Data processing method, device, system and corresponding program

Abstract

The invention relates to a method for synchronizing data (DHrs1) timestamped using a clock of a first electronic device with data (DHrs2) timestamped using a clock of a second electronic device. Such a method comprises: - at least one step (10) of the first electronic device obtaining a first time series Hs(t) representative of the change over time of a metric measured by the first electronic device; - at least one step (20) of the second electronic device obtaining a second time series Hp(t) representative of the change over time of the same metric as that measured by the first electronic device, [said first time series and said second time series at least partially covering a common time period] - a step (30) of computing a phase offset between the first time series Hs(t) and the second time series Hp(t), giving a time difference Δt between these two time series; - a step (40) of synchronizing the data (DHrs1) timestamped using the clock of the first electronic device on the basis of the time difference Δt, producing synchronized timestamped data (U.DHrs1).

Description

[0001] DESCRIPTION

[0002] TITLE: Data processing method, device, system and corresponding program

[0003] 1. Technical field

[0004] The disclosure relates to the field of mobile mapping. More specifically, the disclosure relates to the field of capturing and processing data from mobile mapping devices. Even more particularly, the disclosure relates to the processing of data from a mobile mapping device coupled to a total station, also called a total station.

[0005] 2. Prior Art

[0006] Mobile mapping systems and devices have been developed for many years. Such systems allow for the acquisition of three-dimensional data about the mapped environments. Various technologies can be implemented within a mobile mapping device to obtain this three-dimensional data. In particular, it is possible to use 3D cameras, 2D cameras, real-time positioning and localization devices, LiDAR, etc.

[0007] One or more capture modules are mounted on the mobile mapping device. The mapping device may be mounted on a land vehicle (e.g., a light vehicle, such as a car or van) or an aerial vehicle (e.g., a radio-controlled drone). Such a mobile mapping device may also be in the form of a backpack, allowing an operator to take measurements while moving on foot.

[0008] One of the main problems that a mobile mapping device faces can be summarized in the calculation of the device's movement trajectory: indeed, assuming that a mobile mapping device made up of calibrated sensors moves to "scan" the environment, all the measurements made by the mapping device are related to the position of this mapping device at the instant "t" of the measurement. It is therefore necessary to precisely determine the position of the mobile mapping device. The final accuracy of the mapping result depends on the accuracy of the measurements of the sensor(s), the accuracy of the dating (time stamping) of these measurements, the accuracy of the calibration of the mobile mapping device and this equipment, and finally the accuracy of the trajectory taken by the mobile mapping device.Determining the effective trajectory of the mobile mapping device is thus one of the most complex problems to resolve and an extremely important issue.

[0009] In some situations, it is possible to rely on trajectory calculations that only involve the use of the mobile mapping device. In other situations, however, the usual trajectory calculations (i.e. specific to the mobile mapping device) are not sufficient to provide an effective position of this mobile mapping device. It is therefore necessary to have an additional solution to determine, in the most efficient way possible, the trajectory actually followed by a mobile mapping device during the measurement and capture operations of the environment. To do this, a total station can be used in conjunction with the mobile mapping device. However, to solve the problem of precise positioning, we face a double problem, which is that of synchronizing the position and the clock of the total station and the mobile mapping device.

[0010] However, the inventors have found that the possible solutions for determining the trajectory actually followed by the mobile mapping device are essentially based on wireless communication between the mobile mapping device and the total station. To date, most total stations have a tracking function. This tracking function is used mainly to monitor the surveyor operator in the field to speed up measurement taking and / or to guide construction machinery, for example for the automation of heavy machinery.

[0011] Accuracy and synchronization are not major issues for the two cases mentioned above, communication between the total station and the machine or between the station and the field notebook is therefore carried out in real time via long-range radio modules (e.g. Bluetooth). The dynamics of the machine and / or the precision sought in the surveyor's measurement do not require a better communication method than that currently provided. Furthermore, in the case of tracking the surveyor operator, the measurement in the field is always done statically, the tracking function only allowing the surveyor operator to work alone on site, while controlling the total station remotely. However, communications via radio (e.g. Bluetooth) are subject to variations, particularly in the data transmission and reception times by the devices.These variations can be due to many factors, such as changes in the radio environments operating around the total station or mapping device, or pollution of the frequency ranges used.

[0012] Thus, when the accuracy and synchronization of the clocks of the total station and the mapping device represent a significant issue, as is the case during the precise positioning of the mapping device during its movement, the use of currently available means, and in particular radio communication means, between the total station and the mapping device, do not represent a solution to the problem encountered by the inventors, because the delays in receiving / transmitting information by radio are too long. Another solution could consist of installing a cable connection between the mapping device and the total station. However, this cable connection hinders the movement of the mapping device and therefore poses problems of mobility, but also of extension, in particular in terms of the length of cable available for example.It is therefore necessary to provide a solution that makes it possible to precisely determine the position of the mobile mapping device during its movement while avoiding the problems posed by the solutions of the prior art.

[0013] 3. Summary of the invention

[0014] The technique designed by the inventors has been tested to address at least in part the issues raised by the prior art. Thus, the present disclosure relates to a method for synchronizing time-stamped data using a clock of a first electronic device with time-stamped data using a clock of a second electronic device. Such a method comprises: at least one step of obtaining, by the first electronic device, a first time series Hs(t) representative of the evolution, over time, of a metric representative of the height of the first electronic device, measured by the first electronic device;at least one step of obtaining, by the second electronic device, a second time series Hp(t) representative of the evolution, over time, of the same metric as that measured by the first electronic device, [said first time series and said second time series at least partially covering a common time period] a step of calculating a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time difference At between these two time series; a step of synchronizing the time-stamped data using the clock of the first electronic device as a function of the time difference At, producing synchronized time-stamped data.;

[0015] Thus, it is possible to perform clock synchronization, and then, depending on the embodiments, position synchronization, without the need for a link. In addition, the variation in height over time can be obtained, according to the invention, relatively easily by at least one of the devices while being sufficiently precise, resulting in faster processing of the time series.

[0016] According to a particular characteristic, the step of obtaining, by the first electronic device, the first time series Hs(t), comprises determining the evolution of the relative height of the first electronic device with respect to the ground, delivering the first time series Hs(t).

[0017] According to a particular characteristic, the step of obtaining, by the second electronic device, a second time series Hp(t) comprises determining the evolution of a relative height of a visual tracking device of the first electronic device relative to the ground, delivering the second time series Hp(t).According to a particular characteristic, the step of calculating the phase shift between the first time series Hs(t) and the second time series Hp(t) comprises: a step of calculating, for the first time series Hs(t) and the second time series Hp(t), two sets of local extrema {Es} and {Ep}, corresponding respectively to the extrema of the series Hs(t) and to those of the series Hp(t); a step of carrying out an extremum matching between the data of these two sets of local extrema {Es} and {Ep}, delivering two sets of local extrema {Es} and {Ep} expurgated of the non-correlatable extrema; and a step of calculating an affine distribution by least squares, using the cost function such that:.

[0018] According to a particular characteristic, characterized in that the first electronic device is a mobile mapping device, of the type comprising a prism at one of its vertices, the prism playing the role of a visual tracking device and in that the second electronic device is a total station.

[0019] According to another aspect, the invention also relates to a method for synchronizing time-stamped data using a clock of a mobile mapping device with time-stamped data using a clock of a tachymeter, a method characterized in that it consists in determining a correlation between a change in a height of the mobile mapping device, as measured by the mobile mapping device itself and a change in a height of the mobile mapping device as measured by the tachymeter, so that once correlated, these two height changes deliver a time offset between the two clocks.

[0020] According to another aspect, the invention also relates to a device for synchronizing data time-stamped using a clock of a first electronic device with data time-stamped using a clock of a second electronic device.Such a device comprises: means for obtaining, by the first electronic device, a first time series Hs(t) representative of the evolution, over time, of a metric representative of the height of the first electronic device, measured by the first electronic device; means for obtaining, by the second electronic device, a second time series Hp(t) representative of the evolution, over time, of the same metric as that measured by the first electronic device, [said first time series and said second time series at least partially covering a common time period] means for calculating a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time difference At between these two time series; means for synchronizing the time-stamped data using the clock of the first electronic device as a function of the time difference At.According to another aspect, the invention also relates to a mapping system implementing a synchronization of a clock of a first electronic device with a clock of a second electronic device.Such a system comprises: the first electronic device, generating a first time series Hs(t), representative of the evolution of the altitude of said first electronic device as a function of time; the second electronic device generating a second time series Hp(t) representative of the evolution of the altitude of said first electronic device as a function of time; [said first time series and said second time series at least partially covering a common time period]; means (30) for calculating a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time difference At between these two time series; means (40) for synchronizing the time-stamped data of the first electronic device with the time-stamped data of the second electronic device, as a function of the time difference At.

[0021] According to another aspect, the invention also relates to a mapping system implementing synchronization of a clock of a mobile mapping device with a clock of a tachometer.Such a system comprises: the mobile mapping device, generating a first time series Hs(t), representative of the evolution of the altitude of said mobile mapping device as a function of time; the total station, generating a second time series Hp(t) representative of the evolution of the altitude of said mobile mapping device as a function of time; [said first time series and said second time series at least partially covering a common time period] means (30) for calculating a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time difference At between these two time series; means (40) for synchronizing the time-stamped data of the mobile mapping device with the time-stamped data of the total station, as a function of the time difference At.According to another aspect, the invention also relates to a mapping system implementing synchronization of a clock of a mobile mapping device with a clock of a tachometer.Such a system comprises: the mobile mapping device, generating a first series of values ​​of the altitude of said mobile mapping device, as a function of time; the total station, generating a second series of values ​​of the altitude of said mobile mapping device as a function of time; [said first series and said second series at least partially covering a common time period] means for synchronizing the values ​​of the altitude of said mobile mapping device generated by the mapping device, with the values ​​of the altitude of said mobile mapping device generated by the tachymeter; means for synchronizing the clock of the mapping device with the clock of the tachymeter, the synchronized values ​​of the altitude of said mobile mapping device being linked respectively to the time of the clock of the mapping device and to the time of the clock of the tachymeter.

[0022] According to a preferred implementation, the different steps of the methods according to the present disclosure are implemented by one or more software or computer programs, comprising software instructions intended to be executed by a data processor of an execution terminal according to the present technique and being designed to control the execution of the different steps of the methods, implemented at the level of a mobile mapping device, a remote server and / or a blockchain, within the framework of a distribution of the processing to be carried out and determined by a scripted source code or a compiled code.

[0023] Accordingly, the present technique also relates to programs, capable of being executed by a computer or by a data processor, these programs comprising instructions for controlling the execution of the steps of the methods as mentioned above.

[0024] A program may use any programming language, and may be in the form of source code, object code, or code intermediate between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0025] The present technique also aims at an information medium readable by a data processor, and comprising instructions of a program as mentioned above.

[0026] The information carrier may be any entity or terminal capable of storing the program. For example, the carrier may include a storage medium, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a mobile medium (memory card) or a hard disk or an SSD.

[0027] Furthermore, the information carrier may be a transmissible medium such as an electrical, optical and / or sound signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the present technique may in particular be downloaded over a network such as the Internet.

[0028] Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to perform or to be used in the performance of the method in question.

[0029] According to an exemplary embodiment, the present technique is implemented by means of software and / or hardware components. In this regard, the term "module" may correspond in this document to a software component, a hardware component or a set of hardware and software components.

[0030] A software component corresponds to one or more computer programs, one or more sub-programs of a program, or more generally to any element of a program or software capable of implementing a function or a set of functions, as described below for the module concerned. Such a software component is executed by a data processor of a physical entity (terminal, server, gateway, set-top-box, router, etc.) and is likely to access the hardware resources of this physical entity (memories, recording media, communication buses, electronic input / output cards, user interfaces, etc.).

[0031] Similarly, a hardware component is any element of a hardware assembly capable of implementing a function or set of functions, as described below for the module concerned. It may be a programmable hardware component or one with an integrated processor for running software, for example an integrated circuit, a smart card, a memory card, an electronic card for running firmware, etc.

[0032] Each component of the system described above of course implements its own software modules.

[0033] The different embodiments mentioned above can be combined with each other for the implementation of the present technique.

[0034] 4. Brief description of the drawings

[0035] Other aims, characteristics and advantages of the described technique will appear more clearly on reading the following description, given as a simple illustrative example, and not limiting, in relation to the figures, among which:

[0036] [fig. 1] represents two curves, resulting from two time series, each resulting from the measurement of a quantity [Al] by two different electronic devices;

[0037] [fig. 2] represents the principle of calculating the time shift from the two time series to synchronize the clocks;

[0038] [fig. 3] represents the evolution of the time shift over time, visually expressing the progressive and linear desynchronization of the two clocks; [fig- 4] represents the general process implemented;

[0039] [fig. 5] represents a simplified physical architecture of a device in which the methods previously described can be implemented.

[0040] 5. Detailed description

[0041] 5.1. General principle

[0042] As explained previously, the general principle implemented by the inventors consists of carrying out a synchronization (of the clock, and therefore of the position of the mobile mapping device) based on the evolution of a value (of a metric, of a parameter) which is measured (independently) both by the total station (more generally an electronic device) and by the mobile mapping device (more generally another electronic device).

[0043] More particularly, according to the present technique, a first electronic device is provided with a visual tracking device. This visual tracking device is used by the second electronic device (or an equivalent device) to track the movements of the first electronic device, it being understood that during these movements, the second electronic device is, for its part, fixed and its position is known.Depending on the technologies implemented by the second electronic device, it is for example equipped with an autonomous location device (GPS type) or this location can be entered manually when initializing the second electronic device (the second electronic device is positioned successively in relation to known absolute coordinates, or by creating its own reference frame; the successive “stationing” operations include phases of pointing towards known points to deduce each position of the station; all of these station positions constitute a path). In any event, during the movements of the first electronic device, the second electronic device carries out, according to the method proposed by the inventors, tracking of the visual tracking device positioned on the first electronic device.This tracking of the visual tracking device by the second electronic device is also accompanied by the recording of a certain number of metric values ​​(or parameters), as detailed below. The first electronic device also performs measurements during its movement. More particularly, according to the present technique, the device records at least one value of one (or more) metric(s) (or parameters) common to that(s) recorded independently by the second electronic device.

[0044] The evolution of the value of this metric over time is recorded on the side of the second electronic device and is also recorded independently on the side of the first electronic device (for example in the form of a time series). These two time series are then compared to synchronize the clock of the first electronic device and the clock of the second electronic device.

[0045] Thus, for example, in relation to Figure 1, successive or continuous recordings of the value of the metric [Al] are made on the first electronic device (dashed line curve). These successive or continuous recordings form a time series. Generally speaking, this time series is a representation of the form Xt, where t is time. For the metric Al measured on the first electronic device side, it is noted Hs(t). Similarly, successive or continuous recordings of the metric [Al] are made on the second electronic device (solid line curve). For the metric Al measured on the total station side, this time series is noted Hp(t).

[0046] These two time series are then processed on the time axis (T). The general principle is to exploit the Space / Time duality. More specifically, each instrument (first electronic device, second electronic device or others) is capable of measuring relative positions (or displacements). The principle is therefore to synchronize spatial events to obtain synchronization of the clocks (temporal events). These events can be displacements (events of a spatial nature) relative on any axis x, y or z, as long as these are measurable by the two instruments or any other event in any other situation.

[0047] As a purely illustrative example, we can, for example, perform a synchronization of the undulations on the vertical Z axis. Thus, in this example, the oblique scanner of the first electronic device has a direct relative measurement with respect to the ground. This measurement can be corrected using the inertial unit of the first electronic device, providing the Roll / Pitch reference of the system. Thus, only the Z component of the scanner movements is retained. The first electronic device performs movements from bottom to top (vertical axis), whether it is carried by hand or on the back of an operator. These movements (undulations) are recorded and form the time series Hs(t).

[0048] In this example, the second electronic device is used to determine two angles and a distance. The second electronic device, once positioned, also has a reference in x, y and z. The component on the z axis is thus immediate. The z component of the visual tracking device positioned and rigidly linked to the first electronic device is recorded in order to form the time series Hp(t).

[0049] As shown in the example in Figure 2, provided with these two time series (Hs(t), Hp(t)), the calculation of the phase shift between the two makes it possible to obtain the time difference At of the two reference clocks (offset). In possession of this time difference (and the evolution of this time difference), it is then possible to precisely synchronize the two clocks and consequently to synchronize the positions of the devices, and more particularly the position of the first electronic device over time.

[0050] Thus, in this example (derivable to other situations and to other metrics), the invention relates to a method for synchronizing time-stamped data using the clock of the first electronic device with time-stamped data using the clock of the second electronic device, this method consisting in determining a correlation between a change in a height of the first electronic device, as measured by the first electronic device itself and a change in a height of the first electronic device as measured by the tacheometer (using the visual tracking device present at the height of the first electronic device), so that once correlated, these two height changes deliver a time shift between the two clocks.

[0051] The time series may be partial time series. It is not necessary, in all embodiments herein, for the time series to have a duration that is identical to the total duration of the measurements made by the first electronic device. The time series used to perform the phase shift calculation may thus be shorter and relate to more limited durations, for example at regular intervals, so as not to increase the resources consumed.

[0052] Furthermore, as explained for example in Figure 3, according to the present technique, reproducing this method over time also makes it possible to determine the drift of the clocks and therefore to linearly model the synchronization of the systems. More particularly, in at least one embodiment, several time differences are calculated (Ato,...Atn) and the evolution of these time differences provides an estimate of the drifts of the two clocks, one with respect to the other, in the form of a function (for example affine) of the clock biases, as represented in Figure 3. This function makes it possible to determine the temporal correspondence between a measurable event originating from the device of the first electronic device (for example a mobile mapping device) and an identical, similar or close event originating from the second electronic device (for example the total station).

[0053] Thus, more particularly, in relation to FIG. 4, a method is proposed for synchronizing time-stamped data using a clock of a first electronic device with time-stamped data using a clock of a second electronic device.Such a method comprises: at least one step of obtaining (10), by the first electronic device, a first time series Hs(t) representative of the evolution, over time, of a metric measured by the first electronic device; at least one step of obtaining (20), by the second electronic device, a second time series Hp(t) representative of the evolution, over time, of the same metric as that measured by the first electronic device, [said first time series and said second time series at least partially covering a common time period] a step of calculating (30) a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering at least one time difference At between these two time series; a step of synchronizing (40) the time-stamped data using the clock of the first electronic device as a function of said at least one time difference At.Accordingly, by implementing the present technique, it is possible to solve the problem encountered without using radio resources, without requiring the use of a cable between the first electronic device and the second mobile mapping device.

[0054] Synchronization can take place in “post-processing”, that is to say after the capture of the events themselves. More particularly, in an exemplary embodiment, the first electronic device is a mobile mapping device which is equipped with a prism (visual tracking device) which allows the total station (second electronic device) to follow it (in tracking mode) in its movements.

[0055] More specifically, the prism is used by the total station (which is the second electronic device) to track the movements of the mobile mapping device, it being understood that during these movements, the total station is, for its part, fixed and its position is known. Depending on the technologies implemented by the total station, it is for example equipped with an autonomous location device (GPS type) or this location can be entered manually when initializing the total station (the total station is positioned successively in relation to known absolute coordinates, or by creating its own reference frame; the successive “station setups” include phases of pointing towards known points to deduce each position of the station; all of these station positions constitute a path).

[0056] The mobile mapping device records all the necessary data during the mapping phase while being tracked, via the prism, by the total station. For its part, during the mapping phase, the total station also records all the parameters and values ​​that fall to it, while tracking, via the prism which is positioned at its top, the mobile mapping device. When the mapping phase is finished, the data obtained by the mobile mapping device are processed. This processing, according to the invention, comprises a phase of synchronizing the clock of the mobile mapping device with that of the total station. To do this, the data obtained by the total station are extracted.In the exemplary embodiment, the undulations of the vertical axis of the two devices (total station and mobile mapping device) are extracted, the phase shift is calculated and the clock drift over time is determined. Finally, at least some of the data from the mobile mapping device are time-stamped so that they are consistent with the data from the total station (in particular, for example, with the aim of having the precise locations of the mobile mapping device when processing these measurements, these locations being able to be deduced from the initial position of the total station and the measurements of the total station relative to the prism of the mobile mapping device, and therefore from the measurements of angles and distances relative to the prism of the mobile mapping device).In this "post-processing" embodiment, therefore, no real-time connection is necessary and no communication delay related to range (relative distance between systems) or communication latency is to be feared.

[0057] In another embodiment, the implementation of the described method can also be carried out at least partly in real time. More specifically, rather than seeking to obtain position values ​​in real time, as envisaged in the prior art, via a cable or a radio link, the described technique can comprise the transmission, not of the positions, but of all or part of the time series so as to allow the mobile mapping device to carry out a correction of the timestamp of its measurements as and when this time series is received from the total station: using the time series, the mobile mapping device (which is equipped with the necessary computing hardware resources) can therefore correct in real time the timestamps of the data that it captures. It is therefore not necessary, subsequently, to carry out a time resetting of this data.

[0058] In other examples of implementation, the technique can also be applied, for example, to electronic devices that are both in motion, and that are able to capture or measure one or more different events occurring during their respective movements. This may, for example, be drones or other motorized devices (such as autonomous or semi-autonomous vehicles). According to the present technique, at least one of these two devices is equipped with a visual tracking device (this may be a prism, as for the total station, or an LED of sufficient power and visible from the second electronic device). It may also be any type of means visually identifiable by the second electronic device. In an example of implementation, the two electronic devices are each equipped with a visual tracking device for the attention of the other.And each electronic device follows the movements of the visual tracking device of the other electronic device. In the case of two drones for example, the events that occur during the aerial evolution of the two drones and which stagger the measurements made by one or the other of the two drones can be used, according to the method described herein, to synchronize the clocks of the two drones evolving separately and therefore to synchronize their respective positions, for example with the aim of adding additional precision to these respective positions. These events can for example be variations in altitude, or a quantity of light captured by an appropriate capture module present on the devices, etc.

[0059] In other exemplary embodiments, depending on the configuration of the first electronic device (and the nature of this electronic device), the prism is not necessarily positioned at the height of the first electronic device (for example the mobile mapping device). It may for example be located in the lower part (for example, the case of a drone tracked by a total station).

[0060] 5.2. Description of an embodiment

[0061] In this embodiment, the data from both instruments are recorded in the field and the synchronization chain takes place in post-processing. In this embodiment, the method implemented is as follows: First, the method includes a step of reading the files, each data is dated (timestamp) via the internal clock of the instrument concerned (total station or mobile mapping device); then

[0062] A determination is made of the evolution of the relative height of the mobile mapping device with respect to the ground: for this, in this embodiment, the oblique LiDAR data (of the mobile mapping device) are oriented in the absolute reference frame via the inertial unit (of the mobile mapping device) and the lowest point on the vertical axis of the LiDAR is determined: this makes it possible to obtain the vertical component of the mobile device over time (time series Hs(t));

[0063] In parallel or subsequently, a calculation of the vertical component of the prism measured by the total station is carried out: this makes it possible to obtain the evolution of the vertical component of the prism (measured from the total station) over time (time series Hp(t));

[0064] Once these time series are provided, a calculation of the local extrema is carried out for each of them and a selection of these extrema is made: only the local extrema having an amplitude greater than a predetermined threshold are kept; two sets of extrema are thus obtained {Es} and {Ep}, corresponding respectively to the extrema of the series Hs(t) and those of the series Hp(t). In these two sets {Es} and {Ep}, each extremum is represented by the coordinates (H; t) in the time base specific to each instrument;

[0065] From these two sets, a (robust) extremum matching between the data of these two sets is carried out (for example from a RANSAC algorithm or from an M-Estimation type minimization algorithm) to determine the inliers and the outliers; the outliers (bad extremums) are eliminated;

[0066] Then, finally, we perform a calculation of the affine distribution by least squares: the cost function is defined as:

[0067] We thus determine the time offset A as well as the possible clock drift a by minimizing the cost function. The algorithmic chain makes it possible to exclude the amplitude of the signals. The robust matching eliminates the potential measurement noise of each instrument. In this cost distribution function:

[0068] T represents the time values ​​of the paired couples after RANSAC (only the time component of the extrema {Es} and {Ep});

[0069] “i” represents an element of the set, between 1 and N, considering that each set {Es} and {Ep} each has N elements.

[0070] Depending on the algorithm used to perform the matching, of course, the cost function will be different. 5.3. Other features and benefits

[0071] In relation to Figure 5, a simplified architecture of a mobile mapping device (TProf) capable of carrying out all or part of the processing as presented previously is presented. A mobile mapping device comprises a first electronic module comprising a memory 51, a processing unit 52 equipped for example with a microprocessor, and controlled by a computer program 53.The mobile mapping device optionally comprises, for security features (for example to prevent theft of hardware or compromise of stored data), such as the generation of cryptographic materials, a second electronic module comprising a secure memory 54, which can be merged with the memory 51 (as indicated by dotted lines, in this case the memory 51 is a secure memory), a secure processing unit 55 equipped for example with a secure microprocessor and physical protection measures (physical protection around the chip, by lattice, vias, etc. and protection on the data transmission interfaces, possibly merged with the processing unit 52), and driven by a computer program 56 specifically dedicated to this secure processing unit 55, this computer program 56 implementing all or part of the processing method as previously described.The group consisting of the secure processing unit 55, the secure memory 54 and the dedicated computer program 56 constitutes the secure module (PS) of the mobile mapping device. In at least one embodiment, the present technique is implemented in the form of a set of programs installed in part or in full on this secure portion of the mobile mapping device. In at least one other embodiment, the present technique is implemented in the form of a dedicated component (CpX) capable of processing data from the processing units and installed in part or in full on the secure portion of the mobile mapping device. Furthermore, the device also comprises communication means (CIE) presented for example in the form of network components (WiFi, 3G / 4G / 5G, wired, RFID / NFC, Bluetooth, BLE, LPWan, VLC, etc.) which allow the device to receive data (I) from entities connected to one or more communication networks and transmit processed data (T) to such entities.

[0072] Such a device comprises, depending on the embodiments: means for obtaining a first time series Hs(t) representative of the evolution, over time, of a metric measured by a first electronic device; means for obtaining (20) a second time series Hp(t) representative of the evolution, over time, of the same metric as that measured by the first electronic device, [said first time series and said second time series at least partially covering a common time period]; means for calculating (30) a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time difference At between these two time series; means for synchronizing (40) the time-stamped data using the clock of the first electronic device as a function of the time difference At.

[0073] According to another aspect, the invention also relates to a system, in which two electronic devices (for example a mobile mapping device and a total station) are used together to carry out an independent measurement of a quantity (or metric or parameter [Al]) evolving over time for the first electronic device and the second electronic device in order to form two time series which are used, according to the methods and means described above to synchronize the clock of the first electronic device with the clock of the second electronic device (or vice versa) in order to be able to precisely determine (or refine the determination) of a position of the first electronic device (or the second) over time.

Claims

CLAIMS Method for synchronizing time-stamped data (DHrs1) using a clock of a first electronic device with time-stamped data (DHrs2) using a clock of a second electronic device, method characterized in that it comprises: at least one step of obtaining (10), by the first electronic device, a first time series Hs(t) representative of the evolution, in time, of a metric representative of the height of the first electronic device, measured by the first electronic device;at least one step of obtaining (20), by the second electronic device, a second time series Hp(t) representative of the evolution, in time, of the same metric as that measured by the first electronic device, [said first time series and said second time series covering at least partially a common time period] a step of calculating (30) a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time gap At between these two time series;a synchronization step (40) of the time-stamped data (DHrsl) using the clock of the first electronic device as a function of the time difference At, producing synchronized time-stamped data (U.DHrsl). Synchronization method according to claim 1, characterized in that the step of obtaining (10), by the first electronic device, the first time series Hs(t), comprises determining the evolution of the relative height of the first electronic device with respect to the ground, delivering the first time series Hs(t). Synchronization method according to claim 1, characterized in that the step of obtaining (20), by the second electronic device, a second time series Hp(t) comprises determining the evolution of the relative height of a visual tracking device of the first electronic device with respect to the ground, delivering the second time series Hp(t). A synchronization method according to claim 1, characterized in that the calculation step (30) of the phase shift between the first time series Hs(t) and the second time series Hp(t) comprises: a calculation step, for the first time series Hs(t) and the second time series Hp(t), of two sets of local extrema {Es} and {Ep}, corresponding respectively to the extrema of the series Hs(t) and those of the series Hp(t); a step of performing extremum matching between the data of these two sets of local extrema {Es} and {Ep}, yielding two sets of local extrema {Es} and {Ep} purged of uncorrelatable extrema; and a step of calculating a least-squares affine distribution, using the cost function such that: A synchronization method according to claim 1, characterized in that the first electronic device is a mobile mapping device of the type comprising a prism at one of its vertices, the prism acting as a visual tracking device, and in that the second electronic device is a total station. A method for synchronizing time-stamped data using a clock of a mobile mapping device with time-stamped data using a clock of a total station, characterized in that it consists of determining a correlation between a change in the height of the mobile mapping device, as measured by the mobile mapping device itself, and a change in the height of the mobile mapping device as measured by the total station, such that, once correlated, these two changes in height produce a time offset between the two clocks.Synchronization device for time-stamped data using a clock of a first electronic device with time-stamped data using a clock of a second electronic device, device characterized in that it comprises: means for obtaining (10), by the first electronic device, a first time series Hs(t) representative of the evolution, over time, of a representative metric. of the height of the first electronic device, measured by the first electronic device; means of obtaining (20), by the second electronic device, a second time series Hp(t) representative of the evolution, in time, of the same metric as that measured by the first electronic device, [said first time series and said second time series covering at least partially a common time period] means of calculating (30) a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time difference At between these two time series;means for synchronizing (40) time-stamped data using the clock of the first electronic device as a function of the time difference At. Product: computer program comprising program code instructions for implementing a synchronization method according to claim 1, when executed by a processor. Mapping system implementing synchronization of a clock of a mobile mapping device with a clock of a total station, said system being characterized in that it comprises: said mobile mapping device, generating a first time series Hs(t), representative of the evolution of the altitude of said mobile mapping device as a function of time; said total station, generating a second time series Hp(t) representative of the evolution of the altitude of said mobile mapping device as a function of time;[said first time series and said second time series covering at least partially a common time period] means for calculating (30) a phase shift between the first time series Hs(t) and the second time series Hp(t) delivering a time gap At between these two time series; means for synchronizing (40) the time-stamped data of the mobile mapping device with the time-stamped data of the total station, as a function of the time gap At.;

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