Method for determining angular position of trailer in relation to towing vehicle

Abstract

A method for determining a yaw angle of a longitudinal axis of a trailer with respect to a longitudinal axis of a towing vehicle, the trailer hitched to the towing vehicle at a hitch point, the method comprising:-acquiring an image of at least one side portion of the trailer by means of a camera mounted on a side of the towing vehicle and oriented towards the trailer; -determining a reference on the trailer that is visible on the image; -determining a visible length on the image between the reference and a vertical edge of the image oriented towards the tractor; -determining the yaw angle based at least on the horizontal field of view of the camera, the width of the pixel matrix of the camera along the horizontal axis of the camera, the coordinates of the attachment point, the visible length and the dimensions of at least a portion of the trailer.

Description

Technical Field

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

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

[0003] There are solutions for assisting a driver in driving a vehicle by providing additional information to the driver, such as information about the vehicle configuration and the position of the vehicle relative to its environment. These technologies are also required in the context of fully autonomous vehicles. This is true for private vehicles and also for transport vehicles, which typically include a towing vehicle and a trailer.

[0004] To assist in driving such a vehicle and especially for performing a reverse maneuver aimed at parking, it is important to precisely know the angular position of the trailer relative to the towing vehicle and especially the yaw angle over the largest possible range.

[0005] There are already solutions for determining the yaw angle of a trailer relative to a vehicle, some of which are based on the use of mechanical sensors installed, for example, at the hitch point.

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

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

[0008] However, the field of view of the camera is limited, and the camera installed at the rear of the vehicle is close to the trailer, so it is not possible to detect large yaw angles of the trailer relative to the towing vehicle. In fact, when the yaw angle becomes large, the trailer exits the field of view of the camera, and the yaw angle cannot be detected.

[0009] Therefore, there is a need for a method for precisely determining 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. Summary of the Invention

[0010] To this end, a method for determining the yaw angle of the longitudinal axis of a trailer relative to the longitudinal axis of a towing vehicle, the trailer being attached to the towing vehicle at a hitch point, the method comprising:

[0011] - acquiring an image of at least one side portion of the trailer by means of a camera mounted on a side of the towing vehicle and oriented towards the trailer;

[0012] - determining a reference object visible in the image on the trailer;

[0013] - Determine the visible length on the image between the reference object and the vertical edge of the image that is oriented towards the towing vehicle;

[0014] - Determine the yaw angle based on at least the horizontal field of view of the camera, the width of the pixel matrix of the camera along the horizontal axis of the camera, the coordinates of the hitch point, the visible length, and the dimensions of at least a part of the trailer.

[0015] This method allows for accurately determining the yaw angle of the longitudinal axis of the trailer relative to the longitudinal axis of the towing vehicle within a wide range of yaw angle values.

[0016] The innovation of this method lies in the use of a camera mounted on the side of the vehicle. Thus, regardless of the value of the yaw angle, the reference object will always be within the field of view of the camera and always visible to the camera.

[0017] Furthermore, this method is innovative in determining the yaw angle based on the horizontal field of view of the camera, the width of the pixel matrix, the coordinates of the hitch point, the visible length, and the dimensions of at least a part of the trailer.

[0018] In one embodiment, determining the yaw angle includes:

[0019] - Determine the viewing angle β between the longitudinal axis of the towing vehicle and the straight line connecting the camera and the reference object of the trailer based on at least the 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 norm ;

[0020] - Determine the coordinates of the reference object of the trailer by means of the intersection point between:

[0021] * The straight line represented by the straight line equation, which is defined as:

[0022] y = c * x + d

[0023] where x and y form the point coordinates in the coordinate system including the reference object, c is the gradient, and d is the ordinate value;

[0024] * A circle centered at the hitch point and with a radius equal to the distance between the hitch point and the reference object, where the circle is defined as:

[0025] (x - a) 2 + (y - b) 2 = r 2

[0026] where a and b are the coordinates of the hitch point, and r is the radius of the circle;

[0027] - Determine the yaw angle based on at least the coordinates of the reference object of the trailer and the coordinates of the hitch point.

[0028] In one embodiment, the coordinate system is centered on the camera, and the straight-line equation is defined as:

[0029] y = tan(β norm ) * x

[0030] In one embodiment, the radius of the circle is defined as:

[0031]

[0032] where T L is the distance between the hitch point and the reference along the longitudinal axis of the trailer, and T l is the width of the trailer.

[0033] In one embodiment, the viewing angle is defined as:

[0034]

[0035] where R x is the visible length, hFOV is the horizontal field of view of the camera, w is the width of the pixel matrix of the camera along the horizontal axis of the camera, and C camera is the normalized angle taking into account the orientation of the camera relative to the tractor.

[0036] In one embodiment, the normalized angle C camera is defined as:

[0037]

[0038] where C yaw is the mounting parameter of the camera, and the mounting parameter is described as the angle between the optical axis of the camera and the longitudinal axis of the tractor.

[0039] In one embodiment, determining the yaw angle includes:

[0040] - Determining a first auxiliary angle, the first auxiliary angle being defined as:

[0041]

[0042] where OR y is the distance between the reference of the trailer and the hitch point along the horizontal axis perpendicular to the longitudinal axis of the tractor, and OR x is the distance between the reference and the hitch point along the longitudinal axis of the tractor;

[0043] - Determining a second auxiliary angle, the second auxiliary angle being defined as:

[0044]

[0045] wherein, T L is the distance between the attachment point and the reference object along the longitudinal axis of the trailer, and T l is the width of the trailer.

[0046] - Determine the yaw angle, which is defined as:

[0047] α = Φ - θ

[0048] In one embodiment, the reference object includes at least a part of the rear vertical edge of the trailer.

[0049] In one embodiment, the width and visible length of the pixel matrix are determined as the number of pixels on the camera matrix.

[0050] Another aspect of the present invention relates to a computer program product, which includes instructions that, when executed by a processor, cause the processor to perform the operations of the above - mentioned method.

[0051] Another aspect of the present invention relates to a system for determining the yaw angle of the longitudinal axis of a trailer relative to the longitudinal axis of a tractor, where the trailer is attached to the tractor at an attachment point, and the determination system includes:

[0052] * A camera, which is adapted to be mounted on the side of the tractor in such a way that the camera is oriented towards the trailer, and is adapted to acquire an image of at least one side part of the trailer; and

[0053] * A computer, which is configured to perform the above - mentioned method.

[0054] In one embodiment, the tractor includes at least one rearview mirror, wherein the at least one camera is configured to be mounted on the at least one rearview mirror.

[0055] In one embodiment, the at least one camera is configured to have a digital rearview mirror function.

[0056] In one embodiment, the determination system includes two cameras mounted on opposite sides of the tractor, where each of the cameras is configured to acquire an image of at least one side part of the trailer;

[0057] and wherein, the computer is configured to perform the above - mentioned method for each of the cameras. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Other features, details and advantages will become apparent by reading the following detailed description and referring to the drawings, in which:

[0059] Figure 1 ​Figure 1 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;

[0060] Figure 2 Figure 2 shows a flowchart of 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;

[0061] Figure 3 Figure 3 is a schematic representation of an image of the trailer taken by a camera of the determination system of Figure 1 , wherein the camera is mounted on the left side of the towing vehicle;

[0062] Figure 4 Figure 4 is Figure 1 another schematic representation of a top view of the determination system of

[0063] Figure 5 Figure 5 is a schematic representation of a computer configured to implement the determination method of Figure 2 . DETAILED DESCRIPTION

[0064] The object of the present invention is 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.

[0065] Figure 1 Shows such a determination system S, which includes a towing vehicle V and a trailer T attached to the towing vehicle V at a hitch point O (such as a trailer hitch).

[0066] The relative orientation of the trailer T with respect to the towing vehicle V can be characterized by a yaw angle α, which is defined as the longitudinal axis L of the trailer T T and the longitudinal axis L of the towing vehicle V V the angle in the horizontal plane between.

[0067] The towing vehicle V (which can be in the form of, for example, a car or a truck) includes exterior mirrors M on each side of the towing vehicle V, thus allowing the driver of the towing vehicle V to observe a part of the environment behind it. It is worth noting that the mirror M allows observation of a part of the trailer T and in particular the orientation of the trailer T with respect to the towing vehicle V.

[0068] The mirror M is mounted near the front of the driver's door and the passenger door of the vehicle V.

[0069] Each mirror M can be in the form of a camera C or a mirror equipped with a camera C. ​​​​​​​​​

[0070] 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 side portion of the trailer T. A schematic representation of such an image I is shown in Figure 3 .

[0071] Each camera C includes a pixel matrix, which is generally rectangular and includes a horizontal axis and a vertical axis Thus, the image I captured by the camera is also rectangular and is defined by the same axes (i.e., the horizontal axis and the vertical axis ).

[0072] In the example shown in Figure 3 , a part of the tractor V is visible in the image I. However, the tractor V does not need to be visible in the image I when determining the yaw angle.

[0073] The trailer T includes a reference R on each side, where each reference R is visible to the corresponding camera C on the same side of the trailer T. For example, the reference R can be the rear vertical edge of the trailer T. The corresponding reference R can be identified in the image I captured by one of the cameras C and used to determine the yaw angle α.

[0074] The determination system S further includes a reference Figure 5 computer P described in further detail below. The computer P is configured to implement a method 100 for determining the yaw angle α, the flowchart of which is shown in Figure 2 .

[0075] For simplicity and to better illustrate the method 100 described below, a single camera C and a single reference R on the same side of the trailer T are considered.

[0076] 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 Figure 2 .

[0077] The reference R is detected 102 in the image I. Next, the distance between the reference R and the vertical edge B closest to the tractor V, also referred to as the visible length R x , is determined 103 in the image I.

[0078] The visible length R x can be determined based on the number of pixels along the horizontal axis by which the trailer T and the tractor V are visible .

[0079] Reference Figure 4The angles and distances determined and used in the remainder of method 100 are best understood with reference to the schematic representation of the determination system S shown in the figure.

[0080] The coordinates of the individual points determined and / or used in method 100 are all related to a coordinate system centered on the camera C. In this coordinate system, the first axis is oriented along the longitudinal axis L of the towing vehicle V V and the second axis is oriented along the width of the towing vehicle V (i.e., in the horizontal plane and perpendicular to the first axis ).

[0081] The vertical axis is defined relative to the first axis and the second axis so as to form an orthogonal reference system.

[0082] Next, the viewing angle β norm is determined, which is defined as the angle between the line connecting the camera C and the reference object R and the longitudinal axis L of the towing vehicle V V :

[0083] β norm = β - C camera

[0084] In this case, β is the auxiliary viewing angle, which is defined as the angle between the line connecting the camera C and the reference object R and the line defining the horizontal field of view of the camera C on one side of the towing vehicle V. The horizontal field of view is the horizontal part of the solid angle to which the camera C is sensitive to its environment. The horizontal field of view can be defined by two lines that respectively delimit the region visible to the camera C and the region invisible to the camera C.

[0085] C camera is the normalized angle taking into account the orientation of the camera C relative to the towing vehicle V.

[0086] The auxiliary viewing angle β is defined as:

[0087]

[0088] where w is the width of the image I along the horizontal axis of the image I, and hFOV is the horizontal field of view of the camera C. The width w of the pixel matrix and the horizontal field of view hFOV are known parameters of the camera C.

[0089] The normalized angle C camera is defined as:

[0090]

[0091] where C yaw is the installation parameter of camera C (not shown in the figure), and this installation parameter is described as the angle between the optical axis of camera C and the longitudinal axis L of the towing vehicle V V This 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.

[0092] The linear equation of the straight line including camera C and the reference object R is defined as:

[0093] y = c * x + d

[0094] c is the gradient and d is the ordinate value. In this case, c is equal to tan(β norm ). It should be noted that when the yaw angle α changes, all possible positions of the reference object R will be located on a circle centered at the hitch point O with a radius equal to the distance between the hitch point O and the reference object R.

[0095] The equation describing the circle is:

[0096] (x - a) 2 +(y - b) 2 = r 2

[0097] where a and b are the coordinates of the hitch point O. These coordinates a, b in the coordinate system centered at camera C are known or can be determined.

[0098] The coordinates of the reference object R can be determined by finding the intersection of the circle ((x - a) 2 +(y - b) 2 = r 2 ) and the straight line (y = tan(β norm ) * x). For this purpose, substitute the linear equation for the coordinate y in the equation of the circle:

[0099] (x - a) 2 +(y - b) 2 = r 2

[0100] x 2 - 2ax + a 2 + y 2 - 2by + b 2 - r 2 = 0

[0101] x 2 - 2ax + a 2 +(tan(β norm ) * x) 2 - 2btan(β norm)*x)+b 2 -r 2 = 0

[0102] (1 + tan 2 (β norm ))x 2 -(2a + 2btan(β norm )x)+(a 2 + b 2 -r 2 ) = 0

[0103] A 2 x 2 + A 1 x + A 0

[0104] where A 2 = 1 + tan 2 (β norm ), A 1 = -(2a + 2btanβ norm ), A 0 = a 2 + b 2 -r 2 .

[0105] Using the coefficients A 2 , A 1 , A 0 to obtain a second - order equation.

[0106] A 0 is a function of the radius r of the circle, and this radius can be determined according to the dimensions of the trailer T:

[0107]

[0108] T L is the distance along the longitudinal axis L of the trailer T between the hitch point O and the reference object R T , and T I is the width of the trailer T. In the case where the reference object R is the rear vertical edge of the trailer T, T L corresponds to the length of the trailer T, that is, T L is the distance along the longitudinal axis L of the trailer T between the hitch point O and the reference object R T . The distances T L and the width T l are known parameters of the trailer T. x has two solutions, and these two solutions correspond to the two intersection points between the circle and the line:

[0109]

[0110] where Δ=(A 1 )2 -4*A 2 *A 0 。

[0111] One of the two solutions corresponds to the coordinate x of the reference object R R 。The other solution can be ignored. The corresponding coordinate y of the reference object R R can be obtained by substituting the coordinate x R into the straight-line equation:

[0112] y R =tan(β norm )*x R

[0113] To determine the yaw angle α, it is necessary to determine the first auxiliary angle Φ and the second auxiliary angle θ.

[0114] The first auxiliary angle Φ refers to the angle between the longitudinal axis L of the towing vehicle V V and the straight line connecting the hitch point O and the reference object R, and is defined as:

[0115]

[0116] The second auxiliary angle θ refers to the angle between the longitudinal axis L of the trailer T T and the straight line connecting the hitch point O and the reference object R, and is defined as:

[0117]

[0118] Therefore, the yaw angle α can be determined:

[0119] α = Φ - θ

[0120] To be able to detect the yaw angle α on both sides of the towing vehicle V, cameras C on each side of the towing vehicle V can be used. Therefore, the reference object R on the trailer T will always be visible to one of the two cameras C.

[0121] Method 100 can be repeatedly implemented to repeatedly provide updated values of the yaw angle α.

[0122] Figure 5 An embodiment of a computer P configured to implement at least some of method 100 is shown.

[0123] The computer P includes at least one input interface 201 for receiving messages or instructions, and at least one output interface 202 for communicating with an external device 205.

[0124] The computer P further includes a memory 203 for storing instructions for implementing at least some of the method 100, the received data, and temporary data for performing various operations 101, 102, 103, 104, 105, 106 of the method 100 as described above.

[0125] The computer P further includes a processing circuit 204. This circuit can be, for example:

[0126] - A processor that can interpret instructions in the form of a computer program; or

[0127] - An electronic board on which the operations of the method 100 of the present disclosure can be described in silicon; or even

[0128] - A programmable electronic chip, such as a field programmable gate array (FPGA) chip, a system on chip (SOC) chip, or an application specific integrated circuit (ASIC) chip.

[0129] According to an embodiment, the computer P can be a computer, a computer network, an electronic component, or other facilities including a processor operably connected to a memory, as well as a data storage unit (depending on the selected embodiment) and other associated hardware elements, such as a network interface and a media reader for reading and writing to a removable storage medium ( Figure 5 not shown in the figure). The removable storage medium can be, for example, a compact disc (CD), a digital versatile disc (DVD), a flash drive, a USB key, etc.

[0130] According to an embodiment, the memory 203, the data storage unit, or the removable storage medium contains instructions that, when executed by the processing circuit 204, cause the circuit to control at least one input interface 201, at least one output interface 202, or to store data in the memory 203 and / or process data and / or implement at least some of the Figure 2 method 100.

[0131] The processing circuit 204 can be a component for controlling the computer P.

[0132] In addition, the computer P can be implemented in software. In this case, the computer can be in 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 a combination of hardware and software elements (such as an FPGA), for example, a software program designed to be loaded and executed on the above electronic components.

[0133] The computer P can also use a hybrid architecture, for example, an architecture based on CPU + FPGA, GPU (graphics processing unit), or MPPA (multi-purpose processor array).

[0134] This disclosure is not limited to the examples of devices, systems, methods, uses, and computer program products described above only by way of example, but rather encompasses all variations that can be envisioned by those skilled in the art within the scope of protection desired.

Claims

1. A method for determining the longitudinal axis (L) of a trailer (T) T ) relative to the longitudinal axis (L) of the tractor (V) V ), the trailer (T) being coupled to the tractor at a coupling point (O), the method comprising: - acquiring (101) an image (I) of at least one side portion of the trailer (T) by means of a camera (C) mounted on the side of the tractor (V) and oriented towards the trailer (T); - determining (102) a reference object (R) on the trailer (T) visible in the image (I); - determining (103) the visible length (R) between the reference object (R) on the image (I) and a vertical edge (B) of the image (I) oriented towards the tractor (V) x ); - based at least on the horizontal field of view (hFOV) of the camera (C), the pixel matrix of the camera (C) along the horizontal axis of the camera (C) The width (w), the coordinates of the attachment point (O), the visible length (R x ) and the dimensions of at least a portion of the trailer (T L ,T l ) to determine the yaw angle (α); And wherein determining the yaw angle (α) comprises: - at least based on the visible length (R x ), the horizontal field of view (hFOV) of the camera (C) and the pixel matrix of the camera (C) along the horizontal axis of the camera (C) The width (w) is used to determine (104) the longitudinal axis (L) of the tractor (V) V ) and the straight line (CR) connecting the camera (C) and the reference object (R) of the trailer (T) norm ); - Determine (105) the coordinates (x) of the reference object (R) of the trailer (T) by means of the intersection between R ,y R ): * The straight line (CR) is represented by a straight line equation, which is defined as: y=c*x+d wherein x and y form the coordinates of a point in a coordinate system including the reference (R), c is the gradient and d is the ordinate value; * A circle centered at the attachment point (O) and having a radius equal to the distance between the attachment point (O) and the reference object (R), wherein the circle is defined as: (x-a) 2 +(y-b) 2 =r 2 Where a and b are the coordinates of the attachment point (O), and r is the radius of the circle; - based at least on said coordinates (x R ,y R ) and the coordinates of the attachment point (O) to determine (106) the yaw angle (α).

2. The method according to claim 1, wherein: The coordinate system is centered at the camera (C), and the equation of the line is defined as: and tan(β) norm )*x。 3. The method according to any one of claims 1 and 2, wherein: The radius of this circle is defined as: Among them, T L is the distance between the hitch point (O) and the reference object (R) along the longitudinal axis (L) of the trailer (T). T ) and T l is the width of the trailer (T).

4. The method according to any one of claims 1 to 3, wherein: The observation angle (β norm ) is defined as: Among them, R x is the visible length, hFOV is the horizontal field of view of the camera (C), and w is the pixel matrix of the camera (C) along the horizontal axis of the camera (C). The width of C camera is the normalized angle taking into account the orientation of the camera (C) relative to the tractor (V).

5. The method according to claim 4, wherein: The normalized angle is defined as: Among them, C yaw is the installation parameter of the camera (C), which is described as the distance between the optical axis of the camera (C) and the longitudinal axis (L V ) between the two.

6. A method according to any one of the preceding claims, wherein: Determining the yaw angle (α) includes: - Determine a first auxiliary angle (Φ) which is defined as: Among them, OR y is the distance between the reference object (R) of the trailer (T) and the hitch point (O) along a line perpendicular to the longitudinal axis (L) of the tractor (V). V ) of the horizontal axis, and OR x is the distance between the reference object (R) and the hitch point (O) along the longitudinal axis (L) of the tractor (V) V ) distance; - Determine a second auxiliary angle (θ) defined as: Among them, T L is the distance between the hitch point (O) and the reference object (R) along the longitudinal axis (L) of the trailer (T). T ) and T I is the width of the trailer (T); - Determine the yaw angle (α), which is defined as: α=Φ-θ.

7. A computer program product comprising instructions which, when executed by a processor, cause the processor to perform the operations of the method (100) according to any one of claims 1 to 6.

8. A method for determining the longitudinal axis (L) of a trailer (T) T ) relative to the longitudinal axis (L) of the tractor (V) V ), the trailer (T) being coupled to the tractor (V) at a coupling point (O), the determining system (S) comprising: * a camera (C) adapted to be mounted on the side of the tractor (V) in such a way that the camera is oriented towards the trailer (T) and adapted to acquire an image (I) of at least one side portion of the trailer (T); and * A computer (P) configured to implement the method (100) according to any one of claims 1 to 6.

9. The determination system according to claim 8, wherein: The at least one camera (C) is configured to have a digital rearview mirror function.

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