Field of the invention

[0001] The present invention relates to a method for tracking a user device or a radiation beam emitter by a user device. Background of the invention

[0002] Document WO2017/052938 A1 describes a method wherein gestures performed using a user device, i.e. a wand, are detected through sensors included in the wand. The sensor data representative of the gestures are converted into a spell sequence. The wand transmits then the spell sequence to a computing device.

[0003] The user device has therefore to include sensors, a data treatment device to convert the sensor data into a spell sequence and a transmission device to transmit the spell sequence to a computing device. A problem of such a method is the complexity of the required user device. Summary of the invention

[0004] It is an object of the present invention to provide a method suitable for recognition of gestures performed with a user device, the user device being of lower complexity than the user device described in WO2017/052938 A1 .

[0005] An object of the invention is to provide a method for tracking a user device comprising an emitter and an actuation system having several states, the method comprising the steps of :

• the emitter emits a radiation beam that carries a binary information in such a way that a first binary state of the binary information corresponds to presence of a pulse in the radiation beam and a second binary state of the binary information corresponds to absence of a pulse in the radiation beam, the binary information being suitable for identifying the user device and determining the state of the actuation system, and • a determination system:

o acquires images showing radiation coming from the emitter, and o from the images, identifies the user device, determines the state of the actuation system and a position of the radiation beam.

[0006] In the method according to the invention, gestures performed with the user device are reflected in the motion of the radiation beam, and a determination system, preferably outside the user device, detects the motion of the radiation beam. The determination system can thus deduce the gestures from the motion of the radiation beam. The user device does not have to carry motion sensors.

[0007] From several positions of the radiation beam, the determination system is able to determine a trajectory of the radiation beam.

[0008] When the gesture involves a motion of the user device over a given length, it gives rise to a motion of the radiation beam over a higher length at a given distance from the user device. It results in an amplification of the detected motion that provides an especially high precision to the method according to the invention.

[0009] In the method according to the invention, the radiation beam has a double purpose. First, it carries information for identifying the user device and determining the state of the actuation system. Second, its position makes possible to determine the position of a reflection point or a position of the emitter. The gesture performed with the user device can then be deduced from the position of the reflection point or the emitter. It is therefore possible to very efficiently determine and associate three pieces of information: the identification of the user device, the state of the actuation system and the gesture performed with the user device.

[0010] In the frame of the present document, a“tracking of a user device” might for example be understood as a tracking of at least one of: a means for identifying at least partially the user device, a state of an actuation system located on the user device, a position of the user device or of a part thereof or a position pointed by an emitter located on the user device.

[0011] The method according to the invention may also be considered as a method for tracking a radiation beam emitter by a user device.

[0012] The method according to the invention is performed in “the real world”, not in a virtual world. The method according to the invention may for example be used in an attraction park.

[0013] The user device is preferably rotatable in such a way that the direction of emission of the beam changes with its rotation. Preferably, the user device is portable. Preferably, the user device can be carried in the hand of a user. The user device is a real object, not a virtual object. The user device may have the shape of wand, a magic wand, a gun, a pen or any other object.

[0014] The user device stores, preferably in a memory, an identifier of the user device. The identifier might be fixed or might be changed in time. In such a case, the identifier is preferably stored in a writable memory.

[0015] The user device is preferably able to determine the state of the actuation system and to determine the binary information based on the identifier of the user device and the state of the actuation system. Other information may also be included in the binary information.

[0016] The user device preferably comprises a clock and an output stage to activate the emitter. The user device preferably comprises a modulation means to modulate the radiation beam. The user device preferably comprises a determination means to determine the binary information, for example as at least one coding sequence, and to determine a sequence of pulses that can be emitted by the emitter based on the binary information. This is preferably done using a software executed on the determination means of the user device. [0017] The user device may comprise an "on-off" button that switches off the emitter. The user device may comprise an accelerometer that switches off the emitter when it detects no motion of the user device. The user device may comprise any other sensor or electronic device.

[0018] The actuation system can preferably be actuated by a user carrying the user device.

[0019] The actuation system has at least two states. If it has only two states, these states are typically on and off. It can also have more than two states. The actuation system may comprise one or several actuation devices, each having at least two states. In such a case, the binary information is preferably suitable for determining the state of each actuation devices. Each actuation device might be for example a trigger or a button.

[0020] The emitter is able to emit an electromagnetic radiation beam, preferably infrared radiation and/or visible radiation. The emitter is preferably directional, i.e., it preferably emits the radiation beam essentially in one direction.

[0021] The radiation beam forms preferably a reflection point or a reflection shape, in infrared light and/or visible light, when it intercepts a surface.

[0022] In the frame of the present document, infrared radiation may be understood as infrared light, and visible radiation may be understood as visible light.

[0023] The emitter is preferably a laser, a light-emitting diode (LED) or a laser LED. The user device may comprise several emitters. Preferably, the different emitters emit beams in different directions.

[0024] Preferably, at least one of the emitters is arranged for emitting the radiation beam in the prolongation of the user device, for example by being placed at an end of the user device. For example, if the user device is elongated, the emitter may emit in the direction of elongation of the user device. The user can then "draw" with the user device and his drawing can be acquired by the determination system. [0025] The binary information is preferably made of bits having two states.

[0026] The binary information is preferably provided in the form of at least one sequence of bits. The sequence(s) of bits providing the binary information may be called "coding sequence(s)". Each coding sequence is preferably emitted as a sequence of pulses in the radiation beam. The bits of a coding sequence do not have to be next to each other in the sequence of bits corresponding to the sequence of pulses. For example, other bits might be intercalated between bits of a coding sequence. The bits of a coding sequence may be called "coding bits".

[0027] In an embodiment of the invention, one coding sequence is sufficient for identifying the user device. In such a case, preferably, the part of the coding sequence that represents the identification of the user device is identical every time the sequence of bits is sent. In an embodiment of the invention, several coding sequences are required for identifying the user device. In such a case, preferably, the part of the coding sequence that represents the identification of the user device is modified between several emissions of the sequence of pulses providing the binary information.

[0028] The coding sequence has preferably a fixed duration.

[0029] Preferably, a bit in the coding sequence corresponds to a pulse, or an absence of pulse in the radiation beam.

[0030] The coding sequence is preferably sent at a predetermined frequency, for example 10 to 25 times per second. In an embodiment of the invention, the coding sequence comprises a first data block that is suitable for identifying the user device and a second data block that is suitable for determining the state of the actuation system. The data blocks may be consecutive or combined.

[0031] In an embodiment of the invention, the coding sequence is preceded by a heading independent of the binary information. Preferably, the heading is the same for all user devices. [0032] The coding sequence of bits preferably corresponds to a coding sequence of pulses: one value of the bits (1 for example) corresponds to the presence of a pulse and one value of the bits (0 for example) corresponds to the absence of a pulse.

[0033] The determination system is able to capture images showing the beam emitted by the emitter. For example, if the emitter emits an infrared radiation beam, it is able to capture images including infrared radiation. The images showing radiation are images wherein the presence of the radiation is visible. The images are preferably digital images.

[0034] In the frame of the present invention, an“image” is a set of data that comprise data related to a location. It can be for example a one-dimension, a two-dimensions or a three-dimensions image. It can be a picture, a 2D or 3D matrix of pixels. Several images may be said to form a movie. Preferably, at time-stamp is associated with each acquired image.

[0035] The determination system may be able to acquire images comprising radiation coming directly and/or indirectly from the emitter(s) of the user device. In an embodiment of the invention, the determination system acquires images comprising radiation coming directly from the emitter. In such a case, the emitter typically appears on the images. In an embodiment of the invention, the determination system acquires images comprising radiation coming indirectly from the emitter. In such a case, the radiation beam is reflected by a surface forming thereon a reflection point or shape and the reflection point or reflection shape appears on the images.

[0036] Preferably, the determination system acquires images in continuous acquisition.

[0037] The determination system is a real object, not a virtual object. The determination system may be fixed. It can for example be mechanically coupled to a wall, to a ceiling or to a floor or a plurality thereof.

[0038] The determination system preferably comprises one or several acquisition devices, for example one or several cameras. If it comprises several acquisition devices, they are preferably placed in such a way to acquire images from different points of view, for example in order to follow the motion of the beam. The determination system may be able to use images provided by several acquisition devices to determine a position of the radiation beam.

[0039] The determination system preferably comprises a computer system formed by one or several devices able to perform data treatment, like at least one of: a server, a computer, a laptop or a plurality thereof.

[0040] In an embodiment of the invention, the determination system comprises an acquisition system and a computer system in communication. The communication between the acquisition system and the computer system can be unidirectional from the acquisition system to the computer system, or can be bidirectional. It can be wired, wireless or both.

[0041] The step of identifying the user device, determining the state of the actuation system and a position of the radiation beam from the images is preferably performed by a software running on the determination system.

[0042] The identifier of the user device is preferably linked, in a data base of the determination system, to a user.

[0043] The identification of the user device does not have to be unique. Indeed, if many user devices are used at the same time, a totally unique identification could require many bits. This can be solved by the tracking of the trajectory of the radiation beam.

[0044] The identification may also be improved by the recognition of the frame of the emitted sequence of bits. Since the frame does not start at the same moment for all the user devices, their temporal shift may be recognized by the determination system, in such a way that two user devices having the same identification are discernable by a temporal shift.

[0045] In an embodiment of the invention, the radiation beam includes periodic pulses in such a way that at least some of the periodic pulses are located in between bits providing at least part of the binary information. [0046] The pulses preferably repeat at a regular interval in time within the binary information, independently of the content of the binary information. Therefore, even if the coding sequence comprises only binary states that correspond to absences of pulses in the radiation beam, the emitter is regularly on and it is possible to follow the trajectory of the radiation beam.

[0047] The periodic pulses may be prevented outside the bits providing at least part of the identifier of the user device and the state of the actuation system.

[0048] The periodic pulses may be called non-coding bits. The sequence that is emitted comprises the coding bits of the coding sequence (coded as absence or presence of pulse) and regular non-coding bits (coded as presence of pulse).

[0049] The interlacing of the binary information, which provides an at least partial identification of the user device, with the regular pulses makes possible to maintain an association between a trajectory and a user device with a very high robustness. In other words, it provides an especially high sampling of the radiation beam pulses, which is especially useful when the trajectory of the radiation beam makes sudden changes of direction.

[0050] In an embodiment of the invention, the binary information is coded as a sequence of bits and at least one of the periodic pulses occur between every bit of the sequence.

[0051] In other words, the emitted sequence may comprise one coding bit, one non-coding bit, one coding bit, one non-coding bit, etc. For example, if the binary state that corresponds to presence of a pulse in the radiation beam is a 1 and the binary state that corresponds to absence of a pulse in the radiation beam is a 0, the emitted sequence comprises a sequence like: 1 a1 b1 c1 d... where the letters represent coding bits.

[0052] In an embodiment of the invention, the radiation beam carries a heading comprising at least two consecutive bits that correspond to an absence of pulse in the radiation beam and the periodic pulses are prevented in the heading.

[0053] For example, if the binary state that corresponds to presence of a pulse in the radiation beam is a 1 and the binary state that corresponds to absence of a pulse in the radiation beam is a 0, the heading may comprise a 00. Like that, since the heading does not comprise a 1 at every two bits, it can be recognized as not being part of the binary information.

[0054] Preferably, the heading precedes the binary information in the emitted sequence of pulses.

[0055] The heading may also be called "fixed sequence".

[0056] In an embodiment of the invention, the binary information includes at least twice a piece of information suitable for determining the state of the actuation system.

[0057] For example, the piece of information suitable for determining the state of the actuation system may be coded as one or several bits and said one or several bits may be repeated several times in the coding sequence. Preferably the one or several bits coding for the state of the actuation system are placed once in between bits coding for the identification of the user device and once after the bits coding for the identification of the user device.

[0058] Preferably, the user device and the determination system store, upfront the emission, the position of the piece of information suitable for determining the state of the actuation system in the coding sequence.

[0059] In an embodiment of the invention, a pulse representing the first binary state has a duration at least twice higher than a duration of acquisition of an image.

[0060] In other words, the acquisition frequency of the images is at least twice the pulse frequency when the emitted sequence of pulses comprises only bits corresponding to the presence of pulses. Therefore, the bits are shown in at least two successive images. [0061] In an embodiment of the invention, the actuation system comprises an actuation device having only two states and one of the states of the actuation device is represented in the binary information as the first binary state and the other of the states of the actuation device is represented in the binary information as the second binary state.

[0062] This simplifies the generation of the coding sequence by the user device and the determination of the state of the actuation device by the determination system. It also makes the determination of the state of the actuation device especially robust.

[0063] Preferably, the state of the actuation device is represented by a single bit in the coding sequence.

[0064] If the actuation system comprises several actuation devices having only two states, each actuation device may correspond to a given location in the coding sequence and its state may correspond to a value of this bit.

[0065] In an embodiment of the invention, the determination system acquires images showing the emitter.

[0066] In such a case, the determination system acquires images comprising radiation coming directly from the emitter. This makes easier the determination of the position of the user device.

[0067] In an embodiment of the invention, the determination system acquires images showing the radiation beam reflected on a surface.

[0068] In such a case, the determination system acquires images comprising radiation coming indirectly from the emitter. This makes easier the determination of the position pointed by the user device.

[0069] In an embodiment of the invention, the determination system performs a temporal prediction of a trajectory of the radiation beam based on acquired images.

[0070] It makes possible to anticipate the future positions of the radiation beam and thus to decrease the risk of wrong association between a user device and a position of the radiation beam. This is especially useful when several user devices are used at the same time.

[0071] In an embodiment of the invention, the binary information is provided as one sequence of bits suitable for identifying fully the user device and determining the state of the actuation system.

[0072] In an embodiment of the invention, the binary information is provided as several sequences of bits emitted one after each other and wherein the determination system uses several sequences of bits to identify the user device and determine the state of the actuation system.

[0073] In other words, the information required to determine the identifier is sent piecewise by the emitter. For example, a first sequence of bits may comprise a first part of the information required for identifying the user device and a second sequence of bits, sent alternately with the first sequence, may comprise a second part of the information required for identifying the user device. The determination system determines the identification of the user device from the first and the second parts.

[0074] It is possible that the user device corresponds to two identifiers, for example a local identifier and a global identifier. In such a case, the information providing the local identifier is preferably present more frequently in the emitted sequence of pulses than the information providing the global identifier. For example, the global identifier might be sent only once per second or once every two seconds.

[0075] The invention also relates to a system comprising:

• a user device comprising an emitter and an actuation system having several states, the emitter being suitable for emitting a radiation beam that carries a binary information in such a way that a first binary state of the binary information corresponds to presence of a pulse in the radiation beam and a second binary state of the binary information corresponds to absence of a pulse in the radiation beam, the binary information being suitable for identifying the user device and determining the state of the actuation system,

• a determination system suitable for:

o acquiring images showing radiation coming from the emitter, and

o from the images, identifying the user device, determines the state of the actuation system and a trajectory of the radiation beam.

[0076] The system according to the invention may comprise several user devices. The images can thus show several radiation points corresponding to different user devices. An advantage of the invention is that the determination system is able to link the position of a radiation point with the identifier of the user device and the state of the actuation system of this user device. Even if trajectories corresponding to different user devices are crossing or are chaotic, the determination system can determine the identifier of the user device.

[0077] The invention also relates to a computer program comprising instructions to cause a system according to an embodiment of the invention to execute a method according to an embodiment of the invention.

[0078] The computer program is preferably partially executed on the user device and partially executed on the determination system.

[0079] The invention also relates to a computer-readable medium having stored thereon the computer program according to an embodiment of the invention.

[0080] The computer-readable medium can be distributed on several physically distinct supports, for example it can include a first part on the user device and a second part on the determination system.

Brief description of the figures

[0081] For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings in which: - Figure 1 illustrates a user device and a determination system according to an embodiment of the invention,

- Figure 2 illustrates a user device and a determination system according to an embodiment of the invention,

- Figure 3 illustrates a user device and a determination system according to an embodiment of the invention,

- Figure 4 illustrates a user device according to an embodiment of the invention,

- Figure 5 illustrates a flowchart of a method according to an embodiment of the invention,

- Figure 6 illustrates a flowchart of an exemplary use of a method according to the invention in an attraction of an amusement park, and

- Figure 7 illustrates a flowchart of a method according to an embodiment of the invention.

Description of the invention

[0082] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto. The drawings described are only schematic and are non limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

[0083] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

[0084] Furthermore, the various embodiments, although referred to as “preferred” are to be construed as exemplary manners in which the invention may be implemented rather than as limiting the scope of the invention. [0085] The term“comprising”, used in the claims, should not be interpreted as being restricted to the elements or steps listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising A and B” should not be limited to devices consisting only of components A and B, rather with respect to the present invention, the only enumerated components of the device are A and B, and further the claim should be interpreted as including equivalents of those components.

[0086] On the figures, identical or analogous elements may be referred by a same number.

[0087] Figure 1 illustrates a user device 10 and a determination system 20 according to an embodiment of the invention. The illustrated user device 10 is a wand that can be handled by a user. The user device 10 comprises an emitter 1 1 at one of its ends and an actuation system 12 on its side. The emitter 1 1 emits a radiation beam 15 that can be directly captured by the determination system 20.

[0088] Figure 2 illustrates a user device 10 and a determination system 20 according to an embodiment of the invention. The illustrated user device 10 is a wand that can be handled by a user. The user device 10 comprises an emitter 1 1 at one of its ends and an actuation system 12 on its side. The emitter 1 1 emits a radiation beam 15 that reflects on a surface 30, for example as a reflection beam 32. The reflection beam 32 is therefore part of the radiation beam 15. The radiation beam 15 may for example appear on the surface 30 as a reflection point 31 . The reflection beam 32 can be captured by the determination system 20.

[0089] For example, the surface 30 can be a screen where an interactive movie showing targets is projected. The user acts on the movie by performing a motion with its user device 10 and by shooting with the actuation system 12 on the targets. The determination system 20 acquires images from the screen, these images showing the reflexion beam 32 coming from the emitter 1 1 . Due to the method according to the invention, the determination system 20 is then able to determine if the position of the radiation beam corresponds to a target, to determine if the actuation system is in a state of "shooting" when the radiation beam is on the target and to identify the user device. At the end of the game, the determination system is then able to determine a score linked to the shooting of the user on several targets.

[0090] Figure 3 illustrates a user device 10 and a determination system 20 according to an embodiment of the invention. The illustrated user device 10 is a wand that can be handled by a user. The user device 10 comprises a first emitter 1 1 a at one of its ends and a second emitter 1 1 b on its side. The user device 10 comprises an actuation system 12 on its side.

[0091] The determination system 20 comprises a first acquisition device 21 a directed to a surface 30, a screen, and a second acquisition device 21 b, directed to a location where a user holding the user device 10 is expected to stand. The determination system 20 may comprise more acquisition devices, typically recording images either from the surface 30 or from user devices 10.

[0092] The determination system 20 comprises also a computer system 22 in communication with the acquisition devices 21 a, 21 b.

[0093] In an exemplary use of the invention, the user holds the user device 10 and shoots, with the actuation system 12, on a movie projected on the screen 30. The reflection on a screen of a first radiation beam 15a, emitted by the first emitter 1 1 a, is viewed by the first acquisition device 21 a. The determination system 20 matches the position of the reflection of the first radiation beam 15a to targets visible on the screen. It can determine a score of the user thanks to binary information present in the first radiation beam and carrying the identification of the user device 10 and the state of the actuation system 12. A second radiation beam 15b, emitted by the second emitter 1 1 b, is viewed by the second acquisition device 21 b. The determination system 20 can thus determine the location of the user device 10, and, because of the binary information present in the second radiation beam, the identification of the user device 10 and the state of the actuation system 12.

[0094] Figure 4 illustrates a user device 10 according to an embodiment of the invention. The illustrated user device 10 is a gun that can be handled by a user. The user device 10 comprises a first emitter 1 1 a at one of its ends and a second emitter 1 1 b on its side. The user device 10 comprises a first actuation device 12a on its side and a second actuation device 12b which is a pistol trigger.

[0095] For example, the second actuation device 12b and the first emitter 1 1 a can be used mainly for shooting. The reflection on a surface of a first radiation beam, emitted by the first emitter 1 1 a, is viewed by a first acquisition device (non-illustrated) directed to the surface. The determination system 20 matches the position of the first radiation beam to targets visible on the screen and determines if the second actuation device 12b is triggered where the first radiation beam is on a target to determine a score. The second emitter 1 1 b may be used mainly for tracking of the position of the user device 10 itself, for example to check if at the moment of shooting, the user device 10 is in an area dedicated for shooting.

[0096] Figure 5 illustrates a method according to an embodiment of the invention.

[0097] At step 1 10, the emitter 1 1 of the user device 10 emits a radiation beam 15. The radiation beam 15 carries a binary information in such a way that a first binary state of the binary information corresponds to presence of a pulse in the radiation beam 15 and a second binary state of the binary information corresponds to absence of a pulse in the radiation beam 15. The binary information is suitable for identifying the user device 10 and determining the state of the actuation system 12 of the user device 10. For example, the binary information takes the form of a coding sequence 203, an interlaced sequence 205 or a headed sequence 207, or of several successive coding sequences 203, interlaced sequences 205 or headed sequences 207 (Figure 7).

[0098] At step 120, the determination system 20 acquires images showing radiation coming from the emitter 1 1 .

[0099] At step 130, the determination system 20 identifies the user device 10, determines the state of the actuation system 12 and a position of the radiation beam 15 based on the acquired images.

[0100] Figure 6 illustrates an exemplary use of a method according to the invention in an attraction of an amusement park.

[0101] At step 101 , a user enters the attraction.

[0102] At step 102, the user is provided with the user device 10. The user device 10 may be associated with the name of the user and this association stored in a memory of the determination system 20.

[0103] At step 103, the user goes to a first room of the attraction. His challenge there is to execute a given shape on a screen. Fie triggers the actuation system 12 and performs the expected shape on the screen. The determination system acquires images from the screen showing the radiation beam coming from the emitter and reflected by the screen as a point. The determination system uses the images to identify the user device and to determine a trajectory of the reflection point of the radiation beam. It also determines, from the images, if the actuation system was triggered during the realization of the trajectory. If the actuation system was triggered and if the trajectory is the expected shape, the determination system may send an instruction to a projection system in such a way that the screen indicates that the user, designated by his name, has fulfilled the challenge. A score might be associated with the fulfilment of the challenge. [0104] At step 104, the user goes to a second room of the attraction. His challenge there is to shoot on targets appearing on a screen. He triggers the actuation system 12 to shoot when he sees a target on the screen. The determination system acquires images from the screen showing the radiation beam coming from the emitter and reflected by the screen as a point. The determination system uses the images to identify the user device and to determine a position of the point. It correlates the position of the point, the information indicating that the actuation system 12 was triggered and the timing of the image with the projected target to determine if the target was touched. If the actuation system was triggered and if the point was on a target, the determination system may send an instruction to a projection system in such a way that the screen indicates that the user, designated by his name, has touched the target. A score might be associated with the touching of targets.

[0105] More rooms, with similar or different challenges might be present in the attraction.

[0106] At step 105, the determination system 20 determines a score for the whole attraction, from scores in each room.

[0107] Many users might be present in rooms at the same time.

[0108] Preferably, all users directing their emitter 1 1 on a screen at a given moment have different identifiers.

[0109] Preferably, all users in a given room of the attraction at a given moment have different identifiers. However, if the attraction is such that it is possible to group users into groups, in such a way that users of different groups can only direct their emitter 1 1 to different screens of the room, a same identifier may be present in different groups in the same room. Preferably, there is a record of which group is on which screen at which moment in order to univocally link a radiation beam with a user device 10. [0110] An identifier of user device 10 may also be used several times, for example, if only one user device 10 with a given identifier is present at a time in the attraction.

[0111] The user device 10 may also be provided to the user when he enters the attraction park in such a way that it stays with the user during the whole visit of the attraction park. In such a case, the information required to determine the identifier is preferably sent piecewise by the emitter 1 1 , in such a way that the determination system combines several coding sequences 203 (Figure 7) to determine the identifier.

[0112] Figure 7 illustrates a method according to an embodiment of the invention.

[0113] At step 210, a determination means, comprised preferably in the user device 10, takes as inputs identification information 201 of the user device 10 and the state 202 of the actuation system 12 and determines a coding sequence 203. It is possible that other pieces of information are placed in the coding sequence 203.

[0114] The coding sequence 203 may be said as consisting of“coding bits”, since it is preferred that all bits of the coding sequence 203 carry an information.

[0115] Preferably, the coding sequence 203 comprises at least twice the bit(s) indicating the state 202 of the actuation system 12. In other words, the binary information includes at least twice a piece of information suitable for determining the state of the actuation system 12.

[0116] If an actuation device 12b (Figure 4) of the actuation system 12 has only two states, the state 202 of the actuation system is preferably coded as a single bit in the coding sequence 203. One state of the actuation device 12b is given by a value 1 of this bit and the other by the value 0 of this bit. In other words, one of the states of the actuation device 12b is represented in the binary information as the first binary state and the other of the states of the actuation device 12b is represented in the binary information as the second binary state.

[0117] The identification information 201 may be the identifier of the user device 10, in such a way that the identification information 201 is sufficient to identify the user device 10. The identification information 201 may be part of the identifier of the user device 10, in such a way that the identification information 201 has to be combined with other pieces of information to identify the user device 10, for example with other identification information included in a further coding sequence 203.

[0118] For example, the identification information 201 of the user device 10 may be coded in 8 bits and the actuation system may have two states represented by one bit. It is possible to represent the identification information 201 as abcdefgh where each letter is a binary number that can take the values 0 or 1 and the state 202 of the actuation system as x where x is a binary number that can take the values 0 or 1 . The coding sequence 203 is a sequence of bits that might for example be written as abcdefghx, abcxdefgh or abcxdefghx. The user device and the determination system preferably know in advance where the bit(s) coding the state 202 of the actuation system are located in the coding sequence 203. The user device and the determination system preferably know in advance where the bit(s) coding the identification information 201 are located in the coding sequence 203.

[0119] In the case of the sequence abcxdefghx, the coding sequence 203 includes, in this order, some bits suitable for identifying the user device 10 (abc), at least one bit suitable for determining the state of the actuation system 12 (x), some bits suitable for identifying the user device 10 (defgh) and at least one bit suitable for determining the state of the actuation system 12 (x). [0120] If the identification information 201 is the sequence 01 101001 and the state 202 of the actuation system is 1 , the coding sequence 203 abcxdefghx is 01 1 101001 1 .

[0121] At step 220, the coding sequence 203 is divided into groups of coding bits, and non-coding bits 204 are placed between these groups.

[0122] The result of step 220 might be called an“interlaced sequence” 205. The non-coding bits preferably have all the same value. More preferably, this value corresponds to a pulse in the radiation beam emitted by the emitter 12. The consequence of step 220 is that the radiation beam 15 includes periodic pulses in such a way that at least some of the periodic pulses are located in between bits providing at least part of the binary information.

[0123] A group of coding bits preferably comprise only one bit. In other words, the binary information is coded as a sequence of bits and the periodic pulses occur between every bit of the sequence.

[0124] However, it is possible, within the scope of the invention, that a group of coding bits comprises two, three, four or more bits. Preferably, all groups have the same number of bits.

[0125] For example, if 1 is the binary value that corresponds to a pulse in the radiation beam and 0 is the binary value that corresponds to an absence of pulse in the radiation beam, the interlaced sequence 205 might be written as 1 a1 b1 c1 d1 e1 f1 g1 h1 x, 1 a1 b1 c1 x1 d1 e1 f1 g1 h or 1 a1 b1 c1 x1 d1 e1 f1 g1 h1 x.

[0126] If the identification information 201 is the sequence 01 101001 and the state 202 of the actuation system is 1 , the interlaced sequence 205 1 a1 b1 d x1 d1 e1 f1 g1 h1 x is 101 1 1 1 1 1 101 1 10101 1 1 1 .

[0127] At step 230, the user device 10 places a heading 206 ahead of the interlaced sequence 205 to provide a headed sequence 207.

[0128] Preferably, the heading 206 comprises two consecutive bits that correspond to an absence of pulse in the radiation beam 15. Like that, since the determination device 20 knows that the sequence that comprises the information being suitable for identifying the user device 10 and determining the state of the actuation system 12 comprises a pulse every two bits, the determination device 20 can easily locate the heading 206, which does not comprise a pulse every two bits.

[0129] If the interlaced sequence 205 is 101 1 1 1 1 1 101 1 10101 1 1 1 and the heading 206 is 100, the headed sequence 207 is

100101 1 1 1 1 1 101 1 10101 1 1 1 .

[0130] Steps 210 to 230 may be performed in another order than the order described in reference to Figure 7.

[0131] At step 240, the emitter 12 emits a radiation beam that comprises a sequence of pulses 208. Preferably, the sequence of pulses 208 comprises pulses that correspond to the headed sequence 207. It is also possible that the radiation beam 15 comprises pulses that correspond to the coding sequence 203 or to the interlaced sequence 205. Indeed, the coding sequence 203, the interlaced sequence 205 and the headed sequence 207 are sequences of bits providing binary information suitable for identifying at least partially the user device 10 and determining the state of the actuation system 12.

[0132] For example, if the headed sequence 207 is

100101 1 1 1 1 1 101 1 10101 1 1 1 , the sequence of pulses 208 is on-off-off-on- off-on-on-on-on-on-on-on-off-on-on-on-off-on-off-on-on-on-on . The “on” indicates that there is a pulse. The“off” indicates an absence of pulse.

[0133] A sequence of pulses 208 may for example be emitted by the emitter between 10 and 25 times per second.

[0134] At step 250, the determination system 20 acquires a sequence of images 209 showing the sequence of pulses 208. Preferably, the determination system 20 is arranged for recording each pulse on at least two images of the sequence of images 209. In other words, a pulse representing the first binary state has a duration at least twice higher than a duration for acquisition of an image.

[0135] The images 209 may show the emitter 12 itself or may show the reflection of the radiation beam 15 on a surface 30.

[0136] At step 260, the determination system 20 uses the sequence of images 209 to determine the identification information 201 , the state 202 of the actuation system 12 and a position 21 1 of the radiation beam. The position 21 1 can be the position of the emitter 12 or the position of reflection of the radiation beam 15 on a surface.

[0137] To determine the identification information 201 and the state 202 of the actuation system 12, the determination system 20 uses the sequence of pulses 208. For example, the sequence of images 209 is processed to determine the headed sequence 207. Then, the heading 206 is removed to obtain the interlaced sequence 205. Then, the non-coding bits 204 are removed to obtain the coding sequence 203. Then, the identification information 201 and the state 202 of the actuation system 12 are extracted from the coding sequence 203.

[0138] Steps 210 to 260 are then repeated, taking into account a possible different state 202 of the actuation system 12.

[0139] If the identification information 201 is sufficient to identify the user device 10, step 210 preferably always uses the same identification information 201 . This corresponds to the case where the binary information is provided as one sequence of bits suitable for identifying fully the user device 10 and determining the state of the actuation system 12.

[0140] If the identification information 201 is only part of the identifier of the user device 10, the next iteration of step 210 preferably takes another part of the identifier of the user 10. Preferably, through several iterations of steps 210 to 260, the identifier of the user device 10 is fully transmitted to the determination system through several sequences of radiation beams 208. This corresponds to the case where the binary information is provided as several sequences of bits emitted one after each other. The determination system 20 uses then several coding sequences, obtained through several sequences of pulses 208, to identify the user device 10.

[0141] At step 270, the determination system 20 determines a trajectory 212 of the radiation beam based on the identifier of the user device 10 and on the position 21 1 of the radiation beam or on identification information 201 and on the position 21 1 of the radiation beam. Preferably, the determination system 20 also performs a temporal prediction of a trajectory of the radiation beam based on the same information.

[0142] In other words, the invention relates to a method for tracking a user device 10. The user device 10 comprises an actuation system 12, which can be actuated by a user, and an emitter 1 1 of a radiation beam 15. The radiation beam 15 sends, through pulses, a binary information suitable for identifying at least partially the user device 10 and a state of the actuation system 12. A determination system 20 gets images representing the emitter 1 1 or a reflection point 31 of the radiation beam 15. From these images, the determination system 20 determines the identifier of the user device 10, the state of the actuation system 12 and the position of the emitter 1 1 or of the reflection point 31 of the radiation beam 15.

[0143] Although the present invention has been described above with respect to particular embodiments, it will readily be appreciated that other embodiments are also possible.