Target alignment method and systems for use in calibration of a vehicle forward facing camera

Abstract

The present specification relates to alignment of a target 10 relative to a vehicle 2 to enable accurate calibration of a forward-facing camera of a vehicle 2. Described is a method of aligning a targ

Description

BACKGROUND The present specification relates to alignment of a target relative to a vehicle to enable accurate calibration of a forward-facing camera of a vehicle. Vehicle advanced drive assistance systems (ADAS) such as windscreen mounted cameras require re-calibration from time to time. For example, where a camera mounted to a windscreen is replaced (as a result of crack damage or otherwise) then the camera will need to be re-calibrated following fitment to the replacement windscreen. This involves the camera imaging a target (including a specific calibration pattern) relevant to that make and / or model of vehicle. A problem exists with forward facing vehicle camera alignment in that large, unwieldy stands with vehicle manufacturer defined patterned targets attached are required that sit forwardly of a vehicle and must be accurately positioned relative to the vehicle centre line or thrust angle. This results in the need for a large space and significant equipment. A solution that has been proposed is to mount the target onto the windscreen of a vehicle. The target is positioned so that it is aligned to the forward-facing camera and / or a reference marker and the steps of calibration are performed. However, this technique introduces potential inaccuracies when positioning the target as the target is not aligned to the vehicle. Instead, by aligning the target to the forward-facing camera there is no input on the alignment of the vehicle, and calibration is likely to be inaccurate. If alignment is made to a temporary reference marker positioned on the screen adjacent to the forward-facing camera, then this relies on the temporary reference marker being precisely positioned relative to the windscreen, and if the windscreen was replaced, the windscreen itself being precisely oriented to the perpendicular axis of the vehicle. This is unlikely to be accurate due to the possibility of the bonding material between the glass and frame being of slightly different thicknesses for example around the bond. A problem therefore exists in ensuring accurate alignment of a target relative to a vehicle to enable subsequent accurate calibration of a forward-facing vehicle camera. SUMMARY Aspects of the present disclosure are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims. According to an aspect of the present disclosure, there is provided a method of aligning a target with respect to a vehicle for use in calibration of a forward facing camera on a vehicle, the method comprising: a) positioning a support structure displaying the target in an approximate position within the footprint of a vehicle and facing the forward facing camera; b) determining a midline of the vehicle that bisects the vehicle into equal left and right hand sides; c) moving the support structure along a horizontal axis such that a marker on the support structure is aligned with the midline; and d) moving the support structure in a vertical axis such that the marker is at a predefined height. Completing the aligning of the target thereby enables accurate calibration of a forward facing camera with respect to the vehicle. The footprint the vehicle occupies is the area occupied by the vehicle in plan view. The target is therefore displayed in an area directly above the vehicle. The target may comprise a pattern for example. The target may be a digital image. It will be appreciated that the steps of moving the support structure and thus the target to a predefined height and determining the midline may be completed in either order or simultaneously, and movement of the support structure and thus the target may be made vertically or horizontally in either order or simultaneously. It will be appreciated that the predefined height is a vehicle dependent height which is dependent upon a specific vehicle as set out by a vehicle manufacturer. The height is measured above the ground level, and it is therefore beneficial that the ground is substantially level on which the vehicle sits, and the method is performed. It will be appreciated that it is beneficial that the marker to be aligned with the midline and the marker to be aligned with the predefined height is the same marker. Determining the midline that bisects the vehicle into equal left hand and right hand sides preferably comprises projecting a first alignment line onto the vehicle. The first alignment line is beneficially projected from forward of the vehicle. The first alignment line may be termed a vertical midline. The first alignment line is beneficially aligned with one or more physical features of the vehicle to ensure the midline is identified. The physical feature(s) of the vehicle may be a vehicle badge or other indicia. The first alignment line is preferably aligned with first and second physical features of the vehicle. One vehicle badge or other indicia is typically positioned centrally on the vehicle grille or hood / bonnet, and a second vehicle badge or indicia is positioned on the vehicle boot (trunk) when the boot lid is open. The first alignment line is preferably projected by a light projecting arrangement. The first alignment line is preferably projected by a laser source. The method preferably comprises projecting a horizontal alignment line (second alignment line) in a horizontal axis onto the vehicle at the predefined height relative to the vehicle and subsequently moving the support structure in the vertical axis such that the marker is at the predefined height. The horizontal line is also preferably projected by the same light projecting arrangement that projects the first alignment line. The light projecting arrangement is preferably a laser source. The projecting arrangement (preferably a laser source) is beneficially self-levelling, or at least comprises means to enable accurate levelling. The midline of the vehicle may be determined in other ways instead of alignment of the first alignment line with a physical feature of the vehicle. In another determination method, the step of determining the midline of the vehicle may be performed by positioning a frame relative to the vehicle such that the frame is supported by the opposing rear wheels of the vehicle and further extends across the vehicle, wherein the marker is aligned to a midpoint of the frame between the opposing rear wheels. In another determination method the step of determining the midline of the vehicle may comprise positioning an indicia extending outwardly from each of the rear wheels of the vehicle and providing an imaging arrangement forwardly of the vehicle for imaging the indicia, and based on the imaged indicia moving the imaging arrangement to be aligned between the indicia. A first alignment line is then beneficially output upon alignment between the indicia. The support structure is beneficially arranged to display the target, preferably an electronic calibration target image, towards a forward facing camera of the vehicle. The support structure preferably comprises an electronic display screen for displaying a calibration target image. The support structure may comprise a first portion hung from a second portion, and where the target is displayed by the first portion. The first portion is beneficially pivotally mounted to the second portion. The first portion (typically in the form of a display screen) is beneficially pivotally mounted to the second portion. This enables the target to be oriented vertically under gravity removing any need for adjustment by an operator. The first portion may be hung above the hood / bonnet of the vehicle by the second portion. The support structure is preferably mounted to the windscreen of the vehicle. The marker may comprise one or more sensors for sensing the projected first (and preferably second) alignment line(s) and the method may further comprise the step of outputting an indication of alignment with the first (and preferably second) alignment lines. The indication of alignment that is output is beneficially output from the support structure. The indication of alignment may be an audible and / or visual output. The system beneficially further comprises a control system configured to process the one or more sensor inputs and cause output of an indication of alignment. The control system is preferably operable according to a cycle of determining alignment between the target and the projected first alignment line, determining the target is at the predefined height, and outputting an indication that there is alignment between the target and the projected first alignment line and the target is at the predefined height. According to an aspect of the present disclosure there is a method of calibration of a forward facing camera on a vehicle, the method comprising the steps of: - aligning a target with respect to a vehicle as hereinbefore defined; - presenting a calibration target image on the target; - calibrating the forward facing camera according to the calibration target image presented. The calibration target image presented is determined by the manufacturer of the vehicle and accordingly either the appropriate target image may be physically selected from multiple physical images, or alternatively the appropriate target image may be selected from a library of target images. According to another aspect of the present disclosure there is a system for aligning a target with respect to a vehicle, the target for use in calibration of a forward facing camera on a vehicle, the system comprising: a support structure for presenting a target within the footprint of a vehicle such that the target faces the forward facing camera of a vehicle; - a projector arrangement configured to project an alignment line toward the vehicle that bisects the vehicle into equal left and right hand sides to act as a guide to which the target can be aligned. The support structure preferably further comprises a marker for alignment with the vertical midline. The support structure preferably comprises a front and a rear, and the target is presented on the front side and the marker is positioned at the rear side. The marker preferably comprises one or more sensors. The system preferably further comprises a control system configured to process the sensor(s) input and cause output of an indication of alignment. The control system is preferably operable according to a cycle of determining alignment between the target and the projected midline, determining the target is at the predefined height, outputting an indication that there is alignment between the target and the projected midline, and the target is at the predefined height. The projector arrangement is beneficially a light projector arrangement. According to another aspect of the present disclosure there is a system for aligning a target with respect to a vehicle, the target for use in calibration of a forward facing camera on a vehicle, the system comprising: - a frame having a first and second mounting structures arranged to mount to opposing first and second rear wheels of the vehicle and an arm arrangement for extending between the first and second mounting structures across the width of the vehicle; a support structure mounted to the arm arrangement for presenting a target within the footprint of a vehicle such that the target faces the forward facing camera of the vehicle. The support structure is beneficially moveably mounted relative to the arm arrangement between a plurality of discrete positions. This enables movement of the target relative to the forward facing camera of the vehicle to ensure alignment at the midline of the vehicle. There is beneficially provided a locking arrangement for fixing the support structure relative to the arm arrangement in each of the plurality of discrete positions. According to another aspect of the present disclosure there is a system for aligning a target with respect to a vehicle, the target for use in calibration of a forward facing camera on a vehicle, the system comprising: a support structure for presenting a target within the footprint of a vehicle such that the target faces the forward facing camera of a vehicle; first and second mounting structures for mounting to first and second rear wheels of a vehicle respectively, each mounting structure comprising a display arrangement extending outwardly from each of the rear wheels of the vehicle, each display arrangement configured to present an indicia; an imaging arrangement for imaging the indicia, the imaging arrangement configured to determine a vertical midline that bisects the vehicle into equal left and right hand sides based on the imaged indicia; - a projector arrangement for projecting the vertical midline toward the vehicle, the vertical midline for acting as a guide to which the target can be aligned. The imaging arrangement determines a vertical midline based on a comparison between the images of each indicia When a predetermined match in focus is achieved between the spaced apart indicia by moving the imaging arrangement, then the vertical midline can be determined. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of this disclosure will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which: Figure 1 shows a system for performance of the claimed method according to an embodiment of this disclosure; Figure 2 shows a system for performance of the claimed method according to an embodiment of this disclosure; Figure 3 shows a system for performance of the claimed method according to an embodiment of this disclosure; Figure 4 shows a flowchart of operation of the system as set out in Figure 1; Figure 5 shows a flowchart of operation of the system as set out in Figure 2. DETAILED DESCRIPTION Embodiments of this disclosure are described in the following with reference to the accompanying drawings. Referring to Figures 1 to 3 there is a schematic illustration of first, second and third calibration systems according to illustrative embodiments. All three Figures show the alignment axes by which a target 10 on a forward side of a support structure 18 facing the FFC (and therefore not visible in the Figures) can be satisfactorily aligned vertically (height wise) and transversely (horizontally) with respect to the vehicle. It is important that the target therefore be presented accurately with respect to the vehicle to enable accurate and effective calibration to occur. The vertical axis is represented by reference numeral 12 and the horizontal axis by reference numeral 14. By positioning a marker (such as a sensor) at the intersection between the two alignment axes there is increased certainty that the target is accurately aligned with respect to the vehicle, meaning that an accurate calibration can be completed. An array of sensors may be utilized as described with respect to the embodiments of Figures 1 and 3. The vehicle 2 is presented in forward view showing the vehicle grille 4, bonnet / hood 6, windscreen 8 and front wheels 16. The target is presented by a support structure 18 that enables display of a target 10 to the FFC. The support structure 18 affixes to the vehicle to ensure that the target does not move relative to the vehicle during a calibration process. The support structure 18 comprises an electronic display screen (although printed targets can be utilised) that is arranged to display a target in the form of a pattern appropriate to the specific vehicle arranged to face the FFC in an operational configuration, and facing in an opposing direction towards the front of the vehicle in the operation state there is a marker in the form of a detector 22 for detecting an input such as laser light ensuring alignment with a horizontal and vertical axis. This functionality will be described with respect to the illustrative methodologies. There will now be described two illustrative methodologies that enable alignment of a target with respect to the vehicle. Methodology 1 The methodology is schematically presented with respect to the flowchart of Figure 4. First step 24 is to position the support structure 18 that displays a target 10 within the footprint of the vehicle in front of the Forward Facing Camera (FFC) of the vehicle so that the target 10 is located within the viewing field of the FFC. The target is shown in position in Figure 1. At this stage the target 10 is positioned by a user in an approximately central location relative to a horizontal axis of the vehicle and at a height appropriate to be in front of the FFC. The target is presented onto the screen of the support structure 18 and sized to account for the distance from the FFC. Manufacturers traditionally specify physical targets at a predefined distance from the FFC for calibration purposes meaning that the target image must be resized appropriate to the distance from the FFC. Resizing may be achieved by displaying physically printed images of different sizes or calculated and then digitally displayed. The target 10 must then be positioned such that it is centrally aligned with respect to a vertical and horizontal axis of the vehicle. This is performed by moving the support structure 18. In order to achieve this, a projector arrangement 15 in the form of a laser emitter is positioned in front of the vehicle. The laser emitter 15 is arranged to emit a first alignment line 12 which is a vertical line of light that provides a midline that bisects the vehicle into left and right hand sides. This is in the form of a vertical laser line projected towards the vehicle. Reference is made to step 26 of Figure 4. The first alignment line 12 is aligned with the vehicle manufacturer’s logo 13 located on the bonnet of the vehicle (step 28 of Figure 4). To ensure more accurate alignment it is beneficial to also align with the logo on the boot of the vehicle by opening the boot. Once the alignment line 12 is satisfactorily aligned with the logos, the laser device is levelled. The first alignment line 12 is then projected such that it bisects the vehicle into equal left- and right-hand sides. The detector 22 on the rearward side of the support structure 18 is set to output a positive signal to a control system of the target 10 when the first alignment line is detected by movement of the support structure 18 in a horizontal axis indicating that the support structure 18 is aligned with a vertical center line of the vehicle. Detector 22 may comprise a sensor or may comprise a sensor array. For example, to ensure that the support structure is square relative to the FFC (i.e. is not twisted about a vertical axis) a first step is for a user to visually position the support structure 18 square relative to the FFC. In addition, there may also be a secondary check through for example the use of a plurality of sensors disposed in a horizontal axis where exceeding of a predetermined difference in the measured value by each sensor is indicative that the support structure 18 is not aligned relative to the FFC about a vertical axis of rotation. The support structure 18 must also be aligned to a height / horizontal axis so that the target is aligned according to a manufacturer’s specific requirements. This can be determined in different ways. However in one embodiment it can be achieved by the laser emitter emitting a horizontal or second alignment line 14 at a predefined height relative to the vehicle (step 30 of Figure 4). The second alignment line 14 intersects with the first alignment line and is also detected through a signal from the detector once alignment is achieved height wise (step 32 of Figure 4). The support structure is then fixed in position relative to the FFC and the target is displayed onto the screen. Calibration can then be performed. It will be understood that alignment height wise can be performed before alignment horizontally. The target 10 may be either physically printed onto a carrier or may be a digital target presented on a digital screen. For printed targets, a target must be provided appropriate to a specific vehicle or manufacturer meaning that multiple different targets must be provided. In either embodiment, to ensure that the target is not pitched forwardly or backwardly, the physical target or display screen may be suspended meaning its angle relative to the vehicle is not dependent upon how the support structure is mounted to the vehicle. This may be achieved by the support structure being in the form of a first portion hung from a second portion where the target is displayed by the first portion. The first portion may therefore be hingedly mounted to the second portion and subsequently locked in position to ensure the target remains in the vertical plane relative to the FFC. This beneficially accounts for different planes that the windscreen may occupy for different vehicles. It will be understood that method steps may be reordered whilst still functionally achieving effective positioning of the support structure 18 and thus target with respect to the FFC. Methodology 2 The concept of methodology 2 is the same as methodology 1 with different implementation. Fundamentally however the target must be aligned both vertically and horizontally relative to the vehicle for effective calibration to be performed. According to methodology 2 and as presented schematically as an apparatus in Figure 2 and flowchart in Figure 5, there is a vehicle 2 viewed from the front comprising a windscreen 8, a bonnet / hood 6 and grill 4 showing the vehicle logo or badge 13. Front wheels 16 are shown together with rear wheels 40. Target 10 is displayed on the forward facing side of the support structure 18 facing the FFC (therefore not visible in Figure 2). The support structure 18 is positioned on the bonnet 6 having legs 41 to hold the target 10 at the desired position above the bonnet 6 and generally aligned with the FFC of the vehicle. Carrying the support structure is a frame 42 arranged to mount to both rear wheels. The frame 42 extends forwardly from the rear wheels 40 by side members 44 and extends across the bonnet of the vehicle via a cross member 46. There is provided a width adjustment mechanism in the cross member 46 enabling use with vehicles of differing widths. The support structure 18 is then arranged to cooperate with the frame such that the support structure can be secured relative to the frame 42 in a plurality of positions. It is beneficial that the frame has indicia thereon providing a visual indication of the midline of cross member 46 and thus the vehicle which is the midline between the rear wheels. This ensures that the support structure and thus the target 10 is centrally aligned with respect to the vehicle. The support structure 18 is also arranged to enable vertical or height adjustment relative to the vehicle to enable positioning at a height as specified by the vehicle manufacturer. The height can be determined by a variety of mechanisms that enable height measurement of the target to be determined. For example, this may be via a laser emitter emitting a horizontal alignment line 14 at a height predefined by a vehicle manufacturer relative to the vehicle, and the support structure 18 is then moved until there is alignment of a marker 22 on a rearward face of the support structure 18 with the horizontal alignment line. The steps of effecting alignment of the target with the vehicle are set out in Figure 5, where the frame is positioned in step 60 with the support structure facing the FFC. The support structure 18 is then moved with respect to the frame 42 to align with indicia on the frame as set out in step 62, and the support structure 18 is then moved in a vertical axis to the predefined height as set out in step 64. In another methodology related to methodology two and as presented in Figure 3, again using the rear wheels as reference points for determination of the midline of the vehicle, display arrangements 52a,b are positioned on each of the rear wheels of the vehicle by virtue of first and second mounting structures 50a,b. From this, an imaging arrangement 54 such as one or more cameras are positioned onto a moveable frame in front of the vehicle. The imaging arrangement 54 is then moved by moving the frame on which it is mounted to align between the two displays on the display arrangements 52a,b. Once this central location is identified due to the targets being in substantially equal focus, a projector arrangement 56 such as a laser source which is secured to the frame carrying the imaging arrangement emits a laser at the midline 12 between the display arrangements 52a,b mounted to the rear wheels. The support structure 18 can be moved such that it is aligned with respect to the midline 12. The support structure can then also be adjusted height wise as described above and as specified by the vehicle manufacturer. As described above in either methodolgies, the target may be either a physically printed or digital target. For printed targets, a target must be provided appropriate to a specific vehicle or manufacturer meaning that multiple different targets must be provided. In either embodiment to ensure that the target is not pitched forwardly or backwardly, the physical target or display screen may be suspended meaning its angle relative to the vehicle is not dependent upon how the support structure is mounted to the vehicle. This may be achieved by the target being hingedly mounted at an upper edge to the support structure and being able to pivot to a rest position. Once the support structure 18 and thus target 10 are aligned both vertically (height wise) and horizontally (width wise), the target image is displayed, and recalibration is undertaken by the diagnostic device connected to the vehicle. Although particular embodiments of this disclosure have been described, it will be appreciated that many modifications / additions and / or substitutions may be made within the scope of the claims.

Claims

1. A method of aligning a target with respect to a vehicle for use in calibration of a forward facing camera on a vehicle, the method comprising:- positioning a support structure displaying the target in an approximate position within the footprint of a vehicle and facing the forward facing camera;determining a midline of the vehicle that bisects the vehicle into equal left and right hand sides;moving the support structure along a horizontal axis such that a marker on the support structure is aligned with the midline; and- moving the support structure in a vertical axis such that the marker is at a predefined height.

2. A method according to claim 1 wherein determining the midline that bisects the vehicle into equal left hand and right-hand sides comprises projecting a first alignment line onto the vehicle.

3. A method according to any preceding claim wherein the midline is aligned with one or more physical features of the vehicle.

4. A method according to claim 3 where the physical feature of the vehicle is a vehicle badge or other indicia.

5. A method according to any preceding claim where the midline is projected by a laser source.

6. A method according to any preceding claim wherein the method comprises projecting a horizontal alignment line in a horizontal axis onto the vehicle at the predefined height relative to the vehicle and subsequently moving the support structure in the vertical axis such that the marker is at the predefined height.

7. A method according to any preceding claim where the step of determining the midline of the vehicle is performed by positioning a frame relative to the vehicle such that the frame is supported by the opposing rear wheels of the vehicle and furtherextends across the vehicle, wherein the target is aligned to a midpoint of the frame between the opposing rear wheels.

8. A method according to any of claims 1-6 where the step of determining the midline of the vehicle comprises positioning an indicia extending outwardly from each of the rear wheels of the vehicle and providing an imaging arrangement forwardly of the vehicle for imaging the indicia, and based on the imaged indicia moving the imaging arrangement to be aligned between the indicia. A first alignment line is then beneficially output upon alignment between the indicia.

9. A method according to any preceding claim wherein the support structure comprises an electronic display screen for displaying a calibration target image.

10. A method according to any of claims 8-9 claim where the support structure comprises a first portion hung from a second portion, and the target is displayed by the first portion.

11. A method according to claim 10 wherein the first portion is hung above the hood / bonnet of the vehicle by the second portion.

12. A method according to any of claims 8-11 wherein the support structure is mounted to the windscreen of the vehicle.

13. A method according to any preceding claim where the marker comprises one or more sensors for sensing the projected midline and the method further comprises the step of outputting an indication of alignment with the first and second alignment lines.

14. A method of calibration of a forward facing camera on a vehicle, the method comprising the steps of- aligning a target with respect to a vehicle according to any preceding claim;- presenting a calibration target image on the target;- calibrating the forward facing camera according to the calibration target image presented.16

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