Method and apparatus for reporting a perception region

Abstract

A method of communication in an Intelligent Transport System, ITS, comprising at a transmitting ITS station: generating description information describing a perception region 410; generating a relevan

Description

FIELD OF THE INVENTION The present disclosure relates generally to Intelligent Transport Systems (ITSs) and more specifically to Cooperative Intelligent Transport Systems (C-ITSs). BACKGROUND OF INVENTION Cooperative Intelligent Transport Systems (C-ITSs) is an emerging technology for future transportation management that aims at improving road safety, traffic efficiency and driver experience. Intelligent Transport Systems (ITS), as defined by the European Telecommunications Standards Institute (ETSI), include various types of communication such as: communications between vehicles (e.g., car-to-car), and - communications between vehicles and stationary stations (e.g., car-to-infrastructure). C-ITSs are not restricted to road transport as such. More generally, C-ITS may be defined as the use of information and communication technologies (ICT) for rail, water, and air transport, including navigation systems. Such various types of C-ITS generally rely on radio services for communication and use dedicated technologies. Such C-ITSs are subject to standards, specified for each country and / or territory where C-ITSs are implemented. Today, in Europe, the European Telecommunications Standards Institute is in charge of the elaboration of the specifications forming the standards to which C-ITSs are subjected. Cooperation within C-ITSs is achieved by exchange of messages, referred as to ITS messages, between ITS stations (denoted ITS-Ss). The ITS-Ss may be vehicles, Road Side Units (RSUs), Vulnerable Road Users (VRUs) carrying an ITS equipment (for instance included in a smartphone, a GPS device, a smart watch, or in a cyclist equipment), or any other entities or infrastructure equipped with an ITS equipment, as well as central subsystems (back-end systems and traffic management centers). As observed above, C-ITSs may support various types of communications, for instance between vehicles (vehicle-to-vehicle or “V2V”), referring to all kinds of road users, e.g., car-to-car, or between vehicles and stationary stations such as vehicle-to-infrastructure or“V2l”, and infrastructure-to-vehicle or“l2V”, e.g., car-to-infrastructure. Such exchanges of messages may be performed via a wireless network, referred to as “V2X” (for “vehicle” to any kind of devices) networks, examples of which may include 3GPP LTE- Advanced Pro, 3GPP 5G, or IEEE 802.11p technology (3GPP, LTE, and IEEE are Registered Trade Marks). Exemplary ITS messages include Collective Perception Messages (CPMs), Cooperative Awareness Messages (CAMs), Vulnerable Road Users Awareness Messages (VAMs), and Decentralized Environmental Notification Messages (DENMs). An ITS-S sending an ITS message is referred to as an “originating” ITS-S and an ITS-S receiving an ITS message is referred to as a “receiving” ITS-S. The VAMs are generally periodically sent with a period varying depending, for example, on the speed of the originating ITS-S. It is recalled here that ETSI TS 103 324 (v2.1.1 of June 2023) defines the Collective Perception Service through which an ITS-S having on-board sensor systems detects objects in its vicinity and transmits, using broadcast CPMs, description information (e.g. dynamics such as position and / or kinematic information) thereof. The CPMs are sent periodically with a period from 100 ms to 1 s depending for example on the speed of the objects sensed by the originating ITS-S. It is also to be noted that EN 302 637-2 (V1.4.1 of April 2019) standard defines the Cooperative Awareness Basic Service, that may be used by an ITS-S to transmit, using broadcast CAMs, its ego-vehicle dynamics (e.g., its position and speed). The CAMs are generally periodically sent with a period varying from 100 milliseconds to one second depending, for example, on the speed of the originating ITS-S. It is also to be noted that ETSI TS 103 300-3 (December 2022) standard defines the Vulnerable Road User (VRU) Awareness basic Service (VBS), that may be used by an originating ITS-S to send, using broadcast VAMs, notifications to other ITS-Ss, such as dynamic properties of the VRU (motion, acceleration, etc.). It is also to be noted that ETSI TS 103 831 (v2.1.1 of November 2022) standard defines the Decentralized Environmental Notification Basic Service, that may be used by an originating ITS-S to send, using broadcast DENMs, notifications to other ITS-Ss, such as warnings or alerts. Such a message notifies an event (e.g., a road hazard, driving environment information, traffic condition information, etc.) detected by the originating ITS-S. Each ITS station has an environment model called a Local Dynamic Map (LDM) that is regularly updated with highly dynamic data to locate vehicles, pedestrians, bicycles, etc., in the vicinity of the ITS station. The LDM is updated using information from on-board sensors and completed with information from received ITS messages such as awareness messages containing the ego-position and the speed of connected vehicles (CAM) and / or of connected Vulnerable Road Users (VAM). Received ITS messages used for updating the LDM also comprise collective perception messages (CPM) containing the perceived objects (e.g. vehicles, motorbikes, bicycles or pedestrians) from sensor-equipped ITS stations. CPM messages improve the local perception ability (larger field of view, non-connected objects etc.). As the number of perceived objects by a station may become high, the report of these objects may be organized geographically using the concept of perception regions. Through the definition of a Perception Region, Collective Perception Messages (CPM) allow describing objects detected in a given region. This typically enables an ITS agent to split a monitored area in different regions and to describe them separately in different PerceptionRegion structures, either in a single CPM or in distinct CPMs. A Perception Region is in particular characterized by its shape. In version 2.1.1 of CPM specification, shape shall be specified as a geographical area or volume with respect to the reference position (in case of a vehicle ITS-S disseminating the CPM) or a reference point (in case of a roadside ITS-S disseminating the CPM) in the East-North-Up system. However, in a different version of the specification, a different system may be chosen. The invention is not dependent on the chosen system. When an ITS station receives such a CPM message organized in perception regions, it has to determine how to take corresponding information into consideration, typically based on its own location relatively to a perception region. However, this may not always be a good way to determine whether the perception region is relevant to said ITS station or not. To illustrate this problem, let’s consider an emitting ITS station on a motorway. This station may distinguish two different perception regions, one corresponding to the lanes of vehicles going in a first direction, the other one corresponding to the lanes of vehicles going in the other direction. We assume here that a vehicle cannot cross the separation between lanes in one direction and lanes in the other direction. While a vehicle always belongs to a single region, it may consider itself as being very close to the other one, in which case it would consider both regions as relevant; yet, only the region describing the vehicles going in the same direction is relevant to said vehicle. Even worse, due to inaccuracy in positioning system, vehicle may consider itself in the wrong region, in which case it may ignore the most relevant information. SUMMARY OF THE INVENTION The present invention has been devised to address one or more of the foregoing concerns. When an emitting station distinguishes different Perception Regions, it does so for a reason. For instance, it knows that there are different flows of vehicles, each flow interacting or not with the other ones. Therefore, emitting station has the knowledge of which region may be relevant in which context. As a result, in order to solve described problem, this invention proposes to put an additional information in CPM messages to indicate in which context said region is relevant. In the present disclosure this additional information is called relevance indication. Accordingly, receiving vehicles can then determine whether a given Perception Region is relevant to them or not based on this relevance indication and the knowledge of their own parameters like position, speed and so on. As an example, relevance indication may for instance be one or more traces associated to a Perception Region. Each vehicle may then compare its own trajectory with said one or more traces to determine whether said region is relevant or not. According to a first aspect of the invention there is provided a method of communication in an Intelligent Transport System, ITS, the method comprising at a transmitting ITS station: - generating description information describing a perception region; - generating a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself; - transmitting a Collective Perception Message, CPM, comprising the description information and the relevance indication. In an embodiment, the relevance indication is comprised in the description information associated with the perception region. In an embodiment: - the relevance indication is comprised in a container dedicated to store relevance indications; and - the CPM further comprises association information for associating the relevance indication with the perception region. In an embodiment, the relevance indication is one or more traces, each trace comprising a set of ordered points representative of a trajectory of a station for which the perception region is relevant. In an embodiment, the relevance indication is one or more relevance areas, each relevance area defining a geographical area such that the perception region is relevant for stations located in this geographical area. In an embodiment: - the transmission ITS station transmits MAP messages providing static geographic road information elements; and - the relevance indication is one or more map-based elements, each mapbased element being representative of a trajectory or a location of a station for which the perception region is relevant. According to another aspect of the invention there is provided a method of communication in an Intelligent Transport System, ITS, the method comprising at a receiving ITS station: - receiving a Collective Perception Message, CPM, comprising description information describing a perception region, and a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself; - determining based on the relevance indication whether the perception region is relevant for the receiving ITS station; - interpreting the description information based on the result of the determining step. In an embodiment, the determining step comprises the determination of a relevance level for the receiving station based on the relevance indication. In an embodiment, the relevance level is a Boolean indicating whether the description information associated with the perception region is relevant, and wherein the description information is ignored when the relevance level indicates that the perception region is not relevant for the receiving ITS station. In an embodiment, the relevance level indicates a priority to be applied for interpreting the description information associated with the perception region. According to another aspect of the invention there is provided a computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to the invention, when loaded into and executed by the programmable apparatus. According to another aspect of the invention there is provided a computer-readable storage medium storing instructions of a computer program for implementing a method according to the invention. According to another aspect of the invention there is provided a computer program which upon execution causes the method of the invention to be performed. According to another aspect of the invention there is provided a transmitting station in an Intelligent Transport System, ITS, the transmitting station comprising a processor configured for: - generating description information describing a perception region; - generating a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself; - transmitting a Collective Perception Message, CPM, comprising the description information and the relevance indication. According to another aspect of the invention there is provided a receiving station in an Intelligent Transport System, ITS, the receiving station comprising a processor configured for: - receiving a Collective Perception Message, CPM, comprising description information describing a perception region, and a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself; - determining based on the relevance indication whether the perception region is relevant for the receiving ITS station; - interpreting the description information based on the result of the determining step. At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium. Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible, non-transitory carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: Figure 1 illustrates a typical Intelligent Transport System in which the invention may be implemented; Figure 2 illustrates a typical ITS station 120 in which the invention may be implemented; Figure 3 illustrates an example of a data structure of a collective perception message, CPM; Figure 4 illustrates the main steps of a process according to an embodiment of the invention; Figure 5 illustrates the main steps for processing of a CPM message generated according to embodiments of the invention by an ITS station; Figure 6 illustrates the main steps of a method of checking whether a receiving station is concerned or not with a given perception region based on an obtained relevance indication; Figure 7 is a schematic block diagram of a computing device 700 for implementation of one or more embodiments of the invention. DETAILED DESCRIPTION OF THE INVENTION Please note the following points regarding the terminology used in this document: - This document sometimes refers to “positioning systems” and “localization means”, but the two are considered to be equivalent. In some cases, we refer to “region description” in a CPM, or we mention that “a CPM message describes a given region”. What we mean is that a region is indicated (typically through a definition as a shape as this is what is currently done in CPM specification, but this could also be through a reference to a previously defined region), as well as a set of objects located in a said region. - To facilitate understanding, we distinguish a trajectory (set of ordered points successively occupied by a given object such as a vehicle) from a trace (set of ordered points that is a reference to which a trajectory may be compared to) (i.e. a trace is not defined based on the position of a given objects, but simply as a set of points that define a kind of line - or more precisely, a set of successive segments). - The words “relevance level” and “relevance value” are used, but they are considered to be synonyms. - The document refers extensively to perception regions. Sometimes the wording ‘region’ is used alone as a shortcut referring to perception regions. On the other hand, the wording ‘area’ describes a concept that is somehow similar to a region, but that may not be a perception region. Figure 1 illustrates a typical Intelligent Transport System in which the invention may be implemented. In this example illustration, a road with four lanes is considered. This road may for instance be a motorway, with two lanes for vehicles going in one direction, and two lanes for vehicles going in the opposite direction. It is assumed that there is no possibility for a vehicle to cross the central part separating the two lane directions. In the context of this figure, vehicle in the bottom lanes go from left to right (e.g. vehicles 112, 113 and 114), while vehicles in the top lanes go from right to left (e.g. vehicles 102 and 103). The area represented in Figure 1 is monitored by an ITS station 120 that comprises a road side unit, RSU, and which is associated with a set of sensors, such as for instance one or more cameras, lidars and / or radars. These sensors are used to monitor the traffic, especially to identify vehicles, pedestrians and possibly other kinds of objects, thanks to an analytic module 121. Said analytic module is used to determine a list of objects to be described in a CPM message 130 emitted by the ITS station 120. In the context of this invention, it is considered that two different regions are defined for the monitoring. In this example, the two regions are indicated as 100 (the two upper lanes) and 110 (the two lower lanes). When a CPM is generated, the fact that these two regions are defined is taken into account, and each region is described in its own container, as allowed by CPM specification (for more details about this, see Figure 3, which describes CPM message contents). Please note that the two regions are not necessarily described in each CPM message, as allowed by CPM specification. For instance, it may happen that a single region is described in a given message, while the other region is described in a following message. The way a station, like for example the RSU 120, obtains the perception regions is out of the scope of the present document. These perception regions may be determined through manual configuration or by algorithmic means. While stations generating CPM based on a geographic division of the perceived area in perception regions are typically located in the infrastructure like RSU, these mechanisms may be used by any stations provided with sensors, like vehicles 102-103, 112-114, for example. In this disclosure, upon generation of a CPM message describing a perception region and its objects, ITS station determines a relevance indication adapted to indicate in which context this region may be relevant. More precisely, the relevance indication can be used by a receiving station, especially a receiving vehicle, to determine whether the description of said perception region is relevant or not to itself. This relevance indication is then included in the CPM message and associated with the perception region. In the example of Figure 1, we consider that this relevance indication is provided as a set of points that correspond to a trace referred as 101 in region 100, and 111 in region 110. A trace is defined as a collection of points that are representative of a trajectory of an object. One or several traces may be associated with a perception region. These traces are representative of trajectories of stations that are susceptible to interact with the objects in the perception region. For example, in the case of the perception region 110 in figure 1, in a case where the motorway comprises an on-ramp road (not represented) two different types of vehicles are concerned by the perception region information. Namely a first type of vehicles comprises the vehicles moving on the same lanes which typically have a trajectory close to the trace 111. A second type of vehicles are the vehicles moving on the on-ramp road and which are joining the motorway. These vehicles have a trajectory close to a second trace, not represented, that may be associated with the same perception region. It is to be noted that these traces may comprise points located outside the perception region. When receiving such a CPM message, a vehicle can easily compare its own trajectory to the indicated trace or traces: if the two are matching, then the vehicle determines that, according to the emitting ITS station, the region associated with said trace is relevant in its current situation. As a result, it may prioritize the processing of corresponding perception region description. On the other hand, if the two are not matching, the vehicle determines that, according to the emitting ITS station, the region associated to said trace is not relevant in its current situation. As a result, it may decide not to process the corresponding perception region description. As the relevance indication allows a receiving station to identify itself as concerned by the description of the perception region, the relevance indication may also be seen as an indication of the targeted audience for the associated perception region description. Figure 2 illustrates a typical ITS station 120 in which the invention may be implemented. The analytic module 121 is connected to one or more sensors. Sensors (cameras 210, 211, lidar 212, radar for example) may be located nearby the road for a roadside ITS-S, or sensors may be embedded inside a vehicle, in which case the sensors include also GNSS, IMU (Inertial Measure Unit) to obtain an approximate position of the ITS-S. Objects detected by each sensor are analyzed by the Sensor data fusion module 230. This module can fuse objects detected by several sensors if there is enough confidence that they are the same objects (by analysis of their object type, position, speed, trajectory etc.). Newly detected objects or update about tracked objects are then used to update the environment model 240. The environment model will contain a list of objects, containing information for each tracked object such as: - A unique ID to track the object; - A time of measurement for the object; - The list of sensors that have perceived the object; - The object relative distance and speed from the ITS-S reference position with their confidence level; - The object type (e.g. vehicle, pedestrian) with its confidence level; - An associated ITS station ID with its confidence level. In the case of a moving ITS-S inside a vehicle or on a pedestrian, the sensors are also used to determine the position of the ITS-S. GNSS, IMU can be used to obtain an approximate position at a few meters accuracy in case of a classical GNSS. High precision GNSS are also available but because of their relatively high cost, few stations may have a precise absolute position (within a few dozen of centimetres). Other sensors (like cameras) may also be used to obtain relative position of the ITS-S compared to road signalization such as road marking or road signs. This information can then be used to compute precisely the relative position of a vehicle inside a road lane and to know on which road lane the vehicle is positioned. Optionally, the sensor data fusion module can receive ITS message information extracted from CAM ITS messages received by the ITS station 120 through its ITS Module 250 in charge of transmission and reception of ITS messages. As for the local sensor data fusion, if there is enough confidence that an object perceived by local sensors is corresponding to an ITS-S that has transmitted a CAM, then the corresponding ITS station ID contained in the CAM message is associated with the tracked object in the environment model. The sensor data fusion module 230 is computing a confidence level to the ITS ID association. For example, it is computed based on the accuracy of the position contained in the CAM and the one measured by the local sensors. As another example, it may be computed based on the number of perceived objects versus the number of transmitting ITS-S for a zone. Based on environment model 240, CPM messages are generated and emitted by the ITS Module 250. Such messages are typically periodically transmitted. They contain the list of perceived objects from the environment model. In the context of this disclosure, such CPM messages generally describe at least one perception region, with the corresponding perceived objects. Figure 3 illustrates an example of a data structure of a collective perception message, CPM. The illustrated CPM structure is based on ETSI TS 103 324 Specification. It comprises an ITS PDU header 305, a payload 310, and a Certificate 315. The invention is not specific to this version of CPM and may apply to different versions of CPM. In particular, the invention applies as soon as CPM may contain data associated with at least one perception region. Header 305 is a common header that includes the information of the protocol version, the message type, and the ITS-S identifier (ID) of the originating ITS-S. Payload 310 contains a management container referenced 320 and a cpmContainers component 330, which itself comprises a Wrapped CPM container 340. Wrapped CPM container 340 may contain various kinds of containers: Originating Vehicle Container 350, which is present if the CPM is emitted by a vehicle, Originating RSU Container 360, which is present if the CPM is emitted by an RSU, Sensor Information Container 370, which describes information about sensors used to generate the considered CPM, a Perception Region Container 380, which describes some perception regions, and a Perceived Object Container 390, which describes objects perceived through sensors. The perceived objects located inside a given region are listed in the Perception Region Container through their identifiers, which refer to the objects listed in the Perceived Object Container. As described with regards to Figure 4, the invention proposes to introduce new information to CPM. Figure 4 illustrates the main steps of a process according to an embodiment of the invention. At step 400, a set of objects are detected, identified and localized through a set of sensors connected to an ITS station. This is typically achieved by analytic module 121 of figure 1. At step 410, a perception region is determined. The ITS station typically has knowledge of the different regions in the area it monitors. The regions are for instance defined by an operator based on its knowledge of the traffic in monitored area. When multiple regions are defined, the generation of CPM messages according to embodiments of the invention may either comprise all perception regions, either a subset of them. As an example, the perception regions may be iterated, a distinct CPM being emitted for each perception region. Third, at step 420, an item of information corresponding to the relevance indication associated with said region is generated. The purpose of this relevance indication is to enable a receiver of corresponding CPM to determine whether it is concerned or not by the region. In the example of Figure 1, a vehicle from the upper region is typically not concerned by the description of objects in the lower region since the two regions are strictly separated, and no vehicle from a given region may move to the other region. Various means may be used to provide such relevance indication, as further described in the following. Fourth, at step 430, a CPM describing at least said perception region and comprising the generated relevance indication is broadcasted. The perception region description contains objects that are present in the perception region, as well as a definition of the perception region. In latest CPM specification, perception regions are defined as a set of points in each CPM; however, if a future version allows referring to previously defined regions, only a reference could be added instead of the perception region definition. Any relevant way of defining the geometry of the perceived region may be used in the context of this disclosure. Finally, the process ends at step 490. The relevance indication of step 420 may take various forms. Some examples are herein described. In an embodiment the relevance indication of step 420 may be a trace, similarly to the trace defined in DENM specification (ETSI EN 302 637-3 V1.2.2). Conceptually, a trace is a set of ordered points that form an itinerary. In the example of Figure 1, two traces (101 for the two upper lanes, 111 for the two lower lanes) are illustrated. One or more traces can be associated with a region in order to indicate that said region is relevant to any receiving station (typically a vehicle) with a trajectory that matches an associated trace. As described with regards to Figure 6, whether a given trajectory matches a given trace does not mean that said trajectory should be exactly identical to said trace, but rather that said trajectory should be similar to said trace, i.e. the receiving station tend to go in a similar direction as indicated trace. For instance, a trajectory that remains close to an indicated trace is considered as matching said trace. Accordingly, in an example, the matching may be controlled by the computation of a distance between the trace and the trajectory of the station associated with a threshold. When the calculated distance is below the threshold, a match is determined. To provide further granularity of information, a level of relevance may be defined for each point of the trace. For instance, a first point may be associated with a first relevance value to indicate a low relevance of a given region for a vehicle nearby said point, while further points of the trace may be associated with greater relevance values to indicate a higher relevance of said region for a vehicle nearby said further points. Alternatively, each point is not associated to a numerical relevance value, but to a relevance category such as “low”, “medium” or “high”. Trace indication may be embedded in a CPM message through a dedicated Trace Container, that may be optionally added in WrappedCpmContainer 340. Trace Container may contain one or more traces, each characterized by a list of points. For instance, in the example of Figure 1, a single trace 111 is indicated for region 110, but another trace, parallel to trace 111, could be added at the very bottom of the lower lane, to match a potential pedestrian walking on the side of the road after his / her vehicle has been damaged, or because he / she is providing some help to an injured person. In a given embodiment, the concept of trace may be slightly modified to also enable defining whether a trace should be considered only in one direction, or possibly in both directions. In the example of a pedestrian walking on the side of the road, the data associated with region 110 is indeed relevant for a pedestrian independently of his / her direction. Alternatively, two dedicated traces could be associated with the perception region, each trace comprising the same points, but with two opposite directions; this is less efficient as proposed embodiment since the list of points has to be encoded twice. An association information should also be embedded in the CPM message to indicate an association between a region and a trace. Given that regions have to be described each time they are used (i.e. regions cannot be referred to through indices / identifiers), it may be convenient to complement the description of each region by adding a list of associated traces (each trace being typically referred to through its index in the list of traces). In addition, a relevance information may be added to characterize the relevance of a given trace for considered region; the relevance may concern the whole trace, or it may be indicated for each point of the trace. For instance, a relevance value may be indicated for a first point, followed by the number of consecutive points with the same relevance. Then, another relevance value is indicated, also with an accompanying number of consecutive points with the same relevance value. If a new version of CPM is defined that allows defining regions that can be referred to through indices or identifiers, then the association of a region and a trace could be embedded in the Perception Region container or in the Trace Container (or in another dedicated container, e.g. Region To Trace Container). In another variant, no Trace Container is defined. Instead, each trace is explicitly indicated inside each perception region it is associated with. This is less efficient than referring to traces through indices / identifiers, but it avoids having to define a dedicated container. An advantage of relying on the concept of trace is that this concept is already defined in DENM messages, which is already implemented and deployed in a large number of vehicles. In another embodiment, instead of using traces, the relevance indication may define one or more areas to indicate whether the objects of a given perception region are relevant to a given station. For instance, in the example of Figure 1, some “relevance areas” 140 and 141 could be defined. In this case, a receiving station would determine the level of relevance of a given perception region based on whether said station is located in a corresponding relevance area. Typically, in the case of Figure 1, a CPM could be emitted with two relevance areas 140 and 141 associated to region 110. Therefore, any vehicle that is located in relevance area 140 or 141 would consider the objects of perception region 110 as relevant in its current situation. Vehicles receiving the CPM and which are not present in one of the relevance areas may ignore the objects described in relation with the perception region 110. In a given embodiment, and similarly to what has been described for traces, a level of relevance may be defined for each relevance area. For instance, area 140 may be associated to a given level of relevance, while area 141 may be associated to another level of relevance. While in this example, the relevance areas 140 and 141 are located inside the perception region 110, this is not mandatory. Relevance areas may be located outside the perception region. Using areas of relevance instead of traces is convenient as the definition of an area (especially a rectangle) may be simpler. Another advantage is that it is very easy for a receiving station to determine whether it is located inside such an area. However, positioning means tend to not be sufficiently accurate to enable a reliable determination of whether a receiving station is inside such an area or not. For instance, in the example of Figure 1, a vehicle that is on the 2nd lane (from the top) may believe that it is located in area 140 or 141 since both areas are very close from said lane. On the other hand, using a trace tends to be more reliable as determining whether a moving station trajectory corresponds to a trace information is less dependent on the accuracy of positioning means. In order to embed relevance area information, a dedicated Relevance Area Container may be defined. As described with regards to traces, such container would typically be contained in WrappedCPMContainer, and additional data may also be added to CPM in order to enable the association of a perception region and a relevance area (as well as a level of relevance, if any). In some contexts, a map may be known by stations located nearby the monitoring ITS station. This may typically be the case if said station emits MAP messages. These messages, defined in CEN ISO / TS 19091, provide static geographic road information that in particular define lanes and intersections. In particular, MAP messages define allowed navigational paths, e.g. whether going from one lane to another one at an intersection is allowed. As another example, it has been proposed to define a Road Configuration Container in CPM messages in order to describe the road configuration. Somehow similarly to MAP messages, such container would describe lanes. As a result, in the context of the proposed invention, and if mapping data is shared between stations, the relevance indication of step 420 may be expressed based on a map knowledge. For instance, map items such as lanes or road segments may be relied on to define areas where information from a given perception region is relevant or not. In some cases, an area may be defined as a set of lanes / road segments, or even as a set of successive lanes I road segments (e.g. to describe a kind of trajectory for a vehicle). The relevance of a given region may also be associated to a given navigational path, e.g. a given lane change at an intersection. Similarly to what has been previously described for relevance areas and traces, a specific level of relevance may be defined and a dedicated CPM container may be used to embed the definition of such areas. Figure 5 illustrates the main steps for processing of a CPM message generated according to embodiments of the invention by an ITS station. At step 500, a CPM message is received by the ITS station. It is assumed that this message comprises a description of a perception region, i.e. a list of objects (possibly empty) comprised in a given region. If CPM message does not comprise such information, then the invention does not apply. Then, at step 510, a relevance indication associated with said region and characterizing the context in which said region may be relevant to a receiving station (typically a vehicle) is obtained from the CPM message. This relevance indication may take various forms, in particular the ones proposed in relation to figure 4. At step 520, a relevance level is determined for the considered perception region (this relevance level depends on the situation of the receiving station). Generally speaking, this step consists in comparing current situation of the receiving station with the relevance indication of step 510. In the case of a trace, the recent positions of the receiving stations are compared to the trace; in the case of an area (either based on the definition of relevance area or based on map information), the current position (or possibly recent positions also) are compared to the indicated area. The determined relevance value depends on the result of the comparison. This relevance value may be used directly if Boolean to determine if the receiving ITS station is concerned by the perception region or compared to a threshold, when not Boolean, to determine if the corresponding region is relevant for the receiving ITS station. Relevance value may either be 0 or 1 if no additional relevance information is associated with the considered relevance indication, or it may be another value if specific relevance values are defined for the relevance indication (e.g. for each point of a trace). The case of trace is further described with reference to Figure 6. At step 530, the CPM message is processed based on the determined relevance level. In particular, if the determination result corresponds to a Boolean value (True / False or 1 / 0), receiving station may decide to process the corresponding region if and only if the relevance value is True (or 1). Alternatively, if the relevance level is a numerical value with more than 2 possible values, the receiving station may use this value to prioritize the processing of different perception regions (possibly obtained from different messages). As another alternative, the result of determination may be a level of priority, such as “low”, “medium” or “high”, which also allows prioritizing the processing of perception regions. Finally, at step 590, the process ends. Figure 6 illustrates the main steps of a method of checking whether a receiving station is concerned or not with a given perception region based on an obtained relevance indication (corresponding to step 520 of figure 5). In this figure, we consider that the relevance indication is a trace. First, a given trace, associated to considered perception region, is obtained at step 600. Then, the recent positions of receiving station are obtained at step 610. Then, receiving station recent positions are compared to obtained trace at step 620 to determine whether they match. Receiving station recent positions typically allow determining a recent trajectory, which can be compared to obtained trace. Given the relative accuracy of obtained positions, the goal is not to determine whether each recent position exactly corresponds to obtained trace, but rather to determine whether a vehicle follows a path similar to the one of obtained trace. For instance, in the example of Figure 1, the lower trace is located in between the two lower lanes, and any trajectory that is in one of these two lanes or in both of these two lanes would be considered as matching the obtained trace. As another example, in the case of a road with an on-ramp (respectively an off-ramp), two traces may be defined, one corresponding to the main road, and one corresponding to the on-ramp (respectively off-ramp). A vehicle trajectory may then be compared to these two traces to determine whether it matches at least one of these two traces. A possible method for determining whether a recent trajectory matches an obtained trace consists in determining whether each point of said trajectory is within a given range of at least one point of a segment created based on the points of the trace, and whether the direction of said trajectory is the same as the one of obtained trace: - Regarding the range, a range of 5 meters may be considered, which is equivalent to determining whether points of the trajectory are comprised in between the trace and two other traces parallel to the first one (one on each side), each located at 5 meters from the first one. To determine which points should be considered from the trajectory, it may be decided to keep only the points that follow the first point that falls in that area (including this first point). If there are none of them, then the trajectory does not match the trace; optionally, it may be decided that only trajectories with at least N points (e.g. N=3) in the area should be considered as matching the trace; - The similarity of directions can be evaluated by determining whether the scalar product of a vector based on two points of the trajectory and a vector based on two points of the trace is positive or not, since its sign corresponds to the sign of the cosine value of the angle between the two vectors. More particularly, a threshold may be set on the value of the cosine to ensure that the directions are sufficiently similar (e.g. cosine greater than or equal to 0.75). If the result of step 620 is that recent positions of receiving station match obtained trace, a relevance level can be determined for said receiving station at step 630. The relevance level is determined based on the obtained relevance indication of step 520. If this obtained relevance indication defines specific relevance levels for different points of the trace, the determined relevance level is the level associated with the closest point of the trace compared to latest known position for the receiving station. Alternatively, the determined relevance level may be the one of the closest next point in the trace, as the station is moving toward this point. If no specific relevance level is defined, then the determined relevance level is typically 1 (or True). On the other hand, if the result of step 620 is that trajectory does not match trace, the relevance level is set to 0, which means that the data of corresponding region is not relevant to considered receiving station. The process then ends at step 690. Figure 7 is a schematic block diagram of a computing device 700 for implementation of one or more embodiments of the invention. The computing device 700 may be a device such as a micro-computer, a workstation or a light portable device. The computing device 700 comprises a communication bus connected to: - a central processing unit 701, such as a microprocessor, denoted CPU; - a random access memory 702, denoted RAM, for storing the executable code of the method of embodiments of the invention as well as the registers adapted to record variables and parameters necessary for implementing the method according to embodiments of the invention, the memory capacity thereof can be expanded by an optional RAM connected to an expansion port for example; - a read only memory 703, denoted ROM, for storing computer programs for implementing embodiments of the invention; - a network interface 704 is typically connected to a communication network over which digital data to be processed are transmitted or received. The network interface 704 can be a single network interface, or composed of a set of different network interfaces (for instance wired and wireless interfaces, or different kinds of wired or wireless interfaces). Data packets are written to the network interface for transmission or are read from the network interface for reception under the control of the software application running in the CPU 701; - a graphical user interface 705 may be used for receiving inputs from a user or to display information to a user; - a hard disk 706 denoted HD may be provided as a mass storage device; - an I / O module 707 may be used for receiving / sending data from / to external devices such as a video source or display or any kind of sensors in the context of an ITS station. The executable code may be stored either in read only memory 703, on the hard disk 706 or on a removable digital medium such as for example a disk. According to a variant, the executable code of the programs can be received by means of a communication network, via the network interface 704, in order to be stored in one of the storage means of the communication device 700, such as the hard disk 706, before being executed. The central processing unit 701 is adapted to control and direct the execution of the instructions or portions of software code of the program or programs according to embodiments of the invention, which instructions are stored in one of the aforementioned storage means. After powering on, the CPU 701 is capable of executing instructions from main RAM memory 702 relating to a software application after those instructions have been loaded from the program ROM 703 or the hard-disc (HD) 706 for example. Such a software application, when executed by the CPU 701, causes the steps of the flowcharts of the invention to be performed. Any step of the algorithms of the invention may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC (“Personal Computer”), a DSP (“Digital Signal Processor”) or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA (“Field-Programmable Gate Array”) or an ASIC (“Application-Specific Integrated Circuit”). Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate. Each of the embodiments of the invention described above can be implemented solely or as a combination of a plurality of the embodiments. Also, features from different embodiments can be combined where necessary or where the combination of elements or features from individual embodiments in a single embodiment is beneficial. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims

1. A method of communication in an Intelligent Transport System, ITS, the method comprising at a transmitting ITS station:- generating description information describing a perception region;- generating a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself; and- transmitting a Collective Perception Message, CPM, comprising the description information and the relevance indication.

2. The method of claim 1, wherein the relevance indication is comprised in the description information associated with the perception region.

3. The method of claim 1, wherein:- the relevance indication is comprised in a container dedicated to store relevance indications; and- the CPM further comprises association information for associating the relevance indication with the perception region.

4. The method of any one claim 1 to 3, wherein the relevance indication is one or more traces, each trace comprising a set of ordered points representative of a trajectory of a station for which the perception region is relevant.

5. The method of any one claim 1 to 3, wherein the relevance indication is one or more relevance areas, each relevance area defining a geographical area such that the perception region is relevant for stations located in this geographical area.

6. The method of any one claim 1 to 3, wherein:- the transmission ITS station transmits MAP messages providing static geographic road information elements; and- the relevance indication is one or more map-based elements, each mapbased element being representative of a trajectory or a location of a station for which the perception region is relevant.

7. A method of communication in an Intelligent Transport System, ITS, the method comprising at a receiving ITS station:- receiving a Collective Perception Message, CPM, comprising description information describing a perception region, and a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself;- determining based on the relevance indication whether the perception region is relevant for the receiving ITS station; and- interpreting the description information based on the result of the determining step.

8. The method of claim 7, wherein the determining step comprises the determination of a relevance level for the receiving station based on the relevance indication.

9. The method of claim 8, wherein the relevance level is a Boolean indicating whether the description information associated with the perception region is relevant, and wherein the description information is ignored when the relevance level indicates that the perception region is not relevant for the receiving ITS station.

10. The method of claim 8, wherein the relevance level indicates a priority to be applied for interpreting the description information associated with the perception region.

11. A computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to any one of claims 1 to 10, when loaded into and executed by the programmable apparatus.

12. A computer-readable storage medium storing instructions of a computer program for implementing a method according to any one of claims 1 to 10.

13. A computer program which upon execution causes the method of any one of claims 1 to 10 to be performed.

14. A transmitting station in an Intelligent Transport System, ITS, the transmitting station comprising a processor configured for:- generating description information describing a perception region;- generating a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself; and- transmitting a Collective Perception Message, CPM, comprising the description information and the relevance indication.

15. A receiving station in an Intelligent Transport System, ITS, the receiving station comprising a processor configured for:receiving a Collective Perception Message, CPM, comprising description information describing a perception region, and a relevance indication associated with the perception region providing information allowing a receiving station to determine that the perception region is relevant for itself;- determining based on the relevance indication whether the perception region is relevant for the receiving ITS station; and- interpreting the description information based on the result of the determining step.

Images