FR3071053A1 - CARTOGRAPHY METHOD IMPLEMENTED BY A DRONE - Google Patents

Abstract

The invention relates to a method for mapping an area implemented by a drone flying over the area by automatically following a predetermined flight plan, the drone comprising wings, ailerons, a rudder, the method comprising , during the monitoring of the flight plan, the acquisition of a multitude of shots of the zone by a shooting device carried by the drone and having a fixed optical axis with respect to the drone, the method being characterized in that that it includes, during flight plan tracking, zero roll control to maintain the optical axis at a predetermined angle with respect to a vertical axis with respect to the zone.

Description

MAPPING PROCESS IMPLEMENTED BY A PRONE GENERAL TECHNICAL AREA AND PRIOR ART

The invention relates to the acquisition of digital cartographic data (Geodata) by air, using a drone as a support vector for a shooting device.

Geodata collection by drone over large areas is conventionally carried out by drones of the "airplanes - fixed wing" type, since these aircraft benefit from the significant flight speed and autonomy necessary for this application. They also have the quality of flying according to precise trajectories which is important for collecting good quality Geodata. Finally, this type of aircraft has the advantage of flying stably and thus retaining the orientation of the shooting device with a minimum of angular variations relative to the vertical.

The mapping process is simple: the drone flies over the area to be mapped by taking a multitude of shots, which will then be assembled by computer to reconstruct a vertical image of the area.

A photograph taken at a given altitude covers a plot of the area to be surveyed with longitudinal and transverse dimensions. It is necessary to maintain a constant altitude to avoid disparities in resolution on the map created at the end of the process.

The shots are triggered at defined geographic positions upstream of the flight, and conventionally have an overlap area between shots then allowing them to be assembled together.

Referring to Figure 1, depending on the surface of the area to be mapped 1 and the desired resolution, it is necessary to divide the area to be mapped 1 into a number of bands corresponding to the width that can be captured by the recording device. altitude imagery producing images respecting the required resolution, and allowing a defined overlap between the shots.

A flight plan 2 is therefore established, comprising several segments along which the aircraft will take the pictures.

To cover the entire area as simply as possible from an operational point of view, the subdivision of the area is conventionally carried out by bands parallel to each other, thereby producing parallel sampling segments between them.

The flight plan 2 also contains portions of the trajectory outside the area to be mapped allowing the drone, when it arrives at one end of a sampling segment 3, to position itself by a U-turn to begin the tracking of 'another sampling segment 3.

These out-of-scope segments 4 are generally generated so as to minimize the total path traveled by the drone to perform the mapping operation of the entire area 1, while taking into account the turning radius of the drone and the distance separating the segments d '' sampling 3.

The monitoring of the sampling segments 3 however generates disturbances for the acquisition of imagery. In fact, a deviation from the trajectory lateral to the sampling segment 3 generally results in a slight turn so that the aircraft returns to its sampling segment 3.

This turn, made by tilting the wing (roll), causes the optical axis of the imaging sensor to tilt, thereby shifting the snapshot laterally. In addition, for the shots taken during this turn, the ground will be seen "at an angle" compared to the other shots that will be straight.

Obtaining a map is then highly complex, in addition to reducing its accuracy and resolution, this sometimes involves taking over the entire cartographic survey because "gaps" in data may be present due to the offset of the picture from the planned position.

The roll phenomenon during changes of direction is also particularly troublesome to follow a curved trajectory, or to follow two consecutive sampling segments 3 angularly offset.

The flight of a light drone is particularly sensitive to turbulence and movements of the air mass in which it evolves. These deviations from sampling segment 3 are therefore quite common.

OVERVIEW OF THE INVENTION

An object of the invention is to improve the reliability of imaging acquisition during a mapping process.

Another aim is to simplify the implementation of the mapping process, and therefore consequently to optimize by reducing the duration of the process and its cost.

Another aim is to allow monitoring of several consecutive sampling segments.

Another aim is to allow the tracking of curved trajectories during sampling.

Another aim is to minimize the number of out-of-scope segments in the flight plan.

Another aim is to reduce the flight distance necessary for mapping an area.

Another goal is to increase the size of the areas to be mapped and the speed of acquisition thanks to improvements in device performance.

According to one aspect, the invention provides a method of mapping an area implemented by a drone flying over the area automatically following a pre-established flight plan, the drone comprising a pair of wings equipped with fins and a rudder, the method comprising, during the monitoring of the flight plan, the acquisition of several images of the area by a shooting device carried by the drone and having an optical axis fixed relative to the drone, the method being characterized in that it comprises, during the monitoring of the flight plan, a roll control at zero to maintain the optical axis at a predetermined angle with respect to a vertical axis with respect to the area.

Keeping the roll at zero keeps the optical axis of the vertical imaging device when taking pictures, which optimizes the rate of pictures that can be used for mapping and which greatly improves the quality of the mapping. obtained.

This also makes it possible to minimize the risks of having to start the mapping process again because of too low a quality of the photographs obtained.

This also makes it possible to follow trajectories comprising potions of curves while taking photographs of optimal quality, the follow-up of a curved trajectory no longer causing any variation in roll reducing the quality of the photographs.

This also makes it possible to reduce the distance traveled during the mapping of an area, in particular by making it possible to follow two consecutive sampling segments which have an angular offset.

This makes it possible to define a flight plan minimizing the route traveled outside the area to be mapped, and therefore to increase the time available for sampling, which makes it possible to increase the size of the areas to be mapped using the process.

Such a process is advantageously supplemented by the following characteristics, taken alone or in combination:

the flight plan comprises trajectory segments, the trajectory segments comprising at least two types:

• a sampling segment comprising trajectory information and imagery capture points;

• an off-screen segment with trajectory information;

automatic piloting comprises a first constrained operating mode in which the direction of the drone is controlled by action on the yaw axis only, and a second free operating mode in which the direction of the drone is controlled by action on the roll axes and yaw, the constrained mode being used during the monitoring of the sampling segments, the free mode being used during the monitoring of the segments outside the mapping field;

monitoring a sampling segment includes a trajectory correction method comprising the following steps:

• Calculation of the lateral deviation between the position of the device and the sampling segment;

• Definition of a “corrective action” configured to return to the sampling segment by action on the rudder;

• Roll control generated by movements of the air mass and / or induced by the deflection of the rudder, the roll control being carried out by action on the ailerons and being configured to keep the roll at zero;

the autopilot comprises a method of generating at least one “link trajectory” model outside the flight plan to connect two consecutive flight plan segments offset angularly;

the link trajectory model comprises an entry point included in a first flight plan segment, an exit point included in a second flight plan segment, and a trajectory connecting the entry point and the exit point ;

the link trajectory models include a so-called curve trajectory configured to be able to be traversed by the constrained mode of automatic piloting and a so-called loop trajectory configured to be able to be traversed by the free mode of automatic piloting;

the link trajectory model generated is a function of the angular offset between the two consecutive flight plan segments;

the link trajectory is generated according to criteria comprising the following:

• Tangency at the first segment at the entry point;

• Tangency to the second segment at the exit point;

• Minimization of deviations from the sampling segment (s) when at least one sampling segment is followed;

• Continuous curve;

According to another aspect, the invention provides a device configured to carry out such a mapping method, comprising an aircraft comprising a rudder, elevators and ailerons, an imaging device, an orientation detection means three-dimensional, a three-dimensional position detection means, actuators configured to act on the position of the rudder, elevators and ailerons, a calculation unit for carrying out said method, a computer program comprising the instructions allowing to carry out such a process.

This device is advantageously completed by the following characteristic: the calculation unit is configured to ensure, during the monitoring of the flight plan, a roll control at zero to maintain the optical axis at a predetermined angle relative to a vertical axis relative to the area to be mapped.

PRESENTATION OF THE FIGURES

Other characteristics and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and should be read with reference to the appended figures in which:

Figure 1 is a schematic representation of a flight plan generated by the mapping protocol of the prior art;

Figure 2 is a schematic representation of the control surfaces and conventional axes of rotation of an aircraft;

FIG. 3 is a diagram of the steps of a trajectory tracking method according to the invention;

FIG. 4 is a diagram representing a correction trajectory in the event of an external disturbance, the correction trajectory being produced by a trajectory tracking method according to the invention;

FIG. 5 is a representation of a connection trajectory between two consecutive sampling segments offset angularly, the connection trajectory being produced by a trajectory tracking method according to the invention; more precisely, FIG. 5a represents a curve connection trajectory, produced when the angular offset is below a predefined threshold value; FIG. 5b represents a loop connection trajectory, produced when the angular offset is greater than the threshold value; is a schematic representation of a feasible flight plan according to the invention; and

FIG. 6 represents a flight plan generated by a mapping method according to the invention.

DESCRIPTION OF THE INVENTION

The embodiments described below relate to the case of a mapping method produced from aerial imagery, the method being implemented by an aircraft type drone comprising, with reference to FIG. 2, wings 5, fins 6, elevators 7 and a rudder 8. A shooting device 9 is fixed under the drone and is stationary with respect thereto. Consequently, the orientation of the optical axis 10 of the imaging device depends directly on the orientation of the drone.

The orientation of the drone is defined by a composition of rotations along the roll axes R, pitch T and yaw L.

In order to keep the direction of the optical axis 10 of the imaging device 9 constant, the invention proposes an automatic piloting mode limiting roll taking to zero.

It is understood that the embodiments described below are illustrative and in no way limitative.

The mapping process implements an automatic pilot comprising several operating modes.

Two piloting modes stand out, each one dedicated to a flight phase:

During the course of the out-of-scope segments 4, the imaging device 9 does not work, the inclination of the sensor and therefore of the drone is not constrained;

During the course of the sampling segments 3, the inclination of the optical axis 10 of the imaging device 9 is associated with the vertical, constraining the orientation of the drone in roll.

The first so-called “free” piloting mode corresponding to an unconstrained movement is implemented during the traversing of the out of scope segments 4.

The automatic piloting controls the course conventionally by rotation along the roll axes by action on the ailerons 6.

The second so-called “constrained” piloting mode is implemented during the course of the sampling segments 3, the course modifications ensuring the tracking of the trajectory are carried out by a rotation along the yaw axis.

In the constrained piloting mode, the course modifications are carried out by action on the rudder 8, thus causing a rotation around the yaw axis L.

This action on the yaw axis causes, by so-called “induced roll” effect, a rotation around the roll axis which causes an angular offset of the optical axis of the imaging device 9.

A control loop dedicated to the management of the roll makes it possible, by measuring the roll and by acting on the fins 6, to compensate for this induced roll so as to maintain a stable attitude.

With reference to FIG. 3, the autopilot also implements a method 11 for tracking the trajectory defined by the flight plan 2.

In this embodiment, the lateral deviation 17 from the flight plan is measured to give rise to the calculation of a correction trajectory, making it possible to return to the flight plan.

This trajectory tracking 11 includes a step 22 of estimating the deviation from the trajectory from the flight plan 2 predefined during a step 20 and the GPS data of the drone defined during a step 21.

The estimated deviation and a measurement of the drone heading defined in step 23 are injected into a control loop 24 of the rudder 8 so as to generate a correction on the drone heading to recover the trajectory defined by the flight plan.

The control loop 24 transmits a command to the rudder actuator 25 so as to modify the heading of the drone to reduce the deviation from flight plan 2.

This method is particularly advantageous for overcoming trajectory disturbances due to movements of the air mass, such as a gust of wind, an updraft or a local depression.

With reference to FIG. 4, during a correction of a deviation 17 from a sampling segment 3, a catch-up trajectory 13 will be generated and configured to be followed by control of the rudder 8 only.

During this catching-up trajectory tracking 13, the fins 6 do not act on the heading but maintain the roll at zero, so as to limit the oscillations of the optical axis 10 of the imaging device 9.

An atmospheric disturbance deviating the drone from its trajectory will thus have a limited impact on the mapping of the area, the constrained piloting mode favoring the quality of the imagery rather than a rapid return to the trajectory.

With reference to FIG. 5, the mapping method implements a method for generating connection trajectories 14 allowing the drone to pass from a sampling segment 3 to the following sampling segment 3 in the flight plan 2.

A connecting trajectory 14 comprises an entry point 15 included in a first segment 3 followed, a trajectory and an exit point 16 included in a second segment 3 followed.

In one embodiment, in order to ensure a rapid transition from the connecting trajectory 14 to the flight plan segment 2, the connecting trajectory 14 is tangent to the flight plan segments 2 which it connects, at the point inlet 15 and / or outlet 16.

The connection path 14 generated has radii of curvature adapted to the active driving mode.

This generation of connection trajectories 14 makes it possible in particular to follow several consecutive sampling segments 3 angularly offset, which gives a clear advantage for mapping areas extended longitudinally, such as a rail or electric network.

These connecting trajectories 14 can have different plots depending on the type of segment followed and the angular offset of the consecutive segments:

For a small angular offset, the connection path 14 generated is a portion of the curve, illustrated in FIG. 5a;

For an angular offset greater than a certain threshold, the connection path 14 generated comprises at least one loop, illustrated in FIG. 5b;

The drone does not follow the route established during flight plan 2 when it follows these connecting trajectories 14. Consequently, a significant deviation from flight plan 2 could induce an incomplete mapping of the zone 1 studied.

It is therefore necessary for the connecting paths 14 to be as close as possible to the segments of flight plan 2.

The connecting paths 14 are therefore generated so as to minimize the deviations 17 from the flight plan 2.

With reference to FIG. 5b, in the case of a loop trajectory, this calculation is not necessary, the loop starting at the end of the first segment 3 of the flight plan and ending at the start of segment 3 of the flight plan 2 next. The flight plan segments 2 are therefore followed in full.

When following a link trajectory 14 in a loop, the cartographic reading is interrupted, the drone no longer following the sampling segments 3. It is therefore not necessary to maintain the orientation of the optical axis 10 of the imaging device 9.

A link trajectory 14 in a loop can therefore be covered by the free piloting mode, allowing tighter turns and therefore reducing the length of the link trajectory 14, and incidentally the total length of the flight plan.

With reference to FIG. 5a, in the case of a curve trajectory, the computer evaluates the area of a transition zone 18. The transition zone 18 is delimited by the connection trajectory 14 and the plane plane segments volume 2.

The computer adapts the layout of the connection path 14 to minimize the area of the transition zone 18.

When tracking the connecting trajectory 14 in a curve, the drone follows the flight plan 2 and always flies over the area to be mapped 1. The imaging device 9 therefore operates normally and continues to take pictures.

It is therefore necessary to maintain the roll at zero so as to maintain the verticality of the optical axis 10 of the imaging device 9.

The constrained piloting mode is therefore used to follow a connecting trajectory 14 in a curve, so as to guarantee the quality of the photographs obtained.

Tracking successive 3 sampling segments without suspending the taking of pictures makes it possible to reduce the mapping time of an area.

A connecting trajectory 14 in curve reduces the duration of the flight plan necessary for the mapping of an area compared to connecting trajectories 14 in a loop.

The areas to be mapped during the process can therefore be more extensive.

Another gain in distance is obtained during the definition of the flight plan 2. In fact, the method makes it possible to traverse sampling segments 3 consecutive angularly offset.

The mapping of a long and winding area, for example a railway network, can therefore be carried out by generating sampling segments traversing the area longitudinally, instead of generating a multitude of sampling segments 3 parallel so to cover the area.

Consequently, the number of out-of-scope segments 4 is greatly reduced, thus making it possible to cover a much larger area for the same flight plan distance 2.

The total mapping of a sector made up of several zones to be mapped can therefore be carried out more quickly, because the sector will be divided into a smaller number of zones.

When the angular offset a between the consecutive sampling segments 3 exceeds a predefined threshold value, for example of 30 °, the method generates a link trajectory 14 in a loop.

The automatic piloting process is implemented by a control loop of the various parameters relating to the position and orientation of the drone in space and relative to the trajectory followed.

In one embodiment, the drone is equipped with a GPS tracking device which makes it possible to determine its position and thus to determine its deviation 17 from the trajectory.

An inertial unit equipped on the drone makes it possible to capture information relating to the rotational movements of the drone with respect to the axes of roll, pitch and yaw. These data are then processed and integrated to determine the orientation of the drone in real time and thus make a correction if necessary.

The functions of automatic piloting and generation of link trajectories implemented by the mapping method by overflight of an area by a drone therefore allow monitoring of 3 consecutive sampling segments offset angularly while maintaining imaging quality optimal and constant and minimizing the effects of atmospheric disturbances on imagery.

With reference to FIG. 6, in the case where the consecutive segments are two sampling segments 3, the connection path 14 generated has radii of curvature adapted to be followed by action on the rudder 8, in particular by varying the length of the connecting path 14.

In a case where the consecutive segments are a sampling segment 3 and an off-screen segment 4, the link trajectory 14 generated prioritizes the monitoring of the sampling segment 3. When the drone leaves the sampling segment 3, it catches up the out-of-scope segment 4 in the flight zone where the free piloting mode is active.

The mapping of the area then presents optimum reliability, while minimizing the distance traveled by the drone.

In a case where two consecutive segments are two off-screen segments 4, the link path 14 generated is configured to minimize the distance traveled by the drone.

The connecting trajectory therefore has radii of curvature adapted to be followed by the free piloting mode. These provisions make it possible to minimize the distance traveled by the drone, and therefore incidentally the duration and the cost of the process.

Claims (11)

1. Method for mapping a zone (1) implemented by a drone flying over the zone (1) by automatically following a predetermined flight plan (2), the drone comprising wings (5), ailerons ( 6), a rudder (8), the method comprising, during the monitoring of the flight plan (2), the acquisition of a multitude of shots of the area (1) by an imaging device (9 ) carried by the drone and having an optical axis (10) fixed relative to the drone, the method being characterized in that it comprises, during the monitoring of the flight plan (2), a roll control at zero to maintain the optical axis (10) at a predetermined angle with respect to a vertical axis with respect to the area (1). 2. Mapping method according to claim 1, characterized in that the flight plan (2) comprises trajectory segments, the trajectory segments comprising at least two types: a sampling segment (3) comprising trajectory information and imagery capture points; an off-screen segment (4) including trajectory information. 3. A mapping method according to claim 2, characterized in that the automatic piloting comprises a first constrained operating mode in which the direction of the drone is controlled by action on the yaw axis only, and a second free operating mode in which the direction of the drone is controlled by action on the roll axes, and in that the constrained mode is used when monitoring the sampling segments (3), the free mode being used when monitoring the out-of-scope segments (4 ) of cartography. 4. Mapping method according to one of claims 2 or 3, characterized in that the monitoring of a sampling segment (3) comprises a trajectory correction method comprising the following steps: Measurement of the lateral deviation between the position of the device and the sampling segment (3); Definition of a “correction trajectory” (13) configured to return to the sampling segment (3) by action on the rudder (8); - Roll control generated by disturbances due to the air mass and / or induced by the deflection of the rudder (8), the roll control being carried out by action on the ailerons (6) and being configured to maintain roll to zero. 5. Mapping method according to one of claims 1 to 4, characterized in that the automatic piloting comprises a method of generating at least one “link trajectory” model (14) outside the flight plan (2) to connect two consecutive flight plan segments (2) angularly offset. 6. A mapping method according to claim 5, characterized in that the link trajectory model (14) comprises an entry point (15) included in the first flight plan segment (2), an exit point ( 16) included in the second flight plan segment (2), and a trajectory connecting the entry point (15) and the exit point (16). 7. Mapping method according to one of claims 5 and 6, characterized in that the connection trajectory models (14) comprise a trajectory called curve configured to be able to be traversed by the constrained mode of automatic piloting and a trajectory called in loop configured to be able to be traversed by the free mode of automatic piloting. 8. A mapping method according to claim 7, characterized in that the link trajectory model (14) generated is a function of the angular offset between the two consecutive flight plan segments (2). 9. Mapping method according to one of claims 5 to 8, characterized in that the connection trajectory (14) is generated according to criteria comprising the following: - Tangency at the first segment at the entry point; - Tangency to the second segment at the exit point; Minimization of deviations from the sampling segment (s) (3) when at least one sampling segment (3) is followed; - Continuous curve. 5 10. Device configured to carry out the mapping method according to one of the preceding claims, characterized in that it comprises an aircraft comprising a rudder (8), elevators (7) and ailerons (6), an imaging device (9), a three-dimensional orientation detection means, a three-dimensional position detection means, actuators configured to act on the position of the rudder (8), elevators (7 ) and ailerons (6), a calculation unit making it possible to carry out said process, a computer program comprising the instructions making it possible to carry out such a process. 15 11. Device according to claim 10, characterized in that the calculation unit is configured to ensure during tracking of the flight plan (2), a roll control at zero to maintain the optical axis (10) of the imaging device (9) at a predetermined angle with respect to a vertical axis with respect to the area (1) to be mapped. 1/3