METHOD FOR DETERMINING THE ANGLE POSITION OF A TRAILER RELATIVE TO A TOWING VEHICLE

Description

Domaine technique

[0001] This disclosure falls within the domain of trailer angular position detection.

[0002] More specifically, this disclosure relates to a method for determining the yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a tractor vehicle. Technique antérieure

[0003] Solutions exist to assist drivers in operating vehicles, for example by providing them with additional information about the vehicle's configuration and its position relative to its surroundings. These technologies are also necessary for fully autonomous vehicles. This applies to individual vehicles, but also to transport vehicles, typically consisting of a tractor unit and a trailer.

[0004] For driving assistance with such vehicles, and in particular for reversing maneuvers aimed at parking the vehicle, it is important to know precisely the angular position of the trailer relative to the towing vehicle, and in particular the yaw angle subject to the greatest amplitude.

[0005] Solutions already exist for determining the yaw angle of a trailer relative to a vehicle, some of which rely on the use of mechanical sensors, mounted for example on the attachment point.

[0006] Such mechanical sensors are heavy, and their installation on a vehicle is complicated and requires a calibration phase.

[0007] Other known solutions are based on the analysis of an image acquired by a camera located at the rear of the vehicle.

[0008] However, a camera's field of view is limited, and a camera mounted on the rear of the vehicle is close to the trailer and therefore cannot detect large yaw angles of the trailer relative to the towing vehicle. Indeed, when the yaw angle becomes significant, the trailer moves out of the camera's field of view, and the yaw angle cannot be detected.

[0009] Document JP2002181518A discloses a system in which wide-angle cameras are mounted on both sides of the tractor, so that the rear of the trailer attached to the tractor is within the cameras' field of view. A map illustrating the relationship between the trailer's position as captured by the cameras and the connection angle is displayed to calculate the trailer's connection angle to the tractor.

[0010] There is therefore a need for a method to accurately determine a yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a tractor vehicle over a wide range of yaw angle values. Résumé

[0011] To this end, a method for determining the yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a towing vehicle to which the trailer is attached at an attachment point is disclosed, the method comprising: acquire, by means of a camera mounted on the side of the towing vehicle and oriented towards the trailer, an image of at least one side portion of the trailer; determine on the image a visible marker on the trailer; determine on the image a visible length between the marker and a vertical edge of the image oriented towards the towing vehicle; determine the yaw angle at least on the basis of a horizontal field of view of the camera, a width of a pixel matrix of the camera along a horizontal axis of the camera, coordinates of the attachment point, the visible length, and dimensions of at least one portion of the trailer, and in which determining the yaw angle includes: determine a normal viewing angle β between the longitudinal axis of the towing vehicle and a straight line connecting the camera to the trailer's frame of reference, at least on the basis of said visible length, the horizontal field of view of the camera, and the width of the camera's pixel matrix along the camera's horizontal axis; determine the coordinates of the trailer's frame of reference by means of an intersection between: * said straight line represented by a line equation defined as: y = c ∗ x + d where x and y form coordinates of points in a coordinate system including the frame of reference, c is a slope and d is a ordinate value; * a circle centered on the attachment point and having a radius equal to a distance between the attachment point and the coordinate system, in which the circle is defined as: x − a 2 + y − b 2 = r 2 where a and b are coordinates of the attachment point, and r is the radius of the circle; determine the yaw angle at least on the basis of said coordinates of the trailer frame and coordinates of the attachment point.

[0012] The method allows for the precise determination of the yaw angle of the longitudinal axis of a trailer relative to the longitudinal axis of a towing vehicle over a wide range of yaw angle values.

[0013] The method is innovative in that it uses a camera mounted on the side of the vehicle. This ensures that the reference point will always be within the camera's field of view and visible to the camera, regardless of the yaw angle.

[0014] In addition, the method is innovative in determining the yaw angle based on the camera's horizontal field of view, the width of the pixel matrix, the coordinates of the attachment point, the visible length, and the dimensions of at least a part of the trailer.

[0015] In one embodiment, the coordinate system is centered on the camera and the equation of the line is defined as: y = tan β norm ∗ x

[0016] In one embodiment, the radius of the circle is defined as: r = T L 2 + T l 2 2 where TL is a distance along the longitudinal axis of the trailer between the attachment point and the marker, and Tl is a width of the trailer.

[0017] In one embodiment, the angle of observation is defined as: β norm = R x ∗ hFOV w − C caméra where R x is the visible length, hFOV is the horizontal field of view of the camera, wis the width of the camera's pixel matrix along the camera's horizontal axis, and C camera is a normalization angle that takes into account the camera's orientation relative to the towing vehicle.

[0018] In one embodiment, the camera normalization angle C is defined as: C cam é ra = hFOV 2 − C yaw where C yaw is a camera mounting parameter described as the angle between an optical axis of the camera and a longitudinal axis of the tractor vehicle.

[0019] In one embodiment, determining the yaw angle includes: determine a first auxiliary angle defined as: Φ = arc tan OR y OR x where OR y is a distance between the trailer's reference point and the hitch point along a horizontal axis perpendicular to the longitudinal axis of the towing vehicle, and OR x is a distance between the reference point and the hitch point along the longitudinal axis of the towing vehicle; determine a second auxiliary angle defined as: θ = arc tan T l 2 T L where TL is the distance along the longitudinal axis of the trailer between the hitch point and the reference frame, and Tl is the width of the trailer. Determine the yaw angle defined as: α=Φ−θ

[0020] In one embodiment, the marker includes at least a portion of a rear vertical edge of the trailer.

[0021] In one embodiment, the width of the pixel matrix and the visible length are determined by the number of pixels on the camera matrix.

[0022] Another aspect of the present invention relates to a computer program product comprising instructions which, when executed by a processor, cause the processor to carry out the operations of the process described above.

[0023] Another aspect of the invention relates to a system for determining the yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a towing vehicle to which the trailer is attached at an attachment point, the determination system comprising: * a camera adapted to be mounted on a lateral side of the towing vehicle so that it is oriented towards the trailer, and to acquire an image of at least one lateral part of the trailer; and * a computer configured to implement the method described above.

[0024] In one embodiment, the tractor vehicle includes at least one rearview mirror, in which said at least one camera is configured to be mounted on the at least one rearview mirror.

[0025] In one embodiment, said at least one camera is configured to have a digital rearview mirror function.

[0026] In one embodiment, the determination system comprises two cameras mounted on opposite lateral sides of the tractor vehicle, each of the cameras being configured to acquire an image of at least one lateral part of the trailer; and wherein the computer is configured to implement the method described above for each of the cameras. Brève description des dessins

[0027] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, on which: [ Fig. 1 ] There figure 1 is a schematic representation of a top view of a system for determining the yaw angle of a trailer's longitudinal axis relative to the longitudinal axis of a towing vehicle to which the trailer is attached. Fig. 2 ] There figure 2 shows the flowchart of a method for determining the yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a tractor vehicle to which the trailer is attached. Fig. 3 ] There figure 3 is a schematic representation of an image of a trailer taken by a camera of the system for determining the figure 1 the camera being mounted on the left side of the towing vehicle. Fig. 4 ] There figure 4 is another schematic representation of a top view of the system for determining the figure 1 . [ Fig. 5 ] There figure 5 is a schematic representation of a computer configured to implement the process of determining the figure 2 . Description des modes de réalisation

[0028] The present invention relates to a method and a system for determining a yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a tractor vehicle to which the trailer is attached.

[0029] There figure 1 shows such a determination system S which includes a tractor vehicle V and a trailer T attached to the tractor vehicle V at an attachment point O such as a trailer hitch.

[0030] The relative orientation of the trailer T with respect to the tractor vehicle V can be characterized by the yaw angle α defined as the angle between the longitudinal axis LT of the trailer T and the longitudinal axis Lv of the tractor vehicle V in the horizontal plane.

[0031] The towing vehicle V, which can be, for example, a car or a truck, includes an exterior rearview mirror M on each side of the towing vehicle V, allowing a driver of the towing vehicle V to observe part of the environment behind them. In particular, the mirrors M allow observation of part of the trailer T and, specifically, the orientation of the trailer T relative to the towing vehicle V.

[0032] The M mirrors are installed at the front part of the driver and passenger doors of the V vehicle.

[0033] Each M rearview mirror can be in the form of a C camera or in the form of a mirror on which a C camera is mounted.

[0034] Each camera C is oriented towards the trailer T and is adapted to acquire at least one image I or a series of images I of a lateral part of the trailer T. A schematic representation of such an image I is shown on the figure 3 .

[0035] Each C camera comprises a pixel matrix that is typically rectangular in shape and includes a horizontal axis x and a vertical axis z Therefore, the image I taken by the camera is also rectangular in shape and is defined by the same axes, i.e., the horizontal axis. x and the vertical axis z .

[0036] In the example of the figure 3 Part of the tractor vehicle V is visible in image I. However, it is not necessary for the tractor vehicle V to be visible in image I in determining the yaw angle.

[0037] The trailer T includes a reference point R on each lateral side, each of the reference points R being visible by the respective camera C on the same lateral side of the trailer T. For example, the reference point R may be a rear vertical edge of the trailer T. The respective reference point R can be identified on the image I taken by one of the cameras C and be used in determining the yaw angle α.

[0038] The S determination system further includes a calculator P described in more detail in relation to the figure 5 The calculator P is configured to implement a method 100 for determining the yaw angle α, the flowchart of which is shown in the figure 2 .

[0039] For the sake of simplicity and in order to best illustrate the process 100 below, only one camera C and one reference point R on the same side of the trailer T are considered.

[0040] During the implementation of method 100, camera C acquires 101 at least one image I of a portion of the trailer T as shown in the figure 2 .

[0041] The marker R is detected 102 on the image I. Then, it is determined 103 on the image I the distance, also called the visible length R x, between the marker R and the nearest vertical edge B of the tractor vehicle V.

[0042] The visible length R x can be determined along the horizontal axis x in the number of pixels on which the trailer T and the tractor vehicle V are visible.

[0043] The angles and distances determined and used in the remainder of process 100 are best understood with the help of the figure 4 which shows a schematic representation of the S determination system.

[0044] The coordinates of the various points determined and / or used in process 100 all refer to a coordinate system centered on camera C. In this coordinate system, a first axis x' is oriented along the longitudinal axis Lv of the tractor vehicle V, and a second axis y is oriented along the width of the tractor vehicle V, i.e. in the horizontal plane and perpendicular to the first axis x' .

[0045] The vertical axis z is defined with respect to the first and second axes x' And y so as to form an orthogonal coordinate system.

[0046] Next, an observation angle β norm defined as the angle between a straight line connecting the camera C to the frame R and the longitudinal axis Lv of the tractor vehicle V is determined 104: β norm = β − C caméra

[0047] Here, β is the auxiliary viewing angle, defined as the angle between the line connecting camera C to frame R and a line defining the horizontal field of view of camera C on the side of the tractor vehicle V. The horizontal field of view is the horizontal portion of the solid angle through which camera C perceives its surroundings. The horizontal field of view can be defined by two lines that respectively delimit areas visible to camera C and areas not visible to camera C.

[0048] C camera is a normalization angle that takes into account the orientation of the camera C relative to the tractor vehicle V.

[0049] The auxiliary observation angle β is defined as: β = R x ∗ hFOV w where w is the width of image I along the horizontal axis xof image I, and hFOV is the horizontal field of view of camera C. The width w of the pixel matrix and the horizontal field of view hFOV are known parameters of camera C.

[0050] The camera normalization angle C is defined as: C cam é ra = hFOV 2 − C yaw Or C yaw is a mounting parameter (not shown in the figures) of camera C described as the angle between the optical axis of camera C and the longitudinal axis Lv of the tractor vehicle V. The angle C yaw depends on the orientation of camera C relative to the towing vehicle V and can be determined for a given orientation of camera C.

[0051] The equation of the line containing the camera C and the frame R is defined as: y = c ∗ x + d

[0052] c is a slope coefficient and d is a y-value. c is equal to here tan ( βnorm). It should be noted that, when the yaw angle α changes, all possible positions of the frame R will be located on a circle centered on the attachment point O and having as its radius the distance between the attachment point O and the frame R.

[0053] The equation describing the circle is: x − a 2 + y − b 2 = r 2 where a and b are coordinates of the attachment point O. These coordinates a, b in the coordinate system centered on the camera C are known or can be determined.

[0054] The coordinates of the frame R can be determined by determining the intersection of said circle ((xa) 2< + (yb) 2< = r 2< ) with said line ( y = tan(β norm )* x The coordinate y in the equation of the circle is replaced by the equation of the line for this purpose: x − a 2 + y − b 2 = r 2 x 2 − 2 ax + a 2 + y 2 − 2 by + b 2 − r 2 = 0 x 2 − 2 ax + a 2 + tan β norm ∗ x 2 − 2 b tan β norm ∗ x + b 2 − r 2 = 0 1 + tan 2 β norm x 2 − 2 a + 2 b tan β norm x + a 2 + b 2 − r 2 = 0 A 2 x 2 + A 1 x + A 0 where A 2 = 1 + tan 2< (β norm ), A 1 = -(2 a + 2 btan β norm ), A 0 = a 2< + b 2< - r 2<

[0055] We obtain a second-degree equation with the coefficients A2, A1, A0.

[0056] A 0 is a function of the radius r of the circle, which can be determined based on the dimensions of the trailer T: r = OR = T L 2 + T l 2 2

[0057] TL is the distance along the longitudinal axis LT of the trailer T between the attachment point O and the marker R, and Tl is the width of the trailer T. In the case where the marker R is the rear vertical edge of the trailer T, TL corresponds to the length of the trailer T, i.e., TL is the distance along the longitudinal axis LT of the trailer T between the attachment point O and the marker R. The distance TL and the width Tl are known parameters of the trailer T.

[0058] There are two solutions for x that correspond to the two intersections between the circle and the line: x 1 / 2 = − A 1 ± Δ 2 * A 2 Or Δ = A 1 2 − 4 ∗ A 2 ∗ A 0 .

[0059] One of the two solutions corresponds to the x-coordinate of the coordinate system R. The other solution can be discarded. The corresponding y-coordinate of the coordinate system R can be obtained by inserting the x-coordinate into the equation of the line: y R = tan β norm ∗ x R

[0060] In order to determine the yaw angle α, a first auxiliary angle Φ and a second auxiliary angle θ are determined.

[0061] The first auxiliary angle Φ refers to the angle between the longitudinal axis Lv of the tractor vehicle V and the line connecting the attachment point O and the frame of reference R, and is defined as: Φ = arc tan OR y OR x = arc tan y R − b x R − a

[0062] The second auxiliary angle θ refers to the angle between the longitudinal axis LT of the trailer T and the line connecting the attachment point O to the frame of reference R, and is defined as: θ = arc tan T l 2 T L

[0063] Thus, the yaw angle α can be determined 106: α = Φ − θ

[0064] To detect the yaw angle α on both sides of the tractor vehicle V, a camera C can be used on each lateral side of the tractor vehicle V. Thus, a reference point R on the trailer T will always be visible to one of the two cameras C.

[0065] Method 100 can be implemented iteratively to provide updated values ​​of the yaw angle α iteratively.

[0066] There figure 5 shows an embodiment of the calculator P configured to implement at least part of process 100.

[0067] The calculator P includes at least one input interface 201 for receiving messages or instructions, and at least one output interface 202 for communication with external devices 205.

[0068] The calculator P further includes a memory 203 for storing instructions enabling the implementation of at least part of the process 100, the received data, and temporary data for carrying out the various operations 101, 102, 103, 104, 105, 106 of the process 100 as described previously.

[0069] The computer P also includes a processing circuit 204. This circuit can be, for example: a processor capable of interpreting instructions in the form of a computer program, or an electronic board whose operations of the disclosure process can be described in silicon, or even a programmable electronic chip such as an FPGA chip for " Field-Programmable Gate Array » in English, like a SOC for " System On Chip » in English or as an ASIC for « Application Specific Integrated Circuit » an english.

[0070] Depending on the embodiment, the computing unit P may be a computer, a network of computers, an electronic component, or another device comprising a processor operationally coupled to memory, as well as, depending on the chosen embodiment, a data storage unit, and other associated hardware elements such as a network interface and a media reader for reading and writing to removable storage media not shown in the figure 5 . Removable storage media can be, for example, a compact disc CD, a digital video / multipurpose disc DVD, a flash drive, a USB key, etc.

[0071] Depending on the embodiment, the memory 203, the data storage unit, or the removable storage medium contains instructions which, when executed by the processing circuit 204, cause this circuit to perform or control at least one input interface 201, at least one output interface 202, the storage of data in the memory 203, and / or the processing of data, and / or the implementation of at least one part of the process 100 according to the figure 2 .

[0072] The processing circuit 204 can be a component implementing the control of the computer P.

[0073] Furthermore, the calculator P can be implemented in software form, in which case it takes the form of a program executable by a processor, or in hardware form, or « hardware », such as an application-specific integrated circuit (ASIC), a system-on-chip (SOC), or as a combination of hardware and software components, for example, a software program intended to be loaded and executed on an electronic component described above, such as an FPGA.

[0074] The P computer can also use hybrid architectures, for example architectures based on a CPU+FPGA, a GPU for « Graphics Processing Unit » or an MPPA for " Multi-Purpose Processor Array ».

[0075] This disclosure is not limited to the examples of devices, systems, processes, uses and computer program products described above, only as examples, but encompasses all the variations that a person in the trade may consider in the context of the protection sought.

Claims

1. A method (100) for detecting a yaw angle (α) of a longitudinal axis (LT) of a trailer (T) relative to a longitudinal axis (Lv) of a towing vehicle (V) to which the trailer (T) is attached at an attachment point (O), the method comprising: - acquiring (101), by means of a camera (C) mounted on a lateral side of the towing vehicle (V) and oriented toward the trailer (T), an image (I) of at least one lateral portion of the trailer (T); - determining (102) a reference point (R) on the image (I) that is visible on the trailer (T); - determining (103) on the image (I) a visible length (Rx) between the reference point (R) and a vertical edge (B) of the image (I) oriented toward the towing vehicle (V); - determining the yaw angle (α) based at least on the horizontal field of view (hFOV) of the camera (C), the width (w) of a pixel matrix of the camera (C) along a horizontal (x) axis of the camera (C), the coordinates of the attachment point (O), the visible length (Rx), and the dimensions (TL, Tl) of at least a portion of the trailer (T), and wherein determining the yaw angle (α) comprises: - determining (104) an observation angle (βnorm) between the longitudinal axis (Lv) of the towing vehicle (V) and a straight line (CR) connecting the camera (C) to the reference point (R) of the trailer (T), based at least on said visible length (Rx), of the horizontal field of view (hFOV) of the camera (C), and the width (w) of the pixel matrix of the camera (C) along the horizontal (x) axis of the camera (C); the method being characterized in that it comprises: - determining (105) coordinates (xR, yR) of the reference point (R) of the trailer (T) by means of an intersection between: * said straight line (CR) represented by a straight-line equation defined as: y = c * x + d where x and y are the coordinates of points in a coordinate system comprising the reference point (R), c is a slope coefficient, and d is an ordinate value; * a circle centred at the attachment point (O) and having a radius equal to the distance between the attachment point (O) and the reference point (R), where the circle is defined as: x − a 2 + y − b 2 = r 2 where a and b are coordinates of the attachment point (O), and r is the radius of the circle; - determining (106) the yaw angle (α) at least based on said coordinates (xR, yR) of the reference point (R) of the trailer (T) and on coordinates of the attachment point (O).

2. The method according to Claim 1, wherein the coordinate system is centred on the camera (C) and the straight-line equation is defined as: y = tan β norm * x3. The method according to any of Claims 1 and 2, wherein the radius of the circle is defined as: r = T L 2 + T l 2 2 where TL is a distance along the longitudinal axis (LT) of the trailer (T) between the attachment point (O) and the reference point (R), and Tl is a width of the trailer (T).

4. The method according to any of Claims 1 to 3, wherein the observation angle (βnorm) is defined as: β norm = R x ∗ hFOV w − C camera where Rx is the visible length, hFOV is the horizontal field of view of the camera (C), w is the width of the pixel array of the camera (C) along the horizontal axis(x) of the camera (C), and Ccamera is a normalisation angle that takes into account the orientation of the camera (C) relative to the towing vehicle (V).

5. The method according to Claim 4, wherein the normalization angle is defined as: C camera = hFOV 2 − C yaw where Cyaw is a camera (C) mounting parameter defined as the angle between the optical axis of the camera (C) and the longitudinal axis (Lv) of the towing vehicle (V).

6. The method according to any one of the preceding claims, wherein determining the yaw angle (α) comprises: - determining a first auxiliary angle (Φ) defined as: Φ = arc tan OR y OR x where ORy is a distance between the reference point (R) of the trailer (T) and the attachment point (O) along a horizontal axis perpendicular to the longitudinal axis (Lv) of the towing vehicle (V), and ORx is a distance between the reference point (R) and the attachment point (O) along the longitudinal axis (Lv) of the towing vehicle (V); - determining a second auxiliary angle (θ) defined as: θ = arc tan T l 2 T L where TL is a distance along the longitudinal axis (LT) of the trailer (T) between the attachment point (O) and the reference point (R), and Tl is a width of the trailer (T); - determining the yaw angle (α) defined as: α = Φ − θ7. A computer program comprising instructions which, when executed by a processor, cause the processor to perform operations of a method (100) according to any one of claims 1 to 6.

8. A system (S) for detecting a yaw angle (α) of a longitudinal axis (LT) of a trailer (T) relative to a longitudinal axis (Lv) of a towing vehicle (V) to which the trailer (T) is attached at an attachment point (O), the detection system (S) comprising: * a camera (C) adapted to be mounted on a side of the towing vehicle (V) in such a way that it faces the trailer (T), and to acquire an image (I) of at least one side of the trailer (T); and * a computer (P) configured to implement a method (100) according to any one of claims 1 to 6.

9. A detection system according to claim 8, wherein said at least one camera (C) is configured to function as a digital rear-view mirror.