ASSESSMENT OF POSITION OF MOTION TRACKERS ON A SUBJECT BASED ON WIRELESS COMMUNICATIONS

Abstract

Motion tracking systems and methods for determining how trackers are positioned on body members of a person, the methods including: wirelessly receiving, by a computing device, one or more first data packets of each tracker; digitally determining a first direction in which the computing device is relative to the respective tracker by computing an angle of departure of the one or more first data packets; digitally determining based on the first directions, a second direction in which each tracker is relative to one or more other trackers; and digitally determining on which body member is each tracker positioned on the person at least based on both the second directions and the body members requiring to have a tracker positioned thereon. Also, systems and methods in which angles of arrival are computed for determining the first directions.

Claims

1. A motion tracking system comprising: a plurality of trackers adapted to be arranged on a plurality of body members of a person, and each tracker comprising: at least one inertial sensor, and a plurality of antennas; and a computing device comprising at least one antenna; each tracker of the plurality of trackers being configured to: wirelessly receive, from the computing device, one or more first data packets through each antenna of the plurality of antennas of the respective tracker at least while the tracker is positioned on the body of the person; and digitally determine a first direction in which the computing device is relative to the respective tracker by computing an angle of arrival of the one or more first data packets based on the reception thereof through each antenna of the respective plurality of antennas; and the computing device being configured to: wirelessly receive, from each tracker of the plurality of trackers, one or more second data packets comprising data indicative of or relative to the respective first direction; digitally determine, based on the received data from each tracker of the plurality of trackers, a second direction in which each tracker of the plurality of trackers is relative to one or more other trackers of the plurality of trackers; and digitally determine on which body member is each tracker of the plurality of trackers positioned on the person at least based on both the second directions and the plurality of body members requiring to have a tracker positioned thereon, thereby providing a correspondence between the plurality of trackers and the plurality of body members.

2. The motion tracking system of claim 1, wherein the computing device is further configured to: wirelessly receive, from each tracker of the plurality of trackers, at least one data packet comprising one or more measurements of the respective at least one inertial sensor at least while the tracker is arranged on the body of the person; and digitally provide a motion tracking sequence of a plurality of body members of the person based on both the received one or more measurements from each tracker of the plurality of trackers and the correspondence between the plurality of trackers and the plurality of body members.

3. The motion tracking system of claim 1, wherein the plurality of antennas comprises at least three antennas arranged such that there is no imaginary line that is drawn containing all of the at least three antennas.

4. The motion tracking system of claim 1, wherein each second direction at least includes two perpendicular components thereby being at least indicative of a two-dimensional direction.

5. The motion tracking system of claim 1, wherein the computing device is further configured to digitally estimate a distance that the computing device is apart from each tracker of the plurality of trackers based on the data packets wirelessly received from each tracker of the plurality of trackers; and wherein each second direction at least includes three perpendicular components thereby being indicative of a three-dimensional direction.

6. The motion tracking system of claim 5, wherein the digital determination of on which body member is each tracker of the plurality of trackers positioned on the person further comprises determining a position of each tracker on a surface of the respective body member on which the tracker is positioned.

7. The motion tracking system of claim 1, wherein at least the plurality of trackers is configured to wirelessly receive data packets using a wireless communications protocol comprising computation of angle of arrival.

8. A motion tracking system comprising: a plurality of trackers adapted to be arranged on a plurality of body members of a person, and each tracker comprising: at least one inertial sensor, and a plurality of antennas; and a computing device comprising at least one antenna, the computing device being configured to: wirelessly receive, from each antenna of the plurality of antennas, one or more first data packets of each tracker of the plurality of trackers at least while the respective tracker is positioned on the body of the person; digitally determine a first direction in which the computing device is relative to the respective tracker by computing an angle of departure of the one or more first data packets based on the reception thereof from each antenna of the respective plurality of antennas of the respective tracker; digitally determine, based on the first directions, a second direction in which each tracker of the plurality of trackers is relative to one or more other trackers of the plurality of trackers; and digitally determining on which body member is each tracker of the plurality of trackers positioned on the person at least based on both the second directions and the plurality of body members requiring to have a tracker positioned thereon, thereby providing a correspondence between the plurality of trackers and the plurality of body members.

9. The motion tracking system of claim 8, wherein the computing device is further configured to: wirelessly receive, from each tracker of the plurality of trackers, at least one data packet comprising one or more measurements of the respective at least one inertial sensor at least while the tracker is arranged on the body of the person; and digitally provide a motion tracking sequence of a plurality of body members of the person based on both the received one or more measurements from each tracker of the plurality of trackers and the correspondence between the plurality of trackers and the plurality of body members.

10. The motion tracking system of claim 8, wherein the plurality of antennas comprises at least three antennas arranged such that there is no imaginary line that is drawn containing all of the at least three antennas.

11. The motion tracking system of claim 8, wherein each second direction at least includes two perpendicular components thereby being at least indicative of a two-dimensional direction.

12. The motion tracking system of claim 8, wherein the computing device is further configured to digitally estimate a distance that the computing device is apart from each tracker of the plurality of trackers based on the data packets wirelessly received from each tracker of the plurality of trackers; and wherein each second direction at least includes three perpendicular components thereby being indicative of a three-dimensional direction.

13. The motion tracking system of claim 12, wherein the digital determination of on which body member is each tracker of the plurality of trackers positioned on the person further comprises determining a position of each tracker on a surface of the respective body member on which the tracker is positioned.

14. The motion tracking system of claim 8, wherein at least the computing device is configured to wirelessly receive data packets using a wireless communications protocol comprising computation of angle of departure.

15. A motion tracking system comprising: a plurality of trackers adapted to be arranged on a plurality of body members of a person, and each tracker comprising: at least one inertial sensor, and at least one antenna; and a computing device comprising a plurality of antennas, the computing device being configured to: wirelessly receive, from each tracker of the plurality of trackers, one or more first data packets through each antenna of the plurality of antennas at least while the respective tracker is positioned on the body of the person; digitally determine a first direction in which the computing device is relative to each tracker of the plurality of trackers by computing an angle of arrival of the one or more first data packets based on the reception thereof through each antenna of the plurality of antennas; digitally determine, based on the first directions, a second direction in which each tracker of the plurality of trackers is relative to one or more other trackers of the plurality of trackers; and digitally determine on which body member is each tracker of the plurality of trackers positioned on the person at least based on both the second directions and the plurality of body members requiring to have a tracker positioned thereon, thereby providing a correspondence between the plurality of trackers and the plurality of body members.

16. The motion tracking system of claim 15, wherein the computing device is further configured to: wirelessly receive, from each tracker of the plurality of trackers, at least one data packet comprising one or more measurements of the respective at least one inertial sensor at least while the tracker is arranged on the body of the person; and digitally provide a motion tracking sequence of a plurality of body members of the person based on both the received one or more measurements from each tracker of the plurality of trackers and the correspondence between the plurality of trackers and the plurality of body members.

17. The motion tracking system of claim 15, wherein the plurality of antennas comprises at least three antennas arranged such that there is no imaginary line that is drawn containing all of the at least three antennas.

18. The motion tracking system of claim 15, wherein each second direction at least includes two perpendicular components thereby being at least indicative of a two-dimensional direction.

19. The motion tracking system of claim 15, wherein the computing device is further configured to digitally estimate a distance that the computing device is apart from each tracker of the plurality of trackers based on the data packets wirelessly received from each tracker of the plurality of trackers; and wherein each second direction at least includes three perpendicular components thereby being indicative of a three-dimensional direction.

20. The motion tracking system of claim 15, wherein the digital determination of on which body member is each tracker of the plurality of trackers positioned on the person further comprises determining a position of each tracker on a surface of the respective body member on which the tracker is positioned.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as examples of how the disclosure can be carried out. The drawings comprise the following figures:

[0074] FIG. 1 diagrammatically shows a motion tracking system in accordance with embodiments.

[0075] FIGS. 2A, 2B and 3A, 3B diagrammatically show exemplary angle of arrival and angle of departure computations in motion tracking systems in accordance with embodiments.

[0076] FIG. 4 shows a motion tracking system in accordance with embodiments while the trackers are positioned on a person.

[0077] FIG. 5 diagrammatically shows a representation of how a computing device has established (second) directions of trackers with regards to the embodiment of FIG. 4.

[0078] FIG. 6 diagrammatically shows a coronal plane of a user of a motion tracking system.

DETAILED DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 diagrammatically shows a motion tracking system 5 in accordance with embodiments. The motion tracking system 5 includes a computing device 10, which may be e.g. a tablet, a mobile phone, a personal computer, etc., and one or more trackers 20a-20n, i.e. inertial measurement units.

[0080] Each tracker 20a-20n includes one or more inertial sensors selected from e.g. an accelerometer 21, a gyroscope 22 and a magnetometer 23. In the embodiment of FIG. 1, each tracker 20a-20n includes all three inertial sensors 21-23, but in other embodiments the trackers only include an accelerometer 21 and a gyroscope 22, for instance. Preferably, all IMUs 20a-20n include the same inertial sensors 21-23.

[0081] The trackers 20a-20n further include at least one processor 24, at least one memory 25, and a first wireless communications module 26 for transmitting radiofrequency signals to and receiving radiofrequency signals from the computing device 10. For example, the trackers 20a-20n transmit advertisement packages, data packets with identification data (e.g. one or more identities, keys, etc.), data packets with measurements of the inertial sensor(s) 21-23, data packets with directions computed by the trackers, combinations thereof, etc., and receive packets from the computing device 10 with e.g. instructions to compute an angle of arrival of incoming communications, identification data, etc. At least when no wireless communications connections are established with the computing device 10, the radiofrequency signals of the trackers 20a-20n include advertisement packages for indicating their presence and that they are active. Once the wireless communications connections are established (using a technology and protocol known by a skilled person, for instance but without limitation, Bluetooth and Bluetooth Low Energy communications, cellular network communications such as GSM, UMTS or LTE, wireless LAN communications, etc.) with the computing device 10, the radiofrequency signals of the trackers 20a-20n may include identification data, directions, and/or the measurements, based on which the motion tracking sequence will be provided by the computing device 10.

[0082] In some aspects and in some embodiments, each tracker 20a-20n comprises a plurality of antennas 28 for radiating and capturing electromagnetic waves as part of the operation of the first wireless communications module 26. In some other aspects and in some other embodiments, each tracker 20a-20n comprises one antenna 28.

[0083] Each tracker 20a-20n is adapted to be arranged on the body of a person so that the measurements provided by each tracker 20a-20n can be processed by the computing device 10, thereby providing a motion tracking sequence of the person. The trackers 20a-20n may be attached to body members of the person by means of an attaching device 27 like, for instance, straps, Velcro, etc., that the motion tracking system 5 or the tracker 20a-20n itself comprises.

[0084] Preferably, at least one processor 24 of the trackers 20a-20n runs a sensor fusion algorithm for processing the measurements of the inertial sensors 21-23 within the respective tracker. The sensor fusion algorithm is intended to enhance the raw measurements of the inertial sensors by correcting errors thereof due to drifts of the inertial sensors and, thus, outputs processed measurements that are to be transmitted to the computing device 10.

[0085] The computing device 10 includes at least one processor 11, at least one memory 12, and a second wireless communications module 13 for transmitting radiofrequency signals to the trackers 20a-20n and receive radiofrequency signals therefrom. In some aspects and in some embodiments, the computing device 10 includes a plurality of antennas 14, whereas in some other aspects and in some other embodiments, the computing device 10 includes one antenna 14. The antenna(s) 14 cooperate with the second wireless communications module 13.

[0086] In all aspects and embodiments, at least one among the trackers 20a-20n and the computing device 10 comprise a plurality of antennas 14, 28. In some embodiments, both the trackers and the computing device 10 comprise a plurality of antennas 14, 28.

[0087] The motion tracking system 5 also includes at least one device 15 (which can be part of the computing device 10 or be separate from the computing device 10) for providing user perceptible signals like e.g. a screen or loudspeakers, to name a few examples. That is to say, the at least one device 15 comprises one or more of visual output means (e.g. screen, LEDs), audio output means (e.g. loudspeakers), vibrating means (e.g. a vibrator), etc. for providing user perceptible signals in the form of sounds, vibration, animated graphics, etc.

[0088] When the at least one device 15 comprises a screen, the computing device 10 is capable of showing instructions and/or information to the intended user about the operation of the motion tracking system 5 and the motion tracking procedure to be conducted with the system 5, for example predetermined movements that are to be performed by an intended user of the motion tracking system 5, a list or representation of the body members that shall have a tracker arranged thereon for a given exercise or motion tracking procedure, results of the exercises performed by the user, etc. To this end, the computing device 10 stores, in the at least one memory 12, the predetermined body members where the trackers must be positioned, and also data relative to the physical exercises, i.e. predetermined movements, of intended users. Any of these data can be transmitted to and/or received from another electronic device thanks to the second wireless communications module 13. For example, a therapist is able to receive the feedback at a computing device in a hospital so as to monitor the evolution of the person. Based on the feedback received, the therapist is able to adjust the difficulty of the movement(s), the number of repetitions thereof, prescribe new movements, etc. so that the person may further exercise using the motion tracking system 5.

[0089] FIGS. 2A and 2B diagrammatically show an exemplary angle of arrival 30 computation in motion tracking systems in accordance with embodiments from two different views. For the sake of clarity only, one tracker 20a-20n has been represented although a motion tracking system according to the present disclosure comprises a multiplicity of trackers 20a-20n.

[0090] In this example, the computing device 10 of a motion tracking system comprises at least one antenna 14 (in this example one antenna whereas, in some embodiments, it is two antennas, three antennas or even more antennas), and the trackers 20a-20n of the system each comprises a plurality of antennas 28a-28c (in this example three antennas whereas, in some embodiments, it is two antennas, four antennas or even more antennas) that, moreover, is arranged so as to form a two-dimensional array. This, in turn, allows more accurate computation of angle of arrival in the vertical direction (i.e. the Z axis direction).

[0091] The computing device 10 transmits data packets by way of electromagnetic waves 19 (shown as arcs for the sake of simplicity only, it will be noted that the radiation by the antennas is typically omnidirectional) radiated through at least one antenna 14. The electromagnetic waves 19 are captured by each of the antennas 28a-28c of each tracker 20a-20n, and each tracker 20a-20n computes, based on the waves 19 that the antennas 28a-28c it respectively comprises have captured, an angle of arrival 30. As it can be appreciated from the represented waves 19, a same wave arrives at each antenna 28a-28c with a different phase and time delay, which once processed together with the phase and/or time delay of the same wave as received by the different antennas 28a-28c provides the angle of arrival 30. For the computation of the angles of arrival 30, each tracker has data indicative of how the antennas are arranged in the tracker so as to process the differences in phase and/or time delay, which can include the relative positions of each antenna to the others, the position of the antennas on a printed circuit board of the tracker, the distances between the antennas, etc. Also, in some embodiments, data indicative of the orientation of the trackers is used in addition to the arrangement of the antennas for the computation of the angles of arrival 30, which makes possible to compute the angles more accurately; said data is preferably the measurements of one or more sensor device(s) of the tracker, e.g. measurements of the gyroscope and/or measurements of the accelerometer.

[0092] As shown in the two different views of FIGS. 2A and 2B that each is a 2D representation, the angle of arrival 30 is typically decomposed in two angles or values 30X, 30Z, one for a horizontal component 30X, in this case the horizontal component is with respect to an XY plane, and one for a vertical component 30Z, in this case the vertical component is with respect to an XZ plane. The angle of arrival 30 and the components thereof can be computed with respect to any axis predefined in the trackers, in this example the axis 33 (represented with a dashed line for illustrative purposes only) is parallel to the X axis.

[0093] With the angle of arrival 30X, 30Z computed, each tracker 20a-20n computes a first direction 32 (shown with a dashed line for illustrative purposes only) indicative of where the computing device 10 or the at least one antenna 14 thereof is relative to the respective tracker 20a-20n. In this example, the direction 32 is defined with respect to a middle point of a front face or edge of the illustrated tracker, but other point could be used instead, for example a corner, a center of the tracker, etc.

[0094] The trackers 20a-20n preferably compute angles of arrival 30 during a calibration time window, for instance at the beginning of the motion tracking session. The calibration time may have predetermined minimum and maximum times so as to delimit the time it takes to perform the assessment of the positions of the trackers.

[0095] Additionally, the angles of arrival 30 may be computed for the different packets received from the computing device 10 and then each tracker computes a respective mean angle of arrival by averaging the different angles of arrival 30, thereby reducing errors in angles of arrival due to sudden changes that may be caused, for instance, by interferences. In this sense, mean angles of arrival may be computed for each of the two components, namely the horizontal and vertical components of the angles of arrival. The averaging for the mean angles of arrival is carried out for packets received during the calibration time, and can be of as many packets as received during said calibration time or in a time window within the calibration time, in which case it is preferably a sliding time window that slides within the calibration time; the duration of the time window may have predetermined minimum and maximum times as well and be defined in time (e.g. 1 second, 2 seconds, etc.) or as a percentage of the calibration time (e.g. 10% of the calibration time, 15%, etc.).

[0096] In embodiments like the one illustrated, the angle of arrival 30 is computed by each tracker 20a-20n and is subsequently transmitted to the computing device 10, either as the angle of arrival 30, as the first direction 32, or an analogous value or parameter.

[0097] In other embodiments, the computing device 10 comprises a plurality of antennas and upon reception of electromagnetic waves radiated by each tracker (which may comprise one antenna or a plurality of antennas), the device 10 processes the phase and/or time delay thereof in the same manner described and computes the angle of arrival 30 and the first directions 32 for each tracker 20a-20n. For the computation, the computing device 10 has data indicative of how the antennas are arranged therein (e.g. relative positions of antennas, positions on a printed circuit board of the computing device, the distances between the antennas, etc.) so as to process the differences in phase and/or time delay. Also, in some embodiments, the computing device uses data indicative of the orientation of the trackers (in addition to the arrangement of the antennas) for the computation of the angles of arrival 30, which makes possible to compute the angles more accurately; said data is preferably the measurements of one or more sensor device(s) of the tracker, which are transmitted in packets to the computing device 10 (for instance, said packets are used by the computing device 10 to compute the angles of arrival 30).

[0098] Further, in addition to the angles of arrival 30 and the first directions 32, distances between the computing device 10 and each tracker 20a-20n can also be computed for enhanced position assessment of the trackers. The trackers 20a-20n can include the RSSI in the data packets where the first direction is sent to the computing device 10, or the computing device 10 may estimate the distance by processing the differences in RSSI or level of power between the wireless communications with each tracker 20a-20n, so an RSSI or level of power in the communications with a first tracker that is lower than an RSSI or level of power in the communications with a second tracker represents a greater distance for the first tracker. With reference to what is illustrated in FIGS. 2A and 2B, a distance between the computing device 10 and a tracker 20a-20n is a length of the first direction 32 illustrated.

[0099] The computing device 10 then uses the received data to compute second directions, i.e. the direction that each tracker 20a-20n is relative to the other trackers.

[0100] FIGS. 3A and 3B diagrammatically show an exemplary angle of departure 31 computation in motion tracking systems in accordance with embodiments from two different views. For the sake of clarity only, one tracker 20a-20n has been represented although a motion tracking system according to the present disclosure comprises a multiplicity of trackers 20a-20n.

[0101] In this example, the computing device 10 of a motion tracking system comprises at least one antenna 14 (in this example one antenna whereas, in some embodiments, it is two antennas, three antennas or even more antennas), and the trackers 20a-20n of the system each comprises a plurality of antennas 28a, 28b (in this example two antennas whereas, in some embodiments, it is three antennas, four antennas or even more antennas).

[0102] The trackers 20a-20n transmit data packets by way of electromagnetic waves 29a, 29b (shown as arcs for the sake of simplicity only, it will be noted that the radiation by the antennas is typically omnidirectional) radiated through each antenna 28a, 28b. The electromagnetic waves 29a, 29b are captured by the at least one antenna 14 of the computing device 10, and the device 10 computes, based on the waves 29a, 29b that the at least one antenna 14 has captured, an angle of departure 31. As it can be appreciated from the represented waves 29a, 29b, each antenna 28a, 28b radiates its own waves 29a, 29b of a same data packet, and each wave 29a arrives at the at least one antenna 14 with a different phase and time delay, which once processed together provides the angle of departure 31. For the computation of the angles of departure 31X, 31Z, the computing device 10 has data indicative of how the antennas of each tracker 20a-20n are arranged therein so as to process the differences in phase and/or time delay; to that end, the computing device 10 may have that the data already stored therein, for instance because the motion tracking system has predetermined trackers and the data about the antennas is already stored in a memory communicatively coupled with a processor of the computing device 10, or the trackers 20a-20n also transmit that data to the computing device 10. Likewise, in some embodiments, the computing device 10 uses data indicative of the orientation of the trackers 20a-20n (in addition to the arrangement of the antennas) for the computation of the angles of departure 31, which makes possible to compute the angles more accurately; said data is preferably the measurements of one or more sensor device(s) of the tracker 20a-20n, which are transmitted in packets to the computing device 10 (for instance, said packets are used by the computing device 10 to compute the angles of departure 31).

[0103] Like the angle of arrival 30 described in relation to FIGS. 2A and 2B, the angle of departure 31 is typically decomposed in two angles or values 31X, 31Z in the same manner described. And like the angle of arrival 30, the angle of departure 31 might be computed within a calibration time window and/or a mean angle of departure can be computed, including in decomposed form as horizontal and vertical components.

[0104] Further, in addition to the angles of departure 31 and the first directions 32, distances between the computing device 10 and each tracker 20a-20n can also be computed for enhanced position assessment of the trackers as described with reference to FIGS. 2A and 2B.

[0105] With the angle of departure 31 computed, the computing device 10 computes a first direction 32 (shown with a dashed line for illustrative purposes only) indicative of where each tracker 20a-20n is relative to the computing device 10 or the at least one antenna 14. Then the computing device 10 may further compute the second directions.

[0106] FIG. 4 shows a motion tracking system in accordance with embodiments while the trackers are positioned on a person 1. For the sake of clarity only, the person 1 is shown as a simplified set of segments of body members 3a-3e and joints 2 that the body members 3a-3e are connected with.

[0107] The person 1 has a first tracker 20a positioned on a chest 3a, a second tracker 20b positioned on a left upper leg or thigh 3b, a third tracker 20c positioned on a left lower leg or shank 3c, a fourth tracker 20d positioned on a right upper leg or thigh 3d, and a fifth tracker 20e positioned on a right lower leg or shank 3e. It will be noted that other pluralities of trackers and other tracker positioning are possible within the scope of the present disclosure.

[0108] A computing device 10 intends to assess the position of each of the five trackers 20a-20e. To that end, the computing device 10 has data indicative of the body members that shall have a tracker arranged thereon for the motion tracking procedure or physical exercise that is or is to be carried out. This means that, in this example, the computing device 10 has data indicating that the chest 3a, left thigh 3b, left shank 3c, right thigh 3d and right shank 3e shall have a tracker positioned thereon.

[0109] Following a procedure as described with reference to FIGS. 2A, 2B, 3A and 3B whereby the computing device 10 computes the angles of departure or angles of arrival, or the trackers 20a-20e compute the angles of arrival, the computing device 10 establishes second directions of trackers as described with reference to FIG. 5.

[0110] In FIG. 5 is illustrated a representation of the tracker positions 120a-120e corresponding to the first to fifth trackers 20a-20e of FIG. 4 by a computing device 10. This representation is shown for the sake of clarity only.

[0111] The computing device 10 for example computes the second directions as delta angles of arrival or delta angles of departure, which are the differences in the angles of arrival between each pair of trackers or the differences in the angles of departure between each pair of trackers. These delta angles can likewise be computed or decomposed in the components of the angles of arrival or departure so that there is a horizontal delta angle of arrival component and a vertical delta angle of arrival component for one tracker with respect to another tracker.

[0112] By processing these second directions and a list of body members that shall have a tracker arranged thereon, the computing device 10 provides a correspondence between trackers and body members. In this case, the first tracker position 120a is higher along the Z axis than the rest tracker positions 120b-120e, and so is the chest with respect to the thighs and shanks. The second and fourth tracker positions 120b, 120d are at a lower height (with respect to the Z axis) but at a higher height than third and fifth tracker positions 120c, 120e, like thighs with respect to the chest and the shanks. The second tracker position 120b is to the left (when seen from the user's perspective, not from the computing device's perspective) of the fourth tracker position 120d, so the second tracker position 120b corresponds to the left thigh and the fourth tracker position 120d corresponds to the right thigh. A similar assessment is made regarding the remaining tracker positions.

[0113] For the sake of clarity only, Tables 1 to 4 are presented next to describe numerically with exemplary values the assignation just explained. These Tables in no way limit the scope of the present disclosure to the following types of values, tracker arrangements, body members, etc., and are only intended to illustrate how the assignation is carried out in some embodiments.

TABLE-US-00001 TABLE 1 Possible ranges of the absolute value of the difference between the first directions of each tracker placed on each specific body member. The values presented regard the ranges of angles of arrival (i.e. AoA) on the horizontal plane. Absolute value Rel AoA − X Left Right Left Right (horizontal plane) Chest Thigh Thigh Shank Shank Chest — 10-30° 10-30° 10-30° 10-30° Left Thigh 10-30° — 30-60°  0-5° 30-60° Right Thigh 10-30° 30-60° — 30-60°  0-5° Left Shank 10-30°  0-5° 30-60° — 10-30° Right Shank 10-30° 10-30°  0-5° 30-60° —

TABLE-US-00002 TABLE 2 The possible signal (positive or negative) of the difference between first directions of each tracker placed on each specific part of the body. The signals presented regard the angles of arrival on the horizontal plane. The angle is considered as positive to the right of the virtual 0 axis on the horizontal plane (parallel line to the coronal plane on the computing device − X axis on the FIG. 4). Signal value Rel AoA − X Left Right Left Right (horizontal plane) Chest Thigh Thigh Shank Shank Chest — − + − + Left Thigh + — + +− near 0 + Right Thigh − − — − +− near 0 Left Shank + +− near 0 + — + Right Shank − − +− near 0 − —

TABLE-US-00003 TABLE 3 Possible ranges of the absolute value of the difference between the first directions of each tracker placed on each specific body member. The values presented regard the ranges of angles of arrival on the vertical plane (parallel plane to the sagittal plane). Absolute value Rel AoA − Z Left Right Left Right (vertical plane) Chest Thigh Thigh Shank Shank Chest — 20-30° 20-30° 40-50° 40-50° Left Thigh 20-30° —  0-5° 10-20° 10-20° Right Thigh 20-30°  0-5° — 10-20° 10-20° Left Shank 40-50° 10-20° 10-20° —  0-5° Right Shank 40-50° 10-20° 10-20°  0-5° —

TABLE-US-00004 TABLE 4 The possible signal (positive or negative) of the difference between first directions of each tracker placed on each specific part of the body. The signals presented regard the angles of arrival on the vertical plane (vertical plane is a parallel plane to the sagittal plane). The angle is considered as positive when at higher height of the virtual 0 axis on the vertical plane (perpendicular line to the coronal plane and parallel to the transverse plane on the computing device). Signal value Rel AoA − Z Left Right Left Right (vertical plane) Chest Thigh Thigh Shank Shank Chest — − − − − Left Thigh + — +− near 0 − − Right Thigh + +− near 0 — − − Left Shank + + + — +− near 0 Right Shank + + + +− near 0 —

[0114] FIG. 6 diagrammatically shows a coronal plane 40 of a user of a motion tracking system.

[0115] The person 1 using the motion tracking system, i.e. the user, is substantially facing away from the computing device 10. Even in such situation, the computing device 10 is capable of assessing the positions of the trackers (not illustrated) even if they are arranged on a front-most part of the person 1 like in FIG. 4. The coronal plane 40 goes through the middle of the body of the person 1 and contains the head of the person 1; it will be noted that the dashed line of the coronal plane 40 illustrated a cross-section since it extends along the Z axis.

[0116] In some embodiments, the computing device 10 or each of the trackers 20a-20n receives data packets based on which the first direction (by performing the angle of arrival or angle of departure computations explained above) while the person is in such posture that a normal vector 41 of the coronal plane 40 forms an angle with a line 45 intersecting both the computing device 10 and a belly button of the person 1 having an absolute value less than or equal to 45°, like in FIG. 6.

[0117] In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0118] On the other hand, the disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the disclosure as defined in the claims.