WO2019166850A1

WO2019166850A1 - Ball detection for a ball game

Info

Publication number: WO2019166850A1
Application number: PCT/IB2018/051225
Authority: WO
Inventors: Michael Gasser; Benjamin HABEGGER; Damian WEBER
Original assignee: Axiamo Gmbh
Priority date: 2018-02-27
Filing date: 2018-02-27
Publication date: 2019-09-06

Abstract

System for detecting ball contacts of a player of a ball game comprising: a ball (3) comprising magnetic means (31); a sensor device (2) to be worn or carried by a player, wherein the sensor device (2) comprises a magnetometer (23) for measuring a magnetic field; and a processing means 5 for detecting a ball contact of the player based on the magnetic field measured at the magnetometer (23).

Description

Ball detection for a ball game

Field of the invention

[0001] The present invention concerns the detection of a ball contact of a player of a ball game.

Description of related art [0002] Statistical data about ball games become more and more important to analyse and improve games and players. An important information are the ball contacts of the players of the game.

[0003] In the state of the art, ball contacts are retrieved by an analysis of image data of the game. This is either performed manually which is cumbersome or automatically which is complex and error-prone.

[0004] It is also known to mount a radio emitter in the ball and detect the ball, when it comes into vicinity with the players. This active ball detection can be performed automatically without too many errors.

However, this solution necessitates an energy source like a battery in the ball. In addition, the high impulses received by the ball can damage the circuitry of the radio emitter and lead to a complete shut down of the ball detection.

Brief summary of the invention

[0005] An object of the invention is to improve the ball detection. [0006] The object is solved by using magnetic means in the ball to detect a ball contact of a player with a sensor device worn by the player. Magnetic means combine a high resistance against the strong impulses of the ball and a good detection of the ball contact, when the ball is in the vicinity of the sensor device. [0007] The dependent claims refer to further advantageous

embodiments.

[0008] In one embodiment, the magnetic means comprises a plurality of magnetic spots distributed over the ball surface. Preferably, the magnetic spots are arranged between the inner ball skin and the outer ball skin. This guarantees a stable position of the magnetic spots even after strong impulses of the ball. Preferably, the magnetic spots are arranged in an angular distribution around the centre point of the ball which corresponds to the angular distribution of the normal vectors of the polygonal faces of a Platonic solid passing through the centre point of the Platonic solid. This has the advantage that the ball provides the same magnetic field for each ball section defined by one normal vector of the Platonic solid and facilitates thus the ball detection.

[0009] In one embodiment, the magnetic means and/or each magnetic spot is a permanent magnet. Permanent magnets do not require a power source and are very stable against physical impulses.

[0010] In one embodiment, the system comprises a second sensor device with a second magnetometer, wherein the second sensor device is arranged in another equipment worn by the same player, wherein the processing means is configured to detect the ball contact of the player based on the magnetic field measured at the magnetometer and the magnetic field measured at the second magnetometer. The sensor device and the second sensor device can be worn at different body parts of the player, so that the ball detection can detect a ball contact even at different body parts and even distinguish between those.

[0011] In one embodiment, the system comprises for each of a plurality of players of the ball game at least one sensor device with a magnetometer for measuring a magnetic field, wherein the processing means is configured to detect the ball contact of one of the players based on the magnetic field measured at the magnetic sensors of at least two of the players. This improves the ball detection for situations, where two players are close to the ball and it must be decided who of the two are in possession of the ball.

[0012] In one embodiment, the processing means comprises in each sensor device a decentralised processing means for determining a score indicating the probability of a ball contact of the player based on the magnetic field measured by the magnetometer of the respective sensor device, wherein the processing means comprises a central processing means for receiving the score of at least two decentralised processing means and for determining a ball contact of one of the players based on the score of the at least two decentralised processing means. A centralized processing has the advantage to consider the measurements and information of all players, but has the disadvantage to cause a high data transfer from the sensor devices to a central processing means. A decentralized processing in each sensor device has the advantage to communicate only, if a ball contact has been detected and reduces thus significantly the necessary data transfer volume. However, it has the disadvantage to consider only local information available in each sensor device. The described embodiment, combines the advantages of both systems by performing a decentralised pre-detection of a ball contact in each sensor device with the outcome of a score. The final detection of a ball contact is performed by a central processing means receiving the scores or the pre-detections. Thus, only the scores resulting from the pre-detection have to be sent to the central processing means which reduces the amount of data transfer. Preferably, the score is only sent to the central processing means, if a certain condition is fulfilled. Nevertheless, the central processing means can consider the scores of different sensor devices to decide on the final ball contact detection.

[0013] In one embodiment, the sensor device comprises an

accelerometer and a gyroscope. Preferably, the magnetometer, the accelerometer and the gyroscope is an inertial measurement unit (IMU).

This has the advantage that the same magnetometer used for the detection of the position and/or movement of the sensor device can be used for the ball detection. No extra sensor for the ball detection is required in the sensor device. Therefore, existing movement sensor devices for players can be updated for the present ball detection just by a software update.

Preferably, the processing means, in particular the decentralised processing means, is configured to detecting a ball contact of the player based on the magnetic field measured at the magnetometer and based on the

measurement of the accelerometer, the gyroscope and/or the movement of the sensor device computed based on the accelerometer and the gyroscope. Thus, the ball detection can be improved based on the accelerometer and the gyroscope. In one embodiment, the processing means, in particular the decentralised processing means, is configured to compute the change of the magnetic field measured at the magnetometer caused by the

movement of the sensor device and to detect a ball contact of the player based on the magnetic field measured at the magnetometer corrected by the change of the magnetic field caused by the movement of the sensor device. In one embodiment, the processing means, in particular the decentralised processing means, is configured to detect an impulse caused by a ball contact of the player based on the movement of the sensor device and/or based on the measurement of the accelerometer and/or gyroscope and detecting a ball contact of the player based on the magnetic field measured at the magnetometer and based on the detected impulse.

[0014] In one embodiment, the system is configured to determine the position and/or movement of a plurality of players based on the

measurements of the accelerometer and the gyroscope of the sensor devices worn by the players and/or based on time of arrival of a plurality of position signals received periodically at each sensor device.

[0015] In one embodiment, the sensor device is configured to

(periodically) calibrate the magnetometer to remove the hardiron effect. This step is important to reduce errors caused by magnetizations of the sensor device and its surrounding. [0016] All embodiments can be combined.

Brief Description of the Drawings [0017] The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which:

Fig. 1 shows a schematic view of an exemplary embodiment of the system for detecting a ball contact.

Fig. 2 shows an example distribution of magnetic spots over the ball.

Fig. 3 shows an exemplary arrangement of the sensor devices in a shin guard of a player. Fig. 4 shows an exemplary field of the ball game.

Detailed Description of possible embodiments of the Invention

[0018] Fig. 1 shows a schematic embodiment of the system for detecting ball contacts of at least one player of a ball game. The system comprises a processing means, at least one sensor device 2 and a ball 3. [0019] The ball 3 comprises a magnetic means 31. The ball 3 and/or the magnetic means 31 has preferably a plurality of magnetic spots distributed over the surface of the ball 3. Preferably, the magnetic spots are arranged between the inner ball skin and the outer ball skin such that their position is fixed. However, it is also possible that the ball 3 has only one magnetic spot, maybe arranged at the centre of the ball 3. Each magnetic spot causes a magnetic field, preferably a static magnetic field. The static magnetic field refers to the coordinate system of the ball 3. The static magnetic field could become an alternating field in the coordinate system of the field of the ball game, when the ball 3 is turning and the total magnetic field polarisation of the ball 3 goes through the centre point of the ball 3.

Preferably, the magnetic means and/or each of the magnetic spots is a permanent magnet and/or is made of a permanently magnetic material. This avoids the necessity of an energy source in the ball 3. However, it is also possible to provide an electro-magnet in the ball 3. The ball 3 has preferably a spherical form. However, it is also possible for some ball sports that the ball 3 has a non-spherical form, e.g. for rugby or American football. [0020] In one embodiment, the polarisation of the magnetic spots is such that polarisation direction with respect to the radial direction of the magnetic spot (extending from the centre point of the ball 3 to the magnetic spot) remains the same for all magnetic spots. For example, the north poles of the magnetic spots can be arranged to point radially versus the exterior of the ball 3, while the south poles of the magnetic spots point (all) radially versus the centre point of the ball 3. Alternatively, the south poles of the magnetic spots can be arranged to point radially versus the exterior of the ball 3, while the north poles of the magnetic spots point (all) radially versus the centre point. It is also possible to arrange the

polarisation (direction from north to south or vice versa) of all magnetic spots tangentially to the ball 3 (i.e. perpendicular to the radial direction of the magnetic spot). It is further possible to arrange the polarisations of the magnetic spots (with respect to the radial direction of the magnetic spot) different, for example in alternating manner once south versus the exterior and once north versus the exterior.

[0021] In one embodiment, the magnetic spots are arranged in an angular distribution around the centre point of the ball 3 which

corresponds to the angular distribution of the normal vectors of the polygonal faces of a Platonic solid passing through the centre point of the Platonic solid. A Platonic solid is a regular convex polyhedron constructed by congruent regular polygonal faces with the same number of faces meeting at each vertex (corners). Platonic solids are for example a

tetrahedron (four triangles), a cube (six squares), an octahedron (eight triangles), a dodecahedron (twelve pentagons) or an icosahedron (twenty triangles). Therefore, the preferred number of magnetic spots is (exactly) 4, 6, 8, 12 or 20. The mentioned Platonic distribution of 12 magnetic spots 31.1 over the ball for a dodecahedron is shown in Fig. 2. In an equivalent embodiment, the angular distribution of the magnetic spots around the centre point of the ball 3 can also be described as the angular distribution of the normal vectors of the vertices (corners) of a Platonic solid. With such an angular distribution of the magnetic spots, the surface of the ball 3 (sphere) can be divided in a number of spherical polygons around the magnetic spots which correspond to the projection of the polygons of the Platonic solid on the surface of the ball 3 or the surface of a sphere. If the polarisation of the magnetic spots in each spherical polygon over the ball 3 is the same with respect to the radial direction of the magnetic spot, the magnetic field created by the magnetic spots for each of those spherical polygons corresponds to the magnetic field of all the other spherical polygons of the ball 3. Thus, the magnetic field of the spherical polygons are interchangeable. Due to the symmetry of the Platonic solid, the spherical polygons around each magnetic spot have the same detection behaviour. In other words, the pattern of magnetic spots is preferably such that the pattern of magnetic spots on the ball 3 looks the same from each magnetic spot. In other words, the pattern of magnetic spots is configured such that the arrangement of the magnetic spots with respect to the coordinate system of the field of the ball game remains the same, when the ball 3 is rotated by any angle which rotates one magnetic spot by an angular distance between two magnetic spots. Even if this symmetric pattern of magnetic spots is preferred, other patterns of magnetic spots are possible.

[0022] The sensor device 2 comprises a magnetometer 23 for measuring a magnetic field. This allows to measure the magnetic field caused by the magnetic means 31 of the ball 3, when the ball 3 is in vicinity of the sensor device 2. This magnetic measurement can be used to detect a ball contact of the player wearing or carrying the sensor device 2. Preferably, the magnetometer 23 is a 3-axes magnetometer. Preferably, the magnetometer 23 is a MEMS device. [0023] In one embodiment, the sensor device 2 comprises further an

(three-axes) accelerometer 24 and/or a (three-axes) gyroscope 25. In a preferred embodiment, the accelerometer 24, the gyroscope 25 and the magnetometer 23 are part of an inertial measurement unit 22 configured to measure the position and/or movement of the sensor device 2 based on the measurements of the accelerometer 24, the gyroscope 25 and the magnetometer 23. Preferably, the IMU 22, the accelerometer 24 and/or the gyroscope 25 is a MEMS device. [0024] The sensor device 2 comprises a transmitter 21 for sending out measurements of the IMU 22, the accelerometer 24, the gyroscope 25 and/or the magnetometer 23, processing results based on the IMU 22, the accelerometer 24, the gyroscope 25 and/or the magnetometer 23 or other data preferably to a server 1. The server 1 can be a normal computer.

Preferably, the transmitter 21 is configured for wireless transmission of data, preferably for radio transmission of data. The radio transmission can be for example WLAN, WAN, LORA, a mobile phone connection like GSM, UMTS, LTE, etc. or by any other wireless connection. The radio transmission has preferably a transmission range which covers the total field of the ball sport. However, it is also possible to transfer the data from the sensor device 2 or the transmitter 21 by a wired connection to the server 1.

Preferably, data are sent periodically, continuously and/or in real time to the server 1. However, it is also possible to save the measured and/or processed data and send the data together only after certain

predetermined time periods or only when the sensor device 2 comes in the transmission range of the server 1 (or its receiver 11) or only when the sensor device 1 is connected, maybe by a wire, to the receiver 11 or to the server 1. In one embodiment, the transmitter 21 can be a combined transmitter/receiver for transmitting and receiving data which receives and transmits data with the same transmission standard. However, it is also possible that the receiver is independent from the transmitter and/or that the receiver applies another transmission standard.

[0025] The sensor device 2 comprises an energy source 26 for providing the sensor device 2 with energy. Preferably, this energy source is a battery, preferably a rechargeable battery, preferably a lithium ion battery.

However, it is also possible that the energy source is based on an energy harvesting method. [0026] In one embodiment, the sensor device 2 comprises a

triangulation section 27 for determining the position of the sensor device 5. The triangulation section 27 forms part of a triangulation system described in more detail below. [0027] In a preferred embodiment, the sensor device 2 comprises a decentralised processing means 4.d for processing or pre-processing the measurements of the IMU 22, the magnetometer 23, the accelerometer 24, the gyroscope 25 and/or the triangulation section 27. The functioning of the decentralised processing means 4.d is described in more detail below. [0028] Preferably, the system comprises at least two or more sensor devices 2 (in the Fig. 1 indicated as 2.1, 2.2). The description of the sensor device 2 above applies for all sensor devices 2 of the system. Preferably, all sensor devices 2 are identical (except for an identification of the sensor device 2 which should be unique for each sensor device 2 to distinguish the sensor devices 2). However, it is also possible that some sensor devices 2 are different from other sensor devices 2. For example, a sensor device 2 worn at the hand could be different than another sensor device 2 worn at the foot (of the same or a different player).

[0029] At least one sensor device 2 is worn or carried by at least one of the players of the ball game. Preferably, at least two of the players ware or carry such a sensor device 2 for detecting the ball contacts of different players. Preferably, the sensor devices 2 have an identifier. The identifier of each sensor device 2 is associated with the (part of the body of the) player wearing the sensor device 2. It is also possible that each or some players of the ball game ware or carry at least two sensor devices 2 for detecting ball contacts of different body parts of the player.

[0030] The at least one sensor device 2 worn or carried by a player of the ball game is preferably arranged in an equipment of the player of the ball game. The sensor device 2 or the equipment with the sensor device 2 is arranged in a zone where the player normally interferes with the ball 3. For ball contacts with the feet as present in soccer, American football, rugby, the sensor device 2 can be arranged in a shoe or a shin guard, preferably, the lower extremity of the shin guard in vicinity with the foot. Fig. 3 shows an exemplary position of the sensor device 2 in a shin guard. For ball contacts with the hands as present in handball, volleyball, basket ball American football, rugby or for a goal keeper in football, the sensor device 2 can be arranged in a bracelet or a glove. It is also possible to arrange the sensor device 2 in a ball handling device with a handle to be hold by the player of the ball game, in particular a racquet (e.g. tennis, badminton, squash, table tennis, etc.), a club (golf), a stick (e.g. hockey, lacrosse) or a bat (e.g. baseball, cricket). If two or more sensor devices 2 are worn or carried by the same player, ball contacts of different body zones can be detected. For example, in the two shin guards and/or the two shoes to detect ball contacts of both feed (e.g. for field players of soccer). For example, in the two shin guards or the two shoes and in two gloves or bracelets to detect ball contacts of both feed and both hands (e.g. for goal keeper of soccer).

[0031] The processing means is configured for detecting a ball contact of the player based on the magnetic field measured at the magnetometer 23. Preferably, the processing means is further configured to perform further analysis of the ball game based on the measurements of the at least one sensor device 2.

[0032] In a preferred embodiment, the processing means comprises a central processing means 4.c arranged in the server 1 and a decentralised processing means 4.d in each sensor device 1. A preferred distribution of the processing between the central processing means 4.c and the

decentralised processing means 4.d of each sensor device 2 is described in the following without any restriction of the invention. Any other

distribution between the central processing means 4.c and the

decentralised processing means 4.d of each sensor device 2 is possible. It is further possible that (all) the processing is done either only in the central processing means 4.c or only in the decentral processing means 4.d of each sensor device. In the latter case, the server 1 might be omitted or used just for receiving the ball detection results of the sensor devices 2. In the first case, the measurements of the IMU 22, the magnetometer 23, the accelerometer 24, the gyroscope 25 and/or the triangulation section 27 are sent to the central processing means 4.c for further processing (in real-time and/or with a time-stamp of the measurements). [0033] The server 1 comprises further a receiver 11 configured to receive data from each sensor device 21 or from the transmitter 21 of each sensor device 2. The receiver 11 is preferably configured to receive the same transmission standard applied by the transmitter 21. However, it is also possible that the receiver 11 applies another transmission standard, if the data from the transmitter 21 are retransmitted with another standard. Preferably, the receiver 11 is configured to receive wireless (radio) signals from the transmitter(s) 21. In one embodiment, the server 1 includes the receiver 11. In one embodiment, the server 1 is arranged in the vicinity of the field of the ball game. In another embodiment, the receiver 11 is remote from the server 1 and is arranged in the vicinity of the field of the ball game. The receiver 11 in this embodiment works than like a

transformer which receives the data from the transmitter(s) 21 and transmits it (maybe transformed in another transmission format) to the (remote) server 1. [0034] The processing means, the central processing means 4.c, the decentralised processing means 4.d and/or the server 1 can (each) be constituted of one or more processor(s), chip(s) or computer(s), which in case of more processor(s), chip(s) or computer(s) could be also arranged in different devices or remote from each other. [0035] The ball contact detection is preferably at least partly detected in the decentralised processing means 4.d of each sensor device 2 based on the measurements of the sensor device 2, in particular of the IMU 22, in particular of the magnetometer 23. Preferably, the processing of the decentralised processing means 4.d results in a score indicating a

probability of a ball contact. The score is preferably a number between 0 and 1, but could obviously also a number of any other closed interval or even a number of a (semi-)open interval. The score or any other pre- detection result is only calculated and/or only sent to the central processing means 4.c (via the receiver 11), when a certain ball contact condition is fulfilled. This ball contact condition could be for example that magnetic field measured at the magnetometer 23 and/or the calculated score fulfils a certain condition (e.g. exceeding a threshold). Consequently, the

decentralised processing means 4.d continuously performs the (at least partly) detection of a ball contact in the sensor device 2 and communicates the (at least partly) detected ball contact and/or the score (only) to the central processing means 4.1 or to the server 1, when the ball contact condition is fulfilled. The score could depend on the magnitude of the measured magnetic field and/or the distance of the ball 3 to the

magnetometer 23. The score could further depend on the measurements of the IMU 2, the accelerometer 24 and/or the gyroscope and/or on the position and/or movement of the sensor device 2 as will be described in more detail below.

[0036] The processing means, in particular the decentral processing means 4.d is configured to (pre-)detect a ball contact of a player associated with the sensor device 2 and/or wearing or carrying the sensor device 2, when the measurement of the magnetometer 2 of this sensor device 2 indicates the vicinity of the ball 3. The magnetic field created by the magnetic means 31 of the ball 3 and the detection algorithms of the

(decentralised) processing means is preferably configured such that a ball contact is (pre-)detected, when the surface or the centre of the ball 3 comes into a distance of less than a distance threshold to the magnetometer 23 or the sensor device 2. The distance threshold is preferably less than 50 cm, preferably less than 40 cm, preferably less than 35 cm, preferably less than 30 cm. This can be realized by comparing the magnetic field measured at the magnetometer with a magnetic threshold corresponding to the mentioned distance threshold. [0037] Preferably, the processing means, in particular the decentralised processing means, is configured to (pre-)detecting a ball contact of the player at a certain time instant based on the magnetic field measured at the magnetometer at this time instant and based on the measurement of the accelerometer and/or the gyroscope at this time instant and/or based on the position and/or movement of the sensor device 2 at this time instant. The time instant could also include a short time before and/or after the time instant. The position can be the angular position (orientation) and/or the translational position (location). The above-mentioned score can thus depend on the measurement of the accelerometer and/or the gyroscope at this time instant and/or based on the position and/or movement of the sensor device 2 at this time instant.

[0038] In one embodiment, the processing means, in particular the decentralised processing means, is configured to compute the change of the magnetic field measured at the magnetometer caused by the

movement of the sensor device 2 (in particular the change of the angular position) and to detect a ball contact of the player based on the magnetic field measured at the magnetometer and the change of the magnetic field caused by the movement of the sensor device 2. The magnetometer 23 measures in the absence of the ball 3 the magnetic field of the field of the ball game (natural magnetic field). Due to the movement of the player and thus of the sensor device 2, the orientation of the sensor device 2 with respect to the natural magnetic field changes and thus also the

measurement at the magnetometer 23 changes. In order to avoid false positive detection of a ball contact, the change of the measurement of the magnetic field at the magnetometer 23 is considered for the (pre- )detection of the ball contact. For example, the measured magnetic field can be corrected by the change of the magnetic field to obtain a corrected measured magnetic field which is then used for the above-described (pre- )detection of the ball contact or of the score. Alternatively, it is also possible to correct the threshold or other reference by the change of the magnetic field caused by the movement. The change of the magnetic field caused by the movement can be determined on the basis of the IMU 22 and/or of the gyroscope 25. The change of the magnetic field caused by the movement can be determined further based on the natural magnetic field measured in a reference orientation (reference magnetic field). This reference magnetic field could be measured in a calibration step on the field. The reference magnetic field can be measured also only once or can be looked up or can be calculated and then be communicated to the sensor devices 2.

[0039] In one embodiment, the processing means, in particular the decentralised processing means, is configured to detect an impulse caused by a ball contact of the player based on the movement of the sensor device 2 and/or based on the measurement of the accelerometer 24 and/or gyroscope 25 and to detect a ball contact of the player based on the magnetic field measured at the magnetometer 23 and based on the detected impulse. When the player wearing or carrying the sensor device 2 touches the ball 3, the ball 3 normally creates an impulse on the player and thus on the sensor device 2. This impulse can be detected by the

measurements of the IMU 22, the accelerometer 24 and/or the gyroscope 25 and/or by the movement of the sensor device 2. The above-mentioned score can thus depend on the detected impulse. If such an impulse is detected, the score is adapted such that the indicated probability of a ball contact is increased.

[0040] The processing means, in particular the decentral processing means 4.d is preferably configured to perform at least once before or during the game, preferably periodically, a calibration in order to consider the hardiron effect on the measurement of the magnetometer 23. This calibration must be performed in the absence of the ball 3, to get the current hardiron offset of the sensing unit, uninfluenced by permanent magnets.

[0041] The processing means, in particular the central processing means 4.c is preferably configured to detect a ball contact of a player at a certain time instant based on the scores, the pre-detection results and/or the measurements of the IMU 22, the magnetometer 23, the accelerometer 24 or the gyroscope 25 of this time instant received from at least two or more sensor devices 2. This allows to consider for the final decision of a ball contact at the time instant potential ball contacts at several sensor devices 2, e.g. of two different players or of two different body parts of a player. This allows to distinguish between the ball contacts of different players and/or of different body parts of one player. For example, if two players are fighting for the ball 3, both players and their sensor devices 2 might be in the vicinity of the ball 3. The final decision, if both players or only one of the two (and which one) had a contact with the ball, can then be made in the (central) processing means 4.c. If the central processing means 4.c receives a score from two or more of the decentralised processing means 4.d, then the final decision of the ball contact can be made on the two or more scores. For example, the sensor device 2 with the highest score might be considered as the sensor device 2 associated with a player (or body part of a player) which has made a ball contact.

[0042] The processing means, in particular the central processing means 4.c is preferably configured to detect a ball contact of a player at a certain time instant based further on global information of the game or the recent history of the game before the time instant. For example the processing means, in particular the central processing means 4.c is preferably configured to detect a ball contact of a player at a certain time instant based on

- the position on the field of (the player of) the sensor device 2 having a potential ball contact at the time instant,

- on the position on the field of (the player of) the sensor device 2 having had the last ball contact before the time instant,

- the time difference and/or position distance between the potential ball contact of (the player of) the sensor device 2 at the time instant and the last ball contact before the time instant and/or

- a game state (interruption, goal, playing mode, pause).

[0043] The (central and/or decentralised) processing means is configured to determine the position and/or movement of the sensor devices 2 on the field of the game. The position and/or movement of (parts of the body of) the players can be determined from this position and/or movement of the sensor devices 2. The (central and/or decentralised) processing means is configured to determine the position and/or movement of the sensor devices 2 on the field of the game based on the measurements of the IMU 22, the magnetometer 23, the accelerometer 24 and/or the gyroscope 25 and/or based on the triangulation system. The position of a sensor device 2 at an actual time instant can be determined based on the position of the sensor device 2 at a previous time instant plus the incremental change of the position from the previous time instant and the actual time instant determined based on the IMU 22, the accelerometer 24, the gyroscope 25 and/or the magnetometer 23. The position of a sensor device 2 at an actual time instant can also be determined based the triangulation system described later. The first method has the advantage to detect very precisely the change of position in a short time, but has the disadvantage that over a long time small error accumulate to a large error in the absolute position. The second method might be less precise in the determination of the position, but does not depend on the history of the previous positions. In addition, the second method has normally a very high error in movements perpendicular to the field of the game. Therefore, in a preferred

embodiment, the position of the sensor device 2 is determined based on the measurements of the IMU 22, the magnetometer 23, the accelerometer 24 and/or the gyroscope 25 and based on the triangulation system. This allows to combine the advantages of both position detection systems and to receive the position of each player with higher accuracy. The movement of a sensor device 2 is determined by the sequence of positions of the sensor device 2 in subsequent time instants. It is either possible to

determine the position in the decentralised processing means 4.d and send the determined positions to the centralised processing means 4.c.

Alternatively, it is also possible to send the measurements of the IMU 22, the magnetometer 23, the accelerometer 24 and/or the gyroscope 25 and/or eventually of the triangulation section 27 to the central processing means 4.c and determine the position of the sensor device 2 in there.

[0044] In one embodiment, the (central) processing means is configured to process the determined information like ball contacts of players and/or positions of sensor devices 2 or of players into further information about the game. For example, the trajectory of the ball can be determined based on the ball contacts of the players/sensor devices 2 and the positions of the players/sensor devices 2, when contacting the ball. [0045] The triangulation system comprises the triangulation section 27 of each sensor device 2, triangulation points 5 and the processing means arranged on the field of the game. The triangulation system is configured to detect the position of each sensor device 2 based on signals exchanged between the triangulation points 5 and the respective sensor device 2. Therefore, at least three triangulation points 5 are needed. Preferably, four, five, six or more triangulation points 5 are used to reduce the error. Preferably, the triangulation points 5 are arranged at the corners of the field. Many fields are rectangular. Preferably, another triangulation point 5 are arranged at the centre of each longer side line of the field. Fig. 4 shows an exemplary field of a soccer game with six triangulation points 5. Other arrangements and other numbers of triangulation points 5 are possible.

[0046] The triangulation system is configured to measure a time of flight, a time of arrival or a time difference of arrival (alternatives in the following called triangulation times) of the signals exchanged between each sensor device 2 and the triangulation points 5. Since the velocity of the signal and the position of the triangulation points 5 are known, the position of sensor device 2 relative to the triangulation points 5 and/or on the field can be computed based on the triangulation times. In one embodiment, the signal can be sent out (at the same time) from the triangulation points 5 and received at the sensor device 2. The

triangulation signal can be received at the receiver/transmitter 21 or in a separate receiver for the triangulation system in the triangulation section 27. The triangulation section 27 determines in this embodiment the triangulation times of the signal received from each triangulation point 5 and the (preferably the decentralised) processing means determines the position of the sensor device 2 based on the triangulation times. In another embodiment, the signal can be sent out from the sensor device 2, e.g. the transmitter 11 or a separate transmitter in the triangulation section 27. The signal transmitted from the sensor device 2 is received at different times at the triangulation points 5 resulting in the triangulation times. The triangulation times are then communicated to the (central) processing means which determines the position of the sensor device 2. To distinguish different sensor devices 2, the signal could comprise an information identifying the sensor device 2. This information can be coded in data transmitted or be defined by the transmission scheme. For example, time division multiplexing (TDMA) could be used, wherein each slot is used for one sensor device 2. Other embodiments are possible, for example the signal is sent out by one of the sensor device 2 and the triangulation points 5, received and immediately re-transmitted by the other of the sensor device 2 and the triangulation points and received again by the

transmitting one.

[0047] Outside the scope of the current invention, the described position detection of the players combining the triangulation system 5 with the position detection on the basis of the IMU sensor 22 can also be used without the described magnetic ball detection.

Claims

1. System for detecting ball contacts of a player of a ball game comprising:

a ball (3) comprising magnetic means (31);

a sensor device (2) to be worn or carried by a player, wherein the sensor device (2) comprises a magnetometer (23) for measuring a magnetic field;

a processing means for detecting a ball contact of the player based on the magnetic field measured at the magnetometer (23).

2. System according to claim 1 or 2, wherein the magnetic means (31) comprises a plurality of magnetic spots (31.1) distributed over a surface of the ball (3).

3. System according to claim 2, wherein the magnetic spots (31.1) are arranged between an inner skin of the ball (3) and an outer skin of the ball (3).

4. System according to claim 2 or 3, wherein the magnetic spots

(31.1) are arranged in an angular distribution around the centre point of the ball (3) which corresponds to the angular distribution of the normal vectors of the polygonal faces of a Platonic solid passing through the centre point of the Platonic solid.

5. System according to one of claims 1 to 4, wherein the magnetic means (31) and/or the magnetic spots (31.1) comprise(s) a permanent magnet.

6. System according to one of claims 1 to 5, wherein the sensor device (2) is arranged in an equipment of the player of the ball game.

7. System according to claim 6, wherein the equipment is a shin guard, wherein the sensor device (2) is arranged at the extremity of the shin guard pointing to the foot.

8. System according to claim 6, wherein the equipment is a ball handling device with a handle to be hold by the player of the ball game, in particular a racquet, a club, a stick or a bat.

9. System according to claim 6, wherein the equipment is a bracelet or a glove, wherein the processing means is configured for detecting a ball contact with a hand of the player based on the magnetic field measured at the magnetometer (23).

10. System according to one of claims 6 to 9, wherein the system comprises a second sensor device (2) with a second magnetometer (23), wherein the second sensor device (23) is arranged in another equipment worn by the same player, wherein the processing means is configured to detect the ball contact of the player based on the magnetic field measured at the magnetometer (23) and the magnetic field measured at the second magnetometer (23).

11. System according to one of claims 1 to 10, wherein the system comprises for each of a plurality of players of the ball game at least one sensor device (2) with a magnetometer (23) for measuring a magnetic field, wherein the processing means is configured to detect the ball contact of one of the players based on the magnetic field measured at the

magnetometer of at least two of the players or of at least two sensor devices (2) of the same player.

12. System according to claim 10 or 11, wherein the processing means comprises in each sensor device (2) a decentralised processing means (4.d) for determining a score indicating the probability of a ball contact of the player based on the magnetic field measured by the magnetometer (23) of the respective sensor device (2), wherein the processing means comprises a central processing means (4.c) for receiving the score of at least two decentralised processing means (4.d) and for determining a ball contact of one of the players based on the score of the at least two decentralised processing means (4.d).

13. System according to claim 11 or 12, wherein the processing means is configured to calculate the position of each player on the field of the ball game, wherein the processing means, in particular the central processing means (4.c), is configured to determine the ball trajectory based on the ball contacts of the players and the positions of the players.

14. System according to one of claims 1 to 13, wherein the magnetometer (23) is a three-axes magnetometer.

15. System according to one of claims 1 to 14, wherein the sensor device (2) comprises an accelerometer (24) and/or a gyroscope (25).

16. System according to claim 15, wherein the processing means, in particular the decentralised processing means (4.d) is configured to compute the position and/or movement of the sensor device (2) based on the measurement of the accelerometer (24) and/or the gyroscope (25) and optionally the magnetometer (23).

17. System according to claim 15 or 16, wherein the processing means, in particular the decentralised processing means (4.d), is configured to detect a ball contact of the player based on the magnetic field measured at the magnetometer (23) and based on the measurement of the

accelerometer (24), the gyroscope (25) and/or the movement of the sensor device (25) computed based on the accelerometer (24) and/or the gyroscope (25).

18. System according to claim 17, wherein the processing means, in particular the decentralised processing means (4.d), is configured to compute the change of the magnetic field measured at the magnetometer (23) caused by the movement of the sensor device (2) and to detect a ball contact of the player based on the magnetic field measured at the magnetometer (23) corrected by the change of the magnetic field caused by the movement of the sensor device (2).

19. System according to claim 17 or 18, wherein the processing means, in particular the decentralised processing means (4.d), is configured to detect an impulse caused by a ball contact of the player based on the movement of the sensor device (2) and/or based on the measurement of the accelerometer (24) and/or the gyroscope (25) and detecting a ball contact of the player based on the magnetic field measured at the magnetometer (23) and based on the detected impulse.

20. System according to one of claims 15 to 19, wherein the processing means is configured to determine the position of a plurality of players based on the measurements of the accelerometer (24) and the gyroscope (25) and/or based on triangulation times of signals exchanged between the sensor devices (2) of the players and triangulation points fixed in the coordinate system of the field of the ball game.

21. System according to one of claims 15 to 20, wherein the gyroscope (25) is a three-axes gyroscope and/or the accelerometer (24) is a three-axes accelerometer.

22. System according to one of claims 15 to 21, wherein the accelerometer (24), the gyroscope (25) and the magnetometer (23) form an inertial measurement unit.

23. System according to one of claims 1 to 22, wherein the sensor device (2) is configured to (periodically) calibrate the measurements of the magnetometer (23) to remove the hardiron effect.

24. Method for detecting ball contacts of a player of a ball game, wherein a ball of the ball game comprising magnetic means, the method comprising:

measuring a magnetic field with a magnetometer (23) of a sensor device (2) worn or carried by a player,

detecting with a processing means a ball contact of the player based on the magnetic field measured at the magnetometer (23).

25. Computer program configured to perform the following steps when executed on a processing means:

receiving, in the processing means, a magnetic field measured with a magnetometer (23) of a sensor device (2) worn or carried by a player of a ball game,

detecting, in the processing means, a ball contact of the player with a ball (3) including magnetic means (31) based on the magnetic field received.