A method of calibrating a lidar

Abstract

The application provides a laser radar calibration method, relates to the field of laser radar calibration, and comprises the following steps: arranging to-be-calibrated laser radars in light transmission plates of containers respectively; obtaining a detection distance between the light transmission plate and a light reflection plate; and calibrating each laser radar according to detection distance data of the laser radars and real data between the light transmission plate and the light reflection plate. In the laser radar calibration method, the ranging data of the radars in a specific liquid environment in actual application is collected, each radar is calibrated and corrected individually, and thus the ranging accuracy of each radar in the specific liquid environment is ensured.

Description

Technical Field

[0001] This application relates to the field of lidar technology, and more specifically, to a lidar calibration method. Background Technology

[0002] LiDAR (Light Detection and Ranging) is a radar system that uses laser beams to detect the position, range, and other characteristics of a target. Its working principle involves emitting a detection signal (laser beam) towards the target, then comparing the received signal reflected back from the target (target echo) with the emitted signal. After appropriate processing and calculation, information such as the target's range and azimuth can be obtained.

[0003] Typically, lidar is primarily used for target detection in atmospheric environments. However, with technological advancements, lidar applications are becoming increasingly diversified, including some underwater applications. Among these, underwater calibration of lidar is particularly important. Currently, lidar calibration is mainly performed in air using specific reflectivity plates. In underwater applications, the speed of light in water differs from its velocity in air, requiring a conversion to determine the distance.

[0004] Existing conversion methods are based solely on theoretical data. In practical applications, lidar ranging is affected by various factors such as liquid turbidity and the consistency of ranging between different lidars. Therefore, simple theoretical calculations alone cannot completely solve the problem of lidar ranging accuracy (the degree to which the detected value closely approximates the true value) in liquid environments. Summary of the Invention

[0005] The purpose of this application is to provide a calibration device and method for lidar used in liquid environments. The device allows for lidar calibration based on the liquid state and turbidity in practical applications, thereby ensuring the ranging accuracy of the lidar when used in liquid environments and solving the calibration problem of lidar in liquid media environments.

[0006] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows:

[0007] On one hand, a lidar calibration method is provided, comprising: a lidar to be calibrated; at least two containers for storing liquid, each container having a different length; each container including a light-transmitting plate and a reflective plate, the light-transmitting plate and the reflective plate being respectively disposed at one end of the container to form a liquid storage space; the light-transmitting plate being used to transmit detection light emitted by the lidar, and the reflective plate being used to reflect the detection light emitted by the lidar to form an echo signal; the lidar to be calibrated being disposed on the light-transmitting plate of each container, obtaining the detection distance between the light-transmitting plate and the reflective plate; and calibrating each lidar based on the detection distance data of the lidar and the actual data between the light-transmitting plate and the reflective plate.

[0008] Optionally, each lidar can be calibrated using a piecewise linear interpolation calibration method, based on the lidar's detection distance data and the actual data between the light-transmitting plate and the reflector.

[0009] Optionally, the system includes a first container and a second container. The positions of the lidar are moved to obtain the detection distance N1 between the light-transmitting plate and the reflector of the first container and the detection distance N2 between the light-transmitting plate and the reflector of the second container. The linear correction parameters K1 and B1 between the true distance R1 between the light-transmitting plate and the reflector of the first container and the true distance R2 between the light-transmitting plate and the reflector of the second container are:

[0010] K1=((N2*H-R2) - (N1*H-R1)) / (R2-R1);

[0011] B1 = (N1*H-R1)- K1*R1;

[0012] Where H is the coefficient ratio of the speed of light in a liquid to the speed of light in air.

[0013] Optionally, based on K1 and B1, the correction value for the distance interval from R1 to R2 is obtained: Error = K1*R+B1, where Error is the compensation value and R is the actual distance.

[0014] Optionally, the method includes fixing the lidar in a fixture, connecting the lidar to a host computer via a UART interface.

[0015] Optionally, the method includes controlling the movement of the fixture via a host computer to move the lidar to different detection positions on the transparent plates of the container.

[0016] Optionally, a calibration correction table for the lidar is calculated using the lidar's detection range data. The calculated correction table is then written into the lidar, and a single-unit calibration correction is performed on the lidar using piecewise linear interpolation calibration.

[0017] Compared with the prior art, this application has the following advantages:

[0018] This application provides a lidar calibration method, which includes: a lidar to be calibrated; at least two containers for storing liquid, each container having a different length; each container includes a light-transmitting plate and a reflective plate, which are respectively disposed at one end of the container to form a liquid storage space; the light-transmitting plate is used to transmit the detection light emitted by the lidar, and the reflective plate is used to reflect the detection light emitted by the lidar to form an echo signal; the lidar to be calibrated is respectively disposed on the light-transmitting plate of each container, and the detection distance between the light-transmitting plate and the reflective plate is obtained; each lidar is calibrated based on the detection distance data of the lidar and the actual data between the light-transmitting plate and the reflective plate. Because the lidar calibration method provided in this application collects ranging data of the lidar in a specific liquid environment for actual application of the lidar, and performs single-machine calibration correction on each lidar, the ranging accuracy of each lidar in the specific liquid environment is guaranteed.

[0019] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a lidar calibration device provided in an embodiment of this application.

[0022] Figure 2 This is a schematic diagram of the fixture in the calibration device according to an embodiment of this application.

[0023] Figure 3 This is a flowchart of the calibration method in an embodiment of this application.

[0024] In the diagram: 10-Clamp; 11-LiDAR; 12-Pressure plate; 20-Guide rail; 30-Light-transmitting baffle; 40-Reflector; 51-First container; 52-Second container; 53-Third container. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0027] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0028] It should be noted that in this paper, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0029] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0030] As described in the background section, the calibration process for lidar is usually carried out in an air environment. For scenarios where lidar needs to be used in other liquid environments, calibration in an air environment cannot meet the actual usage requirements. Theoretical calculations based solely on changes in the medium cannot completely solve the problem of lidar ranging accuracy. Therefore, independent calibration is required in the specific liquid environment.

[0031] To address this issue, this application provides a lidar calibration device that improves the ranging accuracy of lidar in specific liquid environments through calibration in actual liquid environments.

[0032] The lidar calibration device provided in this application is described below by way of example:

[0033] As one implementation method, please refer to the appendix. Figure 1The lidar calibration device includes a fixture 10, a guide rail 20, a light-transmitting baffle 30, a reflector 40, a first container 51, a second container 52, and a third container 53. All these components are mounted on the same substrate, which may be, for example, an optical platform.

[0034] To stabilize the lidar under test and reduce other influencing factors during the calibration process, the calibration apparatus includes a fixture 10 for securing the lidar 11, a space for stable placement of the lidar, and a pressure plate 12 for further fixing the lidar's position. This fixture ensures the lidar remains in a fixed position, maintaining a relatively stable positional relationship with other components during calibration. The fixture includes electrical connection components for powering and communicating with the lidar. The pressure plate 12 is connected to a pressure device, such as a cylinder, which provides power to the pressure plate to move and tighten or release pressure, thereby securing or releasing the lidar.

[0035] Based on this, the calibration device is equipped with a guide rail, and the clamp 10 can be connected to a drive device. The drive device drives the clamp to move in the same direction on the guide rail. In one embodiment, the drive device includes a motor and a transmission belt. The motor drives the transmission belt to move, and the transmission belt drives the clamp to move synchronously to different required calibration positions.

[0036] To simulate the operating environment of a lidar in a liquid environment, the calibration device is equipped with a container for storing the liquid. The container is used to seal and store the liquid. The number of containers can be set according to the test points required for calibration. In this embodiment, three containers are used as an example: a first container 51, a second container 52, and a third container 53. These three containers have different lengths, corresponding to different calibration distances. The containers are, for example, cylindrical structures, and the liquid is fully filled to ensure uniform distribution. A light-transmitting baffle is provided at one end of the container, and a reflector is provided at the other end to form a sealed space for storing the liquid. The light-transmitting baffle transmits the detection light signal from the lidar. The detection light signal propagates in the liquid within the container, illuminates the reflector, and the signal light (echo signal) reflected by the reflector is reflected back to the lidar. The lidar's receiving module receives the echo signal and calculates the detection distance. The reflectivity of the reflector can be set according to the calibration requirements, for example, 10%, 30%, 50%, 70%, 90%, etc. The transmittance of the light-transmitting plate can be set according to the calibration requirements. For example, if the light-transmitting plate is made of glass, the transmittance of the light-transmitting plate can be 50%, 70%, 90%, 100%, etc.

[0037] As one implementation method, as shown in the appendix Figure 2As shown in the example, all three containers are cylindrical structures. The first container 51 has a length of 100mm and a cross-sectional diameter of 100mm, the second container 52 has a length of 300mm and a cross-sectional diameter of 100mm, and the third container 53 has a length of 550mm and a cross-sectional diameter of 140mm. The container lengths are selected according to the detection range of the lidar, corresponding to different calibration distances. Since the detection light emitted by the lidar light source has a certain divergence angle, to avoid illuminating the sidewalls of the containers at a distance instead of fully illuminating the emitting plate, the diameter of the longer containers is relatively larger than that of the shorter containers, ensuring calibration accuracy. The three reflectors have the same reflectivity, either 10% or 90%, and the light-transmitting plates have the same transmittance, all being glass with a transmittance of over 90%. The reflectors and light-transmitting plates are arranged parallel to each other and perpendicular to the central axis of the cylindrical containers.

[0038] The liquid in the container is filled according to the application scenario. For example, in underwater exploration scenarios, the liquid in the container is fresh water, clean water, or seawater. It can also be filled with a liquid with a certain degree of turbidity, depending on the water quality. As one implementation method, the liquid in the container is clean water.

[0039] Based on the calibration apparatus described above, this application also provides a calibration method. (See attached...) Figure 3 As illustrated in the flowchart, the lidar 11 is fixed in the fixture 12, and the lidar is connected to the host computer. In one implementation, the lidar and the host computer are connected via a UART interface. The calibration device is also connected to the host computer via a UART interface.

[0040] The host computer controls the movement of the fixture to move the lidar to the first acquisition point facing the light-transmitting plate of the first container. The lidar then operates normally, performing distance detection and collecting data from the first acquisition point. This process is repeated, moving the fixture to position the lidar on the light-transmitting plates of the second and third containers, collecting distance detection data from the second and third acquisition points respectively. A calibration correction table is calculated using the data from these three lidars, and this table is written into the lidar. The lidar's internal algorithm then calibrates and outputs the detection range. Piecewise linear interpolation calibration is used to perform individual calibration correction on each lidar, ensuring the ranging accuracy of each lidar in specific liquid environments.

[0041] Specifically, one implementation of the lidar calibration method is as follows (this embodiment uses a two-stage correction as an example, with water as the liquid):

[0042] The lidar is mounted in a fixture, and a pressure plate firmly secures it. The host computer controls the fixture's movement, positioning the lidar directly opposite the light-transmitting plate of the first container. The lidar operates, performing distance detection. Its light source emits a detection light signal, which passes through the light-transmitting plate. The signal propagates through the liquid in the container, illuminating the reflecting plate. The reflected light (echo signal) returns to the lidar, where its receiving module receives the echo signal. The lidar calculates the detection distance N1 between the light-transmitting plate and the reflector in the first container. The actual distance between the light-transmitting plate and the reflector in the first container is R1.

[0043] The host computer controls the movement of the fixture, positioning the lidar directly opposite the light-transmitting plate of the second container. The lidar operates, performing distance detection. Its light source emits a detection light signal, which passes through the light-transmitting plate. The light propagates through the liquid in the container, illuminating the reflecting plate. The reflected light (echo signal) returns to the lidar, where its receiving module receives it. The lidar calculates the detection distance N2 between the light-transmitting plate and the reflector in the second container. The actual distance between the light-transmitting plate and the reflector in the second container is R2.

[0044] The host computer controls the movement of the fixture, positioning the lidar directly opposite the transparent plate of the third container. The lidar operates, performing distance detection. Its light source emits a detection light signal, which passes through the transparent plate. The light propagates through the liquid in the container, illuminating the reflecting plate. The reflected light (echo signal) returns to the lidar, where its receiving module receives it. The lidar calculates the detection distance N3 between the transparent plate and the reflector in the third container. The actual distance between the transparent plate and the reflector in the third container is R3.

[0045] Taking water as the liquid medium, and the ratio of the speed of light in water to the speed of light in air being 0.75 as an example, the linear correction parameters K1 and B1 between distances R1 and R2 can be calculated. The calculation formula is as follows:

[0046] K1=((N2*0.75-R2) - (N1*0.75-R1)) / (R2-R1);

[0047] B1 = (N1*0.75-R1)- K1*R1.

[0048] Similarly, using the data for distances R2, R3, N2, and N3, and the coefficient ratio of the speed of light in water to the speed of light in air (0.75), the linear correction parameters K2 and B2 between distances R2 and R3 can be calculated.

[0049] Based on parameters K1 and B1, the correction value for the distance interval from R1 to R2 is: Error = K1*R + B1 (where Error is the compensation value and R is the actual distance). Similarly, the correction value for the distance interval from R2 to R3 can be obtained.

[0050] The correction values ​​obtained above are written into the lidar to achieve underwater distance calibration.

[0051] To address the specific properties of liquids used in practical applications of lidar, ranging data is collected from lidars in those specific liquids. Each lidar is then calibrated individually using piecewise linear interpolation to ensure its ranging accuracy in the given liquid medium.

[0052] The above is an example of three containers using a two-segment linear paper insertion calibration. Different numbers and structures of containers, as well as different data calibration methods, can be used depending on specific circumstances.

[0053] In summary, this application provides a lidar calibration method, which includes: a lidar to be calibrated; at least two containers for storing liquid, each container having a different length; each container includes a light-transmitting plate and a reflective plate, which are respectively disposed at one end of the container to form a liquid storage space; the light-transmitting plate is used to transmit the detection light emitted by the lidar, and the reflective plate is used to reflect the detection light emitted by the lidar to form an echo signal; the lidar to be calibrated is respectively disposed on the light-transmitting plate of each container to obtain the detection distance between the light-transmitting plate and the reflective plate; and each lidar is calibrated based on the detection distance data of the lidar and the actual data between the light-transmitting plate and the reflective plate. Because the lidar calibration method provided in this application collects ranging data of the lidar in a specific liquid environment for actual application of the lidar, and performs single-machine calibration correction on each lidar, the ranging accuracy of each lidar in the specific liquid environment is guaranteed.

[0054] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0055] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method of laser radar calibration, characterized by, The laser radar calibration method comprises: a laser radar to be calibrated, not less than two containers for storing liquid, each container having a different length, each container comprising a light-transmitting plate and a reflecting plate, the light-transmitting plate and the reflecting plate being arranged at one end of the container respectively to form a liquid storage space; the light-transmitting plate is used for transmitting the detection light emitted by the laser radar, and the reflecting plate is used for reflecting the detection light emitted by the laser radar to form a return signal; the laser radar to be calibrated is arranged at the light-transmitting plate of each container respectively, the detection distance between the light-transmitting plate and the reflecting plate is obtained, and each laser radar is calibrated according to the detection distance data of the laser radar and the real data between the light-transmitting plate and the reflecting plate.

2. The lidar calibration method of claim 1, wherein, Each laser radar is calibrated according to the detection distance data of the laser radar and the real data between the light-transmitting plate and the reflecting plate through the piecewise linear interpolation calibration method.

3. The lidar calibration method of claim 1, wherein, The first container and the second container are included, the position of the laser radar is moved respectively, the detection distance N1 between the light-transmitting plate and the reflecting plate of the first container and the detection distance N2 between the light-transmitting plate and the reflecting plate of the second container are obtained, the linear correction parameters K1 and B1 between the real distance R1 between the light-transmitting plate and the reflecting plate of the first container and the real distance R2 between the light-transmitting plate and the reflecting plate of the second container are: K1 = ((N2*H-R2) - (N1*H-R1)) / (R2-R1); B1 = (N1*H-R1)- K1*R1; Wherein, H is the coefficient ratio of the speed of light propagation in liquid and the speed of light propagation in air.

4. The lidar calibration method of claim 3, wherein, According to K1 and B1, the correction value of the distance interval R1 to R2 is obtained: Error = K1*R+B1, wherein Error is the compensation value, and R is the actual distance.

5. The lidar calibration method of claim 1, wherein, The laser radar is fixed in the clamp, the laser radar is connected with the upper computer, and the laser radar is connected with the upper computer through the Uart interface mode.

6. The lidar calibration method of claim 1, wherein, The laser radar is moved to the detection position of the light-transmitting plate of different containers respectively by controlling the clamp through the upper computer.

7. The lidar calibration method of claim 1, wherein, The calibration correction table of the laser radar is calculated through the detection distance data of the laser radar, the calculated correction table is written into the laser radar, and the laser radar is calibrated and corrected in a single machine through the piecewise linear interpolation calibration method.

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