Obstacle detection method using a LIDAR obstacle sensor system for a rotary-wing aircraft

Abstract

The present invention relates to a method for detecting obstacles with an aircraft (1) having at least one rotary wing (5). This method comprises: i) acquisition (STP1) of a cloud of detected points with at least one LIDAR obstacle sensor (21, 22, 23, 24), ii) positioning (STP2) of each detected point in an orthonormal frame (100) attached to the aircraft having a first axis (Z) coinciding with an axis of rotation (AXROT) of the rotary wing (5), iii) division (STP3) of the surrounding space into volumetric units, the detected point(s) present in the same volumetric unit being all replaced by a representative point, iv) segmentation of the ground, v) determination (STP5) of the presence or absence of at least one obstacle from the distinct representative points of the ground; and display (STP6) on a display of symbology illustrating said obstacle in relation to the aircraft. Abbreviated figure: Figure 1

Description

Title of the invention: Method for obstacle detection with a LIDAR obstacle sensor system for a rotary-wing aircraft

[0001] The present invention relates to a method of obstacle detection with a LIDAR obstacle sensor system for a rotary-wing aircraft.

[0002] An aircraft may include one or more systems to avoid a mid-air collision with an obstacle, such as, for example, a building, a pylon, a cable, a crane, or the like. The term "obstacle" used hereafter refers to any object capable of colliding with an aircraft.

[0003] Various systems are known to avoid a collision during a flight carried out near obstacles, for example during mountain rescue missions or in an environment cluttered with pylons, cranes or other structures, or during maneuvers close to the ground.

[0004] Such a system may include an active obstacle sensor configured to detect one or more obstacles in flight, and a display highlighting the detected obstacles. The obstacle sensor may include one or more obstacle sensors of the type known by the acronym LIDAR and the English expression "Light Detection and Ranging." A LIDAR system is equipped with a transmitter that sends pulses of light, generally a laser, into a small-aperture detection area. When a pulse encounters an obstacle, it is reflected and captured by a receiver. By measuring the pulse's return time, the system is able to detect and calculate the distance to the obstacle.

[0005] If all obstacles present in the detection field are detected and reported then the display showing these detected points can then be saturated.

[0006] However, the obstacle avoidance warning system for helicopters must not further increase the already significant workload of the pilots. In particular, it is desirable that it not trigger continuous alerts when the aircraft is flying over the ground, but that it focus only on actual obstacles. Otherwise, the pilot may, out of frustration, deactivate the system. Furthermore, the perception system must be capable of rapidly analyzing and understanding the environment in real time. This ensures that each step in the sensor processing chain is executed within a predetermined timeframe, thus enabling pilots to make informed decisions in a safe environment.

[0007] To improve an obstacle detection system, this system can implement a real-time ground segmentation algorithm. Indeed, the pilot looking at the The outside world already has a mental representation of the ground, and displaying symbols illustrating other obstacles may be sufficient to assist it. This technique has the drawback of requiring significant computing resources and therefore potentially resulting in cumbersome, expensive, and / or bulky systems.

[0008] In this context, document CN 116524219 A is outside the scope of the invention, as it relates to an automotive system. This document describes a method comprising preprocessing the point cloud obtained with a sensor, filtering the point cloud by removing outliers, and then subsampling. This method includes separating, on the one hand, a point cloud corresponding to the ground and, on the other hand, a point cloud corresponding to one or more obstacles by means of a linear fitting algorithm that takes into account the rounded shape of a road surface.

[0009] The present invention then aims to propose an innovative method and system for detecting obstacles.

[0010] The invention thus relates to an obstacle detection method implemented by an aircraft having at least one rotary wing. This obstacle detection method comprises:

[0011] - acquisition of a point cloud detected with at least one obstacle sensor LIDAR onboard the aircraft,

[0012] -positioning of each detected point in a predetermined orthonormal frame attached to the aircraft, this frame having a first axis coinciding with an axis of rotation of the rotating wing,

[0013] - division of the surrounding space into volumetric units having a geometry predetermined, the detected point(s) present in the same volumetric unit are all replaced by a representative point,

[0014] - segmentation of the ground by a treatment to detect each ground point belonging on the ground among the representative points; said processing comprising, for each representative point, a detection of whether a normal passing through that representative point has or does not have an angulation, with an axis parallel to the axis of rotation, greater than a predetermined angular threshold, said normal being a normal to a surface, this surface comprising that representative point and neighboring points,

[0015] - determination of the presence or absence of at least one obstacle by grouping of representative points distinct from ground points; and in the presence of at least one obstacle, display on a screen of symbology illustrating said obstacle in relation to the aircraft.

[0016] Thus, one or more LIDAR obstacle sensors make it possible to acquire a cloud of points called "detected points" for convenience.

[0017] From this point on, the detected point cloud is transformed by a person skilled in the art using a process called "voxelization." Each volumetric unit is usually called a "voxel." All detected points within a volumetric unit are replaced by a single point, called a "representative point," for convenience. The size of each volumetric unit influences the number of points to be processed, and consequently the time and resources required to detect obstacles. Large volumetric units will produce a smaller representative point cloud, but with a risk of losing fine details, such as those of electrical cables, and vice versa.For example, each volumetric unit has the shape of a cube with sides between 25 centimeters and one meter, or even between 50 centimeters and one meter, and for example with sides of 55 centimeters, in order to have good precision while limiting the resources needed to implement the process.

[0018] Therefore, the method includes a ground segmentation step to facilitate calculations. Due to the specific characteristics of a rotary-wing aircraft, and for example a helicopter, which exhibits small pitch and roll angles in flight, particularly during flight phases in which the aircraft flies close to obstacles, all representative points associated with a normal substantially parallel to the rotation axis of the rotary wing are likely to belong to the ground.

[0019] The detection of one or more obstacles is then carried out in the usual way on the basis of all representative points that are not considered to belong to the ground. For example, to detect and identify obstacles, the method can implement a grouping algorithm, such as the algorithm known by the acronym "HDBSCAN" and the English expression "Hierarchical Density-Based Spatial Clustering of Applications with Noise" or a grouping algorithm by Euclidean distance.

[0020] The detected obstacle(s) are then represented in a two- or three-dimensional representation, for example.

[0021] Thus, the method of the invention makes it possible to segment the soil quickly and with reasonable computer means, which can be achieved with a potentially lightweight, inexpensive and / or compact system.

[0022] The obstacle detection method may also include one or more of the following features, taken alone or in combination.

[0023] According to one possibility, the representative point of a volumetric unit can be the equally weighted center of gravity of the detected points of that volumetric unit or the center of gravity of the detected points of that volumetric unit weighted by a light intensity of those detected points, said light intensity being provided by said LIDAR obstacle sensor.

[0024] According to a possibility compatible with the preceding ones, the predetermined angular threshold can be equal to 20°.

[0025] Such a threshold makes it possible to achieve acceptable accuracy.

[0026] According to a possibility compatible with the preceding ones, said symbology may include a symbol which has a colour which varies according to a level of danger of the obstacle determined according to a distance or an estimated time of impact between the obstacle and the aircraft.

[0027] A color coding indicating the level of danger, based on distance or time to impact assessed using the current velocity vector and distance, can facilitate visual interpretation and decision-making by the pilot.

[0028] According to a possibility compatible with the preceding ones, if for a representative point said angulation is less than or equal to the predetermined angular threshold then this representative point is a point of interest likely to belong to the ground, said processing comprising a detection of each ground point belonging to the ground among the points of interest.

[0029] A first filter then consists of determining the point(s) of interest likely to belong to the ground, depending on the inclination of the associated normal.

[0030] The normal can be determined by a classical method based on eigenvalue decomposition. For each representative point, the neighboring points are determined, followed by the centroid of the group of points comprising this representative point and the neighboring points. A covariance matrix is ​​determined using the centroid and the neighboring points. This matrix captures both the variation and the orientation of these neighboring points with respect to their centroid, providing information on the local spatial distribution. The eigenvectors of the covariance matrix are then calculated and represent the principal directions of variation of the neighboring points. The eigenvector associated with the smallest eigenvalue is then the normal of interest.

[0031] According to a possibility compatible with the preceding ones, said neighboring points of a representative point whose normal is estimated may include all representative points located at a distance less than a predetermined distance from this representative point.

[0032] According to a possibility compatible with the preceding ones, said detection of each ground point belonging to the ground among the points of interest may include a comparison between an altitude of each point of interest and an average altitude of the representative points of the neighborhood, a point of interest being a ground point when the altitude of the point of interest less the altitude of each representative point of the neighborhood is less than a predetermined limit and that each representative point of the neighborhood of the point of interest is also a point of interest, the altitude of a point of interest being equal to the coordinate of this point of interest along the first axis.

[0033] Each point of interest is definitively considered to belong to the ground if it meets a proximity criterion in altitude (i.e., if it is at approximately the same altitude as its neighbors, within a tolerance) and a neighborhood consistency criterion (i.e., if the neighboring points are also points of interest). This method can optimize computation time. Furthermore, this method allows for precise and robust identification of points belonging to the ground within a point cloud.

[0034] For example, said predetermined limit may be equal to 1.5 meters.

[0035] For example, the neighborhood of a point of interest may include a number predetermined of nearest representative points in a sphere centered on this point of interest.

[0036] For example, the predetermined number is equal to 15. Thus, by way of illustration, the neighborhood of a point of interest studied comprises the 15 closest representative points of this point of interest studied in a sphere centered on this point of interest studied.

[0037] According to another method, said detection of each ground point may include the application of a random sampling consensus algorithm which determines at least one parameter of a planar model and each point of interest consistent with this planar model, each point of interest consistent with this planar model being a ground point.

[0038] The random sampling consensus algorithm is also known by the English expression "RANdom SAmple Consensus" and the acronym RANSAC. This algorithm is an iterative method used to estimate the parameters of a predetermined model that best represent the initial point cloud from which a set of outliers has been subtracted. The model is an affine plane, and the parameters characterize its orientation and a point belonging to it. Typically, the algorithm iteratively selects subsets of points of a predetermined size from among the already filtered points of interest. This selection is performed randomly to estimate planar models, and after a limited number of iterations, the algorithm selects the so-called optimal planar model that is closest to the random subset from which it was derived.Next, points that are at a distance from this plane greater than an optimal threshold are considered as points of interest not belonging to the ground.

[0039] The invention further relates to an aircraft having at least one rotary wing, said aircraft having an obstacle detection system comprising at least one LIDAR obstacle sensor as well as a controller and a display, the controller communicating with said at least one LIDAR obstacle sensor and said display.

[0040] The obstacle detection system is configured to implement the aforementioned method. Thus:

[0041] - said at least one LIDAR obstacle sensor is configured to perform said acquisition of a cloud of detected points,

[0042] - said controller is configured to perform said positioning of each point detected in a predetermined orthonormal frame attached to the aircraft, said division of the surrounding space into volumetric units, said segmentation of the ground, and said determination of the presence or absence of at least one obstacle, and

[0043] -said display is configured to perform, in the presence of at least one obstacle, said display of a symbology illustrating said obstacle in relation to the aircraft.

[0044] The invention and its advantages will become apparent in more detail in the following description, with illustrative examples given by reference to the accompanying figures, which represent:

[0045] [Fig. 1], a top view of an aircraft according to the invention,

[0046] [Fig.2], a diagram illustrating an obstacle detection system according to the invention,

[0047] [Fig. 3], a flowchart illustrating the process implemented by such an obstacle detection system,

[0048] [Fig. 4], a diagram showing a display of such an obstacle detection system representing obstacles in two dimensions, and

[0049] the [Fig.5], a diagram showing a display of such an obstacle detection system representing obstacles in three dimensions.

[0050] Elements present in several separate figures are assigned one and the same reference.

[0051] Fig. 1 presents an aircraft 1 according to the invention equipped with a rotating wing 5 movable in rotation around an axis of rotation AXROT.

[0052] For example, the aircraft 1 comprises a cell 2 which extends longitudinally along its roll axis and from rear to front, from a tail 4 to a nose 3, transversely from one side to a second side and in elevation from a boat to a top. The rotating wing 5 is then mobile in rotation above the cell 2 according to [Fig. 1].

[0053] Furthermore, the aircraft 1 includes an obstacle detection system 10 to detect any obstacles present in the surrounding space, and if necessary, to signal them to a pilot. The detected obstacle(s) are positioned in a predetermined orthonormal frame of reference 100 attached to the aircraft 1. This frame of reference 100 has a first Z-axis coinciding with an axis of rotation AXROT of the rotary wing 5, as well as a second X-axis and a third Y-axis perpendicular to the first Z-axis. The second X-axis extends longitudinally in a direction from rear to front, or vice versa, while the third Y-axis extends transversely in a direction from one side to the other.

[0054] This obstacle detection system 10 includes an obstacle sensor 20 for detecting obstacles, for example 360 ​​degrees around the axis of rotation AXROT.

[0055] The obstacle sensor 20 can be configured to scan obstacles in a first volume covering 360 degrees in azimuth around the rotation axis AXROT of the rotary wing 5 and having an opening in elevation ranging from +10° above the rotary wing 5 to -20° below the rotary wing 5. In addition, the obstacle sensor 20 can be configured to be able to cover forward of the aircraft 1 a second volume encompassing a part of the first volume, extending in azimuth relative to said reference frame over 120 degrees for example, and having an opening in elevation ranging from +10° above the rotary wing 5 to -50° below the rotary wing 5.

[0056] The obstacle sensor 20 can be configured to detect obstacles at speeds up to 30 knots (approximately 55.56 kilometers per hour), and with a maximum range of around 200 meters. Thus, such an obstacle sensor 20 provides a pilot with an acceptable reaction time.

[0057] To this end, the obstacle sensor 20 comprises at least one LIDAR obstacle sensor 21, 22, 23, 24. According to the example in [Fig. 1], the obstacle sensor 20 comprises at least four LIDAR obstacle sensors 21, 22, 23, 24, for example, located near the rotary wing 5. For example, a first LIDAR obstacle sensor 21 is mounted on the cell under the rotary wing and directed towards the front of the aircraft 1, for example, to cover the second volume mentioned above, and can be tilted downwards and forwards with respect to the aircraft 1, and two LIDAR obstacle sensors 22, 23 are mounted on the cell under the rotary wing and directed to cover volumes on the sides of the two flanks respectively, and a fourth LIDAR obstacle sensor 24 is mounted on the cell under the rotating wing and directed towards the rear of aircraft 1. Optionally, the LIDAR obstacle sensors 21, 22, 23, 24 can cover overlapping volumes.We will refer to the literature for examples of a sensor equipped with at least one LIDAR sensor.

[0058] Each obstacle sensor 21 LIDAR can emit light pulses, and for this purpose include, by way of example, a plurality of LASER diodes.

[0059] With reference to [Fig. 2], the obstacle detection system 10 further comprises a controller 15 including at least one processing unit. Such a processing unit may include, for example, at least one processor and at least one memory, at least one integrated circuit, at least one programmable system, at least one logic circuit, these examples not limiting the scope given to the expression "processing unit". The term processor may refer to a central processing unit known by the acronym CPU, a graphics processing unit GPU, a digital signal processing unit known by the acronym DSP, a microcontroller...

[0060] The controller 15 is in communication with the obstacle sensor 20, namely with the obstacle sensor(s) 21, 22, 23, 24.

[0061] Furthermore, the controller 15 can be connected via wired or wireless connection to a speed sensor 31. The speed sensor 31 can include at least one sensor for determining a velocity vector of the aircraft 1. For example, the speed sensor 31 can include a receiver for a satellite positioning device, a navigation system using the Doppler-Fizeau effect, an inertial measurement unit...

[0062] Furthermore, the controller 15 is in wired or wireless connection with a display 25. This display 25 may include a display means 26, such as a screen, a helmet visor, a spectacle lens, a head-up collimator or others.

[0063] The controller 15 may, for example, include a processing unit to implement the invention and a symbol generator to display symbols on the display within one or more processing units. The symbol generator may be integrated into the display 25 or located remotely. For example, the display 25 and the symbol generator may form a single unit, the processing unit being dedicated or not to the process of the invention.

[0064] Regardless of how the obstacle detection system 10 is implemented, [Fig.3] illustrates the obstacle detection method according to the invention implemented by such an aircraft 1 in an iterative manner.

[0065] This method includes acquiring, during a step STP1 and with the obstacle sensor 20, a cloud of detected points. Each LIDAR obstacle sensor 21, 22, 23, 24 emits a light beam 200. When a light beam 200 strikes a point on an obstacle, referred to for convenience as the "detected point PT," an echo 201 is reflected back to the obstacle sensor 21, 22, 23, 24. The obstacle sensor 21, 22, 23, 24 deduces positioning data from this, enabling the obstacle to be located in the coordinate system 100, and even the light intensity of the echo 201. This positioning data may include the distance DL separating the detected point PT from the obstacle sensor 21, as well as a bearing angle and a elevation angle in the obstacle sensor's reference frame.

[0066] Therefore, the process includes positioning, during an STP2 step and with the controller 15, of each detected point PT in the frame 100. The controller 15 is then configured, for example by executing instructions stored in a memory, to implement this step.

[0067] These two initial steps STP1, STP2 allow the detected points PT detected in the surrounding space to be structured in a coherent manner.

[0068] The method then comprises, during an STP3 step and with the controller 15, a division of the surrounding space into volumetric units having a geometry predetermined. All detected PT points present in the same volumetric unit are further replaced by a representative point.

[0069] The controller 15 then applies a commonly used "voxelization" algorithm for this purpose. The controller 15 is then configured, for example by executing instructions stored in memory, to implement this step.

[0070] According to one possibility, the controller 15 calculates the coordinates of the representative point of each volumetric unit, considering that this representative point is the equal-weighted centroid of the detected points of that volumetric unit. The coordinates of the representative point are calculated based on the coordinates of the detected points of the volumetric unit.

[0071] Alternatively, the controller 15 calculates the coordinates of the representative point of each volumetric unit in the frame 100, considering that this representative point is the centroid of the detected points of this volumetric unit weighted by the light intensity of these detected points. The coordinates of the representative point are therefore calculated as a function of the coordinates of the detected points of the volumetric unit weighted by the light intensity of the detected points.

[0072] This method, using various geometric shapes such as cubes or parallelepipeds for example, simplifies the management of a very large number of detected points, by balancing computational complexity and precision.

[0073] The method then includes a ground segmentation implemented with the controller 15. The controller 15 is then configured, for example by executing stored instructions, to implement this step. The controller 15 identifies, among the representative points, the ground points belonging to the ground being overflown in order to reduce the calculation time.

[0074] This soil segmentation includes a processing, during an STP4 step implemented with the controller 15, allowing the identification of representative POBS points not belonging to the soil and representative points called "soil points" belonging to the soil.

[0075] During this processing, the controller 15 is configured to determine points of interest among the representative points during an STP41 step. This processing further includes a detection during an STP44 step of each ground point belonging to the ground among the points of interest.

[0076] To this end, the processing includes, for each representative point, a detection, during an STP41 step implemented with the controller, of whether a normal passing through this representative point has an angle with an axis parallel to the axis of rotation greater than a predetermined angular threshold. This normal is a normal to a surface, this surface passing through this representative point and neighboring points. For example, said predetermined angular threshold is equal to 20°. If the normal If the angle of rotation with an axis parallel to the axis of rotation exceeds the predetermined angular threshold, then the representative point does not belong to the ground.

[0077] Such filtering by normal calculations reduces the complexity of the processing and quickly excludes points not meeting the flatness criteria associated with the ground.

[0078] To this end, for each volumetric unit, the controller 15 is configured to determine the normal, at a representative point, to a surface passing through that representative point and neighboring points. For each representative point, neighboring points include all representative points located at a distance less than a predetermined distance, for example, on the order of 2 to 4 times the length of a side of a volumetric unit, from that representative point. The controller 15 then determines an angle separating this normal from an axis parallel to the axis of rotation and compares it to the predetermined angular threshold. If this angle is not less than or equal to the predetermined angular threshold, in accordance with arrow NI, the representative point is not a point belonging to the ground but a so-called "obstacle point POBS," which may belong to an obstacle.Conversely, and according to the arrow Yl, the representative point is a point of interest which can be a ground point PSOL.

[0079] Therefore, [Fig.3] describes two variants for carrying out the STP44 step aimed at evaluating whether a point of interest is an obstacle point POBS or a ground point PSOL.

[0080] According to the first variant illustrated in solid lines, the STP44 detection of each PSOL ground point belonging to the ground among the points of interest involves a comparison, during an STP42 step, between an altitude of each point of interest and an average of the altitudes of representative points in the neighborhood. The controller 15 thus determines a difference between the altitude of each point of interest and the average of the altitudes of the points in the neighborhood. If this difference is less than a predetermined limit, for example, equal to 1.5 meters, then, according to arrow N2, the point of interest is not a PSOL ground point but an obstacle point POBS. Conversely, and according to arrow Y2, the point of interest may be a PSOL ground point.

[0081] It should be noted that the neighborhood of a point of interest includes a predetermined number, for example equal to 15, of nearest representative points in a sphere centered on that point of interest.

[0082] After, at the same time as, or before step STP42, the controller 15 determines during step STP43 whether each representative point in the vicinity of the point of interest is also a point of interest meeting the aforementioned normal criterion. If not, and in accordance with arrow N3, the point of interest is not a ground point PSOL but an obstacle point POBS. Conversely, and according to arrow Y3, the point of interest may be a ground point PSOL.

[0083] Therefore, controller 15 considers a representative point to be a ground point if three conditions are met simultaneously, namely: i) if the representative point is a point of interest, ii) the altitude of a representative point is substantially equal to the average altitude of the representative points in the neighborhood, iii) the representative points in the neighborhood are points of interest.

[0084] According to the second variant illustrated in dotted lines, the STP44 detection of each PSOL ground point involves the application, during an STP45 step, of a random sampling consensus algorithm which determines at least one parameter of a planar model and each point of interest consistent with this planar model, each point of interest consistent with this planar model being a PSOL ground point.

[0085] Regardless of the variant, the method includes determining, during an STP5 step implemented with the controller 15, the presence or absence of at least one obstacle from distinct representative points on the ground, namely the obstacle points POBS. The controller 15 is then configured, for example by executing stored instructions, to implement this step.

[0086] Thus, after the segmentation of the ground, the detected points PT which do not meet the ground criteria are grouped by the controller 15. This step makes it possible to identify and clearly distinguish potential obstacles in the environment by applying a method known to the person skilled in the art.

[0087] Therefore, in the presence of at least one obstacle, the method includes an STP6 display on a display 25 of a symbology illustrating said obstacle in relation to the aircraft 1.

[0088] For example, the controller 15 transmits a digital signal to the display 25 carrying the information to be displayed. The results can be displayed in two dimensions or three dimensions. In addition, a symbol representing an obstacle can have a color that varies according to a danger level of the obstacle determined based on a distance or time of impact between the obstacle and the aircraft 1.

[0089] For example, an obstacle is not considered dangerous if it is located at an estimated distance or time of impact greater than a first predetermined respective value, moderately dangerous if it is located at a distance or time of impact less than or equal to the first predetermined respective value and greater than a second predetermined respective value, and dangerous if it is located at a distance or time of impact less than or equal to the second predetermined respective value.

[0090] Fig. 4 illustrates an embodiment displaying the results in two dimensions through a polar graph.

[0091] The screen displays an aircraft symbol 60 representing aircraft 1. This aircraft symbol 60 is at the center of concentric circles divided into angular sectors 65-67. Each angular sector represents a symbol that may illustrate the presence of an obstacle. If an obstacle is detected in an angular sector, that angular sector 65-67 is highlighted, possibly according to the level of danger. estimated obstacle. For example, an angular sector 65 is colored green if the obstacle is not considered dangerous, an angular sector 66 is colored orange if the obstacle is moderately dangerous and an angular sector 67 is colored red if the obstacle is considered dangerous.

[0092] Figure 5 illustrates an embodiment displaying the results in three dimensions. Only obstacles are displayed by means of symbols 68, while the ground is either omitted or colored differently to provide better distinction. The symbols can take the form of dots, each symbol representing an obstacle point. Circular arcs 71-75 can be arranged at ground level to illustrate distances from the aircraft.

[0093] Naturally, the present invention is subject to numerous variations in its implementation. Although several embodiments have been described, it is understood that it is not conceivable to exhaustively identify all possible embodiments. It is, of course, conceivable to replace a described means with an equivalent means without departing from the scope of the present invention as defined by the claims.

Claims

Demands

1. An obstacle detection method implemented by an aircraft (1) having at least one rotary wing (5), characterized in that the obstacle detection method comprises: - acquisition (STP1) of a cloud of detected points with at least one LIDAR obstacle sensor (21, 22, 23, 24) onboard the aircraft (1), - positioning (STP2) of each detected point in a predetermined orthonormal frame (100) attached to the aircraft (1), this frame (100) having a first axis (Z) coinciding with a rotation axis (AXROT) of the rotary wing (5), - division (STP3) of the surrounding space into volumetric units having a predetermined geometry, the detected point(s) present in the same volumetric unit being all replaced by a representative point, - segmentation of the ground by a process (STP4) to detect each ground point (PSOL) belonging to the ground among the points representative;said processing (STP4) comprising, for each representative point, a detection (STP41) whether a normal passing through this representative point has or does not have an angulation, with an axis parallel to the axis of rotation, greater than a predetermined angular threshold, said normal being a normal to a surface comprising this representative point and neighboring points, - determination (STP5) of the presence or absence of at least one obstacle by grouping representative points distinct from ground points; and in the presence of at least one obstacle, display (STP6) on a display (25) of a symbology (65-68) illustrating said obstacle with respect to the aircraft (1).;

2. Obstacle detection method according to claim 1, characterized in that the representative point of a volumetric unit is the equally weighted centroid of the detected points of that volumetric unit or the centroid of the detected points of that volumetric unit weighted by a light intensity of those detected points, said light intensity being provided by said LIDAR obstacle sensor.

3. A method for detecting obstacles according to any one of claims 1 to 2, characterized in that said predetermined angular threshold is equal to 20°.

4. Obstacle detection method according to any one of claims 1 to 3, characterized in that said symbology has a symbol (65, 67) which has a color which varies according to a level of danger of the obstacle determined according to an estimated distance or time of impact between the obstacle and the aircraft (1).

5. Obstacle detection method according to any one of claims 1 to 4, characterized in that said points near a representative point whose normal is estimated include all representative points located at a distance less than a predetermined distance from that representative point.

6. Obstacle detection method according to any one of claims 1 to 5, characterized in that if for a representative point said angulation is less than or equal to the predetermined angular threshold then this representative point is a point of interest likely to belong to the ground, said processing (STP4) comprising a detection (STP44) of each ground point belonging to the ground among the points of interest.

7. Obstacle detection method according to claim 6, characterized in that said detection (STP44) of each ground point belonging to the ground among the points of interest comprises a comparison (STP42) between an altitude of each point of interest and an average altitude of the representative points of a neighborhood, a point of interest being a ground point when the altitude of the point of interest less the altitude of each representative point of the neighborhood is less than a predetermined limit and that each representative point of the neighborhood of the point of interest is also a point of interest, the altitude of a point of interest being equal to the coordinate of this point of interest along the first axis.

8. Obstacle detection method according to claim 7, characterized in that said predetermined limit is equal to 1.5 meters.

9. A method for detecting obstacles according to any one of claims 7 to 8, characterized in that the neighborhood of a point of interest comprises a predetermined number of nearest representative points in a sphere centered on that point of interest.

10. Obstacle detection method according to claim 6, characterized in that said detection (STP44) of each ground point comprises the application (STP45) of a random sampling consensus algorithm which determines at least one parameter of a planar model and each point of interest consistent with this planar model, each point of interest consistent with this planar model being a ground point.

11. Aircraft (1) having at least one rotary wing (5), said aircraft (1) having an obstacle detection system (10) comprising at least one LIDAR obstacle sensor (21, 22, 23, 24) as well as a controller (15) and a display (25), the controller (15) communicating with said at least one LIDAR obstacle sensor (21, 22, 23, 24) and said display, characterized in that the obstacle detection system (10) is configured to implement the method according to any one of claims 1 to 10: - said at least one LIDAR obstacle sensor (21, 22, 23, 24) being configured to perform said acquisition of a cloud of detected points, - said controller (15) being configured to perform said positioning of each detected point in a predetermined orthonormal coordinate system attached to the aircraft, said division of the surrounding space into volumetric units, said segmentation of the ground, and said determination of the presence or absence of at least one obstacle, and -said display (25) being configured to perform, in the presence of at least one obstacle, said display of a symbology illustrating said obstacle in relation to the aircraft.

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