Lidar calibration method and apparatus based on spatial encoding

Abstract

A kind of laser radar calibration method and device based on space coding, by the coding plate and high reflection board containing coding area, low reflection area and hollow area are set to the laser radar to be calibrated opposite, make its beam vertical irradiation to the center position of coding plate when no deflection to obtain the distance between radar and coding plate, then by repeatedly irradiating coding plate with different layout multiple times and collecting corresponding reflected light intensity, by decoding reflected light signal and collating corresponding layout, the azimuth angle is calculated by combining the distance between radar and coding plate.The position relationship between fixed laser radar and coding plate and high reflection board is changed, the space layout of coding plate is replaced to realize the coding of space reflectivity, the emission direction of the beam is obtained by decoding the intensity of laser radar reflected light, so as to realize the calibration of laser radar.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of radar calibration, and particularly relates to a laser radar calibration method and device based on space coding. BACKGROUND

[0002] At present, the beam exit angle calibration of a solid-state laser radar, especially a solid-state multi-beam laser radar, is difficult and complex in structure, and an additional environment needs to be set for the calibration mark process. In order to solve the technical problem at low cost and high efficiency, a new laser radar angle calibration method and device need to be invented. SUMMARY

[0003] The application provides a laser radar calibration method and device based on space coding, which fixes the position relationship between the laser radar and a coding plate and a high-reflection plate, replaces the spatial layout of the coding plate to realize the coding of spatial reflectivity, decodes the intensity of reflected light of the laser radar to obtain the exit direction of the beam, and thus realizes the calibration of the laser radar.

[0004] The application is implemented by the following technical scheme:

[0005] The application relates to a laser radar calibration method based on space coding. The coding plate and the high-reflection plate containing a coding area, a low-reflection area and a hollow area are arranged opposite to the laser radar to be calibrated, so that the beam of the laser radar is vertically irradiated to the center position of the coding plate when the laser radar is not deflected, to obtain the distance between the radar and the coding plate. Then, the coding plate with different layouts is irradiated repeatedly, and the corresponding reflected light intensity is collected. The reflected light signal is decoded and compared with the corresponding layout, and the azimuth angle is calculated by combining the distance between the radar and the coding plate.

[0006] The high-reflection plate is a diffuse reflection plate with Lambertian characteristic and a reflectivity greater than 90%.

[0007] The coding plate is a diffuse reflection plate with Lambertian characteristic, which is provided with a rectangular coding area, a rectangular low-reflection area in the coding area and a rectangular hollow area in the coding area. The reflectivity of the low-reflection area is less than 5%, and the hollow area can directly transmit light.

[0008] Technical effects

[0009] The present application realizes the coding of spatial reflectivity by fixing the positional relationship between the laser radar and the coding plate and the high-reflective plate, replacing the spatial layout of the coding plate, decoding the intensity of the reflected light of the laser radar to obtain the emission direction of the light beam, thereby realizing the calibration of the laser radar. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 Fig. 1 is a structural schematic diagram of the high-reflective plate and the bracket.

[0011] Figure 2 Fig. 2 is a three-dimensional schematic diagram of the high-reflective plate and the bracket.

[0012] Figure 3 Fig. 3 is a sectional structural schematic diagram of the high-reflective plate and the bracket.

[0013] Figure 4 Fig. 4 is a schematic diagram of the Gray coding plate.

[0014] Figure 5 Fig. 5 is a three-dimensional schematic diagram of a Gray coding plate.

[0015] Figure 6 Fig. 6 is a sectional schematic diagram of a Gray coding plate.

[0016] Figure 7 Fig. 7 is an operation schematic diagram of collecting the corresponding reflected light intensity.

[0017] Figure 8 Fig. 8 is a schematic diagram of the preparation work before calibrating the laser radar.

[0018] Figure 9 Fig. 9 is a schematic diagram of the use principle of the present application.

[0019] Figure 10 Fig. 10 is a schematic diagram of the spatial coding and a spatial coding value comparison table.

[0020] Figure 11 Fig. 11 is a schematic diagram of the principle of calibrating the pitch angle.

[0021] In the figure: high-reflective plate 1, base 2, coding plate fixing device 3, coding area 4, low-reflective area 5, hollow area 6. DETAILED DESCRIPTION

[0022] As Figures 1-11As shown, this embodiment relates to a laser radar calibration method based on spatial coding, in which a coding plate including a coding area 4, a low-reflection area 5 and a hollow area 6 and a high-reflection plate are placed opposite to the laser radar to be calibrated so that the beam in an undeflected state is vertically irradiated to the center position of the coding area 4 to obtain the distance d between the radar and the coding plate. Then, after repeatedly irradiating the coding plates with different layouts and collecting the corresponding reflected light intensities, the reflected light signal is decoded and compared with the corresponding layout, and the azimuth is calculated in combination with the distance between the radar and the coding plate.

[0023] The cross-sectional structures of the coding region 4, the low reflection region 5 and the hollow region 6 are respectively as follows: Figure 6 As shown in AA, BB and CC. Figure 6 by Figure 5 Taking the coding plate shown in FIG as an example, the cross-sectional structure of the coding area 4 of the other coding plates can be made according to the different layouts of the coding plates. Figure 6 By analogy with AA in the figure, the cross-sectional structures of the low-reflection area 5 and the hollow area 6 of the other coding plates are the same as Figure 6 BB and CC are the same.

[0024] The different layouts refer to: within the coding area 4, using natural binary coding or Gray coding, with the low-reflection area as 0 and the hollow area as 1, the low-reflection area 5 and the hollow area 6 are arranged from left to right.

[0025] like Figure 7 As shown, the acquisition of the corresponding reflected light intensity refers to: manually inserting the code plates 1 to 4 vertically downward into the code plate fixing device in sequence, placing them in front of the high-reflection plate, that is, recording the reflected light intensity on the side close to the laser radar to be calibrated, and taking out the code plate vertically upward to obtain the reflected light intensity I 1 ~I 4 When the beam shines on the low-reflection area, the reflection intensity is low. When the beam shines on the hollow area, the light will be reflected by the high-reflection plate behind it and produce a higher reflection intensity.

[0026] The decoding is: the intensity of the reflected light I 1 ~I 4 Perform analog-to-digital conversion, and generate the spatial encoding value b corresponding to the detection direction after normalization and thresholding. 1 b 2 b 3 b 4 By comparing this code value with the code table, the azimuth of the detection direction can be obtained.

[0027] The normalization mentioned above refers to: Among them I min For I 1 ~I 4 The minimum value in I max For I1 ~I 4 the maximum value in the equation, is the normalized reflected light intensity, i represents that the equation represents the case when the ith encoding board is placed, because there are a total of 4 encoding boards, so the value range of i is 1, 2, 3, and 4.

[0028] The thresholding processing refers to: b i = 1, otherwise b i = 0, where the meaning and value range of i are the same as above.

[0029] The distance of the radar combined with the encoding board is to calculate the azimuth angle, specifically: based on the encoding table as shown in Figure 10 , the azimuth angle corresponding from left to right is , where d is the distance between the laser radar and the encoding board (unit: meter), l is the side length of the encoding area 4 (unit: meter), j is a decimal number corresponding to the binary code introduced for convenience, because the binary code has a total of 4 bits, so the value range of j contains 16 values, -8, -7, -6, …, 5, 6, 7. Considering the specific case in Figure 9 , the beams in the direction shown in the figure respectively irradiate to the hollow area 6, low reflection area 5, low reflection area 5 and hollow area 6 of the encoding boards 1-4, that is, corresponding to 1001, and the azimuth angle of the detection direction can be obtained by comparing the encoding table

[0030] Preferably, as shown in Figure 11 , a square encoding board and encoding area are used, so that the calibration of the pitch angle can be realized by rotating the encoding board by 90° and repeating the above steps.

[0031] Through specific actual experiments, the side length l of the encoding board is set to 0.5 meters, the distance d between the encoding board and the laser radar is set to 0.5 meters, the total number of the encoding boards used for calibration is set to 4, the layout of the encoding boards is the same as that in Figure 4 , the exit azimuth angle of the laser radar beam to be tested is set to 10°, and the exit pitch angle is set to 15°. According to the above-mentioned manner, the above-mentioned device is used, and the encoding board is not rotated by 90°, and the experimental data that can be obtained is: I 1 = 0.98, I 2 = 0.03, I 3 = 0.05, I 4 = 0.02, and after normalization, it is After thresholding, the spatial encoding value b 1 b 2 b 3 b 4 = 1000, and by comparing Figure 10The j value corresponding to the encoding value in the encoding table shown is 2, and the exit azimuth angle of the beam is calculated as After rotating the encoding plate by 90 degrees, the experimental data obtained is: I 1 = 0.91, I 2 = 0.90, I 3 = 0.02, I 4 = 0.93, and after normalization Thresholding obtains the spatial encoding value b 1 b 2 b 3 b 4 = 1101, and according to the encoding table shown Figure 10 The j value corresponding to the encoding value is 4, and the exit azimuth angle of the beam is calculated as After calibration, the exit azimuth angle of the laser radar beam is 8.9 degrees, and the exit elevation angle is 15.7 degrees, which is close to the true value but has some error, because only 4 encoding plates are used in this experiment, the number is small, and increasing the number of encoding plates to 10 will make the calibration error < 0.05 degrees.

[0032] In this embodiment, the spatial encoding accuracy is related to the distance d between the encoding plate and the laser radar, the larger d is, the higher the spatial encoding accuracy is, but at the same time the spatial encoding range will also be smaller. In order to improve the spatial encoding accuracy without reducing the spatial encoding range, the number of encoding plates can be increased, as long as the design of the encoding plate matches the higher number of encoding methods. 11 encoding plates can realize the encoding of 2048x2048 different exit angles, which has exceeded the imaging pixel number of most solid-state laser radars.

[0033] Compared with the prior art, the present application uses a spatial reflectivity encoder to map spatial information onto intensity information of reflected light, realizes the calibration of the exit angle of the laser radar, and the performance index improvement lies in that the algorithm is simple, easy to use, and short in working hours; the function of the spatial reflectivity encoder is realized by a high-reflectivity plate and a plurality of encoding plates with different spatial distributions, without the need for an external power supply, and the number of encoding plates used can be flexibly adjusted according to the demand for encoding accuracy, 11 encoding plates can realize the encoding of 2048x2048 different exit angles, which can meet most demands, and the performance index improvement lies in that the structure is simple, easy to manufacture, low in cost, zero power consumption, and strong in expandability.

[0034] The above specific embodiments can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the present application, the protection scope of the present application is subject to the claims and is not limited by the above specific embodiments, and each implementation scheme within the scope is subject to the constraints of the present application.

Claims

1. A laser radar calibration method based on spatial coding, characterized in that: The coding plate and high-reflection plate containing the coding area, low-reflection area and hollow area are placed perpendicular to the laser radar to be calibrated so that the beam without deflection is vertically irradiated to the center of the coding plate to obtain the distance between the radar and the coding plate. Then, by repeatedly irradiating the coding plates with different layouts and collecting the corresponding reflected light intensities, the reflected light signals are decoded and compared with the corresponding layouts, and the azimuth is calculated in combination with the distance between the radar and the coding plate.

2. The laser radar calibration method based on spatial coding according to claim 1, characterized in that: The high reflective plate is a diffuse reflective plate with Lambertian properties and a reflectivity greater than 90%.

3. The laser radar calibration method based on spatial coding according to claim 1, characterized in that: The coding plate is a diffuse reflection plate with Lambertian properties, which is provided with a rectangular coding area, a rectangular low-reflection area and a rectangular hollow area located in the coding area. The reflectivity of the low-reflection area is less than 5%, and the hollow area can directly transmit light.

4. The laser radar calibration method based on spatial coding according to claim 1 or 3, characterized in that: The different layouts refer to: in the coding area 4, natural binary coding or Gray coding is used, with the low-reflection area as 0 and the hollow area as 1, and the low-reflection area 5 and the hollow area 6 are arranged from left to right.

5. The laser radar calibration method based on spatial coding according to claim 1 or 3, characterized in that: The acquisition of the corresponding reflected light intensity refers to: manually inserting the code plates 1 to 4 vertically downward into the code plate fixing device in sequence, placing them in front of the high reflective plate, that is, close to the side of the laser radar to be calibrated to record the reflected light intensity, and taking out the code plate vertically upward to obtain the reflected light intensity. When the beam shines on the low-reflection area, the reflection intensity is low. When the beam shines on the hollow area, the light will be reflected by the high-reflection plate behind it and produce a higher reflection intensity.

6. The laser radar calibration method based on spatial coding according to claim 1 or 3, characterized in that: The decoding is: the intensity of the reflected light Perform analog-to-digital conversion, and generate the spatial encoding value corresponding to the irradiation direction after normalization and thresholding. By comparing this code value with the code table, the azimuth angle of the irradiation direction can be obtained.

7. The laser radar calibration method based on spatial coding according to claim 6 is characterized in that: The normalization mentioned above refers to: ,in for The minimum value in for The maximum value in is the normalized reflected light intensity, i represents the placement of the i-th encoding plate. Since there are 4 encoding plates in total, the value range of i is 1, 2, 3, and 4.

8. The laser radar calibration method based on spatial coding according to claim 6, characterized in that: The thresholding process is: ,but ,on the contrary , where the meaning and value range of i are the same as above.

9. The laser radar calibration method based on spatial coding according to claim 1, characterized in that: The distance between the radar and the coding plate is used to calculate the azimuth angle. Specifically, based on the coding table, the corresponding azimuth angle from left to right is , where d is the distance between the laser radar and the coding plate, l is the side length of the coding area 4, in meters, and j is a decimal number corresponding to the binary code for the convenience of calculation. Since the binary code has 4 bits, the value range of j includes 16 values, namely -8, -7, -6, ..., 5, 6, 7. Based on the coding of the beam illumination direction, the azimuth of the illumination direction can be obtained by comparing the coding table: .

10. The laser radar calibration method based on spatial coding according to claim 1 or 3, characterized in that: The coding plate and coding area are square.

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