GB2479794A

GB2479794A - Telemetry apparatus for recoding the paths taken by vehicles on a road or rail network

Info

Publication number: GB2479794A
Application number: GB201006866A
Authority: GB
Inventors: David K Linsdall
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2010-04-23
Filing date: 2010-04-23
Publication date: 2011-10-26
Anticipated expiration: 2030-04-23
Also published as: GB2479794B; GB201006866D0

Abstract

A mobile telemetry apparatus is provided for use in a vehicle travelling on a road or rail network. The apparatus comprises a processor, and a data storage unit containing a map database. The apparatus is configured to store in a long term storage unit, or to transmit to an external back-office system, output data representative of the most likely path travelled by the vehicle on a map of the network represented in the map database. The processor is programmed to respond to an input identifying the known position of the vehicle at two fixed locations on the map at different known times to determine all possible paths on the map between those fixed locations taking account of the known times. From the possible paths the processor determines the most likely path to have been taken. The apparatus is particularly suited to identify the path taken by a vehicle whilst operating at a lower position sampling frequency such that it may avoid the higher costs associated with frequently sending position data to an external system.

Description

MOBILE TELEMETRY APPARATUS

This invention relates to mobile telemetry apparatus for use in a vehicle, to a method of mobile telemetry, and to telemetry apparatus for recording the paths taken by vehicles, particularly on a road or rail network. It may use GNSS, Global Navigation Satellite System, or other positioning systems, and it is particularly useful for road vehicle user charging.

Map matching systems used for vehicle tracking, such as road user charging or precise location determination in rail systems, must discover the actual path taken through the road or rail network between reported position points. Thus the system must have a means of finding all the possible paths between two known points so as to determine the most likely.

Map matching systems use algorithms to identify the most likely geo-object (road or rail segment) and then link these together to describe the path taken by the vehicle. In many instances the path taken between these identified segments is obvious as the position points are sufficiently close together to sample the same segment multiple times. Such an approach works well when the map matching is performed on board the same platform as the positioning sensor. However, these systems suffer from the problem of maintaining an accurate map database on every vehicle. Thin client systems split the map matcher, and database, from the sensor by sending the measured positions back to a central processing system i.e. a back-office system via a radio data link. The costs of sending data over this link are directly related to the position sample interval, so it is beneficial to sample the position infrequently and use a more sophisticated path discovery algorithm to find the path taken.

There are numerous existing methods of determining the path through a network but these can be computationally intensive for complex networks with infrequent position samples.

Accordingly, the purpose of the present invention is to identify the most likely path taken by a vehicle from positions identified less frequently, and in a way which avoids intensive computation for complex networks.

Accordingly, the present invention is mobile telemetry apparatus for use in a vehicle travelling on a road or rail network, comprising a processor and a data storage unit containing a map database, the apparatus configured to store in a long term storage unit or to transmit to an external back-office system output data representative of the most likely path travelled by the vehicle on a map of the network represented in the map database, the processor being programmed to respond to an input identifying the known position of the vehicle at two fixed locations on the map at different known times to determine all possible paths on the map between those fixed locations taking account of the known times, and from those possible paths to determine the most likely path to have been taken.

The invention also provides telemetry apparatus for recording the paths taken by vehicles travelling on a road or rail network, comprising a processor and a data storage unit containing a map database, the apparatus configured to store data representative of the most likely path travelled by each vehicle on a map of the network represented in the map database, the processor being programmed to respond to an input identifying the known position of the vehicle at two fixed locations on the map at different known times, to determine all possible paths on the map between those fixed locations taking account of the known times, and from those possible paths to determine the most likely path to have been taken by that vehicle.

Further, the invention provides a method of mobile vehicle telemetry comprising receiving data identifying the known position of the vehicle at two fixed locations at different times on a map of a road or rail network, and using the received data and a map database containing the map to determine all possible paths on the map between those fixed locations taking account of the known times, and from those possible paths to determine the most likely path to have been taken.

The invention overcomes the limitations of the previous telemetry systems by discovering paths using the additional knowledge of the geographical layout of the network, so as to minimise the search options and hence improve the performance of the search. Preferred embodiments of the invention allow for dynamic connectivity in the network, such as time dependent road turnings or railway points, and this is achieved by the use of data for portions of the map database which specify connectivity dependent upon the current time.

In order that the invention may be better understood, a preferred embodiment will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: Fig. I is a block diagram of a preferred embodiment of the invention; and Fig. 2 represents a portion of a map database for use in the preferred embodiment.

A preferred embodiment of the invention is shown in Fig. 1, which is an on-board mobile telemetry apparatus for a vehicle travelling on a road or rail network. This apparatus communicates with a back-office system through for example a GPRS or WiFi communications channel. The network is represented by a map database, at least a portion of which is stored in the data storage unit of the on-board device shown in Fig. 1. The map database could be stored in the back-office system, and portions of it downloaded from time to time into the data storage unit of the mobile device.

Preferably, the database comprises representations of nodes and of segments linking those nodes, as is conventional. The mobile device has a processing unit which receives position data from a GNSS receiver. In this example, there is also a communications transceiver linking the processing unit with the back-office system, and a communications transceiver linking the processing unit with external road side equipment, for example to identify that the vehicle is passing between predetermined zones on the map. The processing unit accesses the data storage unit. A power supply is provided for all the components of the mobile telemetry device.

The processing unit is also connected to receive signals from an odometer in the vehicle, indicative of the distance travelled. Alternatively, the distance signal could be derived as a double integral of acceleration data measured by an on-board inertial measurement system. Alternatively, the distance signal could be derived from the integral of the differences in the position data measured by an on-board GNSS or other positioning receiver.

In this embodiment, it is the processing unit of the mobile telemetry device that determines the most likely path that has been taken by the vehicle between two known locations. However, in alternative configurations of the overall system, the computation may be shared with a processor in the back-office system, so that the mobile telemetry device would be a thin client. It is also feasible for the known position data to be sent to the back-office system and for the back-office system to compute the most likely path for that vehicle using the map database, in which case there woUld be no need for any portion of the map to be stored on board.

The most likely path that has been taken by the vehicle between two known locations at different times will now be described.

The inputs to the processing unit are a pair of basic segment matches (Selected and Target) comprising the unique identity of the segment plus the distance of the position along that segment. This is illustrated in the portion of the map of the network shown in Fig. 2. The algorithm executed in the processing unit finds a path through the road or rail network between the two segments that best matches an estimate of the actual distance travelled by the vehicle. This figure for actual distance is derived from the distance signal described above. The discovered path with a length closest to the distance travelled is selected.

The algorithm works as follows: 1. If the selected segment is the same as the target segment there is no need to search for a path.

2. If the selected and target segments are different, assume that the path connects to the entry node of the selected segment according to the direction of travel and iterate through all the connections to that node to find a path.

3. If a path cannot be found then, if the selected segment allows bi-directional travel, try looking from the opposite end and iterate through all the connections to find a path.

4. Return the discovered path if found within the limits.

The iterate function may be implemented as a pair of nested logical loops which test all possible paths through the "tree" of connections.

At each node, where a segment joins other segments, the possible connections are determined, including any time dependent connectivity, from an estimate of the time at which the vehicle passed that point, and each connection is tested, by following all its connections, node by node, and so on until either the target segment is reached or the test limits are exceeded.

The test limits are designed to limit the search down any particular path as soon as it is evident that the path cannot reach the target. This significantly limits the number of iterations of the algorithm, especially when the segments are separated by a large number of nodes. Two tests are applied: a maximum node count and a maximum path length check.

The node count is supplied as a configuration parameter to the algorithm and is selected according to the characteristics of the vehicle sensor (e.g. maximum distance between reported fixes) and the granularity of the map database.

A maximum distance is calculated as the upper bound for the search allowing for underestimated distance travelled due to GPS errors and no actual vehicle odometer.

The algorithm that has been used effectively in real data trials is as follows: maxLengthLimit = 10.0 + (DistanceTravelled + EstimatedfixError) x Multiplier; Where Multiplier 1.5 if the change in heading is less than 45 degrees or a non-GNSS distance signal is available, otherwise Multiplier = 2.0.

The algorithm checks the maximum path length, as each new node is tested, against the accumulated path length to that node plus the remaining direct distance from that node to the target fix position. Thus the test down a path will be terminated as soon as it is no longer possible to find a path within the maximum length limit. This test effectively constrains the search to a region approximately elliptical in shape with the test and target fixes at the foci, and so significantly limits the number of potential tests in a complex road network.

It is quite likely that a road network allows loops, since roads often connect to each other via several routes. These loops in the connection tree could lead to unnecessary tests following repeated segments so the algorithm checks if a segment has been seen earlier in the path and discards that particular "limb" of the tree.

The target segment is likely to be reached by several possible valid paths and so returns the path that best matches the target length parameter supplied.

Time dependent connectivity of nodes or segments is represented in the map database by data representing time intervals and linked to the nodes or segments. For example, a bridge or level crossing may break the network at time intervals that are recorded and are sent as updates of the database. As another example, a road may always be closed at predetermined times of the day.

In one embodiment of the invention the algorithm may be implemented as methods in a Java class that can be used from within a Java application or web service. The algorithm may process significant quantities of data from different measurement plafforms and allows a very large number of vehicles to be processed in real time on a single server platform.

Claims

CLAIMS: 1. Mobile telemetry apparatus for use in a vehicle travelling on a road or rail network, comprising a processor and a data storage unit containing a map database, the apparatus configured to store in a long term storage unit or to transmit to an external back-office system output data representative of the most likely path travelled by the vehicle on a map of the network represented in the map database, the processor being programmed to respond to an input identifying the known position of the vehicle at two fixed locations on the map at different known times to determine all possible paths on the map between those fixed locations taking account of the known times, and from those possible paths to determine the most likely path to have been taken.
2. Apparatus according to claim 1, in which the processor is programmed to determine the distance travelled by the vehicle between the fixed locations and to use that to determine the most likely path.
3. Apparatus according to claim 2, in which the processor is programmed to determine the distance between the fixed locations to be the direct linear separation between them on the map.
4. Apparatus according to claim 2, in which the processor is programmed to determine the distance between the fixed locations using an output from an odometer in the vehicle or an output from an inertial measurement system in the vehicle.
5. Apparatus according to any preceding claim, in which the processor is programmed to determine the fixed locations as points on segments between nodes of the network, the input being representative of the length along the segment and of the unique identity of the segment.
6. Apparatus according to any preceding claim, in which the map is subject to predetermined variations over time and the map database comprises data for at least portions of the map as a function of time, and the processor is programmed to take into account the time that the vehicle would have passed the respective portions of the map when determining the possible paths.
7. Telemetry apparatus for recording the paths taken by vehicles travelling on a road or rail network, comprising a processor and a data storage unit containing a map database, the apparatus configured to store data representative of the most likely path travelled by each vehicle on a map of the network represented in the map database, the processor being programmed to respond to an input identifying the known position of the vehicle at two fixed locations on the map at different known times, to determine all possible paths on the map between those fixed locations taking account of the known times, and from those possible paths to determine the most likely path to have been taken by that vehicle.
8. Apparatus according to claim 7, further comprising for each vehicle mobile telemetry apparatus according to any of claims I to 6, wherein the map database of each mobile telemetry apparatus is arranged to store at least a portion of the complete map database for the network.
9. A method of mobile vehicle telemetry comprising receiving data identifying the known position of the vehicle at two fixed locations at different times on a map of a road or rail network, and using the received data and a map database containing the map to determine all possible paths on the map between those fixed locations taking account of the known times, and from those possible paths to determine the most likely path to have been taken.
10. Mobile telemetry apparatus substantially as described hereinwith reference to the accompanying drawings.
11. Telemetry apparatus for recording the paths taken by vehicles, substantially as described herein with reference to the accompanying drawings.