WO2008040896A2

WO2008040896A2 - Method of locating a vehicle

Info

Publication number: WO2008040896A2
Application number: PCT/FR2007/051990
Authority: WO
Inventors: Juliette Marais; Amaury Flancquart; Sébastien AMBELLOUIS; Marion Berbineau
Original assignee: Inrets - Institut National De Recherche Sur Les Transports Et Leur Securite
Priority date: 2006-09-29
Filing date: 2007-09-21
Publication date: 2008-04-10
Also published as: WO2008040896A3; FR2906632B1; FR2906632A1

Abstract

Method of locating a vehicle (6), comprising the steps consisting in: a) determining a mask characterizing the environment of an antenna of a GPS system (2) with the aid of recording means (4) carried in said vehicle, b) determining, as a function of said mask, a set of visible satellites whose signals are able to be received directly by said antenna and c) determining a position of said vehicle (6) by using said visible satellites.

Description

METHOD FOR LOCATING A VEHICLE

The present invention relates to a method and a device for locating a vehicle.

Locating vehicles using satellite signals is gradually becoming an essential tool in transportation systems. However, known satellite positioning systems may lack accuracy, availability and / or reliability, particularly when the propagation channel is obstructed by the presence of masks, particularly in dense urban areas or on a railway network. In order to guarantee the requirements of a given application, satellite positioning systems are therefore generally supplemented by dead reckoning systems, ground beacons and / or systems broadcasting correction information. The vehicle must therefore be equipped with a complex device, using jointly with the aid of a sophisticated expensive calculator, the various sensors (GPS receiver (Global Positioning System), gyrometers, odometers, onboard mapping, etc.) but also a communication device (RDS radio receiver (Direct Satellite Broadcasting) or DAB (Digital Audio Broadcasting), GSM (Global System for Mobile Communications), etc.). Such systems already equip a number of private vehicles but represent a significant investment for the equipment of a fleet of public transport (trains, bus networks).

For the development of low-cost location and communication applications of a safety nature in the road or rail sector, it is therefore important to develop solutions that make it possible to overcome these multi-sensor systems or at least simplify them. .

A known solution consists in building a database gathering information relating to the availability of a constellation of satellites along a given trajectory, then, a posteriori, using this database to correct a position determined by a system. satellite location of the vehicle.

Such systems require knowing the route of the vehicle in advance. In addition, they may lack reliability and / or accuracy, particularly when the mask characterizing the environment of the antenna varies, for example in the case of an environment with vegetation.

The present invention aims to provide a method and a location device that avoid at least some of the aforementioned drawbacks, which allow a precise and reliable location, regardless of the route of the vehicle, and which therefore increase the safety of the vehicle. vehicle while reducing the cost of ground maintenance.

To this end, the subject of the invention is a method for locating a vehicle comprising the steps of: a) determining a mask characterizing the environment of an antenna of a GPS system using means of embedded recording in said vehicle, b) determining, according to said mask, a set of visible satellites whose signals are able to be received directly by said antenna, and c) determining a position of said vehicle using said visible satellites, characterized in that that said mask is defined by a height and a distance associated with each direction, step b) comprising the sub-steps consisting of: d) using geometric and propagation optical laws to determine a set of reflected satellites of which the signals are able to be received by said antenna through at least one reflection, and e) for each satellite of said set of reflected satellites, calculate a the signal associated with the reflection, said position being determined in step c) using, on the one hand, each visible satellite and, on the other hand, each reflected satellite taking into account the delay of the corresponding signal.

Preferably, step b) comprises the substep of comparing an elevation angle of a satellite with an elevation angle of the mask in the corresponding direction and, when the elevation angle of said satellite is greater than at the elevation angle of said mask, to consider that said satellite is visible. Preferably, step c) comprises a substep of calculating a confidence index relative to the determined position.

According to one embodiment of the invention, said vehicle is equipped with a secondary locating device capable of determining a position of the vehicle when the confidence index is below a predetermined threshold.

Preferably, the secondary locating device comprises an odometric sensor.

According to one embodiment of the invention, said recording means are video means comprising a fish-eye objective camera disposed on the roof of said vehicle so that an image made by said camera is substantially centered on said antenna .

Preferably, the data transmitted by said camera is combined with data from a distance sensor to determine said mask.

According to another embodiment of the invention, said recording means are video means comprising two cameras arranged on the roof of said vehicle. Advantageously, said mask is determined using a stereovision method applied to two successive images from a camera.

The invention also relates to a device for locating a vehicle using the location method. The invention will be better understood, and other objects, details, features and advantages thereof will become more clearly apparent in the following detailed explanatory description of several embodiments of the invention given as examples. purely illustrative and non-limiting examples, with reference to the attached schematic drawings.

In these drawings: FIG. 1 is a schematic functional view of a locating device according to a first embodiment of the invention; Figure 2 is a simplified schematic perspective view of a vehicle in which is embedded the locating device of Figure 1; Fig. 3 is a block diagram showing the steps of a first location method performed by the location device of Fig. 1; FIG. 4 is a simplified schematic view of an image made by a camera of the locating device of FIG. 1; FIG. 5 is a simplified schematic representation of satellites of a constellation of satellites capable of transmitting data to a GPS system of the locating device of FIG. 1; Fig. 6 is a block diagram showing the steps of a second location method performed by a location device according to a second embodiment of the invention; Figure 7 is a schematic functional view of a locating device according to a third embodiment of the invention; Figure 8 is a simplified schematic view of two cameras of the locating device according to the third embodiment of the invention; Fig. 9 is a block diagram showing the steps of a third location method performed by the location device of Fig. 7; and FIG. 10 is a simplified schematic view showing two images taken respectively by the two cameras of FIG. 8. FIG. 1 shows a locating device 1 embedded in a vehicle 6 (represented in FIG. T), for example a railway vehicle . The vehicle 6 is also equipped with a secondary locating device (not shown), comprising for example an odometric sensor, which is intended to allow the determination of a position of the vehicle 6 when the locating device 1 does not allow not a sufficiently reliable and / or precise location of the vehicle 6, as will be described in detail below.

The device 1 comprises a GPS system 2 and video recording means 3. The GPS system 2 comprises, in a conventional manner, an antenna, disposed on the roof of the vehicle 6, and processing means able to determine a position of the vehicle 6, said potentially erroneous position, from satellite signals received by the antenna.

The video recording means 3 comprise, for example, a fish-eye objective camera 4, disposed on the roof of the vehicle 6, close to the antenna of the GPS receiver 2, so that an image supplied by the camera 4 is substantially centered on the antenna.

The device 1 comprises processing means 5, comprising a module 21 for determining a mask, a module 22 for determining the state of a satellite and a module 23 for locating the vehicle 6. The processing means 5 are for determining a position of the vehicle 6, said corrected position, from data provided by the GPS system 2 and data provided by the video recording means 3.

In order to determine a potentially erroneous position of the vehicle 6, the GPS system 2 measures the propagation times of a set of signals coming from the satellites of a satellite constellation and deduces therefrom pseudo-distance values between each of the satellites considered and the system 2. Today, the accuracy of the location information of a conventional GPS system is of the order of 10 m. The main causes of inaccuracy result from a poor estimation of the pseudo-distance (delays related to the propagation of signals in the atmosphere, synchronization errors of the clocks, bad geometry of the available satellites, etc.). A number of mathematical models or equipment can reduce these errors. However, the antenna environment of the GPS system 2

(Buildings, trees, bridges, etc.) form a radio mask and may also limit the accuracy and availability of the location. Radio masks can not be corrected a priori because there is no generalizable modeling for all environments. These masks can cause errors, especially by multipath propagation. Figure 2 shows three satellites S ₁ , S ₂ and S ₃ of a satellite constellation. The vehicle 6 circulates in a valley 7 having two slopes 9. In the remainder of the description, three possible states for a satellite S are considered, these states depending on the reception by the system 2 of signals from the satellite S.

The most favorable case for the reception of a satellite signal is the line-of-sight reception because in this case the signal does not undergo the attenuations and the delays due to the multiple paths. A satellite is called in a visible state, or visible satellite, a satellite whose signals are able to be received directly by the system 2. In FIG. 2, the satellite S ₁ is visible.

When a satellite S is masked, that is to say when the signals from the satellite can not be received directly by the system 2, the signals coming from the satellite S are either not received or received by multipath, that is to say after one or more reflection (s). A satellite is called in a blocked state, or a blocked satellite, a satellite whose signals are not able to be received by the receiver 2. A satellite is called in a reflected state, or reflected satellite, a satellite whose signals are capable of being received through multiple trips. In FIG. 2, the satellite S ₂ is reflected, since a signal emitted by the satellite S ₂ is able to be reflected on a slope 9 in the direction of the antenna, and the satellite S ₃ is blocked.

Referring to Figure 3, will now be described the steps of a first locating method performed by the device 1 according to the first embodiment.

In step 200, the camera 4 realizes an image 12 (FIG. 4) representing a 360 ° view of the obstacles arranged around the antenna of the GPS system 2. The camera 4 transmits to the module 21, via a line of communication 17, data relating to the image 12. It will be noted that the expression communication line does not imply that the connection between the camera 4 and the processing means 5 is wired, this connection can also be wireless.

The camera 4 provides for example 25 frames / second. However, the synchronization of the image recording with the odometric sensor makes it possible to record the images according to the distance traveled. For example, an image 12 is recorded every meters. The use of spatial rather than temporal sampling has the particular advantage of avoiding the storage of unnecessary data, for example when the vehicle is stationary or is traveling slowly. The first method of localization is for example carried out each time an image is made.

Simultaneously, the GPS system 2 receives data from satellites S of the satellite constellation, processes the received data, and transmits to the module 22, for each satellite for which data has been received, position data of the satellite, via a communication line 14, GPS time data, via a communication line 15, and pseudo-distance data, via a line 16. It will be noted that these data are potentially erroneous, particularly in the case of the presence of paths multiple. The GPS system 2 also transmits to the module 23, via a communication line 33, the GPS time data.

In step 201, the module 21 determines a mask characterizing the environment of the antenna for the current position of the vehicle 6 from the data transmitted by the camera 4. It will be noted that an advantage of the camera 4 with fish objective -eye is that it allows a direct reading of an elevation angle E1 of the mask around the antenna in each direction az passing through the antenna. An elevation angle E1 (t ₀ , az) in a given az direction is the angle between a horizontal plane and a plane passing through the apex of the highest obstacle in the given az direction, t ₀ being the moment at which the image was made. In FIG. 4, the mask corresponds to the dark part 13. The module 21 sends the data El (t _o , az) to the module 22 via a communication line 24.

In step 202, the module 22 determines the elevation and azimuth angles of the satellites of the satellite constellation, for example using data transmitted by the GPS system 2 at step 200 or ephemeris that is, satellite position and speed data that allows satellite positions to be calculated at any time. FIG. 5 represents the position of satellites Si at S ₅ with respect to the antenna of the GPS system 2 as a function of their elevation angle and their azimuth angle. The module 22 compares the elevation angle of a satellite, for example the satellite S l, and the elevation angle E1 of the mask in the corresponding az direction, that is to say with the angle d corresponding azimuth. In this embodiment, the module 22 only considers the satellites visible in the optical sense of the term from the antenna of the GPS system 2, that is to say the satellites that are above the mask. This approach is therefore binary, a satellite S can be in two states, visible or masked. In other words, the elevation angle of the satellite constitutes the classification criterion, a satellite being considered masked as soon as its elevation angle is less than the elevation angle of the mask in the corresponding direction.

The module 22 stores the state of the satellite S ₁ , visible or masked, and transmits to the module 23, via a communication line 26, the state of the satellite S ₁ and a position of the satellite S ₁ .

Step 202 is repeated for each satellite S ₂ to S ₅ of the satellite constellation.

In step 203, the module 23 determines, using the positions of the visible satellites, a corrected position of the vehicle 6. The module 23 also determines a confidence index relative to the determined corrected position, the confidence index being in particular dependent the number of satellites S used to determine the position, here the visible satellites. The corrected position and the confidence index are respectively issued by communication lines 34 and 35 to, for example, a control device (not shown). The confidence index may be used to determine whether or not the secondary locating device is to be used to determine a vehicle position, for example by comparing the value of the confidence index with a predetermined threshold. The first location method is particularly effective in an environment with few reflections, for example a mountain range. Indeed, the mountains do not have substantially vertical facades strongly generating reflections.

This method therefore allows a more precise location and a good characterization of the confidence that can be given to the location, given the environment. It should be noted that an odometer, intended to measure a distance traveled by a vehicle, is reliable over short distances but has a drift for larger distances. It is therefore well suited to be used as a secondary location system whose operation is controlled when the location obtained with the location device 1 is not sufficiently accurate and / or reliable.

Alternatively, to complete the device 1, beacons can be arranged in tunnels or other places causing poor reception of satellite signals. With reference to FIG. 6, a second location method executed by a device 1 according to a second embodiment will now be described. The device 1 according to the second embodiment comprises, in addition to the elements described in the first embodiment, a distance sensor 30, for example an optical sensor of the LIDAR (Llght Detection And Ranging) type, represented in broken lines on the It will be noted that the device 1 according to the second embodiment could be used to execute the first method of localization.

In step 300, the camera 4 realizes an image 12 and transmits it to the module 21. The GPS device 2 transmits to the module 22 the position data, the GPS time data, and the pseudo-distance data. The GPS system 2 also transmits the GPS time data to the module 23.

Simultaneously, the distance sensor 30 makes a measurement of the distance of the obstacles relative to the antenna in each direction. The sensor 30 transmits the distance data to the module 21 via a communication line 31.

In step 301, the module 21 determines a mask characterizing the environment of the antenna for the current position of the vehicle 6 from the data transmitted by the camera 4 and by the distance sensor 30. Here, the mask is defined by an elevation angle El (t ₀ , az) and a distance d (t ₀ , az) associated with each direction az. The module 21 determines for each direction az a height h (t ₀ , az) of the mask. The module 21 sends to the module 22 elevation data El (t _o , az), via a communication line 24, data of height h (t _o , az), via a communication line 25, and distance data d (t ₀ , az), via a communication line 32. In step 302, the module 22 determines the elevation and azimuth angles of the satellites Si at S ₅ .

The module 22 compares the elevation of a satellite and the elevation of the mask in the corresponding direction. In this embodiment, the module 22 considers laws of geometrical optics and propagation to differentiate, among the masked satellites, the blocked satellites and the reflected satellites.

The module 22 transmits to the module 23, via the communication line 26, the state of the satellite, the position of the satellite and, in the case of a reflected satellite, the delay of the signal associated with the reflection.

Step 302 is repeated for each satellite in the satellite constellation.

Step 303 is similar to step 103. Here, the module 23 also uses the positions of the reflected satellites and corrects the error due to reflection using the delay calculated in step 302. Thus, trust is a function of the number of visible satellites and the number of satellites reflected.

A third embodiment of the locating device, shown in FIG. 7, will now be described. The elements of the locating device identical to the first embodiment are designated by the same reference numeral increased by 100 and are not described again. .

Here, the recording means 103 comprise, in place of the camera 4, two cameras 140 and 141 arranged back to back on the roof of the vehicle, as shown in FIG. 8, around the antenna of the system GPS 102. The cameras 140, 141 are, for example, black and white analog matrix cameras equipped with a CCD sensor (charge transfer sensor).

With reference to FIG. 9, a third location method executed by the device 101 according to the third embodiment will now be described.

At step 400, the camera 140 sends an image 112 _A, to (Figure 10). Simultaneously, the camera 141 produces an image 112 _B , each camera 140, 141 provides for example 25 frames / second. However, the synchronization of the image recording with the odometric sensor makes it possible to record the images according to the distance traveled. For example, an image 112 _A, to, 112β, is recorded to all meters. Two images 112 _A , to and 112 _A , successive ti realized by the camera

140 and two successive images 112 _B , to, and 112 _B , ti taken by the camera

141 are transmitted to module 121.

Simultaneously, the GPS device 2 transmits to the module 122 the position data, the GPS time data, and the pseudo-distance data. The GPS system 102 also transmits the GPS time data to the module 123.

In step 401, the module 121 determines a mask characterizing the environment of the antenna. The mask comprises a first sub-mask determined from the two images 112 _{A) t0} and 1 12 _{A; t1} transmitted by the camera 140. The mask comprises a second sub-mask determined from the two images 1 12 _B , to and 112 _B , ti transmitted by the camera 141.

The first sub-mask is determined by considering the two successive images 112 _{A) t0} and 112 _{A; t1} as two images coming from two parallel cameras whose distance is a function of the displacement of the vehicle between the two images, here Im. A single-camera stereovision method is applied to the images 112A _{; t0} and _{112A: t1} , which makes it possible to calculate the distance d of each of the obstacles seen in the image 112A _{) t0 as} well as their height h. The second sub-mask is determined similarly by considering the two successive images 112 _{B) t0} and

The combination of the two sub-masks then makes it possible, by making the assumption that the obstacles are located along the trajectory, parallel to the direction of the vehicle, to reconstitute the environment in 3 dimensions and to consider each of the obstacles forming the mask 360 ° around the antenna.

The mask is characterized by an elevation angle El (t ₀ , az) and a distance d (t ₀ , az) associated with each direction az. The module 121 transmits to the module 122 elevation data El (t _o , az), via a communication line 124, data of height h (t _o , az), via a communication line 125, and data of distance d (t ₀ , az), via a communication line 132.

Steps 402 and 403 are similar to steps 302 and 303 described above. Due to the geometrical hypotheses applied, the results obtained with the device 101 are particularly interesting when the obstacles can be modeled by vertical planes and especially as their edges are marked. This method is particularly well suited to urban location, especially when obstacles are buildings.

In the three embodiments described above, the position of the vehicle is determined in real time, which makes it possible to obtain a more reliable and more precise location. The locating devices 1 and 101 are in particular intended to be used for safety applications, for example the command control of the trains or the optimization of the tilting of the trains. For this type of application, the expected location accuracies vary from 50 m to 1 m, for a service availability greater than 99% of time and space. In general, the devices 1, 101 are suitable for any application requiring a precise and reliable location.

It will be noted that the devices 1, 101 are not limited to railway applications. For example, devices 1, 101 may be used for vehicle guidance, which requires being able to position the vehicle on a lane and therefore requires an accuracy of about 5 m.

Although the invention has been described in connection with several particular embodiments, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims

A method of locating a vehicle (6) comprising the steps of: a) determining a mask characterizing the environment of an antenna of a GPS system (2, 102) by means of recording means (4, 140, 141) embedded in said vehicle, b) determine, according to said mask, a set of visible satellites whose signals are able to be received directly by said antenna, and c) determine a position of said vehicle using said visible satellites, characterized in that said mask is defined by a height (h (tθ, az)) and by a distance (d (tθ, az)) associated with each direction (az), step b) comprising the sub steps of: d) using geometric and propagation optics laws to determine a set of reflected satellites whose signals are receivable by said antenna through at least one reflection, and e) for each satellite of said set of satellites reflected his, calculate a delay of the signal associated with reflection, said position being determined in step c) using, on the one hand, each visible satellite and, on the other hand, each satellite reflected taking into account the delay of the signal corresponding.

2. Method according to claim 1, characterized in that step b) comprises the substep of comparing an elevation angle of a satellite with an elevation angle (El) of the mask in the direction (az ) and, when the elevation angle of said satellite is greater than the elevation angle of said mask to consider that said satellite is visible.

3. Method according to claim 1 or 2, characterized in that step c) comprises a substep of calculating a confidence index relative to the determined position.

4. Method according to claim 3, characterized in that said vehicle (6) is equipped with a secondary location device able to determine a position of the vehicle when the confidence index is below a predetermined threshold.

5. Method according to claim 4, characterized in that the secondary location device comprises an odometric sensor.

6. Method according to any one of claims 1 to 5, characterized in that said recording means are video means (4) comprising a fish-eye lens camera, disposed on the roof of said vehicle so that a image made by said camera is substantially centered on said antenna.

7. The method of claim 6, characterized in that the data transmitted by said camera (4) is combined with data from a distance sensor to determine said mask.

8. Method according to any one of claims 1 to 5, characterized in that said recording means are video means comprising two cameras (140, 141) disposed on the roof of said vehicle.

9. The method of claim 8, characterized in that said mask is determined using a stereovision method applied to two successive images from a camera (140, 141).

10. Device for locating a vehicle using the locating method according to one of claims 1 to 9.