Patent Publication Number: US-2022237408-A1

Title: Method of collecting data and computer-readable recording medium storing data collection program

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2021-10001, filed on Jan. 26, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a method of collecting data and a computer-readable recording medium storing a data collection program. 
     BACKGROUND 
     There have been a known technique by which vehicle data is collected from a plurality of vehicles and a known technique by which a waste of communication costs is suppressed when collecting sensing information obtained by sensors of target vehicles. 
     Examples of the related art include as follows: Japanese Laid-open Patent Publication No. 2019-040305. 
     SUMMARY 
     According to an aspect of the embodiments, there is provided a computer-implemented method of collecting data. In an example, the method includes: collecting pieces of metadata associated with pieces of image data from a plurality of moving objects that hold the pieces of image data; and determining, when a specific piece of metadata that satisfies a condition is found in the collected pieces of metadata, based on information for making collected numbers of the pieces of image data close to be an equalized value and a map that manages the collected numbers in a mesh shape, whether to request transmission of a specific piece of image data with which the specific piece of metadata is associated to a specific moving object from which the specific piece of metadata is collected. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  explains an outline of a collection server; 
         FIG. 2  is a block diagram illustrating an example of a hardware configuration of the collection server; 
         FIG. 3  is a block diagram illustrating an example of a functional configuration of the collection server according to a first embodiment; 
         FIG. 4A  is a block diagram illustrating an example of a hardware configuration of a vehicle, and  FIG. 4B  is a block diagram illustrating an example of a functional configuration of the vehicle; 
         FIG. 5  is a flowchart illustrating an example of processing executed by a metadata collection unit; 
         FIG. 6A  explains an operation example of the metadata collection unit, and  FIG. 6B  explains states before and after metadata stored in the metadata DB is stored; 
         FIG. 7  is a flowchart illustrating an example of processing executed by a collection determination unit according to the first embodiment; 
         FIG. 8A  explains part of an operation example of the collection determination unit,  FIG. 8B  illustrates an example of a collection request, and  FIG. 8C  explains metadata that satisfies the conditions; 
         FIG. 9  explains an example of a mesh size; 
         FIG. 10A  explains part of another operation example of the collection determination unit,  FIG. 10B  explains a state in which a collection ratio is obtained from a mesh ID via a management map stored in a management map DB,  FIG. 10C  illustrates an example of management information, and  FIG. 10D  illustrates an example of a data request; 
         FIG. 11  explains states before and after the management information stored in the data request management DB is stored; 
         FIG. 12A  is a flowchart illustrating an example of processing executed by a data request distribution unit, and  FIG. 12B  explains an operation example of the data request distribution unit; 
         FIG. 13  is a flowchart illustrating an example of processing executed by an image data storing unit; 
         FIG. 14A  explains an operation example of the image data storing unit, and  FIG. 14B  explains a state before and after updating of the management map stored in the management map DB; 
         FIG. 15  is a block diagram illustrating an example of a functional configuration of the collection server according to a second embodiment; 
         FIG. 16  is a flowchart illustrating an example of part of processing executed by the collection determination unit according to the second embodiment; 
         FIG. 17A  is another diagram explaining the state in which the collection ratio is obtained from the mesh ID via the management map stored in the management map DB,  FIG. 17B  explains an operation example of a data request adjustment unit, and  FIG. 17C  is another diagram illustrating an example of the data request; and 
         FIG. 18A  is a flowchart illustrating an example of processing executed by a data request storing unit, and  FIG. 18B  is a flowchart illustrating an example of processing executed by a data request transmission unit. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In some cases, image data from a camera mounted on a moving object such as a vehicle is collected from the moving object to create, for example, a map. In such cases, it is desired that the image data be entirely evenly collected. However, the image data is not necessarily entirely evenly collected. For example, there is a possibility that a piece of image data at a specific position is concentratedly collected and also a possibility that a piece of image data at a specific position is not collected at all. For example, there is a possibility that variation of the collection occurs in collecting the image data, and accordingly, the collected numbers of pieces of image data are not made to be an equalized value. 
     Accordingly, in one aspect, it is an object to provide a method of collecting data and a data collection program that makes collected numbers of pieces of image data close to an equalized value. 
     Hereinafter, embodiments of the present disclosure are described with reference to the drawings. 
     First Embodiment 
     First, an outline of a collection server  100  that executes a method of collecting data is described with reference to  FIG. 1 . The collection server  100  is coupled to base stations BS 1 , BS 2  via a communication network NW. The communication network NW includes, for example, at least one of a local area network (LAN) and the Internet. The LAN may be a wired LAN or a wireless LAN. The base stations BS 1 , BS 2  are coupled to a plurality of vehicles  300  via wireless communication. For example, wide-area wireless communication such as long term evolution (LTE) may be used for the wireless communication. Thus, the collection server  100  is coupled to the plurality of vehicles  300  via wired communication and wireless communication. Although the vehicles  300  are each indicated as an example of a moving object in  FIG. 1 , the moving object may be a mobile terminal such as a smart device (for example, a smartphone, a tablet terminal, or the like) instead of a vehicle  300 . 
     Each of the vehicles  300  periodically transmits metadata D 1  to the collection server  100 . The metadata D 1  is data for explaining image data D 2  of an image captured by a camera (not illustrated) installed in the vehicle  300 . The metadata D 1  is associated with the image data D 2 . The metadata D 1  includes a vehicle identifier (ID) for identifying the vehicle  300 , positional information of the vehicle  300 , the time when the image is obtained, controller area network (CAN) bus information, and so forth. The CAN bus information is information that flows through a bus of an onboard network called the CAN (CAN bus) and is, for example, detected by various sensors (for example, onboard sensors) such as an acceleration sensor and a vehicle speed sensor. The image may be a still image or a moving image in which still images continue in time series. A moving image may also be referred to as, for example, a video. 
     The collection server  100  collects and stores various pieces of the metadata D 1  periodically transmitted from each of the vehicles  300 . When a user  10  operates an input device  11  to input predetermined conditions, the collection server  100  determines whether there is a specific piece of metadata D 1  that satisfies the predetermined conditions among the various pieces of metadata D 1 . When the collection server  100  finds the specific piece of metadata D 1 , the collection server  100  identifies the vehicle  300  from which the identified piece of metadata D 1  is collected and makes a request, to the identified vehicle  300 , of transmission of a specific piece of image data D 2  associated with the specific piece of metadata D 1 . 
     Thus, the vehicle  300  identified by the collection server  100  transmits to the collection server  100  the piece of image data D 2  that the vehicle itself holds. When the piece of image data D 2  is transmitted from the vehicle  300 , the collection server  100  collects and stores the piece of image data D 2  transmitted from the vehicle  300 . The user  10  is able to check the image of the piece of image data D 2  via a display device  12  by operating the input device  11  to access the collection server  100 . 
     With reference to  FIG. 2 , a hardware configuration of the collection server  100  is described. 
     The collection server  100  includes, as a processor, a central processing unit (CPU)  100 A and, as memory, a random-access memory (RAM)  100 B and a read-only memory (ROM)  100 C. The collection server  100  also includes a network interface (I/F)  100 D and a hard disk drive (HDD)  100 E. A solid-state drive (SSD) may be used instead of the HDD  100 E. 
     The collection server  100  may include, as desired, at least one of an input I/F  100 F, an output I/F  100 G, an input and output I/F  100 H, and a drive device  100 I. The elements from the CPU  100 A to the drive device  100 I are coupled to each other via an internal bus  100 J. For example, the collection server  100  may be realized by a computer. 
     The input device  11  is coupled to the input I/F  100 F. Examples of the input device  11  include, for example, a keyboard, a mouse, a touch pad, and the like. The display device  12  is coupled to the output I/F  100 G. Examples of the display device  12  include, for example, a liquid crystal display and the like. A semiconductor memory  13  is coupled to the input and output I/F  100 H. Examples of the semiconductor memory  13  include, for example, a Universal Serial Bus (USB) memory, a flash memory, and the like. The input and output I/F  100 H reads a data collection program stored in the semiconductor memory  13 . The input I/F  100 F and the input and output I/F  100 H include, for example, a USB port. The output I/F  100 G includes, for example, a display port. 
     A portable recording medium  14  is inserted into the drive device  100 I. Examples of the portable recording medium  14  include, for example, a removable disc such as a compact disc (CD)-ROM and a Digital Versatile Disc (DVD). The drive device  100 I reads the data collection program recorded in the portable recording medium  14 . The network I/F  100 D includes, for example, a LAN port, a communication circuit, and the like. 
     The data collection program stored in at least one of the ROM  100 C, the HDD  100 E, and the semiconductor memory  13  is temporarily stored in the RAM  100 B by the CPU  100 A. The data collection program recorded in the portable recording medium  14  is temporarily stored in the RAM  100 B by the CPU  100 A. When the stored data collection program is executed by the CPU  100 A, the CPU  100 A realizes various types of functions to be described later and executes various types of processes to be described later. The data collection program may be configured to perform processing of a flowchart to be described later. 
     A functional configuration of the collection server  100  according to a first embodiment is described with reference to  FIG. 3 .  FIG. 3  illustrates main functional parts of the collection server  100 . 
     As illustrated in  FIG. 3 , the collection server  100  includes a storage unit  110 , a processing unit  120 , an input unit  130 , an output unit  140 , and a communication unit  150 . The storage unit  110  may be realized by, for example, the RAM  100 B or the HDD  100 E described above. The processing unit  120  may be realized by the CPU  100 A described above. The input unit  130  may be realized by the input I/F  100 F described above. The output unit  140  may be realized by the output I/F  100 G described above. The communication unit  150  may be realized by the network I/F  100 D described above. Accordingly, the storage unit  110 , the processing unit  120 , the input unit  130 , the output unit  140 , and the communication unit  150  are coupled to each other. 
     The storage unit  110  includes, as elements thereof, a metadata database (DB)  111 , a data request queue  112 , a data request management DB  113 , a management map DB  114 , and an image data DB  115 . At least one of the elements of the storage unit  110  may be distributed to and provided in another server (not illustrated) different from the collection server  100 . 
     The processing unit  120  includes, as elements thereof, a metadata collection unit  121 , a collection determination unit  122 , a data request distribution unit  123 , and an image data storing unit  124 . At least one of the elements of the processing unit  120  selectively accesses an element of the storage unit  110  to execute various types of processes. For example, the metadata collection unit  121  collects the metadata D 1  transmitted from the vehicle  300  via the communication unit  150  and stores the collected metadata D 1  in the metadata DB  111 . In this way, the metadata DB  111  stores the metadata D 1 . The other elements will be described in detail in the description of operations of the collection server  100 . 
     A hardware configuration and a functional configuration of the vehicle  300  is described with reference to  FIGS. 4A and 4B .  FIG. 4B  illustrates a main functional parts of the vehicle  300 . 
     As illustrated in  FIG. 4A , the vehicle  300  includes an electronic control unit (ECU)  300 A. The ECU  300 A includes, for example, a CPU, a RAM, a ROM, and an input and output interface. The vehicle  300  also includes a sensor  300 B and a global positioning system (GPS) receiver  300 C. The vehicle  300  also includes a camera  300 D and a data communication module (DCM)  300 E. An antenna  300 F is coupled to the DCM  300 E. The elements from the ECU  300 A to the DCM  300 E are coupled to each other via a CAN bus  300 G. The vehicle ID of the vehicle  300  is assigned to the ECU 300 A or the DCM 300 E. 
     As illustrated in  FIG. 4B , the vehicle  300  includes a control unit  310 , an information detection unit  320 , a position obtaining unit  330 , an imaging unit  340 , and an onboard communication unit  350 . The control unit  310  may be realized by the ECU  300 A described above. The information detection unit  320  may be realized by the sensor  300 B described above. The position obtaining unit  330  may be realized by the GPS receiver  300 C described above. The imaging unit  340  may be realized by the camera  300 D described above. The onboard communication unit  350  may be realized by the DCM  300 E and the antenna  300 F described above. Accordingly, the control unit  310 , the information detection unit  320 , the position obtaining unit  330 , the imaging unit  340 , and the onboard communication unit  350  are coupled to each other. 
     The information detection unit  320  detects various types of information such as the speed and the acceleration of the vehicle  300  and outputs the detected information as the CAN bus information to the CAN bus  300 G. The position obtaining unit  330  obtains positional information of the vehicle  300  based on GPS function. The positional information may be information on a running position of the vehicle  300  or information on a stop position of the vehicle  300 . The imaging unit  340  captures an image within the predetermined field angle range in front of the vehicle  300  and generates and holds the image data D 2  of the image within the predetermined field angle range. The onboard communication unit  350  receives a data request to be described later and transmits the metadata D 1  and the image data D 2 . 
     The control unit  310  controls operations of the entirety of the vehicle  300  including the information detection unit  320 , the position obtaining unit  330 , the imaging unit  340 , and the onboard communication unit  350 . For example, the control unit  310  obtains the image data D 2  generated and held by the imaging unit  340  and associates the image data D 2  with, for example, the vehicle ID, the positional information, the CAN bus information, and the time when the image data D 2  is obtained as the metadata D 1  and holds the image data D 2 . Instead of the time when the image data D 2  is obtained, the time when the imaging unit  340  captures the image may be used. The control unit  310  periodically transmits the metadata D 1  via the onboard communication unit  350 . Upon receiving the data request via the onboard communication unit  350 , the control unit  310  transmits the image data D 2  corresponding to the data request via the onboard communication unit  350 . 
     Next, the operations of the collection server  100  are described with reference to  FIGS. 5 to 14B . 
     First, operations of the metadata collection unit  121  are described with reference to  FIGS. 5, 6A, and 6B . As illustrated in  FIGS. 5 and 6A , when the metadata D 1  is transmitted from the vehicle  300 , the metadata collection unit  121  collects the metadata D 1  by receiving the metadata D 1  (step S 1 ). Upon receiving the metadata D 1 , the metadata collection unit  121  stores the metadata D 1  in the metadata DB  111  (step S 2 ). 
     Thus, for example, when a piece of metadata D 1  including the vehicle ID “#A”, a piece of metadata D 1  including the vehicle ID “#B”, and the like are stored in the metadata DB  111  as illustrated in the upper part of  FIG. 6B , in the case where a piece of metadata D 1  is transmitted from the vehicle  300  having the vehicle ID “#C”, the piece of metadata D 1  including the vehicle ID “#C” is added to and stored in the metadata DB  111  as illustrated in the lower part of  FIG. 6B . 
     Next, operations of the collection determination unit  122  according to the first embodiment are described with reference to  FIGS. 7 to 11 . First, as illustrated in  FIGS. 7 and 8A , the collection determination unit  122  receives a collection request D 3  input to the input device  11  by an operation of the user  10  (step S 11 ). Upon receiving the collection request D 3 , the collection determination unit  122  holds the collection request D 3  and waits. As illustrated in  FIG. 8B , the collection request D 3  includes extraction conditions and equalization conditions. 
     The extraction conditions are conditions related to the positional information and the CAN bus information when a specific piece of metadata D 1  is found and extracted from the various pieces of metadata D 1  stored in the metadata DB  111 . A piece of image data D 2  associated with the piece of metadata D 1  extracted according to the extraction conditions is to be collected by the collection server  100 . Accordingly, the extraction conditions may also be referred to as the collection conditions of the image data D 2 . 
     The equalization conditions include a mesh size and a collection upper limit. The mesh size is the level that defines the granularity of a mesh (grid). For example, as illustrated in  FIG. 9 , when a global map is divided into eight regions by latitude and longitude, the mesh size may be defined from a first-level mesh to a sixth-level mesh for each of the eight regions. The first-level mesh has a latitude interval of 40 minutes and a longitude interval of 1 degree. The second-level mesh is a mesh region defined by equally dividing the first-level mesh by eight in each of the latitude direction and the longitude direction. The second-level mesh has a latitude interval of 5 minutes and a longitude interval of 7 minutes and 30 seconds. 
     Although it is not illustrated, the third-level mesh is a mesh region defined by equally dividing the second-level mesh by ten in each of the latitude direction and the longitude direction. The third-level mesh has a latitude interval of 30 seconds and a longitude interval of 45 seconds. The fourth-level mesh is a mesh region defined by equally dividing the third-level mesh by two in each of the latitude direction and the longitude direction. The fourth-level mesh has a latitude interval of 15 seconds and a longitude interval of 22.5 seconds. Although description of the fifth-level mesh and the sixth-level mesh is omitted, these meshes may be viewed in a predetermined web page the uniform resource locator (URL) of which is https://www.fttsus.jp/worldgrids/ja/top-ja/. According to the present embodiment, a fourth-level mesh defined as follows is described as an example: the third-level mesh is equally divided by three in each of the latitude direction and the longitude direction to have nine mesh regions having a latitude interval of 10 seconds and a longitude interval of 15 seconds. The collection upper limit included in the equalization conditions represents an upper limit number when pieces of image data D 2  are collected. The collection determination unit  122  generates a management map in accordance with the mesh size, sets the collection upper limit of the pieces of image data D 2  for individual sections (hereafter, referred to as mesh regions), and stores the collection upper limit in the management map DB  114 . 
     As illustrated in  FIG. 7 , upon detecting collection of a piece of metadata D 1  (step S 12 ), the collection determination unit  122  checks the conditions (step S 13 ) and determines whether the conditions are satisfied (step S 14 ). In more detail, as illustrated in  FIG. 8A , the collection determination unit  122  monitors the metadata DB  111  and, when determining that a new piece of metadata D 1  is added to and stored in the metadata DB  111 , the collection determination unit  122  detects the collection of the piece of metadata D 1 . Thus, the collection determination unit  122  checks the extraction conditions of the collection request D 3  held by the collection determination unit  122  itself with the entirety or part of the piece of metadata D 1  to determine whether the conditions are satisfied. 
     When the collection determination unit  122  determines that the conditions are not satisfied (step S 14 : NO), the processing ends. In contrast, when the collection determination unit  122  determines that the conditions are satisfied (step S 14 : YES), the collection determination unit  122  calculates the mesh ID (step S 15 ). According to the present embodiment, as illustrated in  FIG. 8C , the metadata DB  111  stores the piece of metadata D 1  of the vehicle ID “#C” that satisfies the extraction conditions. Thus, the collection determination unit  122  determines that the conditions are satisfied. Accordingly, the collection determination unit  122  calculates the mesh ID. Although the details will be described later, the mesh ID is an identifier that identifies the mesh regions included in the management map. The mesh ID may be calculated by using the latitude, the longitude, and a predetermined function: mesh ID=f(longitude, latitude) for calculating the mesh ID from a combination of the latitude and the longitude. The details of the technique of calculating the mesh ID may be viewed in a predetermined web page the URL of which is https://www.fttsus.jp/worldgrids/ja/document-ja/. For example, according to the present embodiment, the collection determination unit  122  calculates the mesh ID “#5” from the positional information (Ing 1 , Int 1 ) designated by the extraction conditions of the collection request D 3 . 
     When the mesh ID is calculated, the collection determination unit  122  obtains a collection ratio (step S 16 ). As described above, when the mesh ID “#5” is calculated, as illustrated in  FIGS. 10A and 10B , the collection determination unit  122  refers to a management map MM of the fourth-level mesh which is stored in a management map DB  114  and for which the collection upper limit “3” is set, and the collection determination unit  122  obtains the collection ratio “2/3” corresponding to the mesh ID “#5”. The numerator of the collection ratio “2/3” represents a collected number up to this point in time (present collected number), and the denominator of the collection ratio “2/3” represents the collection upper limit designated by the equalization conditions. The collection upper limit corresponds to information for making the collected numbers close to be an equalized value. 
     After obtaining the collection ratio, the collection determination unit  122  next determines whether the collection ratio is less than the collection upper limit (step S 17 ). When the collection ratio is not less than the collection upper limit (step S 17 : NO), the collection determination unit  122  ends the processing. In contrast, when the collection ratio is less than the collection upper limit (step S 17 : YES), the collection determination unit  122  generates management information and a data request (step S 18 ). For example, the collection determination unit  122  issues a request ID to identify the data request, and as illustrated in  FIG. 10C , generates the management information including the issued request ID and the vehicle ID, the time, and the positional information of the extracted piece of metadata D 1 . As illustrated in  FIG. 10D , the collection determination unit  122  generates the data request including the issued request ID and the vehicle ID and the time of the extracted piece of metadata D 1 . As described above, the collection determination unit  122  determines whether to generate the data request to request transmission of a specific piece of image data D 2  associated with the extracted piece of metadata D 1  depending on whether the collected number is less than the collection upper limit. 
     When the collection determination unit  122  generates the data request and the management information, the collection determination unit  122  stores the management information and the data request (step S 19 ) and ends the processing. For example, as illustrated in  FIG. 10A , the collection determination unit  122  stores the management information in the data request management DB  113 . Thus, when the management information including the vehicle ID “#A” and the management information including the vehicle ID “#B” are stored in the data request management DB  113  as illustrated in the upper part of  FIG. 11 , the management information including the vehicle ID “#C” is added to and stored in the data-request management DB  113  as illustrated in the lower part of  FIG. 11 . The collection determination unit  122  stores the data request in the data request queue  112 . Thus, the data request waits in the data request queue  112  until the data request is obtained by the data request distribution unit  123 . 
     Next, operations of the data request distribution unit  123  are described with reference to  FIGS. 12A and 12B . First, as illustrated in  FIG. 12A , the data request distribution unit  123  receives an obtaining request (step S 21 ). For example, as illustrated in  FIG. 12B , the obtaining request transmitted from the vehicle  300  with the vehicle ID “#C” is received. The obtaining request includes the vehicle ID of “#C”. The data request distribution unit  123  receives obtaining requests transmitted from the vehicle  300  with the vehicle ID “#A” and the vehicle  300  with the vehicle ID “#B” other than the vehicle  300  with the vehicle ID “#C”. These obtaining requests also include the vehicle ID “#A” or the vehicle ID “#B” corresponding to the source vehicle  300 . 
     Upon receiving the obtaining request, the data request distribution unit  123  subsequently refers to the data request queue  112  (step S 22 ) and determines whether there is a data request (step S 23 ). In more detail, the data request distribution unit  123  refers to the data request queue  112  based on the vehicle ID “#C” included in the obtaining request and determines whether there is a data request including the vehicle ID “#C”. 
     When there is the data request (step S 23 : YES), the data request distribution unit  123  obtains and distributes the data request (step S 24 ) and ends the processing. According to the present embodiment, as described above, the data request queue  112  stores the data request for the vehicle ID “#C” (see  FIG. 10D ). Thus, the data request distribution unit  123  determines that there is the data request and distributes, as illustrated in  FIG. 12B , the data request to the vehicle  300  with the vehicle ID “#C” that is the transmission source of the obtaining request. When there is no data request (NO in step S 23 ), the data request distribution unit  123  distributes an empty response to the vehicle  300  with the vehicle ID “#C” that is the source of the obtaining request (step S 25 ) and ends the processing. 
     In the vehicle  300  with the vehicle ID “#C”, different processes are executed depending on whether the vehicle  300  receives the data request or the empty response. When the onboard communication unit  350  receives the data request, the control unit  310  identifies the piece of image data D 2  with which the time included in the data request is associated as the metadata D 1 . When the control unit  310  identifies the piece of image data D 2 , the onboard communication unit  350  associates the identified piece of image data D 2  with the request ID “3” (see  FIG. 10D ) included in the data request and transmits the identified piece of image data D 2  to the collection server  100 . In contrast, when the onboard communication unit  350  receives the empty response, the control unit  310  does not execute the processing or the control unit  310  executes a predetermined process corresponding to the empty response by which no image data D 2  is transmitted. 
     Next, operations of the image data storing unit  124  are described with reference to  FIGS. 13, 14A and 14B . First, as illustrated in  FIGS. 13 and 14A , the image data storing unit  124  receives the piece of image data D 2  (step S 31 ). As described above, the piece of image data D 2  is associated with the request ID “3” and transmitted from the vehicle  300  with the vehicle ID “#C”. The image data storing unit  124  receives the piece of image data D 2  transmitted from the vehicle  300  with the vehicle ID “#C” together with the request ID “3”. 
     Upon receiving the piece of image data D 2 , as illustrated in  FIGS. 13 and 14A , the image data storing unit  124  stores the piece of image data D 2  in the image data DB  115  (step S 32 ). When the image data storing unit  124  stores the piece of image data D 2  in the image data DB  115 , the image data storing unit  124  issues a storage destination address of the piece of image data D 2  in the image data DB  115 . According to the present embodiment, the image data storing unit  124  issues an address “URL#3” as the storage destination address. For example, the piece of image data D 2  is stored in a storing region of the address “URL #3” in the image data DB  115 . 
     When the piece of image data D 2  is stored, as illustrated in  FIGS. 13 and 14B , the image data storing unit  124  updates the management map MM (step S 33 ). In more detail, based on the request ID “3” associated with the piece of image data D 2 , the image data storing unit  124  searches for the management information including the same request ID “3” from the data request management DB  113 . As described above, the management information including the request ID “3” is stored in the data request management DB  113  (see  FIG. 11 ). Thus, the image data storing unit  124  registers the issued storage destination address in a storage region for the storage destination address in the management information including the request ID “3”. In this way, the address “URL#3” is registered in this storage region. 
     The image data storing unit  124  obtains the positional information from the management information including the request ID “3” before or after the registration of the address. According to the present embodiment, the image data storing unit  124  obtains the positional information (Ing 1 , Int 1 ) (see  FIG. 11 ). When the image data storing unit  124  obtains the positional information, the image data storing unit  124  calculates the mesh ID from the obtained positional information. According to the present embodiment, similarly to the process in step S 15 , the image data storing unit  124  calculates the mesh ID “#5”. When the image data storing unit  124  calculates the mesh ID, as illustrated in  FIG. 14B , the image data storing unit  124  increments by one the collected number of the collection ratio in the mesh region corresponding to the mesh ID. According to the present embodiment, the image data storing unit  124  increments the collected number “2” of the collection ratio “2/3” in the mesh region of the mesh ID “#5” to the collected number “3”. 
     Thus, the collected number “3” reaches the collection upper limit, and thereafter, the piece of image data D 2  corresponding to the mesh region of the mesh ID “#5” is not requested. Accordingly, when the above-described processing is similarly executed for the mesh regions other than the mesh ID “#5”, all the mesh regions converge to the collection ratio “3/3”. Thus, the collected numbers of pieces of the image data D 2  are made to be an equalized value without the occurrences of variation of the collection of the pieces of image data D 2 . Also, since the collection of the image data D 2  is stopped by the collection upper limit, the collection efficiency of the image data D 2  is improved. When the user  10  operates the input device  11  to access the image data DB  115 , the user  10  may view the image data D 2  by causing the display device  12  to display the image data D 2 . 
     Second Embodiment 
     Referring next to  FIGS. 15 to 18B , a second embodiment of the present disclosure is described. First, a functional configuration of the collection server  100  according to the second embodiment is described with reference to  FIG. 15 . The same elements as those of the collection server  100  according to the first embodiment are denoted by the same reference signs, and detailed description thereof is omitted. 
     As illustrated in  FIG. 15 , the collection server  100  according to the second embodiment is different from that of the first embodiment in that the processing unit  120  of the collection server  100  according to the second embodiment includes a data request adjustment unit  125  as an element. Although the details will be described later, the data request adjustment unit  125  adjusts order of the distribution of the data requests generated by the collection determination unit  122  based on the information for making the collected numbers of the pieces of image data D 2  close to be an equalized value. For example, based on the information including the priority for collecting the pieces of image data D 2 , the data request adjustment unit  125  delays the distribution of the data request when the priority is relatively low. This may make the collected numbers of the pieces of the image data D 2  close to be an equalized value. 
     Next, operations of the collection determination unit  122  according to the second embodiment are described with reference to  FIGS. 16, 17A  and  17 B. First, as illustrated in  FIGS. 16 and 17A , when the mesh ID is calculated in the process in step S 15 , the collection determination unit  122  obtains the collection ratio (step S 51 ) and further obtains an average of the collected numbers (step S 52 ). As described above, when the mesh ID “#5” is calculated, as illustrated in  FIG. 17A , the collection determination unit  122  refers to the management map MM of the fourth-level mesh which is stored in the management map DB  114  and for which the collection upper limit is not set, and the collection determination unit  122  obtains the collection ratio “2/−” corresponding to the mesh ID “#5”. The numerator of the collection ratio “2/−” represents the collected number up to this point in time (present collected number), and the denominator of the collection ratio “2/−” represents that the collection upper limit is not designated by the equalization condition. The average of the collected numbers is calculated based on the total sum of the collected numbers and the number of mesh regions of the management map MM and is associated with the management map MM. According to the present embodiment, the total sum of the collected numbers is “9” and the number of mesh regions is “9”. Thus, an average “1.0” is calculated and associated with the management map MM. The collection determination unit  122  obtains the average “1.0” together with the collection ratio “2/−”. 
     When the collection determination unit  122  obtains the average of the collected numbers, the collection determination unit  122  next generates the management information and the data request (step S 53 ). In the process in step S 53 , the collection determination unit  122  generates the management information and the data request in a similar manner to that in step S 18 . Thus, the management information and the data request described with reference to  FIGS. 10C and 10D  are generated. 
     When the collection determination unit  122  generates the management information and the data request, the collection determination unit  122  next determines whether the collected number is greater than the average (step S 54 ). For example, the collection determination unit  122  determines whether the collected number of the pieces of image data D 2  corresponding to the target mesh ID is greater than the collected numbers of the pieces of image data D 2  corresponding to the mesh IDs other than the target mesh ID. 
     When the collected number is greater than the average (YES in step S 54 ), as illustrated in  FIG. 17C , the collection determination unit  122  sets a priority Low in the data request (step S 55 ). The priority Low is information for delaying the distribution of the data request relative to the other data requests in the distribution order. For example, when the collected number of the pieces of image data D 2  corresponding to the target mesh ID is relatively greater, an increase in the collected number cause variation of the collection. Thus, collection of the image data D 2  is restrained. According to the present embodiment, the collected number of the mesh region with the mesh ID “#5” is “2” and greater than the average “1.0”. Thus, the priority Low is set in the data request. 
     In contrast, when the collected number is smaller than or equal to the average (NO in step S 54 ), although it is not illustrated, the collection determination unit  122  sets a priority Mid in the data request (step S 56 ). The priority Mid is information for not adjusting the distribution order of the data requests. For example, when the collected number of the pieces of image data D 2  corresponding to the target mesh ID is relatively smaller, collection of the image data D 2  is enhanced so as to make the collected numbers of pieces of the image data D 2  close to be an equalized value. When the collected number is 0 (zero), the collection determination unit  122  may set a priority High in the data request. 
     When the collection determination unit  122  sets the priority Low or Mid in the data request, the collection determination unit  122  next stores the management information generated in the process in Step S 53  (Step S 57 ). For example, similarly to the first embodiment, the collection determination unit  122  stores the management information in the data request management DB  113 . When the collection determination unit  122  stores the management information, as illustrated in  FIG. 17B , the collection determination unit  122  outputs the data request to the data request adjustment unit  125  (step S 58 ) and ends the processing. 
     As illustrated in  FIG. 17B , the data request adjustment unit  125  includes a data request storing unit  126 , a data request transmission unit  127 , a first queue  128 A, a second queue  128 B, and a third queue  128 C. The first queue  128 A, the second queue  128 B, and the third queue  128 C may be included in the storage unit  110 . The details of the data request storing unit  126 , the data request transmission unit  127 , the first queue  128 A, the second queue  128 B, and the third queue  128 C will be described later. 
     Next, operations of the data request adjustment unit  125  are described with reference to  FIGS. 18A and 18B . As described above, when the collection determination unit  122  outputs the data request, as illustrated in  FIG. 18A , the data request storing unit  126  receives the data request (in step S 61 ). Upon receiving the data request, the data request storing unit  126  determines the priority (step S 62 ). As described above, any one of the priorities Low, Mid, and High is set in the data request. 
     When the data request storing unit  126  determines the priority, the data request storing unit  126  stores the data request in the corresponding queue (step S 63 ) and ends the processing. For example, when it is determined that the priority Low is set in the data request, the data request storing unit  126  stores the data request in the third queue  128 C as illustrated in  FIG. 17B . Although it is not illustrated, when it is determined that the priority Mid is set in the data request, the data request storing unit  126  stores the data request in the second queue  128 B. When it is determined that the priority High is set in the data request, the data request storing unit  126  stores the data request in the first queue  128 A. 
     When the data request storing unit  126  stores the data request, as illustrated in  FIGS. 17B and 18B , the data request transmission unit  127  obtains the data request in accordance with a scheduling algorithm (step S 71 ). Examples of the scheduling algorithm include, for example, priority scheduling and weighted fair queuing (WFQ). The data request transmission unit  127  obtains the data request in accordance with the scheduling algorithm. Accordingly, when a case where the data request is obtained from the second queue  128 B is set as a reference, the data request transmission unit  127  obtains the data request from the third queue  128 C at a lower frequency than that of the reference. The data request transmission unit  127  obtains the data request from the first queue  128 A at a higher frequency than that of the reference. Thus, when the data request is stored in the third queue  128 C, an obtaining frequency of the data request transmission unit  127  decreases. For example, when the priority Low is set in the data request, the obtaining frequency of the data request transmission unit  127  decreases. 
     Upon receiving the data request, as illustrated in  FIG. 17B , the data request transmission unit  127  stores the data request in the data request queue  112  (in step S 72 ). Thus, the data request distribution unit  123  may obtain and distribute the data requests stored in the data request queue  112 . When the priority Low is set in the data request, the distribution of the data request is delayed compared to the case where the priority Mid is set in the data request. This may delay the collection of the image data D 2  from the vehicle  300  and consequently make the collected numbers of pieces of the image data D 2  close to be an equalized value. 
     Although the preferred embodiments according to the present disclosure have been described in detail above, the embodiment is not limited to the specific embodiments related to the present disclosure, and various modifications and changes may be made without departing from the gist of the present disclosure described in the claims. 
     For example, according to the embodiments described above, it has been described that the collection determination unit  122  receives and holds the collection request D 3  input by the user  10  in advance and checks the extraction conditions of the collection request D 3  against the metadata D 1  every time the metadata D 1  is collected. In contrast, the metadata D 1  may be periodically collected and stored and the extraction conditions of the collection request D 3  may be checked against the metadata D 1  when the collection determination unit  122  receives and holds the collection request D 3  input by the user  10  afterward. 
     Although the management map corresponding to the positional information is used according to the above-described embodiment, a management map corresponding to time or the vehicle ID may be used. This may suppress a situation, in which, for example, images are concentratedly collected for a specific one minute even when the user  10  wants to view a change over time at predetermined intervals before and after an accident, and collection of the image data D 2  may be made to be equalized. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.