Patent Publication Number: US-2023141561-A1

Title: Method for quantifying object detection performance

Description:
TECHNICAL FIELD 
     The present disclosure relates to methods, control units and vehicles for quantifying object detection performance. The methods disclosed herein find applications in, e.g., autonomous drive, advanced driver assistance systems, and other safety critical vehicle functions. 
     The invention can be applied in heavy-duty vehicles, such as trucks, semi-trailers, and construction equipment. Although the invention will be described mainly with respect to a cargo transport type vehicle, the invention is not restricted to this particular vehicle, but may also be used in other types of vehicles such as in construction equipment, busses and also in cars. 
     BACKGROUND 
     Autonomous drive systems (ADS) and other advanced driver assistance systems (ADAS) constantly make decisions on how to control an ego vehicle in order to fulfil a given objective while not subjecting the vehicle to risk. These decisions are based on a wide variety of different factors related both to the state of the ego vehicle but also to the surrounding environment and to the ability of the vehicles to perform different types of maneuvers. 
     When controlling a vehicle there are always uncertainties which need to be accounted for in order to not subject the vehicle to risk. Many use cases for ADS and/or ADAS require some sort of object detection solution. In ADS and/or ADAS there is typically a need to understand how well the objection detection system is performing. Therefore, extensive testing is often performed using different types of objects in in different conditions. 
     A problem with evaluating object detection performance on observations is that a lot of data is required in order to accurately capture rare events, such as extreme weather, vehicle control loss etc. Gathering such large quantities of data is both costly and time consuming and may in some cases not even be feasible from a practical point of view. 
     WO2021037329 A1 and WO2021037330 A1 relate to similar problems. 
     There is a need for improved methods of quantifying object detection performance which allow efficient modelling of rare events in a reliable manner. 
     SUMMARY 
     It is an object of the present disclosure to provide methods for quantifying and modelling objection detection performance. This object is obtained by a method for controlling a vehicle based on a quantified objection detection performance. The method comprises obtaining samples of objection detection performance p i     i=1     n-1 , wherein the objection detection performance comprises a comparison of an estimated object state with a reference object state a.k.a. ground truth data, selecting a subset of the objection detection performance samples such that the selected samples follow a pre-determined statistical extreme value distribution, parameterizing the pre-determined statistical extreme value distribution based on the selected samples of objection detection performance, quantifying objection detection performance based on the parameterized statistical extreme value distribution, and controlling the vehicle based on the quantified objection detection performance. 
     An important feature of the disclosed method is that the required amount of data that is needed in order to quantify objection detection performance is reduced. By allowing modelling of objection detection performance based on a reduced set of data, development and testing time is reduced, which is an advantage. Also, some types of analysis which were previously not possible to perform since they simply required too much data is now enabled by the disclosed methods. 
     The disclosed methods are applicable for both off-line and/or on-line processing, which is an advantage. On-line processing may, e.g., be used to complement more extensive off-line processing, leading to improved model verification and thus improved vehicle operation. 
     The pre-determined statistical extreme value distribution may, e.g., be a Generalized Pareto Distribution (GDP) or a Generalized Extreme Value distribution (GEV). These types of extreme value distributions have been extensively studied, which means that the disclosed methods can make use of well-known and robust analysis techniques, which is an advantage. 
     According to aspects, the method comprises measuring a time between exceedances metric indicating the time passed between objection detection performance samples exceeding a threshold ζ, and monitoring operational design domain (ODD) based on the time between exceedances metric. This is a relatively simple metric to determine, yet it is a powerful indicator of when a vehicle is operating outside its ODD. 
     According to some examples, a sample of objection detection performance comprises any of object position, object heading, object longitudinal velocity, object lateral velocity, object longitudinal acceleration, object lateral acceleration, object yaw rate, object motion relative to a road surface object motion relative to a road lane, object motion relative to another object, and minimum distance for reliable object classification. Notably, these quantities are examples, several additional examples can of course be given. 
     A sample of objection detection performance may, for example, be obtained dependent on any of; type of vehicle, type of vehicle combination, vehicle physical dimension parameters, weather condition, road friction, road geometry, and path trajectory geometry. 
     According to some aspects, the method also comprises quantifying the objection detection performance as a bounded model by bounding the performance to lie within a range − w ≤b k ≤ w  with probability greater than 1−γ, based on the pre-determined statistical extreme value distribution. 
     Bounds on objection detection performance enable risk assessment of various driving scenarios, both off-line and in real time. The bounded models obtained from the disclosed methods can also be used to decide, e.g., when to trigger an emergency maneuver by the vehicle. 
     According to some other aspects, the method further comprises determining a confidence value β associated with the pre-determined statistical extreme value distribution. 
     This confidence value will be discussed in more detail below. It indicates the confidence obtained in the parameterized GEV or GDP, i.e., if the GEV or GDP can be accurately fitted to the available data or if more data is needed for a good fit. 
     According to some further aspects, the method comprises assessing a sufficiency of gathered objection detection performance data for vehicle modelling based on the confidence value β associated with the pre-determined statistical extreme value distribution. 
     The methods disclosed herein also enable providing constructive feedback on when data collection for a given purpose is done, e.g., when a sufficient amount of data has been collected for quantifying objection detection performance in some scenario. For instance, according to aspects, the method comprises assessing a sufficiency of gathered model data for model correctness verification based on the confidence value β associated with the parameterized GEV or GDP. 
     The disclosed methods may optionally also comprise monitoring an operational design domain (ODD) associated with the vehicle by comparing the parameterized statistical extreme value distribution to a set of baseline distribution parameters, wherein operation outside the ODD is indicated by a difference between the parameterized statistical extreme value distribution parameters and the baseline distribution parameters. 
     In other words, yet another feature of the disclosed methods is that intermediate results can be used to construct a monitor of at least part of the ODD. These particular aspects are also applicable as a foundation for independent stand-alone methods not depending on the above discussed methods. Consequently, there is disclosed herein a method for monitoring an ODD associated with a vehicle. The method comprises obtaining a parameterized GEV or GDP from samples of objection detection performance during vehicle operation, like described herein or in some other way. The method also comprises monitoring an ODD associated with the vehicle by comparing the parameterized GEV or GDP to a set of baseline GEV or GDP parameters, wherein operation outside the ODD is indicated by a difference between parameterized GEV or GDP parameters and baseline parameters. 
     There are furthermore disclosed herein control units, computer programs and vehicles associated with the same advantages as discussed above in connection to the different methods. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings: 
         FIG.  1    schematically illustrates a vehicle; 
         FIG.  2    illustrates an example situation avoidance maneuver by a vehicle; 
         FIG.  3    shows an example safe set; 
         FIG.  4    shows an example thresholding operation; 
         FIG.  5    shows another example thresholding operation; 
         FIG.  6    is a flow chart illustrating methods; 
         FIG.  7    schematically illustrates a control unit; and 
         FIG.  8    shows an example computer program product. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION 
     Aspects of the present disclosure will now be described more fully with reference to the accompanying drawings. The different devices and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout. 
     The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
       FIG.  1    schematically illustrates a vehicle  100  comprising a control unit  110 . The control unit  110  may implement various types of support systems and systems for vehicle functional safety, such as advanced driver assistance systems (ADAS) and functions for autonomous drive (AD). The methods and techniques disclosed herein are applicable with combustion powered vehicles (as shown in  FIG.  1   ), and also with electrically powered vehicles and hybrid electric vehicles. 
     The vehicle may be connected  120  to a processing device  130  arranged to perform off-line calculations to assist the vehicle control system comprising the control unit  110 . The connection  120  is preferably wireless but may also be a wireline connection or a connection via some storage module such as a hard drive or the like. 
     One example function that the control unit  110 , and potentially also the processing device  130 , may support is the planning and execution of a situation avoidance maneuver (SAM). A safe stop maneuver is an example of a SAM. However, SAMs may also comprise maintaining a constant velocity in a given lane or performing an obstacle avoidance maneuver. In general, the class of situation avoidance maneuvers comprise all maneuvers which can be executed to avoid undesired situations, such as detected risk situations. A SAM may however also relate to, e.g., a difficult parking situation or the like. 
       FIG.  2    illustrates an example SAM  200 . The vehicle  100  detects at point A that something is wrong and that the vehicle needs to execute a safe stop maneuver. For instance, the vehicle  100  may have experienced some type of sensor failure at point A, such as radar system failure or a camera malfunction condition. 
     The example SAM illustrated in  FIG.  2    comprises moving the vehicle  100  to the side of the road  210  and stopping the vehicle in a controlled manner at point B. The control unit  110  therefore determines a track with an associated speed profile that is to be followed by the vehicle  100  during the SAM. 
     A problem when determining the suitable track and speed profile is that objects in vicinity of the vehicle must be accounted for. For instance, the vehicle may risk colliding with an object, which of course is undesirable (in most cases).  FIG.  2    shows example objects in the form of another vehicle  230 , a pedestrian  240 , and a boulder  250 . In order to determine a SAM which is associated with a sufficiently high probability of being successfully executed in a safe manner, it becomes important to accurately detect the objects  230 ,  240 ,  250  during the maneuver. Verifying object detection performance is crucial for the SAM being safely executed with high probability. 
     Herein, “safe” is given a broad interpretation. A safe maneuver or a safe vehicle state may be a maneuver or state in which the vehicle and/or vehicle occupant and/or other road user and/or object in general is not subject to risk in terms of injury or damage. 
     Some examples may be given of a safe condition and of an unsafe condition. 
     According to some aspects, a situation where a risk of collision is unlikely may be considered a safe state. 
     According to some other aspects, a situation where a risk of collision is not unlikely may still be considered a safe state depending on the object. As an example, colliding with a small bush or tree may be considered safe, while colliding with another vehicle or a larger object like a brick wall may be considered unsafe. 
     According to some further aspects, colliding with another vehicle where it has been determined beforehand, e.g., via vehicle-to-vehicle (V2V) communications, that a collision can be tolerated with low risk, may be considered safe. 
     According to aspects, a situation where the vehicle risks exiting a drivable area is considered unsafe. 
     According to other aspects, exiting a drivable area may be considered safe depending on the properties of the ground outside the drivable area, as discussed above. 
     A vehicle state is a collection of variables which together describe in what state the vehicle is currently in. Herein, vehicle state comprises variables associated with vehicle location (coordinates) and orientation (such as, e.g., heading, steering angle and articulation angle). The vehicle state also comprises information associated with vehicle dynamic state, i.e., vehicle velocity, acceleration, turn rate, and so on. The vehicle state is often represented as a vector of state variables x. As will be discussed in more detail below, an allowable vehicle state space may, in general, comprise both upper and lower limits on state variables such as lateral position for the duration of a maneuver. 
     The vehicle transitions between states based on issued control commands, e.g., braking commands or turning commands. Vehicle state can often be bounded to lie within some set with high probability. 
     With reference to  FIG.  3   , a vehicle  100  may currently be associated with a state that is comprised in some set S of states, and wishes to transition into some other set of states X. The control unit  110  therefore issues a control command u, which is an example of vehicle control. For a given target set X, a one-step robust controllable set (or preimage set) S is defined as the set of states that gets robustly mapped to X. Preimage sets were discussed by, e.g., F. Borrelli, A. Bemporad, and M. Morari, in “Predictive Control for linear and hybrid systems”, Cambridge University Press, 2015, and will therefore not be discussed in more detail herein. The set S is the set of vehicle states for which there exist a control signal u that transitions the vehicle state into a state comprised in the target set of states X, for all possible disturbances. The set of disturbances can be assumed bounded, or it can be assumed to be some set representing a fixed probability of occurrence. In other words, it can be ascertained using various known methods that the vehicle will transition into a state x comprised in the set of states X as a consequence of issuing the control signal u, starting from a set of vehicle states S. 
     In order to determine a suitable target set X which the vehicle may safely transition into without risk of colliding with objects, such as other vehicles  230 , a pedestrian  240 , or a boulder  250 , the states of objects need to be quantified, and preferably bounded to lie within some set V which should then be disjoint from the set X with high probability (two sets are said to be disjoint sets if they have no element in common). For instance, a spatial dimension  310  of the set V may be determined based on a model of object state in terms of acceleration and braking. However, this behavior preferably also accounts for very rare actions, such as extreme braking and strong acceleration. 
     Various states of the object, such as position, heading, velocity, acceleration etc. are estimated with some degree of certainty. In other words, there will likely be a discrepancy between an estimated object state (e.g., position) and the actual object state. The actual object state can be referred to as ground truth data. This discrepancy can be denoted an error and can be used as a measure of objection detection performance. To correctly bound the set V of the object, the objected detection performance should accurately be quantified. This way uncertainties in state estimation can be accounted for. It may not be possible to obtain ground truth data. However, it possible to obtain data of an object state with a much higher accuracy compared to “normal” estimation methods. Therefore, the objection detection performance comprises a comparison of an estimated object state with a reference object state. Here, the reference object state is ground truth data or an approximation with much higher accuracy compared to the estimated object state. 
     Generating reference data can be done in a number of different ways, which are previously known and will therefore not be discussed in detail herein. For example, reference data can be generated by using expensive high-performing sensors which are only mounted during an evaluation period of the system but not on the final product. Alternatively, or in combination of, data from different sources can be used. These ways of obtaining ground truth data may be used in combination with non-causal analysis methods. Non-casual methods can typically produce more accurate and reliable results, although by their nature they are of course hard to use during online operation due to the use of data with a future time-stamp with respect to the time-stamp of the state estimate. 
     Suppose densely sampled objection detection performance data has been obtained. Although it is possible to use this data directly to determine the occurrence rate for extreme instances of a state estimation error or other discrepancies, it does not necessarily capture the behavior of the vehicle well. Instead, it is herein proposed to, optionally, filter the densely sampled data to extract a series of low dimensional aggregate samples describing the specific objection detection performance we are interested in modelling. For example, if the purpose is to quantify how often large lateral offsets occur when attempting to estimate the position of an object, then aggregate samples could be formed by first detecting instances of lateral offset based on some criteria (e.g. thresholding), and then quantifying these instances using aggregate measures, e.g. a two dimensional sample consisting of maximum offset or threshold value and the duration of time the offset is above some threshold. A cumulative density function can also be used to describe aggregate behavior in terms of the relative percentage of time the offset is above some value. The densely sampled data can also be replaced by, e.g., block maxima, block means, or block median values determined for consecutive blocks of the densely sampled data, thus provided less dense sampled data. 
     Extreme value theory (EVT) is an area of statistics which focuses on properties of rare events. EVT is discussed in, e.g., C. Scarrott and A. MacDonald, “A review of extreme value threshold estimation and uncertainty quantification,” REVSTAT Statistical Journal, vol. 10, no. 1, 2012, and references cited therein. 
     In probability theory and statistics, the generalized extreme value (GEV) distribution is a family of continuous probability distributions developed within extreme value theory to combine the Gumbel, Fréchet and Weibull families also known as type I, II and III extreme value distributions. By the extreme value theorem, the GEV distribution is the only possible limit distribution of properly normalized maxima of a sequence of independent and identically distributed random variables. It is noted that a limit distribution need not exist since this requires regularity conditions on the tail of the distribution. Despite this, the GEV distribution is often used as an approximation to model the maxima of long (finite) sequences of random variables. In some fields of application, the generalized extreme value distribution is known as the Fisher-Tippett distribution, named after Ronald Fisher and L. H. C. Tippett. However, usage of this name is sometimes restricted to mean the special case of the Gumbel distribution. 
     Peaks Over Threshold (POT) is a class of methods in EVT that model the extreme events that exceed some threshold. Under some assumptions the exceedances converge asymptotically to a so-called Generalized Pareto (GDP) distribution. For a specific data set, the exceedances can be used to estimate the parameters of a GDP distribution which in turn can be used to predict the likelihood of even rarer events. This enables statistical arguments on the limits of assumptions with significantly less data than traditional methods. The results from this analysis can also be used to verify that a set of assumptions does appear to hold true for the Operational Design Domain (ODD) where the data was collected. The ODD may, e.g., be characterized by maximum ego velocity, maximum road slope, maximum road banking, weather, etc. 
     Furthermore, the assumptions can then be used when evaluating whether an ego vehicle can perform a certain action, i.e. is the action safe given the expected objection detection performance of the vehicle. 
     The parameters for the GEV and/or GDP distribution can also be used in order to create a monitor for certain aspects of the ODD, i.e. assumptions on objection detection performance. More specifically, if the current objection detection performance deviates from the GDP distribution (with more than a certain probability threshold), there is an indication of a risk that the ego vehicle is no longer within the defined ODD, and thus the ego vehicle may need to take precautionary measures. 
     The ODD monitor is also the reason why it is possible to argue that the system will remain safe over time with regards to changing objection detection performance. This is because the system will be able to detect changes in objection detection performance before an extreme event occurs, which could lead to an accident. 
     It is noted that a benefit of using the methodology proposed herein is that there is no explicit need to observe objection detection errors where the assumptions are broken in order to detect that there is a risk that original ODD (i.e. original data collection) is no longer valid. It is enough to detect a distribution of semi rare events (these events are still within the ODD) which does not match the expected distribution. 
       FIG.  4    schematically illustrates a thresholding operation  400 , where samples of objection detection performance  410 ,  420  have been collected. A threshold is applied in order to select a subset of the objection detection performance samples such that the selected samples follow a pre-determined statistical extreme value distribution. 
       FIG.  5    illustrates another thresholding operation, here in two dimensions x 1 , x 2 . Samples  510 ,  520  of objection detection performance have been collected. A threshold ζ is again applied in order to select a subset of the objection detection performance samples such that the selected samples follow a pre-determined statistical extreme value distribution. 
       FIG.  6    is a flow chart illustrating methods which summarize the discussions above. There is illustrated a method for controlling a vehicle  100  based on a quantified objection detection performance, the method comprising. The method comprises obtaining S1 samples of objection detection performance p i     i=1     n-1 , wherein the objection detection performance comprises a comparison of an estimated object state with a reference object state. The samples may, e.g., be obtained S11 as a previously stored set of samples or obtained S12 as a set of samples during operation of an ego vehicle  100 . 
     A sample of objection detection performance may as discussed above comprise any of object position, object heading, object longitudinal velocity, object lateral velocity, object longitudinal acceleration, object lateral acceleration, object yaw rate, object motion relative to a road surface object motion relative to a road lane, object motion relative to another object, minimum distance for reliable object classification. It is appreciated that this list is not exhaustive, further examples can be given. 
     Interestingly, the methods disclosed herein can be used to quantify object classification performance. For instance, the system may be associated with an object detection performance involving an expected or minimum distance at which a reliable object classification can be made. Samples of such object detection performance can be treated in the same manner as the other examples provided herein. 
     According to some other aspects, a sample of objection detection performance is obtained dependent on any of; type of vehicle, type of vehicle combination, vehicle physical dimension parameters, weather condition, road friction, road geometry, and path trajectory geometry. 
     The method comprises selecting S2 a subset of the objection detection performance samples such that the selected samples follow a pre-determined statistical extreme value distribution. The pre-determined statistical extreme value distribution may, e.g., be a Generalized Pareto Distribution (GDP), or an instance of a Generalized Extreme Value distribution (GEV). 
     According to some aspects, the selecting comprises determining S21 a threshold ζ such that the samples of objection detection performance in excess of the threshold ζ, {p i :p i ≮ζ}, follow the pre-determined statistical extreme value distribution. Some example thresholds were illustrated in  FIGS.  4  and  5    above. The thresholds may be fixed or dynamically adjusted based on some performance criterion. 
     The method further comprises parameterizing S3 the pre-determined statistical extreme value distribution based on the selected samples of objection detection performance, and quantifying S4 objection detection performance based on the parameterized statistical extreme value distribution. Methods for extreme value distribution parameterization are known and will therefore not be discussed in more detail herein. The method also comprises controlling the vehicle  100  based on the quantified objection detection performance. Example of controlling the vehicle are situation avoidance maneuver planning and operational design domain monitoring. 
     According to some aspects, the method comprises measuring S7 a time between exceedances metric indicating the time passed between objection detection performance samples exceeding the threshold ζ, and monitoring ODD based on the time between exceedances metric. This way it can be determined if the vehicle is operating in its ODD, or if traffic situation conditions have changed so much that the vehicle  100  is no longer operating in the intended ODD. 
     According to some aspects, the method comprises comprising quantifying S41 the objection detection performance as a bounded model by bounding the performance to lie within a range − w ≤b k ≤ w  with probability greater than 1−γ, based on the pre-determined statistical extreme value distribution. 
     According to some aspects, the method comprises determining S5 a confidence value β associated with the pre-determined statistical extreme value distribution. The exceedances b i :b i ≮ζ can be used to estimate the parameters of the GDP or GEV (with corresponding confidence). The identified distribution can in turn be used to find bounds on objection detection performance which are fulfilled with a confidence β. The objection detection performance model has a verified correctness of γ with confidence value β, which confidence value β is associated with the parameterized GEV or GDP. Methods for determining the confidence value β are known and will not be discussed in more detail herein. The confidence value depends at least in part on the number of observations collected over the threshold ζ and provides constructive feedback on the needed amount of data. This way, it can be estimated when a sufficient data set has been gathered for modelling objection detection performance, and when more data is needed. An advantage of the disclosed methods is therefore that they can be used to assess a sufficiency of gathered model data for model correctness verification based on the confidence value β associated with the parameterized GEV or GDP. Thus, if the confidence value β is too low after the GEV or GDP has been parameterized, then more data may be needed in order to increase the confidence value. In other words, according to some aspects, the method comprises assessing S51 a sufficiency of gathered objection detection performance data for quantification based on the confidence value β associated with the pre-determined statistical extreme value distribution. 
     According to some other aspects, the method comprises monitoring S6 an operational design domain, ODD, associated with the vehicle by comparing the parameterized pre-determined statistical extreme value distribution to a set of baseline distribution parameters, wherein operation outside the ODD is indicated by a difference between parameterized pre-determined statistical extreme value distribution parameters and the baseline distribution parameters. 
     Although the described objection detection performance modelling may be performed off-line (i.e. in a design phase), the identified GDP or GEV distribution can also be used to construct monitors of the ODD for on-line use as well. In particular, if objection detection performance samples are collected online, the distribution of the exceedances can be monitored. A significantly different distribution of exceedances compared to the distribution that was obtained offline indicates that the system is out of its ODD. In other words, by the disclosed techniques is becomes possible to monitor an ODD associated with the vehicle by comparing the parameterized GDP or GEV to a set of baseline GDP or GEV parameters. Operation outside the ODD is for instance indicated by a difference between parameterized GDP parameters and baseline GDP parameters. A warning signal or SAM may be triggered in case operation outside the ODD is detected. 
     A simple monitor of this kind is to calculate the return period (i.e. the average time between exceedances) over some time window. A significant decrease of the return period is then an indication that the vehicle is operated outside of its ODD. 
       FIG.  7    schematically illustrates, in terms of a number of functional units, the components of the control unit  110  according to an embodiment of the discussions herein. Processing circuitry  710  is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium  730 . The processing circuitry  710  may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA. 
     Particularly, the processing circuitry  710  is configured to cause the control unit  110  to perform a set of operations, or steps, such as the methods discussed in connection to  FIG.  6   . For example, the storage medium  730  may store the set of operations, and the processing circuitry  710  may be configured to retrieve the set of operations from the storage medium  730  to cause the control unit  110  to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry  710  is thereby arranged to execute methods as herein disclosed. 
     The storage medium  730  may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. 
     The control unit  110  may further comprise an interface  720  for communications with at least one external device, such as the remote server  130  and/or on-board vehicle systems. As such the interface  720  may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication. 
     The processing circuitry  710  controls the general operation of the control unit  110  e.g. by sending data and control signals to the interface  720  and the storage medium  730 , by receiving data and reports from the interface  720 , and by retrieving data and instructions from the storage medium  730 . Other components, as well as the related functionality, of the control node are omitted in order not to obscure the concepts presented herein. 
       FIG.  8    schematically illustrates a computer program product  800 , comprising a set of operations  810  executable by the control unit  110 . The set of operations  810  may be loaded into the storage medium  730  in the control unit  110 . The set of operations may correspond to the methods discussed above in connection to  FIG.  6   . 
     In the example of  FIG.  8   , the computer program product  800  is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product could also be embodied as a memory, such as a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program is here schematically shown as a track on the depicted optical disk, the computer program can be stored in any way which is suitable for the computer program product.