WO2007122408A1

WO2007122408A1 - Radar system and method

Info

Publication number: WO2007122408A1
Application number: PCT/GB2007/001486
Authority: WO
Inventors: Ian Michael Treherne
Original assignee: Pi Research Limited
Priority date: 2006-04-25
Filing date: 2007-04-24
Publication date: 2007-11-01
Also published as: GB0608165D0; EP2016442A1

Abstract

A system for tracking players on a playing area uses one or more radar units, each positioned so as to transmit a substantially horizontally-scanned beam covering a scanned area of at least a portion of the playing area. Echoes of the beam(s) from players in the scanned area are received and processed by a processing unit coupled to the radar unit(s) in order to track the players.

Description

Radar System And Method

The invention relates to a radar system and method, in particular for tracking players of a game on a playing area.

Team coaches in professional sports, such as premiership soccer, want to know where all of the players were throughout every match to assist in strategic analysis and to tailor individual fitness-training plans for each player. Media customers, such as television companies, are also interested in similar graphical and statistical information.

Current systems for obtaining this information rely on human classification of video images. Such existing systems may use a fixed camera recording video images of the playing area, and employ human operators manually to track the position of each player on a video screen. This information is entered by the human operators into a computer, together with information concerning the position of the fixed video camera. Each position on the video screen corresponds approximately to a position on the playing area but the tracking information generated suffers from a number of sources of inaccuracies. For example, human operators may not accurately track the positions of players on the video screen. Also, the video screen is a two-dimensional projection of the playing area and the perspective of the image inevitably causes variations in track accuracy depending on whether a player is close to the camera or far away. In addition, human operators cannot produce the player tracks in real time. These problems are compounded when it is required to track a large number of players on a playing area, such as all twenty two players in a soccer match. Current practice is to address this problem by employing large numbers of human operators to track individual players on separate video screens, so as to try to produce information for all players with an acceptably short delay, but this process is labour intensive and does not address the inaccuracy of the system.

Summary of the Invention

The invention provides a system for tracking players of a game on a playing area, a radar unit, a processing unit and a method as defined in the appended independent claims, to which reference should now be made. Preferred or advantageous features of the invention are set out in dependent subclaims.

In a preferred embodiment, the invention thus provides a system comprising one or more radar units, each positioned so as to transmit a substantially horizontally-scanned beam covering a scanned area of at least a portion of the playing area, and for receiving echoes of the beam from players in the scanned area. The one or more radar units are coupled to a processing unit for tracking the positions of the players. The system is advantageously capable of tracking multiple players, and may therefore preferably track all of the players on the playing area at the same time. Advantageously, the system may also track the position of match officials, such as the referee and any assistant referees, or touch judges. This may involve the scanned area or areas extending slightly beyond the edges of the playing area itself, so as to monitor areas just outside the touchlines. References in this document to the playing area should be interpreted as including, where appropriate, these adjacent areas.

Embodiments of the invention may thus address the problems in the prior art discussed above, by automatically tracking a number of players on a playing area in real time. Since the radar echoes can provide both range and bearing information, relative to the fixed position of the corresponding radar unit, the system may advantageously be able to output accurate tracks for each player over substantially the entire playing area.

Although the invention may find particular application in relation to sports such as soccer, as mentioned above, it may in principle be applied to substantially any game or sports activity, and preferably any game played on a predetermined playing area. This may include, for example, games such as soccer or American football or ice hockey played by multiple players on a predetermined pitch or other area, and athletics events such as track and field events played by individual or multiple players on a predetermined track or playing area. It may also include games involving animals or vehicles, such as greyhound or other animal racing, bicycle, motorcycle, windsurfer, or car racing, which are commonly played on a predetermined track or other predetermined area. The playing area may be housed within a stadium or arena or other closed area, or may be outdoor or in some other form of sports ground. The skilled person would readily be able to extend these lists of examples and alternatives appropriately within the spirit of the invention, and the terms player and playing area used herein should be construed accordingly.

Preferably, the radar unit or units are millimetre-wavelength radar unit(s). Suitable operating frequencies may be 77GHz or 94GHz or, in general, any frequency between about 60GHz and 110GHz. These wavelengths produce suitable resolution for detecting and tracking movement of the players and are substantially unaffected by atmospheric conditions such as rain, snow or fog. This provides a significant advantage over the video-based prior art systems, which cannot operate in adverse weather conditions.

Preferably, a radar unit should be positioned so as to transmit a substantially horizontally-scanned beam because this maximises the resolution of the system across the playing area, which is typically horizontal, and reduces the effect of perspective, as in the case of using a video image recorded by a camera positioned to one side of a playing area as the basis for tracking players.

In a preferred embodiment, the scanned area for each radar unit should correspond to a portion of the playing area distant from, or spaced from, the position of the radar unit. Thus, for example, in the case of a soccer pitch, one or more radar units at or near each end of the pitch should scan the opposite half of the pitch.

In a preferred embodiment, the scanned areas of two or more radar units may overlap, the radar units preferably being spaced from each other so that the scanning directions of the radar units (for example when tracking the same player) are at a significant angle to each other. The angle between the scanning directions may be, for example, between 15° and 165°, preferably between 30° and 150°, and particularly preferably between 45° and 135°. For maximum resolution, the scanning directions of two radar units may be separated by about 90°. Since these radar units scan the same scanned area, they can track the same players and the processing unit can combine the player positions derived from each radar unit in order to improve the accuracy of tracking. By its nature, a rotary-scanning radar unit tends to have better range resolution than bearing resolution. Thus, combining the outputs from two radar units scanning in different directions may significantly enhance tracking accuracy, as well as reducing the frequency of occlusions as described further below.

Advantageously, the or each radar unit is elevated above the height of the players on the playing area to reduce the risk of one player occluding another, when viewed by a radar unit. If a radar unit is positioned to scan a more distant portion of a playing area, spaced from the position of the radar unit, it may be advantageous to increase the height of the radar unit further above the playing area to, for example, two to five times the height of a player. Thus, for example, a radar unit may advantageously be positioned between 2 and 4 metres, and preferably about 3 metres, above the playing area if it is to scan a playing area such as a soccer pitch.

The vertical spread of a millimetre-wavelength radar beam is typically between 1° and 2°, or may be up to 3° or 4°. When a radar beam is used to scan a playing area, the angle of incidence between the beam direction and the surface of the playing area may preferably be small enough to reduce or minimise reflection of the beam from the playing area; this may improve the relative strength of the signals reflected from the players. In general, therefore, the height of the or each radar unit should preferably be set taking into account the requirements for the radar unit to be high enough to reduce occlusion of the players by other players, low enough to reduce reflections from the playing area, and such that the unit can scan the whole of the desired portion of the playing area bearing in mind the available vertical spread of the radar beam. The height of the radar unit may also be affected by the distance from the unit to the scanned area; the further away the unit is positioned the higher it is likely to be positioned in order to meet the requirements described above, such as to reduce occlusions. In general, it may be desirable to position a radar unit as close to the scanned area as possible in order to increase the strength of radar reflections from players, but in a stadium, for example, it may be necessary to site a radar unit further away from the playing area to avoid obstructing the audience's view.

In a particularly-preferred embodiment, four radar units are positioned for tracking players on a rectangular playing area such as a soccer pitch. The radar units are positioned near, or behind, each corner of the pitch and have scanning areas corresponding to the opposite half of the pitch. Each radar unit may be elevated to a height of between 2 and 4 metres above the pitch, and preferably about 3 metres above the pitch. The radar units positioned near the comers at one end of the pitch both scan the opposite end of the pitch and are spaced by a sufficient angle that their outputs can be combined to improve the resolution of the tracks of the players in the opposite half of the pitch. .

Advantageously, each radar unit may only scan through a horizontal angle corresponding to the desired scanned area. Alternative, it may scan through a larger angle, up to 360°, and the system may disregard signals (echoes) received from areas outside the scanned area.

The radar beam may be scanned in any convenient manner, including mechanical or electronic scanning.

The processing unit is advantageously coupled to the or each radar unit by fibre-optic cabling and can derive a range and a bearing for each player in each corresponding scanned area. Signals from each radar unit may advantageously be processed by comparing successive scans and subtracting substantially-static features, for example in the manner of an adaptive background subtraction scheme. This approach may suffer disadvantages, however, in that players who remain stationary for a period of time may not be tracked continuously. In that case, adaptive background subtraction may not be used.

The processing unit may advantageously incorporate a track-combiner application, for example comprising a Kalman filter, in order to combine the track information generated by each radar unit. As noted above, this may be particularly advantageous if radar units scanning the same scan area are positioned at a significant angle to each other.

The processing unit may also advantageously comprise a tracking filter containing a kinematic model of a player for comparison with tracks derived from the radar units in order to assist in identifying genuine tracks or to improve tracking accuracy.

In a further preferred embodiment, the system may advantageously track objects other than the players and match officials, such as the ball in a soccer game. This may involve modifying the radar units so that at least one or more of the units can vary its scanning direction, such as using a pan-and-tilt control. In addition, the processing unit may comprise a tracking filter containing a kinematic model of the ball, incorporating factors such as gravity, air resistance, cross winds, spin etc.

Under certain playing conditions, the tracks of players may cross and players may occlude one another, at least when viewed from any individual radar unit. Under these conditions, if more than one radar unit scans a particular scanned area, the track data from other radar units may be used to resolve a track crossing or an occlusion. If this cannot be done, however, the system may be combined with a video image which can be used to resolve the track crossing or occlusion, either through user intervention or image recognition.

In one embodiment of the invention, a stand-alone system, such as a portable system, may comprise one or more radar units and a processing unit in order to track players of a given game on a playing area where a more permanent installation of radar units does not exist. This might be the case, for example, on a training ground.

References are made in this document to a processing unit for processing signals received from radar units. However, the processing of radar echoes may be divided in any appropriate way between the radar units and the processing unit. For example, the basic timing of radar echoes may be transmitted to the processing unit where the range and bearing of the echo source may be derived. Alternatively, this portion of the processing may be carried out at the radar unit itself and the range and bearing information transmitted to the processing unit.

Specific embodiments of the invention will now be described by way of example, with reference to the accompanying drawings in which:

Figure 1 is a schematic plan view of a playing area showing the positions of four radar units;

Figure 2 is a schematic side view of a playing area showing the position of one of the radar units of Figure 1 ; and

Figure 3 is a block diagram of the four radar units of Figure 1 coupled to a processing unit.

Figure 1 illustrates a rectangular playing area 2 having a goal 4, 6 at each end. The playing area is divided into two halves by a halfway line 8. This is the conventional layout of, for example, a soccer pitch.

Four radar units 10, 12, 14, 16 are located outside the playing area, one near each comer of the pitch. Each radar unit is elevated to a height of approximately 3 metres above the playing area, as illustrated in Figure 2. Each radar unit rotates to generate a scanned beam in a substantially-horizontal plane. The vertical section of the scanned beam 18 for radar unit 12 is illustrated in Figure 2. Although the beam is referred to as substantially horizontal, depending on the elevation of the radar unit and the size of the playing area it may be slightly tilted downwards towards the playing area.

The scanned beam from each radar unit covers a scanned area spaced from the radar unit and substantially covering the opposite half of the playing area. By way of illustration, the boundaries of the scanned areas 110, 112 corresponding to two of the radar units 10, 12 are illustrated in Figure 1. These scanned areas are spaced from the radar units themselves and overlap to cover the half of the pitch distant from radar units 10 and 12. The radar units 14, 16 at the opposite end of the pitch cover scanned areas symmetrical to those of radar units 10 and 12, covering the half of the pitch closer to radar units 10 and 12. These scanned areas are not shown in Figure 1.

The scanned areas 110, 112 extend slightly beyond the edges of the playing area, in order to track players who may occasionally leave the playing area and match officials who may be outside the playing area, such as assistant referees or touch judges.

For each radar unit, the boundaries of the scanned area are defined as follows. The edge of the scanned area nearest the radar unit is defined by the elevation of the radar unit and the bottom edge of the scanned beam as it rotates around the radar unit. The other edges of the scanned area are defined by range and bearing limits applied to the received radar signal during processing. Echoes received from areas outside the scanned area can be disregarded.

Figure 2 illustrates the effect of elevation of one of the radar units 12 (the other radar units are similarly elevated). It should be noted that the vertical scale and the vertical beam spread as shown in Figure 2 are enlarged for clarity; the vertical beam spread in the embodiment is between 1° and 4°. The radar unit 12 is elevated such that players on the playing area near the radar unit, such as players 24, 26 in Figure 2, fall below the radar beam and so do not occlude players further from the radar unit. Players 20, 22 within the scanned area generate echoes that are received by the radar unit. As illustrated in the plan view of Figure 1 , players may sometimes partially or wholly occlude each other, when viewed from any particular radar unit. For example, player 20 occludes player 22 to some extent when viewed from radar unit 12 in Figure 1. However, as shown in Figure 2, the elevation of the radar unit may help to reduce such occlusions to some extent, for example such that radar unit 12 may be able to continue tracking partially-occluded player 22 as a weak or tentative target. Nevertheless, players 20 and 22 may still be tracked by radar unit 10 as illustrated in Figure 1. Where partial occlusions occur, a radar unit such as radar unit 12 may receive a weaker signal from player 22 due to the partial occlusion created by player 20. Radar unit 10 covering an overlapping scanned area would still receive strong echoes from both players 20 and 22. This is one reason for separating radar units covering overlapping areas, such that they have widely differing viewpoints. A second reason is to assist in 5 tracking weak or tentative targets (players), such as partially-occluded targets, as described further beiow.

The radar units in the embodiment comprise rotating scanners and emit narrow beams in a substantially-horizontal plane, which rotate through 360° about the io radar unit. The beam is reflected by any targets in the beam. The bearing to each target is obtained from the direction of the beam at the time and the range to each target is obtained from the time taken for the echo to reach the detector, which comprises part of the radar unit. As noted above, although the radar units scan through 360°, echoes from bearings and ranges outside the

I₅ scanned area are disregarded. It would also be possible to use radar units that scan through a more limited angle, as long as the angle is sufficient to encompass the scanned area.

The vertical beam width and any slight inclination of the beam may be 0 predetermined in order to ensure that an appropriate scanned area is covered. As illustrated in Figures 1 and 2, the vertical beam width should be sufficient to detect players in an area from the halfway line to a point just beyond the furthest edge of the playing area. The upper edge of the beam may, however, be positioned above the furthest edge of the pitch, in order to obtain strong S echoes from players at the furthest end of the pitch. It is also important to ensure that the lower edge of the beam is positioned so as to detect players near the halfway line, so that no player tracks are lost as players cross the halfway line moving from the scanned area of one pair of radar units to the scanned area of the other pair of radar units. 0

The vertical spread of each radar-unit beam is limited to allow a small target (players) to be identified above the noise floor of the sensor. To achieve this, a suitable compromise is made between maximum detection range and vertical beam spread, depending on the playing area to be covered. A suitable 5 compromise is also made between range and maximum rotational scan rate set by the time of flight (speed of light) of the radar signal. Again, this depends on the size of the playing area being covered.

As illustrated in Figure 3, each of the radar units 10, 12, 14, 16 is coupled 5 through a fibre-optic Ethernet connection 30 to a processing unit 32. The processing unit may comprise a suitably-programmed computer or PC. At the processing unit, the signal from each radar unit is received by a corresponding feature server 34, 36, 38, 40, which processes echoes received by each radar unit to identify targets, such as players.

10

Each radar unit scans its scanned area at a sufficiently high rate to track players. Preferably, a scan rate of at least 5 Hertz may be used. Particularly, preferably higher scan rates may be used such as rates of as high as 100Hz.

is In one embodiment, each feature server subtracts static background features, or the background static scene, from the output of each radar unit in order to identify target features, effectively using an adaptive background subtraction scheme. However, depending on the nature of the game being played, and the players' movements, adaptive background subtraction may not be desirable; for o example soccer players, such as goalkeepers, may remain stationary for long periods of time. In that case, the feature servers may use a modified adaptive background subtraction scheme. For example, each feature server may record when a tracked player stops moving and continue to track that target area even though it receives no indication that further movement is occurring. 5 Alternatively, no adaptive background subtraction scheme may be used.

In some embodiments the nature of the background may be known, and/or substantially fixed or stationary. For example in a soccer game in a stadium, the background may be sufficiently static either that no background subtraction o is required or that a measurement or fixed model of the background may be made before the game starts and subtracted from radar signals during the game.

At each feature server, over successive scans moving features are monitored 5 as potential targets. Once a target (player) has been identified, it is tracked. Each feature server may also track weak or tentative targets; these can be validated as described below by comparison with tracks from other radar units and/or a kinematic model of a player.

Each feature server outputs information regarding tracked players to a tracking client 42. This comprises a track combiner, which uses the feature information extracted by each radar unit to track all of the players on the playing area. The track combiner combines the track information provided by each radar unit covering overlapping scanned areas and, knowing the positions of the radar units themselves, can identify common targets tracked by different radar units. The track combiner may use, for example, a Kalman filter to achieve this. This approach may improve the accuracy of player tracks and also enable resolution of occlusions or track crossings, as players move near to each other. When a single radar unit generates a track in terms of range and bearing from that radar unit, the resolution in range is typically better than the resolution in bearing, and therefore combining the track information for two widely-spaced radar units can significantly improve track resolution.

As described above, when a target (player) is partially occluded as viewed from a first radar unit, a second radar unit scanning the same area may have a clearer view. Under these circumstances it is possible that the (second) feature server for the second radar unit may track the target but that the (first) feature server for the first radar unit may not track the weaker return, or signal, that it receives from the same target. In that case the track combiner may be programmed to feed back to the first feature server the location of the target as tracked by the second radar unit, so that the first feature server can use this approximate location information to help it to track the target using the weaker return to the first radar unit. Even if this does not permit accurate tracking using the first radar unit, the weak return may nevertheless improve knowledge of the target position by providing approximate range and/or location information from the alternative viewpoint of the first radar unit. The feature servers and the tracking client can thus be operated as a single tightly-coupled filter to benefit from this kind of feedback and knowledge. In this way, the feature servers may be able to provide better information on weak and tentative targets to the track combiner. The tracking client may additionally be programmed with a kinematic model of a player for comparison with tracks derived from the radar units, in order to improve track accuracy and resolve occlusions or crossings. For example, if the track combiner generates a player track on the basis of radar unit information , and the track corresponds to a movement that a player could not physically have made, comparison with the kinematic model should assist in resolving this or at least allow the processing unit to alert a human operator to a potential error and request an input from the operator if required.

The kinematic model may vary significantly for different games or sports and different types of target. For example very different movements would be expected, and possible, for a soccer player, an athlete on a running track or a cyclist on a track.

A comparison with a kinematic model may be made earlier with the tracks as derived from individual radar units, or after these tracks are combined, or both. Comparison with the tracks as derived from individual radar units may advantageously allow the track combiner to assess the likelihood that such a track may be incorrect or inaccurate, and then, when combining the tracks, to rely more heavily on a corresponding track for the same target from a different radar unit that may fit the kinematic model more closely.

Feedback from the kinematic model may also be used by the feature servers to assist in tracking weak or tentative targets. If a weak target is tracked and, over time, the movement of the target matches the kinematic model, confidence that the weak target is genuine is increased.

The tracking client outputs player track information to a track server for storage and for output to a display device if required. This output may advantageously be overlaid with a video image of the game for display or analysis. As the skilled person would appreciate, the processing of the radar information by the processing unit may be performed in real time, so that player tracks may, for example, be overlaid on a video image in real time. In a further refinement, a user viewing the tracks and the video image may be able to identify any errors in the tracking due to player occlusions or crossings, and resolve these errors. To do this, the user would feed information corrections back to the processing unit so that the tracks stored in the track server may be reprocessed and updated. The user may also be able to assign individual tracks to specific players through observation of the video image.

In further embodiments, in a sport such as soccer the ball may additionally be tracked. In this embodiment, if the ball is likely to rise above the plane of the radar beams, at least one ball-tracking radar unit may be operated using pan/tilt tracking rather than scanning in a fixed plane. In addition, if the ball moves faster than the players a higher scan rate may be required.

Claims

1. A system for tracking players on a playing area, comprising;

one or more radar units each positioned so as to transmit a substantially horizontally-scanned beam covering a scanned area of at least a portion of the playing area, and so as to receive echoes of the beam from players in the scanned area; and

a processing unit coupled to the radar unit(s) for tracking the positions of the players.

2. A system according to Claim 1 , in which the radar unit(s) are millimetre- wavelength radar unit(s).

3. A system according to Claim 1 or 2, in which each radar unit is elevated above the height of the players on the playing area.

4. A system according to any preceding claim, in which at least one radar unit is positioned so that its scanned area corresponds to a portion of the playing area spaced from the radar unit.

5. A system according to any preceding claim, in which the scanned areas of two or more of the radar units overlap.

6. A system according to Claim 5, in which the scanning directions of the two or more radar units are at a substantial angle to each other, for example greater than 15°, or greater than 30°, or greater than 45°.

7. A system according to any preceding claim, in which the scanned areas of a first plurality of radar units overlap in a first portion of the playing area and the scanned areas of a second plurality of radar units overlap in a second portion of the playing area.

8. A system according to Claim 7, in which the playing area comprises two halves, and each half substantially corresponds to one of the first and second portions of the playing area.

9. A system according to Claim 7 or 8, in which four radar units are spaced around the playing area, such that the scanned areas of a first pair of the radar units overlap in a first scanned area and the scanned areas of a second pair of the radar units overlap in a second scanned area, the first scanned area corresponding to a portion of the playing area distant from the first pair of radar units and closer to the second pair of radar units, and the second scanned area corresponding to a portion of the playing area distant from the second pair of radar units and closer to the first pair of radar units.

10. A system according to any preceding claim, in which each radar unit scans through an angle greater than the angle corresponding to its scanned area and echoes received at the radar unit from outside its scanned area are disregarded.

11 . A system according to any of Claims 1 to 9, in which each radar unit scans through an angle approximately corresponding to its scanned area.

12. A system according to any of Claims 1 to 9, in which a beam from each radar unit is electronically scanned and is optionally directed to track each player in the scanned area.

13. A system according to any preceding claim, in which the echoes received at each radar unit are used to derive a range and a bearing for each player in the radar unit's scanned area.

14. A system according to any preceding claim, in which each radar unit is connected to the processing unit by means of fibre-optic cables.

15. A system according to any preceding claim, in which for each radar unit the processing unit subtracts a substantially-static background signal from a signal received from the radar unit.

16. A system according to any preceding claim, in which for each radar unit the processing unit monitors features detected in successive scans to identify and track players.

17. A system according to any preceding claim, in which the processing unit comprises a track combiner for combining the tracks of a player as detected by two or more radar units and generating a track for the player having improved accuracy.

18. A system according to any preceding claim, in which the processing unit compares a track derived from one or more radar units with a kinematic model of a player.

19. A system according to any preceding claim, in which the processing unit uses the comparison of tracks for a plurality of players derived from the one or more radar units with a kinematic model of a player to resolve crossings of the tracks or occlusions of one or more of the players.

20. A system according to any preceding claim, in which the tracks of players derived by the processing unit can be compared with video images of the players to resolve crossings of the tracks or occlusions of one or more players.

21. A system according to any preceding claim, comprising one or more radar unit(s) coupled to the processing unit, constructed as a portable apparatus.

22. A system according to any preceding claim, in which the playing area is within a stadium or arena.

23. A system according to any preceding claim, in which the playing area comprises a playing field or a track.

24. A system according to any preceding claim, in which the players are people, animals or vehicles.

25. A radar unit for use with a system as defined in any preceding claim.

26. A processing unit for use with a system as defined in any preceding claim.

27. A method for tracking players on a playing area, comprising the steps of;

positioning one or more radar units so that each transmits a substantially horizontally-scanned beam over a scanned area covering at least a portion of the playing area, and receives echoes from players in the scanned area; and

processing an output from the or each radar unit to track the positions of the players.

28. A method according to Claim 27, in which each radar unit is positioned above the height of the players in the playing area.

29. A method according to Claim 27 or 28, comprising positioning a radar unit so that its scanned area covers a portion of the playing area distant from, or spaced from, the position of the radar unit.

30. A method according to Claim 27, 28 or 29, in which two or more radar units are positioned so that their scanned areas overlap.

31. A method according to Claim 30, in which four or more radar units are positioned so that the scanned areas of a first two or more radar units overlap in a first portion of the playing area and the scanned areas of a second two or more radar units overlap in a second portion of the playing area.

32. A method according to any of Claims 27 to 31 , comprising the step of processing at the processing unit signals from two or more radar units having overlapping scanned areas, by combining the tracks of players as detected by the two or more radar units.

33. A method according to any of Claims 27 to 32, comprising the step of comparing tracks of one or more players as detected by one or more radar units with a kinematic model of a player.

34. A method according to any of Claims 27 to 33, comprising the step of comparing tracks of one or more players as detected by one or more radar units with video images of the one or more players, for example to resolve crossings of the tracks, resolve occlusions of players, or to identify the tracks of specific players.

35. A system for tracking players of a game substantially as described herein, with reference to the accompanying drawings.

36. A radar unit substantially as described herein, with reference to the accompanying drawings.

37. A processing unit substantially as described herein, with reference to the accompanying drawings.

38. A method for tracking players of a game substantially as described herein, with reference to the accompanying drawings.