NL2016351B1 - System and method for event reconstruction from image data - Google Patents

Abstract

System for event reconstruction from image data comprising: - a plurality of mobile data recorders (1) each of them at least comprising a time recording device (2), an image recording device (3), a position recording device (4), and a memory (5) to store recorded data; - a data analysis unit (6) comprising - a data retrieval device (7) connectable to said mobile data recorder (1) and arranged to retrieve at least part of said data recorded by said mobile data recorder, - a memory (8) arranged to store retrieved data, and - a processing unit (9) arranged to synchronize said retrieved data from the plurality of data recorders (1); - a display unit (10) to display said retrieved data.

Description

Title: System and method for event reconstruction from image data

The invention relates to a system for event reconstruction from image data comprising: - a plurality of mobile data recorders each of them at least comprising a time recording device, an image recording device, a position recording device, and a memory to store said recorded data; - a data analysis unit comprising - a data retrieval device connectable to said mobile data recorder and arranged to retrieve at least part of said data recorded by said mobile data recorder, - a memory arranged to store said retrieved data, and - a processing unit arranged to synchronize said retrieved data from the plurality of data recorders; - a display unit to display said retrieved data. US 2015/0200984 discloses a system for sharing network multimedia data in real time and in a wireless manner for the purpose of extending vision. The system comprises a plurality of devices including a camera, comprising a host device and a plurality of devices surrounding the host device, which can share images of each other over a wireless ad-hoc network in real time so as to complete the viewing angle of the host device, for example in case of an accident in which the host device is involved.

These shared data can be transmitted to an external server to be used for example by a police station, insurance company or hospital. US 2011/0161005 discloses a tracking system and a method to track media content from a personal communications device associated with a physical location of this device. The location information comprises global positioning system coordinates from a GPS device coupled to the personal communications device. Media content can comprise pictures or videos generated by a camera coupled to the personal communications device, or voice recording generated by a microphone coupled to the personal communications device. A geographical map can be provided showing a visual indication on the map corresponding to the location information of the personal communications device, in conjunction with the media content. WO 2010/100538 describes a method for synchronization of content from multiple content sources. Time data associated with an event may be provided in varying time bases depending on the network from which time information is determined. All content capturing the same event may be synchronized and aligned by adjusting the various timing information to a common time base, for example using very fine time bases or using a time almanac. The content may further be assembled into a content item that provides multiple perspectives of the same event.

One of the major problems with these prior art systems, in case these systems are used for event reconstruction, for example by police officers or insurance companies, is a “big data” problem: if all data recorded by a plurality of data recorders have to be stored, a large storage capacity is needed, which costs a lot of money, although only a fraction of these data will be exploited for event reconstruction. In order to avoid large storage capacity, the recorded data can also be transmitted to a central data analysis unit, where the recorded and transmitted data, for example through real time streaming, are permanently surveyed / viewed by a person, for example by a dedicated police officer, who can store only relevant data. However, this is also a time-consuming, money-wasting, and inefficient way of proceeding.

It is an aim of the present invention to solve or alleviate one or more of the above-mentioned problems. Particularly, the invention aims at providing a relatively cost-efficient system for event reconstruction from image data (e.g. multimedia data). The invention also aims at providing a time-efficient system for event reconstruction, avoiding a continuous monitoring of recorded data.

To this aim, according to a first aspect of the present invention, there is provided a system characterized by the features of claim 1.

By indicating a position recorded by said position recording device of a number (e.g. a plurality of each) of said plurality of data recorders on a geographical map on said display unit using a visual indicator, a user can then select, for example by ‘clicking’ or tapping on a visual indicator (using a suitable user interface) or e.g. via a keyboard, these data recorders for which the user wishes to allow a synchronized display of the data recorded by the mobile data recorders positioned at the positions corresponding to said at least two selected visual indicators. The selection of data recorders to be displayed can for example depend on the localization of an event to be reconstructed. As only a selection of recorded data is retrieved and displayed, a cost-efficient and time-efficient and very user friendly system is obtained, whereas a relatively small data storage capacity can be used and long human surveying hours of recorded data can be avoided.

The selecting of a said visual indicator can be achieved in various ways as will be clear to the skilled person. For example, the system can include a user interface (e.g. a keyboard, touch pad, mouse, voice control joystick, and/or other type of user controllable interface) for controlling the display and/or a data analysis unit to make the selection.

The data analysis unit can also be configured in various ways as will be appreciated by the skilled person. It can be or include one or more data processors, computers, a controller or microcontroller, hardware and/or software or similar devices or systems. The data analysis unit can be configured to drive the display unit, that is, to cooperate with the display unit or to send a signal or information to the display unit in order to indicate the plurality of data recorders indicated on the geographical map on said display unit using the visual indicator . The a data analysis unit can be configured to cooperate with one or more user interfaces for achieving the selecting of said visual indicators, allowing synchronized display of respective data recorded (and synchronized playback of recorded sound of at least one of those data recorders if available and e.g. selected).

Also, the system (e.g. the display unit and data analysis unit) can be configured such, that retrieved and synchronized image data is displayed with or without image correction, the image correction including but not being limited to one or more of: image improvement, image scaling, image rendering, color correction and video codec modification.

For example, the image recording device of said data recorder can be configured to record images or video of a local scene (near/in front of the respective data recorder), for example in a suitable imaging or video codec as will be clear to the skilled person.

In addition, the data recorder can be configured to record audio as well, preferably via at least one microphone integrated in the respective portable, data recorder. In case the data recorders record audio/sound, the system can be configured such (e.g. a said user interface, a data analysis unit and display unit) that a user can select at least audio data of one of the sound recorders to be played during playback of images (e.g. via a respective sound generator, loudspeaker, headphone and/or the-like).

Each data recorder as such is mobile/portable, meaning that it can be carried with ease by a single person. Each data recorder is preferably very compact (e.g. with a maximum dimension of 10 cm) and has a relatively low mass, e.g. less than 1 kg and preferably less than 0.5 kg, or more preferably less than 250 gram, for example less than 150 gram. Each data recorder is preferably configured to be removably worn by a user, e.g. to be attached or coupled to or worn by a user’s arm, neck, shoulder, clothing, jacket, hat, helmet or the-like.

Besides, each data recorder is preferably configured to function entirely autonomously, that is: it can record and store data itself, locally. After a recording session, the locally stored data can be uploaded to a said

In a preferred embodiment, said data analysis unit can be configured to retrieve data from at least one data recorder only for a predetermined time range. By selecting a time range before data retrieval, the recorded data to be retrieved and displayed can be further reduced and become more focalized on an event to be reconstructed, which happened not only at a given location, but also in a certain time range. This makes the system still more cost- and time efficient.

In a more preferred embodiment, said display unit comprises an operable timeline indicator arranged to allow a user to select a time, for example within a predetermined time range, for which data from the plurality of data recorders are displayed simultaneously and in a synchronized manner. The operable timeline indicator allows a user to wander back and forth in the retrieved data, according to what is of interest to said user, while all data remain being displayed simultaneously and in a synchronized manner, without having to view all data chronologically, thus saving time.

It is advantageous if said position recording device is a Global Navigation Satellite System device, for example a GPS device, as this provides a very precise position recording device including precise time reference. Alternatively, it can also be a device functioning on the Galileo, Glonass or BeiDou system.

It is still more advantageous when said data analysis unit is configured to synchronize data retrieved from at least two data recorders using GNSS timestamps recorded by the position recording device, particularly in combination with the individual recorder time data recorded by the respective time recording devices of the data recorders.

The GNSS timestamps provide a well sampled and precise timeline common to all data retrieved from different data recorders, with possibly deviating time recordings, to which these data can be synchronized. Thus, an accurate image data synchronization can be achieved in an efficient manner.

Preferably, said data recorder can further comprise an audio recording device, which adds extra useful audio information for event reconstruction. At the same time, audio data can also be used for synchronization purposes. For example, according to a further embodiment, data streams of at least two data recorders can be synchronized based on their respective recorded audio contents.

In a further exemplary embodiment, the system can comprise audio reproduction means arranged to render recorded audio data from at least one data recorders.

Advantageously, the system can comprise audio reproduction means arranged to render simultaneously and in a synchronized way recorded audio data from at least two data recorders, for example mixed audio data. This feature allows an objective event reconstruction, in which the focus is on the event, instead of being on a single viewpoint provided by a data recorder.

In a preferred embodiment, a resolution and/or recording rate of a recording device, for example an image recording device and/or an audio recording device, of said mobile data recorder is adjustable, for example between a low resolution recording mode and a high resolution recording mode (the low resolution being lower than the high resolution) and/or adjustable between a low recording rate and a high recording rate (the low recording rate being lower than the high recording rate).

In this way, a user equipped with a mobile data recorder can switch for example to a high resolution mode (e.g. in case the recorder is already recording in the low resolution mode, or in case the recorder is e.g. in a standby-mode) when he deems it necessary, for example when the user is a witness of an incident or an accident. Before or during recording, the user can e.g. switch to the low resolution recording mode, allowing longer recording, when nothing special happens around him. Naturally, the recorder can be configured to record in more than two different resolutions, particularly more than two different image/video resolutions.

Regarding the recording of video, instead of, or in combination with, an adjustable resolution, a video recording frame rate may be adjustable, for example from a low frame rate, in which for example a low number (e.g. about 3) images per second are recorded, to a high frame rate, in which for example a high number (e.g more than 10, such as about 20 or more) images per second are recorded.

Similarly, regarding the recording of audio, an audio recording bit or sample rate may be adjustable between at least a low and high bit rate.

Preferably, said mobile data recorder can further comprise a direction recording device arranged to indicate in which direction said data recorder is pointed. The direction in which a data recorder is pointing may in some cases, especially in confusing situations, be difficult to derive from, for example, visual information. Indications from a direction recording device may then be very helpful to speed up and clarify an event reconstruction. A said direction to be recorded can for example be a cardinal (compass) or cardinal related direction.

It is more preferred that said data recorder further comprises a force recording device arranged to measure forces to which said data recorder is submitted, for example G-forces. G-force measurements may be of interest in case a user of a mobile data recorder gets physically involved in for example a car accident, or a riot, and provides extra information which can help to reconstruct the event.

Still more preferably, said data recorder can further comprise a gyroscope arranged to indicate an orientation of said data recorder. Also a gyroscope can provide extra three-dimensional information which can help in an event reconstruction, especially when a user of a mobile data recorder has become involved in a confusing situation.

In an advantageous embodiment, said data recorder may comprise a streaming mode, in which recorded data is transmittable wirelessly and in real time to said data analysis unit. In case a user of a mobile data recorder witnesses an exceptional situation, for example implying danger, he may have the possibility to immediately transmit recorded data so that a surveying person can react adequately based on real-time information. The streaming mode can for example be activated via an alarm button on the mobile data recorder, and may for example be coupled to an adjusting of the recording settings, for example to a high resolution and/.or a high video recording frame rate.

It is preferred that said data recorder comprises data compressing means, for example image compressing means, which enhances storage capacity of the mobile data recorder’s memory, and reduces the time needed for data retrieval to the data analysis unit.

It is also preferred that said data recorder comprises encrypting means arranged to encrypt recorded data for encrypted storage on the data recorder memory, thus protecting the system against unwanted use or even reading of the recorded data, for example in case of theft of a data recorder.

Another aspect of the invention provides a method for event reconstruction from image data according to claim 15, leading to one or more of the above-mentioned advantages.

Further advantageous embodiments are described by the dependent claims.

The present invention will be further elucidated with reference to figures of exemplary embodiments. Therein, corresponding elements are designated with corresponding reference signs.

Figures la, lb, lc and Id show a front, back and side view and schematic drawing of a non-limiting embodiment of a mobile data recorder of a system according to the invention;

Figure 2 shows a schematic view of a system according to an example of the invention;

Figure 3 shows an embodiment of a display unit of a system according to the invention, during operation;

Figure 4 shows a flow chart of a synchronization method which is executable by a data analysis unit of a system according an embodiment to the invention.

Figure 1 shows a front, back, side and schematic view of a preferred embodiment of a mobile data recorder of a system according to the invention. The data recorder 1 comprises at least a time recording device 2, an image recording device 3, a position recording device 4, and a memory 5 to store recorded data. The time recording device 2 may for example be an internal clock, or, alternatively, may be a timer relative to the image recording device 3. The image recording device 3, for example a digital camera known per se, is preferably directed to an area in front of the data recorder 1, so that the data recorder 1, which can for example be worn on the shoulder or the breast by, for example, a policeman, records data with a similar field of view as the field of view of a person wearing the data recorder 1. The data recorder can for example be clipped on a jacket or a helmet, or fastened otherwise, for example attached to an existing strap on (protective) clothing.

The data recorder 1 preferably include an electric power source for powering its components. The data recorder 1 preferably comprises a rechargeable battery, for example a battery allowing continuous recording of at least for example 10 to 12 hours, implying that a user need not recharge the data recorder during a normal working day. The recorder may be configured such that the rechargeable battery may be recharged for example via a usb-entry on the data recorder, or via any other conventional battery recharging device.

The data recorder 1 may include its own user interface for controlling the device. For example, the data recorder may comprise an on/off button to start a recording of data, but more preferably, it is configured to automatically start recording once it is disconnected from a recharging device, so that a user does not have to operate the data recorder.

The mobile data recorder 1 preferably comprises a housing which is dust- and water-resistant. The housing may for example comply at least with the International Protection Rating or Ingress Protection IP66 according to the standard IEC 60529, in which 6 stands for dust-tight and/or protected against powerful water jets.

The data recorder 1 preferably comprises data compressing means 19, for example image compressing means, for example video codec means according to a H.264 standard, or according to any other codec standard. To secure the storage of recorded data in the data recorder’s memory 5, the data recorder 1 may include tamper proof measures, comprising encrypting means 20 arranged to encrypt recorded data for encrypted storage on the data recorder memory 5.

The position recording device 4 of the data recorder can be configured in various ways. For example, it may use a mobile phone network or any other local area network to find a position of the data recorder 1 and store it in the data recorder’s memory 5. This is preferably done at regular intervals, for example every 5 seconds, or more or less often. It is however more advantageous to use a Global Navigation Satellite System device, for example a GPS device, as a position recording device 4. Alternatively, or in the future, also the Galileo, Glonass or BeiDou network may be used for position recording.

In a preferred embodiment the data recorder may further comprise an audio recording device 14, a direction recording device 16, for example a compass, arranged to indicate in which direction said data recorder 1 is pointed, a gyroscope 18 arranged to indicate an orientation of said data recorder 1, and/or a G-force recording device 17 arranged to measure G-forces to which said data recorder 1 is submitted. These recording devices are preferably recording data continuously.

In a preferred embodiment, as in Figures la-ld, the data recorder may further comprise a panic mode initiating device, e.g. a panic button 21. In emergency cases, for example when the user of the data recorder witnesses a serious incident, he may push the panic button, so that the data recorder enters a panic mode of operation, causing for example an adjustment of a recording frame rate and/or sample rate and/or resolution of at least one recording device, for example an image recording device 3 and/or an audio recording device 14, of said mobile data recorder 1, for example from a low frame rate and/or resolution mode to a high frame rate and/or resolution mode. The pushing of the panic button 21 may also start a streaming mode, in which recorded data is transmittable wirelessly and in real time to a data analysis unit 6.

Figure 2 shows a schematic view of a system according to an example of the invention. The system comprises a plurality of mobile data recorders 1, for example a data recorder as illustrated in Figure 1, each of them at least comprising a time recording device 2, an image recording device 3, a position recording device 4, and a memory 5 to store recorded data. In practice the system may include a relatively large number of recorders 1, for example more than 10, or for example at least 100.

In this example, the plurality of data recorders are not configured to communicate with each other. Each data recorder can be worn by a user, for example a policeman, or any other person with a surveying or helping task. The system further comprises a remote central data analysis unit 6 including a data retrieval device 7 connectable to said mobile data recorder 1 and arranged to retrieve at least part of said data recorded by said mobile data recorder.

The system further comprises a (at least one) display unit 10 (e.g. a monitor, display screen or the-like) to display said retrieved data (see also Figure 3). The data retrieval unit 7 may be or include a usb cable and respective data transmission/communication means or any other wired or wireless retrieval system. In case a usb cable is used, a usb entry on the mobile data recorder may have a double function, for battery recharging and data retrieval.

The data analysis unit 6 also comprises a memory 8 arranged to store retrieved data, and a processing unit 9 arranged to synchronize said retrieved data from the plurality of data recorders 1.

Synchronization of image data may be performed using various methods, for example using overlapping audio recordings or based on a common timeline, as will be explained in more detail under Figure 4. It is advantageous when the data analysis unit 6 is configured to retrieve data from at least one data recorder 1 only for a predetermined time range, for example for the time range in which an event to be reconstructed took place, which is in general more limited than the 10 to 12 hours recording of a mobile recording device. The synchronization and display can thus be focused on the data recorded during the time range of interest.

During use of the system, for example by a team of policemen or security personnel surveying a big event, for example a football match, concert, demonstration or large gathering in the streets , each individual user, for example each policeman of a unit, can be equipped with a mobile data recorder 1, which preferably records data during an entire duty cycle (or most of it) of the user without intervention of the user. These recorded data include at least time (i.e. device time, as provided by the internal diming device 1), image (recorded by the image recorder 3) and position recordings (recorded by the position recorder 4), and are preferably complemented with one or more of: audio (recorded by audio recorder 14), direction (recorded by direction recorder 16) and orientation data (provided by gyroscope 18) and G-force measurements (from the respective sensor 20. These recorded data are stored in a memory 5 of each data recorder 1, preferably in an encrypted and compressed way (therein, preferably, at least the image data is compressed since uncompressed image data may consume relatively large amounts of storage).

After duty or at a desired time, the recorded data of a plurality of the mobile data recorders (e.g. all) can be centrally collected processed. To that aim, for example, the mobile data recorders 1 can be connected e.g. one after the other via a data retrieval device 7 to a data analysis unit 6, so that at least part of said recorded data from said plurality of mobile data recorders 1 can be retrieved. The said retrieved data can be stored in a memory 8 of the data analysis unit 6, for further processing, particularly time synchronization.

Regarding image data synchronization, preferably, a time range is (pre)determined for which recorded data are retrieved from said plurality of mobile data recorders 1, for example an estimated time range of an event irregularity to be reconstructed (for example a riot or an accident, which has been recorded, partially or entirely, by multiple data recorders, each having their own point of view). Retrieved data can then be synchronized by the processing unit 9, for example using overlapping audio recordings. Preferably, the synchronization is carried out by the data analysis unit based on a common timeline, as will be explained in more detail under Figure 4.

In a next step (i.e. after synchronization), a position recorded by a position recording device 4 of each of said plurality of data recorders 1 can be indicated on a geographical map 11 on a display unit 10 using a visual indicator 12. This is indicated in Figure 3, showing a geographical map 11 that is displayed on the display unit 10, wherein the positions of three of the data recorders 1 (recorded by their respective position recording devices 4) are indicated by three respective visual indicators 12. Preferably, at least two of said visual indicators can now be selected using a suitable user interface (not shown), for example based on their proximity to an event to be reconstructed. The selecting of the visual indicators 12 leads to a synchronized display of the data recorded by the respective mobile data recorders 1 positioned at the positions corresponding to said at least two selected visual indicators 12. It should be observed that the displaying of the data, images (video) and indicators on the display unit 10 can be achieved in various ways, particularly under the control of or via display signal generation by the data analysis unit 6 (e.g. a computer or the-like) as will be clear to the skilled person.

In the advantageous embodiments of Figures 2 and 3, the display unit 10 can comprise an operable timeline indicator 13 arranged to allow a user to select a time, for example within a predetermined time range, for example the predetermined time range for which data have been retrieved, for which data from the plurality of data recorders 1 are displayed simultaneously and in a synchronized manner. Preferably, the system can be handled/operated such that a system operator can wander back and forth in time using the operable timeline indicator 13, including e.g. buttons 23, so that he can skip uninteresting sequences, and/or watch again important sequences, while always keeping a synchronized display of all retrieved data from the plurality of data recorders. For example, the positions recorded by the position recording devices 4 and displayed on the digitally created geographical map by respective visual indicators 12, can be moving on the map (in case of actual movement of the respective recording devices) while operating the timeline indicator 13 (unless the corresponding data recorder did not move). A direction recorded by a direction recording device 16 arranged to indicate in which direction said data recorder 1 is pointed, can for example be indicated by a respective direction indicator 22 on the display, e.g. a short line 22 attached to the visual indicator 13, or in a different manner.

The system (e.g. its display unit 10) may also comprise audio reproduction means 15 arranged to render simultaneously and in a synchronized way recorded audio data from one or more data recorders 1, for example mixed audio data. All data retrieved from each of the, for example four in Figure 2, selected mobile data recorders are displayed simultaneously and in a synchronized way, for example visually (e.g. video data) and/or graphically (e.g. G-forces, audio), in a mixed (e.g. audio) and/or parallel (e.g. video, direction, orientation) way. Graphical display, for example 24, can include data from different data recorders for example displayed on a common/mixed graph using different colors or lines, or for example displayed on parallel separate graphs.

Figure 4 shows a flow chart of a synchronization method which is executable by a data analysis unit 6, particularly the processing unit 9 thereof, of a preferred system according to the invention. For each recording device, the data recording includes a local device time recording by a time recording device 2. In addition, in case the position recording device 4 is a Global Navigation Satellite System device, for example a GPS device, the data recording also includes GNSS timestamps recorded by each position recording device 4.

Time recorded by the time recording device 2 might be slightly off, or run at a slightly different speed, relative to a more precise time reference, for example provided by the GNSS timestamps. During recording or during subsequent data processing, an index file 25 can be created, in which for a given GNSS time, a corresponding time recorded by the time recording device 2 is listed at regular intervals, for example every 5 seconds or more or less. During analysis by the data analysis unit 6 and display on the display unit 10, the GNSS time is used as a common time base for all data retrieved from the plurality of mobile data recorders 1, for example the time displayed on the operable timeline indicator 13, or for example the time used to choose a predetermined time range for which recorded data should be retrieved from the plurality of data recorders. Therefore, according to an embodiment, for each mobile data recorder 1, the time recorded by the time recording device 2 corresponding to a given GNSS time can be calculated continuously during central display/playback by applying for example a regression analysis to the index file 25 created for a given mobile data recorder 1, starting from the indexed time position in such an index file which is closest to a chosen GNSS start time for display.

In an alternative embodiment, the data analysis unit 6 can be configured to synchronize image data, utilizing e.g. the above described indexing method, before it is displayed, and store the synchronized data centrally.

It should be clear to the person skilled in the art that the invention is not limited to the embodiments described above. Many alternatives are possible within the scope of protection as formulated in the claims hereafter.

The mobile data recorders can for example include various other types of data recorders, for example for recording meteorological data. The housing of the data recorders can for example be adapted for underwater use. The synchronization of data can for example be effected in many different alternative ways.

The term “device” is to be broadly construed, it can for example be or include any device, unit, means or structure that can carry out the described function of the device. Also, the functions of a plurality of devices may be incorporated, integrated or included in a single device, unit, processor or the-like as will be appreciated by the skilled person.

Transmission of data between e.g. individual data recorders and a central data processing/analysis unit can be achieved in various ways, for example using wired and/or wireless communication means, a computer network, Internet and/or differently, as will be clear to the skilled person.

Recording of time by a mobile data recorder 1 can be achieved in various ways. In a preferred embodiment, use is made of GNSS time stamps, as follows from the above. In that case, e.g., the time recording device 2 may be configured to record GNSS data packets that include GNSS-time, which data packets can be unpacked or processed by the mobile data recorder 1 itself to retrieve respective GNSS timestamps, or preferably by a data processing unit, e.g. (of) said data analysis unit 6.

Also, the mobile data recorder 1 may be configured to take various actions in case of activation of a said panic device (e.g. button), such as automatic adjustment of one or more recording parameters of its image recorder, activation of a light source (if available), automatic adjustment of one or more recording parameters of its audio recorder (if available), et cetera.

Claims (18)

An event reconstruction system from image data comprising: - a plurality of mobile data recording devices (1), each of which comprises at least one time recording device (2), an image recording device (3), a position recording device (4), and a memory (5) to store registered data; - a data analysis unit (6) comprising - a data retrieval device (7) connectable to said mobile data recording device (1) and adapted to retrieve at least a part of said data recorded by said mobile data recording device, - a memory (8) arranged to store retrieved data, and - a processing unit (9) adapted to synchronize said retrieved data from the plurality of data recording devices (1); - a display unit (10) connectable to the data analysis unit for displaying said retrieved data, characterized in that the system is configured such that during operation positions recorded by said position recording device (4) of at least a plurality of said plurality of data recording devices (1) are designated on a geographic map (11) on said display unit (10) using a visual indicator (12), at least two of said visual indicators (12) being selectable to allow a synchronized display of the data recorded by the mobile data recording devices (1) positioned at the positions corresponding to said at least two selected visual indicators (12). A system according to claim 1, wherein said data analysis unit (6) is arranged to retrieve data from at least one data recording device (1) only for a predetermined time range. A system according to any one of the preceding claims, wherein said display unit (10) comprises an operable timeline indicator (13) arranged to allow a user to select a time, for example within a predetermined time range, for which data of the plurality of data recording devices (1) are displayed simultaneously and synchronized. A system according to any one of the preceding claims, wherein said position recording device (4) is a Global Navigation Satellite System device, for example a GPS (Global Positioning System) device. The system of claim 4, wherein said data analysis unit (6) is adapted to synchronize data retrieved from at least two data recording devices using GNSS time stamps recorded by the position recording device (4), and in particular in combination with the time data recorded by the respective time recording devices (2). The system according to any one of the preceding claims, wherein said data recording device (1) further comprises a sound recording device (14). A system according to claim 6, wherein the system comprises sound reproduction means (15) adapted to display sound data from at least two data recording devices (1) recorded simultaneously and in a synchronized manner, for example mixed sound data. A system according to any one of the preceding claims, wherein a resolution of a recording device, for example an image recording device (3) and / or a sound recording device (14), of said mobile data recording device (1) is adjustable, for example between a low resolution mode and high resolution mode. A system according to any preceding claim, wherein said mobile data recording device (1) further comprises a direction recording device (16) adapted to indicate in which direction said data recording device (1) is directed. The system of any preceding claim, wherein said data recording device (1) further comprises a force recording device (17) adapted to measure forces to which said data recording device (1) is subjected. The system of any preceding claim, wherein said data recording device (1) further comprises a gyroscope (18) adapted to indicate an orientation of said data recording device (1). A system according to any one of the preceding claims, wherein said data recording device (1) comprises a streaming mode, wherein recorded data can be transmitted wirelessly and in real time to said data analysis unit (6). A system according to any one of the preceding claims, wherein said data recording apparatus (1) comprises data compression means (19), for example image compression means. A system according to any one of the preceding claims, wherein said data recording apparatus (1) comprises encryption means (20), arranged to encrypt recorded data for encrypted storage on the memory of the data recording apparatus (5). A method for event reconstruction from image data, for example using a system according to any one of the preceding claims, comprising the following steps of: - registering data by a plurality of mobile data recording devices (1), each of which has at least one time recording device ( 2), an image recording device (3), a position recording device (4), and a memory (5) for storing said recorded data; - retrieving at least a portion of said recorded data from said plurality of mobile data recording devices (i); - storing said retrieved data in a memory (8) of a data analysis unit (6); - synchronizing said retrieved data from the plurality of data recording devices (1); - indicating a position recorded by said position recording unit (4) of each of said plurality of data recording devices (1) on a geographical map (11) on a display unit (10) using a visual indicator (12) ); characterized in that the method further comprises the steps of - selecting at least two of said visual indicators (12), for example by using a user interface; - displaying on said display unit (10) in a synchronized manner the data recorded by the data recording apparatuses (1) positioned at the positions corresponding to said at least two selected visual indicators (12). The method of claim 15, comprising the step of predetermining a time range for which recorded data is retrieved from said plurality of mobile data recording devices (1). A method according to claim 15 or 16, comprising the step of selecting a time on an operable timeline indicator (13), for which data from said plurality of data recording devices (1) is displayed simultaneously and in a synchronized manner. A method according to any one of the preceding claims 15-17, wherein data retrieved from at least two data recording devices are synchronized using GNSS time stamps recorded by the position recording device (4).