Method for locating a vertical landing aircraft relative to a runway and associated devices

Abstract

Method for locating a vertical landing aircraft relative to a runway and associated devices. The present invention relates to a method for locating an aircraft (2) relative to a runway (4) comprising reflective elements (8A, …, 8H), the method comprising the following steps: - receiving a reflected signal comprising a plurality of measurement points having a characteristic quantity, - filtering the plurality of measurement points according to a criterion, - determining a set of filtered measurement points satisfying a condition of number and / or positioning relative to the measurement points, - selecting a set from among the determined sets by minimizing a positional difference between the actual measurement points and the expected measurement points, and - locating the aircraft (2) based on the positions of the measurement points of the selected set. Figure for the abstract: Figure 1

Description

Title of the invention: Method for locating a vertical landing aircraft relative to a runway and associated devices

[0001] The present invention relates to a method for locating an aircraft relative to a runway. The present invention also relates to the associated devices, namely a locating device and a runway.

[0002] The invention relates to the field of aircraft, in particular autonomous vertical landing aircraft, more particularly the field of localization of the latter during takeoff and landing.

[0003] It is essential to be able to locate an aircraft in relation to the runway on which it can land or take off in order to guarantee a satisfactory level of safety during the takeoff and landing phases.

[0004] The so-called "vertical" landing of certain aircraft involves specific landing procedures and the use of runways adapted to these procedures commonly called heliport or vertiport.

[0005] Typically, the tracks are circular in shape and have a diameter of approximately 25 meters (m).

[0006] The approach speed of an aircraft seeking to land on such a runway implies a rapid localization of the latter.

[0007] For this purpose, there is known in ILS technology (from the English, "Instrument Landing System") a reference system with regard to the location of an aircraft in relation to a runway in the landing phase.

[0008] This technology uses transmitting antennas located at the end of the runway, the sum of the signals received by the aircraft being characterized by a carrier and a modulation, themselves a direct function of the lateral and longitudinal offsets of the aircraft relative to the reference approach axis in the vertical and horizontal plane.

[0009] However, this technology is expensive and therefore not widely deployed and does not allow the detection of the possible presence of obstacles on the track.

[0010] Moreover, this technology is not used during takeoff and is not necessarily suitable for a vertical landing.

[0011] There is therefore a need for a method of locating a vertical landing aircraft relative to a runway which is easy to implement.

[0012] To this end, the description describes a method for locating an aircraft relative to a runway on which aircraft can land or take off, the runway comprising a plurality of reflective elements for a radio signal, the plurality of reflective elements arranged according to a spatial arrangement, the process comprises the following phases:

[0013] - transmission of a radio signal from the aircraft to the runway,

[0014] - reception of a signal reflected by the track in response to the emitted radio signal, the reflected signal comprising a plurality of measurement points, each measurement point being defined by a position and exhibiting at least one characteristic quantity,

[0015] - filtering the plurality of measurement points according to at least one criterion depending on at least one characteristic quantity, to obtain filtered measurement points,

[0016] - determination of at least one set of filtered measurement points respecting a condition of number and / or positioning relative to the measurement points, to obtain determined sets,

[0017] - selection of a set from among the sets determined by minimizing a positional difference between the actual measurement points and the measurement points expected after reflection by the plurality of reflecting elements, to obtain a selected set, and

[0018] - location of the aircraft relative to the runway based on the positions of the points measurement of the selected set.

[0019] According to other advantageous aspects, the localization method comprises one or more of the following features, taken individually or in all technically possible combinations.

[0020] - the selection step comprises the following sub-steps:

[0021] - determination of at least one change-of-basis variable between the reference frame of the radar and runway marker,

[0022] - calculation of the plurality of positional errors, a positional error being associated with a group of reflective elements and being calculated as a function of at least one basis change variable and the positions in the radar coordinate system of the measurement points forming the group of reflective elements, and

[0023] - identification of the selected set, the selected set being the group of reflective elements with the lowest positional error. - The filtering step is implemented according to two criteria, each criterion depending

[0024] of the value of a respective characteristic quantity. - at least one characteristic quantity is the reflected power or the velocity

[0025] Doppler. - one criterion is that the reflected power is between two thresholds. - a track diameter is defined, a relative positioning condition

[0026] being that the distance between the measurement points of the determined set is less than twice the diameter of the track. - the radio signal belongs to a frequency band chosen from among the

[0027] X, K, Ka, Ku and W bands. - according to the spatial arrangement, a first half of the reflective elements is aligned along a first line tangent to the track and a second half of the reflective elements is aligned along a second line distinct from the first line and also tangent to the track. - the reflective elements are offset by a distance

[0028] with respect to the reflective elements along a longitudinal axis U. - each of the reflective elements in the same line are

[0029] spaced apart from each other according to a predetermined line spacing. - the aircraft is an airplane, a helicopter or a drone.

[0030] The description also relates to a device for locating a vertical landing aircraft relative to a runway on which aircraft can land or take off, the runway comprising a plurality of reflective elements for a radio signal, the plurality of reflective elements being arranged in a spatial arrangement, said locating device comprising a computer configured to:

[0031] - to transmit a radio signal from the aircraft to the runway,

[0032] - receive a signal reflected by the track in response to the radio signal The emitted reflected signal comprises a plurality of measurement points, each measurement point being defined by a position and exhibiting at least one characteristic quantity.

[0033] - filter the plurality of measurement points according to at least one criterion dependent on the value of the characteristic quantity, to obtain filtered measurement points,

[0034] - determine at least one set of filtered measurement points satisfying a condition of relative positioning of the measurement points, to obtain determinate sets,

[0035] - select a set from among the sets determined by minimizing a positional difference between the actual measurement points and the measurement points expected after reflection by the plurality of reflecting elements, to obtain a selected set, and

[0036] - locate the aircraft relative to the runway according to the positions of the points measurement of the selected set.

[0037] The description also describes a runway on which aircraft can land or take off, the runway having a shape suitable for vertical landing and comprising a plurality of reflective elements for a radio signal arranged on one edge of the track.

[0038] According to one embodiment, at least one reflective element is a trihedral reflector.

[0039] In the following description, a quantity is substantially equal to a value when the quantity is greater than or equal to 90% of the value and the quantity is less than or equal to 110% of the value.

[0040] The invention will become clearer upon reading the following description, given solely by way of non-limiting example and with reference to the drawings in which: - [Fig. 1] [Fig. 1] is a schematic representation of a top view of an aircraft equipped with a positioning device and landing on a runway, - [Fig.2] [Fig.2] is a flowchart illustrating an example of implementation work of a method for locating an aircraft relative to a runway, and - [Fig.3] [Fig.3] is a flowchart illustrating an example of the implementation of a selection step in the method for locating an aircraft relative to a runway.

[0041] An aircraft 2 and a runway 4 are schematically represented in [Fig.1].

[0042] An aircraft is a means of transport capable of rising and moving in altitude, within the Earth's atmosphere.

[0043] For example, an aircraft is an airplane, a helicopter or a drone.

[0044] More specifically, here, aircraft 2 is a vertical landing or takeoff aircraft.

[0045] Aircraft 2 is attempting to land on runway 4.

[0046] For example, a known vertical landing protocol on such a runway is described in the EASA document (PTS-VPT-DSN, available at the following address: "https: / / www.easa.europa.eu / en / document-library / general-publications / prototype-technical-design-specifications-vertiports"), which consists of the following sequence of steps: - approach of aircraft 2 towards runway 4 with an angle relative to the ground of runway 4 between 3° and 30°, this angle is commonly called the slope, - arrival at a Landing Decision Point (LDP) located at a longitudinal distance usually between 10 and 250 m from runway 4, and - landing or go-around of aircraft 2 depending on the situation.

[0047] Alternatively, runway 4 can also be used for the takeoff of aircraft 2 and has a shape adapted for vertical landing

[0048] For example, runway 4 has a disc shape and is reserved for the takeoff and landing of aircraft.

[0049] Depending on the case, the position of an object refers either to the geographical position or to a location relative to track 4.

[0050] In the following description, a geographical position of an object is defined by three coordinates of it in a given frame of reference.

[0051] In the remainder of this description, a location of an object relative to track 4 is defined as the coordinates of the projection of the object into a frame of reference of the track.

[0052] The track frame is the frame formed by three orthogonal axes (X, Y, Z) of center O having coordinates (0,0,0) in the track frame.

[0053] In the rest of the description, the center O also represents the center of the disk formed by track 4.

[0054] As seen in [Fig.1], track 4 comprises a plurality of reflective elements 6A, 6B, ..., 6H for a radio signal.

[0055] Each reflective element 6A, 6B, ..., 6H is arranged on the edge of track 4.

[0056] In the example described, only eight reflective elements 6A, 6B, ..., 6H are represented but this number is not limited, the number of reflective elements can vary according to needs.

[0057] Each reflective element 6A, 6B, ..., 6H is, for example, a reflector.

[0058] A reflector is a device that reflects an electromagnetic wave incident and, above all, a radar signal.

[0059] Each reflector can be a trihedral reflector.

[0060] A trihedral reflector is well suited for radar waves because it has the property of generating radar echoes of relatively high amplitude.

[0061] However, any form of reflector is conceivable here, including parabolic, planar or elliptical reflectors, as well as reflectors using passive, active electronic components, or those with frequency-selective properties.

[0062] For example, such reflectors include Van Atta grating type reflectors or Luneberg lenses.

[0063] Advantageously, the reflective elements 6A, 6B, ..., 6H are arranged according to a specific spatial arrangement, which is now described.

[0064] In one embodiment, the spatial arrangement is such that a first half of the reflective elements 6A, 6B, 6C, 6D is aligned along a first line L1 tangent to track 4 while a second half of the reflective elements 6E, 6F, 6G, 6H is aligned along a second line L2, distinct (not confused with) the first line L1, also tangent to track 4.

[0065] Thus, the first half of the reflective elements 6A, 6B, 6C, 6D are arranged parallel to the second half of the reflective elements 6E, 6F, 6G, 6H on either side of the Z-axis of the track 4 coordinate system. Advantageously, the elements reflective elements 6A, 6B, 6C and 6D will be offset by a distance ([)^ relative to reflective elements 6E, 6F, 6G and 6H along a longitudinal axis U, so that each reflective element is detected at a different distance by the radar.

[0066] According to the example described, each of the reflective elements of the same line L1 or L2 are spaced from each other according to a respective predetermined line spacing De.

[0067] According to the example described, the predetermined line spacing De is the same for each of the lines L1 or L2 of reflective elements (8A, ..., 8H).

[0068] Denoting Dp as the diameter of track 4 (which is generally approximately equal to 25 m), the line spacing De is, advantageously, approximately equal to one third of the diameter of track Dp.

[0069] Aircraft 2 includes a location device 20 configured to transmit a radio signal towards runway 4 and receive a signal reflected by runway 4 (and more specifically, at least one reflective element 6A, 6B, ..., 6H) in order to deduce a position of aircraft 2.

[0070] The location device 20 comprises a radio transceiver 28 and a computer 30.

[0071] The radio transceiver 28 is configured to transmit a signal radio transmission from aircraft 2 to runway 4 and to receive a signal reflected by runway 4.

[0072] For example, the radio transceiver 28 is a radar.

[0073] According to a preferred embodiment, the radar 28 is a continuous wave radar.

[0074] Such a radar is more often referred to as an FMCW radar, which refers to the corresponding English name for “Frequency Modulated Continuous Wave”.

[0075] Such a radar operates here with millimeter or centimeter waves

[0076] Preferably, the radio transceiver 28 is suitable for transmitting or receiving signals with a frequency between the X and W bands, i.e. between 8 Gigahertz (GHz) and 110 GHz.

[0077] For such a radar, transmission and reception are almost simultaneous.

[0078] Typically, the radio transceiver 28 is suitable for transmitting or receiving signals having a frequency selected from the bands: X, K, Ka, Ku and W.

[0079] Advantageously, the signals emitted or received by the radar 28 have a frequency substantially equal to 15GHz, 24 GHz, 77GHz or 95 GHz.

[0080] In the following description, a radar reference frame 28 is an orthonormal frame (U, V, W) whose longitudinal axis U follows the angle of the trajectory of the aircraft 2 with respect to the runway 4 and whose origin is the localization device 20.

[0081] In the example of [Fig. 1], the location device 20 comprises a calculator 30.

[0082] The calculator 30 includes, for example, a processor 32 and a memory 34 associated with the processor 32.

[0083] The computer 30 is configured to process signals from the radio transceiver 28.

[0084] The calculator 30 is an electronic circuit designed to manipulate and / or transform data represented by electronic or physical quantities in registers of the calculator and / or memories into other similar data corresponding to physical data in register memories or other types of display devices, transmission devices or storage devices.

[0085] As specific examples, the calculator 30 is implemented in the form of a programmable logic component, such as an FPGA (Field Program Gate Array), or an integrated circuit, such as an ASIC (Application Specified Integrated Circuit).

[0086] Alternatively, when the method is implemented in the form of one or more software programs, that is to say, in the form of a computer program, also called a computer program product, it is further capable of being stored on a computer-readable medium, not shown. The computer-readable medium is, for example, a medium capable of storing electronic instructions and being connected to a bus of a computer system. By way of example, the readable medium is an optical disc, a magneto-optical disc, ROM, RAM, any type of non-volatile memory (for example, FLASH or NVRAM), or a magnetic card. A computer program comprising software instructions is then stored on the readable medium.

[0087] The operation of the localization device 20 is now described with reference to [Fig.2] which illustrates an example of the implementation of a localization method.

[0088] The localization process comprises an emission step 100, a reception step 200, a filtering step 300, a determination step 400, a selection step 500 and a localization step 600.

[0089] During the first transmission stage 100, the radio transceiver 28 transmits a radio signal from the aircraft 2 to the runway 4.

[0090] The radio signal thus emitted interacts with the reflective elements 6A, 6B, ...,6H.

[0091] The reflective elements 6A, 6B, ..., 6H return a reflected signal towards the aircraft 2 and more specifically towards the radio transceiver 28.

[0092] During the reception step 200,1 the radio transceiver 28 receives a signal reflected by track 4.

[0093] According to the example described, the reflected signal comprises a plurality of measurement points each defined by a position in the radar frame 28 and at least one characteristic physical quantity.

[0094] Examples of physical quantities are given in filtering step 300.

[0095] Advantageously, the measurement points whose positions correspond to the positions of the reflective elements 6A, 6B, ..., 6H are defined by at least one specific and identifiable characteristic quantity.

[0096] During the filtering step 300, the calculator 30 filters the plurality of measurement points according to at least one criterion depending on the values ​​of at least one characteristic quantity.

[0097] In one embodiment, two criteria, each depending on a respective characteristic quantity, are used

[0098] For example, the two respective characteristic quantities are the reflected power and the Doppler velocity.

[0099] The reflected power of a measurement point corresponds to the power of the signal received by the radio transceiver 28 at that point and is generally expressed in watts (W).

[0100] The Doppler velocity of a measurement point is defined as the velocity of the point along an axis passing through said point and the radar measuring the velocity.

[0101] The speed is calculated from the Doppler effect between the signal emitted and the signal received by the radio transceiver 28 and is generally expressed in ms~\

[0102] In this embodiment, one of the two criteria used during the filtering step 300 is that the reflected power is between two predetermined power thresholds while the other criterion is that the Doppler velocity is equal to the projection of the carrier velocity vector onto a radar-reflector axis (reflector velocity relative to the ground zero).

[0103] In the following description, the measurement points retained during the filtering step 300 are called filtered measurement points, the number of filtered measurement points being less than or equal to the number of measurement points.

[0104] During the determination step 400 of at least one set of filtered measurement points, the calculator 30 determines at least one set of measurement points satisfying a condition of number and / or positioning relative to the filtered measurement points.

[0105] In the example of [Fig. 1], a set of measurement points consists of eight measurement points corresponding to the eight reflective elements 6A, 6B, ..., 6H. The number condition will then be eight.

[0106] In one embodiment, the relative positioning criterion is that the maximum distance between two points of the same set 6A, 6B, ..6H is less than 2 times the diameter of the track Dp, which can be mathematically translated by the following equations:

[0107] max(q) -min(ri) <2Dp

[0108] (max(Azi) -min(Azi)) xmin(r]) <2Dp

[0109] (max (El,) - min (El,)) x min (q) < 2Dp

[0110] With: - rî: vector whose terms are the radial distance between aircraft 2 and each of the reflective elements 6A, 6B, ..., 6H, - Az~: vector whose terms are the azimuth between aircraft 2 and each of the reflective elements 6A, 6B, ..., 6H, and - El, : vector whose terms are the elevation between aircraft 2 and each of the reflective elements 6A, 6B, ..., 6H.

[0111] At the end of the determination step 400, a plurality of sets is determined.

[0112] During the selection step 500, the calculator 30 selects a set from among the sets determined in the previous step.

[0113] For example, the selected set is the set among the determined sets minimizing a positional difference between actual measurement points and measurement points expected after reflection by the plurality of reflecting elements 6A, 6B, ..., 6H.

[0114] According to the embodiment of [Fig.3], the selection step 500 comprises a determination substep 510, a calculation substep 520 and an identification substep 530.

[0115] During the substep of determining 510 at least one basis change variable between the radar marker 28 and the runway marker 4, the computer 30 calculates at least one basis change variable from the coordinates of at least one determined set and the expected coordinates.

[0116] In the example, the basis change variable is the rotation matrix R between the runway frame and the radar frame 28 and the translation matrix T between the runway frame 4 and the radar frame 28.

[0117] For example, the computer 30 calculates the rotation matrix R and the translation matrix T between the runway reference frame and the radar reference frame 28 by implementing the following operations: - calculation of the centroids Bx and Py associated with the coordinates of the reflecting elements 6A, 6B, ..., 6H of each of the sets determined according to the following equations:

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] With : • X (the coordinates of the i-th reflecting element of the determined set being studied, • Y / the expected measurement points of each of the reflectors, and • n: number of reflective elements in the determined set studied (n = 8 in our example). In the example described, the reference point of track 4, being centered on the center of track 4, is zero due to the spatial arrangement also being centered on the center of track 4. - Calculation of the covariance matrix of X and Y according to the following equation: With : • Exy: covariance matrix of X and Y, • XT: transpose of matrix X, • Calculation of the singular value decomposition of Lys: T> xy =UDVt With : • U, V: orthogonal matrices of the same dimension as ^xy- and • D: diagonal matrix whose elements are the singular values ​​of rows in ascending order. • Calculation of a matrix S according to the following equation: $I, if > 0 diag (1, 1, ..., 1, -1 ), if det^xy) < 0 With : • I: identity matrix of the same dimension as • Diag: diagonal matrix of the same dimension as LXY, and • det: determinant function of a matrix. • Calculation of the rotation matrix R and the translation matrix T according to the following equations: r=usvt,t=my-Rmx As previously stated, in this example, R and T are the base change variables between the runway 4 marker and the radar 28 marker. During calculation substep 520, calculator 30 calculates a plurality of position errors. A positional error is associated with a specific set.

[0131] Each position error is calculated as a function of at least one basis change variable calculated in the previous substep and the positions in the radar frame 28 of the points of each of the determined sets.

[0132] For example, calculator 30 implements the following equation on each of the determined sets:

[0133] e2j-Æj|Yi-(RX, + T)||2.

[0134] With: - "2: quadratic deviation associated with a given set j, and - ||X|| :1a norm of X.

[0135] The calculator 30 thus obtains a position error for each determined set.

[0136] During the identification substep 530, the calculator 30 identifies a set among the determined sets.

[0137] According to the example described, the calculator 30 identifies the determined set whose positional deviation is the smallest.

[0138] The determined set thus identified is the set selected during selection step 500.

[0139] During the localization step 600, the computer 30 obtains a localization / \ of the aircraft 2 relative to runway 4. Go? There? ^2 /

[0140] For example, the calculator determines the location / \ based on the y-*2' ^2 / positions of the measurement points of the selected set by applying the following equation:

[0141] (x2, j2, z2) = Rpx + T

[0142] Computer 30 thus obtains a precise location of aircraft 2 relative to the runway.

[0143] The method just described is thus a method for locating a vertical landing aircraft relative to a runway which is easy to implement.

[0144] Indeed, modifying an existing runway represents a moderate cost for an airport wishing to equip itself with it and is easy to implement.

[0145] Such dimensions are dimensions easily achievable in practice.

[0146] Furthermore, the process has a hybrid character since it makes it possible to guarantee a precise location of the aircraft during landing and takeoff phases.

[0147] Other embodiments offering the same advantages are also conceivable.

[0148] For example, in one embodiment, the location of aircraft 2 is stored in an accessible memory.

[0149] The computer 30 is then configured to estimate the consistency of the evolution of the location of aircraft 2 as a function of said locations and the speed of aircraft 2.

Claims

Demands

1. A method for locating an aircraft (2) relative to a runway (4) on which aircraft (2) can land or take off, the runway (4) comprising a plurality of reflective elements (8A, 8H) for a radio signal, the plurality of reflective elements (8A, ..., 8H) being arranged in a spatial arrangement, the method comprising the following steps: - transmission (100) of a radio signal from the aircraft (2) to the runway (4), - reception (200) of a signal reflected by the runway (4) in response to the transmitted radio signal, the reflected signal comprising a plurality of measurement points, each measurement point being defined by a position and having at least one characteristic quantity, - filtering (300) the plurality of measurement points according to at least one criterion depending on at least one characteristic quantity, to obtain filtered measurement points,- determination (400) of at least one set of filtered measurement points satisfying a condition of number and / or positioning relative to the measurement points, to obtain determined sets, - selection (500) of a set among the determined sets by minimizing a positional difference between the actual measurement points and the measurement points expected after reflection by the plurality of reflective elements, to obtain a selected set, and - localization (600) of the aircraft (2) relative to the runway (4) as a function of the positions of the measurement points of the selected set.

2. A localization method according to claim 1, wherein the selection step (500) comprises the following substeps: - determination (510) of at least one basis change variable between the radar reference frame and the runway reference frame (4), - calculation (520) of the plurality of position errors, a position error being associated with a group of reflective elements (8A, ..., 8H) and being calculated as a function of the at least one basis change variable and the positions in the radar reference frame of the measurement points forming the group of reflective elements (8A, ..., 8H), and - identification (530) of the selected set, the selected set being the group of reflective elements (8A, 8H) with the lowest position error.

3. A method according to claim 1 or 2, wherein the filtering step (300) is implemented according to two criteria, each criterion depending on the value of a respective characteristic quantity.

4. Method according to claim 3, wherein at least one characteristic quantity is the reflected power or the Doppler velocity.

5. A method according to claim 4, wherein one criterion is that the reflected power is between two thresholds.

6. A method according to any one of claims 1 to 5, wherein a diameter (Dp) of the track (4) is defined, a relative positioning condition being that the distance between the measurement points of the determined assembly is less than twice the diameter (Dp) of the track (4).

7. A method according to any one of claims 1 to 6, wherein the radio signal belongs to a frequency band selected from the X, K, Ka, Ku and W bands.

8. A method according to any one of claims 1 to 7, wherein according to the spatial arrangement, a first half of the reflective elements (6A, 6B, 6C, 6D) is aligned along a first line (L1) tangent to the track (4) and a second half of the reflective elements (6E, 6F, 6G, 6H) is aligned along a second line (L2) distinct from the first line (L1) and also tangent to the track (4).

9. Method according to claim 8, wherein the reflective elements (6A, 6B, 6C and 6D) are offset by a distance (p^ with respect to the reflective elements (6E, 6F, 6G and 6H) along a longitudinal axis U.

10. Method according to claim 8 or 9, wherein each of the reflective elements (8A, ..., 8H) of the same line (L1, L2) are spaced from each other according to a predetermined line spacing (De).

11. A method according to any one of claims 1 to 10, wherein the aircraft (2) is an airplane, a helicopter or a drone.

12. A device for locating (20) an aircraft (2) relative to a runway (4) on which aircraft (2) can land or take off, the runway (4) comprising a plurality of reflective elements (8A, ..8H) for a radio signal, the plurality of reflective elements (8A, 8H) being arranged in a spatial arrangement, said positioning device (20) comprising a computer (30) configured to: - transmit a radio signal from the aircraft (2) towards the runway (4), - receive a signal reflected by the runway (4) in response to the transmitted radio signal, the reflected signal comprising a plurality of measurement points, each measurement point being defined by a position and having at least one characteristic quantity, - filter the plurality of measurement points according to at least one criterion depending on the value of the characteristic quantity, to obtain filtered measurement points, - determine at least one set of filtered measurement points satisfying a condition of relative positioning of the measurement points, to obtain determined sets,- select a set from among the determined sets by minimizing a positional difference between the actual measurement points and the measurement points expected after reflection by the plurality of reflective elements, to obtain a selected set, and - locate the aircraft (2) relative to the runway (4) according to the positions of the measurement points of the selected set.

13. Runway (4) on which aircraft (2) can land or take off, runway (4) having a shape suitable for vertical landing and comprising a plurality of reflective elements (8A, ..., 8H) for a radio signal arranged on one edge of runway (4).

14. Track (4) according to claim 13, wherein at least one reflective element (8A, ..., 8H) is a trihedral reflector.

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