Communications: electrical – Vehicle detectors – Density
Reexamination Certificate
1999-10-12
2001-01-23
Wu, Daniel J. (Department: 2736)
Communications: electrical
Vehicle detectors
Density
C340S910000, C340S933000, C701S118000
Reexamination Certificate
active
06177886
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and a system involving registration plates of vehicles, and to a method of transmitting data.
BACKGROUND OF THE INVENTION
WO90/05969 discloses a traffic congestion monitoring system comprising infra-red monitoring units bolted to the sides of bridges over a motorway network and emitting information as to traffic congestion at their locations, a control centre which receives and transmits the information, and paging units in respective vehicles and receiving the information and visually displaying the same upon diagrams of the network or zones thereof.
The infra-red monitoring units in effect look at one location underneath a bridge or gantry to measure the average speed. Of course this works well on motorways and dual carriageway standard trunk roads where there is a continual flow of traffic. However, unless these units are put very close together (300-500 meters), they are an inaccurate way of measuring average speed or journey time on roads where there are traffic flow interruptions caused by traffic lights, roundabouts and other obstacles.
Vehicle licence-plate reading systems are known but these have been designed for law enforcement purposes, tolling and entry control for car parks, for example. These systems require a very high degree of accuracy as clearly if a licence-plate is misread it may not allow access through a barrier, or if used for enforcement cannot be legally enforceable. Because of this general requirement for a very high degree of accuracy, hardware platforms for reading licence-plates are very expensive and the data content and thus cost that would be required to communicate these licence-plates over a radio link would be very high because of the detail involved.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a method of monitoring traffic flow, comprising reading registration plates of the vehicles of a first series of vehicles passing a first location along a road, selecting a sample of readings from the readings relating to the respective vehicles of the series, reading the registration plates of the vehicles of a second series of vehicles passing a second location along said road, and determining whether readings of said sample are deemed to be present in the readings relating to the respective vehicles of said second series.
According to a second aspect of the present invention, there is provided a system for monitoring traffic flow, comprising first reading means serving to read registration plates of the vehicles of a first series of vehicles passing a first location along a road, second reading means serving to read registration plates of the vehicles of a second series of vehicles passing a second location along said road, and selecting and determining means serving to select a sample of readings from the readings relating to the respective vehicles of said first series and serving to determine whether readings of said sample are deemed to be present in the readings relating to the respective vehicles of said second series.
According to a third aspect of the present invention, there is provided a method of reading a registration plate of a vehicle, in which characters between the leading character and the trailing character of the registration plate are reported, but the leading character and/or the trailing character is/are not reported.
According to a fourth aspect of the present invention, there is provided a method of reading a registration plate of a vehicle, in which characters, of the plate having a statistical distribution more even than at least another character of the plate are reported and the or each said other character is not reported.
According to a fifth aspect of the present invention, there is provided a method of reading a registration plate of a vehicle, comprising reading a character of said plate, and reporting said character as being one of a restricted group of characters.
According to a sixth aspect of the present invention, there is provided a method of transmitting data comprising transmitting a progressively changing value as a sequence of signals by which differences of magnitude, but not actual magnitudes, are communicated.
Owing to these aspects of the invention, it is possible to reduce the amount of data to be handled and consequently the complexity of the hardware and software is reduced and thus the cost of handling the same is reduced.
It is preferred to employ a character recognition system, for example a per se known system supplied by Racal, to read the whole of the registration plate. There is, however, an alternative way of doing this, and that is to interpret the characters—the letters and numerals—on the registration plate not as a collection of individual characters that actually have to be interpreted and identified as such but simply as a pattern which merely has to be stored and then compared with other patterns of the same type subsequently acquired by the system. Thus, according to an alternative aspect of the invention, there is provided a vehicle registration plate reading method in which all or some of the characters of the registration plate are scanned to derive a pattern image thereof, and this pattern is used as such in subsequent comparison and vehicle identification stages of the method.
Advantageously, the registration plate is irradiated with radiation which is invisible to the human naked eye and the radiation reflected from the plate is utilised in performing the reading.
It is thus possible to read-vehicle plates during both daylight and darkness and without distracting drivers of the vehicles.
The invisible radiation employed is preferably infra-red (IR), particularly laser IR, since an IR laser can produce a higher intensity of irradiation than conventional IR sources.
In a preferred embodiment of the invention, a small sample of vehicles is used as probes or targets passing two or more fixed points along the road to measure the average journey time. A series of vehicles is identified and recorded by means of a closed circuit television (CCTV) camera and computer at a fixed point and then, after converting this data into a format that can be transmitted by means of a radio link, the vehicles are identified again at a second fixed point and the two sightings matched up. The average time for a sample of vehicles to travel between the two fixed points is compared with the expected or usual average journey time for that stretch of road. The comparison of journey time(s) is particularly appropriate for roads where there may not be a constant flow of traffic, but rather interruptions by traffic lights or roundabouts for example.
The identification of the vehicles in the sample is by matching two registration plates between the first and second fixed points but need not be a definitive reading of the whole registration plate and matching this with official data records.
The preferred system includes a low-cost hardware platform using infra-red CCTV cameras and laser infra-red illumination which are cheap to install. It reads the registration plate and uses some of the characters thereof to create a vehicle tag, which might be as little as two bytes, which is later transmitted over a radio link either to an adjacent reading location or to a remote control centre. Tags from a second reading location are compared with the transmitted tag. The software which carries out this function can operate on a low cost personal computer (PC) processor and can reliably match two or more sightings of the same vehicle.
In the preferred embodiment, the selecting of the samples at the respective reading locations is performed on a road network according to an algorithm common to all of the locations. The use of an algorithm increases the possibility of a match because of the use of intelligent selection of the sample rather than random selection. The algorithm comprises the step of excluding readings below a confidence factor threshold. Characters between the leading character and the trailing char
Barnes Christopher Michael
Billington Peter Eric
Wakefield Jonathan Paul
Hall William D.
Pham Toan
Trafficmaster PLC
Wu Daniel J.
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