DE102022126246A1 - METHOD FOR VERIFYING A CALIBRATION OF A DISTANCE MEASUREMENT CARRIED OUT BY MEANS OF A CAMERA INSTALLATED IN A VEHICLE - Google Patents

Abstract

Method for checking a calibration of a distance measurement which is carried out using a camera (120) installed in a vehicle (100), comprising the steps of:a) recognizing a first traffic sign (210, 230, 260, 290) which indicates a distance to a second traffic sign (210', 250, 280, 290') in a first image recorded with the camera (120),b) recognizing the second traffic sign (210', 250, 280, 290') in a second image recorded with the camera (120),c) measuring a distance between the camera (120) and the second traffic sign (210', 250, 280, 290') by evaluating the second image, andd) checking the calibration as a function of the measured and indicated distance.

Description

The present invention relates to a method for checking a calibration of a distance measurement carried out by means of a camera installed in a vehicle, a computer program product, a control device for a vehicle and a vehicle.

Vehicle systems and driver assistance systems are based on images of the vehicle's surroundings taken by cameras installed in the vehicle, for example to measure the distance to a vehicle ahead and to initiate and/or carry out braking if the distance is too small. In order to be able to accurately determine a distance from images taken by the camera installed in the vehicle, for example, the camera must be calibrated. According to official regulations, a measurement inaccuracy in the calibration of the distance measurement is permitted. This varies depending on the actual distance or the actual distance, from which the measured distance or the measured distance may deviate by a predetermined percentage. The camera is calibrated before being installed in the vehicle, but dynamic effects such as vehicle loading, tire pressure and long-term effects such as aging of the vehicle body can have a negative influence on the calibration of the camera, making it necessary to recalibrate the camera installed in the vehicle. An incorrectly or poorly calibrated camera means that camera-based vehicle and driver assistance systems can no longer work reliably because, for example, the distance to a vehicle in front is measured incorrectly. Therefore, regular calibration checks are a point that should not be neglected when using camera-based vehicle and driver assistance systems.

For example, the WO 2019 066770 A1 a method for calibrating a camera using traffic signs is known. For this purpose, certain dimensions of several objects, in particular traffic signs, are stored on a vehicle processor. An image from a camera installed in the vehicle is received and an object is recognized in the image. The distance to the object, as well as the width and height of the object, are determined on the basis of the image. The width and height of the object determined in this way are compared with the stored width and height of the object and measurement errors are derived from this. One or more calibration parameters are determined on the basis of these measurement errors, which are then used to calibrate subsequently recorded images.

Against this background, an object of the present invention is to provide a method, a computer program product, a control device for a vehicle and a vehicle for checking a calibration of a distance measurement carried out using a camera installed in a vehicle.

1. a) Erkennen eines ersten Verkehrszeichens, das eine Distanz zu einem zweiten Verkehrszeichen angibt, in einem mit der Kamera aufgenommenen ersten Bild,
2. b) Erkennen des zweiten Verkehrszeichens in einem mit der Kamera aufgenommenen zweiten Bild,
3. c) Messen einer Distanz zwischen der Kamera und dem zweiten Verkehrszeichen durch Auswertung des zweiten Bildes, und
4. d) Überprüfen der Kalibration in Abhängigkeit der gemessenen und angegebenen Distanz.

According to a first aspect, a method is provided for checking a calibration of a distance measurement carried out using a camera installed in a vehicle. The method comprises the steps:

1. a) detecting a first traffic sign indicating a distance to a second traffic sign in a first image taken with the camera,
2. b) Recognition of the second traffic sign in a second image taken with the camera,
3. c) measuring a distance between the camera and the second traffic sign by evaluating the second image, and
4. d) Checking the calibration depending on the measured and specified distance.

The method has the advantage that poor calibration or a calibration that deteriorates over time of a distance measurement that is carried out using a camera installed in a vehicle can be detected at an early stage. This means that the distance measurement can be recalibrated as required and the correct determination and measurement of distances in the images recorded by the camera can be ensured. This leads to improved use of camera-based vehicle systems and driver assistance systems in the vehicle.

Calibration is necessary to measure distances by evaluating the image taken by the camera and converting these into distances in the real environment. Only if the calibration is correct do the distances measured in the image taken with the camera match the actual distances. Calibration therefore corrects, for example, extrinsic and intrinsic camera parameters as well as other imaging errors.

According to one embodiment, an odometric measurement of a distance travelled by the vehicle is started when the vehicle passes the first traffic sign, and step d) is carried out depending on the measured distance, the distance covered and the indicated distance.

If the procedure is carried out while driving, an odometric measurement is started and the distance covered by the vehicle is measured using wheel sensors, for example. The wheel sensors are, for example, wheel rotation sensors, from whose sensor data the distance covered by the vehicle is determined.

The distance covered by the vehicle is taken into account when checking the calibration, or the calibration is carried out depending on the distance covered. For example, the check can be carried out by ensuring that the sum of the measured distance and the distance covered corresponds to the specified distance. The distance covered determined using the odometric measurement has a very low measurement inaccuracy, which is why this type of distance measurement is suitable for comparison. If a deviation occurs when comparing the distances, the assumption can be made that the distance measurements in the camera images have a measurement inaccuracy due to the low measurement inaccuracy of the odometric distance measurement.

According to one embodiment, in step c) the distance between the camera and a vehicle stopping adjacent to the second traffic sign is measured by evaluating the second image.

The distance measurement can, for example, be set up to continuously measure a distance to a vehicle that is in front of the ego vehicle while driving. Accordingly, a distance to a vehicle that is stopped next to the second traffic sign is already provided. The distance to the second traffic sign is therefore determined indirectly here (namely by means of the vehicle stopped at the second traffic sign).

1. a) Erkennen von zumindest zwei Verkehrszeichen in einem mit der Kamera aufgenommenen Bild, wobei das erste Verkehrszeichen eine Distanz zu dem zweiten Verkehrszeichen angibt,
2. b) Messen einer Distanz zwischen dem ersten Verkehrszeichen und dem zweiten Verkehrszeichen durch Auswertung des Bildes, und
3. c) Überprüfen der Kalibration in Abhängigkeit der angegebenen und der gemessenen Distanz.

According to a second aspect, a method is provided for checking a calibration of a distance measurement carried out using a camera installed in a vehicle. The method comprises the steps:

1. a) detecting at least two traffic signs in an image taken with the camera, the first traffic sign indicating a distance to the second traffic sign,
2. b) measuring a distance between the first traffic sign and the second traffic sign by evaluating the image, and
3. c) Checking the calibration depending on the specified and measured distance.

The method offers the advantage that the distance between at least two traffic signs is determined in a recorded image. This method can therefore be carried out both while driving and when stationary. The calibration is determined depending on the distance indicated on the first traffic sign and the distance between the first and second traffic signs determined by evaluating the recorded image.

According to one embodiment, in step b) the distance between the camera and a vehicle stopping adjacent to the second traffic sign is measured by evaluating the image.

According to one embodiment, the first traffic sign comprises an additional sign which indicates the distance to the second traffic sign as a numerical value.

The first traffic sign in conjunction with the additional sign indicates a second traffic sign ahead. The distance between the first and second traffic signs is indicated as a number on the additional sign.

Different combinations of first and second traffic signs can occur. For example, the first and second traffic signs can be identical traffic signs or different traffic signs; in particular, the second traffic sign can also be a traffic light.

According to one embodiment, the first traffic sign and the second traffic sign are traffic signs that display a numerical indication that indicates a distance from the respective traffic sign to a reference point ahead, wherein the distance between the first and the second traffic sign is determined by the amount of the difference in the numerical indications.

Traffic signs that each indicate a distance to a reference point ahead are, for example, traffic signs that indicate an exit on a motorway. There can also be more than two traffic signs of this type, for example four. However, the first and second traffic signs are adjacent Traffic signs if several traffic signs are installed.

Accordingly, they can, for example, show the distances 300 m and 200 m. The distances shown can also be larger or smaller. For example, the multiple traffic signs can also show the distances 400 m, 300 m, 200 m, 100 m, whereby a distance between two adjacent traffic signs of the multiple traffic signs is identical. The first and second traffic signs can, for example, be the first and second traffic signs of the multiple traffic signs, or the third and fourth traffic signs of the multiple traffic signs.

According to one embodiment, the first traffic sign and the second traffic sign have a predetermined distance from each other and the predetermined distance is made available to the vehicle wirelessly or is stored on a data storage device of the vehicle.

Even if a first traffic sign does not indicate a distance to a second traffic sign using a number, a first and a second traffic sign have a predetermined distance from each other. Such a first and second traffic sign are, for example, guide posts that are set up at a predetermined distance from each other or traffic signs that indicate a railway crossing ahead. If such a first traffic sign is recognized, the predetermined distance to the second traffic sign is made available wirelessly or the predetermined distance is stored and can then be retrieved.

According to one embodiment, information is output to a driver of the vehicle depending on the verification of the calibration of the distance measurement.

Information about the calibration check and/or the status of the calibration is issued to the driver of the vehicle. The driver can be informed, for example, that the calibration is deteriorating over time and/or that a new calibration must be carried out, for example by a specialist workshop.

Furthermore, in the event of poor calibration, for example, a driver can be informed that camera-based vehicle systems and driver assistance systems can only be used to a limited extent and/or are switched off.

According to one embodiment, a calibration of the distance measurement is carried out depending on the verification of the calibration of the distance measurement.

For example, a distance measurement using the camera installed in the vehicle can have a maximum specified measurement inaccuracy of 10% for an actual distance of 100 m, but this measurement inaccuracy can also be smaller or larger. However, if the inspection reveals that the measurement inaccuracy is greater than a specified maximum measurement inaccuracy, the distance measurement is not correctly calibrated.

Recalibration of the camera can be performed, for example, via a wireless network, by comparing size dimensions of traffic signs with stored size dimensions or the like.

According to one embodiment, driver assistance systems of the vehicle are switched off depending on the calibration check.

If the calibration check reveals that it is faulty, camera-based driver assistance systems may not work correctly and may lead to accidents if a vehicle driver relies on them anyway. Therefore, they can be switched off depending on the check.

According to a third aspect, a computer program product is proposed which comprises instructions which, when the program is executed by a computer, cause the computer to carry out the method described above.

A computer program product according to a third aspect, such as a computer program means, can be provided or delivered, for example, as a storage medium, such as a memory card, USB stick, CD-ROM, DVD, or also in the form of a downloadable file from a server in a network. This can be done, for example, in a wireless communication network by transmitting a corresponding file with the computer program product or the computer program means.

According to a fourth aspect, a control device for a vehicle is provided. The control device for a vehicle comprises: a processor unit, and a memory unit on which means for carrying out the method described above are stored.

A processor unit in the vehicle is set up to recognize first and second traffic signs, for example using image recognition software based on artificial intelligence. This is also set up, for example, to draw conclusions about the second traffic sign from the combination of the first recognized traffic sign and the additional sign indicating the distance.

The respective unit can be implemented in hardware and/or software. In a hardware implementation, the respective unit can be designed as a computer or as a microprocessor, for example. In a software implementation, the respective unit can be designed as a computer program product, as a function, as a routine, as an algorithm, as part of a program code or as an executable object. Furthermore, each of the units mentioned here can also be designed as part of a higher-level control system of the vehicle, such as a central electronic control device and/or an engine control device (ECU: Engine Control Unit).

According to a fifth aspect, a vehicle is provided with one or more cameras for taking images, and a control device according to the fourth aspect.

One or more cameras are mounted on the vehicle so that they have the largest possible field of view. For example, in the middle of the vehicle and/or as a satellite camera on the side of the vehicle.

The embodiments and features described for the first aspect apply accordingly to the other aspects (second to fifth aspects) and vice versa.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

Further advantageous embodiments and aspects of the invention are the subject of the subclaims and the embodiments of the invention described below.

• 1 zeigt eine schematische Aufsicht auf ein Fahrzeug mit einer Kamera und einem Steuergerät;
• 2 zeigt eine schematische Darstellung von ersten erkannten Verkehrszeichen und zugehörigen zweiten Verkehrszeichen;
• 3 zeigt eine schematische Darstellung einer Anwendungssituation eines ersten Aspekts eines Verfahrens zum Überprüfen einer Kalibration einer Distanzmessung, die mithilfe in einem Fahrzeug eingebauten Kamera durchgeführt wird, im Straßenverkehr;
• 4 zeigt ein Flussablaufdiagram eines ersten Aspekts eines Verfahrens zum Überprüfen einer Kalibration einer Distanzmessung, die mithilfe einer in einem Fahrzeug eingebauten Kamera durchgeführt wird;
• 5 zeigt eine schematische Darstellung einer Anwendungssituation eines Verfahrens zum Überprüfen einer Kalibration einer Distanzmessung, die mithilfe einer in einem Fahrzeug eingebauten Kamera durchgeführt wird, gemäß einem zweiten Aspekt; und
• 6 zeigt ein Flussablaufdiagramm eines zweiten Aspekts eines Verfahrens zum Überprüfen einer Kalibration einer Distanzmessung, die mithilfe einer in einem Fahrzeug eingebauten Kamera durchgeführt wird.

In the following, the invention is explained in more detail using preferred embodiments with reference to the accompanying figures.

• 1 shows a schematic view of a vehicle with a camera and a control unit;
• 2 shows a schematic representation of first recognized traffic signs and corresponding second traffic signs;
• 3 shows a schematic representation of an application situation of a first aspect of a method for checking a calibration of a distance measurement, which is carried out using a camera installed in a vehicle, in road traffic;
• 4 shows a flow diagram of a first aspect of a method for checking a calibration of a distance measurement carried out using a camera installed in a vehicle;
• 5 shows a schematic representation of an application situation of a method for checking a calibration of a distance measurement carried out using a camera installed in a vehicle, according to a second aspect; and
• 6 shows a flow diagram of a second aspect of a method for checking a calibration of a distance measurement performed using a camera installed in a vehicle.

In the figures, identical or functionally equivalent elements have been given the same reference numerals unless otherwise stated.

1 shows a schematic plan view of a vehicle 100 with a camera 120, a wheel sensor 130 and a control unit 110 according to an embodiment. The vehicle 100 is in the 1 The example shown is a motor vehicle, in particular a passenger car. The camera 120 is mounted centrally on the vehicle 100 so that it covers as large a field of view as possible in the direction of travel. Furthermore, at least one wheel (in 1 A wheel sensor 130 is attached to the wheel (not shown). One wheel sensor can be attached to each wheel, whereby the number of wheel sensors can be one or equal to the number of wheels of the vehicle 100. The wheel sensor 130 can in particular be a wheel pulse sensor, i.e. a wheel speed sensor. The vehicle 100 can also have further sensors such as ultrasonic sensors, which are designed as part of a driver assistance system or the like of the vehicle 100.

The control unit 110 of the vehicle 100 comprises a processor unit and a memory unit. The control unit 110 is - preferably with the help of software that is stored on the memory unit is stored and is executed using the processor unit - to carry out a method described below for checking a calibration of a distance measurement that is carried out using a camera 120 installed in a vehicle 100. The control unit 110 is configured to output several variables, but in particular the result of the calibration check, for example to the driver assistance system and/or to a driver of the vehicle.

The driver assistance system requires precise detection of an environment 200 in which the vehicle 100 is located, including, for example, distances to objects and from objects to each other in the environment 200. A driver assistance system that is designed to support a driver of the vehicle 100, for example by assisting with braking or even semi-autonomous or fully autonomous operation of the vehicle, must be able to accurately determine distances of the vehicle to objects and distances between two or more objects in the environment 200 of the vehicle 100.

In carrying out the method according to a first aspect, as shown in the flow chart in 4 As shown, a first traffic sign 210, 230, 260 is recognized in a first image taken with the camera and then a second traffic sign 210', 250, 280 is recognized in a second image taken with the camera, as in 2 The second recognized traffic sign 210', 250, 280 depends on the first recognized traffic sign 210, 230, 260, it can be different from the first, identical to the first and, in addition, it can also be a traffic light system 280.

In order to better understand the relationship between the first recognized traffic sign 210, 230, 260 and the second recognized traffic sign 210', 250, 280, 2 several first traffic signs 210, 230, 260 (left column) and the corresponding second traffic signs 210', 250, 280 (right column) are shown.

2 a) shows the first recognized traffic sign 210 "No entry" with an additional sign 220 "after 100 m", which is an additional sign indicating the distance. According to the combination of the traffic sign 210 with the additional sign 220, a second traffic sign 210'"Noentry" is located at a distance of 100 m.

2 B) shows the first recognized traffic sign 230 "Give way" with an additional sign 240 "Stop in 100 m". According to the combination of the traffic sign 230 with the additional sign 240, a second traffic sign 250 "Stop. Give way" is located at a distance of 100 m.

2c) shows the first recognized traffic sign 260 "traffic light system" with an additional sign 270 "after 200 m". According to the combination of the traffic sign 260 with the additional sign 270, a traffic light system 280 is located at a distance of 200 m. Accordingly, the second recognized traffic sign is a traffic light system 280.

A processor unit of the control unit 110 of the vehicle 100 is set up to deduce the second traffic sign 210', 250, 280 depending on the combination of the first recognized traffic sign 210, 230, 260 with the distance-indicating additional sign 220, 240, 270. This ensures that the second recognized traffic sign 210', 250, 280 is the traffic sign associated with the first recognized traffic sign 210, 230, 260 and thus also that the distance to the associated second traffic sign is measured.

In the 2 The combinations shown of first recognized traffic signs 210, 230, 260 and additional signs indicating distance 220, 240, 270 are shown here only as examples and the method is not limited to the combinations shown of first traffic signs 210, 230, 260 with additional signs indicating distance 220, 240, 270 and second traffic signs 210', 250, 280.

In relation to 3 and 4 The method for checking a calibration of a distance measurement carried out using a camera 120 installed in a vehicle 100 will now be explained in more detail.

3 shows a schematic representation of a situation in road traffic in which the method for checking a calibration of a distance measurement carried out by means of a camera 120 installed in a vehicle 100 is carried out while 4 shows a schematic flow diagram of the method with steps S1 to S9.

In 3 A pair of first and second traffic signs was chosen as an example and representative, which in 2 B) is shown.

In 3 the vehicle 100 drives, which as in 1 shown, on a road at the edge of which are the first traffic sign 230 and the second traffic sign 250. The road can be, for example, a country road, It can be a highway or a street within a city.

The vehicle 100 is located at position POS1 and the control unit 110 receives in this position a first image of the surroundings 200 of the vehicle 100, which was recorded by the camera 120 installed in the vehicle 100 (step S1). The processor unit of the control unit 110 processes the first received image and recognizes a first traffic sign 230, which indicates a distance to a second traffic sign 250. The processor unit recognizes the distance to the second traffic sign, which is indicated on the additional sign 240, and sets this as the first distance A (step S3). In addition, the processor unit processes the combination of the first recognized traffic sign 230 and the additional sign 240 in order to recognize the second traffic sign 250 depending on this combination.

The vehicle 100 is now at position POS2 and thus passes the first recognized traffic sign 230 with additional sign 240. The passing of the first traffic sign is detected, for example, by the camera 120 installed in the vehicle 100 and an odometric measurement of the distance traveled is started (step S4). The odometric measurement is carried out by the wheel sensor 130 of the vehicle 100. Furthermore, a value of the odometric distance measurement is set as the second distance B (step S5).

If the vehicle 100 is, for example, at position POS3, a second image taken by the camera 120 is received by the processor unit of the control unit 110 (step S6). The position POS3 is in 3 selected as an example and can be anywhere between the first traffic sign 230 and the second traffic sign 250. Depending on the first recognized traffic sign 230, an associated second traffic sign 250 is recognized in the second image recorded with the camera (step S7).

Using the processor unit of the control unit 110, a third distance C of the camera 120 of the vehicle 100 to the second traffic sign 250 is measured by evaluating the second image (step S8).

The calibration is then checked depending on the three determined distances A, B, C (step S9). As can be seen from the illustration in 3 , the sum of the second distance B and the third distance C must be equal to the first distance A. Since the camera 120 installed in the vehicle 100 may have a measurement inaccuracy, the verification of the calibration depending on the three distances A, B, C must be within this measurement inaccuracy.

A check of the calibration depending on the three distances and then a deviation of the calibration can be carried out, for example, using the expression 1 A - (B + C) 1, where A, B, C here represent the three specific distances A, B, C. For example, the distance on the additional sign 240 is 100 m, so the first distance A is 100 m. For an odometrically measured second distance B of 30 m, a third distance C from the camera 120 to the second recognized traffic sign 250 of C equal to 80 m is measured by evaluating the second image. This results in a deviation of |100 - (30 + 80)| = 10. For example, a distance in an image taken by the camera may have a measurement inaccuracy of 8.5%. In this example, however, a measurement inaccuracy of 10% is determined. Accordingly, the distance measurement using the camera 120 installed in the vehicle 100 is no longer calibrated and therefore a new calibration must be carried out.

If it is determined that the camera 120 needs to be recalibrated, the vehicle 100 is configured to perform a recalibration, for example via a wireless network. Alternatively or additionally, information can also be issued to the driver of the vehicle 100. This can, for example, alert the driver of the vehicle 100 to the faulty calibration and request that he no longer rely on camera-based driver assistance systems until the vehicle's own camera 120 has been recalibrated.

In relation to 5 and 6 A second aspect of the method for checking a calibration of a camera 120 installed in a vehicle 100 will now be explained in more detail.

5 shows the situation in road traffic in which the method for checking a calibration of a distance measurement, which is carried out using a camera 120 installed in a vehicle 100, is carried out, while 6 a flow chart of the method with steps S10 to S14.

A vehicle 100, equipped as in 1 shown, is driving on a road, for example on a highway. The vehicle 100 is now at position POS10 and the control unit 110 receives an image from the camera 120 installed in the vehicle (step S10). The processor unit of the control unit 110 recognizes several traffic signs 290, 290', each of which indicates a distance to a reference point (step S11). The processor unit recognizes a first distance D between the traffic signs 290, 290' depending on the numerical information on the first and second traffic signs (step S12). A second distance E between the first and second traffic signs 290, 290' is measured by the processor unit by evaluating the image (step S13).

The calibration is then checked as a function of the first distance D and the second distance E (step S14). For example, the first traffic sign 290 shows a number of 100 m, while the second traffic sign 290' shows a number of 50 m. The processor unit is set up to determine from this that the specified distance D, i.e. the distance between the first and second traffic signs, is 50 m. By evaluating the image from the camera 120 installed in the vehicle 100, a second distance E of 51 m is measured between the first and second traffic signs 290, 290'.

Checking the calibration depending on the specified and measured distance, for example comparing (|D - E|) the two distances D, E, results in a deviation of 1 m. This corresponds to a percentage deviation of 2%. With a permitted measurement inaccuracy of, for example, 5% over a distance of 50 m, this value is within the specified measurement inaccuracy. Therefore, the camera 120 installed in the vehicle is not recalibrated.

In a further embodiment, the at least two traffic signs 290, 290' were recognized by the vehicle 100 and the specified distances D were determined. The vehicle 100 is located at position POS20, while a vehicle 201 is located at position POS30 and is adjacent to the second traffic sign 290'. The processor unit now determines a distance F to the vehicle 201 by evaluating the image. The calibration is then checked as a function of the distance F and the specified distance D.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

LIST OF REFERENCE SYMBOLS

100

vehicle

110

Control unit

120

camera

130

Wheel sensor

200

Vicinity

201

vehicle ahead

210, 230, 260

first traffic sign

210', 250

second traffic sign

220, 240, 270

distance-indicating additional sign

280

Traffic light system

290, 290'

Traffic signs

A, D

first distance

B, E

second distance

C, F

third distance

POS1, POS2, POS3

position

POS10, POS20, POS30

position

S1 to S9

Process steps

S10 to S14

Process steps

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• WO 2019066770 A1 [0003]

Claims (14)

Method for checking a calibration of a distance measurement that is carried out using a camera (120) installed in a vehicle (100), comprising the steps: a) recognizing a first traffic sign (210, 230, 260, 290) that indicates a distance to a second traffic sign (210', 250, 280, 290') in a first image recorded with the camera (120), b) recognizing the second traffic sign (210', 250, 280, 290') in a second image recorded with the camera (120), c) measuring a distance between the camera (120) and the second traffic sign (210', 250, 280, 290') by evaluating the second image, and d) checking the calibration depending on the measured and indicated distance. Procedure according to Claim 1 , wherein an odometric measurement of a distance traveled by the vehicle (100) is started when the vehicle (100) passes the first traffic sign (210, 230, 260, 290), and step d) is carried out depending on the measured distance, the distance traveled and the indicated distance. Procedure according to Claim 1 or 2 , wherein in step c) the distance between the camera and a vehicle (201) stopping adjacent to the second traffic sign (210', 250, 280, 290') is measured by evaluating the second image. Method for checking a calibration of a distance measurement which is carried out using a camera (120) installed in a vehicle (100), comprising the steps: a) recognizing at least two traffic signs in an image recorded with the camera, wherein the first traffic sign (210, 230, 260, 290) indicates a distance (D) to the second traffic sign (210', 250, 280, 290'), b) measuring a distance (E) between the first traffic sign and the second traffic sign by evaluating the image, and c) checking the calibration depending on the indicated and the measured distance. Procedure according to Claim 4 , wherein in step b) the distance between the camera and a vehicle (201) stopping adjacent to the second traffic sign (210', 250, 280, 290') is measured by evaluating the image. Method according to one of the preceding claims, wherein the first traffic sign (210, 230, 260) comprises an additional sign (220, 230, 240) which indicates the distance to the second traffic sign (210', 250, 280) as a numerical indication. Method according to one of the preceding claims, wherein the first traffic sign (290) and the second traffic sign (290') are traffic signs which display a numerical indication which indicates a distance from the respective traffic sign to a reference point ahead, wherein the distance between the first and the second traffic sign is determined by the amount of the difference in the numerical indications. Method according to one of the preceding claims, wherein the first traffic sign and the second traffic sign have a predetermined distance from each other and the predetermined distance is made available to the vehicle (100) wirelessly or is stored on a data storage device of the vehicle (100). Method according to one of the preceding claims, wherein information is output to a driver of the vehicle (100) depending on the verification of the calibration of the distance measurement. Method according to one of the preceding claims, wherein a calibration of the distance measurement is carried out depending on the check of the calibration of the distance measurement. Method according to one of the preceding claims, wherein driver assistance systems of the vehicle (100) are switched off depending on the check of the calibration. Computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method according to one of the Claims 1 - 11 to execute. Control device (110) for a vehicle (100), comprising: a processor unit; and a memory unit on which means for carrying out the method according to one of the Claims 1 until 11 are stored. Vehicle (100), comprising: one or more cameras (120) for taking pictures; and a control device according to Claim 13 .

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