WO1996013023A1

WO1996013023A1 - A device for the identification of vehicles at a control station

Info

Publication number: WO1996013023A1
Application number: PCT/SE1995/001253
Authority: WO
Inventors: Lars-Åke WARNSTAM; Rune Jonsson
Original assignee: Combitech Traffic Systems Ab
Priority date: 1994-10-24
Filing date: 1995-10-20
Publication date: 1996-05-02
Also published as: SE9403631L; SE9403631D0; AU3862595A; SE503707C2

Abstract

A device for the identification of vehicles in a road control station by means of image processing of at least one image recorded by a video camera. The vehicles (4, 5), that shall be identified are illuminated by means of an illumination device (12) with light in a pattern, so that a light structure is obtained on the surfaces of the vehicles (4, 5) facing the source of light. Thereby, stereo recordings can be used in the image processing for the determination of the height contour (4, 5) of the vehicles by using the ligth structure of the surfaces of the objects.

Description

TITLE:

A device for the identification of vehicles at a control station TECHNICAL FIELD:

The present invention relates to a device for the identification of a vehicle in a control station by means of image processing of some kind of image recording, preferably video recording is intended. Especially intended is the successive position identification of vehicles that pass a road toll facility or other control station.

BACKGROUND:

It is known in image recording to identify the position of an object by starting with its contour. Sometimes parts of objects are also identified within this contour as different part-contrasts, for example various illustrated height conditions with the object (see US, A, 5,253,302, Massen). In an advanced form of such identification, a video recording in stereo is used by means of which the position of the object is identified through electronic processing. Such a method is also applicable when it is desired to follow the displacement of an object over the image surface by determining its successively changeable position.

It is known to use such position identification in the tracking of vehicles in connection with different types of traffic checks, so that a vehicle can be tracked, selected from other vehicles, from a control station to a capture point.

In the capture point, vehicles are stopped which have broken against the rule, the following of which is checked in the control station, or alternatively the identity of the vehicle is registered with the aid of its number plates.

One area of particularly great interest in the present case is application in road toll facilities where a toll fee is collected in a free-flow system. The free-flow system is based on the presumption that the vehicles are provided with an equipment by which a transmitter and receiver equipment in the road toll facility can ccππtunicate with the vehicle and carry out the registration of the toll fee either by drawing means from a prepaid balance in the vehicle equipment or by registering the identity of the vehicle for post-debiting or deduction from a special account. For vehicles that are not provided with said equipment, or have an equipment that does not allow any payment manouever for example due to insufficient balance, it is understood that the vehicle driver assists in paying the fee in some other way, for example manually in a cash-desk. If however the driver attempts to pass the toll facility without paying the fee in any manner, it must be possible to perform a registration for post-debiting. There is also an interest to use the possibilities that such a surveillance system has, of collecting data for traffic statistics and research.

As is suggested in WO, 94/28516 Jonsson, Isacsson, the vehicle is tracked through recording by means of video cameras frcm the point where the payment status is checked to a point where the number plates of the vehicle are recorded through video recording. It must then be absolutely certain that the particular vehicle that has been found breaking the fee rules and also has been registered for a debiting, will be connected with the rule breaking. In said case, such tracking, that is, successive position indication, will be connected with many difficulties.

Vehicles of many different types shall be tracked, for example motor cycles, lorries and trucks with trailers. The displacement can occur at varying speed and in a free roadway within the limits that the width of the road allows and the image of each vehicle is to be kept separate frcm irrelevant image elements such as shadows, reflections and also with changes in the mutual positions of the vehicles.

In the device for tracking vehicles according to said specification, a stereo recording is used to obtain greater certainty in the classi¬ fication, in that in addition to the contour of the vehicle, the position of certain portions of the vehicle in the direction of the cameras can also be read. In practice, the video recording is performed frcm above down at the roadway and thereby the external contour of the vehicle is caught in the horizontal plane up and at the same time its various height levels. To make it possible in a stereo recording to separate different levels in the direction of the two cameras displaced sideways away from each other, a certain structuring is required of the object to be recorded. On big surfaces without shadings, as is the case with a vehicle roof or even more with a covered, big truck, the mere contour can be used to determine the position and height profile of the vehicle in the image processing. This can cause some uncertainty in the position identification, particularly during unfavourable conditions such as heavy rain or snow or with trail shadows due to sun radiation at certain angles.

DESCRIPTION OF THE INVENTION:

The problem to be solved by the invention is that in position identi¬ fication and classification of the vehicles, means must be found to structure particularly big surfaces of similar colour. As mentioned, the solution to this problem has particularly great importance in the use of stereo recordings for the tracking of vehicles in motion and above all vehicles on a road in a control station.

According to the invention, this problem is solved in that the area in which the position of the vehicle shall be indicated, is illuminated by a structured light.

In the invention, a device is provided to achieve such a light, so that a structuring of light that is clear to the apparatus can be obtained also in conditions with full sunlight and limited vision. This is done with the aid of several interacting factors: the concentration of the light spot-wise, concentration through illumination in short time intervals, so that a high concentration of light is obtained despite low average illumination, and a choice of a favourable light wavelength.

DESCRIPTION OF DRAWINGS:

In the following, an embodiment of a device for the identification of vehicles in a road toll facility is described, partly based on the arrangement described in the last-mentioned specification. The embodiment is illustrated by the accompanying drawings and their Figures showing according to the following: Fig 1. a view in persp-ective of a road toll facility with an illumination device according to the invention;

Fig. 2 a schematic picture in a vertical plane of the road toll facility with the illumination device;

Fig. 3 a front view of the illumination device;

Fig. 4 a cross-section through the illumination device cut along the line IV-IV in Fig. 3; and

Fig. 5 two images beside each other representing the recording in the image plane of two video cameras representing a recording in the camera arrangement shown in Fig. 2.

PREFERRED EMBODIMENT:

In Fig. 1 an overview of a road toll facility 1 is shown by a roadway 2 with lanes 3 in which a number of vehicles 4 are driven and thereby passing the toll facility. In order to collect toll fees without the vehicles having to slow down or stop and in order that they shall be allowed to perform lane changes while passing the toll facility, this is equipped with wireless comπunication between the road toll facility and the vehicles. For this end, there are arranged on a gantry 5 above the road a number of radio communication units 7. How a payment operation is carried out by means of radio coπmunication and how the equipment in question is arranged is not a matter for this invention and shall therefore not be described in more detail here. In for example US, A, 4,303,904, Chasek, such a system is described, however.

On the gantry 5 there are additionally arranged in both directions, video cameras 8 directed along the roadway by means of which the number plates of the vehicles can be recorded in the event a vehicle passes without performing a correct payment manouever, so that it can be searched and post-debited.

It is important, however, that the vehicles can be tracked between the position where the check occurs of whether a correct payment manouever has been carried out and the site where recording of the number plate takes place or such recording is stored, so that absolute certainty can be obtained that only those vehicles for which fees have not been paid will be searched and post-debited. The vehicles shall be successive- position-indicated along a certain travelling length, mainly the maximum travelling length required for the operation with check of payment status and as the case may be registration of payment, considering the time the operation takes in relation to occurring vehicle speeds.

For this tracking, a device 9 is arranged with video cameras 10 and 11 in a stereo arrangement. The cameras are directed downwards at the roadway and each camera can cover an area at least corresponding to said length that the vehicle must be tracked. In the arrangement the surveillance area is caught from different angles in the two cameras.

Furthermore, in connection with the camera device 9, there is an illu¬ mination device 12, which shall be described in more detail in the following.

In Fig. 2 the device is presented schematically in a vertical plane. To illustrate more clearly the principles of the invention, the positions of its different parts are altered compared with the overview in Fig. 1, the roadway and the vehicle being somewhat different than in Fig. 1.

However, the pair of video cameras 10 and 11 is illustrated. Between the cameras there is the device 12 for the structured illumination. The cameras and the illumination device are arranged in a height level above the roadway with its lanes. This arrangement is also evident from Fig. 1.

It can be presumed that an optic central axis 15 and 16 for the cameras 10 and 11 runs through the respective objectives of the cameras. Here it is understood that the cameras are adjusted so that these central axes meet on the surface of the roadway. Because the cameras are located at a distance from each other, only the images of the roadway will coincide on the respective image planes, while all contours over same will have various displaced positions relative to the central axis. This is a known condition in stereo arrangements and makes it possible by comparing the position of the image parts to get an idea of the position not only in the image plane but also along the central axis.

On the road two vehicles are shown, a higher one 18, which can be a lorry or truck, and a lower one 19, which can be a passenger car. In the figure, projection lines 20, 21 have been drawn from the contour of the up>per surface of the truck 18 to the camera objective 10. It is then evident from the figure how the positions of these lines are located relative to the central axis 15. In a similar way the projection lines 22 and 23 have been shown for the contours of the passenger car 19. For camera 11 the corresponding projection lines 25 and 26 are shown for the truck 18 and 27, and 28 for the passenger car 19.

It is clearly evident from Fig. 2 how the projection lines spread dif¬ ferently about the central axis by the two cameras. This also means that the respective contours will receive different location in the image plane of the respective cameras. This is also illustrated in Fig. 5 by showing the recordings in the image plane of the respective cameras (the image plane to the left relates to the camera 10 and the image plane to the right relates to the camera 11).

In Fig. 3 the illumination device is shown in a front view, that is, the illumination device as seen from below in Fig. 2. In Fig. 4, a cross- section of the illumination device is shown, cut along the line IV-IV in Fig. 3. In Fig. 4 the device has the same position as shown in Fig. 2 with the front turned downwards. According to Figs. 3 and 4 the illumination device consists of a house 35 with an opening 36 in the front side. In the house there is inserted an interwall parallel to the front side, which carries a number of sources of light 38 directed at the opening 36. These have here been shown as light diodes 39 with integrated reflectors, which reflect the light against the opening 36. Other sources of light can naturally be used, but it is important for the effect of the device that they can be controlled to a periodically twinkling light.

In the opening 36 a Fresnel lens 37 is inserted. As known, such a lens is used to focuse light in the same way as other lenses, but by succes¬ sively, stepwise bringing back the lens surface towards the central plane of the lens, it can be made thin with principally even thickness. The lens 37 is so adapted to its optical characteristics that the light frcm the sources of light 38 is focused to delimited light spots on the roadway or a plane somewhat above same. The focusing shall be such, that the limited light spots appear on the vehicle irrespective of how high the vehicle portions are located.

A pattern is projected in this way on the respective portions of the vehicles, and most important is that it appears on the large, upwardly turned portions of vehicles, that is the vehicle roof.

Experience shows that it is especially crucial to get a position indication for surfaces of the type roof of cargo space on trucks and trailers and also buses. In addition, in a road toll facility one is interested not only in tracking a vehicle, which can be done if its contour can be registered, but one is also interested in measuring the height of the various portions of the vehicle. Hereby, a relatively safe identi¬ fication of the vehicle class can be obtained, which usually determines the toll fee.

Through height determination it is possible to distinguish between big passenger cars and small lorries and mini-buses by different height contours. Trains of lorries, trucks and trailers are also possible to separate from a number of individual vehicles that are driven close to each other, in that their height graphs are different.

For the purpose of tracking the vehicles as well as for identifying their height graphs, the possibility of structuring the upwardly turned vehicle surfaces by means of the illumination device according to the invention is of great importance. In Figs. 2 and 5 said light spots on the vehicles are designated by 30 and on the roadway 2, by 31. From Fig. 5, which to the left shows a recording in the camera 10 and to the right a recording in the camera 11, it is evident how the spot pattern appears in such recordings. From the Figures it should be apparent that a clear separation of the vehicles from each other, as well as from the roadway is obtained through the spot pattern. As has been mentioned before, the demand must be placed that the device for the tracking and classification of the vehicles must function in all types of weather and types of sun radiation. The light radiation from the sources of light must therefore be capable of travelling through fog and falling snow, and must also give a clear light pattern in full sunshine. To achieve this, the following means are used:

1. For illumination, infrared light is used. The video cameras can be made more sensitive to this light with limited sentitivity to the shortwave sunlight, through which the relation of strength between illumination and sunlight becomes more favourable in the video recording. In addition, the advantage is gained that the infrared light does not affect the human eye and therefore does not disturb the vehicle driver.

2. The cameras work with short time of exposure, for example 0.1 millisecond, and the spot-wise illumination is pulsed at the same rate. Hereby, the effect of the sun radiation is strongly reduced, while the effect from the pulsed sources of light is used at least almost to its full extent.

3. A good focusing of the light, which gives a greater light intensity in the light spots.

Through said arrangement in itself, and particularly in combination, it becomes possible to obtain light patterns that can be captured by the video cameras also in competition with sunlight.

The described illumination device to obtain a light pattern can be varied in its embodiment. An embodiment with light diodes or other point-formed sources of light, for each light beam, is preferable. Alternatively, the light can be divided from one or two sources of light by means of a grid or an optic screen. Instead of a Fresnel lens for focusing, a required number of lenses or focusing reflectors can be used.

As an example the application of the device in a road toll facility has been described, for tracking and classification of vehicles. It can however be used for other purposes of identification in other types of control stations for vehicles. It can also be applied and adapted for use in conjunction with other arrangements than stereo arrangements; a light pattern gives a clear indication of objects also seen in a mono arrangement. Thereby, a sloping direction of the light relative to a principle plane for the vehicles and the ground can be of value.

Claims

1. A device for the identification of vehicles in a control station, c h ar a c t e r i z e d in that it comprises at least a video camera (10, 11) located and arranged to record the vehicles (18, 19) that shall be identified and the ground on which they are forwarded, a computer equipment for image processing of the images recorded by the video camera or video cameras for the identification, and an illumination device (12) arranged to direct a structured light at the area for the location of the object, focused to form a light pattern on the vehicles and the ground.

2. A device according to Claim 1, c h a r a c t e r i z e d in that the illumination device (12) is arranged to form light spots as a light pattern, the light spots being focused from a number of sources of light (39) and by means of a Fresnel lens (37).

3. A device according to Claim 2, c h a r a c t e r i z e d in that the illumination device (12) is arranged to emit infrared light, to emit the light pulsed synchronically with exposures in the video camera or cameras (10, 11) and in that in the illuminated portions (30) of the light pattern, enhanced light intensity is provided for through the focusing of the light, and in that the video camera/cameras (10, 11) is/are arranged to be highly sensitive to infrared light and little sensitive to shortwave daylight, so that in this way a light pattern identifiable for the video cameras is obtained in competition with other sources of illumination such as the sun.

4. A device according to any one of Claims 1-3, c h a r a c t e r¬ i z e d in that two video cameras (10, 11) are arranged in a stereo arrangement above the road (2) through the control station, and in that a source (12) for said structured illumination is arranged in connection with the video cameras and is directed at the road, the light pattern being focused at same or at a plane immediately thereabove.