Method and device for determining an operational geographical zone observed by a sensor

Abstract

A determination method for determining at least one region of interest in at least one operational geographical zone. The operational geographical zone determined relative to a sensor to observe and measure the radial speed of an object traveling in a region of interest. The method may include steps simulating the position of the sensor in the region of interest at a determined position and orientation; determining at least one first zone of a region of interest; and determining a second zone of the region of interest, the second zone constituting a coverage zone of the sensor in which an object travelling in the region is observable while accounting for at least the position of the object relative to the sensor. One operational geographic zone is defined by taking account the intersection between the first and second zones.

Claims

1. A determination method for determining at least one operational geographical zone in a region of interest, said zone being determined relative to a sensor configured to observe and measure the radial speed of an object traveling at a non-zero minimum speed “VT” in the region of interest, the method comprising: a step of simulating the position of said sensor in said region of interest at a position and in an orientation that are determined; a step of determining at least one first zone of said region of interest that is constituted by points for each of which, said object at said point and traveling at a speed greater than or equal to said non-zero minimum speed “VT” and in a given direction “DT”, would be seen from said sensor to have a radial speed greater than a threshold value defined for that point; and a step of determining a second zone of said region of interest, the second zone constituting a coverage zone of said sensor in which said object is observable while taking account at least of the intrinsic characteristics of said sensor and of the intrinsic characteristics of said object, and also of the position of said object relative to said sensor; said at least one operational geographical zone being defined by taking account of the intersection between at least said first and second zones.

2. The determination method of claim 1, wherein said threshold speeds defined for the various points of the region of interest are equal to a constant.

3. The determination method of claim 1, wherein the threshold speed defined for at least one point of said region of interest is defined as a function of the position of that point relative to said sensor.

4. The determination method of claim 3, wherein the threshold speed defined for at least one point of the region of interest is defined as a function of the distance between that point and the sensor.

5. The determination method of claim 3, wherein the threshold speed defined for at least one point of the region of interest is defined as a function of the bearing of that point relative to a reference direction linked to the sensor.

6. The determination method of claim 3, wherein the threshold speed defined for at least one point of the region of interest is defined as a function of the elevation of that point relative to said sensor.

7. The determination method of claim 1, further comprising a step of determining at least one shadow zone taking account of the characteristics of said region of interest, said at least one shadow zone being constituted by the points that correspond to positions at which said object is not detectable by the sensor when positioned thereat, and wherein said operational geographical zone is defined by taking account of the intersection between the complement of at least one of said shadow zones and said first and second zones.

8. The determination method of claim 1, further comprising a step of determining an interference zone taking account of the characteristics of said region of interest, said interference zone being constituted by points corresponding to positions at which said objects might not be detected by the sensor when positioned at said position.

9. The determination method of claim 1, characterized in that it comprises determining a plurality of said first zones, said first zones being determined for different travel directions of said object.

10. The determination method of claim 1, comprising a set of representing the position of said sensor, of said at least one first zone, of said second zone, and optionally of said shadow zone and/or of said interference zone in said region of interest.

11. The determination method of claim 9, wherein the first zones obtained for each of said directions are represented in different manners.

12. The determination method of claim 1, wherein said sensor is a Doppler radar.

13. A method of assisting installation of a sensor configured to observe and measure a radial speed of an object traveling at a non-zero minimum speed “VT” and in at least one given direction “DT” in a region of interest, the method comprising: at least one iteration, each iteration comprising determining an operational geographical zone of said sensor by simulating said sensor being positioned in said region of interest at a determined position and in a determined orientation, by performing a method of determining such a zone in accordance with claim 1; a step of determining at least one preferred position among said positions enabling an optimized operational geographical zone to be determined in accordance with an optimization criterion; and a step of reproducing said at least one preferred position.

14. The method of claim 13, wherein a computer program includes instructions for executing steps for assisting in installing a sensor, when said program is executed by a computer.

15. The method of claim 13, wherein a computer readable data medium including instructions of a computer program enabling steps of a determination method to be executed, and/or including instructions of a computer program enabling steps of a method for assisting in installing a sensor.

16. A device for assisting installing a sensor that is configured to observe and measure the radial speed of an object traveling at a non-zero minimum speed “VT” and in at least one given direction “DT” in a region of interest, the device comprising: a controller configured to execute at least one iteration, each iteration comprising determining an operational geographical zone of said sensor by simulating said sensor being positioned in said region at a determined position and in a determined orientation, by implementing a method of determining such a zone in accordance with claim 1; a unit for determining at least one preferred position from among said positions enabling an optimized operational geographical zone to be determined in accordance with an optimization criterion; and a unit for representing said at least one preferred position.

17. The determination method of claim 1, wherein a computer program includes instructions for executing steps of the determination method when said program is executed by a computer.

18. A device for determining at least one operational geographical zone in a region of interest, said zone being determined relative to a sensor configured to observe and measure the radial speed of an object traveling at a non-zero minimum speed “VT” in the region of interest, the device comprising: a unit for simulating said sensor being positioned in said region of interest at a determined position and in a determined orientation; a unit for determining at least one first zone of said region of interest that is constituted by points at each of which, said object at said point and traveling at a speed greater than or equal to said non-zero minimum speed “VT” and in a given direction “DT”, would be seen by said sensor to have a radial speed greater than a threshold speed defined for that point; and a unit for determining a second zone of said region of interest, the second zone constituting a coverage zone of said sensor in which said object is observable while taking account at least of the intrinsic characteristics of said sensor and of the intrinsic characteristics of said object, and also of the position of said object relative to said sensor; said at least one operational geographical zone being defined by taking account of the intersection of at least said first and second zones.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1, described above, shows the prior art with an antenna suitable for measuring the bearing of an object;

(2) FIG. 2, described above, shows a first high-sensitivity zone for elevation angles corresponding to a zone without foliage;

(3) FIG. 3, described above, shows a first zone for a given travel direction of the object;

(4) FIG. 4A, described above, shows the second zone and two first zones for two given travel directions of the object;

(5) FIGS. 4B and 4C, described above, show the operational zones obtained for two given travel directions of the object;

(6) FIG. 5, described above, shows an operational zone defined by taking a shadow zone into account;

(7) FIG. 6, described above, shows a shadow zone;

(8) FIG. 7 is a diagram of a device for assisting in installing a sensor in accordance with a particular embodiment of the invention;

(9) FIG. 8 is a flow chart showing the main steps of a method of assisting in installing a sensor in accordance with a particular implementation of the invention;

(10) FIG. 9 shows the display on the screen of the FIG. 7 device, showing a region of interest, a surveillance zone, and a travel direction of an object;

(11) FIG. 10 shows a radial speed calculation;

(12) FIG. 11 shows a first zone for a given travel direction of the object;

(13) FIG. 12 shows two resulting first zones for two travel speeds of an object;

(14) FIG. 13 shows the resultant of a plurality of first zones of arbitrary shapes;

(15) FIG. 14 shows an example of a coverage zone of the sensor for a given object;

(16) FIGS. 15A to 15C show an example of determining an interference zone in a particular implementation of the invention;

(17) FIG. 16 shows an interference zone in another particular implementation of the invention;

(18) FIG. 17 shows an example of a surveillance zone and of an operational zone; and

(19) FIG. 18 shows a computer screen, a sensor, a surveillance zone, a first zone, a second zone, and an operational zone.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(20) There follows a detailed description of non-limiting embodiments of the invention.

(21) FIG. 7 is a diagram showing a device 10 for assisting in installing a sensor in accordance with a particular embodiment of the invention. In this particular embodiment, the device has the conventional architecture of a computer. In particular, it comprises a processor 11, a ROM 12, a random access memory (RAM) 13, a keyboard 14, a mouse 15, and a screen 16. The device may be connected to a sensor 17.

(22) In the presently-described embodiment, only one sensor is used, which sensor comprises a single-lobe anisotropic antenna.

(23) In an alternative embodiment, the device 10 does not use a keyboard or a mouse, but rather a touch screen that serves both to input information and to display it. In this embodiment, the device 10 may be constituted by a smartphone or a touch tablet, possibly connected to a server.

(24) The ROM 12 constitutes a data medium in accordance with the invention. It stores a computer program PG in accordance with the invention. The computer program PG includes instructions for executing steps of a method of assisting in installing a sensor in accordance with an implementation of the invention, with the main steps of the method being described below with reference to FIG. 8.

(25) In the presently-described embodiment, the ROM 12 of the computer also includes a digital map showing a region of interest ROI including a surveillance zone ZS. This digital map may be displayed on the screen 16 of the computer.

(26) The keyboard 14 and the mouse 15 may be used by the operator to input configuration settings for the method of assisting installation, e.g.: the perimeters of the region of interest ROI and of the surveillance zone ZS; Optionally, the obstacles and the relief in the region of interest ROI serve to calculate potential shadow zones; the characteristics of the object T to be observed, e.g. a person, a type of vehicle, . . . ; a minimum travel speed VT of the object; one or more travel directions DT of the object; threshold speeds Vmin_i at the various points Ti of the region of interest ROI; an optimization criterion for installing the sensor; an option enabling the operator to take account of potential shadow zones while determining the operational zone of the sensor; optionally the characteristics and the locations of sources of interference, serving in particular to determine potential zones of interference; and the position POS and the orientation γ of the sensor, in the “manual” mode of operation as described below.

(27) These settings may be saved in the ROM 12.

(28) FIG. 9 shows the display on the screen 16 of a region of interest ROI, of a surveillance zone ZS, and of a travel direction DT of an object.

(29) In the presently-described embodiment, the man/machine interface of the computer 10 provides the user with two modes of operation: in a so-called “manual” mode, the operator selects a position POS for the sensor S, and if the sensor is anisotropic, an orientation γ, e.g. by clicking with the mouse on the digital map, and the computer program PG determines and displays on the screen 16 the operational zone of the sensor S when in this position POS for the speed VT and the travel direction(s) of the object T; and in a so-called “automatic” mode, the computer program calculates and displays to the operator on the screen 16 one or more preferred positions and/or orientations for the sensor in order to optimize the geographical zone, which zone is optimized in compliance with an optimization criterion.

(30) In general manner, and as mentioned above, the operational zone Z corresponds to the positions in which an object is visible to the sensor and is defined by the intersection between at least one first zone A1 and a zone A2, which zones are described in greater detail below.

(31) Concerning the First Zone A1

(32) It should be recalled that a point Ti of the region of interest ROI belongs to the first zone A1 if, and only if, an object at the point Ti traveling at a given speed VT and in a given direction DT has, when seen from the sensor S, a radial speed Vr that is greater than a threshold speed Vmin_i defined for that point.

(33) FIG. 10 illustrates these concepts. It shows a sensor S positioned in a region of interest ROI and an object T traveling in this region at a speed VT in a direction DT. The radial component (or radial speed) Vr of this object T forms an angle α with the direction DT, such that:
Vr=VT.Math.cos α
when the direction DT, the sensor, and the object are all situated in the horizontal plane.

(34) In the general situation, if the angle formed between the direction DT and the straight line connecting the target to the sensor is written β, as shown in FIG. 6, then:
Vr=VT×cos α×cos β

(35) FIG. 11 shows such a first zone A1 shaded for when the threshold speeds Vmin_i associated with the various points in the region of interest ROI are all equal to the same constant Vmin.

(36) This first zone A1 in this implementation is in the form of two angular sectors: that meet at their vertices at a position corresponding to the position of the sensor S; of bisector corresponding to the direction DT; and of aperture 2α.sub.0 associated with the sensitivity Vmin of the sensor, where:
α.sub.0=arccos(V min/VT)

(37) In other words, at constant speed VT, the more it is desired to be able to detect objects, the lower the value that needs to be given to the threshold speed Vmin, such that α.sub.0 tends towards π/2. In this implementation, the sensitivity of the Doppler sensor is said to be high, since numerous objects (e.g. vegetation stirred by the wind) become visible to the sensor.

(38) Conversely, at constant speed VT, with decreasing sensitivity of the Doppler sensor (Vmin close to VT), then α.sub.0 tends towards 0.

(39) Because of this particular geometry, the first zone A1 may be referred to by a person skilled in the art of radars or of aerial navigation as a “Doppler rose.”

(40) With reference to FIG. 12 there can be seen the first zone A1 in an example in which the speed Vmin_i associated with a point Ti of the region of interest ROI depends on the distance between that point Ti and the sensor S, and only on that distance.

(41) More precisely, in this figure, it is considered that: the points Ti situated at a distance from the sensor S that is less than a limit distance RL are associated with a first threshold speed Vmin1; and the points Ti situated at a distance from the sensor S that is greater than this limit distance RL are associated with a second threshold speed Vmin2.

(42) This figure shows the situation in which the threshold speed Vmin1 is lower than the threshold speed Vmin2 such that α1 is greater than α2. Such a configuration may correspond to a scenario in which the sensitivity of the sensor is increased for the zone located in the proximity of the sensor, e.g. when the sensor is positioned in a zone that is unobstructed.

(43) The geometry of the first zone A1 is not necessarily made up of portions of angular sectors as shown in FIGS. 11 and 12. Specifically, with reference to FIG. 13, there is shown a first zone A1 (union of the shaded portions) that corresponds to an embodiment in which the threshold speed Vmin_i associated with the points Ti of the region of interest ROI takes account of the distance of the point Ti from the sensor, and also its bearing angle θ.

(44) In general manner, the shape of the first zone A1 is arbitrary, this shape depending exclusively, for given speed VT and direction DT, solely on the threshold values Vmin_i associated with the points Ti in the region of interest ROI.

(45) Concerning the Second Zone A2

(46) In accordance with the invention, the second zone A2 constitutes a coverage zone of the sensor S in which the object T that is to be observed is observable, this coverage zone being defined by taking account at least of the intrinsic characteristics of the sensor S, the intrinsic characteristics of the object T, and also the position of the object T relative to the sensor S.

(47) It should be recalled that for a radar, the coverage of the radar corresponds to the zone in which an object of the size under consideration can reflect sufficient energy for it to be detected. In particular, it is possible to calculate the received power P by using the radar equation known to the person skilled in the art and based on the antenna pattern (gain in a given direction), on the distance to the object, and on the size of the object expressed as a radar cross-section (RCS):
P=P.sub.t.Math.G.sub.t.Math.G.sub.r.Math.λ.sup.2.Math.σ/((4.Math.π).sup.3.Math.R.sup.4)
with: P.sub.t: transmitted power; G.sub.t/G.sub.r: transmit receive gain; λ: wavelength; σ: radar cross-section; R: distance between the radar and the object.

(48) With reference to FIG. 14, the person skilled in the art of radars recognizes that this second zone is essentially in the form of a lobe in the particular situation in which the sensor has a directional antenna and consideration is given only to the main lobe of that antenna.

(49) In an embodiment where the sensor is anisotropic, it possesses a preferred direction generally referred to as the “boresight”. In this situation, which is particularly representative when the sensor is a radar, a sonar, or a lidar, the second zone A2 also takes account of the orientation of the sensor relative to the object.

(50) Concerning the Interference Zone A4

(51) In accordance with the invention, an interference zone A4 is constituted by points in the region of interest that correspond to positions at which an object T might not be detected by a sensor S.

(52) An interference zone is typically due to the presence of interference sources, by way of example and as shown in FIG. 15A, to the presence of vehicles 51 traveling along a road 50 that passes through the region of interest ROI and in the coverage zone A2 of a sensor used for detecting human intrusions. It should be observed that in this example the coverage zone that takes account of the intrinsic characteristics of vehicles traveling on the road is wider than the coverage zone of the sensor that takes account of the intrinsic characteristics of the objects that it is desired to detect.

(53) In a first example, the sensor S is configured to observe and measure only distance and radial speed Vr. Under such circumstances, if the distance at which the vehicles are visible lies in the range D min to D max, the vehicles are seen by the sensor as having the same distance and radial speed characteristics as the objects to be observed that are situated in the range D min to D max, which objects might thus not be detected by the sensor. The interference zone A4 is thus constituted by points situated in the range D min to D max, i.e. the ring centered on the sensor S that is of inside radius D min and of outside radius D max, as shown in FIG. 15B. FIG. 15C shows the intersection between the interference zone A4 and the coverage zone A2.

(54) It should be observed that certain sensors suitable for measuring radial speed are the subject of a known “folding” phenomenon that leads to objects traveling at high radial speed being confused with objects traveling at low radial speed.

(55) In another example, the sensor S is a continuous wave Doppler radar configured to observe and measure distance, radial speed Vr, and bearing by phase difference between the signals generated by the echoes received from spaced-apart sensors, as described above with reference to FIG. 1. In that embodiment, it is possible to determine the zone of false alarms generated by vehicles as showed by cross-hatching in FIG. 16. Nevertheless, each individual receiver RX1 and RX2 operates like the sensor S in FIG. 15A, such that the objects that are to be observed can also be confused in each of those individual receivers with false alarms generated by vehicles in each of the receivers, thus potentially making bearing measurements of the azimut ineffective or erroneous.

(56) As in the above example, the interference zone A4 in the meaning of the invention, i.e. the zone corresponding to positions in which an object might not be detected by the sensor, is the masking zone defined by the ring centered on the sensor S and of inside radius D min and outside radius D max.

(57) However, and in most advantageous manner, it is also possible in this example to distinguish within the interference zone, the zone of false alarms generated by vehicles and corresponding to the location of the road.

(58) Representation of an Operational Zone

(59) FIG. 17 shows in cross-hatching an operational zone ZO in an implementation of the invention.

(60) In this example, the operational zone ZO is the intersection between the first zone A1 of FIG. 11 and the second zone A2 of FIG. 14.

(61) This operational zone ZO constitutes the set of positions in which an object traveling in the direction DT at the speed VT is visible to the sensor S.

(62) The sensor S as positioned in this way can provide effective surveillance of intrusions into a surveillance zone ZS by objects traveling at the speed VT in the direction DT, the surveillance zone ZS being constituted by a straight fence, as shown in this figure.

(63) Example of a Method of Assisting Installing the Sensor S

(64) With reference to FIG. 8, there follows a description of the main steps of a method of providing assistance in installing a sensor in accordance with a particular implementation of the invention.

(65) This method comprises a loop made up of steps E10 to E50, with each iteration of the loop serving to determine, for a different position POSj of the region of interest ROI, the operational geographical zone ZOj of said sensor S by simulating said sensor S being positioned at said position POSj.

(66) More precisely, each iteration of the loop comprises: a simulation step E10 for simulating positioning the sensor S in the region of interest ROI at a position POSj with an orientation γj. In practice, the position POSj may be selected to occupy potential zones for positioning the sensor as predetermined by the operator, and by shifting position by steps of a determined size between two iterations; a determination step E20 for determining a first zone A1j for each travel direction DT of the object T, as described above with reference to FIGS. 11 to 13; a determination step E30 for determining a second zone A2j corresponding to the coverage zone of the sensor S, as described above with reference to FIG. 14; optionally, depending on the option selected by the operator, a determination step E40 for determining potential shadow zones A3 in which the object T is not detectable by the sensor when positioned in the position POSj; and a determination step E50 for determining the operational zone ZOj by taking account of the intersection between the first zones A1, the second zone A2, and optionally the zone that is complementary to the shadow zones A3 in the region of interest ROI.

(67) The steps E10 to E50 show the main steps of a method of determining an operational zone for the sensor S in the meaning of the invention for the sensor in the position POSj.

(68) In a particular embodiment, the sensor possesses characteristics that are anisotropic. In this embodiment, the step E30 of the method of determining the operational zone serves to determine a second zone A2jk for each orientation k of the coverage zone of the sensor S. Said method thus has two loops, iterating on different positions POSj in the region of interest ROI and iterating on the orientation k of the sensor.

(69) FIG. 18 shows the screen 16 of the computer 10 for a position POSj of the sensor S, the surveillance zone ZS, the first zone A1j, the second zone A2j, and the operational zone ZOj. In this example, the first zone A1 is truncated beyond a certain distance that is set arbitrarily.

(70) In the presently-described implementation, once the operational zone ZOj has been determined for all of the positions POSj of the sensor S, the method of providing assistance in installing the sensor includes a determination step E60 for determining at least one preferred position POSopt for the sensor among the positions POSj, this preferred position serving to determine an optimized operational geographical zone ZOopt complying with an optimization criterion. In the presently-described implementation, the optimized position POSopt for the sensor is the position that serves to maximize the area of the surveillance zone ZS that is covered by the operational zone ZOopt obtained for the position of the sensor.

(71) The optimized positions POSopt for the sensor may be marked on the screen 16 for the operator so as to enable the operator to install the sensor in that position in the region of interest.