Method and device for determining a position to be reached by at least one drone

Abstract

The present invention relates to a computer-implemented method for determining a target position for at least one drone (Dk) in a fleet of drones following a ground vehicle (V) and controlled by a control device, comprising: - Determination, by a processor of the control device, of a current reference position for the fleet of drones, - Determination, by the processor of the control device, of said target position for at least one drone (Dk), from the current reference position, a drone arrangement, and an arrangement width, the target position for at least one drone (Dk) being calculated by adding a periodic deviation vector to a vertex position of the polyline corresponding to said at least one drone. [Fig. 1]

Description

Title of the invention: Method and device for determining a position to be reached by at least one drone

[0001] The invention relates to the field of coverage path tracking coupled with that of tracking land vehicles.

[0002] Methods are known for solving coverage trajectory planning problems. These problems arise particularly in the context of using automated devices for inspecting structures or spaces, applying treatments in agriculture, or cleaning soils. Examples include grid discretization methods, graph-based methods, sampling methods, optimization methods, machine learning methods, and the potential field method.

[0003] Furthermore, other methods, different from those mentioned above, are also known for solving problems related to vehicle tracking. Examples of such methods include GPS tracking, camera tracking, Wi-Fi tracking, sensor tracking, Lidar, or radar.

[0004] There are situations where the two problems overlap. In this situation, automated devices are tasked with following a vehicle while optimizing, through their trajectory, the coverage of a predefined area. An example is fire detection and drone support for firefighting vehicles.

[0005] To date, no method for resolving such situations appears to be known. Therefore, combining the first methods, previously mentioned in connection with the problem of coverage trajectory planning, with the second, mentioned in connection with the problem of tracking land vehicles, in order to solve both problems simultaneously, seems counterintuitive. Indeed, the first methods are costly in terms of time and resources, while the second require the shortest possible response time.

[0006] The invention presented aims to solve this problem. Description of the invention

[0007] To this end, the invention proposes a method and a system enabling a set of automated systems, such as a fleet of drones, to follow a land vehicle moving in a predefined geographical area, where the coverage by the set of automated systems is optimized.

[0008] A computer-implemented method is thus proposed for determining a position to be reached by at least one drone in a fleet of drones controlled by a command device and following a land vehicle moving at a vehicle speed (vx), the command device receiving, at a current instant, a current position of the land vehicle, the method comprising: - Determination, by a processor of the control device, of a current reference position of the fleet of drones from the current position of the land vehicle, of a current rotation angle of the land vehicle and, optionally, of a relative positioning vector of the fleet of drones; - Determination, by said processor, of said position to be reached by at least one drone, from the current reference position, of a drone arrangement and of an arrangement width; the arrangement of the drones being defined by a reference point and by a polyline of which each of the vertices is occupied by one of the drones, the width of arrangement corresponding to a scale factor of the polyline; the reference point of the layout being positioned at the current reference position; the angle of rotation of the arrangement being defined in a relative manner with respect to the current angle of rotation of the land vehicle; the position to be reached by at least one drone is calculated by adding a periodic deviation vector to a position of the vertex of the polyline corresponding to said at least one drone.

[0009] Thanks to the invention, the fleet of drones can follow the ground vehicle in real time while optimally covering a predefined geographical area by maintaining a layout following the trajectory of the followed vehicle at all times. The layout width defines a geographical band covered by the fleet of drones during tracking. Furthermore, the inclusion of a periodic deviation vector in determining the target position of at least one drone makes it possible to optimize the geographical area covered by the fleet of drones, and in particular the overall field of view of the fleet of drones.

[0010] Advantageously, the polyline forms a line.

[0011] Advantageously, the arrangement forms a non-flat polygon such as a square, a pentagon, a hexagon, a heptagon, an octagon.

[0012] Advantageously, the layout width is a parameter representative of a scale factor of the polyline.

[0013] In some embodiments, the at least one drone consists of all the drones in the drone fleet.

[0014] In some embodiments, the periodic deviation vector of at least one drone is determined from a maximum flight speed of at least one drone, the flight altitude of at least one drone, the angular field of at least one drone and / or the speed of the vehicle.

[0015] Thus, according to the invention, it is possible to act on the area covered by the fleet of drones, via the periodic deviation vector, as a function of parameters of the tracking mission such as the speed of the ground vehicle or other operating parameters of the drones.

[0016] In some embodiments, the periodic deviation vector is calculated as a function of an amplitude coefficient that is a function of the maximum flight speed of at least one drone and the speed of the vehicle.

[0017] Thus, the tracking of the land vehicle by drones takes into account the speed of the vehicle being tracked.

[0018] In some embodiments, a time period of the periodic deviation vector is calculated as a function of the average speed, the flight altitude of at least one drone and an angular field of at least one drone.

[0019] In some embodiments, the direction of the periodic deviation vector varies periodically.

[0020] In some embodiments, the relative angle between the arrangement and the reference direction of movement is predetermined.

[0021] In some embodiments, the relative angle between the arrangement and the reference displacement direction is calculated as a function of the reference displacement direction.

[0022] In some embodiments, at the current time, the land vehicle moves along a current direction of movement, defined for example by a vector formed by the last received position of the land vehicle and the current position, and the periodic deviation vector has a direction perpendicular to the current direction of movement and an amplitude that varies sinusoidally with time.

[0023] In some embodiments, the method includes in step b) a determination of the flight altitude of at least one drone, the flight altitude being a function of the amplitude coefficient, the layout width and / or the angular field of view of at least one drone.

[0024] Thus, according to the method according to the invention, when following the land vehicle, the flight altitude of the drones is also adjusted to optimize the coverage of the area covered by the fleet of drones during the following.

[0025] In other words, advantageously, the altitude correction performed during the implementation of the method according to the invention makes it possible to ensure that, while Optimizing the geographical area covered by the drone fleet by taking into account the speed of movement of the vehicle being followed, the resulting image from all the images recorded by the drone fleet covers the entire imaged geographical band.

[0026] In certain embodiments, wherein at the current instant the land vehicle is moving along a current direction of movement, defined for example by a vector formed by the last received position of the land vehicle and the current position, the method further comprises: - Determination, at a time called the detection time, that the distance between a drone and at least one obstacle is likely to become less than a threshold value; - Change of polyline, and / or reduction of layout width, and / or change of relative angle between layout and current direction of travel, such that each of the drones in the drone fleet remains at least at a distance greater than said threshold value from said at least one obstacle.

[0027] Thus, advantageously, the method according to the invention makes it possible to take into account various obstacles encountered during the flight mission of the fleet of drones and to maintain the desired arrangement of the drones.

[0028] In certain embodiments, when the layout width is reduced, the layout width is reduced to a value equal to the minimum value between twice the distance between the reference position at the time of detection and the obstacle on the one hand, and the product of a metric field of view of at least one drone by the number of drones in the drone fleet on the other hand.

[0029] In some embodiments, the method further includes a conversion of the current position of the ground vehicle into local coordinates of a local geodetic system, the current position of at least one drone being determined from the local coordinates.

[0030] The conversion into local coordinates of the global coordinates initially received improves the accuracy of the position to be reached by the drones determined by the method according to the invention.

[0031] The present invention also relates to a computer program comprising instructions for implementing the process described above, when this program is executed by a processor.

[0032] This program may use any programming language (for example, an object-oriented language or other), and may be in the form of interpretable source code, partially compiled code or fully compiled code.

[0033] Another aspect relates to a non-transient storage medium for a computer executable program, comprising a set of data representing one or several programs, said one or more programs comprising instructions for, when said one or more programs are executed by a computer comprising a processing unit operationally coupled to memory means and an input / output interface module, to execute all or part of the process described above.

[0034] Another aspect of the invention relates to an assembly comprising a fleet of drones, the assembly comprising a control device, the control device comprising at least a processor and a recording medium as described above. Brief description of the drawings

[0035] Other features, details, and advantages of the invention will become apparent upon reading the detailed description below. This description is purely illustrative and should be read in conjunction with the accompanying drawings, in which: Fig. 1

[0036] [Fig.1] schematically represents a configuration of a flight mission of a fleet of drones during which the method of determining a position to be reached by at least one drone according to an embodiment of the invention can be implemented; Fig. 2

[0037] [Fig.2] represents an example of a control device that can implement the method of determining the trajectory of at least one drone according to an embodiment of the invention; Fig. 3

[0038] [Fig.3] represents an example of a flowchart representing steps that can be executed during the implementation of the method of determining a position to be reached by at least one drone from a fleet of drones according to an embodiment of the invention; Fig. 4

[0039] [Fig. 4A] and [Fig. 4B] represent two examples of arrangements of a fleet of drones according to embodiments of the invention; Fig. 5

[0040] [Fig. 5] schematically represents a change of direction of a land vehicle followed by a fleet of drones according to embodiments of the invention; Fig. 6

[0041] [Fig.6] represents a change in the arrangement of a fleet of drones according to embodiments of the invention; Fig. 7

[0042] [Fig. 7A] and [Fig. 7B] represent two situations where a new arrangement of a fleet of drones is calculated (line on [Fig. 7A], circle on [Fig. 7B]) according to embodiments of the invention. Detailed description

[0043] This disclosure proposes a method 100 for determining a position to be reached by at least one drone from a fleet of drones when following a ground vehicle V and a control device 200 for implementing this method.

[0044] By drone, we mean a motorized aircraft without a human pilot on board.

[0045] The method 100 can be used, but not limited to, within the framework of a flight mission that a fleet of drones must perform. An example of such a flight mission, illustrated in [Fig. 1], consists of assisting a firefighting vehicle moving on the ground, which the fleet of drones must follow from the air. During this flight mission, the fleet of drones will be controlled to optimally scan an outdoor area S, delimited on the ground by a predetermined perimeter P. Examples of area S include: a forest, a residential area, and an agricultural field. Other types of flight missions can be considered, in which the fleet of drones follows a ground vehicle V. During this tracking, the drones can, for example, monitor the surroundings, detect information using integrated sensors, and send this information in real time to the ground vehicle V.

[0046] Method 100 according to this disclosure can be used to determine a set of instructions to be sent to each drone in the drone fleet. Advantageously, the set of instructions is sent dynamically, that is, at different successive times during the flight mission, each drone receives instructions relating to the trajectory it must follow.

[0047] The method 100 can, for example, be implemented by a control device 200, a schematic representation of which is shown in [Fig. 2]. The control device 200 can be a distributed or non-distributed computing device. The control device 200 can be mounted in the ground vehicle V, and / or in one or more of the drones in the drone fleet, and / or integrated into one or more remote servers. The control device 200 can, for example, be a ground command station for the drones in the drone fleet.

[0048] The control device 200 includes one or more memories 202, 203 for storing instructions enabling the implementation of the method 100 of determining a position to be reached by at least one drone, the received position data, and temporary data to carry out the different steps of the method 100.

[0049] The control device 200 further comprises a circuit 201. This circuit may be, for example: - a processor capable of interpreting instructions in the form of a computer program, or - an electronic board whose steps of the process of the invention are described in silicon, or - a programmable electronic chip such as an FPGA chip (for "Field-Programmable Gate Array" in English), such as a SoC (for "System On Chip" in English) or such as an ASIC (for "Application Specified Integrated Circuit" in English).

[0050] SoCs or system on chip are embedded systems that integrate all the components of an electronic system into a single chip.

[0051] An ASIC is a specialized electronic circuit that combines features tailored to a specific application. ASICs are generally configured during manufacturing and can only be simulated by the user.

[0052] Field-Programmable Gate Array (FPGA) type programmable logic circuits are electronic circuits that can be reconfigured by the user.

[0053] This control device 200 includes input and output interfaces 207 for receiving measurement data. Finally, the control device 200 may include a screen and a keyboard to allow for easy interaction with a user. Of course, the keyboard is optional, particularly in the case of a computer in the form of a touchscreen tablet, for example.

[0054] Depending on the embodiment, the control device 200 may be a computer, a computer network, an electronic component, or another device comprising a processor operationally coupled to memory, as well as, depending on the chosen embodiment, a data storage unit, and other associated hardware elements such as a network interface and a media reader for reading and writing to removable storage media (not shown in the figure). The removable storage media may be, for example, a compact disc (CD), a digital video / multipurpose disc (DVD), a flash drive, a USB flash drive, etc.

[0055] Depending on the embodiment, the memory, data storage unit or removable storage medium contains instructions which, when executed by the control circuit 201, cause this control circuit 204 to perform or control the input interface and output interface 207, data storage in memory 405 and / or data processing parts of the implementation examples of the proposed method described herein.

[0056] Advantageously, the position of the ground vehicle V that the fleet of drones is to track is known in real time. Thus, the position of the ground vehicle V is known at successive instants and received at these successive instants by the control device 200. As an example, the ground vehicle V is connected to the control device 200 so that it can send its position at different successive instants. The position of the ground vehicle V received at a current instant tj is denoted P(tj). For example, the position P(tj) can consist of the GPS coordinates of the ground vehicle V at a current instant tj. Furthermore, when the ground vehicle V is connected to the control device 200, the latter can also send its direction at different successive instants.

[0057] We now describe the method 100 of determining a target position of at least one drone from a fleet of drones, of which a possible example of steps is shown on the flowchart of [Fig.3].

[0058] Initialization

[0059] It is assumed that before the start of the flight mission, the drones in the drone fleet are positioned on the ground. Then, as the start of the flight mission is imminent, the drones in the drone fleet take off to position themselves at a given location Po in the sky and maintain a hover, awaiting the start of the flight mission.

[0060] During a preliminary step S10, which can be performed before the drones in the drone fleet take off to maintain a hover or while they are hovering, the control device 200 receives a set of data comprising: - the outer perimeter P of zone S which must be covered by the fleet of drones during the flight mission; - optionally, the positions of known obstacles that the drone fleet will have to avoid during the flight mission; - the initial disposition Do of the drones in the drone fleet during the flight mission; - a layout width L corresponding to the spatial range covered by the fleet of drones during the flight mission; - the average speed of movement vm of the land vehicle V.

[0061] By outer perimeter, we mean the perimeter of the geometric figure defined by the zone S. According to an example, the perimeter P of the zone S includes a list of GPS (“Global Positioning System”) coordinates.

[0062] According to one example, the obstacles are buildings, natural structures (such as bodies of water) that the drones in the drone fleet must not fly over. For example, obstacle positions can include a list of GPS coordinates. The obstacles together define an inner perimeter of zone S.

[0063] The arrangement Do of the drones in the drone fleet represents the relative position to be reached of the drones with each other at an initial instant t0 when a first position P(t0) of the ground vehicle is received.

[0064] At a current time (tj) during the tracking mission, the drones in the drone fleet are arranged in a configuration D(tj) that mirrors the configuration Do and follows the trajectory of the ground vehicle V. More specifically, the drone configuration D(tj) is defined by a reference point and a polyline, each vertex of which is occupied, during the tracking of the ground vehicle V, by one of the drones. For example, the configuration Do or the configuration D(tj) of the drones is a line along which the drones are aligned. In another example, the drone configuration Do or D(tj) is a circle on which the drones are positioned at regular intervals. When the configuration D(tj) is a line, the drones in the drone fleet will fly in the same direction as the ground vehicle V is moving, maintaining the configuration D(tj) as a line.When the arrangement D(tj) is a circle, the drones in the drone fleet fly along the radial direction in the opposite direction.

[0065] The average speed vm of the land vehicle can be expressed in meters per second (m / s). This speed is defined beforehand, for example, during the planning of the mission to track the land vehicle V by the fleet of drones.

[0066] The layout width L is the width of a band covered by the drone fleet during the flight mission, specifically during the tracking of the ground vehicle V. When the drone layout is a line, the layout width L can be the length of the line. When the drone layout is a circle, the layout width L can be the diameter of the circle. In other words, the layout width L represents a scale factor of the layout D. The layout width L defines the width of a spatial band that will be covered by the drone fleet, and in particular, an overall field of view imaged by imaging devices onboard each drone in the drone fleet. For example, when the drone fleet comprises 3 drones, the layout width L can vary between 20 meters and 150 meters.As will be seen later, method 100 according to the invention allows certain flight parameters of the drones in the drone fleet to be adjusted relative to each other based on the predefined layout width L.

[0067] In a step S15, the control device 200 converts the outer perimeter P and, where applicable, the positions of known obstacles, into local coordinates. By local coordinates, it is understood that coordinates are linked to a local geodetic coordinate system, for example, specific to the country or region where the area is located. S. A geodetic coordinate system can be defined by an EPSG code (from the European Petroleum Survey Group working group). The conversion performed in step S20 will allow for a more precise determination of the drones' flight paths. Any global-to-local coordinate conversion module can be used.

[0068] In some embodiments, step S15 takes place after the S10 acceptance step, and just before the start of the flight mission. In other embodiments, step S15 takes place after the start of the flight mission.

[0069] At an initial time t0, the control device 200 receives a first position P(t0) of the ground vehicle V that the fleet of drones must follow. For example, the first position P(t0) includes the GPS coordinates of the ground vehicle V at the initial time t0.

[0070] Calculation of the first instructions:

[0071] During step S20, the control device 200 converts the first position P(t0) into local coordinates called the first local position Ploc(t0). Local coordinates are understood to be coordinates linked to a local geodetic system, for example, specific to the country or region where zone S is located. The conversion performed during step S20 will allow the trajectory of the drones in the drone fleet to be determined more precisely.

[0072] During a step S25, the control device 200 calculates, based on the first local position Ploc(t0) of the ground vehicle V, the initial arrangement of the drones Do, and the arrangement width L, a first position POk for each drone Dk in the drone fleet. The number of drones is denoted Ndrones. Advantageously, NdroneS is an integer greater than or equal to two. For example, the drone fleet comprises four drones. In another example, the drone fleet comprises six drones. Figures 4A and 4B are schematic representations of the initial positions of the drones in a fleet of four drones in the respective cases of a linear arrangement Do ([Fig. 4A]) and a circular arrangement ([Fig. 4B]). In Figures 4A and 4B, the drones in the drone fleet start from a common initial position Po, for example, the position in which they were hovering.

[0073] According to the invention, the arrangement D(tj) of the drones is maintained in flight, so that the shape of the polyline is maintained during tracking and the reference point follows a trajectory similar to that of the ground vehicle V. The arrangement D(tj) includes a reference point positioned at a reference position, which may be, when the arrangement D(tj) is a line, the midpoint (or centroid) of the line, or when the arrangement D(tj) is a circle, the center of the circle. In some embodiments, this reference point may have, in a substantially horizontal plane, coordinates coinciding with the coordinates of the current position of the ground vehicle V received by the control device 200, or translated relative to these coordinates. For example, the reference point is translated 100 meters in front of the ground vehicle V.

[0074] During the tracking of the land vehicle V, the reference point follows the trajectory of the land vehicle V. In other words, when the trajectory of the land vehicle V at a time tj, defined by its positions P(tj.2) and P(tj1) at two successive times tj.2 and tj4 preceding time tj, is transformed into a new trajectory defined by the position P(tj) and the position received at time tj_i P(tj_j), so as to undergo a rotation by an angle of rotation α, the reference point also undergoes a change of trajectory determined by the angle of rotation α. ​​Figure 5 shows an example of the arrangement of the positions P(tj2), P(tj1), P(tj) and the corresponding angle α. More precisely, the angle of rotation α is determined by: [Math. 1] si a~ ^0^)1

[0075] with the notation I. I denoting the norm of a vector.

[0076] Subsequently, the angle of rotation a corresponding to a new position P(tj) received at a current instant tj will be denoted a(tj).

[0077] When the arrangement D(tj) of the drones is a line, the drones can be regularly positioned along this line, with two drones positioned at the ends of the line. When the arrangement D(tj) of the drones is a circle, the drones can be regularly positioned on the circle.

[0078] It will now be described how, when a new position of the ground vehicle V is received by the control device 200, the latter calculates a new position of the drones in the drone fleet.

[0079] Calculation of the position to be reached _ by the _ drones of the drone fleet at a current instant tj of reception of a current position P(tj ) of the ground vehicle V:

[0080] An embodiment of method 100 is now described at a current time tj at which the control device 200 receives a current position P(tj) of the ground vehicle V. The previous positions of the ground vehicle V received at the preceding times tj₂ and tj₁, P(j₂) and P(j₁), are known, and the corresponding positions of each drone Dk in the drone fleet, Pj₂k and Pj₁ik, are known. For example, the current position P(tj) includes the GPS coordinates of the ground vehicle V at time tj.

[0081] Advantageously, the current position P(tj) is converted into a local current position composed of local coordinates Ploc(tj). By local coordinates, we mean the coordinates in a local geodetic coordinate system.

[0082] In a step S30, from the current position P(tj), the control device 200 calculates the rotation angle a(tj) defined previously.

[0083] In some embodiments, the land vehicle V can also send its direction, so that the rotation angle a(tj) can be calculated by the control device 200 on the basis of two directions received consecutively.

[0084] In some embodiments, the local positions of the land vehicle V are used to calculate the angle of rotation a(tj), these local positions being obtained for example by conversion of GPS coordinates as in step S20.

[0085] In a step S40, given the rotation angle a(tj) determined in step S30 and the relative position of the reference point of the arrangement D(tj) with respect to the current position of the land vehicle V, the control device 200 calculates a current reference position Pref(tj). For example, as seen previously, the relative position of the reference point could be a position 100 meters ahead of the current position P(tj) of the land vehicle V.

[0086] In a step S50, from the reference position at time tj Pref(tj), the arrangement D of the drones and the width L, the control device 200 calculates the new respective positions to be reached of the drones, Pjjkde in the following way.

[0087] Initially, the control device 200 calculates the new arrangement D(tj) by applying a rotation of the angle a(tj) to the arrangement D(tj i) which had been calculated at the time tj.i preceding the current time tj. In other words, the new arrangement D(tj) is the polyline obtained by rotating the previous polyline by the angle a(tj).

[0088] Fig. 6 shows an example of the rotation of the polyline D corresponding to the arrangement D(tj4) in order to obtain the polyline D' corresponding to the arrangement D(tj), as well as the corresponding reference positions Pref(tj 2), Pref(tj i) and Pref(tj).

[0089] In a second step, the position to be reached Pjk, for a drone Dk, is calculated by adding a periodic deviation vector to the position of the vertex of the new polyline corresponding to the drone Dk.

[0090] The deviation vector is determined from a maximum flight speed vmax of the drones, the flight altitude of the drone Dk, the angular field [3k of the at least one drone Dk and e of the speed of movement of the land vehicle V.

[0091] At time tj, the land vehicle V follows a current direction of movement defined by the vector formed by the last position P(tj i) received and the current position P(tj).

[0092] In one embodiment, the Ndrones drones of the drone fleet will each describe a sinusoidal trajectory of amplitude yk(t), centered along the line (Pj. ijk Pjjk). In other words, the periodic deviation vector has a direction perpendicular to the current direction of movement of the ground vehicle V.

[0093] According to the invention, the deviation vector is determined by an amplitude coefficient yk of a drone Dk defined by:

[0094] [Math.2] yk-

[0095] where vmax represents the maximum speed at which each of the drones in the drone fleet can fly, and Vx represents the speed of the land vehicle V at time tj.

[0096] As can be seen in the formula for the amplitude coefficient yk, this coefficient varies with the speed of the ground vehicle V, preferably between 0 and 1, and decreasing as a function of the speed vx of the ground vehicle. In particular, when the ground vehicle V is traveling at a speed lower than the maximum speed of the drones, the fleet of drones describes a sinusoidal trajectory of greater amplitude, so as to cover a wider geographical area.

[0097] The amplitude of the sinusoidal trajectory, perpendicular to the direction of movement of the fleet of drones, and described by a Dk drone, can be written as: , . — . / 7TVJ \ 4(0 = ^111(-^). with Rk being the metric view radius of the drone Dk. The metric view radius Rk is dimensionally consistent with a distance.

[0098] By field of view, we mean the metric field of view detected by an imaging device, such as a camera, onboard the Dk drone. For example, the field of view can be calculated using the formula: / A \ Rk-hkï^n\-^ p with hk the flight altitude of the Dk drone and the angular field of view of the camera on board the Dk drone, in degrees.

[0099] Thus, by construction, the time period of the sinusoidal trajectory of the drones depends on the flight altitude hk of the drone Dk.

[0100] Advantageously, when drones follow such a sinusoidal trajectory, the coverage of the surface S by the fleet of drones is optimized. In other words, flying drones along such a sinusoidal trajectory optimizes the effective width of the area S covered by the fleet of drones.

[0101] According to the invention, the flight altitude hk of each drone Dk is corrected as a function of the amplitude coefficient yk in the following manner:

[0102] [Math.3] ,___L________

[0103] with N^es the total number of drones. Thus, by this adjustment of the flight altitude of the drones in the drone fleet, the layout width L of the band covered by the drone fleet is effectively covered by the union of the fields of view of the drones in the drone fleet.

[0104] Advantageously, the respective positions of the drones Pj, k are converted back into global coordinates, such as GPS coordinates.

[0105] In other embodiments, it may be envisaged that the direction of the deviation vector varies periodically.

[0106] In a step S70, the control device 200 then sends an instruction to the drones in the drone fleet with the corresponding new drone positions Pj>k.

[0107] The sequence of steps S30, S40, S50, S60 and S70 is repeated each time a new current position of the land vehicle V is received.

[0108] The mission ends when a final position of the ground vehicle V is received by the control device 200. The latter then calculates the final positions of the drones. At the end of the mission, the drones in the fleet descend and land on the ground.

[0109] Taking obstacles into account

[0110] Advantageously, the method 100 for determining a position to be reached by at least one drone takes into account obstacles encountered by the fleet of drones during the flight mission, as illustrated in Figures 7A and 7B. In other words, the method 100 according to the invention makes it possible to calculate new positions to be reached by the drones, in the event that it is detected that the fleet of drones is approaching an obstacle, by executing additional steps S80 and S90.

[0111] In some embodiments, the position of the obstacles is known in advance. The obstacles are called known obstacles. For example, the set of positions of the known obstacles is received by the control device 200 during step S10. The known obstacle can also be the outer perimeter P of the area S that the fleet of drones covers.

[0112] Advantageously, an additional first step S80 is triggered when a condition COND is met at a time called the detection time td. For example, this condition COND could be the determination that a distance between a drone Dk and at least one obstacle O is likely to fall below a threshold value.

[0113] For example, this condition may be that a drone in the fleet of drones, or the reference point of the arrangement D(L), is located at a distance less than a distance minimum of an obstacle O among the known obstacles, or less than a minimum distance from the perimeter of the area S to be covered.

[0114] In another example, an unexpected obstacle O may be encountered by the fleet of drones. For example, one of the drones may, via its onboard camera, detect this unexpected obstacle. Advantageously, this detection may be implemented by an object detection algorithm. The satisfied condition COND leading to the execution of step S80 may be the detection of the unexpected obstacle O by one of the drones in the fleet.

[0115] During the first additional step S80, the control device 200 calculates a new configuration, denoted D', of the arrangement D(td) of the drones at the detection time td in the following manner.

[0116] The new configuration D' can result from a change in the arrangement of the drones, a reduction in the width of the arrangement L, a change in the relative angle between the arrangement D(td) and the current direction of travel of the ground vehicle V, or a combination of these three cases. In this way, the control device 200 can ensure that each of the drones in the drone fleet remains at least at a distance greater than the threshold value by modifying the arrangement D(td).

[0117] For example, when the drone arrangement D(td) is a line D comprising two drones at its ends in positions Pa and Pb, as illustrated in [Fig. 7A], the control device 200 calculates the extreme positions of a new line D' with endpoints Pa' and Pb'. According to one example, the distance between the endpoints Da' and Db' is reduced compared to the distance between the endpoints Pa and Pb.

[0118] For example, the length defined by the endpoints Da' and Db' can be calculated as the minimum value between twice the distance between the reference position at the detection time td and the obstacle O, on the one hand, and the product of a metric field of view of the drones by the number of drones Ndrones. The metric field of view can be predefined and of constant value. In another example, the metric field of view can be defined in relation to the predefined angular field of view of one of the drones and to the flight altitude hk of the drones.

[0119] Then, in a second additional step S90, the control device 200 calculates the new corresponding positions of the set of drones from the positions Pa' and Pb' and the length of the line D'.

[0120] In another example, during the first additional step S 80, when the arrangement of the drones D(td) is a circle D centered at the reference point Pref(td) and of diameter L, as illustrated in [Fig. 7B], the control device 200 calculates the position of a new reference point P'ref(td) and a new diameter together defining a new circle D'.

[0121] According to one example, the new diameter of the new circle D' is reduced compared to the diameter L. For example, the new diameter can be calculated as the minimum value between twice the distance between the reference position Pref(td) at the detection time td and the obstacle O on the one hand, and the product of a metric field of view of at least one drone by the number of drones Ndrones in the drone fleet.

[0122] Then, during the second additional step S90, the control device 200 calculates the corresponding new positions of all the drones from the new reference point and the new diameter.

[0123] Step S70 is executed, during which the control device 200 transmits to each drone in the drone fleet the new position calculated in the second additional step S90, towards which the drone must head.

[0124] The method 100 for determining a position to be reached by at least one drone from a fleet of drones has been previously described in the case where the position of the tracked ground vehicle V is received at successive times by the control device 200.

[0125] Other embodiments of method 100 are possible, for example, when the ground vehicle V follows a trajectory T known beforehand. For example, the trajectory T is a list of positions, such as GPS coordinates. Thus, during step S10, the control device 200 also receives the trajectory T. The coordinates of the trajectory T are converted into local coordinates during step S20. Then, steps S30, S40, S50, and S60 are executed by processing all the positions in batches, so as to obtain, after step S60, the total trajectory of at least one drone, corresponding to the trajectory T of the ground vehicle.

[0126] In these embodiments, during the preliminary step S10, the data set received by the control device 200 also receives a sampling step.

[0127] The sampling step refers to the time interval between two positions on the trajectory that the control device 200 will calculate for a drone in the drone fleet and represents the number of positions that the control device 200 must calculate, using the average speed vm of the ground vehicle V, for each drone trajectory within the drone fleet. For example, the sampling step is a duration in seconds. For example, the sampling step could be 2 seconds. In another example, the sampling step could be 1 / 10 of a second.

[0128] Of course, the present invention is not limited to the embodiments described above by way of example; it extends to other variants. Other embodiments are possible.

[0129] Depending on the embodiment chosen, certain acts, actions, events, or functions of each of the methods described in this document may be performed or occur in a different order than described, or may be added, merged, or not performed or occur, as the case may be. Furthermore, in some embodiments, certain acts, actions, or events are performed or occur concurrently rather than sequentially.

[0130] Although described through a number of detailed embodiments, the proposed method and the equipment for implementing the method include various variants, modifications, and improvements that will be obvious to those skilled in the art, it being understood that these various variants, modifications, and improvements form part of the scope of the invention, as defined by the following claims. Furthermore, different aspects and features described above may be implemented together, separately, or substituted for one another, and all the different combinations and subcombinations of aspects and features form part of the scope of the invention. In addition, some of the systems and equipment described above may not incorporate all of the modules and functions described for the preferred embodiments. Industrial application

[0131] The invention may be applied in particular in the field of fire protection and suppression. It may be applied in any other field where a land vehicle must be tracked by a plurality of automated devices in a predetermined geographical area that must be optimally covered by the automated devices.

Claims

Demands

1. A computer-implemented method (100) for determining a target position (Pjk) for at least one drone (Dk) in a fleet of drones controlled by a control device (200) and following a land vehicle (V) moving at a vehicle speed (vx), the control device (200) receiving, at a current time (tj), a current position P(tj) of the land vehicle (V), the method (100) comprising: a. Determination (S40), by a processor of the control device (200), of a current reference position Pref(tj) of the fleet of drones from the current position P(tj) of the land vehicle (V), of a current rotation angle (a(tj)) of the land vehicle (V) and, optionally, of a relative positioning vector of the fleet of drones; b.Determination (S50), by said processor, of said position to be reached (Pjk) by at least one drone (Dk), from the current reference position Pref(tj), of a drone arrangement (D(tj)) and of an arrangement width (L); the drone arrangement (D(tj)) being defined by a reference point and by a polyline of which each vertex is occupied by one of the drones, the arrangement width (L) corresponding to a scale factor of the polyline; the reference point of the arrangement (D(tj)) being positioned at the current reference position; the rotation angle of the arrangement being defined relative to the current rotation angle (a(tj)) of the ground vehicle (V); the position to be reached (Pjk) by at least one drone (Dk) being calculated by adding a periodic deviation vector to a position of the vertex of the polyline corresponding to said at least one drone.

2. Method according to claim 1, characterized in that the periodic deviation vector of at least one drone (Dk) is determined from a maximum flight speed (vmax) of at least one drone (Dk), the flight altitude (hk) of at least one drone (Dk), the angular field (|3k) of at least one drone (Dk) and / or the vehicle speed (vx).

3. Method (100) according to any one of the preceding claims, characterized in that the periodic deviation vector is calculated as a function of an amplitude coefficient (yk) that is a function of the maximum flight speed (vmax) of at least one drone (Dk) and the vehicle speed (vx).

4. A method according to any one of the preceding claims, characterized in that a time period of the periodic deviation vector is calculated as a function of the vehicle speed (vx), the flight altitude (hk) of at least one drone (Dk) and an angular field (|3k) of at least one drone (Dk).

5. A method according to any one of the preceding claims, characterized in that, at time tj, the land vehicle (V) moves along a current direction of movement, defined for example by a vector formed by the last position P(tj_i) of the land vehicle (V) received and the current position P(tj), and the periodic deviation vector has a direction perpendicular to the current direction of movement and an amplitude that varies sinusoidally with time.

6. A method according to any one of the preceding claims, comprising in step b) a determination of the flight altitude (hk) of at least one drone (Dk), the altitude (hk) being a function of the amplitude coefficient (yk), the layout width (L) and / or the angular field of view (|3k) of at least one drone (Dk).

7. A method according to any one of the preceding claims, wherein at time tj, the ground vehicle (V) is moving along a current direction of movement, defined for example by a vector formed by the last received position P(tj.i) of the ground vehicle (V) and the current position P(tj), the method further comprising: - Determining (COND), at a time called detection time (td), that a distance between a drone in the drone fleet and at least one obstacle (0) is likely to become less than a threshold value; - (S 80) Changing the polyline, and / or reducing the layout width (L), and / or changing the relative angle between the layout and the current direction of movement, such that each of the drones in the drone fleet remains at least at a distance greater than said threshold value from said at least one obstacle (0).

8. A method according to the preceding claim, characterized in that, at step S80, when the layout width L is reduced, the layout width is reduced to a value L' equal to the minimum value between twice the distance between the reference position at the detection time (td) and the obstacle (0) on the one hand, and the product of a metric field of view of at least one drone by the number of drones in the drone fleet on the other hand.

9. Product computer program comprising instructions for carrying out the method according to any one of claims 1 to 8, when this program is executed by a processor.

10. A non-transient, computer-readable recording medium on which a program is recorded for the implementation of the method according to any one of claims 1 to 8 when this program is executed by a processor.

11. Assembly comprising a fleet of drones, the assembly comprising a control device (200), the control device (200) comprising at least one processor and a recording medium according to claim 10.

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