Method for determining the angular position of a trailer relative to a towing vehicle

Abstract

A method for determining a 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 method comprising:- acquiring, by a camera mounted on a lateral side of the towing vehicle and oriented towards the trailer, an image of a lateral part of the trailer;- determining on the image a visible mark on the trailer; - determining on the image a visible length between the mark and a vertical edge of the image oriented towards the vehicle; - determining 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 a part of the trailer. Abstract figure: Figure 4

Description

Title of the invention: Method for determining the angular position of a trailer relative to a towing vehicle Technical field

[0001] The present disclosure relates to the field of detecting the angular position of a trailer.

[0002] More particularly, the present disclosure relates to a method for determining a yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a towing vehicle. Prior art

[0003] There are solutions to assist drivers in driving vehicles, for example by providing them with additional information on the configuration of the vehicle and its position relative to its environment. These technologies are also necessary in the perspective of fully autonomous vehicles. This is the case for individual vehicles, but also for transport vehicles, typically comprising a towing vehicle and a trailer.

[0004] To assist in driving such vehicles, and in particular for reversing maneuvers intended to park 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] There are already solutions 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, the field of view of a camera 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 large, the trailer moves out of the field of view of the camera, and the yaw angle cannot be detected.

[0009] There is therefore a need for a method for accurately determining a yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a towing vehicle over a wide range of yaw angle values. Abstract

[0010] For this purpose, there is disclosed a method for determining a 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 method comprising: - acquire, by a camera mounted on a lateral side of the towing vehicle and oriented towards the trailer, an image of at least one lateral part of the trailer; - determine on the image a visible mark 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; - determining 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 a portion of the trailer.

[0011] The method makes it possible to precisely determine 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.

[0012] The method is innovative in that it uses a camera mounted on the lateral side of the vehicle. Thus, the marker will always be in the camera's field of view and will always be visible to the camera, regardless of the value of the yaw angle.

[0013] Furthermore, the method is innovative in determining the yaw angle as a function of the horizontal field of view of the camera, the width of the pixel array, the coordinates of the attachment point, the visible length, and the dimensions of at least a portion of the trailer.

[0014] In one embodiment, determining the yaw angle comprises: - determine an observation angle Pnorm between the longitudinal axis of the towing vehicle and a straight line connecting the camera to the trailer reference mark, at least on the basis of said visible length, the horizontal field of view of the camera, and the width of the pixel matrix of the camera along the horizontal axis of the camera; - determine the coordinates of the trailer reference point by means of an intersection between: * said straight line represented by a straight line equation defined as: y — c*x + where x and y form coordinates of points in a coordinate system including the reference frame, c is a slope coefficient and d is an ordinate value; * a circle centered on the attachment point and having a radius equal to a distance between the attachment point and the reference frame, in which the circle is defined as: (xa)2 + (yb)2 = a ct 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 reference frame and coordinates of the attachment point.

[0015] In one embodiment, the coordinate system is centered on the camera and the equation of the line is defined as: y = tan(finm)*.x

[0016] In one embodiment, the radius of the circle is defined as: / ' / T \ 2 where Tl is a distance along the longitudinal axis of the trailer r = y (Tl) + ) between the attachment point and the mark, and Ti is a width of the trailer.

[0017] In one embodiment, the viewing angle is defined as: r — RUkFQV p where Rx is the visible length, hFOV is the field of view t norm ^camera horizontal axis of the camera, H' is the width of the camera pixel matrix along the horizontal axis of the camera, and Ccamera is a normalization angle that takes into account an orientation of the camera relative to the towing vehicle.

[0018] In one embodiment, the normalization angle Ccamera is defined as: Ç , — 1ÆQY _ C^where Cyaw is a camera mounting parameter described as the angle between an optical axis of the camera and a longitudinal axis of the towing vehicle.

[0019] In one embodiment, determining the yaw angle comprises: - determine a first auxiliary angle defined as: O = arc tan°R' where ORy is a distance between the trailer reference mark and the attachment point along a horizontal axis perpendicular to the longitudinal axis of the towing vehicle, and ORX is a distance between the reference mark and the attachment point along the longitudinal axis of the towing vehicle; - determine a second auxiliary angle defined as: G = arc tan r! °ù Tl is a distance along the longitudinal axis of the trailer between 2^l the attachment point and the mark, and Ti is a width of the trailer. - determine the yaw angle defined as:

[0020]

[0021]

[0022] In one embodiment, the marker comprises at least a portion of a rear vertical edge of the trailer. In one embodiment, the width of the pixel array and the visible length are determined by the number of pixels on the camera array. Another aspect of the present invention relates to a computer program product comprising instructions which, when these instructions are executed by a processor, cause the processor to implement the operations of the method described above.

[0023] Another aspect of the invention relates to a system for determining a 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 determining system comprising: * a camera adapted to be mounted on a lateral side of the towing vehicle in such a way 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 towing vehicle comprises at least one rearview mirror, wherein 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 towing vehicle, each of the cameras being configured to acquire an image of at least one lateral portion of the trailer; and in which the calculator is configured to implement the method described above for each of the cameras. Brief description of the drawings

[0027] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0028] [Fig-1] [Fig.l] is a schematic representation of a top view of a system for determining a yaw angle of a longitudinal axis of a trailer relative to a longitudinal axis of a towing vehicle to which the trailer is attached.

[0029] [Fig.2] [Fig.2] shows the flowchart of a method for determining an angle yaw of a longitudinal axis of a trailer relative to a longitudinal axis of a towing vehicle to which the trailer is attached.

[0030] [Fig.3] [Fig.3] is a schematic representation of an image of a trailer taken by a camera of the determination system of [Fig.l], the camera being mounted on the left side of the towing vehicle.

[0031] [Fig.4] [Fig.4] is another schematic representation of a top view of the system for determining [Fig.l].

[0032] [Fig.5] [Fig.5] is a schematic representation of a computer configured to implement the method of determining [Fig.2]. Description of the embodiments

[0033] 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 towing vehicle to which the trailer is attached.

[0034] [Fig.l] shows such a determination system S which comprises a towing vehicle V and a trailer T attached to the towing vehicle V at an attachment point O such as a trailer hitch.

[0035] The relative orientation of the trailer T with respect to the towing vehicle V can be characterized by the yaw angle defined as the angle between the longitudinal axis LT of the trailer T and the longitudinal axis Lv of the towing vehicle V in the horizontal plane.

[0036] The towing vehicle V, which may be for example in the form of a car or a truck, comprises an exterior rearview mirror M on each lateral side of the towing vehicle V, allowing a driver of the towing vehicle V to observe part of the environment behind him. In particular, the rearview mirrors M make it possible to observe part of the trailer T and in particular the orientation of the trailer T relative to the towing vehicle V.

[0037] The rearview mirrors M are installed at the front part of the driver's and passenger's doors of the vehicle V.

[0038] Each rearview mirror M can be in the form of a camera C or in the form of a mirror on which a camera C is mounted.

[0039] Each camera C is oriented towards the trailer T and is adapted to acquire an image I or a series of images I of at least one lateral part of the trailer T. A schematic representation of such an image I is shown in [Fig.3].

[0040] Each camera C comprises a pixel matrix which is typically rectangular in shape and which comprises a horizontal axis x and a vertical axis 7. Consequently, 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 J.

[0041] In the example of [Fig.3], a part of the towing vehicle V is visible in image I. However, it is not necessary in determining the yaw angle that the towing vehicle V be visible in image I.

[0042] The trailer T comprises a marker R on each lateral side, each of the markers R being visible to the respective camera C from the same lateral side of the trailer T. For example, the marker R may be a rear vertical edge of the trailer T. The respective marker R may be identified on the image I taken by one of the cameras C and be used in determining the yaw angle a.

[0043] The determination system S further comprises a calculator P described in more detail in relation to FIG. 5. The calculator P is configured to implement a method 100 for determining the yaw angle a, the flowchart of which is shown in [Fig.2].

[0044] For the sake of simplicity and in order to best illustrate the method 100 below, a single camera C and a single marker R on the same side of trailer T are considered.

[0045] When implementing the method 100, the camera C acquires 101 an image I of at least a part of the trailer T as shown in [Fig.2].

[0046] The reference mark R is detected 102 on the image I. Then, the distance, also called visible length Rx, between the reference mark R and the vertical edge B closest to the towing vehicle V is determined 103 on the image I.

[0047] The visible length Rx can be determined along the horizontal axis x as the number of pixels on which the trailer T and the towing vehicle V are visible.

[0048] The angles and distances determined and used in the remainder of the method 100 are better understood with the aid of [Fig.4] which shows a schematic representation of the determination system S.

[0049] The coordinates of the different points determined and / or used in the method 100 all relate to a coordinate system centered on the camera C. In this coordinate system, a first axis P is oriented along the longitudinal axis Lv of the towing vehicle V, and a second axis y is oriented along the width of the towing vehicle V, i.e. in the horizontal plane and perpendicular to the first axis p.

[0050] The vertical axis 7 is defined relative to the first and second axes and y so as to form an orthogonal reference frame.

[0051] Then, an observation angle Pnorm defined as the angle between a straight line connecting the camera C to the reference point R and the longitudinal axis Lv of the towing vehicle V is determined 104: 6-6-C 1 standard camera

[0052] Here, |3 is the auxiliary observation angle defined as the angle between the straight line connecting the camera C to the reference point R and a straight line defining the horizontal field of view of the camera C on the side of the towing vehicle V. The horizontal field of view is the horizontal part of the solid angle through which the camera C is sensitive to its environment. The horizontal field of view can be defined by two straight lines which respectively delimit areas visible to the camera C from areas not visible to the camera C.

[0053] Ccamera is a normalization angle which takes into account the orientation of the camera C relative to the towing vehicle V.

[0054] The auxiliary observation angle P is defined as: P _ Rx*hFOV where w is the width of image I along the horizontal axis x of image I, and hFOV is the horizontal field of view of camera C. The width w of the pixel array and the horizontal field of view hFOV are known parameters of camera C.

[0055] The normalization angle Ccamera is defined as: £ — hFOV _ (^^.where Cyaw is a mounting parameter (not shown on the figures) of camera C described as the angle between the optical axis of camera C and the longitudinal axis Lv of the towing vehicle V. The angle Cyaw depends on the orientation of camera C relative to the towing vehicle V and can be determined for a given orientation of camera C.

[0056] The straight line equation of the line which includes the camera C and the reference frame R is defined as: y = c*x + d

[0057] c is a slope coefficient and d is an ordinate value. c is here equal to both 6 V It should be noted that, when the yaw angle changes, all possible positions of the reference frame R will be located on a circle centered on the attachment point O and having as radius the distance between the attachment point O and the reference frame R.

[0058] The equation describing the circle is: ( Xa ) 2 + ( yb ) 2 = r2°where adb 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.

[0059] The coordinates of the reference frame R can be determined 105 by determining the intersection of said circle (( Xa)2 + (yb)2 _ r2) with said straight line ( V ~ tanf 6 )*r). The y coordinate in the equation of the circle is replaced by v norm / the right equation for this purpose: (xa)2 + (vb)2 = r2 x2-2ax+a2+ y2-2by + b2- r2 = 0 x2 - 2ax + a2 + (tan (0norm) *x)2 - 2b(tan (pnorm) *x) + b2 - r2 = 0 (1 + tan2 (pnorm)) b2 - r2) = 0 A2x2 + A1x + A0where A2 = i + tan2(p K Ai = - (2a + 2btan(3 h A0^a2 + b2-r2

[0060] We obtain a second degree equation with the coefficients A2, Ab Ao.

[0061] Ao is a function of the radius r of the circle which can be determined as a function of the di trailer dimensions T: r = or = / crA+ïff

[0062] TL is the distance along the longitudinal axis LT of the trailer T between the attachment point O and the reference mark R, and T! is the width of the trailer T. In the case where the reference mark 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 reference mark R. The distance TL and the width Tt are known parameters of the trailer T.

[0063] There are two solutions for x which correspond to the two intersections between the circle and the line: where , * \2 • Xl / 2-~2*ÂT 4 A2 A0

[0064] One of the two solutions corresponds to the XR coordinate of the R frame. The other solution can be discarded. The corresponding coordinate of the R frame can be obtained after inserting the XR coordinate into the equation on the right: y„ = tan (6 ) * x R R x ^nonn / K

[0065] In order to determine the yaw angle, a first auxiliary angle $ and a second auxiliary angle 0 are determined.

[0066] The first auxiliary angle 0 refers to the angle between the longitudinal axis Lv of the towing vehicle V and the straight line connecting the attachment point O and the reference point R, and is defined as: , . ORV yR-b <p = arc tan-^="arc" tan^

[0067] The second auxiliary angle © refers to the angle between the longitudinal axis LT of the trailer T and the straight line connecting the attachment point O to the reference point R, and is defined as: O - arc

[0068] Thus, the yaw angle can be determined 106: a^OO

[0069] In order to be able to detect the yaw angle a on both sides of the towing vehicle V, a camera C on each lateral side of the towing vehicle V can be used. Thus, a marker R of the trailer T will always be visible by one of the two cameras C.

[0070] The method 100 may be implemented repeatedly to provide updated values ​​of the yaw angle repeatedly.

[0071] [Fig.5] shows an embodiment of the calculator P configured to implement at least part of the method 100.

[0072] The computer P comprises at least one input interface 201 for receiving messages or instructions, and at least one output interface 202 for communication with external devices 205.

[0073] The computer P further comprises a memory 203 for storing instructions allowing the implementation of at least part of the method 100, the received data, and temporary data for carrying out the different operations 101, 102, 103, 104, 105, 106 of the method 100 as described previously.

[0074] The calculator P further comprises 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 card whose operations of the method 100 of the disclosure can be described in silicon, or - a programmable electronic chip such as an FPGA chip for “Field-Programmable Gate Array” in English, as a SOC for “System On Chip” in English or as an ASIC for “Application Specified Integrated Circuit” in English.

[0075] Depending on the embodiment, the calculator P may be a computer, a computer network, an electronic component, or another apparatus comprising a processor operatively coupled to a memory, as well as, depending on the embodiment selected, a data storage unit, and other associated hardware elements such as a network interface and a media reader for reading and writing to a removable storage medium not shown in [Fig. 5]. The removable storage medium may be, for example, a compact disc CD, a digital video / versatile disc DVD, a flash disk, a USB key, etc.

[0076] Depending on the embodiment, the memory 203, the data storage unit or the removable storage medium contain instructions which, when executed by the processing circuit 204, cause this circuit to perform or control the at least one input interface 201, the 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 a part of the method 100 according to [Fig.2].

[0077] The processing circuit 204 may be a component implementing the control of the computer P.

[0078] 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, such as an application-specific integrated circuit ASIC, a system on chip SOC, or in the form of a combination of hardware and software elements, for example a software program intended to be loaded and executed on an electronic component described above such as FPGA.

[0079] The calculator P 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”.

[0080] The present disclosure is not limited to the examples of devices, systems, methods, uses and computer program products described above, only by way of example, but it encompasses all the variants that the person skilled in the art may envisage within the framework of the protection sought.

Claims

Claims

1. Method (100) for determining a yaw angle (a) 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 a camera (C) mounted on a lateral side of the towing vehicle (V) and oriented towards the trailer (T), an image (I) at least of a lateral part of the trailer (T); - determine (102) on the image (I) a mark (R) visible on the trailer (T); - determine (103) on the image (I) a visible length (Rx) between the reference mark (R) and a vertical edge (B) of the image (I) oriented towards the towing vehicle (V); - determining the yaw angle (a) at least on the basis of a horizontal field of view (hFOV) of the camera (C), a width (H?) of a pixel matrix of the camera (C) along a horizontal axis (î) of the camera (C), coordinates of the attachment point (O), the visible length (Rx), and dimensions (Tl, T}) of at least a part of the trailer (T).

2. A method according to claim 1, wherein determining the yaw angle (a) comprises: - determining (104) an observation angle (Pnorm) between the longitudinal axis (Lv) of the towing vehicle (V) and a straight line (CR) connecting the camera (C) to the reference mark (R) of the trailer (T), at least on the basis of said visible length (Rx), the horizontal field of view (hFOV) of the camera (C), and the width (^) of the pixel matrix of the camera (C) along the horizontal axis (J) of the camera (C); - determine (105) the 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 form coordinates of points in a coordinate system including the reference frame (R), c is a slope coefficient and d is an ordinate value; * a circle centered on the attachment point (O) and having a radius equal to a distance between the attachment point (O) and the reference point (R), in which the circle is defined as: ( x - a ) 2 + ( v - b ) 2 = f2°where a and b are coordinates of the point attachment point (0), and r is the radius of the circle; - determine (106) the yaw angle (a) at least on the basis of said coordinates (xR, yR) of the reference frame (R) of the trailer (T) and coordinates of the attachment point (0).

3. A method according to claim 2, wherein the coordinate system is centered on the camera (C) and the straight line equation is defined as: v = tant fi \ ^norm /

4. Method according to any one of claims 2 and 3, in which the radius of the circle is defined as: i 7 / T x 2 where Tl is a distance along the longitudinal axis r = ÿ (Lt) of the trailer (T) between the attachment point (0) and the reference mark (R), and T) is a width of the trailer (T).

5. Method according to any one of claims 2 to 4, in which the observation angle (Pnorm) is defined as: o _ Ry^hFOV p where Rx is the visible length, hFOV is the r norm camera horizontal field of view of the camera (C), w is the width of the pixel matrix of the camera (C) along the horizontal axis (x) of the camera (C), and Ccamera is a normalization angle which takes into account an orientation of the camera (C) relative to the towing vehicle (V).

6. A method according to claim 5, wherein the normalization angle is defined as: f = hf.QY _ CvaM,°ù Cyaw is a mounting parameter of the camera (C) described as an angle between an optical axis of the camera (C) and the longitudinal axis (Lv) of the towing vehicle (V).

7. A method according to any one of the preceding claims, wherein determining the yaw angle (a) comprises: - determining a first auxiliary angle (0) defined as: O — arc tan°Ry°ù ORy is a distance between the reference mark (R) of the trailer (T) and the attachment point (0) along a horizontal axis perpendicular to the longitudinal axis (Lv) of the towing vehicle (V), and ORX is a distance between the reference mark (R) and the attachment point (0) along the longitudinal axis (Lv) of the towing vehicle (V); - determining a second auxiliary angle (O) defined as: Q — where TL is a distance along the longitudinal axis (LT) of the trailer (T) between the attachment point (0) and the reference mark (R), and T! is a trailer width (T). - determine the yaw angle (a) defined as: a = 0-e

8. A computer program product comprising instructions which, when these instructions are executed by a processor, cause the processor to implement operations of a method (100) according to any one of claims 1 to 7.

9. System (S) for determining a yaw angle (a) 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 (0), the determination system (S) comprising: * a camera (C) adapted to be mounted on a lateral side of the towing vehicle (V) in such a way that it is oriented towards the trailer (T), and to acquire an image (I) at least of a lateral part of the trailer (T); and * a computer (P) configured to implement a method (100) according to any one of claims 1 to 7.

10. Determination system according to claim 9, wherein said at least one camera (C) is configured to have a digital rearview mirror function.

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