EP2715390A1

EP2715390A1 - Method and system for tracking a mobile unit using a tracking device

Info

Publication number: EP2715390A1
Application number: EP12729681.2A
Authority: EP
Inventors: Eric WILLEMENOT DE NANC
Original assignee: Move'n See
Current assignee: Move'n See
Priority date: 2011-05-27
Filing date: 2012-05-22
Publication date: 2014-04-09
Also published as: WO2012164202A1; US20140111653A1; FR2975783A1

Abstract

The invention relates to a method for tracking at least one mobile unit using a tracking device. The method comprises at least the following steps: (a) the tracking device receiving a signal emitted by the mobile unit(s), said signal comprising a first piece of information on the position of the mobile unit(s) determined according to information received from a satellite positioning system; (b) determining a second piece of information on the relative altitude of the mobile unit(s) with respect to the tracking unit, said second piece of information being calculated according to the atmospheric pressures measured at the altitude of the tracking device and on the mobile unit(s); (c) calculating the relative position of the mobile unit(s) with respect to the tracking means, according to the first and second pieces of information using a data-merging technique; and (d) directing the tracking means toward the relative position calculated in step (c).

Description

Process and continuation of a mobile unit

by a positit itif of continuation uite

The present invention relates to methods and systems for tracking a cooperative mobile unit to a tracking device, including a camera.

The present invention applies in particular, but not exclusively, to the pursuit of cooperative targets, such as sports in motion, so that they can visualize their physical and technical performance.

More particularly, it relates to a method of tracking at least one mobile unit by a tracking device, the tracking device comprising at least one tracking means, such as an articulated mount on a fixed or movable support, easily transportable.

Automatic tracking systems of moving subjects by cameras are known in the prior art. It is notoriously known systems having an automatically adjustable line of sight so that it follows the moving subject or video systems having a zoom and / or focus automatically adjusted according to the information collected by the system.

Document US2007 / 0133979 describes such a system in which transmitters arranged on the objects to be monitored communicate with a receiver connected to the camera and transmit information enabling the camera to be automatically oriented on the basis of the signal strength received by directional antennas. However, this type of antenna has the disadvantage of being cumbersome and expensive to accurately follow subjects moving at great distances.

The document US2010 / 0208941 also describes a system in which transmitters arranged on the objects to follow unite with a receiver connected to the camera. In this solution, the calculation of the angle of inclination of the camera is based on the positioning information by satellite and / or that of the radar. The altimetric accuracy of positioning by satellite is known to be worse than the ude or longitude estimate. This precision is typically of the order of 100m when that on the latitude or longitude is of the order of 10m. Moreover, when the mobile unit and the system are close to the ground, the radar is particularly disturbed, for the estimation of the angle of inclination, by the reflections of the signal on the ground and the refraction in the layer of air when it has a temperature gradient.

Indeed, it is known that a signal reflected on the ground or refracted by the air layer does not have the same direction of origin as the signa in direct line, which can disturb the determination of the arrival of the direct line signal. The false radar targets created by these phenomena are called "ghosts", and sometimes difficult to identify and eliminate. When they can be identified and eliminated, it is at the cost of extremely sophisticated algorithms, whose real-time process is expensive. The system of the state of the art has as a major disadvantage a complex and non-efficient determination of the angle of inclination.

In the prior art, tracking of a moving subject can be achieved by automatic image analysis to adjust the orientation of the camera. Monitoring can also be done by placing infrared emitters on the subject, or presence detectors located in the ground. These three methods can be combined to give the system the information needed to orient the camera's aiming axis and possibly adjust its zoom. However, these solutions are expensive, relatively complex to implement, and have a low range, making it impossible to track a distant subject unrecognizable image.

In sports clubs with little financial means, and not being able to invest in the existing lexes and too expensive technical solutions, the recording of the performances of the athletes is carried out either by leaving the camera with fixed station without possibility or stop of filming or guiding and zoo sea to properly observe the over an entire course, either by filming it with the help of a person who has to manipulate the camera. However, in practice, an instructor can not at times film athletes and ensure safety and education. It is necessary to use a third person which represents a cost that is rarely accessible for a sports club. Moreover, the intervention of an additional person filming the athletes, leads to choices of pursuit different from those which the monitor might have wished.

The aim of the present invention is to overcome these drawbacks and to propose a method and a system making it possible to follow a moving subject indoors or outdoors, at short or long distance, in a robust, efficient and inexpensive manner and which is particularly suitable for sports teaching applications.

For this purpose the tracking method is characterized in that it comprises at least the following steps:

(a) reception by the tracking device of a signal transmitted by the mobile unit (s) and comprising a first position information of the mobile unit (s) determined from information received from a satellite positioning system, (b) determining a second relative elevation information of the at least one mobile unit relative to the tracking device, and said second information is calculated based on the atmospheric pressures measured at the altitude of the tracking device and the one or more mobile units, (c) calculating the relative position of the at least one moving unit relative to the tracking means, from the first and second information by a data merging technique, (d) orienting the tracking means toward the relative position calculated in step (c).

Thanks to these provisions, the information concerning the position of the mobile unit to be continued is optimized and obtained by a simple and robust system, without requiring the use of expensive equipment u bulky as is the case for the solutions of the prior art.

The determination of the relative altitude of a mobile unit relative to the tracking means by means of atmospheric pressure measurements constitutes a particularly advantageous means for such a system, since the desired accuracy of a few meters is exactly that achieved by very good sensors. cheap (a few euros), very small (some cubic millimeters), and very simple to implement on a completely standard electronic board. This avoids the inconvenience of cumbersome, expensive radar antennas requiring complex signal processing; the disadvantages of the altitude delivered by satellite positioning systems whose precision is insufficient to fit an athlete to a few meters so as to zoom without losing the image; the disadvantages of image processing techniques where I can be very complex or impossible to recognize the athlete to film when he is drowned in the crowd or in a complex landscape; the disadvantages on the limited scope of some systems since here the pressure data can be transmitted by radio at distances of the order of one kilometer by radio systems.

According to other characteristics:

the method also comprises a step (e) of determining a third position information of the tracking device (12) on the basis of information received from a satellite positioning system;

the method also comprises a step (f) of determining a fourth piece of information of the distance between the mobile unit (s) and the tracking device;

the method also comprises a step (g) of determining a fifth information of the arrival angle of the signal in a horizontal plane; Such information can be delivered by antennas sensitive to the direction of arrival of the signal. When the mobile unit is at short range, typically less than 50m, this information can be read reliably than that delivered by the satellite positioning system, to direct the tracking device to the mobile unit. For example, an error of 5 ° in the horizontal direction of arrival of the signal from a mobile unit located 30m from the tracking device corresponds to an error of 2.6m on the position of the mobile unit, while the information given by satellite positioning system may have an error of the order of 10m.

the method comprises in step (c) the third and / or the fourth and / or the fifth information;

- the calculation of the relative position of the island unit (s) takes into account a model of behavior of the mobile unit or units by adding information to said calculation on the nature of the movements.

By nature of the movement is meant for example a speed and / or a bounded acceleration, and / or a minimum radius of gyration, and / or any other hypothesis;

at least one of the first, second, third, fourth, and fifth information further includes associated error estimates;

the second information relating to the altitude is calculated from the estimate of the angle of arrival in a vertical plane. Such information can be delivered by antennas sensitive to the direction of arrival of the signal. This information may be more accurate than that provided by a satellite positioning system. For example, a 10 ° error on the vertical direction of arrival of the signal of a mobile unit located 30m from the tracking device corresponds to an altitude error of 5.2m, when the altitude error of the information delivered by a satellite positioning system may be of the order of 100m.

the tracking device comprises tracking means comprising means for adjusting the shooting of the tracking means, such as a zoom and / or a focus or an angle of aperture, characterized in that the method comprises in addition, a step of controlling the adjustment means as a function of the distance of the mobile unit or units relative to the tracking means;

the tracking device comprises a tracking means comprising means for adjusting the shooting of the tracking means, such as a zoom and / or a focus or an opening angle characterized in that it comprises a control step of the adjusting means as a function of the uncertainty of the relative position of the mobile unit or units relative to the tracking means;

the method also comprises a step (h) of reception by the tracking device of a follow-up call from the mobile unit (s), then a step (i) of issuing a follow-up signal attesting to the follow-up of the mobile unit from the tracking device; the method comprises at least two mobile units and a step (j) for receiving a signal transmitted from one of the mobile units indicating the mobile unit to be continued, and then a step (k) of sending a signal. tracking track attesting the tracking of said mobile unit to follow from the tracking device;

the method comprises a prior step of calibrating the tracking device so as to know the orientation of a reference proper to the support and / or the means of tracking relative to the local vertical, or in a local geographical trihedron; The term "local geographical trihedron" refers to the reference mark consisting of the three north, east and vertical axes. Local vertical means the direction of gravity.

the calibration step consists in determining the orientation of a reference mark specific to the support or the tracking means, by means of accelerometers or inciometers disposed on the support and determining the local vertical. In this way, the calibration step makes it possible to know the horizontality of a reference specific to the support and / or the tracking means in the local geographical trihedron;

- The calibration step determining the orientation of a reference specific to the support further comprises a compass that determines the North. Thus, the calibration step makes it possible to completely know the orientation of a mark specific to the medium and / or the tracking means;

if the first information and the third information are non-definable, the calculation of the relative position of the mobile unit (s) relative to the tracking means is made from the second, fourth and fifth information.

The relative altitude of the tracking device and the mobile unit is achieved reliably and simply by using pressure sensors. The precision required is all the easier to achieve when the measurement is differential as in our case and not absolute nsi the subject to be filmed can be framed to a few meters, which allows a sufficient zoom to very well observe the unity mobile.

The invention also relates to a tracking system for implementing the tracking method of a mobile unit described above, remarkable in that it comprises a tracking device comprising at least one means mounted tracking device mounted on a fixed support, a satellite positioning system and at least one pressure sensor on the at least one mobile unit, the tracking system further comprising a satellite positioning system disposed on the at least one mobile unit, a transmitter and a receiver arranged on the mobile unit or units and adapted to transmit and receive a signal with the tracking device.

According to other features, the system comprises a tracking device comprising at least one tracking means mo articulated on a fixed support, a satellite positioning system and at least one set of antennas sensitive to the direction, the tracking system. further comprising a satellite positioning system disposed on the at least one mobile unit, a transmitter and a receiver disposed on the at least one mobile unit and adapted to transmit and receive signal with the tracking device.

According to other features, the tracking means is a camera mounted on a solidarity platform articulated on the support.

The present invention will be better understood on reading the detailed description which follows, made on the basis of the appended drawings in which:

FIG. 1 schematically represents a set of mobile units 14, one of which is followed by the tracking device according to the invention,

FIG. 2 is a schematic representation of one embodiment of the method;

FIG. 3 illustrates a schematic representation of the elements constituting a mobile unit 14.

In the description that follows, the terms "horizontal, vertical, high, low" will be used according to their usual meaning in the terrestrial reference system.

The teaching of certain sports benefits from video when it can be used easily and at an affordable cost. Team sports, for example football, volleyball ... use video to analyze their game and the opponents. A sport like skydiving fully integrates video with sport using it for performance analysis from the beginner level. Registration of athletes during their training or their competitions is therefore of real interest, provided that this recording can be made simply and at an acceptable cost, which is not the case in all sports. In some sports, for example, it is necessary to avoid the need for a third person to function. The present invention provides a solution having the advantages described above, its application to sport is just one example.

More particularly, the invention relates to a tracking system 10 consisting in particular of a tracking device 12 adapted to follow a mobile unit 14 such as a sportsman. The tracking device 12 comprises a support 16, such as a tripod, on which is articulated a tracking means 18, such as a camera. The camera 18 is connected to the support via a platform 20 on which it is mounted. The platform 20 is articulated on the support 16 and extends in a pre-plane. A set of motors 22 makes it possible to move the platform 20 relative to the support 16. The motors 22 allow the platform 20 to move in rotation about a vertical axis so that the camera 18 can be moved in a horizontal rocking movement ( PAN) and a rotational movement about a horizontal axis so that the camera 18 can be moved in a vertical rocking motion (TILT). The slave platform 20 makes it possible to reach a set of angular positions making it possible to track the mobile units 14.

The tracking device 12 is further equipped with means 24 for transmitting and receiving a signal of the radio or ultrasound type. These means consist in particular of a set of direction-sensitive antennas 24, for example of the Adcock antenna type, which in a particular embodiment is mounted on the camera 18 or on the platform 20, so that that the direction of arrival of signals from the mobile unit 14 is always viewed at the same angle, thereby reducing the errors as is known in zero-tracking. According to another embodiment, the set of antennas is mounted on the fixed support 16 so that the environment outside the system is viewed from constant angles in order to limit the disturbances of the measurements. The device is further provided with a satellite positioning system 26, such as a GPS. The tracking device 12 further comprises a processing unit 28 which is connected to the set of antennas 24. The processing unit 28 processes the information relating to the signal received by the set of antennas 24 and the information of position of the tracking device 12 from the satellite positioning system, as well as commands ux motors 22, and possibly any type of interface with ursuite means 18, as well as any type of interface with the user.

The tracking system also comprises a transmitter 30a-receiver 30b assembly disposed on the mobile unit 14. According to a preferred embodiment, the system comprises several transmitting assemblies 30a-receiver 30b, each set being disposed on a mobile unit 14 to be continued . Each mobile unit 14 is further provided with a satellite positioning system 32, such as a GPS. The transmitter 30a-receiver 30b are adapted to communicate with the tracking device 12 and to transmit a signal containing at least one specific identifier to each mobile unit and a first position information of the mobile unit 14.

The position data of the tracking device 12 the position data of the mobile unit 14 present errors due in particular to the calculation uncertainties or to the measurement tolerances of the devices. For example, the position information collected from a GPS position includes the position data and a loss of accuracy coefficient to determine whether an evolved GPS position is reliable or not. The method of the present invention takes into account these errors, and the position of the mobile unit 14 and the position of the tracking device 12 will be respectively determined by a first and a third position information including the position data from the system. satellite positioning and associated error estimates.

The operation of the tracking system 10 of a moving unit 14 by the tracking device 12 will be described hereinafter, based on FIG.

At first, a calibration step of the system is carried out so as to know the position of the support of the local geographical trihedron. For this purpose, in a preferred embodiment, the tracking system 10 according to the invention comprises a compass 34 and two inclinometers or accelerometers providing perpendicular measurements 36 located on the support 16. With these provisions, it is possible to easily determine the position of the support 16 in the local geographical trihedron , identified by the three axes North, East and vertical, then to deduce, from the knowledge of the state of the engines, the initial orientation of the tracking means 18 in order to determine in which direction to turn to aim at the mobile unit 14.

The information from the compass 34 and the inclm meters 36 are taken into account when the tracking device 12 is placed on the ground and before any follow-up of a mobile unit 14. The calibration step consists in determining the orientation a mark specific to the support (16) or the tracking means (18), via accelerometers or inci no meters arranged on the support or the tracking means (18) and determining the local vertical, and a compass that determines the north. The addition of a compass 34 and inci no meters or accelerometers 36 on the system is inexpensive, simple and reliable, and allows the portability of the system in different places without compelling the user to complex manipulations to recalibrate the system .

After the calibration step, the tracking method to acquire, synchronously or not, successively or not, different information and to merge to obtain at any time an estimate of the direction and distance of the unit mobile to follow, and therefore different pursuit commands:

The transmitter 30a disposed on the mobile unit 14 emits a nal several times per second, for example between 1 and 1000 times per second. The transmission of the signal may be carried out regularly automatically, or it may be carried out in response to an interrogation signal, or a call from the tracking device 12. At regular intervals, for example 1 to 100 times a second, the signal comprises the identification codes of the mobile unit 14 and the first position information of the mobile unit in real time. In addition, the signal may comprise an identification code of the tracking system 10, so that several systems can operate in the same zone. without interference.

- The tracking device 12 determines the third position information via the data from the satellite positioning system 26. According to an alternative embodiment, the third position information may have been entered manually by a user interface, or the position may be derived from a solid external element of a GPS receiver and having been arranged in close proximity to the tracking device 12 and adapted to communicate with it.

When the signal is received by the set of antennas 24, it is then analyzed by the processing unit 28. If the processing unit 28 detects the presence of the identification code of the system and, if applicable, that of the mobile unit to be followed in the signal, then the signal is taken into account in updating the estimates, and the first and third information of the GPS position are then processed by the processing unit 28. In one embodiment, the first position information of the mobile unit 14 is used to calculate, with the third position information of the tracking device 12, a first arrival direction value a1, b1 and a first distance value D1 between the device tracking 12 and the mobile unit 14.

Furthermore, the set of antennas 24 connected to the tracking means 18 is sensitive to the direction of arrival of the signal transmitted by the mobile unit 14. When the signal is received by the set of antennas 24, and its identification validated, the processing unit 28 estimates at least a first arrival angle of the signal from the mobile unit 14 in the pre plane so as to deduce a second direction value a2. A second piece of information comprising the second arrival direction and the associated error estimates is then determined.

According to a preferred embodiment, the system comprises two sets of direction-sensitive antennas and the second direction value is defined by a pair of angles. The angles can be determined respectively with respect to the first plane ns which extends the platform 20 and with respect to a second plane perpendicular to the first plane. According to another variant of the invention, the tracking system 10 comprises a pressure sensor 42 fixed on the tracking device 12 and a pressure sensor 44 fixed on the mobile unit, so that a difference in altitude DZ2 can be calculated, and that a direction angle b can be deduced therefrom by the processing unit by combining the distance information, derived from the position information, by the angle angle b = atan (DZ2 / distance)

The processing unit 28 also comprises means enabling it to estimate a second distance value D2 of the moving subject with respect to the camera 18 on the basis of the intensity of the signal received from the moving subject. Alternatively, the second distance value D2 can be estimated based on the round trip time of a round trip signal between the tracking device 12 and the moving subject. A fourth piece of information comprising the second distance value D2 of the mobile unit 14 with respect to the tracking device 12 and error estimates associated with its calculation is then established.

The processing unit 28 comprises calculation means adapted to calculate from the first, second, third and fourth information previously determined, the relative position D, a, b of the mobile unit. For this purpose the calculation is performed by a data fusion technique. These techniques allow information from different sources to be mixed together to obtain an estimate and more specifically to integrate multiple pieces of information to reduce the uncertainty of the resulting information, as described in the article entitled "The Merger". of data, from the sensor to reasoning "published in the journal" Signal Processing 1994 - Volume 11 - n¾ "

For this purpose, the calculation using the fusion technique takes into account the reliability of the data used and the degrees of uncertainty of the incoming information. The merger is based on a combination of information items weighted by their respective uncertainties. Data fusion is a process of best combining, from existing and known calculation methods, a multisource data set for better quality resulting information. It is specified that a technique of Data fusion consists in keeping only the most known data. For example, between precision sensor data and a GPS, the GPS data would not be taken into account in order to have a better accuracy.

As a simple example, if the measurement uncertainties on a1, a2, b1, b2, D1 and D2 are expressed as specific standard deviations σ ₃ ι, σ ₃ 2, o _b i, o _{b 2} , ODI, O _D 2, the estimates of a, b, and D can be obtained as follows:

+ σ ₀ ι ² / (σ ₀ ι ² + σ ₀ 2 ² ) * D 2;

a = Oa2 ² (aai ² + Oa2 ² ) ^* a1 + σ ₃ ι ² / (σ ₃ ι ² + σ ₃ 2 ² ) * a2;

b = o _b 2 ² / (a _b1 ² + o _b 2 ² ) ^* b1 + a _b1 ² / (a _b1 ² + a _b2 ² ) ^* b2.

For example, when the moving subject is located at a great distance from the tracking device 12, more than 50 meters away, the first direction values a1, b1 and distance D1 from the satellite positioning system will be preferred, because of Satellite positioning is independent of distance. On the other hand, at short distances, that is to say for distances of less than 50 m, the second distance values D 2 and of direction a 2, b 2 will be preferred, for example affected by a larger weighting factor. The weighting coefficient is defined based on the error estimates and the second value of the distance.

Thus, when the first and third information are definable, the processing unit 28 takes advantage of the redundancy between the data from the first and third information and data from the second and fourth information in order to optimize the calculation of the relative position D, a, b of the mobile unit 14, despite the errors specific to each type of calculation or measurement.

The use of data from the satellite positioning system and those from the set of sensitive antennas 24 is intended primarily to improve pointing accuracy. Indeed, the set of antennas 24 directives informs the system on its orientation relative to the mobile unit but is likely to have errors of several degrees, a hundred meters distance an error of 10 ° on the line of sight leads to a difference of about 17 meters between the target mobile unit and the actual point u center of the video image. At five hundred meters, it becomes about 87 meters. As a result, the long-range information obtained from satellite rental is much more relevant than that from antennas 24.

The calculation means of the processing unit 28 use known signal processing techniques which make it possible to take advantage of the redundancy of the information relating to the direction and the distance to make better than with each of the sources of information taken separately. .

When the system is used inside a sal for example in a pool, to track and shoot swimmers, the first direction values a1, b1 and distance D1 from satellite positioning systems are not definable. In this case, only the second and fourth information are used to determine relative position D, a, b of the mobile unit 14.

According to a variant of the invention, the calculation of the relative position of the mobile unit with respect to the tracking means takes into account a model of behavior of the mobile unit, for example speed and acceleration are bounded. The taking into account of this model, like other information, is done for example by Kalman filtering, so as to improve the accuracy of the calculation of the position of the mobile unit.

By model of behavior, one understands all the physical information that one will add to the measurements, in mathematical model form (S). For example we can add the information that the mobile never exceeds a certain acceleration, and / or a certain speed, and / or a steering angle, and / or that its acceleration averaged over time is zero, etc.

The relative position of the mobile unit 14 is expressed with respect to the position and the orientation of the camera 18. It is then used to determine the controls of the motors 22 so as to control the displacement of the platform 20 in order to orient the camera 18 towards the moving unit 14 on the move.

The camera 18 includes means for adjusting the shooting, such as a zoom and / or a focus or an opening angle. According to a variant the relative position is used to control the adjustment means as a function of the distance of the mobile unit 14 from the tracking means 18. It may also be provided that the method according to the invention further comprises a step controlling the adjustment means as a function of the uncertainty of the relative position of the moving unit relative to the tracking means, so as to modify the optical field of the tracking means as a function of the uncertainty. For example, this command widens the field when the uncertainty of the relative position is large and reduces the field when the uncertainty of the position ive is relatively small.

The invention described above has been illustrated on the basis of a tracking system comprising a tracking device 12 and a mobile unit 14. The invention operates in a similar manner with several mobile units 14. In this case, it is then necessary to manage the exchanges between the tracking device 12 and the multitude of mobile units 14. The following description describes in a non-exhaustive way some examples of exchange management between the tracking device 12 and the moving tees 14. The method no longer limited to the examples described below.

According to a first embodiment, the system comprises a main mobile unit 14 and secondary mobile units 14.

According to a first variant, the main mobile unit 14 comprises designation means adapted to send a signal to the tracking device 12 to designate the mobile unit 14 to follow. This designation can be activated by a remote control function, for example pressing a button 38. The secondary mobile units 14 do not have this functionality. The main mobile unit 14 may designate itself to be followed. When the device receives such a designation signal, it transmits a tracking signal so as to inform the mobile unit to be monitored and the main mobile unit and, if appropriate, so that the transmitter 30a can transmit the signal comprising the information necessary for the implementation of the tracking method described in the first part of the description.

According to a second variant of the invention, the main mo unit 14 sends a signal to the tracking device 12, indicating that the latter must automatically answer calls from the secondary mobile units 14. Thus, when the transmitter 30a of one of the mobile units sends a follow-up call, the tracking device 12 receiving the signal transmits, in response, a tracking signal to said calling mobile unit 14, and the tracking method described in FIG. first part of the description is applied to said mobile unit 14.

The mobile units 14 communicate with the tracking device 12 by communication techniques known to those skilled in the art, in particular by radio or ultrasound link. The follow-up call from a secondary mobile unit 14 may be activated by pressing a button 38 or by voice command, or any other means.

According to an alternative embodiment, the tracking of the calling mobile unit 14 is performed during a determined time interval, for example 1 minute. During this time interval, the possible follow-up calls of the other secondary mobile units 14 are recorded no particular action. At the end of the tracking period of a caller unit 12, the tracking device 12 is controlled to monitor another mobile unit, preferably that indicated by the last received tracking IAP.

It can also be expected that, in the absence of another follow-up call, the mobile unit 14 is tracked beyond the determined time interval.

Preferably, the mobile units 14 are aware of the information relating to their tracking, for example by turning on or off a Del 40 disposed on the mobile unit 14. The main unit can also be aware of the mobile unit 14 followed.

The invention is not limited to the embodiments and variants described above which have been given by way of example. It can especially apply to the photo with cameras, lighting systems to pursue a moving target on a theater stage.

Claims

Claimants

1. Method for tracking at least one mobile unit (14) by a tracking device (12), the tracking device (12) comprising at least one tracking means (18) mounted on a fixed support (16), characterized in that it comprises at least the following steps:

(a) reception by the tracking device (12) of a signal transmitted by the mobile unit (s) and comprising first position information of the mobile unit (s) determined from information received from a positioning system; satellite,

(b) determining a second relative altitude information of the at least one mobile unit (14) relative to the tracking device (12), and said second information is calculated based on the atmospheric pressures measured at the altitude of the tracking device (12) and on the one or more mobile units (14),

(c) calculating the relative position of the at least one mobile unit (14) relative to the tracking means (18) from the first and second information by a data fusion technique,

(d) orienting the tracking means (18) toward the relative position calculated in step (c).

2. Tracking method according to the preceding claim, characterized in that it also comprises a step (e) for determining a third position information of the tracking device (12) from information received from a system. satellite positioning.

3. Tracking method according to one of the preceding claims, characterized in that it also comprises a step (f) for determining a fourth information of the distance between the mobile unit (s) (14) and the tracking device. (12).

4. Tracking method according to one of the preceding claims, characterized in that it also comprises a step (g) of determination a fifth information of the arrival angle of the signal in a horizontal plane.

5. Tracking method according to one of claims 2, 3 or 4, characterized in that it further comprises in step (c) the third and / or fourth and / or fifth information.

6. Tracking method according to claim 1 or 5, characterized in that the calculation of the relative position of the mobile unit or units takes into account a model of behavior of the mobile unit or units by adding information to said calculation on the nature of the movements.

7. Tracking method according to one of the preceding claims, characterized in that at least one of the first, second, third, fourth and fifth information further comprises associated error estimates.

8. Tracking method according to one of the preceding claims, characterized in that the second altitude information is calculated from the estimation of the arrival angle in a vertical plane.

9. Tracking method according to one of the preceding claims, the tracking device (12) comprising a po means (18) comprising means for adjusting the shooting of the tracking means (18), such that a zoom and / or a focus or a vertex angle, characterized in that the method further comprises a step of controlling the adjustment means as a function of the distance of the mobile unit or units (14) relative to the tracking means ( 18).

10. Tracking method according to one of the preceding claims, the tracking device (12) comprising a po means (18) comprising means for adjusting the shooting of the tracking means (18), such that a zoom and / or a focus or an opening angle characterized in that it comprises a step of controlling the adjustment means as a function of the uncertainty of the relative position of the mobile unit or units (14) relative to the tracking means (18).

1 1. Tracking method according to one of the preceding claims, characterized in that it also comprises a step (h) of reception by the tracking device of a follow-up call of the mobile unit or units (14), then a step ( i) transmitting a tracking signal attesting the tracking of said mobile unit from the tracking device (12).

12. Tracking method according to one of claims 1 to 8 characterized in that it comprises at least two mobile units (14) and a step (j) for receiving a signal transmitted from one of the mobile units indicating the mobile unit (14) to be continued, and a step (k) of sending a tracking signal attesting to the tracking of said mobile unit to follow from the tracking device (12).

13. Tracking method according to one of the preceding claims, characterized in that it comprises a prior step of calibration of the tracking device (12) so as to know the orientation of a specific mark support (16) and / or by means of tracking (18) with respect to the local vertical, or in the local geographical trihedron.

14. Tracking method according to the preceding claim wherein the calibration step is to determine the orientation of a specific mark support (16) or tracking means (18), via accelerometers or d Including no meters arranged on the support (16) and determining the local vertical.

15. Tracking method according to claim 13 or 14, characterized in that the calibration step determining the orientation of an own support also comprises a compass that determines the North.

16. Tracking method according to one of the preceding claims, characterized in that, if the first information and the third information are non-definable, the calculation of the relative position of the mobile unit or units (14) relative to the means of continuation is carried out to second, fourth and fifth information.

17. Tracking system for implementing the tracking method of a mobile unit (14) according to one of the preceding claims, characterized in that it comprises a tracking device (12) comprising at least one tracking means. (18) hinged to a fixed support (16), a satellite positioning system (26) and a pressure sensor to the at least one movable unit (14), the tracking system (10) further comprising a satellite positioning system disposed on the at least one mobile unit (14), a transmitter (30a) and a receiver arranged on the at least one mobile unit (14) and adapted to transmit and receive a signal with the tracking device (12). ).

18. Tracking system for implementing the tracking method of a mobile unit (14) according to one of claims 1 to 16, characterized in that it comprises a tracking device (12) comprising at least one tracking means (18) hingedly mounted to a fixed support (16), a satellite positioning system (26) and at least one directional antenna assembly (24), the tracking system (10) furthermore a satellite positioning system disposed on the at least one mobile unit (14), a transmitter (30a) and a receiver disposed on the at least one mobile unit (14) and adapted to transmit and receive a signal the tracking device (12). ).

19. Tracking system (10) according to the preceding claim, characterized in that the tracking means (18) is a camera mounted integral on a platform (20) articulated on the support (16).