as to drive pallet (8) by motor (7) Rotation, pallet (8) drives two dimensional laser scanning instrument (1) rotation；Encoder (4) is arranged in rotating shaft (2), to calculate rotating shaft (2) the anglec of rotation；Multi-path conducting slip ring (5) is arranged in rotating shaft (2)；Encoder (4) is by multi-path conducting slip ring (5) It is connected with serial ports of computers, the data that it is obtained are read by serial ports of computers；Laser data on two dimensional laser scanning instrument (1) Interface connects the network interface of computer by multi-path conducting slip ring (5), and by computer network interface two dimensional laser scanning instrument (1) is read Laser scanning data.

2. a kind of three dimensional point cloud coordinate transformation method based on claim 1 described device, it is characterised in that including as follows Step：

Step a：Assume that the time point for obtaining laser scanning data from computer network interface is T_l, now read from serial ports of computers The anglec of rotation of device is θ₀, its time point is T_s, both time differences are T_d=T_s-T_l, the angular error that the time difference causes For ω * T_d, correct the error and obtain T_lWhen engraving device the actual anglec of rotation be θ₁=θ₀-ω*T_d, wherein ω represents the angle of device Speed；

Step is a.1：The angular velocity omega of computing device；

If the two neighboring anglec of rotation read from serial ports is respectively α₁, α₂, the corresponding time is respectively T₁, T₂, then wink of device When angular speed be：

ω=(α₁-α₂)/(T₁-T₂) (1)

Step is a.2：The amendment of time is obtained to serial data：

If by having the anglec of rotation in the first data that serial ports reads, keeping T now_sIt is constant；If the first data In without the anglec of rotation, the anglec of rotation is obtained from the second data of serial ports, then the now actual anglec of rotation is obtained Time point should be T '_s=T_s-0.01；

Step b：With the laser scanning center in a laser scanning cycle as origin, horizontal direction is x-axis, and vertical direction is y Axle, sets up coordinate system；If the x of laser spots P, y-coordinate is respectively P [0], P [1], then its rotation within the laser scanning cycle Gyration is a tan 2 (P [1], P [0]), and within the laser scanning cycle, device have rotated ω * t degree, and t is laser scanning Cycle, therefore skew of laser spots P within this cycle is：

θ₂=[α tan 2 (P [1], P [0]+λ]/(2 π × ω × t)

Wherein λ is the scanning angle of two dimensional laser scanning instrument；

For each laser point data, the revised anglec of rotation is θ₃=θ₁+θ₂；

Step c：Obtain the differential seat angle θ of laser scanner and horizontal plane₄, and the spindle central phase of laser scanning center and device Adjust the distance r；

Step d：Construction spin matrix M₁, M₂, wherein

$M_1=\left[\begin{array}{cccc}{\mathrm{cos\θ}}_4& {\mathrm{sin\θ}}_4& 0& 0\\ -{\mathrm{sin\θ}}_4& {\mathrm{cos\θ}}_4& 0& 0\\ 0& 0& 1& 0\\ 0& 0& 0& 1\end{array}\right],M_2=\left[\begin{array}{cccc}1& 0& 0& 0\\ 0& {\mathrm{cos\θ}}_3& -{\mathrm{sin\θ}}_3& -r{\mathrm{sin\θ}}_3\\ 0& {\mathrm{sin\θ}}_3& {\mathrm{cos\θ}}_3& r{\mathrm{cos\θ}}_3\\ 0& 0& 0& 1\end{array}\right]$

M₁Have modified the horizontal level deviation of laser scanner, M₂Have modified the position at laser scanning center and the spindle central of device Put the deviation that deviation and laser spots anglec of rotation error cause.

Step e：To each laser spots, make following conversion：

P_out=M₂*M₁*P_in

P_inBe by serial ports of computers read device the anglec of rotation, P_outFor the anglec of rotation of the device after Coordinate Conversion.

3. a kind of laser data point coordinates method for transformation according to claim 2, it is characterised in that in step a, leads to Cross Kalman filtering algorithm to filter angular velocity of rotation ω；Specific design is as follows：

State vector：X=[ω], measurement vector：Z=[ω], state equation is X_k+1=X_k+W_k, k=0,1,2 ... n, W is system Noise；

Observational equation is obtained using formula (1), dynamic noise Q=0.0001, and initial value chooses X₀=360 °, state vector estimation side Difference P₀=(5 °)², measurement noise R by observation vector mean square deviation obtain, result of calculation R=4.03 °.

4. a kind of laser data point coordinates method for transformation according to claim 2, it is characterised in that lead in step c Cross the differential seat angle θ that high accuracy inclinometer measures laser scanner and horizontal plane₄Value；Laser scanning center is measured using slide measure With the spindle central relative distance r value of device.