The present disclosure relates to a vehicle control method and apparatus. In particular, but not exclusively, the present disclosure relates to a control apparatus and method for a host vehicle. The control apparatus and method identify a target vehicle and determine a vertical offset between the host vehicle and the identified target vehicle. The host vehicle may be controlled in dependence on the determined vertical offset.
BACKGROUND
It is known to provide a host vehicle with an adaptive cruise control (ACC) module. A driver typically sets a target speed for the host vehicle and the host vehicle target speed is controlled to maintain the target speed. If another vehicle is detected in front of the host vehicle, the ACC module adapts the host vehicle target speed to maintain a distance to the other vehicle on a road, for example in a traffic jam or at higher speeds. Known ACC modules generally operate by determining a distance to other (target) vehicle(s), either measured as a length or as a function of time, based on the current road speed. The target vehicle may be detected using one or more different types of sensor. For example, the host vehicle have an on-board imaging system, such as a camera or Lidar system. In a situation where the target vehicle moves out of view it is no longer possible to track the target vehicle. In an off-road situation, the track may follow turns which are tighter than those usually encountered in an on- road situation. Similarly, in an off-road situation, the vehicle may traverse peaks and troughs which are more extreme than those generally encountered in an on-road situation. These different situations may make it more difficult for the control system to maintain tracking of the target vehicle in an off-road situation. Furthermore, in an on-road situation, it is a reasonable to assume that the host vehicle will follow a similar route to that of the target vehicle (since the target vehicle route is at least in part defined by the road surface). However, this approach may be less appropriate in an off-road situation where the driver of the host vehicle may choose an alternative path through or around an obstacle. Since the likelihood that tracking of the target vehicle will be lost or interrupted in an off-road situation, the need for a modified control strategy for a control system for use in an off-road situation has been identified.
SUMMARY OF THE INVENTION
Aspects of the present invention relate to a control system, a vehicle, a method and a non-transitory computer-readable medium as claimed in the appended claims.

According to an aspect of the present invention there is provided a control system for controlling operation of a host vehicle, the control system comprising a processor operable to:
track a target vehicle to determine a target vehicle route;
determine a speed of the target vehicle travelling along the target vehicle route; and
control a target speed of the host vehicle in dependence on the determined target vehicle speed;
wherein, in the event that tracking of the target vehicle is interrupted, the processor is operable to control the host vehicle target speed in dependence on the determined target vehicle speed at a known location on the target vehicle route. The processor may be operable to control the host vehicle target speed at an instant location on the target vehicle route at least substantially to match the determined target vehicle speed when the target vehicle was at that location. The host vehicle target speed may be controlled as the host vehicle travels along the target vehicle route.
The target vehicle speed along the target vehicle route may define a target vehicle speed profile. At least in certain embodiments, a speed profile of the host vehicle may at least substantially match the speed profile of the target vehicle along the target vehicle route. The processor may determine the target vehicle speed substantially continuously or at a plurality of intervals along said route.
The target vehicle route may be used as a target route for the host vehicle.
The processor may identify when and/or where tracking of the target vehicle is lost or interrupted, for example when the target vehicle is no longer detected. Rather than revert to a set speed, for example a driver speed specified by a cruise control module, the processor may control the host vehicle target speed in dependence on the target vehicle speed determined prior to interruption of the target vehicle tracking.
The known location of the target vehicle may correspond to the location where tracking of the target vehicle was interrupted. Thus, when the host vehicle arrives at the location where tracking was interrupted, the processor may be operable at least substantially to match the host vehicle target speed to the determined target vehicle speed at that location.
The processor controls a host vehicle target speed while the host vehicle is travelling along the target vehicle route. The processor may be operable to control the host vehicle target speed so as at least substantially to match the determined target vehicle speed when the

target vehicle was at substantially the same location on the target vehicle route. Thus, the speed of the host vehicle may at least substantially match the target vehicle speed along the target vehicle route.
The processor may be operable to identify the location where tracking of the target vehicle was interrupted. The processor may be operable to continue to control the host vehicle target speed in dependence on the determined target vehicle speed along the target vehicle route up to the location where tracking of the target vehicle was interrupted. The processor may be operable to determine when the location of the host vehicle substantially corresponds to the identified location where tracking of the target vehicle was interrupted. The processor may be operable to set the host vehicle target speed at the determined target vehicle speed when it was at the identified location. In other words, when the host vehicle reaches the identified location on the target vehicle route, the host vehicle target speed may be set at a last-known target vehicle speed.
According to an aspect of the present invention there is provided a control system for controlling operation of a host vehicle, the control system comprising a processor operable to:
track a target vehicle to determine a target vehicle route;
determine a speed of the target vehicle travelling along the target vehicle route; and
control a target speed of the host vehicle in dependence on the determined target vehicle speed;
wherein, in the event that tracking of the target vehicle is interrupted, the processor is operable to identify the location where tracking of the target vehicle was interrupted and to continue to control the host vehicle target speed in dependence on the determined target vehicle speed along said route up to the identified location. The processor may be operable to determine when the location of the host vehicle substantially corresponds to the identified location where tracking of the target vehicle was interrupted. The processor may be operable to set the host vehicle target speed at the determined target vehicle speed when it was at the identified location. In other words, when the host vehicle reaches the identified location on the target vehicle route, the host vehicle target speed may be set at a last-known target vehicle speed. Alternatively, the processor may be configured to reduce the target speed as the host vehicle approaches the identified location, for example to bring the host vehicle to a halt at or proximal to the identified location.
The target vehicle speed may be determined continuously. Alternatively, the target vehicle speed may be determined at a plurality of intervals along the target vehicle route. For

example, the target vehicle speed may be determined at predetermined temporal or spatial intervals.
The processor may be operable to generate a target vehicle trace. The target vehicle trace may comprise (geospatial) location data, for example defining the target vehicle route. The target vehicle trace may comprise the speed and/or trajectory of the target vehicle along the target vehicle route.
The processor may be operable to determine an acceleration of the target vehicle along the target vehicle route. For example, the processor may determine the rate of change of the target vehicle speed. The processor may be operable to control acceleration of the host vehicle while the host vehicle is travelling along the target vehicle route in dependence on the determined acceleration of the target vehicle. The processor may be operable to control the acceleration of the host vehicle at least substantially to match the determined acceleration of the target vehicle at a corresponding location on the target vehicle route.
The processor may be operable to determine a trajectory of the target vehicle along the target vehicle route. The processor may determine a trajectory of the target vehicle. The processor may be operable to control a steering angle of the host vehicle while the host vehicle is travelling along the target vehicle route in dependence on the determined trajectory of the target vehicle. The processor may be operable to control the trajectory of the host vehicle at least substantially to match the trajectory of the target vehicle at a corresponding location on the target vehicle route.
The processor may be operable to receive a signal from at least one sensor provided on the host vehicle and to process said signal to track the target vehicle. The signal may comprise image data captured by one or more image sensors. The processor may be operable to process said image data to track the target vehicle. The or each image sensor may comprise an optical sensor, such as a camera. The image sensor may be configured to detect light in a visible spectrum or an infrared spectrum.
The target vehicle route may be used to define a target route to be taken by the host vehicle. The processor may be operable to control a steering angle of the host vehicle to cause the host vehicle to follow the target route. The processor may, for example, control an electric power assist steering (EPAS) system. At least in certain embodiments, the control system described herein may provide autonomous or semi-autonomous steering control of the host vehicle.

The processor may be operable to process said image data to determine a pitch angle and/or a roll angle and/or a yaw angle of the target vehicle.
5 In a variant, rather than control the host vehicle target speed in dependence on the
determined target vehicle speed at a known location on the target vehicle route, the processor may be configured to maintain a target speed of the host vehicle substantially constant in the event that tracking of the target vehicle is interrupted.
According to a further aspect of the present invention there is provided a control system for controlling operation of a host vehicle, the control system comprising:
a controller comprising a processor and a memory device, the processor being configured to execute a set of instructions stored on the memory device;
wherein, when executed, said instructions cause the processor to: track a target vehicle to determine a target vehicle route;
determine a speed of the target vehicle travelling along the target vehicle route;
control a target speed of the host vehicle in dependence on the determined target vehicle speed;
wherein, in the event that tracking of the target vehicle is interrupted, the processor is operable to control the host vehicle target speed in dependence on the determined target vehicle speed at a known location on the target vehicle route. The host vehicle target speed may be controlled as the host vehicle travels along the target vehicle route.
According to a further aspect of the present invention there is provided a vehicle comprising a control system as described herein.
According to a further aspect of the present invention there is provided a method of
30 controlling operation of a host vehicle, the method comprising:
tracking a target vehicle to determine a target vehicle route;
determine a speed of the target vehicle travelling along the target vehicle route;
controlling a target speed of the host vehicle in dependence on the determined
target vehicle speed; and
35 in the event that tracking of the target vehicle is interrupted, controlling the host
vehicle target speed in dependence on the determined target vehicle speed at a known
6

location on the target vehicle route. The host vehicle target speed may be controlled as the host vehicle travels along the target vehicle route.
The known location of the target vehicle may correspond to the location where tracking of
5 the target vehicle was interrupted.
The method may comprise determining an acceleration of the target vehicle along the target vehicle route.
10 The method may comprise controlling acceleration of the host vehicle while the host vehicle
is travelling along the target vehicle route in dependence on the determined acceleration of the target vehicle. The method may comprise controlling an acceleration of the host vehicle at least substantially to match the acceleration of the target vehicle at a corresponding location on the target vehicle route.
15
The method may comprise determining a trajectory of the target vehicle along the target vehicle route. The method may comprise controlling a steering angle of the host vehicle while the host vehicle is travelling along the target vehicle route in dependence on the determined trajectory of the target vehicle.
20 The method may comprise controlling a trajectory of the host vehicle at least substantially to
match the trajectory of the target vehicle at a corresponding location on the target vehicle route.
The method may comprise receiving a signal from at least one sensor provided on the host
25 vehicle and processing said signal to track the target vehicle. The signal may comprise
image data captured by one or more image sensors. The method may comprise processing
said image data to track the target vehicle. An image processing algorithm may be applied to
said image data to track the target vehicle. The method may comprise processing said
image data to determine a pitch angle and/or a roll angle and/or a yaw angle of the target
30 vehicle.
According to a further aspect of the present invention there is provided a control system for
controlling operation of a host vehicle, the control system comprising a processor operable
to:
35 track a target vehicle to determine a target vehicle route;
determine a trajectory of the target vehicle along the target vehicle route; and
7

control a host vehicle target speed in dependence on the determined target vehicle speed;
wherein the processor is operable to control a steering angle of the host vehicle
while the host vehicle is travelling along the target vehicle route in dependence on the
5 determined trajectory of the target vehicle.
In the event that tracking of the target vehicle is interrupted, the processor may be operable
to control the steering angle of the host vehicle in dependence on the determined trajectory
of the target vehicle at a known location on the target vehicle route. The processor may be
10 configured to control the steering angle of the host vehicle in dependence on the determined
trajectory of the target vehicle at the known location of the target vehicle when tracking was interrupted.
According to a further aspect of the present invention there is provided a method of
15 controlling operation of a host vehicle, the method comprising:
tracking a target vehicle to determine a target vehicle route;
determining a trajectory of the target vehicle along the target vehicle route; and
controlling a target speed of the host vehicle in dependence on the determined
target vehicle speed;
20 wherein a steering angle of the host vehicle is controlled while the host vehicle is
travelling along the target vehicle route in dependence on the determined trajectory of the
target vehicle. In the event that tracking of the target vehicle is interrupted, the method may
comprise controlling the steering angle of the host vehicle in dependence on the determined
trajectory of the target vehicle at a known location on the target vehicle route. The method
25 may comprise controlling the steering angle of the host vehicle in dependence on the
determined trajectory of the target vehicle at the known location of the target vehicle when tracking was interrupted.
According to a further aspect of the present invention there is provided a non-transitory
30 computer-readable medium having a set of instructions stored therein which, when
executed, cause a processor to perform the method(s) described herein.
The host vehicle may be a land vehicle. The target vehicle may be a land vehicle. The term
“land vehicle” is used herein to refer to a vehicle configured to apply steering and drive
35 (traction) forces against the ground. The vehicle may, for example, be a wheeled vehicle or a
tracked vehicle.
8

The term “location” is used herein to refer to the relative position of an object on the surface of the earth. Unless indicated to the contrary, either explicitly or implied by the context, references herein to the location of an object refer to the geospatial location of that object.
5 It is to be understood that by the term 'type of terrain' is meant the material comprised by the
terrain over which the vehicle is driving such as asphalt, grass, gravel, snow, mud, rock
and/or sand. By 'off-road' is meant a surface traditionally classified as off-road, being
surfaces other than asphalt, concrete or the like. For example, off-road surfaces may be
relatively compliant surfaces such as mud, sand, grass, earth, gravel or the like.
10 Alternatively, or in addition, off-road surfaces may be relatively rough, for example stony,
rocky, rutted or the like. Accordingly, in some arrangements an off-road surface may be classified as a surface that has a relatively high roughness and/or compliance compared with a substantially flat, smooth asphalt or concrete road surface.
Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller” or “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.
Within the scope of this application it is expressly intended that the various aspects,
embodiments, examples and alternatives set out in the preceding paragraphs, in the claims
and/or in the target following description and drawings, and in particular the individual
35 features thereof, may be taken independently or in any combination. That is, all
embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to
9

change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.
5 BRIEF DESCRIPTION OF THE DRAWINGS
One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which:
Figure 1 shows a plan view of a host vehicle incorporating a control system in
accordance with an embodiment of the present invention;
10 Figure 2 shows a side elevation of the host vehicle shown in Figure 1 incorporating
the control system in accordance with an embodiment of the present invention;
Figure 3 shows a schematic representation of the control system incorporated into the host vehicle shown in Figures 1 and 2;
Figure 4 illustrates the operation of the control system to set a target follow distance
15 for a vehicle control module of the host vehicle;
Figure 5 illustrates the operation of the control system to calculate a target vehicle trace;
Figure 6 illustrates an instrument cluster generating a driver notification;
Figure 7 shows a schematic representation of the control system in accordance with
20 a further embodimnet of the present invention;
Figure 8 shows a comparison of the path of the host vehicle to the tracked movements of the target vehicle; and
Figure 9 shows determination of a deviation between the path of the host vehicle and the tracked movements of the target vehicle. 25
DETAILED DESCRIPTION
A control system 1 for controlling operation of a following (host) vehicle 2 in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures. 30
The control system 1 is described herein with reference to a host vehicle reference frame
comprising a longitudinal axis X, a transverse axis Y and a vertical axis Z. The control
system 1 is operative to assist in the control of the host vehicle 2 particularly, but not
exclusively, in an off-road driving scenario. As shown in Figures 1 and 2, the control system
35 1 is operable to track a target vehicle 3 in front of the host vehicle 2. The target vehicle 3
may, for example, be a target vehicle or a vehicle in front of the host vehicle 2 in a convoy.
10

The host vehicle 2 is a wheeled vehicle having four wheels W1-4. A torque is transmitted to the wheels W1-4 to apply a tractive force to propel the host vehicle 2. The torque is generated by one or more torque generating machine, such as an internal combustion engine or an electric traction machine, and transmitted to the driven wheels W1-4 via a 5 vehicle powertrain. The host vehicle 2 in the present embodiment has four-wheel drive and, in use, torque is transmitted selectively to each of said wheels W1-4. It will be understood that the control system 1 could also be installed in a host vehicle 2 having two-wheel drive. The host vehicle 2 in the present embodiment is an automobile having off-road driving capabilities. For example, the host vehicle 2 may be capable of driving on an unmetalled
10 road, such as a dirt road or track. The host vehicle 2 may, for example, be a sports utility vehicle (SUV) or a utility vehicle, but it will be understood that the control system 1 may be installed in other types of vehicle. The control system 1 may be installed in other types of wheeled vehicles, such as light, medium or heavy trucks. The target vehicle 3 may have the same configuration as the host vehicle 2 or may have a different configuration.
15
A schematic representation of the control system 1 installed in the host vehicle 2 is shown in Figure 3. The control system 1 comprises a controller 4 having at least one electronic processor 5 and a memory 6. The processor 5 is operable to receive a data signal S1 from a sensing means 7. As described herein, the processor 5 is operable to process the data
20 signal S1 to track the target vehicle 3. The processor 5 is operable to control operation of the host vehicle 2 in dependence on the relative location of the target vehicle 3. As described herein, the processor 5 is operable to control a target follow distance D1 in dependence on a determined vertical offset ΔV between the host vehicle 2 and the target vehicle 3. The target follow distance D1 is a target distance to be maintained between the host vehicle 2 and the
25 target vehicle 3. The processor 5 is operable to output a target follow distance signal SD1 to a vehicle control module. In the present embodiment, the vehicle control module comprises a cruise control module 8. The cruise control module 8 is operable in a follow mode to control the host vehicle 2 to follow the target vehicle 3. When the follow mode is activated, the cruise control module 8 controls the host vehicle target speed to maintain the target
30 follow distance D1 between the host vehicle 2 and the target vehicle 3. The cruise control module 8 may output a target speed signal SV1 to an engine control module 9 which controls the output torque transmitted to the wheels W1-4. The cruise control module 8 may also generate a brake control signal for controlling a braking torque applied to said wheels W1-4.
35
The processor 5 is operable to receive a reference speed signal VRef for indicating a current reference host vehicle target speed. The reference speed signal VRef may, for example, be
11

generated by one or more wheel speed sensors 10. The processor 5 is operable to receive a vehicle attitude signal VAtt for indicating a current attitude of the host vehicle 2 about at least one axis. The vehicle attitude signal VAtt comprises one or more of the following: a vehicle pitch signal Sα indicating a vehicle pitch angle α; and a vehicle roll signal Sβ indicating a 5 vehicle roll angle β. The vehicle attitude signal VAtt is generated by a vehicle attitude sensor module 11 comprising one or more accelerometers and/or gyroscopes. The vehicle pitch angle α and the vehicle roll angle β define the current angular orientation of the longitudinal axis X and the transverse axis Y respectively to a horizontal plane. The vehicle attitude signal VAtt may also comprise a vehicle yaw signal Sγ indicating a vehicle yaw angle γ
10
As shown in Figure 3, the sensing means 7 is mounted in a forward-facing orientation to establish a detection region in front of the host vehicle 2. The sensing means 7 comprises at least one optical sensor 12 mounted to the host vehicle 2. The sensing means 7 may comprise a single camera. Alternatively, the sensing means 7 may comprise a stereoscopic
15 camera. The at least one optical sensor 12 may be mounted at the front of the vehicle, for example incorporated into a front bumper or engine bay grille; or may be mounted within the vehicle cabin, for example in front of a rear-view mirror. The at least one optical sensor 12 has a field of view FOV having a central optical axis VX extending substantially parallel to a longitudinal axis X of the host vehicle 2. The field of view FOV is generally conical in shape
20 and extends in horizontal and vertical directions. The at least one optical sensor 12 comprises a digital imaging sensor for capturing image data. The at least one optical sensor 12 captures image data substantially in real-time, for example at 30 frames per second. The at least one optical sensor 12 in the present embodiment is operable to detect light in the visible spectrum of light. The sensing means 7 comprises optics (not shown) for directing the
25 incident light onto an imaging sensor, such as a charge-coupled device (CCD), operable to generate image data for transmission in the data signal S1. Alternatively, or in addition, the sensing means 7 may be operable to detect light outside of the visible light spectrum, for example in the infra-red range to generate a thermographic image. Alternatively, or in addition, the sensing means 7 may comprise a Lidar sensor for projecting a laser light in
30 front of the host vehicle 2. Other types of sensor are also contemplated.
The sensing means 7 is connected to the controller 4 over a communication bus 13 provided in the host vehicle 2. The data signal S1 is published to the communication bus 13 by the sensing means 7. In the present embodiment, the connection between the sensing means 7 35 and the controller 4 comprises a wired connection. In alternative embodiments, the connection between the sensing means 7 and the controller 4 may comprise a wireless connection, for example to enable remote positioning of the sensing means 7. By way of
12

example, the sensing means 7 may be provided in a remote targeting system, such as a drone vehicle. The processor 5 is operable to read the data signal S1 from the communication bus 13. The processor 5 extracts the image data from the data signal S1 and implements an image processing algorithm to identify the target vehicle 3 within the image 5 data. The image processing algorithm may recognise a shape or profile of the target vehicle 3, for example using pattern matching techniques. Alternatively, or in addition, the image processing algorithm may identify the target vehicle 3 based on relative movement of the target vehicle 3 between frames of the image date. The image processing algorithm may optionally use a known vehicle colour and/or vehicle type to identify the target vehicle 3 in
10 the image data. By applying the image processing algorithm to successive frames of the image data, the processor 5 tracks the movement of the target vehicle 3. The processor 5 may also calculate a distance (range) to the target vehicle 3 from the host vehicle 2. The processor 5 may compare the size of the target vehicle 3 in the image data to a reference image taken at a known distance between the host vehicle 2 and the target vehicle 3. The
15 reference image could, for example, be captured during a calibration phase.
The processor 5 may optionally calculate an attitude of the target vehicle 3, for example to calculate a pitch angle and/or a roll angle and/or a yaw angle of the target vehicle 3. The processor 5 may, for example, analyse the image data to identify one or more edges and/or 20 one or more sides of the target vehicle 3. The processor 5 may compare the edges and/or sides identified in the image data to a virtual model of a vehicle to determine the attitude of the target vehicle 3. The virtual model could be generated based on one or more images of the target vehicle 3 captured during a calibration phase.
25 As shown in Figures 2 and 4, the processor 5 is operable to determine the vertical offset ΔV (relative elevation) of the target vehicle 3 in relation to the host vehicle 2. The vertical offset ΔV is calculated from a predetermined reference point on the host vehicle 2 and an identifiable reference point on the target vehicle 3, such as a base of the body or a wheel centre of the target vehicle 3. The processor 5 receives the vehicle pitch signal Sα and the
30 vehicle roll signal Sβ indicating the vehicle pitch angle α and the vehicle roll angle β of the host vehicle 2. The processor 5 uses the vehicle pitch signal Sα to determine the orientation of the central optical axis VX in a vertical plane and thereby determines the orientation of the field of view FOV1 in three-dimensional space. The processor 5 identifies the target vehicle 3 in the image data and determines an elevation angle α1 (positive or negative) relative to
35 the central optical axis VX. The processor 5 sums the elevation angle α1 and the known pitch angle α and the total is used to calculate the vertical offset ΔV of the target vehicle 3 in dependence on the distance to the target vehicle 3. A positive value for the vertical offset ΔV
13

indicates that the target vehicle 3 is at a higher elevation (i.e. above the height of) the host vehicle 2; and a negative value for the vertical offset ΔV indicates that the target vehicle 3 is at a lower elevation (i.e. below the height of) the host vehicle 2. It will be understood that the vehicle roll signal Sβ may alter the apparent vertical offset ΔV depending on the position of 5 the target vehicle 3 within the image. The processor 5 may also apply a correction based on the known vehicle roll angle β of the host vehicle 2.
The processor 5 may track the target vehicle 3 to determine a target vehicle route, i.e. the route taken by the target vehicle 3. The processor 5 may optionally analyse the data signal
10 S1 to calculate a target vehicle speed and/or a target vehicle trajectory as the target vehicle 3 travels along said target vehicle route. The speed and/or trajectory may be calculated at known time or spatial intervals along said target vehicle route. The processor 5 may store the calculated target vehicle speed to build a speed profile for the target vehicle 3 as it travels along a route. The calculated speed and/or trajectory (direction of travel) of the target
15 vehicle 3 may optionally be stored along with an instant location of the target vehicle 3 (either known or calculated). The calculated speed and/or trajectory at any given location may be defined as a movement vector Vn having a magnitude (representing the target vehicle speed) and direction (representing the trajectory of the target vehicle 3). As illustrated in Figure 5, multiple movement vectors Vn can be calculated for the target vehicle
20 3 to generate a target vehicle trace 14. The target vehicle trace 14 represents the (geospatial) target vehicle route as well as the target vehicle speed along that route. The target vehicle trace 14 may optionally also comprise the trajectory of the target vehicle 3 along the target vehicle route. The position of each movement vector Vn indicates a calculated position of the target vehicle 3. The length of the movement vectors Vn
25 represents a calculated target vehicle speed at that location; and the direction of the movement vectors Vn represents a trajectory of the target vehicle 3 at that location. The processor 5 stores each movement vector Vn in conjunction with the calculated location of the target vehicle 3 to build the target vehicle trace 14. The movement vectors Vn may be calculated at predetermined time intervals, for example one calculation per second. The
30 movement vectors Vn may optionally be time-stamped to indicate the time at which they were generated. The location of the target vehicle 3 may be calculated relative to the host vehicle 2 (for example a separation distance and/or orientation). Alternatively, the location of the target vehicle 3 may comprise a real-world location, for example determined with reference to positional data (for example GPS data) and/or map data. The movement
35 vectors Vn can be stored as a sequence along a target vehicle route. The target vehicle trace 14 may subsequently be used by the processor 5 as an input for controlling the host vehicle 2, for example to match a host vehicle target speed to a calculated target vehicle
14

speed at a corresponding location on a route. The target vehicle trace 14 illustrated in Figure 5 is defined in two dimensions corresponding to a plan view of the target vehicle route. However, it will be appreciated that the target vehicle trace 14 may be generated in three dimensions, for example to represent the elevation of the target vehicle 3. 5
The speed at which the target vehicle 3 is travelling may be calculated in dependence on a detected movement of the target vehicle 3 between frames of the image data. The processor 5 may compensate for movements of the host vehicle 2 when estimating the speed at which the target vehicle 3 is travelling. In particular, the processor 5 may take account of the
10 reference host vehicle target speed (which is known from the reference speed signal VRef) and/or angular movements of the host vehicle 2 (which are known from the vehicle roll signal Sβ and/or the vehicle pitch signal Sα and/or the vehicle yaw signal Sγ).The movements of the target vehicle 3 within the image data may thereby be adjusted to compensate for movements of the host vehicle 2 (which affect the orientation of the sensing means 7).
15
The control system 1 is operative to assist in the dynamic control of the host vehicle 2. The processor 5 outputs the follow distance signal SV1 to the communication bus 13 to control dynamic operation of the host vehicle 2 in dependence on the determined vertical offset ΔV between the host vehicle 2 and the target vehicle 3. In the present embodiment, the control
20 system 1 is operative to set the target follow distance D1 between the host vehicle 2 and the target vehicle 3. The target follow distance D1 is the distance to be maintained between the host vehicle 2 and the target vehicle 3. In the present embodiment, the control system 1 sets the target follow distance D1 in dependence on the determined vertical offset ΔV. The target follow distance D1 could be calculated dynamically in dependence on the determined
25 vertical offset ΔV. The target follow distance D1 may be calculated in dependence on one or more of the following factors: the determined vertical offset ΔV; the reference host vehicle target speed; the calculated target vehicle speed; the pitch angle α of the host vehicle 2; and the pitch angle of the target vehicle 3. In the present embodiment, the processor 5 is operable to access a lookup table T1 stored in the memory 6 to determine the target follow
30 distance D1. As shown in Figure 4, the target follow distance D1 is defined in the lookup table T1 with reference to the determined vertical offset ΔV. The processor 5 reads the target follow distance D1 for the vertical offset ΔV from the lookup table T1 and generates the target follow distance signal S1 to set the target follow distance D1 for the cruise control module 8.
35
The processor 5 may be operable to process the vertical offset ΔV to identify terrain features and characteristics. For example, the processor 5 may determine a rate of change of the
15

vertical offset ΔV. The rate of change of the vertical offset ΔV may provide an indication of a change in the gradient of a slope on which the target vehicle 3 is travelling. Identifying when the rate of change of the vertical offset ΔV changes from a substantially steady state condition may indicate that the target vehicle 3 is beginning to ascend a slope. Conversely, 5 identifying when the rate of change of the vertical offset ΔV changes to a substantially steady state condition may indicate that the target vehicle 3 is cresting a slope. As shown in Figure 6, a notification may be output to a display screen 15 provided in the host vehicle 2, for example provided in an instrument cluster 16, to notify the driver of the host vehicle 2 that a slope has been detected. A prompt may be output requesting that the driver press a 10 resume button (not shown) to continue. It will be understood that, when determining the rate of change of the vertical offset ΔV, the processor 5 may allow for changes resulting from the movements of the host vehicle 2, for example to compensate for changes in the elevation of the host vehicle 2.
15 There may be circumstances when it is no longer appropriate for the cruise control module 8 to operate in the follow mode described herein. The processor 5 may optionally be operable to deactivate the cruise control module 8 in dependence on the vertical offset ΔV between the host vehicle 2 and the target vehicle 3. The processor 5 may, for example, be operable to deactivate the cruise control module 8 when the vertical offset ΔV exceeds a
20 predetermined first offset threshold. The first offset threshold may, for example, be stored in the memory 6. The processor 5 is operable to monitor the vertical offset ΔV and, upon determining that the vertical offset ΔV is greater than the predetermined first offset threshold, to deactivate the cruise control module 8. Alternatively, or in addition, the processor 5 may be operable to increase the target follow distance D1 if the determined vertical offset ΔV
25 exceeds the first offset threshold. The processor 5 may optionally deactivate the cruise control module 8 if the determined vertical offset ΔV exceeds a second offset threshold which is larger than the first offset threshold. Alternatively, or in addition, the processor 5 may be operable to bring the host vehicle 2 to a halt when the determined vertical offset ΔV exceeds the predefined first offset threshold. Alternatively, or in addition, the processor 5
30 may be operable to output an alert or notification to a driver of the host vehicle 2 when the determined vertical offset ΔV exceeds the predefined first offset threshold.
The present invention has been described in relation to determining a vertical offset ΔV between the host vehicle 2 and the target vehicle 3. In a variant, the control system 1 in 35 accordance with the present invention may be operable to determine an absolute elevation of the target vehicle 3, for example with reference to sea level. The elevation of the host vehicle 2 may be known, for example with reference to GPS data. The absolute elevation of
16

the target vehicle 3 may be calculated in dependence on the elevation of the host vehicle 2. The absolute elevation of the target vehicle 3 may be used to calculate the location of the target vehicle 3, for example in dependence on map data stored in the memory 6 or a separate data storage device. 5
The operation of the control system 1 in conjunction with the cruise control module 8 will now be described. The cruise control module 8 is activated and dynamically controls the host vehicle target speed in order to maintain a target follow distance D1 between the host vehicle 2 and the target vehicle 3. The control system 1 is operable to adjust the target follow
10 distance D1 in dependence on the determined vertical offset ΔV between the host vehicle 2 and the target vehicle 3. The at least one optical sensor 12 is forward-facing and has a field of view FOV which captures a scene in front of the host vehicle 2. In use, the at least one optical sensor 12 captures image data which is transmitted to the processor 5 in the data signal S1. The processor 5 processes the image data to identify the target vehicle 3 within
15 the captured scene. The processor 5 analyses of the image data to determine the vertical offset ΔV between the host vehicle 2 and the target vehicle 3. The processor 5 then accesses the lookup table T1 stored in memory 6 and reads a target follow distance D1 in dependence on the determined vertical offset ΔV. The processor 5 then outputs a target follow distance signal SD1 to the cruise control module 8. The cruise control module 8
20 controls the host vehicle target speed to maintain the target follow distance D1 determined by the processor 5 in dependence on the determined vertical offset ΔV.
The processor 5 may be operable to generate a host vehicle trace 18. The host vehicle trace 18 may represent the (geospatial) route taken by the host vehicle 2 as well as the speed of
25 the host vehicle 2 along that route. The host vehicle trace 18 may optionally also comprise the trajectory of the host vehicle 2 along the target vehicle route. The host vehicle trace 18 may optionally comprise vehicle attitude data generated by the vehicle attitude sensor module 11. For example, the host vehicle trace 18 may comprise one or more of the following: the pitch angle α, and the roll angle β, and the yaw angle γ. The vehicle attitude
30 data may be stored along said host vehicle trace 18, for example by defining the orientation of the longitudinal axis X, a transverse axis Y and a vertical axis Z making up the reference frame of the host vehicle 2. The vehicle attitude data may optionally also comprise acceleration data about one or more of said axis.
35 In use, tracking of the target vehicle 3 may be lost or interrupted, for example due to the presence of obstacles or terrain features between the host vehicle 2 and the target vehicle 3 which partially or completely obscure the target vehicle 3. The target vehicle trace 14 may be
17

used to predict the location of the target vehicle 3 after tracking is lost or interrupted. For
example, the processor 5 may be operable to predict movement of the target vehicle 3 in
dependence on one or more of the following: an identified location of the target vehicle 3
when tracking was interrupted; a trajectory of the target vehicle 3 when tracking was
5 interrupted; a speed of travel of the target vehicle 3 when tracking was interrupted; and map
(geographic) data showing possible routes from a last-known location of the target vehicle 3. By predicting a location of the target vehicle 3, at least in certain embodiments the processor 5 may be operable more quickly to re-establish tracking of the target vehicle 3.
10 As outlined above, the processor 5 may track the target vehicle route. At least in certain
embodiments, the processor 5 may calculate the speed and/or the trajectory of the target vehicle 3. The calculated speed and/or trajectory at a given location may be defined as a movement vector Vn having a magnitude (representing the target vehicle speed) and direction (representing the trajectory of the target vehicle 3). By repeating these calculations
15 (for example at predetermined temporal or spatial intervals), the processor 5 builds the
target vehicle trace 14 for the target vehicle 3, as illustrated in Figure 5. A modified embodiment of the control system 1 described herein with reference to Figures 1 to 6 may utilise the resulting target vehicle trace 14 for controlling the host vehicle 2. The modified embodiment of the control system 1 will now be described with reference to Figure 7, 8 and
20 9. Like reference numerals are used for like components and the description of this
embodiment will focus on the modifications.
The control system 1 according to the modified embodiment is operable to compare the movements of the host vehicle 2 to the tracked movements of the target vehicle 3. As
25 described herein, the processor 5 is operable to build the target vehicle trace 14. As shown
in Figure 7, the processor 5 is configured to receive a location signal SGPS from a GPS module 17. The location signal SGPS comprises location data specifying a current location of the host vehicle 2. The processor 5 uses the location data from the GPS module 17 to compare a current route of the host vehicle 2 to the (historic) tracked target vehicle route.
30 The processor 5 in the present embodiment is operable to compare the location data from
the GPS module 17 with the target vehicle trace 14 stored in the memory 6. The processor 5 correlates the movements of the host vehicle 2 to the recorded movements of the target vehicle 3. As illustrated in Figure 8, the processor 5 determines a deviation δ between the current route of the host vehicle 2 and the tracked route of the target vehicle 3. The deviation
35 δ in the present embodiment comprises a distance between the current location of the host
vehicle 2 and the nearest point on the tracked route of the target vehicle 3.
18

If the processor 5 determines that the deviation δ exceeds a predetermined deviation
threshold, a deviation signal SDEV may be generated. In the present embodiment, the
processor 5 determines that the host vehicle 2 is deviating from the target vehicle route if the
distance between the location of the host vehicle 2 and the target vehicle trace 14 exceeds a
5 predefined distance threshold. The deviation signal SDEV is published to the communication
bus 13 and read by the cruise control module 8. The cruise control module 8 is configured to deactivate a currently active follow mode in dependence on said deviation signal SDEV. Thus, if the processor 5 determines that the host vehicle 2 is deviating from the target vehicle route, the deviation signal SDEV is generated to deactivate the follow mode of the
10 cruise control module 8.
If the processor 5 determines that the deviation δ is within the predetermined deviation threshold, a correlation signal SCOR may be generated. In the present embodiment, the processor 5 determines that the path of the host vehicle 2 at least substantailly corresponds to that of the target vehicle route if the distance between the location of the host vehicle 2
15 and the target vehicle trace 14 remains with a predefined distance threshold. The deviation
signal SCOR is published to the communication bus 13 and read by the cruise control module 8. The cruise control module 8 is configured to activate a follow mode in dependence on the correslation signal SCOR. Thus, if the processor 5 determines that the host vehicle 2 is following the target vehicle route, the correlation signal SCOR is generated
20 to activate the follow mode of the cruise control module 8. It will be understood that this
control strategy may be used to detect a lead vehicle 3 and to automatically or semi-automatically activate the vehicle control module.
Alternatively, or in addition, the processor 5 may compare the trajectory of the host vehicle 2
25 to the trajectory of the target vehicle 3 along the target vehicle route. The processor 5 may
determine that the host vehicle 2 has deviated from the target vehicle route if the comparison
of the trajectory of the host vehicle 2 and that of the target vehicle 3 at a corresponding
location exceeds a predefined angular threshold or is within a predefined angular threshold.
This operating mode is illustrated in Figure 9. The target vehicle route taken by the host
30 vehicle 2 initially follows the tracked route of the target vehicle 3, which may be determined
with reference to the target vehicle trace 14. When the trajectory of the host vehicle 2
exceeds the predefined angular threshold, the processor 5 outputs the deviation signal
SDEV to deactivate the follow mode of the cruise control module 8. In the illustrated
arrangement, the processor 5 determines that the host vehicle 2 is no longer following the
35 tracked route of the target vehicle 3 at a deviation point 19 (denoted by a star indicia in
Figure 9). When the trajectory of the host vehicle 2 is within the predefined angular
19

threshold, the processor 5 outputs the correlation signal SCOR to activate the follow mode of the cruise control module 8.
Alternatively, or in addition, the processor 5 may consider a steering angle θ of the host
5 vehicle 2 when comparing the current route of the host vehicle 2 and the tracked routed of
the target vehicle 3. The steering angle θ is published to the communication bus 13, for example by a steering angle sensor 20 associated with a steering wheel (not shown), and is read by the processor 5. A comparison of the trajectory of the target vehicle 3 and the steering angle θ provides an indication of whether the host vehicle 2 is following the tracked
10 route of the target vehicle 3. The processor 5 may calculate the divergence of the target
vehicle route taken by the host vehicle 2 and the target vehicle route. At least in certain embodiments, the processor 5 may determine if the driver of the host vehicle 2 is intentionally steering away from the target vehicle route. The processor 5 may determine when the intended path of the host vehicle differs from the target vehicle route. By
15 measuring any such deviation, the processor may determine that the host vehicle 2 is no
longer following the target vehicle 3. The processor 5 may, for example, be operable to resume a driver requested speed, rather than to set the target speed in dependence on the determined target vehicle speed.
The processor 5 may be operable to determine the trajectory of the target vehicle 3 in dependence on the target vehicle trace 14. This may be used to provide an element of prediction of a possible location of the target vehicle 3 when tracking is interrupted. For example, knowledge of the steering angle θ of the host vehicle and/or odometry data can be used to establish if the host vehicle 2 is taking a similar path to the target vehicle 3. In this situation, action can be taken by the host vehicle 2 to improve confidence, for example holding the current target (follow) speed or the speed at which the target vehicle 3 was travelling when tracking was interrupted. The target speed of the host vehicle 2 can be held for a time or distance to allow re-establishment of tracking of the target vehicle 3, for example when the target vehicle 3 reappears from around a corner or from behind an obstacle.
The processor 5 could be modified to generate a host vehicle trace 18 for comparison with
the target vehicle trace 14. The location data generated by the GPS module 17 to identify
the geospatial location of the host vehicle 2 could be stored in the memory 6. The processor
35 5 may also store dynamic operating parameters of the host vehicle 2, such as the reference
speed (derived from the GPS module 17 or other on-board sensors, such as the wheel speed sensors 10). The host vehicle trace 18 and the target vehicle trace 14 could be
20

compared using a pattern matching algorithm to assess the correlation between the traces. The comparison may, for example, compare the relative positions of the host vehicle 2 and the target vehicle 3; and/or the trajectory of the host vehicle 2 and the target vehicle 3. If the deviation δ between the host vehicle trace 18 and the target vehicle trace 14 exceeds a 5 predefined deviation threshold δ”, the processor 5 is configured to output the deviation signal SDEV. If the deviation δ between the host vehicle trace 18 and the target vehicle trace 14 is within a predefined deviation threshold δ”, the processor 5 is configured to output the correlation signal SCOR.
10 It will be appreciated that various modifications may be made to the embodiment(s) described herein without departing from the scope of the appended claims. The target vehicle 3 may comprise an active or passive marker to facilitate identification by the processor 5. A passive marker may, for example, comprise a visible target or reflector (either an optical or radio wave reflector) which may be detected by appropriate detection means
15 provided on the host vehicle 2. An active marker may comprise an active source, such as a wireless radio frequency (RF) transmitter or a light source (for emitting visible or infrared light), to facilitate identification by the processor 5. The host vehicle 2 may comprise detection means.
20 As outlined herein, the processor 5 may process the image data generated by the at least one optical sensor 12 to calculate the attitude of the target vehicle 3. The processor 5 may, for example, determine an orientation of a reference frame of the target vehicle 3. The processor 5 may analyse the image data captured by the at least one optical sensor 12 to calculate the orientation a longitudinal axis X1, a transverse axis Y1 and a vertical axis Z1 of
25 the target vehicle 3. The processor 5 may be operable to store the resulting target vehicle attitude data in conjunction with the location data. For example, the processor 5 may store the target vehicle attitude data with said target vehicle trace 14. The processor 5 may be operable to control the host vehicle target speed and/or the target follow distance D1 in dependence on the angular attitude of the target vehicle 3 about one or more of said axes.
30 For example, the processor 5 may reduce the following target speed and/or increase the target follow distance D1 if the angular orientation of the target vehicle 3 is greater than or equal to a predefined angular threshold. Alternatively, or in addition, when comparing the routes taken by the host vehicle 2 and the target vehicle 3, the processor 5 may be configured to compare the attitude of the host vehicle 2 and the target vehicle 3.
35
The target vehicle trace 14 and/or the host vehicle trace 18 may be stored indefinitely. The historic data may be referenced at a later time, for example when repeating the target
21

vehicle route. The target vehicle trace 14 and/or the host vehicle trace 18 could optionally be shared, for example transferred to another vehicle intending to follow the same route.
The control system 1 described herein is operable to selectively activate and/or deactivate the cruise control module 8. Alternatively, or in addition, the control system 1 may be operable to selectively activate and/or deactivate a steering control module (not shown) operable to control a steering angle 0 of the host vehicle 2. The steering control module may, for example, be incorporated into the vehicle control module described herein. The steering control module may provide autonomous or semi-autonomous control of the steering of the host vehicle 2, for example by controlling an electric power assist steering (EPAS) system. The target vehicle route may be used to define a target route to be taken by the host vehicle 2. The EPAS system may be operable to control the host vehicle 2 to follow the target route. The control system 1 described herein may selectively activate and/or deactivate the steering control module to enable and/or disable autonomous or semi-autonomous control of the steering. When the trajectory of the host vehicle 2 is within the predefined angular threshold, the processor 5 outputs the correlation signal SCOR to activate the steering control module. When the trajectory of the host vehicle 2 exceeds the predefined angular threshold, the processor 5 outputs the deviation signal SDEV to deactivate the steering control module. It is envisaged that the control functions described herein in relation to the cruise control module 8 may be equally applicable to these control functions.
The processor 5 has been described as generating a target vehicle trace 14 by storing the movement vectors along a calculated route of the target vehicle 3. Alternatively, or in addition, the processor 5 may be operable to store data relating to a determined attitude of the target vehicle 3 along the calculated route. For example, the processor 5 may store a calculated pitch angle and/or roll angle and/or yaw angle of the target vehicle 3 as it travels along the calculated route. The processor 5 may be operable also to evaluate the terrain over which the target vehicle 3 is travelling. Alternatively, or in addition, the processor 5 may be operable to store terrain data generated as a result of this evaluation process along the calculated route travelled by the target vehicle 3. The processor 5 may utilise one or more of the stored datasets when planning a route for the host vehicle 2.

CLAIMS:
1. A control system for controlling operation of a host vehicle, the control system
comprising a processor operable to:
track a target vehicle to determine a target vehicle route;
determine a speed of the target vehicle travelling along the target vehicle route; and
control a target speed of the host vehicle in dependence on the determined target vehicle speed;
wherein, in the event that tracking of the target vehicle is interrupted, the processor is operable to control the host vehicle target speed in dependence on the determined target vehicle speed at a known location on the target vehicle route.
2. A control system as claimed in claim 1, wherein the known location of the target vehicle corresponds to the location where tracking of the target vehicle was interrupted.
3. A control system as claimed in claim 1 or claim 2, wherein the processor is operable to determine an acceleration of the target vehicle along the target vehicle route.
4. A control system as claimed in claim 3, wherein the processor to control acceleration of the host vehicle while travelling along the target vehicle route in dependence on the determined acceleration of the target vehicle.
5. A control system as claimed in any one of the preceding claims, wherein the processor is operable to determine a trajectory of the target vehicle along the target vehicle route.
6. A control system as claimed in claim 5, wherein the processor is operable to control a steering angle of the host vehicle while travelling along the target vehicle route in dependence on the determined trajectory of the target vehicle.
7. A control system as claimed in any one of the preceding claims, wherein the processor is operable to receive a signal from at least one sensor provided on the host vehicle and to process said signal to track the target vehicle, optionally, wherein the signal comprises image data captured by one or more image sensors; and the processor is operable to process said image data to track the target vehicle, further optionally wherein the processor is operable to process said image data to determine a pitch angle and/or a roll angle and/or a yaw angle of the target vehicle.

A method of controlling operation of a host vehicle, the method comprising:
tracking a target vehicle to determine a target vehicle route;
determine a speed of the target vehicle travelling along the target vehicle route;
controlling a target speed of the host vehicle in dependence on the determined target vehicle speed; and
in the event that tracking of the target vehicle is interrupted, controlling the host vehicle target speed in dependence on the determined target vehicle speed at a known location on the target vehicle route.
9. A control system for controlling operation of a host vehicle, the control system
comprising a processor operable to:
track a target vehicle to determine a target vehicle route;
determine a trajectory of the target vehicle along the target vehicle route; and
control a target speed of the host vehicle in dependence on the determined target vehicle speed;
wherein the processor is operable to control a steering angle of the host vehicle while the host vehicle is travelling along the target vehicle route in dependence on the determined trajectory of the target vehicle.
10. A method of controlling operation of a host vehicle, the method comprising:
tracking a target vehicle to determine a target vehicle route;
determining a trajectory of the target vehicle along the target vehicle route; and controlling a target speed of the host vehicle in dependence on the determined
target vehicle speed;
wherein a steering angle of the host vehicle is controlled while the host vehicle is
travelling along the target vehicle route in dependence on the determined trajectory of the
target vehicle.