Method and system for calculating a vehicle trailer angle

Abstract

The invention relates to a method for determining the yaw angle (YA) of a trailer (2) relative to the longitudinal axis (LAV) of a towing vehicle (1) by setting a perpendicular bisector (B1) on the basis of features included in a plurality of captured images.

Description

Technical Field

[0001] This invention generally relates to the field of vehicle assistance systems. More specifically, this invention relates to a method and system for calculating the yaw angle of a trailer connected to a tractor based on image information provided by a vehicle camera device. Background Technology

[0002] Methods for calculating the angle of the trailer relative to the tractor based on image information provided by the vehicle's camera device are known.

[0003] Specifically, known methods have low computational complexity, but cannot provide robust angle information when image quality is poor.

[0004] Furthermore, in known methods, the exact position of the tow bar must be known in order to determine the yaw angle. Summary of the Invention

[0005] The objective of this invention is to provide a robust and reliable method for calculating trailer yaw angles without requiring prior knowledge of the tow bar position. This objective is achieved through the features of the independent claims. Preferred embodiments are given in the dependent claims. Unless otherwise expressly stated, embodiments of the invention can be freely combined with each other.

[0006] According to one viewpoint, the present invention relates to a method for determining the yaw angle of a trailer relative to the longitudinal axis of a tractor. The method includes the following steps:

[0007] First, at least one first and one second image of the trailer is captured using a camera device. The method for capturing the first and second images is such that the orientation of the trailer relative to the vehicle is different in at least the two images.

[0008] After taking the images, at least a first feature of the trailer must be identified. This first feature must be visible in both the first and second images. The first feature could be, for example, a prominent feature at a first location on the trailer.

[0009] After the feature is determined, a ray is established between the first feature determined by the camera device and the first image, and this ray is projected onto a horizontal plane to obtain the position of the first projected feature. Similarly, a ray is established between the first feature determined by the camera device and the second image, and this ray is projected onto the horizontal plane to obtain the position of the second projected feature. The projection of the feature or ray can be performed in the vertical direction, that is, an inclined ray can travel in a horizontal ray without changing its azimuth angle.

[0010] Based on the projection of the first feature, a first vertical bisector is established between the first projected feature position and the second projected feature position. More specifically, the first vertical bisector can be a vertical straight line passing through the center of the line connecting the first ray and the horizontal plane (e.g., at z=1) and the line connecting the second ray and the horizontal plane. The first ray is determined by converting the image coordinates of the first feature in the first image into light rays using camera device calibration information. The second ray is determined by converting the image coordinates of the first feature in the second image into light rays using camera device calibration information. The first vertical bisector can be established on the horizontal plane.

[0011] After establishing the first perpendicular bisector, the first intersection point between the first perpendicular bisector and the reference axis is determined. The reference axis can be the central longitudinal axis of the vehicle on which both the camera device and the tow bar are located. Therefore, this intersection point represents the center of rotation of the first feature.

[0012] Finally, the yaw angle of the trailer is calculated based on the first angle estimate, wherein the first angle estimate refers to the angle between a first line from the first projection feature position to the first intersection point and a second line from the second projection feature position to the first intersection point on the horizontal plane.

[0013] The method is advantageous because, by using two or more images and establishing one or more vertical bisectors using one or more trailer features, and calculating the yaw angle based on these vertical bisectors, the yaw angle determination is highly accurate and robust, even when trailer feature detection is affected by high noise or poor image quality. Furthermore, by using the vertical bisectors to determine the yaw angle, the exact location of the tow bar can be unknown.

[0014] According to one embodiment, in the first or second image, the yaw angle of the trailer relative to the vehicle is zero. Therefore, this image can serve as a "zero-attitude image," i.e., a reference for accurate alignment of the vehicle's longitudinal axis with the trailer's longitudinal axis. However, another yaw angle value can also be used as a reference. If the other yaw angle is unknown, the system can calculate the change in the trailer's angle, rather than the absolute angle of the trailer.

[0015] According to one embodiment, the method further includes the following steps:

[0016] In addition to the first feature, determine a second feature of the trailer that is visible in the first and second images. This second feature is located at a different trailer position than the first feature. The second feature can be a prominent feature at the second trailer position.

[0017] Furthermore, a ray between the camera device and the second feature determined on the first image is projected onto a horizontal plane to obtain the position of the third projected feature. Similarly, a ray between the camera device and the second feature determined on the second image is projected onto a horizontal plane to obtain the position of the fourth projected feature.

[0018] - In addition, a second vertical bisector is established between the third and fourth projection feature positions.

[0019] -Based on the second perpendicular bisector, determine the second intersection point between the second perpendicular bisector and the reference axis.

[0020] -Based on the second perpendicular bisector, a second angle estimate is established, where the second angle estimate refers to the angle between the first line from the third projection feature position to the second intersection point and the second line from the fourth projection feature position to the second intersection point on the horizontal plane.

[0021] Finally, the yaw angle is calculated based on the first and second angle estimates.

[0022] By using two or more trailer features and multiple perpendicular bisectors, noise and mismatches can be reduced when determining the perpendicular bisector and the interaxial sway angle of the reference axis.

[0023] According to one embodiment, in addition to the first and second features, at least one more trailer feature is used for yaw angle calculation. Using three or more features further improves the robustness and reliability of yaw angle determination.

[0024] According to one implementation, the yaw angle is calculated by establishing the median of at least two angle estimates. This results in a very stable yaw angle determination.

[0025] According to other implementations, the yaw angle is calculated by establishing the average of at least two angle estimates or by using statistical methods applied to the angle estimates.

[0026] According to one embodiment, the method further includes the step of determining an angle window. The angle window may include an upper and lower limit for the yaw angle. Furthermore, a set of features is determined, wherein features in the feature set result in an angle estimate that falls within the angle window. Preferably, only features included in the determined feature set are used for future yaw angle calculations. In other words, information previously used to determine the yaw angle is used to determine two or more features of the trailer that result in an angle estimate that is quite close to the determined yaw angle (i.e., within the angle window), and those features that cause the angle estimate to deviate significantly from the determined yaw angle (i.e., beyond the angle window) are not tracked. The computational complexity and accuracy requirements for angle estimation are thus significantly reduced.

[0027] According to one embodiment, camera device calibration information is used to transform the position of the first and / or second feature from a local domain of the image to a local domain of the vehicle. If, for example, the position of the camera device using the camera device calibration information is known, the position of a specific feature on the image can be transmitted to, or associated with, the position of the camera device included in or fixed to the vehicle.

[0028] According to one embodiment, if the camera device and the vehicle tow bar are positioned in a vertical plane including the longitudinal axis of the tractor, then the reference axis is the longitudinal axis of the tractor. In other words, the yaw angle is determined based on an angle estimate, wherein the angle estimate refers to the angle between the longitudinal axis of the tractor and a predetermined vertical dividing line.

[0029] According to another embodiment, if the camera device and / or the tow bar has a lateral offset relative to the longitudinal axis of the tractor, the reference axis is a straight line between the camera device and the tow bar. This allows for compensation of the lateral offset between the camera device and the tow bar.

[0030] According to one embodiment, the camera device is a rear-view camera for a vehicle. Based on the rear-view camera device, less technical effort is required to capture images of the trailer.

[0031] According to one embodiment, the position of the first feature is determined not only in the first and second images, but also in at least one third image. The position of the first feature in the third image differs from the position of the first feature in the first and second images. A first vertical bisector can be determined between the first feature in the first image and the first feature in the second image. Another vertical bisector can be determined between the first feature in the first image and the first feature in the third image. Then, another intersection point can be determined based on the intersection of the first vertical bisector and the other vertical bisector.

[0032] A first angle estimate is calculated based on a first vertical bisector. The first angle estimate is the rotation angle around the second intersection point (the intersection of the first ray and the horizontal plane) and the intersection of the second ray and the horizontal plane. The first angle estimate corresponds to the change in the trailer's yaw angle between the first and second images. In other words, the trailer's rotation point is not determined by the intersection of the first vertical bisector with the reference axis, but by the intersection of at least two vertical bisectors obtained through tracking features on three or more images.

[0033] According to another perspective, a system for determining the yaw angle of a trailer relative to the longitudinal axis of a tractor unit has been disclosed. The system includes a camera device for capturing images of the trailer and a processing entity for processing the captured images. Furthermore, the system is configured to perform the following steps:

[0034] - Use a camera device to detect at least one first and second images of the trailer, wherein the orientation of the trailer relative to the vehicle is different in at least two images;

[0035] - Identify at least one first feature of the trailer that is visible in the first and second images;

[0036] - Project a ray between the camera device and the first feature determined on the first image onto a horizontal plane to obtain the position of the first projected feature, and project a ray between the camera device and the first feature determined on the second image onto a horizontal plane to obtain the position of the second projected feature.

[0037] - Set a first vertical bisector between the first projection feature position and the second projection feature position.

[0038] - Determine the first intersection point of the first perpendicular bisector with the reference axis.

[0039] - Calculate the yaw angle based on the first angle estimate, wherein the first angle estimate refers to the angle between a first line from the first projection feature position to the first intersection point and a second line from the second projection feature position to the first intersection point on the horizontal plane.

[0040] Any of the features described as embodiments of the method described above may also be used as system features in the system described in this patent application published herein.

[0041] According to another embodiment, a vehicle including the system described in any of the above embodiments is disclosed.

[0042] The term "vehicle" as used in this invention may refer to automobiles, trucks, buses, rail vehicles or any other means of transportation.

[0043] The term "yaw angle" as used in this patent application published herein may refer to the yaw angle between the longitudinal axis of the vehicle and the longitudinal axis of the trailer.

[0044] The term “median” as used in this patent application published herein may refer to the value that separates the higher half of a data sample or probability distribution from the lower half.

[0045] The terms “substantially” or “approximately” as used in this invention refer to deviations from the exact value by + / -10%, preferably + / -5%, and / or variations that are not significant to function and / or to traffic rules. Attached Figure Description

[0046] Different aspects of the invention, including its particular features and advantages, will be more readily understood from the following detailed description and accompanying drawings, wherein:

[0047] Figure 1 An exemplary top view of a vehicle towing a trailer is shown;

[0048] Figure 2 A schematic diagram illustrating angle estimation of a single feature detected at different swing angles between a trailer and a tractor unit based on images from a camera device;

[0049] Figure 3 A schematic diagram illustrating angle estimation of first and second features detected at different swing angles between the trailer and the tractor based on images from a camera device;

[0050] Figure 4 The illustration schematically shows the geometric determination of the rotation point based on the first and second vertical bisectors obtained from a single trailer feature contained in three different images; and

[0051] Figure 5 A schematic block diagram of the steps for determining the yaw angle of a trailer relative to the longitudinal axis of a tractor is shown. Detailed Implementation

[0052] The invention will now be described in more detail with reference to the accompanying drawings, which illustrate exemplary embodiments. The embodiments in the drawings relate to preferred embodiments, and all elements and features described in connection with the embodiments can be used, where possible, in conjunction with any other embodiments and features discussed herein, particularly in relation to any other embodiments further discussed above. However, the invention should not be construed as limited to the embodiments described herein. Throughout the following description, similar reference numerals are used to denote similar elements, parts, items, or features, where applicable.

[0053] The features of the invention disclosed in the description, claims, embodiments and / or drawings can be used individually or in any combination to implement the invention.

[0054] Figure 1 The diagram shows a top view of vehicle 1 towing trailer 2. Vehicle 1 includes a longitudinal axis LAV passing through its center. Similarly, trailer 2 has a longitudinal axis LAT passing through its center. Trailer 2 is connected to vehicle 1 via a trailer hitch assembly including a drawbar 4.

[0055] In certain driving situations, the longitudinal axis LAV of vehicle 1 and the longitudinal axis LAT of trailer 2 may not be parallel or coincident; instead, the two longitudinal axes may define a yaw angle YA. In other words, the yaw angle YA defines the angular deviation of the longitudinal axis LAT of trailer 2 relative to the longitudinal axis LAV of vehicle 1. The yaw angle YA can be measured on a horizontal plane that includes the longitudinal axis LAT of trailer 2 and the longitudinal axis LAV of vehicle 1.

[0056] Understanding the yaw angle YA is also beneficial, for example, in trailer assist systems.

[0057] To determine the yaw angle YA, multiple images of at least a portion of the trailer 2 are captured using a camera device 3. The camera device 3 can be, for example, a rearview camera of the vehicle, or it can be used to capture images of the vehicle's surroundings while reversing. One of the captured images may refer to a known angular setting of the trailer 2 relative to the tractor 1. This image can be used as a reference for calculating the yaw angle YA. In the known angular setting of the trailer 2 relative to the tractor 1, the yaw angle YA can be 0 degrees or any other angular value.

[0058] Figure 2 The diagram shows the angular relationship of the first feature F1 of trailer 2 at different points in time, at which trailer 2 has different yaw angles YA relative to tractor 1.

[0059] The camera device 3 can capture two or more images of the trailer 2 at different times with different angular positions relative to the vehicle 1. For example, a series of images can be captured.

[0060] In this example, the second image shows the orientation of the trailer relative to the vehicle at a yaw angle YA = 0 degrees.

[0061] Due to the angular movement of trailer 2 over time, specific features detected at the trailer may appear at different locations in the first and second images. Figure 2 The first feature is represented by a square.

[0062] In the first image, the upper representation of the first feature (associated with the solid ray R connecting the feature to the camera device 3) is identified, and at another point in time, the lower representation of the first feature (associated with the dashed ray R connecting the feature to the camera device 3) is identified in the second image. To associate the position of the first feature in each corresponding image with the position of the vehicle 1—especially with a specific fixed point of the vehicle 1—calibration information of the camera device 3 can be used. Specifically, to determine the ray R connecting the first feature to the camera device 3, calibration information of the camera device 3 can be used to convert the position of the first feature in image coordinates into a ray. In other words, to associate the camera device position with the feature position, the feature position in the image is associated with the position of the vehicle fixed point based on the calibration information of the camera device 3.

[0063] Features on the trailer are located and matched using feature detection and matching algorithms. For example, Harris Corner Detector, Scale Invariant Feature Transform (SIFT), Speed-Up Robust Features (SURF), Binary Robust Invariant Scalable Keypoints (BRISK), Binary Robust Independent Basic Features (BRIEF), Oriented Fast Rotating Briefing (ORB), or another suitable feature detection and matching algorithm can be used.

[0064] The feature detection and matching algorithm can detect image features that are on or off the trailer. Several different methods can be used to separate trailer features from non-trailer features. For example, when traveling in a straight line, trailer features can be separated from non-trailer features by finding features that remain in the same position over time. Alternatively, the motion of background features can be modeled using known vehicle motion over time. This can be extracted from CAN (Controller Area Network) data regarding speed and steering. Features that do not conform to the basic matrix epipolar constraints can be considered trailer features.

[0065] After feature recognition in each corresponding image, the first feature of the first and second images is projected onto a common horizontal plane. More specifically, the ray between the imaging device 3 and the first feature determined in the first image is projected onto the horizontal plane to obtain the first projected feature position PFP1a. Furthermore, the ray between the imaging device 3 and the first feature determined in the second image is projected onto the same horizontal plane to obtain the second projected feature position PFP1b. It is worth noting that the projection is performed in the vertical direction, thus only changing the elevation angle of the light rays, without changing the azimuth angle.

[0066] After determining the first and second projection feature positions PFP1a and PFP1b, a first vertical bisector B1 is set based on the first and second projection feature positions PFP1a and PFP1b. For example... Figure 2 As shown, the first vertical bisector B1 is a line perpendicular to the line connecting the first and second projected feature positions PFP1a and PFP1b. Furthermore, the first vertical bisector B1 passes through the center of the connecting line. The first vertical bisector B1 intersects a reference axis, which in this embodiment is the vehicle's longitudinal axis LAV. The intersection of the first vertical bisector B1 and the reference axis provides the point of rotation around which the trailer rotates. More specifically, the intersection provides the position of the tow bar 4.

[0067] Based on the first perpendicular bisector B1, a first angle estimate α1 is calculated. The first angle estimate α1 refers to the angle between the first line L1 connecting the first projected feature position PFP1a and the intersection of the first perpendicular bisector B1 and the reference axis, and the second line L2 connecting the second projected feature position PFP1b and the intersection of the first perpendicular bisector B1 and the reference axis. The intersection point indicates the position of the tow bar 4. More specifically, the first angle estimate α1 characterizes the angle of swing around the first intersection point IP1 (i.e., the position of the tow bar 4) between the projected position of the first feature in the first image of the trailer 2 on the horizontal plane and the projected position of the first feature in the second image on the horizontal plane.

[0068] The first angle estimate α1 represents the yaw angle YA of trailer 2 around its actual rotation point.

[0069] Figure 3 What is shown is with Figure 2 Similarly, an implementation method is used to determine the yaw angle YA by using the first and second features F1, F2 of the trailer 2 taken at different time points (at which time point the trailer 2 has a different yaw angle YA relative to the tractor 1).

[0070] Multiple different features can be identified in the images captured by camera device 3. For example... Figure 3 As shown, the features are identified at different angular positions relative to a fixed point on vehicle 1. The first feature is represented by a square, and the second feature by a triangle. The fixed point can be the location of the camera device 3 or the location of the tow bar 4.

[0071] exist Figure 3 In the first image, the upper pair of first and second features (represented by PFP1a and PFP2a, and associated with the solid line light connecting the feature to the camera device 3) are identified, and the lower pair of first and second features F1 and F2 (represented by PFP1b and PFP2b, and associated with the dashed line light connecting the feature to the camera device 3) are identified at different time points in the second image.

[0072] The method for determining the yaw angle YA and Figure 2 The implementation shown is similar. The main difference is that two angle estimates α1 and α2 are set, and the yaw angle of the trailer is developed based on the two angle estimates α1 and α2. More specifically, as described above, a first vertical bisector B1 is established and a first angle estimate α1 is implemented.

[0073] Furthermore, by setting a third projection feature position PFP2a and a fourth projection feature position PFP2b, and setting a second vertical bisector B2, a second intersection point IP2 is obtained. The third projection feature position PFP2a and the fourth projection feature position PFP2b are then connected to the second intersection point IP2 to obtain a second angle estimate α2. The third projection feature position PFP2a is obtained by projecting the second feature in the first image onto the horizontal plane, and the fourth projection feature position PFP2b is obtained by projecting the second feature in the second image onto the horizontal plane. The second intersection point IP2 can be the intersection of the second vertical bisector B2 and the reference axis, which in this embodiment is the vehicle's longitudinal axis LAV. The second angle estimate α2 is the angle between the first line connecting the third projection feature position PFP2a and the intersection point IP2 and the second line connecting the fourth projection feature position PFP2b and the intersection point IP2.

[0074] In this embodiment, the reference axis is the longitudinal axis LAV of the tractor 1, because the camera device 3 and the tow bar 4 are located on the longitudinal axis LAV of the vehicle 1. In other embodiments, if the camera device 3 or the tow bar 4 has a lateral offset relative to the longitudinal axis LAV of the vehicle 1, or if the lateral offsets of the camera device 3 and the tow bar 4 relative to the longitudinal axis LAV of the vehicle 1 are different, the reference axis may be formed by a straight line connecting the camera device 3 and the tow bar 4.

[0075] Ideally, the first angle estimate α1 and the second angle estimate α2 should be equal (α1 = α2) and should represent the yaw angle YA. However, due to noise and mismatch, the first and second angle estimates α1 and α2 may differ.

[0076] It is worth mentioning that the two features of trailer 2 mentioned above can be determined and tracked on multiple images. Furthermore, it is preferable to take two or more images at different time points to obtain better yaw angle estimation results. Therefore, two or more angle estimates α1 and α2 can be set to improve the quality of yaw angle determination.

[0077] To determine the yaw angle YA based on first and second angle estimates α1 and α2 with different values, statistical measures can be used. According to a first embodiment, to determine the yaw angle YA, the median of two or more angle estimates α1 and α2 can be used. According to other embodiments, statistical methods can be used to determine the yaw angle YA based on two or more angle estimates α1 and α2. The statistical method can be, for example, the RANSAC algorithm (RANSAC: random sample consensus) or the least squares method.

[0078] It appears that not all features visible in the captured images are suitable for calculating the yaw angle YA. To reduce computational complexity and improve robustness, features whose provided yaw angles are very close to the actual yaw angle are selected and further used to determine the yaw angle YA. To select features, only those features providing yaw angles α1 and α2 within a specific window around the actual yaw angle are tracked in subsequent images. This window can be defined, for example, by an upper and lower bound, which define the angle window around the actual yaw angle. For example, the window can cover a range of 2 to 10 degrees, particularly 3 to 5 degrees. In the last two or more steps of determining the yaw angle, all features within this window that cause the yaw angle are further tracked in subsequently captured images.

[0079] If tracking of a specific feature of the trailer 2 is required across multiple images due to the movement of the trailer 2, samples of that feature can be set on an arc-shaped section. The center of the arc-shaped section indicates the position of the tow bar 4. Thus, by tracking a specific trailer feature across multiple images, the position of the tow bar 4 can be determined.

[0080] To reduce noise, determining the position of the tow bar 4 can be achieved by tracking multiple trailer features across multiple images over a period of time. Each trailer feature can correspond to an arcuate portion with a specific center estimate. The actual position of the tow bar 4 can be determined by applying statistical methods to these multiple center estimates. These statistical methods can be, for example, the RANSAC (Random Sample Consensus) algorithm or the least squares method.

[0081] Figure 4 This demonstrates another implementation of determining the rotation point geometrically without using the reference axis described above.

[0082] The rotation point was determined by developing at least two perpendicular bisectors B1 and B2, based on three images showing a specific feature at different angular positions relative to the tractor 1. Figure 4 In this context, the first projection feature position PFP1a refers to the feature included in the first image and projected onto a common horizontal plane as previously described. Similarly, the second projection feature position PFP1b refers to the feature included in the second image, and the third projection feature position PFP1c refers to the feature included in the third image.

[0083] The first vertical bisector B1 refers to a line connecting the first and second projected feature positions PFP1a and PFP1b. The second vertical bisector B2 refers to a line connecting the first and third projected feature positions PFP1a and PFP1c. The intersection of the first and second vertical bisectors B1 and B2 defines an intersection point IP, which represents the rotation point of the trailer 2, i.e., the position of the tow bar 4.

[0084] The intersection point IP can be as follows: Figure 2 and Figure 3 As shown in the implementation, the yaw angle YA of the trailer is used to determine the yaw angle.

[0085] Figure 5 The diagram shows a method for determining the yaw angle YA of trailer 2 relative to the longitudinal axis LAV of tractor 1.

[0086] First, take first and second images of the trailer (S10).

[0087] After the images are captured, at least one visible feature of the trailer in the first and second images is determined (S11).

[0088] After determining the features, the positions of the first and second projected features are set by feature projection (S12).

[0089] After feature projection, the first vertical bisector is established (S13).

[0090] After setting the first perpendicular bisector, the first intersection point of the first perpendicular bisector with the reference axis or another perpendicular bisector is developed (S14).

[0091] Finally, the yaw angle (S15) is calculated based on the first angle estimate.

[0092] It should be noted that the description and accompanying drawings are merely illustrative of the principles of the invention. Those skilled in the art will be able to implement various arrangements that are not explicitly described or shown herein but embody the principles of the invention.

[0093] List of reference numerals

[0094] 1 vehicle

[0095] 2 trailers

[0096] 3. Camera device

[0097] 4. Traction rod

[0098] α1 First Angle Estimation

[0099] α2 Second Angle Estimation

[0100] B1 First perpendicular bisector

[0101] B2 Second perpendicular bisector

[0102] The first feature projection position in the first image of PFP1a

[0103] The first feature projection location in the second image of PFP1b

[0104] The first feature projection position in the third image of PFP1c

[0105] Second feature projection location in the first image of PFP2a

[0106] The second feature projection location in the second image of PFP2b

[0107] IP intersection

[0108] IP1 First intersection point

[0109] IP2 Second Intersection

[0110] LAT trailer longitudinal axis

[0111] LAV vehicle longitudinal axis

[0112] R light rays

[0113] YA Yaw angle

Claims

1. A method for determining the yaw angle of a trailer (2) relative to the longitudinal axis of a tractor (1), wherein, The method includes the following steps: - Use a camera device (3) to detect at least one first and second images of the trailer (2), wherein the orientation of the trailer (2) relative to the vehicle (1) is different in at least two images; - Identify at least one first feature of the trailer (2) that is visible in the first and second images; - Project the ray between the camera device (3) and the first feature determined on the first image onto the horizontal plane to obtain the position of the first projected feature, and project the ray between the camera device (3) and the first feature determined on the second image onto the horizontal plane to obtain the position of the second projected feature; - Set a first vertical bisector between the first projection feature position and the second projection feature position; - Determine the first intersection point of the first vertical bisector with the reference axis or another vertical bisector, wherein the other vertical bisector is determined between the first feature in the first image and the first feature in the third image, wherein the position of the first feature is determined not only in the first and second images but also in the third image, wherein if the camera device (3) and the tow bar (4) of the vehicle (1) are arranged in a plane in the vertical direction including the longitudinal axis of the tow vehicle (1), then the reference axis is the longitudinal axis of the tow vehicle (1); if the camera device (3) and / or the tow bar (4) have a lateral offset relative to the longitudinal axis of the tow vehicle (1), then the reference axis is a straight line between the camera device (3) and the tow bar (4); - Calculate the yaw angle based on the first angle estimate, wherein the first angle estimate refers to the angle between the first line from the first projection feature position to the first intersection point and the second line from the second projection feature position to the first intersection point on the horizontal plane, wherein the yaw angle of the trailer (2) relative to the vehicle (1) is zero or any known yaw angle that can be used as a reference angle in the first or second image.

2. The method according to claim 1, further comprising the following steps: - Determine the second feature of the trailer (2) visible in the first and second images, wherein, The second feature is located at a different position on the trailer (2) than the first feature. - Project the ray between the camera device (3) and the second feature determined on the first image onto the horizontal plane to obtain the third projected feature position, and project the ray between the camera device (3) and the second feature determined on the second image onto the horizontal plane to obtain the fourth projected feature position. -In addition, a second vertical bisector is set between the third projection feature position and the fourth projection feature position; - Determine the second intersection point between the second perpendicular bisector and the reference axis; - Calculate a second angle estimate, wherein the second angle estimate refers to the angle between a first line from the third projection feature position to the second intersection point and a second line from the fourth projection feature position to the second intersection point on the horizontal plane, wherein the second angle estimate is also considered when calculating the yaw angle.

3. The method according to claim 2, wherein, In addition to the first and second features, at least one other feature of the trailer (2) is used for the calculation of the yaw angle.

4. The method according to claim 2, wherein, The yaw angle is calculated by using the median value constructed based on at least two angle estimates.

5. The method according to claim 2, wherein, The yaw angle is calculated by averaging at least two angle estimates or by using a statistical method applied to the angle estimates.

6. The method according to any one of claims 1 to 5, further comprising the step of determining an angle window, wherein, The angle window includes an upper and lower limit around the yaw angle, a set of features that lead to the angle estimation within the angle window are determined, and the determined set of features is used for future yaw angle calculations.

7. The method according to any one of claims 2 to 5, wherein, The camera device calibration information is used to convert the position of the first feature and / or the second feature from the local domain of the image to the local domain of the vehicle (1).

8. The method according to any one of claims 1 to 5, wherein, The camera device (3) is a rear-view camera device of the vehicle (1).

9. A system for determining the yaw angle of a trailer (2) relative to the longitudinal axis of a tractor (1), wherein, The system includes a camera device (3) for capturing images of the trailer (2) and a processing entity for processing the captured images. Furthermore, the system is configured to perform the following steps: - Use a camera device (3) to detect at least one first and second images of the trailer (2), wherein the orientation of the trailer (2) relative to the vehicle (1) is different in at least two images; - Identify at least one first feature of the trailer (2) that is visible in the first and second images; - Project the ray between the camera device (3) and the first feature determined on the first image onto the horizontal plane to obtain the position of the first projected feature, and project the ray between the camera device (3) and the first feature determined on the second image onto the horizontal plane to obtain the position of the second projected feature; - Set a first vertical bisector between the first projection feature position and the second projection feature position; - Determine the first intersection point of the first vertical bisector with the reference axis or another vertical bisector, wherein the other vertical bisector is determined between the first feature in the first image and the first feature in the third image, wherein the position of the first feature is determined not only in the first and second images but also in the third image, wherein if the camera device (3) and the tow bar (4) of the vehicle (1) are arranged in a plane in the vertical direction including the longitudinal axis of the tow vehicle (1), then the reference axis is the longitudinal axis of the tow vehicle (1); if the camera device (3) and / or the tow bar (4) have a lateral offset relative to the longitudinal axis of the tow vehicle (1), then the reference axis is a straight line between the camera device (3) and the tow bar (4); - Calculate the yaw angle based on the first angle estimate, wherein the first angle estimate refers to the angle between the first line from the first projection feature position to the first intersection point and the second line from the second projection feature position to the first intersection point on the horizontal plane, wherein the yaw angle of the trailer (2) relative to the vehicle (1) is zero or any known yaw angle that can be used as a reference angle in the first or second image.

10. A vehicle, wherein, The vehicle includes the system according to claim 9.

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