FR2825500A1 - Method for guiding a vehicle, comprises on board unit and fixed server and a number of data exchange strategies which are selected according to factors such as server load and communication coverage - Google Patents

Abstract

The vehicle on-board equipment (1) includes a terminal (17), control unit (5), modules for communication (9), e.g. GSM or UMTS, and localization (11), vehicle equipment interface (19) and audio unit (21). The fixed server (25) has formatting and route servers (35,29), customer and route databases (33,27) and traffic data (32). Data interchange between vehicle and server is varied dynamically to suit varying vehicle speed, trajectory, server load and coverage of terrain Independent claims are also included for the following: onboard equipment used by the method including the means to dynamically select data exchange procedures; and a vehicle that uses the guidance method.

Description

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 The present invention relates to a method of guiding a vehicle, to a device for implementing this method, and to a vehicle using this device.

 Document WO 99 09374 discloses a method for guiding a vehicle of the type in which, in response to a request for guidance made by a user, a) an on-board unit is transmitted to at least one fixed server in particular position data of said vehicle, b) this position data is transferred to a map extracted from at least one cartographic database connected to said fixed server and c), from said report, it is transmitted from said fixed server to said on-board unit route data for providing guidance service to said user.

 This method of the prior art makes it possible to deport outside the vehicle, in particular the entire vehicle positioning system on the basis of cartographic data.

 This method also makes it possible to centralize the offer of guidance service for a plurality of vehicles, and thus in particular to simultaneously communicate information to these vehicles, to make these vehicles benefit instantly from the latest updates of the cartographic databases, etc. .

 The disadvantage of this method is that it provides a relatively poor level of service.

 Thus, according to a first example, when the on-board unit is in a gray area, that is to say in an area where the exchange of data with the fixed server is impossible for lack of sufficient wireless coverage, the user can no longer be guided.

 In a second example, when the fixed server is saturated due to too many requests from vehicles, the user can no longer be guided.

 According to a third example, when a traffic jam suddenly forms on the route which has been advised to the user, the method according to the prior art may not be sufficiently reactive to quickly propose an avoidance route.

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 The main object of the present invention is to improve the level of service provided to the user.

 This object of the invention is achieved with a method of guiding a vehicle of the type in which, in response to a guiding request made by a user, a) a unit is transmitted from an on-board unit to at least one fixed server in particular position data of said vehicle, b) this position data is transferred to a map extracted from at least one cartographic database connected to said fixed server and c), from said report, it is transmitted from said fixed server to said on-board unit route data with a view to providing a guidance service to said user, remarkable in that it predefines a plurality of strategies for exchanging data between said on-board unit and said fixed server and in that it is selected dynamically that of said strategies which makes it possible to provide the best possible level of guidance service to said user taking into account the constraints linked to the operating context of said uni embedded tee and said fixed server.

 Thanks to these characteristics, the data exchange strategy between the on-board unit and the fixed server is no longer fixed: there is always a choice between several strategies, and one can choose at any time the one that allows '' optimize user guidance taking into account the communications and environmental conditions in which the on-board unit and the fixed server are located.

 According to other characteristics of the method according to the invention: - said context is determined in particular from parameters characterizing the quality of communications between said on-board unit and said fixed server, - said communication parameters are chosen from the group of parameters characterizing: - the load of said fixed server, - the coverage of the route of said vehicle by a non-wired telecommunications network, and - the bandwidth of said on-board communication unit,

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 - said context is determined in particular from parameters characterizing the environment in which said vehicle circulates, - a first exchange strategy is predefined in which said data is exchanged regardless of the position of said vehicle, - said data is exchanged at time intervals regular, - a second exchange strategy is predefined in which said data is exchanged as a function of the position of said vehicle, - new route data is transmitted to said on-board unit when said vehicle leaves a predefined part of the area of validity of the last route data received, - a new route data set is transmitted to said on-board unit when said vehicle arrives in the last validity area of the last route data set received, - it is also transmitted to said on-board unit additional route data useful in the event of so rtie of said vehicle on its route, - a third exchange strategy is predefined in which said route data is sent to said on-board unit in the form of a roadmap, - an update of the data of route transmitted to said on-board unit as and when said vehicle moves, - the route is calculated in said fixed server, so as to reduce the volume of route data transmitted to said on-board unit, - it is transmitted said route data to said on-board unit in the form of guidance information directly usable by said on-board unit, - said route data is transmitted to said on-board unit in the form of guide pages in a format chosen from the group including WAP, HTML, c-HTML, and XML,

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 - said route data are transmitted to said on-board unit following a request formulated by said on-board unit, this request notably containing the position of said vehicle, - said request is formulated from a script sent to said on-board unit at the same time as said route data, - to use said script, a language chosen from the group comprising JavaScript, VBScript, Perl / CGI and WMLScript, - to use said data exchanges , a communication protocol chosen from the group comprising GSM, GPRS / GSM Phase II and UMTS, - said data exchanges are made secure.

 The present invention also relates to a device for implementing the above-mentioned method, comprising a) an on-board unit on board said vehicle, b) on-board means for indicating the position of said vehicle interfaced with said on-board unit, c) at at least one fixed server having access to at least one cartographic database, d) means for exchanging data between said on-board unit and said fixed server, e) means for generating route data from the reporting of said position on a map extracted from said cartographic database, and f) means for transmitting this route data to said on-board unit, remarkable in that it further comprises means for predefining a plurality of data exchange strategies between said on-board unit and said fixed server and to select dynamically the one of said strategies which makes it possible to provide the best their level of service of guidance possible to said user taking into account the constraints linked to the operating context of said on-board unit and of said fixed server.

 According to other characteristics of this device: - said on-board position indication means comprise a GPS receiver, - this device comprises a gyrometer interfaced with said on-board unit,

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 - said on-board unit comprises means for interfacing with equipment of said vehicle, - said fixed server also has access to a database of information on traffic, - said means for exchanging data are adapted to operate with a cell phone network.

 The present invention also relates to a motor vehicle, remarkable in that it uses a device in accordance with the above.

 Other characteristics and advantages of the present invention will appear on reading the description which follows and on examining the appended drawing, in which: FIG. 1 is a schematic overview of the device according to the invention, - Figure 2 shows a guide page as it can appear on the terminal of the on-board unit of the device according to the invention, - Figures 3 and 4 show a first strategy for data exchange between the on-board unit and the fixed server of the device according to the invention, - Figures 5 and 6 are similar to Figures 3 and 4 respectively, for a first variant of a second data exchange strategy, - Figures 7 and 8 are similar respectively in Figures 3 and 4, for a second variant of the second data exchange strategy, - Figures 9 and 10 are similar to Figures 3 and 4 respectively, for a third variant of the second data exchange strategy data exchange, and - Figure 11 is similar to Figure 4, a third strategy for data exchange.

 In these figures, identical references designate identical or analogous entities or sets of entities.

 Referring now to FIG. 1, in which it can be seen that the device according to the invention firstly comprises a unit 1 intended to be taken on board a motor vehicle 3.

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 This on-board unit 1 comprises a control unit 5 as well as at least one communication module 9 and a location module 11 connected respectively to a modem 13 and to a GPS and / or to a gyrometer 15.

 It is recalled here that the acronym GPS designates a three-dimensional positioning system (Global Positioning System). It goes without saying that any other similar positioning system could be suitable.

 It is also recalled that a gyrometer is a device making it possible to know at all times the position of the steered wheels of a vehicle, and thereby to estimate the position of a vehicle.

 The control unit 5 is also connected to a terminal 17 which may include a screen for displaying guidance information and a control actuator.

 Optionally, the on-board unit 1 can further comprise a vehicle equipment interface 19 and an audio unit 21 connected respectively to the CAN buses 22 of the vehicle 3 and to a set of speaker / microphone 23.

 The device according to the invention also comprises a stationary server 25, that is to say, disembarked from vehicle 3.

 This fixed server 25 includes at least one cartographic database 27, a route server 29 and a communication front end 31.

 Optionally, this fixed server 25 can also include a traffic information server 32, a client database 33 and a formatting server 35.

 The on-board unit 1 and the fixed server 25 are capable of exchanging data with each other via the modem 13, the communication front end 31 and a non-wired telecommunications network symbolized by the dashed line 37.

 This network can for example be a mobile telephone network using one of the following communication protocols: GPRS / GSM phase II or UMTS.

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 As an option, it is possible to secure data exchanges between the on-board unit 1 and the fixed server 25.

 The on-board unit 1 preferably has a real-time operating system supporting four software programs: a browser making it possible to display the guidance information transmitted on the terminal 17, to execute scripts linked to this information, and to offer a certain number of useful menus for the user when handling the terminal; a vehicle location program 3, responsible for communicating with the positioning means: GPS and / or gyrometer 15; a program for managing communications between the on-board unit 1 and the fixed server 25, responsible for ensuring a good interface and the transfer of data between this unit and this server; an interface program between the on-board unit 1 and the vehicle 3, responsible for listening to the CAN buses present and for recovering the data useful for guidance as well as the data useful for the comfort of use of the terminal 17 by the driver; these data include the vehicle speed, the state of the high beams, etc.

 We will now describe the operating mode of the device according to the invention.

 The user begins by formulating a request for guidance on the terminal 17 (and / or using the microphone of the assembly 23), which request can typically consist of a place name to be reached, such as a street name, and a route selection criterion: shortest, fastest route, without a highway, etc.

 This guidance request is then transmitted to the control unit 5 which then transmits a guidance request to the communication module 9, then to the modem 13 and to the communication front end 31 via the network 37.

 Using then on the one hand the data coming from the GPS and / or the gyrometer 15, which are also transmitted by the network 37, and on the other hand the cartographic database 27, the fixed server 25 can precisely position the vehicle 3 on a road map.

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 Optionally, the route server 29 can request the traffic information server 27, so as to take into account the traffic condition of the lanes for guidance.

 The route server 29 can also extract data from the customer database 33 for the purpose of identifying the user, his habits, etc.

 From all of this data, the route server 29 then calculates a route.

 Once this route is calculated, it is transmitted back in the form of route data to the user via the network 37, the control unit 5, the terminal 17 and / or the loudspeaker of the assembly. 23.

 Preferably, before being transmitted to the on-board unit 1, the route data is formatted by the formatting server 35 into guidance information usable by the on-board unit 1 without any additional transformation.

comprenant le WAP, l'HTML, le c-HTML, et le XML. Particularly preferably, this guide information consists of guide pages in a format chosen from the group

including WAP, HTML, c-HTML, and XML.

 FIG. 2 shows a typical example of a guide page 39 as it appears on the terminal 17 after formatting by the formatting page server 35 and transmission by the network 37 to the control unit 5.

 As shown in this figure, the guide page 39 can typically include the destination to be reached 41, the name of the axis 43 on which the vehicle 3 is traveling, the direction to follow 45, the distance and the duration 47 separating vehicle 3 from the destination to be reached, and information 49 relating to the intersections encountered.

 In a preferred embodiment, the route data transmitted by the fixed server 25 to the on-board unit 1 also includes scripts, that is to say lists of instructions that the control unit 5 will be loaded applying.

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 These scripts can in particular make it possible to decide under what conditions a new guidance request must be sent to the fixed server 25, in order to satisfy the guidance request made by the user.

 These scripts can also make it possible to manage the data exchange strategies between the on-board unit 1 and the fixed server 25 (see below).

 To train the scripts, one could for example use a language chosen from the group comprising JavaScript, VBScript, Perl / CGI and WMLScript.

 Thus, to satisfy the request for guidance formulated by the user, a succession of requests / responses is established between the on-board unit 1 and the fixed server 25, thanks to which the user will be guided step by step until 'at the desired destination.

 Thanks to the fact that an already calculated route is sent to the on-board unit 1, it is possible to considerably reduce the volume of route data transmitted to the on-board unit 1, and thus to substantially reduce the response times to guidance requests. formulated by the user.

 It will also be noted that the fact of sending to the on-board unit 1 an already calculated route makes it possible to dispense with any specific application in this on-board unit: this unit can therefore be simplified to the extreme, which makes it possible to significantly lower its manufacturing cost.

 The absence of a specific application makes it possible to envisage using the on-board unit 1 in a versatile manner, that is to say with a plurality of servers providing services which have nothing to do with each other: guidance, information, weather ...

 This versatility opens up many perspectives, given the growing offer of tele-services for motorists.

 In the case where, before transmitting the calculated route to the on-board unit 1, it is formatted into guidance information directly usable by this on-board unit, the aforementioned advantages are increased.

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 We will now describe different possible data exchange strategies between the on-board unit 1 and the fixed server 25.

 These strategies will be described in the particular case where the guidance information is transmitted to the on-board unit 1 in the form of guide pages with which scripts are associated, but it goes without saying that these strategies could also apply in the case where this information is transmitted in any other way, and in particular as taught in application WO 99 09374.

 Reference is now made to FIGS. 3 and 4, on which a first data exchange strategy between the on-board unit 1 and the fixed server 25 has been materialized.

 In FIG. 3, the line 51 represents the route actually taken by the vehicle 3, the squares 53 of the guide pages transmitted to the on-board unit 1 throughout this route, and the circles 55 the respective validity zones of the information provided by guide pages 53.

 According to this first strategy (see FIG. 4), a script is attached to each page 53 transmitted ordering the on-board unit 1 to transmit the position 57 of the vehicle 3 to the fixed server 25 after a predetermined duration, independently of the position of the vehicle.

 The fixed server 25 then locates at 59 the position of the vehicle on a road map, then generates a guide page at 61 which it then transmits at 63 to the on-board unit 1 for the display of this page at 65 on terminal 17.

 In this first strategy, the guide pages 53 are transmitted to the on-board unit 1 at regular time intervals, at the risk of being redundant if the vehicle is stopped or moving slowly.

 This is illustrated by FIG. 3 where it can be seen that the zones 53 overlap, that is to say that a new guide page has been transmitted before the vehicle 3 has even left the zone of validity of the previous guide page.

 This first strategy, in which the exchanges between the on-board unit 1 and the fixed server 25 are independent of the position of the

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 vehicle 3, has the advantage of offering the user great responsiveness to road exits, changes in traffic conditions, etc.

 However, this first strategy has the drawback of maximizing the number of exchanges between the on-board unit 1 and the fixed server 25.

 Thus, this strategy is not suitable when the exchanges between the on-board unit 1 and the fixed server 25 are difficult or impossible, for example when the fixed server 25 is saturated due to a large number of calls from other vehicles, or when the on-board unit 1 operates in a gray area, that is to say in an area not covered by the network 37 (see FIG. 1).

 Reference is now made to FIGS. 5 to 10, in which three variants of a second data exchange strategy between the on-board unit 1 and the fixed server 25 have been materialized.

 In a first variant of this second strategy (see FIG. 6), a script is attached to each page 53 transmitted to determine the position of the vehicle at 67 and not to order at 57 on-board unit 1 to transmit the position of the vehicle 3 to the fixed server 25 only when this vehicle exits at 68 from part 69 (see FIG. 5) located inside the area of validity of the information provided by the guide page 53 in progress.

 Each part 69 is delimited in FIG. 5 by a concentric circle with the corresponding circle 55, and the point where the vehicle 3 leaves this part bears the reference 71.

 Once the position of the vehicle 3 has been transmitted to the on-board unit 25, the operations take place as in the case of the first strategy (see FIG. 6).

 This first variant makes it possible to reduce the number of exchanges between the on-board unit 1 and the fixed server 25 compared to the first strategy, while guaranteeing the accuracy of the information provided by each guide page.

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 Reference is now made to FIGS. 7 and 8, in which the second variant of the second data exchange strategy between the on-board unit 1 and the fixed server 25 has been materialized.

 In this second variant (see FIG. 8), a script is sent to each guide page 53 transmitted to update certain information on this page at 73.

 This information can for example be icons indicating the direction to take at a crossroads, or the distance separating vehicle 3 from the destination to be reached.

 The updating of this information can be carried out according to techniques known to those skilled in the art, for example by using the browser cache of the on-board unit 1.

 Due to this update, the size of each part 69 (see FIG. 7) may be larger than in the previous case.

 This second variant is more complex as regards the algorithms making it possible to generate the scripts placed on the side of the fixed server 25, and heavier as regards the data transmitted because it requires an increase in the size of the scripts.

 However, this second variant makes it possible to reduce the number of exchanges between the on-board unit 1 and the fixed server 25.

 Reference is now made to FIGS. 9 and 10, on which the third variant of the second data exchange strategy between the on-board unit 1 and the fixed server 25 has been materialized.

 In this third variant (see FIG. 10), 74 sets of guide pages are sent to the on-board unit 1.

 The scripts contained in the page sets will then allow the navigator to display at 75 guide pages corresponding to the actual position of the vehicle 3.

 There are two types of page sets: those which follow the route 51 proposed by the fixed server 25, and those which are useful in the event of departure from the route by the vehicle 3.

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 These last sets of pages contain a script for transmitting the position of the vehicle at 79 in order to download a new set of pages which corresponds to the current situation.

 The same principle is used when the vehicle turns around or when the last page of the transmitted game is displayed.

 There is shown in FIG. 9, at 81, the area of validity of the first page 82 of a game 83, at 84 the area of validity of the last page 85 of this game, and at 86 the areas of validity of the pages Intermediaries 87 of this game.

 In 88, route departure zones have been shown for which the fixed server 25 will be asked for a new set of guide pages.

 This third variant significantly increases the data transmitted and reduces the positioning accuracy of the vehicle 3 insofar as between two transmissions of this position to the fixed server 25, this position is not directly compared with a cartographic database.

 On the other hand, this third variant makes it possible to significantly reduce the number of exchanges between the on-board unit 1 and the fixed server 25, given that after having received the set of guide pages and as long as the vehicle 3 is located in an area covered by this game, the on-board unit 1 manages this game completely independently.

 As can be understood in the light of the above, the three variants of the second strategy have the common feature that the data exchanges between the on-board unit 1 and the fixed server 25 depend on the position of the vehicle 3.

 Reference is now made to FIG. 11, on which a third data exchange strategy between the on-board unit 1 and the fixed server 25 has been materialized.

 In this third strategy, we are content to transmit a simple roadmap 90 to the on-board unit 1.

 This roadmap consists of a series of instructions to follow to reach the desired destination, these instructions being frozen, that is to say

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 that they are not updated regularly unlike previous strategies.

 There is no relationship between the current position of the motor vehicle and the information displayed by the on-board terminal 17: in the event of departure from the vehicle, the roadmap will only be modified after an exchange between the unit on-board 1 and the fixed server 25, if this is possible.

 This third strategy is a minimal solution for the guidance service when the quality of communications between the on-board unit 1 and the guidance service 25 is too limited: in this case the useful bit rate is too low to be able to transmit guide pages in time real.

 The choice between the strategies which have just been presented is made within the fixed server 25 and / or the on-board unit 1 as a function of the operating context of this server and of this on-board unit.

 By operating context is meant here in particular a series of parameters characterizing the quality of the communications between the on-board unit 1 and the fixed server 25, and a series of parameters characterizing the environment in which the vehicle 3 travels.

 For example, the communication parameters can characterize the bandwidth of the on-board terminal 1 in communication and / or the load of the fixed server 25 for the calculation of the guide pages and / or the degree of coverage by the network 37 of the vehicle location 3.

 By way of example, the environmental parameters can characterize the traffic conditions and / or the weather conditions on the route of the vehicle 3.

 So for example, if it turns out that traffic conditions suddenly deteriorate on a route previously calculated by the fixed server 25, we can imagine that the on-board unit 1 issues a priority request making it possible to move from the third strategy to the second or the first, as far as the communication conditions allow, so as to provide the user with up-to-date information in a very reactive manner.

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 The general principle which governs the choice of strategies consists in continuously providing the best possible level of guidance service to the user, taking into account the constraints, in particular of communications and environment, encountered by the guidance device.

 By best possible level of service, it is meant here that the guidance device constantly endeavors to determine which of the data exchange strategies which can provide the most useful information for guidance, that is to say d '' information enabling the user to be taken to the desired destination while respecting his route selection criteria (shortest, fastest route, without motorway, etc.).

 As we can now understand, the dynamic choice, that is to say in real time between the aforementioned strategies, allows the guidance service to be very flexible in operation and, ultimately, to considerably improve the level of service rendered compared to the prior art.

 Of course, the present invention is not limited to the embodiment described and shown, provided by way of illustrative and nonlimiting example.

 For example, we could consider other data exchange strategies than those which have been described, and / or we could consider combining some of these strategies.

Claims (27)

1. A method of guiding a vehicle (3) of the type in which, in response to a request for guidance made by a user, a) it is transmitted from an on-board unit (1) to at least one fixed server (25) in particular position data of said vehicle (3), b) said position data is transferred to a map extracted from at least one cartographic database (27) connected to said fixed server (25) and c), from said reporting , it transmits from said fixed server (25) to said on-board unit (1) route data with a view to providing a guidance service to said user, characterized in that a plurality of data exchange strategies are predefined between said on-board unit (1) and said fixed server (25) and in that one dynamically selects that of said strategies which makes it possible to provide the best possible level of guidance service to said user taking into account the constraints linked to the operating context of the adite on-board unit (1) and said fixed server (25).  2. Method according to claim 1, characterized in that said context is determined in particular from parameters characterizing the quality of communications between said on-board unit (1) and said fixed server (25).  3. Method according to claim 2, characterized in that said communication parameters are chosen from the group of parameters characterizing: - the load of said fixed server (25), - the coverage of the route (51) of said vehicle (3 ) by a non-wired telecommunications network (37), and - the bandwidth of said on-board unit (1) in communication.  4. Method according to any one of the preceding claims, characterized in that said context is determined in particular on the basis of parameters characterizing the environment in which said vehicle (3) travels.  5. Method according to any one of the preceding claims, characterized in that a first exchange strategy is predefined in which said data is exchanged regardless of the position of said vehicle (3). <Desc / Clms Page number 17>  6. Method according to claim 5, characterized in that said data are exchanged at regular time intervals.  7. Method according to any one of the preceding claims, characterized in that a second exchange strategy is predefined in which said data is exchanged as a function of the position of said vehicle (3).  8. Method according to claim 7, characterized in that new route data is transmitted to said on-board unit when said vehicle (3) leaves a predefined part (69) of the validity area (55) of the last route data received.  9. Method according to one of claims 7 or 8, in which route data sets are transmitted to said on-board unit (1), characterized in that a new set of information is transmitted to said on-board unit (1). route data when said vehicle (3) arrives in the last validity zone (84) of the last set of route data received.  10. Method according to claim 9, characterized in that further transmits to said on-board unit (1) additional route data useful in the event of said vehicle (3) leaving its route (51).  11. Method according to any one of the preceding claims, characterized in that a third exchange strategy is predefined in which said route data are sent to said on-board unit (1) in the form of a roadmap. .  12. Method according to any one of the preceding claims, characterized in that the route data transmitted to said on-board unit (1) is updated as and when said vehicle (3) is moving.  13. Method according to any one of the preceding claims, characterized in that the route calculation is carried out in said fixed server (25), so as to reduce the volume of route data transmitted to said on-board unit (1 ). <Desc / Clms Page number 18>  14. Method according to any one of the preceding claims, characterized in that said route data is transmitted to said on-board unit (1) in the form of guidance information directly usable by said on-board unit (1).  15. The method of claim 14, characterized in that said route data is transmitted to said on-board unit (1) in the form of guide pages (39) in a format chosen from the group.

 including WAP, HTML, c-HTML, and XML.  16. Method according to any one of the preceding claims, characterized in that said route data is transmitted to said on-board unit (1) following a request made by said on-board unit (1), this request containing in particular the position of said vehicle (3).  17. The method of claim 16, characterized in that said request is formulated from a script sent to said on-board unit (1) at the same time as said route data.  18. The method of claim 17, characterized in that one uses, to form said script, a language chosen from the group comprising JavaScript, VBScript, Perl / CGI and WMLScript.  19. Method according to any one of the preceding claims, characterized in that a communication protocol chosen from the group comprising GSM, GPRS / GSM Phase II and UMTS is used to carry out said data exchanges.  20. Method according to any one of the preceding claims, characterized in that the said data exchanges are made secure.  21. Device for implementing a method according to any one of the preceding claims, comprising a) an on-board unit (1) on board said vehicle (3), b) on-board means (15) for indicating the position of said vehicle (3) interfaced with said on-board unit (1), c) at least one fixed server (25) having access to at least one cartographic database (27), d) means (13,31, 37 ) to exchange data between said on-board unit (1) and said fixed server (25), e) means for generating route data from the report <Desc / Clms Page number 19>  from said position on a map extracted from said cartographic database (27), and f) means for transmitting this route data to said on-board unit (1), characterized in that it further comprises means (29 ) to predefine a plurality of data exchange strategies between said on-board unit (1) and said fixed server (25) and to dynamically select which of said strategies which makes it possible to provide the best possible level of guidance service to said user account given the constraints linked to the operating context of said on-board unit (1) and said fixed server (25).  22. Device according to claim 21, characterized in that said on-board means (15) for indicating position comprise a GPS receiver.  23. Device according to one of claims 21 or 22, characterized in that it comprises a gyrometer (15) interfaced with said on-board unit (1).  24. Device according to any one of claims 21 to 23, characterized in that said on-board unit (1) comprises interface means (19) with equipment (22) of said vehicle (3).  25. Device according to any one of claims 21 to 24, characterized in that said fixed server (25) also has access to a database (32) of traffic information.  26. Device according to any one of claims 21 to 25, characterized in that said data exchange means are adapted to operate with a cellular telephone network (37).  27. Motor vehicle (3), characterized in that it uses a device according to any one of claims 21 to 26.