Method for calibrating a lidar sensor

Abstract

The present invention relates to a method for calibrating a lidar sensor (2.1) of a vehicle (1) or a robot. According to the present invention, in a reference calibration, a reference object having a predetermined reflectivity and located at a predetermined distance from the lidar sensor (2.1) is loaded with the laser radiation of the lidar sensor (2.1). The laser radiation reflected by the reference object is received by a lidar receiver (2.1.1) of the lidar sensor (2.1), the lidar sensor (2.1) generates a sensor signal (S) related to the laser radiation and having a reference intensity, and the sensitivity of the lidar receiver (2.1.1) is calibrated according to the reference intensity. During the operation of the vehicle (1) or the robot, in an operational calibration, it is detected by means of at least one camera (3) whether there is at least one object within the detection range of the lidar sensor (2.1), the reflectivity of which corresponds to that of the reference object in the reference calibration. If such an object exists, the distance to the object is determined by means of the lidar sensor (2.1). In addition, the intensity (I) of the sensor signal (S) generated based on the laser radiation reflected by the object is determined, the determined intensity (I) is compared with the associated reference intensity, and the sensitivity of the lidar receiver (2.1.1) is calibrated according to the comparison between the intensity (I) and the reference intensity.

Description

Technical Field

[0001] The invention relates to a method for calibrating a lidar sensor of a vehicle or a robot. Background Art

[0002] DE 102016009327 A1 discloses a method for calibrating a vehicle camera, with which an image of the vehicle environment is captured. A defined pattern is emitted into at least one section of the camera's detection range in the vehicle environment by means of at least one lidar sensor, and the pattern is detected by means of the camera. Distance values ​​to the pattern contained in the image captured by the camera are determined by an evaluation unit coupled to the camera or integrated therein, and the camera is calibrated as a function of these distance values. The lidar sensor is designed to be self-calibrating, the self-calibration being based on object tracking.

[0003] Furthermore, DE 19607345 A1 discloses a laser distance measuring device, which has a pulsed laser, a light deflection device, a photoelectric receiving array with photoelectric receivers, and a control and evaluation electronics device, wherein the pulsed laser emits light pulses in a controlled manner and the continuously emitted light pulses are deflected into a measuring range at a varying angle by the light deflection device. The light pulses reflected from an object located in the measuring range are received by the photoelectric receiving array and a scanning signal representing the distance of the object from the light deflection device is determined in the control and evaluation electronics device from the time between the emission and reception of the light pulses taking into account the speed of light according to the pulse propagation time method and the propagation time measurement errors occurring due to the signal dynamics are compensated. The control and evaluation electronics device includes a device for measuring the charge flowing through the photoelectric receiver as a whole during the reception of the light pulse and for measuring the pulse width of the received light pulse, and the compensation of the propagation time measurement errors occurring due to the signal dynamics is carried out based on the measured charge and pulse width on the basis of corresponding correction values. The correction values ​​are determined by the control and evaluation electronics device based on the charge and pulse width and the pulse propagation time, which are measured for reference objects at a defined distance from the light deflection device and having different reflectivities. Scan reference objects before and during normal LiDAR operation. Summary of the invention

[0004] The object of the present invention is to provide a new method for calibrating a lidar sensor of a vehicle or a robot.

[0005] According to the invention, this object is achieved by the method according to the invention.

[0006] In a method for calibrating a laser radar sensor of a vehicle or a robot according to the present invention, in a reference calibration, a reference object having a predetermined reflectivity and located at a predetermined distance from the laser radar sensor is loaded with laser radiation of the laser radar sensor. In addition, the laser radiation reflected by the reference object is received by means of a laser radar receiver of the laser radar sensor and the laser radar sensor generates a sensor signal related to the laser radiation and having a reference intensity, wherein the sensitivity of the laser radar receiver is calibrated according to the reference intensity. During the operation of the vehicle or the robot, in the operation calibration, it is detected by means of at least one camera whether there is at least one object in the detection range of the laser radar sensor, the reflectivity of which corresponds to the reflectivity of the reference object of the reference calibration. If such an object exists, the distance to the object is determined by means of the laser radar sensor. In addition, the intensity of the sensor signal generated based on the laser radiation reflected by the object is determined, the determined intensity is compared with the associated reference intensity and the sensitivity of the laser radar receiver, such as a photodetector array, is calibrated according to the comparison of the intensity with the reference intensity.

[0007] The robot is configured, for example, as a mobile, floating or stationary robot. For example, the robot is also configured as a vehicle, such as a highly or fully automated car, a highly or fully automated transport vehicle or a highly or fully automated truck. The robot can also be an industrial robot, an automatic lawn mower, a sweeping robot, a mopping robot or an automatic boat.

[0008] For example, the sensitivity of the lidar receiver and / or the transmission power of the lidar sensor is changed according to the calibration in such a way that the sensor signal output by the lidar receiver has the same intensity as in the reference calibration at the same distance as in the reference calibration. In this case, for example, the transmission power and the receiver sensitivity are adapted in such a way that an object with a certain reflectivity is displayed in the same way by all the transceiver units of the lidar or by the deflection of individual transceiver units.

[0009] Taking a calibration surface with a defined Lambertian reflectivity of 10% as an example, the same intensity must be determined at a given distance in each section of the laser radar's visible range so that the object can be identified as the same object everywhere. Since the reflection intensity is related to the distance, the reflectivity is often calibrated. In a specific application example, a truck usually has a painted metal surface at its rear, which is surrounded by a highly reflective strip. In addition, the truck has taillights and license plates. Since the laser radar does not recognize colors, but only recognizes the backscattered intensity of monochromatic light, the described characteristics of the truck's rear are reflected as a characteristic distribution of intensity or calibrated reflectivity. These characteristics should appear monotonous in all sections of the laser radar's visible range and at distances, that is, uniformly scaled. If the laser radar's transceiver unit now sends back different values, the pattern will change, making it more difficult for the algorithm to recognize the object. Similar problems occur when the intensity output of a single transceiver unit, for example, deflected in the visible range by a mirror, fluctuates. The calibration of the intensity output implemented by the present method and the calibration of the reflectivity derived therefrom do not have these problems and are therefore very important for the reliability of object recognition by the laser radar.

[0010] In addition to the spatial information from the lidar detection, the intensity of the reflection is also of interest to the algorithm. Depending on color, material and orientation, objects reflect differently, so that characteristics of the object can be derived, similar to the so-called HOC classification in cameras. Since lidars typically have multiple, at least partially independent lasers and lidar receivers, which vary in manufacturing, the intensity of the same object varies depending on the laser / receiver combination. Calibration based on objective reference targets during production can help, but this is complex and not easy to verify and correct during the service life.

[0011] The method also allows the lidar sensor to be calibrated during operation of the vehicle or robot. Thus, a calibration possibility is achieved during the service life of the lidar sensor in order to also detect aging effects, environmental condition dependencies (such as temperature dependencies) and / or dirt and / or fluctuations in the energy supply of the lidar sensor or fluctuations over time and dynamic changes in the semiconductor resistance of the lidar sensor. Thus, calibration can also be carried out and repeated during operation of the lidar sensor, which is also particularly advantageous in vehicles or robots that operate automatically, in particular highly automatically, autonomously or partially autonomously. Thus, calibration allows the sensitivity of the lidar receiver and / or the transmission power of the lidar sensor to be set in such a way that the strength of the sensor signal is adjusted.

[0012] Since the existing basic calibration of the lidar can be used as a basis during the operation of the vehicle or robot, only a so-called recalibration is required during the operational calibration. In this case, for example, the intensity or reflectivity values ​​reported back by the lidar are overlaid with the color and contour evaluation of the camera, so that a homogeneous surface is detected. The expected intensity is then derived from the average value of the installed sensors and can be additionally refined by map data, which contain information from other vehicles or robots with corresponding sensor technology and can thus provide further measurement points for the surface.

[0013] Furthermore, the method allows the camera and the lidar sensor to be calibrated relative to one another, so that objects recognized by the camera and the lidar sensor can be better correlated and with increased precision. If the camera and the lidar sensor are calibrated directly to one another, the relative error between them is reduced. By means of the resulting direct calibration of the camera relative to the lidar sensor or vice versa, the raw data of the camera and the lidar sensor can be directly fused. Furthermore, the fusion of the independent data of the camera and the lidar sensor is also improved. The result of the calibration is taken into account that the camera and the lidar sensor see the same objects at the same position.

[0014] The performance of the classifier and thus of the recognition algorithm is significantly improved by a calibration process of the intensity output of the lidar sensor. By using a camera installed together with the lidar sensor on or in the vehicle or robot, this process can also be performed during the service life of the lidar sensor to check the calibration and, if necessary, correct it and compensate for aging effects. This can be done, for example, in an autonomous, in particular highly autonomous, autonomous or partially autonomously operating vehicle or robot, when it is parked and, for example, charging at a charging station.

[0015] In one possible embodiment of the method, during operation of the vehicle or robot, in the event of a change in the distance of the lidar sensor to an object, an intensity determined at a distance corresponding to the distance of the associated reference object to the lidar sensor is compared with a reference intensity. The sensitivity of the lidar receiver and / or the transmission power of the lidar sensor can thereby be controlled in such a way that the intensity of the currently determined sensor signal corresponds to the reference intensity, i.e. the deviation between the compared intensities is minimized. Thus, the physical properties of the lidar receiver can be influenced in such a way that the current intensity of the sensor signal corresponds to a reference intensity of the sensor signal determined during a previous reference calibration for a reference object with the same reflectivity and the same object distance.

[0016] In another possible embodiment of the method, during operation of the vehicle or robot, in the case of a changing distance from the lidar sensor to an object, an intensity determined by extrapolating intensities determined at a plurality of different distances from the lidar sensor to the object is compared with a reference intensity. This allows a reliable calibration of the lidar sensor even if the distance of the identified object from the lidar sensor differs from the distance of the reference object from the lidar sensor. In this case, for example, the extrapolated intensity is compared with the reference intensity and the sensitivity of the lidar receiver and / or the transmission power of the lidar sensor is controlled in such a way that the deviation between the compared intensities is minimized.

[0017] In another possible embodiment of the method, the laser radiation emitted by the lidar sensor is deflected by a rotating mirror of the lidar sensor for impinging on the reference object and the object. As a result, the reference object can be impinged on by the laser radiation in a particularly simple and reliable manner.

[0018] In another possible embodiment of the method, infrared laser radiation is used as laser radiation directed toward the object, so that the reflected laser radiation can be detected by a camera.

[0019] In another possible embodiment of the method, in order to generate the image captured by means of the camera, the light radiation incident on the camera is filtered by means of the camera's own infrared filter at least during the calibration run. The infrared filter can reduce interference and improve the color quality.

[0020] In another possible embodiment of the method, an infrared filter is used which is transparent to the infrared laser radiation emitted by the lidar sensor and reflected by the object, so that the reflected infrared laser radiation can be detected.

[0021] In another possible embodiment of the method, an infrared filter is used, which in the calibration mode of the camera is switched to be transparent to the infrared laser radiation emitted by the lidar sensor and reflected by the object. Thus, the infrared filter can be used during normal operation of the camera to reduce interference and improve color quality, and deactivated in the calibration mode in order to optimally detect the infrared laser radiation emitted by the lidar sensor and reflected by the object.

[0022] In another possible embodiment of the method, when an object is detected by a camera, integration is performed over a plurality of sequentially detected images of the camera. The integration increases the resolution of the camera in the infrared range, which is advantageous because a camera constructed as a conventional color camera has its highest sensitivity in the visible light range and a lower sensitivity in the infrared range. In addition, small fluctuations in illumination are compensated. If the camera uses a single image and is not integrated in time, a beat may occur due to the different illumination times of the camera and the lidar, which leads to a rolling shutter effect (jelly effect). This rolling shutter effect is also mitigated by time integration over a plurality of frames, for example when stationary. Based on measurements over a plurality of frames, it is not important when the camera and the lidar are started relative to each other and how exactly they operate. The method is also designed in particular for calibrating sensors with gapless scanning, i.e., not only can areas within an image be compared, but also between different frames when the lidar is activated and deactivated.

[0023] Based on the time integration, the camera records many laser pulses of the lidar, so that the synchronization deviations of the camera image and the lidar light pulses are also compensated. The camera thus detects the reflection pattern of the lidar. The intensity of the reflection pattern can also be determined from the camera image. Due to the very high resolution of the imager in terms of intensity and high dynamic range, in combination with methods such as high dynamic range (HDR for short), the minimum intensity differences between different rows can be determined and the relative intensities can therefore be calibrated in the lidar. These relative intensities are very important for object recognition algorithms, for example, so that objects always have similar intensities no matter which laser beam currently hits them.

[0024] In another possible embodiment of the method, the camera is switched to a calibration mode in order to calibrate the lidar sensor.

[0025] In another possible embodiment of the method, the distance to the object is determined by measuring the propagation time between the time of emitting the laser radiation and the time of receiving the laser radiation reflected from the object. Such a distance determination can be realized very simply and reliably and provides precise results. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The accompanying drawings are as follows:

[0027] Figure 1 showing a schematic perspective view of a vehicle;

[0028] Figure 2 a schematic diagram showing a lidar receiver; and

[0029] Figure 3Schematic diagram showing the calibration process of running a lidar sensor. DETAILED DESCRIPTION

[0030] In all the figures, parts that correspond to one another are provided with the same reference symbols.

[0031] Figure 1 2 shows a perspective view of a vehicle 1 . The vehicle 1 comprises a lidar 2 having at least one lidar sensor 2 . 1 and a camera 3 , which are designed to detect the vehicle surroundings.

[0032] The following description is also applicable similarly to a robot comprising at least one camera 3 and / or at least one laser radar sensor 2.1. Such a robot is designed, for example, as a mobile, floating or stationary robot. For example, the robot is also designed as a vehicle, such as a highly or fully automated car, a highly or fully automated transport vehicle or a highly or fully automated truck. The robot can also be an industrial robot, an automatic lawn mower, a sweeping robot, a mopping robot or an automatic boat.

[0033] Figure 2 A schematic diagram of a lidar receiver 2 . 1 . 1 of a lidar sensor 2 . 1 , which is designed as a photodetector array and is used to receive laser radiation, is shown, and its mode of operation is illustrated.

[0034] The environment of the vehicle 1 is scanned by means of a lidar sensor 2.1, the scanning being based on the emission of infrared laser radiation, in particular infrared laser pulses P, and the detection of infrared laser radiation reflected from an object, in particular infrared laser pulses P. From the propagation time between the emission of the infrared laser pulse P and the detection of the infrared laser pulse P, the distance from the lidar sensor 2.1 to the object which reflected the corresponding infrared laser pulse P is determined.

[0035] The laser radar sensor 2.1 includes a laser array for emitting infrared laser pulses P, a rotating mirror for deflecting the infrared laser pulses P emitted by the laser array onto a detection area to be scanned, and a laser radar receiver 2.1.1 for detecting the infrared laser pulses P reflected from objects in the detection area. The laser radar receiver 2.1.1 converts the infrared radiation of the received infrared laser pulses P into a corresponding electrical or digital sensor signal S. The intensity I of the sensor signal S, i.e., the pulse height or pulse amplitude or the integration of the infrared laser pulses P, can be changed by controlling the sensitivity of the laser radar receiver 2.1.1 and / or the transmission power of the laser radar sensor 2.1. The control of the sensitivity and / or the transmission power can be based on the working point setting, the amplification setting or the digital signal processing and can be performed by the corresponding control signal C.

[0036] The calibration of the lidar sensor 2.1, which is carried out, for example, during vehicle production, is carried out, for example, on a test bench and as a reference calibration. For this purpose, reference objects with a predetermined reflectivity are positioned at different positions of the detection range of the lidar sensor 2.1 at a predetermined longitudinal spacing or a predetermined distance, i.e., a reference spacing, and reference measurements are carried out, in which the infrared laser pulses P reflected back to the lidar receiver 2.1.1 are detected.

[0037] According to the calibration, the sensitivity of the lidar receiver 2.1.1 and / or the transmission power of the lidar sensor 2.1 is changed in such a way that for the sensor signal S originating from the same reference object at the same reference distance, the same intensity I is generated over the entire detection range of the lidar sensor 2.1. These steps can be repeated with a changed reference distance and / or with other reference objects having different reflectivities.

[0038] However, the sensitivity of the lidar receiver 2.1.1 depends on environmental conditions, such as temperature and / or contamination, as well as on aging effects. Such environmental dependencies, contamination and / or aging effects can lead to undesired changes in the intensity I of the sensor signal S. These changes cannot be taken into account in the reference calibration.

[0039] In order to avoid undesired changes in the intensity I of the sensor signal S, an operating calibration is performed during operation of the vehicle 1 in addition to the reference calibration.

[0040] In the operational calibration, camera 3 of vehicle 1 for detecting surroundings is used to calibrate intensity I of sensor signal S of lidar sensor 2.1 during operation of vehicle 1. Thus, recalibration can be performed during operation of lidar sensor 2.1.

[0041] This requires that the intensity I of the sensor signal S determined in a reference calibration for different reference objects and corresponding reference distances is stored as a reference value.

[0042] To run the calibration, the camera 3 is switched to the calibration mode, for example. In this calibration mode, the camera 3 is used to detect whether there is an object in the detection range of the lidar sensor 2.1 that corresponds to one of the reference objects in terms of reflectivity. The camera 3 can be used for this detection because the camera 3 detects colors and the colors allow inferences about the reflectivity of the objects. For example, white objects have high reflectivity and black objects have low reflectivity.

[0043] If the detection by means of camera 3 indicates the presence of such an object, the distance to the object is determined using lidar sensor 2.1. In addition, the intensity I of the sensor signal S resulting from the reflection of the infrared laser pulse P on the object is determined. In addition, the intensity I of the sensor signal S determined during the reference calibration for a corresponding reference object with the same reflectivity, i.e. the reference intensity, is retrieved from the memory, as well as the associated distance between the reference object and lidar sensor 2.1.

[0044] Thus, there is a current measured value of the intensity I of the sensor signal S and an associated stored reference value. These two values ​​can be compared with each other because they originate from objects with the same reflectivity. However, for a direct comparison, it must be taken into account that the intensity I depends on the object distance, i.e. the distance of the lidar sensor 2.1 from the object or reference object.

[0045] For this reason, the distance to the object is determined with the aid of lidar sensor 2 . 1 .

[0046] Since the distance to an object changes during the travel of the vehicle 1, in a first method, when the distance to an object equals the reference distance, the intensity I of the sensor signal S determined at this distance is compared with the reference intensity retrieved from the memory. The sensitivity of the lidar receiver 2.1.1 and / or the transmission power of the lidar sensor 2.1 is then controlled in such a way that the intensity I of the sensor signal S currently determined is consistent with the reference intensity, that is, the deviation between the compared intensities I is minimized. The physical properties of the lidar receiver 2.1.1 are influenced in such a way that the current intensity I of the sensor signal S is consistent with the intensity I of the sensor signal S obtained during a previous reference calibration for a reference object with the same reflectivity and the same object distance (i.e. the same distance between the lidar sensor 2.1 and the reference object).

[0047] If, for example, during the calibration run, the distance to the object does not equal the reference distance, then in the second method the intensity I which would be determined at the reference distance can be determined by extrapolation based on the intensity I of the sensor signal S determined at different object distances. This extrapolated intensity I is compared with the reference intensity retrieved from the memory and the sensitivity of the lidar receiver 2.1.1 and / or the transmission power of the lidar sensor 2.1 is again controlled in such a way that the deviation between the compared intensities I is minimized.

[0048] Therefore, based on the comparison of intensity I with the reference intensity, the sensitivity of the lidar receiver 2.1.1 is calibrated.

[0049] In order for the camera 3 to be able to identify objects within the detection range of the laser radar sensor 2.1, the camera 3 needs to be configured to identify reflected infrared laser pulses P. The camera 3 has, for example, an infrared filter to reduce interference and / or improve color quality. For example, the infrared filter is designed so that it is transparent to the reflected infrared laser pulses P or it can be switched to a transparent state for the infrared laser pulses P in the calibration mode.

[0050] Since the camera is set up for environmental detection, it has its highest sensitivity in the visible light range. Its sensitivity is lower in the infrared light range. In order to still achieve high resolution in the infrared light range, in a possible embodiment, the measurement from the camera 3 is integrated over a plurality of images from the camera.

[0051] Figure 3 One possible embodiment of running a calibration is shown in more detail.

[0052] In a first method step V1, the camera 3 and the lidar 2 are activated. In this case, the camera 3 is switched to a calibration mode, for example.

[0053] In a second method step V2 , integration is performed over a plurality of, for example at least ten, successively captured images of the camera 3 .

[0054] In a third method step V3, the so-called ground truth is determined, which includes the position, shape and distribution of the illumination generated by the laser radar 2. The vehicle environment is taken into account here, which is known (e.g. on a test bench at the end of the production plant) or determined by triangulation (e.g. using multiple cameras and difference measurements) and / or by distance measurement (direct determination by the laser radar 2). In addition, high-precision maps can be used to determine the geometry of the environment. The expected reflection pattern, i.e. the distribution of the intensity I, is again obtained by design in the test bench.

[0055] Subsequently, in a fourth method step V4 , regions in the image of camera 3 and frames having detected laser radiation of lidar sensor 2 . 1 are determined.

[0056] In method step V5 , a white balance and / or a luminescence measurement is performed.

[0057] In a sixth method step V6 , the light intensity and the white value are determined intraline by means of the camera 3 and the lidar 2 .

[0058] In a seventh method step V7 , the light intensity and the white value are determined interline by means of the camera 3 .

[0059] In an eighth method step V8 , the light intensities and white values ​​determined in the sixth and seventh method steps V6 , V7 are then compared with one another and / or subtracted from one another.

[0060] In a ninth method step V9 , the associated value of the intensity I of the sensor signal S of the lidar sensor 2 . 1 and the associated sensitivity of the camera 3 is stored.

[0061] In a tenth method step V10 , the settings for the transmission power of lidar sensor 2 . 1 and the sensitivity of lidar receiver 2 . 1 . 1 are stored.

[0062] Reference numerals list

[0063] vehicle

[0064] LiDAR

[0065] LiDAR Sensor

[0066] LiDAR Receiver

[0067] Camera

[0068] C control signal

[0069] I Strength

[0070] P infrared laser pulse

[0071] S sensor signal

[0072] V1 to V10 Method Steps

Claims

1. A method for calibrating a lidar sensor (2.1) of a vehicle (1) or a robot, characterized in that, in a reference calibration - irradiate a reference object having a predetermined reflectivity and located at a predetermined distance from the lidar sensor (2.1) with the laser radiation of the lidar sensor (2.1), - receive the laser radiation reflected by the reference object by means of the lidar receiver (2.1.1) of the lidar sensor (2.1), - the lidar sensor (2.1) generates a sensor signal (S) related to the laser radiation and having a reference intensity, and - calibrate the sensitivity of the lidar receiver (2.1.1) according to the reference intensity, during the operation of the vehicle (1) or the robot, in an operation calibration, - detect by means of at least one camera (3) whether there is at least one object within the detection range of the lidar sensor (2.1), the reflectivity of which corresponds to that of the reference object in the reference calibration, - if such an object exists, determine the distance to the object by means of the lidar sensor (2.1), - determine the intensity (I) of the sensor signal (S) generated based on the laser radiation reflected by the object, - compare the determined intensity (I) with the associated reference intensity, and - calibrate the sensitivity of the lidar receiver (2.1.1) according to the comparison between the intensity (I) and the reference intensity.

2. The method according to claim 1, characterized in that, during the operation of the vehicle (1) or the robot, in the case of a change in the distance from the lidar sensor (2.1) to the object, compare the intensity (I) determined at a distance corresponding to the distance from the associated reference object to the lidar sensor (2.1) with the reference intensity.

3. The method according to claim 1, characterized in that, during the operation of the vehicle (1) or the robot, in the case of a change in the distance from the lidar sensor (2.1) to the object, compare the following intensity (I) with the reference intensity, which intensity is determined by extrapolating the intensities (I) determined at a plurality of different distances from the lidar sensor (2.1) to the object.

4. The method according to any one of claims 1 to 3, characterized in that, in order to irradiate the reference object and the object, deflect the laser radiation emitted by means of the lidar sensor (2.1) by means of a rotating mirror of the lidar sensor (2.1).

5. The method according to any one of claims 1 to 3, characterized in that, use infrared laser radiation as the laser radiation for aligning the object.

6. The method according to any one of claims 1 to 3, characterized in that, in order to generate an image detected by means of the camera (3), at least during the operation calibration, filter the light radiation incident on the camera (3) through the infrared filter of the camera itself.

7. The method according to claim 6, characterized in that, - use an infrared filter that is transmissive to the infrared laser radiation emitted by the lidar sensor (2.1) and reflected by the object, and / or - Switch the infrared filter to be transmissive for the infrared laser radiation emitted by the lidar sensor (2.1) and reflected by the object in the calibration mode of the camera (3).

8. The method according to any one of claims 1 to 3, characterized in that, when detecting an object by the camera (3), integration is performed on a plurality of sequentially detected images of the camera (3).

9. The method according to any one of claims 1 to 3, characterized in that, the camera (3) is switched to the calibration mode to calibrate the lidar sensor (2.1).

10. The method according to any one of claims 1 to 3, characterized in that, the distance to the object is determined by measuring the propagation time between the time point of emitting the laser radiation and the time point of receiving the laser radiation reflected from the object.

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