Method for controlling a graphical interface to display the throwing of projectiles in a virtual environment

Abstract

The present invention relates to a method for controlling a graphical interface (2) to display an image of a digital representation (31) of a projector (10) in a virtual environment Ev, said projector comprising a projection arm (12) equipped with a magnet (15). A magnetometer M i array measures the magnetic field generated by said magnet (15), a state vector of said projection arm (12) in a virtual reference frame Rv is determined, and standby and then launch phases of a projectile in said virtual reference frame Rv are identified. An image is then constructed and displayed on said graphical interface (2).

Description

Technical Field

[0001] The present invention relates to a method and a device for controlling a graphical interface to display an image of a three-dimensional object (here a projector) in a predefined virtual environment. Background Art

[0002] There are devices and methods for controlling a graphical interface to display an image of a virtual three-dimensional object, such as a building or a vehicle, or even a town. The virtual three-dimensional object can form a "virtual environment" to be displayed on the graphical interface, especially when it is a town or a neighborhood.

[0003] To this end, the virtual three-dimensional object is encoded in a digital file and the control method enables the image of the virtual three-dimensional object to be displayed on a graphical interface, for example, on the screen of a computer or electronic tablet. The digital file then includes the positions of all points of the virtual three-dimensional object in a so-called three-dimensional virtual reference system.

[0004] Patent EP2994813 B1 describes an example of a device and method for controlling a graphical interface to display an image of a virtual three-dimensional object. It comprises a pointer equipped with a magnet that can be manipulated by the user in a tracking area. The positioning of the pointer is ensured by a positioning device comprising an array of magnetometers. When the pointer approaches or moves away from the virtual three-dimensional object, the displacement of the pointer in the tracking area makes it possible to determine the optical axis of the field of view of the virtual three-dimensional object, as well as the scale factor.

[0005] However, there is a need for apparatus and methods for controlling a graphical interface that enable dynamic interaction with a virtual environment represented in a displayed image. Summary of the invention

[0006] The object of the present invention is to at least partially remedy the deficiencies of the prior art, and more specifically, to propose a method for controlling a graphical interface, which enables a user to dynamically interact with a virtual environment using actual (i.e., physical, non-digital) three-dimensional objects that can be manipulated by the user, and more specifically, to propose casting a projectile in a virtual environment along a trajectory defined by the user.

[0007] To this end, the subject of the invention is a method for controlling a graphical interface to display an image of a digital representation of a three-dimensional object, called a projectile, in a virtual environment, the projectile being designed to project projectiles in the virtual environment and comprising a structure made of non-magnetic material to which a projection arm is assembled in a movable and motion-restricted manner, and to which a magnet is fixed.

[0008] The method is implemented by a computing unit and comprises the following steps:

[0009] o providing a positioning device for positioning a projector in a tracking area, comprising: a magnetometer array fixed to a supporting surface; a computing unit connected to the magnetometer array and a graphical interface; a predefined tracking area for tracking the projector relative to the magnetometer array, and a so-called actual three-dimensional reference system associated with the tracking area;

[0010] o In the computing unit are stored: a digital file and a digital model; the digital file encodes the virtual environment in a so-called virtual three-dimensional reference system, which is associated to the real reference system by means of a predefined mapping relationship; the digital model enables the state vector X of the projection arm representing the position and / or orientation of the projection arm in the virtual reference system to be converted into a real reference system; b,v The state vector X of the magnet represents the position and orientation of the magnet in the actual reference frame. a|r associated with and enabling a digital representation of the projector in a virtual reference system to be obtained;

[0011] o the projection arm is operated by a user, the projector is located in the tracking area and arranged to contact the support surface, the projection arm can be moved away from the rest position by the user, and the resetting component applies a resetting force on the projection arm in the direction of the rest position;

[0012] ○ The magnetometer array measures the magnet at different successive measurement times t n The generated magnetic field;

[0013] ○At the measuring time t n , based on the measured values ​​of the magnetic field generated by the magnet, determine the state vector X of the magnet in the actual reference frame a|r ;

[0014] ○ Based on a pre-stored digital model and a predetermined state vector X a|r , at the measuring time t n , determine the state vector X of the projection arm in the virtual reference system b|v , and the projectile's position P p|v ;

[0015] ○According to the measurement time t n and the state vector X at the previous measurement time b|v The so-called standby factor K1 is defined to identify the standby phase of the projection arm, when the standby factor K1 is greater than or equal to a predetermined threshold value K 1S When the system is in standby mode, identify the standby phase;

[0016] ○ When the standby phase is identified, according to the measurement time t n By the state vector X b|v The so-called projection factor K2 is defined to identify the launch of a projectile when the projection factor K2 is greater than or equal to a predetermined threshold value K 2S When a missile is launched, the launch of the missile is identified;

[0017] o When the launch of a projectile is identified, the subsequent positions P of the projectile in the virtual reference system at subsequent measurement times are determined p|v ;

[0018] ○ Based on the predetermined state vector X of the projection arm b|v and the projectile's intended position P p|v , constructs a two-dimensional image representing the virtual environment, the digital representation of the projector and the projectile in the virtual reference system, and then controls the graphical interface through the computing unit to display the constructed image.

[0019] Some preferred but non-limiting aspects of the control method are as follows.

[0020] The digital model also enables the state vector X of the projectile, which represents the position and orientation of the projectile in the virtual reference system, to be l,v With the state vector X of the magnet a|r In this case: during the operating step, the user can also operate the projectile; when determining the state vector X of the projectile arm b|v During the step, it is also possible to calculate the state vector X based on the pre-stored digital model and the predetermined state vector X. a|r , determine the state vector X of the projector l,v During the construction step, the two-dimensional image can be based on the state vector X of the projector l|v , showing a digital representation of the projector.

[0021] Determine the successive positions P of the projectiles p|v The step can include identifying the determined successive positions P p|v An intersection between one of the surfaces of the virtual environment and a surface representing an impact of the projectile is determined, and a flight time is determined between a measurement time identifying the launch of the projectile and a measurement time corresponding to the impact.

[0022] During the measurement moments belonging to the said flight time, the phase of identifying the standby, identifying the launch of the missile and determining the successive positions P of the missile may not be carried out. p|v steps.

[0023] The standby factor K1 can be defined based on the tilt angle of the magnet when the projection arm is assembled to the structure by the pivot link, and / or the position along an axis normal to the support surface, and / or the position along a plane parallel to the support surface.

[0024] For a projection arm having a value greater than or equal to a predetermined threshold value K 1S The standby factor K1(t ref ) of the reference measurement time t ref Any so-called current measurement time t after n, can identify the standby phase, at the current measurement time t n The projection arm is then moved away from the resting position.

[0025] When the standby phase is identified, it is possible to l|v and the state vector X of the projection arm b|v An estimated trajectory of the projectile in the virtual reference frame is determined, and a digital representation of the estimated trajectory can be displayed on the constructed image during the step of controlling the graphical interface.

[0026] The launch of the projectile can be identified at the measuring moment when the launch arm has reached its rest position, and the standby phase can be identified at least at a previous measuring moment.

[0027] The projection factor K2 can be defined based on the instantaneous speed and / or the average speed of the projection arm at at least one measuring moment when it reaches its rest position.

[0028] The state vector X of the magnet can be determined by Bayesian estimation algorithm or optimization method a|r .

[0029] The virtual environment can be a three-dimensional space having dimensions larger than the dimensions of the tracking area.

[0030] The invention also relates to an information storage medium comprising instructions for executing a control method according to any one of the above characteristics when the instructions are executed by an electronic computing unit.

[0031] The invention also relates to a device for controlling a graphical interface to display an image of a digital representation of a three-dimensional object, called a projector, in a virtual environment, said device being suitable for implementing a control method according to any of the above characteristics, comprising:

[0032] o a projectile comprising a structure made of non-magnetic material, to which a projectile arm is assembled in a movable and restricted motion manner, to which a magnet is fixed;

[0033] ○ Graphical interface;

[0034] ○ Positioning equipment, which includes:

[0035] A magnetometer array fixed to a supporting surface;

[0036] A computing unit comprising a memory in which is stored a digital file encoding a virtual environment in a virtual reference frame and a digital model of the projectile and the projectile arm, the computing unit being programmed to:

[0037] ■ Obtain measurements of the magnetic field generated by a magnet;

[0038] ■ Calculate the state vector X of the magnet in the actual reference frame associated with the tracking area defined relative to the support surface a|r ;

[0039] ■Determine the state vector X of the projector in the virtual reference frame l|v , the state vector X of the projection arm in the virtual reference frame b|v , and the position P of the projectile in the virtual reference system p|v ;

[0040] ■ Identification of the arming phase and, if appropriate, of the launch of the missile and determination of the successive positions P of the missile at different moments in time in the virtual reference system p|v ;

[0041] ■ construct a two-dimensional image representing the virtual environment, a digital representation of the projector, and the projectile in the virtual reference frame;

[0042] ■Control the graphical interface to display the constructed image. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Other aspects, objects, advantages and features of the invention will become apparent upon reading the following detailed description of preferred embodiments of the invention provided as non-limiting examples with reference to the accompanying drawings, in which:

[0044] Figure 1A and 1B is a schematic partial cross-sectional view of a control device of a graphical interface according to one embodiment;

[0045] Figure 2A and 2B is the tracking area associated with the actual 3D reference system ( Figure 2A ) and the virtual environment associated with the virtual three-dimensional reference system ( Figure 2B ) is a schematic partial stereogram of

[0046] Figure 3 is a schematic diagram of a graphical interface that displays a digital representation of a projector controlling a device in a virtual environment;

[0047] Figure 4 is an example of the time variation of the tilt angle formed by a magnet fixed to a control arm of a catapult when it is operated by a user;

[0048] Figure 5 is a flow chart illustrating steps of a method for controlling a graphical interface according to one embodiment. DETAILED DESCRIPTION

[0049] In the drawings and in the following of this specification, the same reference numerals represent the same or similar elements. Moreover, the individual elements are not shown to scale, in order to give priority to the clarity of the drawings. In addition, the various embodiments and variations are not mutually exclusive, but can be combined with each other. Unless otherwise specified, the terms "substantially", "approximately", "about" refer to a difference within plus or minus 10%, preferably within 5%. In addition, "including ... to ... between" and equivalent terms refer to inclusive boundaries unless otherwise specified.

[0050] The present invention relates to a method for controlling a graphical interface to display graphics of digital representations of actual three-dimensional objects in a virtual environment and to implement actions dynamically determined by a user using the actual three-dimensional objects in the virtual environment.

[0051] According to the present invention, the actual three-dimensional object is an object called a projectile that is designed to throw a projectile (i.e., a virtual projectile) in a virtual environment. The projectile includes a structure and a projection arm that is mounted to be movable by displacement on the structure. The magnet is fixed to the projection arm without freedom. The projectile can be a catapult, a jet, or any other object capable of throwing a projectile. The projectile is designed to contact a support surface to throw a projectile.

[0052] The control method is implemented when the projector is operated by a user, and the magnet is tracked by a positioning device including a magnetometer array. The magnet moves in a tracking area associated with the magnetometer array. In other words, the positioning device estimates the position and orientation of the magnet in the actual three-dimensional reference system associated with the tracking area at different consecutive measurement moments.

[0053] Figure 1A and 1B It is used to control the graphical interface 2 to V The digital representation 31 of the projector 10 is displayed in the virtual environment E. V A partial schematic diagram of the control device 1 for implementing the action of throwing a projectile 32. Figure 1B yes Figure 1A The control device 1 comprises a projector 10 provided with a magnet 15 , a positioning device 20 for positioning the magnet in a real reference system Rr, and a graphical interface 2 .

[0054] The projector 10 is intended to be operated by a user (eg, by hand) to display a virtual environment E. V A physical (ie, actual, non-digital) three-dimensional object from which projectiles 32. In this example, this involves a catapult, but it could be a jet, a slingshot, a crossbow, or any other object capable of projecting a projectile.

[0055] The projectile 10 comprises a rigid structure 11 made of non-magnetic material, for example plastic, to which a projection arm 12 is assembled in a movable and limited-motion manner. The structure 11 here comprises wheels 14 by means of which it can rest on a support surface Sa of a positioning device 20 .

[0056] The projection arm 12 comprises a longitudinal portion 12.1 and a support portion 12.2 for the projectile 32. The longitudinal portion 12.1 extends along a longitudinal axis between a first end, via which the longitudinal portion is assembled to the rigid structure 11, and an opposite second end, to which the support portion 12.2 is fixed. The projection arm 12 is here also made of a non-magnetic material.

[0057] The projection arm 12 is assembled to the rigid structure 11 in a movable manner (e.g. by rotation and / or translation). In the present example of a catapult, the projection arm 12 is assembled by a pivot link. Moreover, it is limited in movement (here rotation) by a return member. The return member can be a helical spring or a leaf-type spring. In the case of an ejector, the projection arm 12 can move in translation relative to the rigid structure 11.

[0058] At rest, the projection arm 12 is in a stop position, in which it is maintained by the resetting means in contact with the stop portion 13 of the rigid structure 11. In fact, the resetting means continuously exert a resetting force on the projection arm 12 in the direction of the stop portion 13. When the user actuates the projection arm 12, the user moves the projection arm 12 more or less away from its stop position. If the user releases the projection arm 12, the further it is from its stop position, the faster the resetting means resetting it. In the present example, the projection arm 12 is in a stop position (in contact with the stop portion 13), but in general, at rest, it is in a so-called rest position, in which, as in the case of a slingshot, it is not necessarily in contact with the stop portion of the catapult 10.

[0059] The projectile 10 comprises a magnetic object 15, here a permanent magnet, fixed to the projectile arm without freedom. The magnetic object 15 comprises a material having magnetization, such as remanence, for which a magnetic moment is defined. m It can be a cylindrical, for example annular, permanent magnet as shown in document WO 2014 / 053526, or even an electromagnet.

[0060] The magnetic material is preferably ferrimagnetic or ferromagnetic. It has a non-zero instantaneous magnetic moment even in the absence of an external magnetic field. m It is capable of having a current higher than 100A.m -1 or 500A.m -1 The coercive field and magnetic moment m The intensity is preferably higher than 0.01Am 2, even higher than 0.1Am 2 , for example, equal to about 0.8Am 2 Consider that a magnetic object can be approximated by a magnetic dipole, but other models can be used. The magnetic axis of a magnetic object is defined as the magnetic moment of the magnetic object. m Collinear axes.

[0061] like Figure 1B As shown, when the projection arm 12 is in the stop position, the magnetic moment of the magnet m The axis of the magnetic field m ) forms a static tilt angle This angle is determined by the magnetic axis m The angle of repose is defined relative to a vertical axis orthogonal to a plane passing through the wheels of the projectile. Can be equal to 45°. The magnetic axis of the magnet m Can be parallel or non-parallel to the longitudinal axis of the projection arm.

[0062] When the user actuates the projection arm 12 and thus moves it away from the stop position, the tilt angle becomes greater than the angle of rest The tilt angle Able to be at the repose angle With maximum tilt angle Changes between.

[0063] The positioning device 20 is designed to locate the position in the so-called real three-dimensional reference system Rr, more precisely in the same three-dimensional reference system as the magnetometer M. i Array associated with tracking area Z S The magnet 15 is positioned in the middle.

[0064] "Location" means determining that the magnet 15 is in the tracking area Z S The position and orientation of the magnet 15 is a|r Corresponds to the coordinates of the geometric center of the magnet, i.e. the unweighted center of all points of the magnet. In addition, the magnetic moment of magnet 15 m is a vector whose components in the actual reference frame Rr are (m x ,m y ,m z ). Its modulus (also called strength or amplitude) is denoted by ||m|| or m.

[0065] Here and for the purposes of this specification hereinafter defined herein is a direct actual three-dimensional reference system Rr, (Or, Xr, Yr, Zr), wherein the Xr and Yr axes form a plane parallel to the support surface Sa of the positioning device 20, and wherein the Zr axis is oriented approximately orthogonal to the support surface and opposite to the magnetometer. In the present specification hereinafter, the terms "vertical" and "vertically" refer to an orientation approximately parallel to the Zr axis, and the terms "horizontal" and "horizontally" refer to an orientation approximately parallel to the (Xr, Yr) plane. Furthermore, the terms "down" and "up" refer to an increasing positioning as one moves away from the support surface Sa in the +Zr direction. In this example, the origin Or is located in the tracking area Z S edge, but it can be located in the tracking area Z S Other positions of the support surface Sa, such as the edge of the support surface Sa.

[0066] The magnet 15 is intended to be in the tracking zone Z S This is the space in which the signal-to-noise ratio (SNR) of at least one of the magnetometers of the positioning device is higher than or equal to a predetermined threshold. S It can be a space in which the signal, i.e. at least one component or modulus of the magnetic field generated by the magnet and measured by the corresponding magnetometer, is higher than or equal to, for example, 20 times the noise. The noise associated with each magnetometer can be equal to about 0.3 μT. In this case, the tracking area Z S corresponds to the region of space in which the magnetic field generated by the magnet 15 and detected by the magnetometer M i At least one of the magnetic fields measured is higher than or equal to about 6 μT, which corresponds to the magnetic field along the path passing through the magnetometer M under consideration. i The distance d of the guide axis is equal to about 20 cm max More simply, the tracking area Z S can be defined as a space in which every point is located at a distance less than or equal to the distance along the path passing through the nearest magnetometer M i The maximum distance d from the guide axis max , this maximum distance is for example equal to 20 cm, or even 10 cm, or even 5 cm.

[0067] The positioning device 20 is able to measure, in the real reference system Rr, during the tracking time T, at different measurement instants, the ambient magnetic field, one of the contributions of which is the magnetic field generated by the magnet 15, and then based on the magnetometer M i The measured values ​​of , estimate the position and orientation of the magnet 15.

[0068] To this end, it comprises magnetometers M arranged relative to each other so as to form a measurement plane. iArray. They are fixed to the support surface Sa without freedom. Magnetometer M i The number can be, for example, greater than or equal to 2, preferably greater than or equal to 16, for example equal to 32, in particular when a three-axis magnetometer is involved. i The array comprises at least three measurement axes which are remote from each other and are not parallel in pairs.

[0069] The magnetometers Mi are fixed without freedom to the support surface Sa and can be located at the rear face of the plate 21 whose front face forms the support surface Sa, made of non-magnetic material. They are aligned here in lines and columns, but can be arranged approximately randomly relative to each other. i The positions of are known. For example, they can be 1 cm to 10 cm, for example 5 cm.

[0070] Magnetometer M i Each of the axes has at least one measurement axis, for example three axes, denoted by x i ,y i 、z i Each magnetometer therefore measures the ambient magnetic field B i The magnitude and direction of the ambient magnetic field contribution generated by the magnet. More precisely, each magnetometer M i Measuring the ambient magnetic field B i On the axis x of the magnetometer i ,y i 、z i The modulus of the orthogonal projection of . Magnetometer M i The calibration parameter of can be the noise associated with the magnetometer, which is about 0.3 to 0.4 μT here. The ambient magnetic field B refers to the magnetic field that is not disturbed by any magnetic elements and is formed in particular by a ground contribution of about 50 μT, to which the magnetic field B generated by the magnet is added. a Other magnetic contributions can be added, such as contributions associated with the noise of the sensor and contributions related to offset errors, which are neglected here.

[0071] The positioning device 20 also includes a magnetometer M i The measured value of the magnet 15 is determined as X a|r The electronic calculation unit 22 is capable of determining the position and orientation of the state vector in the real reference system Rr. Moreover, as described below, the calculation unit 22 is capable of determining the position and orientation of the state vector in the virtual three-dimensional reference system Rr. V The state vector X associated with the projector 10 in l|v , in the virtual reference system R V The state vector X associated with the projection arm 12 in b|v , and the projectile 32 in the virtual reference system R V Position P inp|v The calculation unit 22 is also designed to recognize the arming phase A of the launch arm 12, as well as the launch of the projectile 32 and its position in the virtual reference system R V The trajectory T p|v Finally, it is designed to construct the image to be displayed and to control the graphical interface 2 to display the constructed image.

[0072] To this end, each magnetometer M i It is electrically connected to a computing unit 22 via an information transmission bus (not shown). The computing unit 22 comprises a programmable processor 23 capable of executing instructions stored on an information storage medium. It also comprises a memory 24 containing the instructions required to implement the method for positioning the magnet 15 and controlling the graphical interface 2. The memory 24 is also designed to store information calculated at each measurement moment.

[0073] The calculation unit 22 performs the calculation of the position of the magnet 15 in the actual reference system Rr and its magnetic moment m The orientation and strength of the magnetometer M i The mathematical model is constructed based on the electromagnetic, in particular magnetostatic equations and its parameters are set in particular by the position and orientation of the magnetometer in the real reference system Rr. The model is nonlinear. The calculation unit implements an algorithm for estimating its solution, such as a Bayesian filter (e.g. an extended Kalman filter) or an optimization, or even any other algorithm of the same type.

[0074] Preferably, in order to approximate the magnet 15 as a magnetic dipole, the magnet 15 and each magnetometer M i The distance between the magnets 15 is greater than 2 or even 3 times the largest dimension of the magnet. This dimension can be less than 20 cm, even less than 10 cm, even less than 5 cm. The magnet 15 can be connected in particular according to the magnet and each magnetometer M of the array. i The distance between them is modeled by (among other things) a dipole model.

[0075] Furthermore, the computing unit 22 comprises a coded virtual reference system R stored in its memory 24 V Virtual environment E V and also includes a digital model 26 of the projector 10 stored in its memory 24, which in particular enables the projector 10 to be provided in the virtual reference system R V The number in represents 31.

[0076] Figure 2A and 2B is the tracking area Z S ( Figure 2A ) and virtual environment E V ( Figure 2B ) is a schematic partial stereogram of the invention.

[0077] exist Figure 2A The tracking area Z is schematically shown in FIG. S The support surface Sa is located in the tracking area Z S Tracking area Z S Each point in has coordinates defined in the real reference system Rr. In this example, the origin Or in the real reference system is located in the tracking area Z S At the edge. Tracking area Z S It is a physical area of ​​space where the SNR is greater than a predetermined threshold and where a user is able to operate the projector 10, for example by hand.

[0078] exist Figure 2B , a virtual environment Ev is schematically shown. A positioning surface Sp of a digital representation 31 of a projector 10 is shown, which corresponds to a digital representation of a support surface Sa. The virtual environment Ev can include a ground surface, a surface, a wall, etc. In the present example, the virtual environment Ev is a basketball court and includes a basket 30.3 arranged between the positioning surface Sp and a background wall 30.2. Each point of the virtual environment has coordinates defined in a so-called virtual three-dimensional reference system Rv (Ov, Xv, Yv, Zv) directly here. In the present example, the origin Ov of the virtual reference system Rv is located at the edge of the virtual environment Ev. The virtual environment Ev is encoded in a digital file 25, which is stored in a memory 24 of a computing unit 22. In other words, the digital file 25 provides the position of each of the points defining the elements of the virtual environment Ev. The elements or some of the elements of the virtual environment Ev can be static or dynamic.

[0079] Figure 3 2 is a schematic diagram of a graphical interface 2 showing a two-dimensional image of a virtual environment Ev in which a digital representation 31 of a projector 10 and a projectile 32 are located. The virtual environment Ev is here the area of ​​a basketball court, formed by the ground 30.1, the background wall 30.2 and the basket 30.3. A positioning area Sp is shown, in which the digital representation 31 of the projector and the projectile 32 are displayed. In this image, the projector 10 is in a standby configuration A, in which the projectile 32 can be launched. The estimated trajectory of the projectile 32 is displayed

[0080] Furthermore, the calculation unit 22 integrates a mapping relationship F between the actual reference system Rr and the virtual reference system Rv. In other words, each point of the tracking area in the actual reference system Rr is associated with one and only one point of the virtual environment Ev in the virtual reference system Rv. The mapping relationship F is not necessarily a bijective function, because the virtual environment Ev can be larger than the tracking area Z. S A larger three-dimensional space.

[0081] The calculation unit 22 also integrates a digital model 26 of the projectile 10 and its projection arm 12, which makes it possible to calculate the state vector X of the magnet 15 representing its position and orientation in the real reference system Rr. a|r Related:

[0082] ○ The state vector X of the projector 10 representing the position and orientation of the projector 10 in the virtual reference system Rv l,v ,and

[0083] o The state vector X of the projection arm 12 representing the position and / or orientation of the projection arm 12 in the virtual reference system Rv b,v .

[0084] In other words, by knowing the position and orientation of the magnet 15 in the real reference system Rr, the calculation unit 22 can deduce the position and orientation of the projector 10 in the virtual reference system Rv in the form of the state vector X l|v The digital model 26 also includes information about the type of catapult (catapult, ejector, etc.) and its dimensions. From this, the calculation unit 22 is able to construct a digital representation 31 of the catapult 10 in the virtual reference system Rv.

[0085] Furthermore, by knowing the position and orientation of the magnet 15 in the real reference system Rr, the calculation unit 22 can deduce therefrom the position and / or orientation of the projection arm 12 in the virtual reference system Rv in the form of a state vector X b|v The digital model 26 also includes information about the type of projection arm 12 and its restricted movements relative to the structure 11 of the projectile 10 (pivot connection, sliding, etc.; strength of the restoring force, etc.) and its dimensions. Thus, the calculation unit 22 is able to construct a digital representation of the projection arm 12 in the virtual reference system Rv. It should be noted here that the state vector X of the projection arm 12 b|v The state vector X of the projector 10 can be l|v is derived or even included in the state vector of the projector, i.e. it can be derived from the state vector X l|v One or more coordinates of .

[0086] Finally, the computing unit 22 can integrate a digital model of the projectile 32 to be projected in the virtual environment Ev. The digital model can be included in the digital model 26 associated with the projector 10 and the projection arm 12. The characteristics of the projectile 32 to be represented in the virtual environment Ev, i.e. its dimensions and its mass, can thus be defined in the digital model. The computing unit can include one or more processors and one or more memories, which may be remote from each other.

[0087] Figure 5 is a flow chart of a method for controlling the graphical interface 2 according to one embodiment.

[0088] In this example, the virtual environment Ev is formed by a three-dimensional basketball sport area, which is formed by a ground 30.1 including a positioning surface Sp, a background wall 30.2, and a basket 30.3 arranged between the positioning surface Sp and the background wall 30.2, and the digital model 31 of the projector 10 is intended to be displayed in the positioning surface.

[0089] The control method comprises an initialization phase 10 .

[0090] At step 11, a digital file encoding the virtual environment Ev is stored in the memory 24 of the computing unit 22. Thus, each point defining an element of the virtual environment Ev (ground, walls, objects, etc.) is defined in the virtual reference system Rv. In this example, the positioning surface Sp, the ground 30.1, the background wall 30.2, and the basket 30.3 are defined in the virtual reference system Rv.

[0091] At step 12, a digital model 26 of the projectile 10 and the projectile arm 12 is stored in the memory 24 of the computing unit 22. As described above, the digital model 26 enables the calculation of the state vector X of the magnet 15 based on the state vector X of the magnet 15. a|r , the projectile 10 and its projection arm 12 are represented in a virtual reference system Rv. The digital model 26 can also integrate data (dimensions, etc.) about the projectile 32 to be represented.

[0092] At step 13, the tracking area Z S The dimensions are stored in the memory 24 of the computing unit 22. The mapping relationship F pre-stored in the memory 24 of the computing unit 22 makes it possible to ensure the mapping between the positions in the actual reference system Rr and the positions in the virtual reference system Rv. In this example, the Xr and Xv axes are selected to be parallel to each other, just like the Yr and Yv, and Zr and Zv axes.

[0093] At step 14, the calculation unit 22 determines the dimensions of the field of view. The field of view can be defined, for example, by a first angle in the horizontal plane (Xv, Yv) and a second angle in the vertical plane (Yv, Zv). The orientation of the field of view on the optical axis can be selected to be constant or can depend on the orientation of the projector 10 in the virtual reference system Rv.

[0094] The control method then comprises a phase of use 20 of the device 1 to control the graphical interface 2 and to display in the virtual environment Ev an image representing the projector 10 and the projected projectile 32 .

[0095] In step 21, the user places the projector 10 in the tracking area Z S The user operates the projector 10, ie changes its position in the horizontal plane (Xv, Yv) and / or its orientation. However, the projector 10 remains in contact with the support surface Sa.

[0096] Initially, the projection arm 12 can be in its rest position, here a stop position, ie here it is held in contact with the stop portion 13 of the rigid structure 11 by means of the return means. is equal to the rest angle The user can change the projector 10 in the tracking area Z s and observe a digital representation 31 of the projector 10 as displayed in the virtual environment Ev by a graphical interface.

[0097] The user can actuate the projection arm 12 to launch the projectile 32 in the virtual environment. To do this, the user moves the projection arm 12 away from the stop position. increases and becomes greater than or equal to the predetermined threshold The projectile 10 has a standby configuration C designed to launch a projectile 32. a On the other hand, when the tilt angle Keep included in the static angle With threshold When the projectile 10 is in the intermediate configuration C that does not result in the projectile 32 being thrown, i .

[0098] Finally, the user can release the launch arm 12 more or less suddenly. If the launcher 10 has an intermediate configuration C at the moment of release i , the projection arm 12 returns to its stop position C b , no launch of the missile 32 is performed. On the other hand, if the catapult 10 has the armed configuration C at the time of release a , then the launch of the projectile 32 in the virtual environment Ev is implemented.

[0099] Figure 4 The tilt angle of the magnet 15 is shown An example of evolution over time.

[0100] Tilt Angle Here, a first factor K1 representing the readiness of the projection arm 12 is determined by the calculation unit 22 based on the measured values ​​of the magnetic field of the magnet 15 and the state vector X b|v More specifically, this first factor represents the position of the projection arm 12 and therefore the configuration of the projection device 10 at the moment of measurement (stop C b , Middle C i , Standby C a ). For other types of projectors, the stop structure C b It can be a static structure. Obviously, it is possible to convert the vector state X b|vThe other derived indicator serves as a first factor K1 that represents the readiness of the projection arm 12. This can thus be the tilt angle at the time of measurement With rest angle The deviation between Even normalized deviation It can also be the vertical position of the magnet 5 on the Zr axis or the projection arm 12 on the Zv axis, or the horizontal position of the magnet 15 in the plane (Xr, Yr) or even the projection arm 12 in the plane (Xv, Yv). The first factor K1 can be obtained by the state vector X of the projection arm 12 b|v Or the state vector X of the magnet 15 a|r Derived. It can thus be the inclination angle of the projection arm 12 in the virtual reference system Rv or the inclination angle of the magnet 15 in the real reference system Rr. These two angles are related to each other due to the fact that the magnet 15 is fixed without degrees of freedom on the projection arm 12 of the projector 10. In this example, these two angles are considered equal.

[0101] Initially, the user actuates the projection arm 12 so that the tilt angle From the resting value It increases until it is less than The first maximum value of , so that the projector 10 remains in the middle configuration C i and then returns to the rest value The projection arm 12 thus returns to its stop position C b .

[0102] Then, the user actuates the projection arm 12 again so that the tilt angle Increase until it is greater than the threshold The projector 10 is in the standby configuration C a In the case of the intermediate configuration C1, the arming phase A is identified: the launch of the projectile 32 is possible. The arming phase A is changed from the intermediate configuration C1 to the arming configuration C a From the moment of b In this example, the user causes the projection arm 12 to transition to the standby configuration at time t1. Then, at time t3, the projection arm 12 is returned to the stop configuration.

[0103] The launching of the projectile 32 is then carried out or not carried out according to a second factor K2 representing the launching of the projectile 32, which factor is calculated by the calculation unit based on the measured value of the magnetic field of the magnet 15 or more directly on the state vector X of the magnet 15. a|r Determine the state vector X b|v Derivation.

[0104] Different factors can be used. According to a first example, it is possible to compare the a Transition to Structure C i The delay Δt(t3) before the moment t3 (referred to as t2 here) is equal to t3-t2. When the delay Δt(t3) is greater than the predetermined threshold delay Δt s , it is estimated that no launch of the projectile 32 has been carried out: the user, for example, simply uses his hand to return the projectile arm 12 to its rest position, here the stop position. On the other hand, if it is less than or equal to the threshold delay Δt s , it is estimated that the launch of the projectile 32 is carried out: the user suddenly releases the projection arm 12, which is quickly brought back to its rest position by the reset member, where it is the stop position. More generally, when the projection factor K2 is greater than or equal to the predetermined threshold value K 2S When t3 is reached, the launch of the projectile 32 is identified. Moreover, in this example, the projection factor K2 is 1 / Δt(t3), and the threshold K 2S is 1 / Δt s .

[0105] According to another example, the second projection factor can be the instantaneous angular velocity of the projection arm 12 at the moment it reaches the rest position (here the stop position): If the instantaneous angular velocity is less than a predetermined threshold It is estimated that the launch of the projectile 32 is not carried out. On the other hand, if the instantaneous angular velocity is greater than or equal to the threshold The launch of the projectile 32 is estimated.

[0106] Of course, it is possible to use the state vector X b|r Or the state vector X a|r Other indicators derived. Thus, it is possible to involve the average angular velocity calculated based on the sliding average of the previous N measurement moments at the measurement moment t3, or even the maximum value of the angular velocity selected between the moment t3 and the previous N measurement moments, or even the angular velocity at the moment when the acceleration has an inflection point. Here, the second factor is calculated based on the angular velocity, but it can involve the linear velocity based on the change of the vertical or horizontal position of the projection arm 12.

[0107] exist Figure 4 In the example shown, whether it involves a delay of 1 / Δt (t3) or an instantaneous angular velocity The launch factor K2 indicates that no launch of the projectile 32 was carried out.

[0108] Finally, the user actuates the projection arm 12 again to tilt the projection arm 12 to a certain angle. Increase until it exceeds the threshold The projector 10 is again in the standby configuration C a, then the standby phase A is identified from time t4: launching the projectile 32 is possible. The user then releases the launch arm 12, which suddenly returns to its stop configuration at time t6

[0109] Here, the projection factor K2 indicates that the launch of the projectile 32 is carried out. In fact, the delay 1 / Δt(t6) is greater than or equal to the threshold delay 1 / Δt S Similarly, the instantaneous angular velocity Greater than or equal to the threshold speed As described below, the computing unit then determines the actual trajectory T of the projectile 32 in the virtual reference system Rv. p|v .

[0110] Reference Figure 5 Now, the positioning device and the tracking area Z are described. S The steps are performed in parallel with step 21 of operating the projector 10. At the measuring time t n These steps are iteratively performed at a predetermined sampling frequency, for example 140 Hz, discretizing time. Each iteration of rank n is associated with a measurement instant t, also called the current instant n Associated.

[0111] During step 22 , the magnetometer measures the ambient magnetic field at the current moment in time, and in particular the contribution of the ambient magnetic field generated by the magnet 15 fixed to the projection arm 12 of the projectile 10 .

[0112] Then, at step 23, the calculation unit receives the measured values ​​of the ambient magnetic field, deduces therefrom the magnetic field contribution generated by the magnet 15 and determines the state vector X associated with the magnet 15 in the time reference system Rr at the current moment. a|r The state vector X a|r The state vector comprises the position and orientation of the magnet 15 in the real reference frame Rr. This estimation of the state vector can be implemented by means of an algorithm of the Bayesian type for estimating the position and orientation of the magnet 15, such as an extended Kalman filter, or by means of an optimization method (gradient descent, etc.), or by means of any other algorithm of the same type. An example of estimating the state vector associated with the magnet 15 is described in particular in the application WO2018 / 219891.

[0113] In step 24, the calculation unit calculates the state vector X of the magnet 15 based on the state vector X of the magnet 15. a|r and the stored digital model to determine the state vector X associated with the projector 10 l,v and the state vector X associated with the projection arm 12 b|v The state vector X l,v This includes the position and orientation of the projector 10 in the virtual reference system Rv. And the state vector X b|vThe position and / or orientation of the projection arm 12 in the reference system Rv, here the tilt angle of the magnet 15 Thus, the projector 10 can be digitally represented by its projection arm 12 in the virtual environment Ev.

[0114] In this step, the calculation unit also calculates based on the state vector X l|v and X b|v , and based on the digital model of the projectile 32, determine the position P of the projectile 32 in the virtual reference system Rv p|v The projectile 32 can thus be digitally represented in the virtual environment Ev, which is here placed in the support part 12.2 of the projection arm 12 and whose coordinates in the reference system Rv are determined by at least the state vector X b|v Derivation.

[0115] In step 25, the calculation unit determines a first factor K1 representing the readiness of the projection arm 12, which is determined by the calculation unit based on the state vector X a|r Determine the state vector X b|v This involves, for example, the tilt angle at the current moment

[0116] When the condition about the standby factor K1 is that the standby factor K1 is greater than or equal to the predetermined threshold value K 1S When the time t is satisfied (which indicates that the projection arm 12 has been armed but has not yet returned to the stop position), the arming phase A is identified. In other words, when the current time t n Greater than or equal to the reference time t ref At this reference time, the projector 10 enters the standby configuration C. a , but for this reference moment, the projection arm 12 remains away from the stop position, that is, here: and Here, the standby factor K1 is the tilt angle and the predetermined threshold is

[0117] When the arming phase A is identified, the calculation unit can determine the position P of the projectile 32 based on the position P of the projectile 32. p|v and the state vector X based on the projection arm 12 b|v (For example, based on the current tilt angle ), and the state vector X based on the projector 10 l|v (position and orientation), determine the estimated trajectory of the projectile 32 in the virtual reference system Rv The estimated trajectory can be determined based on known and traditional physical models of ballistic launch It indicates the trajectory of the projectile 32, i.e. the position of the physical model in the virtual reference system Rv over time based on the velocity vector (strength, orientation) of the projectile 32 at the stop position, the coordinates of the stop position and the parameters representing the gravity in the virtual environment Ev.

[0118] like Figure 3 As shown, the estimated trajectory can be shown in an image constructed and displayed by a graphical interface It shows a hypothetical trajectory that the projectile 32 might take if the user suddenly released the projection arm 12, and shows the point of impact of the projectile 32 on an object (here, a basketball hoop) in the virtual environment Ev.

[0119] In the event that a standby phase A is not detected, the control method continues by directly proceeding to step 28 . On the other hand, in the event that a standby phase A is detected, the control method continues with step 26 .

[0120] In step 26, the calculation unit determines a second factor K2 representing the thrown projectile 32, which is determined by the calculation unit based on the state vector X a|r Determine the state vector X b|v This relates to the instantaneous angular velocity when the projection arm 12 reaches its stop position.

[0121] When the condition about the projection factor K2 is satisfied, that is, when the projection factor K2 is greater than or equal to the predetermined threshold K 2S When the tilt angle Equal to the rest angle At the current moment, the instantaneous angular velocity Greater than or equal to a predetermined threshold When the launch of the projectile 32 is identified.

[0122] In the event that the launch of a projectile 32 is not identified (ie when no projectile 32 is thrown), the control method continues by directly proceeding to step 28. On the other hand, when the launch of a projectile 32 is identified, the control method continues with step 27.

[0123] In step 27, the actual trajectory Tp|v of the projectile 32 in the virtual reference frame Rv is calculated by the computing unit 22 based on the position P of the projectile 32 at the stop position. p|v , and the state vector X based on the projection arm 12 b|v (For example, based on the current tilt angle ), and the state vector X based on the projector 10 l|vIt takes into account, for example, the actual speed (strength, orientation) of the projectile 32 at the stop position, the coordinates of the stop position, and the parameters representing the gravity in the virtual environment Ev.

[0124] The actual trajectory T p|v is stored and replaces the previous estimated trajectory Furthermore, the calculation unit 22 determines the successive positions of the projectile 32 in the virtual reference system Rv at different subsequent moments during the flight time also determined.

[0125] In step 28, the computing unit 22 constructs a virtual environment Ev, based on the state vector X l|v The projector 10, based on the state vector X b-v The projection arm 12 and possibly the actual trajectory T determined previously p|v A two-dimensional image of the position of the derived projectile 32 is constructed by taking into account the optical axis and the angle of the previously defined field of view, as described in particular in the aforementioned patent EP2994813 B1. The calculation unit 22 then controls the display of the constructed image on the graphic interface 2.

[0126] Steps 22 to 28 are then repeated with a defined sampling frequency, which can be constant or not constant in time. At the measurement instants of the subsequent launch of the missile 32 and belonging to the determined flight time, steps 26 and 27 are not performed. The position P of the missile 32 in the virtual reference system Rv is p|v The actual trajectory T p|v Derivation.

[0127] As a result, the user can very easily and particularly intuitively not only control the three-dimensional object (projector 10) provided with magnets 15, displaying graphics on a graphical interface, but also act on the represented virtual environment Ev, here by projecting a projectile 32 in this virtual environment Ev. Operating the projector 10 thus makes it possible to intuitively and particularly accurately orient and direct the projectile 32 in the virtual environment Ev.

[0128] The control device is particularly simplified, because the identification of the launch of the projectile 32 does not require the projectile 10 in the tracking area to be equipped with complex devices for analyzing and positioning the projectile 10 and actuating the projection arm 12. In fact, the projectile 10 is only equipped with a magnet 15, which can then have a simple mechanical structure and be made of inexpensive non-magnetic material (such as plastic). The launch of the projectile 32 is no longer controlled by actuating a button (such as a keyboard or mouse), but by simply releasing the projection arm 12 by the user, which makes it possible to improve the user experience.

[0129] Furthermore, the digital representation of the projector 10 and the actuation of the projection arm 12 can be smooth and precise, since the measurement frequency can be relatively high, for example, can be about 140 Hz. Furthermore, each measurement moment and possibly each displayed image can be separated from the following moment by only a few milliseconds, which makes it possible to faithfully reproduce the operation of the projector 10 in the tracking area by the user.

[0130] In particular, because the projector 10 remains in contact with the support surface in the tracking area, the signal-to-noise ratio SNR remains particularly high, and due to the contact on the support surface, the degree of freedom of operating the projector 10 in the tracking area is reduced to two dimensions of the horizontal plane (Xr, Yr), and the accuracy is particularly high. The accuracy of the positioning of the projector 10 and the actuation of the projection arm 12 is high.

[0131] It is then possible to interact with elements of the virtual environment Ev that are not in the digital representation of the tracking area, when the virtual environment Ev is a larger 3D space than the tracking area. The interaction can trigger a given action in the virtual environment (setting the movement or actuation of a virtual object).

[0132] Specific embodiments have been described above. Different modifications and variations will be apparent to those skilled in the art.

[0133] Thus, the sampling frequency associated with the positioning magnets (eg, 140 Hz), the display frequency of the constructed image, and the frequency of updating the digital representation of the projector and the position of the projectile can be different from each other.

[0134] Furthermore, at the moment of identifying the launch of the projectile, the trajectory T of the projectile is determined, as described in detail above. p|v Then, during the flight time, based on the previously determined trajectory and possibly on parameters regarding the virtual environment, the position P of the projectile at the current moment is defined. p|v For example, during the flight time, the direction of gravity can change, in which case the position P of the projectile is updated accordingly. t|v .

[0135] As mentioned above, the stop position can be a simple rest position in which the launch arm does not come into contact with the stop portion. This is particularly the case with a slingshot or even a possible ejector. The above-mentioned steps of identifying the arming and firing then take into account the rest position, not the stop position.

Claims

1. A method for controlling a graphical interface (2) to display an image of a digital representation (31) of a three-dimensional object, called a projector (10), in a virtual environment (Ev), the projector (10) being designed to project a projectile (32) in the virtual environment (Ev) and comprising a structure (11) made of non-magnetic material, to which a projection arm (12) is assembled in a movable and motion-restricted manner, to which a magnet (15) is fixed, the method being implemented by a computing unit (22), the method comprising the following steps: o Provides for tracking in the area (Z S ) for positioning the projector (10), comprising: A magnetometer array fixed to a supporting surface (Sa); said computing unit (22) connected to said magnetometer array and to a graphical interface; A predefined tracking zone (Zs) for tracking the projector relative to the magnetometer array, and a real three-dimensional reference frame (Rr) associated with the tracking zone; o storing in the computing unit (22): a digital file (25) encoding said virtual environment (Ev) in a virtual three-dimensional reference system (Rv) associated to said real three-dimensional reference system (Rr) by a predefined mapping relationship (F); A digital model (26) which enables the state vector X of the projection arm (12) representing the position and / or orientation of the projection arm in a virtual three-dimensional reference system (Rv) to be transformed into b|v and the state vector X of the magnet (15) representing the position and orientation of the magnet in the actual three-dimensional reference system (Rr) a|r associated with and enabling to obtain a digital representation (31) of said projector in a virtual three-dimensional reference system (Rv); o the projection arm (12) is operated by a user, the projection arm is located in the tracking area and arranged to be in contact with the support surface, the projection arm can be moved away from the rest position by the user, and the restoring component exerts a restoring force on the projection arm in the direction of the rest position; o The magnetometer array measures the magnet (15) at different successive measurement times t n The generated magnetic field; At the measuring time t n , based on the measured value of the magnetic field generated by the magnet, determine the state vector X of the magnet in the actual three-dimensional reference system (Rr) a|r ; At the measuring time t n , based on the pre-stored digital model (26) and the determined state vector X a|r Determine the state vector X of the projection arm (12) in the virtual three-dimensional reference system (Rv) b|v , and based on the pre-stored digital model (26) and the determined state vector X b|v Determine the position P of the projectile (32) p|v ; o According to the measurement time t n and the state vector X at the previous measurement time b|v A defined standby factor K1 is used to identify the standby phase (A) of the projection arm (12), when the standby factor K1 is greater than or equal to a predetermined threshold value K 1S , identifying the standby stage (A); o When the standby phase (A) is identified, according to the measurement time t n By the state vector X b|v The projection factor K2 is defined, and the emission of the projectile (32) is identified, when the projection factor K2 is greater than or equal to a predetermined threshold value K 2S When the launch of the projectile (32) is detected; o When the launch of the projectile (32) is detected, determining the subsequent position P of the projectile (32) in the virtual three-dimensional reference system (Rv) at a subsequent measuring time p|v ; o Based on the determined state vector X of the projection arm b|v and the determined position P of the projectile p|v , constructing a two-dimensional image representing the virtual environment (Ev), the digital representation of the projector (31) and the projectile (32) in the virtual three-dimensional reference system (Rv), and then controlling the graphical interface (2) through the computing unit (22) to display the constructed image.

2. The method according to claim 1, wherein: o The digital model also enables the state vector X of the projector (10) representing the position and orientation of the projector in a virtual three-dimensional reference system (Rv) to be converted into l|v The state vector X of the magnet (15) a|r associated; o During the operation steps, the user also operates the projector (10); o In determining the state vector X of the projection arm b|v In the determining step, the digital model (26) stored in advance and the determined state vector X are also used. a|r , determine the state vector X of the projector (10) l|v ; o In the construction step, the two-dimensional image is based on the state vector X of the projector l|v , displaying a digital representation of the projector (31).

3. The method according to claim 1, wherein: Determining the successive positions P of the projectiles (32) p|v The step of determining comprises identifying the determined successive positions P p|v An intersection between one of the surfaces of the virtual environment (Ev) and a surface representing an impact of the projectile (32) is determined, and a flight time between a measured instant at which the launch of the projectile is identified and a measured instant corresponding to the impact is determined.

4. The method according to claim 3, wherein: During the measurement moments belonging to said flight time, the identification steps of the standby phase (A), the identification steps of the launch of said projectile and the determination of the successive positions P of said projectile are not carried out. p|v The determination steps.

5. The method according to claim 1, wherein: The standby factor K1 is defined based on the tilt angle of the magnet (15) when the projection arm (12) is assembled to the structure (11) by a pivot connection, and / or the position along an axis orthogonal to the support surface (Sa), and / or the position along a plane parallel to the support surface (Sa).

6. The method according to claim 1, wherein: For the projection arm to have a value greater than or equal to a predetermined threshold value K 1S The reference measurement time (t ref ) after any current measurement time t n , identifying the standby phase (A), the projection arm is at the current measurement time t n Then move away from the static position.

7. The method according to claim 1, wherein: When the standby phase (A) is identified, the state vector X of the projector is based on the image constructed in the step of controlling the graphical interface (2). l|v and the state vector X of the projection arm b|v Determine the estimated trajectory of the projectile in the virtual three-dimensional reference system Rv And display the estimated trajectory digital representation.

8. The method according to claim 1, wherein: The launch of the projectile is detected at the measuring point in time when the launch arm has reached its rest position, the arming phase (A) being detected at at least one previous measuring point in time.

9. The method according to claim 1, wherein: The projection factor K2 is defined based on the instantaneous speed and / or the average speed of the projection arm at at least one measuring moment when the projection arm reaches its rest position.

10. The method according to claim 1, wherein: Determine the state vector X of the magnet by using a Bayesian estimation algorithm or an optimization method. a|r .

11. The method according to claim 1, wherein: The virtual environment (Ev) is larger than the tracking area (Z S )'s size in a three-dimensional space.

12. An information storage medium comprising instructions for executing the method according to claim 1 when these instructions are executed by an electronic computing unit.

13. A control device (1) of a graphical interface (2) for displaying an image of a digital representation (31) of a three-dimensional object, called a projector (10), in a virtual environment (Ev), suitable for implementing the method according to claim 1, comprising: o a projectile (10) comprising a structure (11) made of non-magnetic material, to which a projection arm (12) is assembled in a movable and limited-motion manner, and to which a magnet (15) is fixed; oGraphical interface (2); o A positioning device (20), comprising: A magnetometer array fixed to a supporting surface (Sa); A computing unit (22) comprising a memory (24) in which are stored a digital file (25) encoding a virtual environment in the virtual three-dimensional reference system (Rv) and a digital model (26) of the projector and the projectile arm, the computing unit being programmed to: - obtaining measurements of the magnetic field generated by said magnet; - Calculate the tracking area (Z) defined relative to the support surface (Sa) S The state vector X of the magnet in the actual three-dimensional reference system (Rr) associated with a|r ; - Determine the state vector X of the projector in the virtual three-dimensional reference system (Rv) l|v , the state vector X of the projection arm in the virtual three-dimensional reference system (Rv) b|v , and the position P of the projectile in the virtual three-dimensional reference system (Rv) p|v ; - Identify the standby phase (A); - constructing a two-dimensional image representing said virtual environment, a digital representation of said projector and said projectile in said virtual three-dimensional reference system (Rv); The graphical interface is controlled to display the constructed image.

14. A control device according to claim 13, wherein the computing unit is further programmed to: identify the launch of the projectile and determine the successive positions P of the projectile in the virtual three-dimensional reference system (Rv) at different moments in time p|v .

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