Patent Publication Number: US-2023160718-A1

Title: Central apparatus, map generation system, and map generation method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a central apparatus, a map generation system, and a map generation method. 
     BACKGROUND ART 
     The map generation system generates map information with submeter positional accuracy by measuring a space to be mapped with a space measuring sensor and estimating positional information and shape information on features based on the result of measurements. Such a map generation system may be configured by, for example, one or more mobile terminals that measure a space to be mapped, and a central apparatus that generates map information based on the result of measurements performed by the mobile terminals. 
     In this map generation system, the result of measurements is transmitted from the mobile terminals to the central apparatus by wireless communication. Since the result of measurements is large in data volume, it is necessary to reduce data volume associated with communication. For example, the map generation system described in Patent Document 1 reduces communication data volume by causing the mobile terminals to extract necessary information from the result of measurements based on a predetermined feature quantity. 
     PRIOR ART DOCUMENT 
     Patent Documents 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2014-228637 
     SUMMARY 
     Problem to be Solved by the Invention 
     There is, however, a problem with the map generation system according to Patent Document 1 in that it has not been possible to appropriately reduce communication data volume because in some cases the mobile terminals may also transmit unnecessary information to the central apparatus. 
     The present disclosure has been made in light of problems as described above, and it is an object of the present disclosure to provide a technique with which it is possible to appropriately reduce communication data volume. 
     Means to Solve the Problem 
     A central apparatus according to the present disclosure includes is a central apparatus for communicating with a mobile terminal that is movable with a mobile body. The mobile terminal includes positional-information acquisition means that acquires positional information on the mobile body, measurement-information acquisition means that acquires measurement information by measuring a space around the mobile body as a space to be mapped, and extraction-information generation means that generates extraction information by extraction from the measurement information based on the positional information and command information transmitted from the central apparatus to the mobile terminal. The central apparatus includes map-information generation means that generates map information based on the extraction information transmitted from the mobile terminal to the central apparatus, and map generation control means that evaluates completeness of the map information generated by the map-information generation means and generates the command information based on the completeness. 
     Effects of the Invention 
     According to the present disclosure, the central apparatus generates command information based on the completeness of the map information. With this configuration, it is possible to appropriately reduce communication data volume. 
     These and other objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of the present disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram illustrating a functional configuration of a map generation system according to Embodiment 1. 
         FIG.  2    is a block diagram illustrating a functional configuration of a mobile terminal according to Embodiment 1. 
         FIG.  3    is a diagram showing one example of operations of command-information selection means of the mobile terminal according to Embodiment 1. 
         FIG.  4    is a diagram showing one example of operations of measurement-information extraction means of the mobile terminal according to Embodiment 1. 
         FIG.  5    is a diagram showing one example of operations of the measurement-information extraction means of the mobile terminal according to Embodiment 1. 
         FIG.  6    is a diagram showing one example of operations of the measurement-information extraction means of the mobile terminal according to Embodiment 1. 
         FIG.  7    is a diagram showing one example of operations of the measurement-information extraction means of the mobile terminal according to Embodiment 1. 
         FIG.  8    is a block diagram illustrating a functional configuration of a central apparatus according to Embodiment 1. 
         FIG.  9    is a diagram showing one example of operations of the central apparatus according to Embodiment 1. 
         FIG.  10    is a diagram showing one example of the operations of the central apparatus according to Embodiment 1. 
         FIG.  11    is a diagram showing one example of the operations of the central apparatus according to Embodiment 1. 
         FIG.  12    is a diagram showing one example of the operations of the central apparatus according to Embodiment 1. 
         FIG.  13    is a flowchart showing one example of operations of the mobile terminal according to Embodiment 1. 
         FIG.  14    is a flowchart showing one example of the operations of the central apparatus according to Embodiment 1. 
         FIG.  15    is a block diagram illustrating a functional configuration of a map generation system according to Embodiment 2. 
         FIG.  16    is a diagram showing one example of the operations of a mobile terminal according to Embodiment 2. 
         FIG.  17    is a diagram showing one example of the operations of the mobile terminal according to Embodiment 2. 
         FIG.  18    is a diagram showing one example of the operations of the mobile terminal according to Embodiment 2. 
         FIG.  19    is a diagram showing one example of the operations of a central apparatus according to Embodiment 2. 
         FIG.  20    is a block diagram illustrating a functional configuration of a map generation system according to Embodiment 3. 
         FIG.  21    is a diagram showing one example of the operations of a central apparatus according to Embodiment 3. 
         FIG.  22    is a diagram showing one example of the operations of the central apparatus according to Embodiment 3. 
         FIG.  23    is a diagram showing one example of the operations of the central apparatus according to Embodiment 3. 
         FIG.  24    is a block diagram illustrating a functional configuration of a map generation system according to Embodiment 4. 
         FIG.  25    is a diagram showing one example of the operations of a central apparatus according to Embodiment 4. 
         FIG.  26    is a block diagram illustrating a hardware configuration of the central apparatus according to a variation. 
         FIG.  27    is a block diagram illustrating a hardware configuration of the central apparatus according to another variation. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     Embodiment 1 will be described with reference to the drawings.  FIG.  1    is a block diagram illustrating a functional configuration of a map generation system A 1  according to Embodiment 1 of the present disclosure. The map generation system A 1  includes one or more mobile terminals  1  that are movable with mobile bodies V 1  to V 3 , and a central apparatus  2  that communicates with the mobile terminals  1 . 
     The map generation system A 1  generates map information by measuring spaces around the mobile bodies V 1  to V 3  as spaces for which the map information is generated, i.e., spaces to be mapped, (hereinafter, also referred to as “target spaces”) and performing mapping processing based on the result of measurements. The mobile terminals  1  are movable with the mobile bodies V 1  to V 3  and may, for example, be mounted on the mobile bodies V 1  to V 3 . Note that the number of mobile bodies with the mobile terminals  1  mounted thereon and the number of mobile terminals  1  are not limited to three. The central apparatus  2  is installed on the ground and generates map information based on extraction information that is extracted from the result of measuring by the mobile terminals  1 . 
     The map information as used herein refers to information on features that exist in target spaces, the information recording either or both of the positions and shapes of the features existing in each target space with submeter positional accuracy. The map information may, for example, be road map information that records features on roads or indoor map information that records indoor features. The map information may further include attributes of features and relations of connection of the features in addition to the positions and shapes of the features. 
     Features include real features that actually exist in target spaces and virtual features that virtually exist in the target spaces. In the case of road map information, examples of the features include road shoulder edge, mark line, stop line, signal, road sign, road mark, street lamp, road center line, and traffic-lane center line. In the case of indoor map information, examples of the features include strut, door, illumination, air conditioner, elevator, escape leading light, virtual lane, and virtual wall. 
     The mobile bodies V 1  to V 3  may be either animals or machines each having means of transportation in target spaces. Examples of the mobile bodies include humans, vehicles, mobile robots, and drones. The mobile terminals  1  may travel in target spaces accompanying the mobile bodies. For example, the mobile terminals  1  may be mounted on the mobile bodies, or may be possessed by the mobile bodies. The following description is given on the assumption that the mobile terminals  1  are mounted on the mobile bodies. 
     The mobile terminals  1  and the central apparatus  2  may, for example, be calculators each configured by a storage device that stores programs and parameters, a central processing unit (CPU) that executes programs, a memory that temporarily retains the result of calculation by the CPU and programs to be executed by the CPU, and an interface for communication with other equipment. 
     The central apparatus  2  may, for example, be a cloud server installed on the Internet, a multi access edge computing (MEC) server installed on a core network such as a mobile telephone network, or an off-line server installed by a business company. Note that details of the hardware configurations of the mobile terminals  1  and the central apparatus  2  will be described as variations. 
     Mobile Terminal  1   
       FIG.  2    is a block diagram illustrating a functional configuration of a mobile terminal  1  according to Embodiment 1 of the present disclosure. The mobile terminal  1  is an information processor that (i) acquires positional information on the mobile body and measurement information on surroundings of the mobile body, based on measurement results obtained by sensors mounted on the mobile body, (ii) generates, as extraction information, an extraction result extracted from the measurement information based on the positional information and the command information transmitted from the central apparatus  2  to the mobile terminal  1 , and (iii) transmits the positional information and the extraction information to the central apparatus  2  and receives the command information from the central apparatus  2 . 
     As will be described later, according to Embodiment 1 of the present disclosure, the extraction information substantially includes the positional information. Thus, when the extraction information is transmitted, both of the positional information and the extraction information are also transmitted. Alternatively, the positional information and the extraction information may be transmitted separately. In the following description, transmitting the extraction information may also be referred to as transmitting the positional information and the extraction information. Although the extraction information according to Embodiment 1 of the present disclosure includes the positional information, the extraction information does not necessary have to include the positional information. 
     The mobile terminal  1  includes positional-information acquisition means  10  that acquires the position of the mobile body, measurement-information acquisition means  11  that acquires measurement information by measuring a target space around the mobile body, extraction-information generation means  12  that generates extraction information extracted from the measurement information, and mobile-terminal communication means  13  that carries out information communication with the central apparatus  2 . 
     The positional-information acquisition means  10  acquires positional information on the mobile body based on the measurement result obtained from the positioning sensor mounted on the mobile body. The measurement-information acquisition means  11  acquires measurement information by measuring a space around the mobile body as the space to be mapped, based on the measurement result obtained from the space measuring sensor mounted on the mobile body. The extraction-information generation means  12  generates, as the extraction information, partial measurement information by extraction from the measurement information based on the positional information and command information transmitted from the central apparatus  2  to the mobile terminal  1 . The mobile-terminal communication means  13  carries out information communication with the central apparatus  2 . 
     The command information is generated by the central apparatus  2  and used by the extraction-information generation means  12  of the mobile terminal  1 . The command information includes a target place and a target feature type, the target place representing the place to be extracted from the measurement information through processing for extracting the extraction information, and the target feature type being a feature type that represents a feature to be extracted from the measurement information through the processing for extracting the extraction information. 
     The target place refers to information that represents a location or a region in the target space as a place to which the extraction processing using the command information is applied. The form of presentation of the target place may, for example, be the form of presentation using central coordinates and the distance from the central coordinates, may be the form of presentation using a sequence of coordinate points and the distances from the sequence of coordinate points, or may be the form of presentation using a region of a sequence of coordinate points. 
     The feature type refers to information that uniquely represents the type of one or more features in the mobile terminals  1  and the central apparatus  2 , and the target feature type refers to information that represents the feature type to which the extraction processing using the command information is applied. The feature type may be a name or an identifier that is assigned to each feature in the map information, or may be a name or an identifier that collectively represents a plurality of features included in the map information. For example, the feature types in the road map information may include “road shoulder edge”, “mark line,” “stop line,” “road center line,” and “traffic-lane center line” assigned to each feature type, or may include “white line” that collectively represents a plurality of features such as “mark line” and “stop line.” 
     Note that the command information may further include information other than the target place and the target feature type. For example, the command information may include information such as an identifier for uniquely identifying the command information, a generation time that represents the time when the command information is generated, the term of validity that represents a period of time during which the command information is valid, and an applied condition that represents a condition for applying the command information. 
     Next, the constituent elements of the mobile terminal  1  will be described in detail. The positional-information acquisition means  10  is a processing unit that estimates the current location of a mobile body with the mobile terminal  1  mounted thereon, and acquires the result of the estimation as positional information. For example, the positional-information acquisition means  10  may use a positioning sensor that estimates positions to estimate the current location of a mobile body. 
     The positioning sensor of the positional-information acquisition means  10  may be of any kind as long as the positional information can be acquired directly or can be estimated from output values of the positioning sensor. The positioning sensor may use, for example, a global navigation satellite system (GNSS), a radio beacon, or an inertial measurement unit (IMU), or may use any combination of the above. 
     The positional information as used herein refers to information that uniquely indicates coordinates where the mobile body exists and the direction of travel of the mobile body as the position of the mobile body. The positional information may, for example, be expressed in the form of latitude, longitude, and azimuth angle or in the form of X coordinate, Y-coordinate, and rotation angle. The positional-information acquisition means  10  provides the positional information to the extraction-information generation means  12 . Although details will be described later, the extraction-information generation means  12  that receives the positional information from the positional-information acquisition means  10  provides the positional information to the mobile-terminal communication means  13 . Note that the positional-information acquisition means  10  may provide the positional information directly to the mobile-terminal communication means  13 . For convenience of description, the position indicated by the positional information and the positional information may not be differentiated in the following description. 
     The measurement-information acquisition means  11  is a processing unit that measures a target space around the mobile body with the mobile terminal  1  mounted thereon and acquires the result of the measurement as measurement information. For example, the measurement-information acquisition means  11  may use a space measuring sensor for measuring spaces to measure the target space around the mobile body. 
     The space measuring sensor of the measurement-information acquisition means  11  may be of any kind as long as the relative distance between the space measuring sensor and each feature around the mobile body can be measured directly or can be estimated from the output value of the space measuring sensor. The space measuring sensor may, for example, use a laser range finder (LRF), a stereo camera, or a time of flight (ToF) camera, or may use any combination of the above. 
     The measurement information as used herein refers to information that includes a set of distance points each representing the relative distance between the space measuring sensor and each feature. Note that the measurement information may further include a set of color pixels. For example, the measurement information may be expressed in the form of a set of distance, azimuth angle, and angle of elevation and depression, in the form of a set of X coordinate, Y-coordinate, and Z coordinate, or in the form of a set of distance, X coordinate, and Y-coordinate. The measurement-information acquisition means  11  provides the measurement information to the extraction-information generation means  12 . 
     The extraction-information generation means  12  is a processing unit that (i) associates and estimates feature types and feature regions from the measurement information, the feature types each indicating the type of a feature, the feature regions each indicating the region of the feature, and (ii) based on the result of determination as to whether the positional information and each feature type correspond respectively to the target place and the target feature type that are included in the command information, generates extraction information by extraction from the measurement information on the feature region corresponding to the feature type. 
     Specifically, the extraction-information generation means  12  (i) selects command information that is used in the generation of the extraction information, based on the result of determination as to whether the positional information corresponds to the target place included in the command information received from the central apparatus  2 , (ii) associates and estimates feature types and feature regions from the measurement information, and (iii) based on the result of determination as to whether each feature type obtained by the estimation corresponds to the target feature type included in the selected command information, generates partial measurement information by extraction from the measurement information on the feature region corresponding to the feature type, as the extraction information. 
     The extraction-information generation means  12  transmits the extraction information to the central apparatus  2  via the mobile-terminal communication means  13 . At this time, the extraction-information generation means  12  may successively transmit the extraction information to the central apparatus  2 , or may transmit a plurality of extraction information by one operation to the central apparatus  2 , using means for temporarily storing the extraction information. 
     The extraction-information generation means  12  may successively process the measurement information acquired by the measurement-information acquisition means  11 , or may combine time-series data in the measurement information and process the combined data by one operation. As a method of combining time-series data in the measurement information, the data may be combined by superimposing each measurement information while using the positional information as a reference, or by performing alignment processing on a plurality of measurement information. 
     The extraction-information generation means  12  includes command-information storage means  121  that stores command information, command-information selection means  122  that selects command information, and measurement-information extraction means  123  that generates partial measurement information as the extraction information based on the command information selected by the command-information selection means  122 . 
     The command-information storage means  121  is a database that stores the command information transmitted from the central apparatus  2  to the mobile terminal  1 , i.e., the command information received by the mobile-terminal communication means  13 , and provides the command information to the command-information selection means  122  in response to a request from the command-information selection means  122 . 
     The command-information selection means  122  is a processing unit that (i) determines whether the positional information acquired by the positional-information acquisition means  10  corresponds to the target place included in the command information stored in the command-information storage means  121 , and (ii) selects the command information that has been determined as corresponding to the positional information as command information that is used by the measurement-information extraction means  123 . The command-information selection means  122  provides the selected command information or a list of the selected command information to the measurement-information extraction means  123 . Although the command-information selection means  122  according to Embodiment 1 further provides the positional information to the measurement-information extraction means  123 , the positional information does not necessarily have to be provided to the measurement-information extraction means  123  if the measurement information is not combined as will be described later. 
     In the determination method used by the command-information selection means  122 , for example, it is geometrically determined whether coordinates included in the positional information are included in the position or region that represents the target place. When it is determined that the positional information is included in the target place, the command-information selection means  122  determines that the positional information corresponds to the target place included in the command information, and when it is determined that the positional information is not included in the target place, the command-information selection means  122  determines that the positional information does not correspond to the target place included in the command information. 
     Next, one example of the operations of the command-information selection means  122  will be described with reference to the drawings.  FIG.  3    is a diagram showing one example of the operations of the command-information selection means  122 .  FIG.  3 ( a )  is a diagram illustrating command information C 1  to C 3  stored in the command-information storage means  121 . Each of the command information C 1  to C 3  includes a target place and a target feature type, the target place being designated by a shape type and shape details.  FIG.  3 ( b )  is a diagram illustrating the mobile body V 1  with the mobile terminal  1  mounted thereon, a target space E that is a space around the mobile body V 1  and in which the mobile body V 1  travels, and target places included in the command information C 1  to C 3 . In  FIG.  3 ( b ) , the broken lines indicate the target places included in the command information C 1  to C 3 . 
     First, the command-information selection means  122  determines whether the positional information on the mobile body V 1  corresponds to the target place included in the command information C 1 . The command-information selection means  122  compares the positional information on the mobile body V 1  with the target place included in the command information C 1 , and if the mobile body V 1  exists in the target place included in the command information C 1  as illustrated in  FIG.  3 ( b ) , determines that the positional information on the mobile body V 1  corresponds to the target place included in the command information C 1 . In this case, the command-information selection means  122  selects the command information C 1  as command information that is used by the measurement-information extraction means  123 . 
     Next, as in the case of the command information C 1 , the command-information selection means  122  determines whether the positional information on the mobile body V 1  corresponds to the target place included in the command information C 2 . If the mobile body V 1  exists outside the target place included in the command information C 2  as illustrated in  FIG.  3 ( b ) , the command-information selection means  122  determines that the positional information on the mobile body V 1  does not correspond to the target place included in the command information C 1 . 
     Then, as in the case of the command information C 1  and C 2 , the command-information selection means  122  determines whether the positional information on the mobile body V 1  corresponds to the target place included in the command information C 2 . If the mobile body V 1  exists outside the target place included in the command information C 3  as illustrated in  FIG.  3 ( b ) , the command-information selection means  122  determines that the positional information on the mobile body V 1  does not correspond to the target place included in the command information C 3 . 
     As a result of the above, the command-information selection means  122  provides the selected command information C 1  to the measurement-information extraction means  123 . 
     The descriptions will now return to the mobile terminal  1  illustrated in  FIG.  2   . The measurement-information extraction means  123  is a processing unit that, based on the positional information, the measurement information, and the command information selected by the command-information selection means  122 , (i) combines one or more measurement information, (ii) associates and estimates feature types and feature regions from the measurement information, and (iii) based on the result of determination as to whether each feature type corresponds to the target feature type included in the command information, generates extraction information by extraction from the measurement information on the feature region corresponding to the feature type. Hereinafter, the measurement-information extraction means  123  will be described in detail. 
     First, the measurement-information extraction means  123  adjusts reference positions of multiple measurement information, which are acquired by the measurement-information acquisition means  11 , by rotating or translating the multiple measurement information based on multiple positional information acquired by the positional-information acquisition means  10  and the multiple measurement information, and combines the multiple measurement information. In the case of using only one measurement information, the measurement-information extraction means  123  may skip this processing of combining the measurement information and as a result does not use the positional information. 
     Next, the measurement-information extraction means  123  applies feature estimation processing to the measurement information combined through the combining processing so as to associate and estimate feature types and feature regions, the feature types each representing the type of a feature included in the measurement information, and the feature regions each representing the region where the feature exists. 
     Then, if it is determined that the feature type obtained by the aforementioned estimation corresponds to the target feature type included in the command information selected by the command-information selection means  122 , the measurement-information extraction means  123  selects this feature type. 
     Finally, the measurement-information extraction means  123  extracts a subset of the measurement information that corresponds to the feature region corresponding to the selected feature type, and generates the result of the extraction as extraction information. Note that the feature region corresponding to the selected feature type is the feature region that is estimated with the selected feature type. In addition to the subset of the measurement information that corresponds to the aforementioned feature region, the measurement-information extraction means  123  may further extract a subset of the measurement information that corresponds to the surroundings of the aforementioned feature region, and generates the result of the extraction as the extraction information. The measurement-information extraction means  123  provides the generated extraction information to the mobile-terminal communication means  13 . 
     The feature region as used herein refers to the range (region) in the target space or the range (region) in the measurement information, which are both estimated to include a feature as a result of the feature detection processing. The feature region may only need to represent the range where the feature exists and may be expressed as, for example, a rectangular parallelepiped that surrounds the feature, a polyhedron that is shaped according to the shape of the feature, or a rectangle that surrounds the feature in a two-dimensional bird&#39;s eye plan view. 
     The feature estimation processing performed by the measurement-information extraction means  123  may be estimation processing for estimating the feature type and the feature region from the measurement information. For example, the feature estimation processing may be performed by a geometric estimation method in which a feature that is associated in advance with a threshold value preset for each feature type, such as position, shape, or size, is estimated based on the threshold value. As another alternative, the feature estimation processing may be performed by, for example, a model estimation method in which a feature is estimated by a random extraction consensus (RANSAC) method using a model that is preset for each feature type. As yet another alternative, the feature estimation processing may be performed by, for example, an estimation method using machine learning in which the feature type and the feature region are detected using a convolutional neural network for estimation of the feature type and the feature region. 
     The number of command information selected by the command-information selection means  122  may be zero or two or more. In the case where the number of command information is zero, the measurement-information extraction means  123  may extract the measurement information by using a default feature type that is set in advance, may stop the extraction, or may extract the measurement information by using all the feature types. In the case where the number of command information is two or more, the measurement-information extraction means  123  may integrate multiple extraction information into one extraction information, or may handle multiple extraction information as-is. 
     Next, one example of the operations of the measurement-information extraction means  123  will be described with reference to the drawings.  FIGS.  4  to  7    are diagrams showing one example of the operations of the measurement-information extraction means  123 . In the example illustrated in  FIGS.  4  to  7   , the target feature type included in the command information is assumed to be “utility pole.” 
     First, the measurement-information extraction means  123  acquires measurement information M 1  as illustrated in  FIG.  4    from the measurement-information acquisition means  11 .  FIG.  4    is a bird&#39;s eye view of the measurement information M 1 , the measurement information M 1  being expressed as a point group of relative distances centered on the mobile body. 
     Next, the measurement-information extraction means  123  performs feature estimation processing on the measurement information M 1  and obtains the result of estimation as illustrated in  FIG.  5   .  FIG.  5    is a diagram illustrating four features D 1  to D 4  estimated (detected) from the measurement information M 1 .  FIG.  5    shows the result of estimating (detecting) the feature type and the feature region through the feature detection processing. The feature types of the features D 1  to D 4  are respectively “building,” “curb,” “vehicle,” and “utility pole,” and the feature regions of the features D 1  to D 4  are indicated by broken frames. 
     Finally, the measurement-information extraction means  123  determines whether each of the feature types of the features D 1  to D 4  corresponds to the target feature type of “utility pole” included in the command information. In the example illustrated in  FIG.  5   , the feature type of the feature D 4  is determined to correspond to the target feature type. The measurement-information extraction means  123  extracts information on the feature region of the feature D 4  from the measurement information M 1  to generate extraction information M 2  as illustrated in  FIGS.  6  and  7   . Note that  FIG.  6    is a bird&#39;s eye view of the extraction information M 2 .  FIG.  7    is a diagram that represents the extraction information M 2 . 
     According to Embodiment 1 of the present disclosure, the extraction information includes, as illustrated in  FIG.  7   , positional information that is used as the reference position of the measurement information, data that represents a subset of distance data on the feature region, extracted from the measurement information, and the feature type of the feature that corresponds to the target feature type and that is indicated by the above data. 
     The description will now return to the mobile terminal  1  illustrated in  FIG.  2   . The mobile-terminal communication means  13  is a communicator that carries out information communication with the central apparatus  2 . The mobile-terminal communication means  13  transmits the extraction information provided by the extraction-information generation means  12  to the central apparatus  2 , and receives the command information from the central apparatus  2  and provides the received command information to the extraction-information generation means  12 . Since the extraction information according to Embodiment 1 of the present disclosure includes the positional information and the feature type, the positional information and the feature type are also transmitted to the central apparatus  2  by the transmission of the extraction information to the central apparatus  2 . 
     The communication system used by the mobile-terminal communication means  13  may be of any kind as long as communication is possible between the central apparatus  2  and the moving mobile terminal  1 . For example, wide-area radio frequency communication such as long term evolution (LTE) or world interoperability for microwave access (WiMAX) may be used, narrow-area radio frequency communication such as 5-Generation (5G), wireless local area network (LAN), Bluetooth (registered trademark), or dedicated short range communication (DSRC) may be used, or a mobile communication system using light or sound other than radio waves may be used. The mobile terminal  1  and the central apparatus  2  do not necessarily have to carry out direct information communication, and may carry out information communication via a cable communication network or a wireless communication network. 
     Configuration of Central Apparatus  2   
     Next, details of the central apparatus  2  will be described with reference to  FIG.  8   .  FIG.  8    is a block diagram illustrating a functional configuration of the central apparatus  2  according to Embodiment 1 of the present disclosure. 
     The central apparatus  2  is an information processor that (i) generates map information based on the extraction information provided by a mobile terminal  1 , (ii) evaluates completeness of the map information, (iii) generates command information based on the completeness, and (iv) selects and transmits the command information to the mobile terminal  1 . 
     The central apparatus  2  includes central-apparatus communication means  20  that carries out information communication with each mobile terminal  1 , map-information generation means  21  that generates map information based on extraction information, and map generation control means  22  that generates command information based on the map information. 
     The central-apparatus communication means  20  is a communicator that carries out information communication with each mobile terminal  1 . The central-apparatus communication means  20  receives extraction information from a mobile terminal  1  and provides the extraction information (the positional information and the feature type) to the map-information generation means  21  and the map generation control means  22 , and transmits the command information generated by the map generation control means  22  to the mobile terminal  1 . 
     The communication system used by the central-apparatus communication means  20  may be of any kind as long as communication is possible between the central apparatus  2  and a moving mobile terminal  1  and may, for example, be the same as the communication system used by the mobile-terminal communication means  13 . 
     The map-information generation means  21  is a processing unit that (i) selects a feature estimation method for each feature type included in the extraction information based on the extraction information provided by one or more mobile terminals  1 , and (ii) generates map information for each feature type, using the selected feature estimation method. 
     The map-information generation means  21  includes estimation-method selection means  211  that selects a feature estimation method from among a plurality of feature selection methods, and feature estimation means  212  that estimates the positions or shapes of features, using the feature estimation method selected by the estimation-method selection means  211 . Note that the feature estimation means  212  prepare a plurality of feature estimation methods for each feature type, and in the example illustrated in  FIG.  8   , feature estimation methods A to C are prepared. 
     The estimation-method selection means  211  is a processing unit that selects, from among a plurality of feature estimation methods, a feature estimation method that corresponds to the feature type included in the extraction information transmitted from the mobile terminal  1  to the central apparatus  2 , as feature estimation means that is used by the feature estimation means  212 . 
     The correspondence between the feature types and the feature estimation methods is set in advance, and the estimation-method selection means  211  retrieves, from the correspondence, the same feature type as the feature type included in the extraction information. Then, the estimation-method selection means  211  selects, from among the feature estimation methods, a feature estimation method that corresponds to the above feature type as feature estimation means that is used by the feature estimation means  212 . 
     The feature estimation means  212  is a processing unit that (i) estimates the positions or shapes of features, using the feature estimation method selected by the estimation-method selection means  211 , (ii) improves the accuracy of the positions or shapes of the features by appropriately applying statistical processing, and (iii) generates map information for each feature type based on the position or shape of the feature. 
     For example, the feature estimation means  212  first corrects the reference position indicated by the positional information included in the extraction information, using the feature estimation method, if any map information is in preparation. Next, the feature estimation means  212  performs feature estimation processing such as geometric calculation, model estimation, or machine learning on the extraction information to estimate the positions or shapes of features. Then, the feature estimation means  212  performs matching of the currently estimated feature and each previously estimated feature based on the feature type included in the extraction information and the position or shape of the feature so as to estimate the same feature, or appropriately applies statistical processing on the features so as to improves the accuracy of the positions or shapes of the features. Finally, the feature estimation means  212  generates or updates map information for each feature type by recording the result of estimating the map information for each feature type. At this time, if there are already different map information for a plurality of feature types, the feature estimation means  212  may integrate these map information. 
     The map generation control means  22  is a processing unit that (i) evaluates the completeness of the map information generated by the map-information generation means  21  and (ii) while switching the target feature type according to the completeness, generates and selects command information that includes the target feature type. The map generation control means  22  switches the target feature type in a predetermined order of completeness based on the completeness of the map information. For example, in a map generation system for generating road map information, the map generation control means  22  switches the target feature type in the order of “road, “white line,” and “structure.” 
     The map generation control means  22  includes map-information evaluation means  221 , command-information generation means  222 , a feature extraction sequence table  223 , command-information management means  224 , and transmit-command selection means  225 . 
     The map-information evaluation means  221  evaluates the completeness of the map information generated by the map-information generation means  21 . The map-information evaluation means  221  may evaluate the completeness of the map information generated by the map-information generation means  21 , collectively for all target feature types or separately for each target feature type. 
     The feature extraction sequence table  223  shows the correspondence between the completeness and the target feature types. While switching the target feature type corresponding to the completeness according to the feature extraction sequence table  223 , the command-information generation means  222  generates command information that includes the target feature type, based on the completeness evaluated by the map-information evaluation means  221 . The command-information management means  224  manages the command information generated by the command-information generation means  222 , by registering, storing, or deleting the command information. 
     The transmit-command selection means  225  predicts an accessible range that represents the range that the mobile terminal  1  can reach, based on the positional information included in the extraction information transmitted from the mobile terminal  1  to the central apparatus  2 . Then, the transmit-command selection means  225  selects command information that is to be transmitted from the central apparatus  2  to the mobile terminal  1 , from the command-information management means  224  based on the accessible range and the target place included in the command information. 
     Next, each constituent element of the map generation control means  22  will be described in detail. The map-information evaluation means  221  is a processing unit that (i) evaluates the positional accuracy of features included in the map information generated by the map-information generation means  21 , based on the map information and (ii) calculates the completeness of the map information based on the result of the evaluation. 
     Specifically, the map-information evaluation means  221  first determines an evaluation range that is the range to be evaluated, out of the range indicated by the map information. The evaluation range is the range that is included in the range indicated by the map information. 
     The method of determining the evaluation range used by the map-information evaluation means  221  may be of any kind as long as one or more evaluation ranges can be determined from the map information by, for example, dividing the map information into one or more ranges (regions). For example, the map-information evaluation means  221  may determine one or more cells that are divided in a preset grid as evaluation ranges. Alternatively, for example, the map-information evaluation means  221  may determine a range that is updated by the map-information generation means  21  as an evaluation range. As another alternative, for example, the map-information evaluation means  221  may acquire points of division between features (e.g., branch points of roads) based on the map information in preparation and determines ranges that are divided by the points of division and in which features exist, as evaluation ranges. 
     Next, the map-information evaluation means  221  evaluates reliability that represents the degree of reliability of the positional accuracy of features in each evaluation range and calculates the completeness of the map information based on the result of evaluation of the reliability. 
     The method of evaluating positional accuracy used by the map-information evaluation means  221  may be of any kind as long as the completeness can be evaluated as higher as the positional accuracy increases. For example, based on the number of times that features of the feature type are measured in the evaluation range, the map-information evaluation means  221  may evaluate the completeness as higher as this number of times increases. Alternatively, for example, based on the time of measurement for the evaluation range, the map-information evaluation means  221  may evaluate the completeness as higher as this time of measurement increases. As another alternative, for example, the map-information evaluation means  221  may evaluate the completeness as higher as improves with the number of fluctuation errors in the positions of features decreases, based on the result of statistical processing performed by the map-information generation means  21 . 
     The completeness as used herein refers to an index that represents the degree of completeness of the whole or part of the map information. The completeness may be any information that enables determining in which stage the process of generating the map information is. For example, the completeness may be the feature type and the positional accuracy of the feature type as-is, or may be a value obtained by converting the feature type and the positional accuracy of the feature type into numbers. The value obtained by converting the feature type and the positional accuracy of the feature type into numbers may be a value obtained by converting the feature type and the positional accuracy of the feature type into a truth or false value, using a threshold value, may be a value obtained by normalization of the feature type and the positional accuracy of the feature type, or may be a numeric value or an identifier that represents the process of generating a map from the start to the end as continuous values by converting the feature type and the positional accuracy of the feature type, using a preset list. 
     The command-information generation means  222  is a processing unit that retrieves, based on the completeness evaluated by the map-information evaluation means  221 , the target feature type that corresponds to the completeness according to the feature extraction sequence table  223  and generates command information that includes the target feature type to be extracted. 
     The command-information generation means  222  generates command information that includes, as the target place, the entire or part of the evaluation range determined by the map-information evaluation means  221 . As described above, the command information generated by the command-information generation means  222  includes the entire or part of the evaluation range determined by the map-information evaluation means  221  as the target place, and also includes the target feature type that is indexed by completeness in the feature extraction sequence table  223 . 
     The feature extraction sequence table  223  is an index table that shows the target feature type to be extracted by the mobile terminal  1  on a completeness basis. For example, in a map generation system for generating road map information, if the completeness is evaluated in three stages, a completeness of “1” may be set as “road,” a completeness of “2” may be set as “white line,” and a completeness of “3” may be set as “structure” in the feature extraction sequence table  223   
     Note that, in the feature extraction sequence table  223 , one target feature type may be listed multiple times. For example, in a map generation system for generating road map information, if the completeness is evaluated in four stages, a completeness of “1” may be set as a first iteration of “road,” a completeness of “2” may be set as “white line,” a completeness of “3” may be set as “structure,” and a completeness of “4” may be set as a second iteration of “road” in the feature extraction sequence table  223 . 
     The command-information management means  224  is a database that manages one or more command information generated by the command-information generation means  222 , by registering, storing, or deleting the command information and provides command information in response to a request from the transmit-command selection means  225 . 
     Note that the command-information management means  224  may also retain the completeness calculated by the map-information evaluation means  221 , in addition to the command information. In that case, the command-information generation means  222  may determine the command information with reference to the completeness. 
     The transmit-command selection means  225  is a processing unit that (i) predicts the accessible range of a mobile terminal  1  based on the positional information included in the extraction information transmitted from the mobile terminal  1  to the central apparatus  2 , (ii) selects command information that includes a target place in the accessible range from among the command information stored in the command-information management means  224 , and (iii) transmits the command information to the mobile terminal  1  via the central-apparatus communication means  20 . 
     In the processing for predicting the accessible range, for example, the transmit-command selection means  225  may predict, as the accessible range, a range that is located within a certain distance (e.g., within three kilometers) from the position indicated by the positional information as the center, based on the positional information transmitted from the mobile terminal  1 . Alternatively, in the processing for predicting the accessible range, for example, the transmit-command selection means  225  may predict, as the accessible range, a range that the mobile body can reach within a certain period of time (e.g., in five minutes), using the position indicated by the positional information as the center. As another alternative, for example, the transmit-command selection means  225  may predict, as the accessible range, a route that exists within a certain range of distances from the position of the mobile body indicated by the positional information, based on information on the route and the positional information. As yet another alternative, the transmit-command selection means  225  may predict a range that is set by the user of the central apparatus  2  as the accessible range. 
     Next, one example of the operations of the central apparatus  2  will be described with reference to the drawings.  FIGS.  9  to  12    are diagrams showing one example of the operations of the central apparatus  2 . It is assumed herein that the central apparatus  2  generates road map information. In the example illustrated in  FIGS.  9  to  12   , a case is assumed in which the central apparatus  2  evaluates the completeness in three stages of “1,” “2,” and “3” and the target feature types include “road,” “white line,” and “structure.” 
       FIG.  9    is a diagram illustrating the initial state of the central apparatus  2 .  FIG.  9    illustrates map information P 0  generated by the map-information generation means  21  and a feature extraction sequence table  223 T stored in the map generation control means  22 . In the feature extraction sequence table  223 T illustrated in  FIG.  9   , a completeness of “1” corresponds to the target feature type of “road,” a completeness of “2” corresponds to the target feature type of “white line,” and a completeness of “3” corresponds to the target feature type of “structure.” Since the map information has the lowest completeness of “1” in the initial state, the map generation control means  22  generates command information that includes the target feature type of “road.” 
       FIG.  10    is a diagram illustrating a first state of the central apparatus  2  after the initial state. The map-information generation means  21  generates map information P 1  that includes the target feature type of “road” based on the extraction information transmitted from the mobile terminal  1  that has received the command information. In  FIG.  10   , a road shoulder edge D 11  and a road center line D 12  correspond to the target feature type of “road” included in the map information P 1 . The map generation control means  22  evaluates the map information P 1 , and when it is determined that the map information on the target feature type of “road” is completed, the map generation control means  22  changes the completeness from “1” to “2.” Following this, the map generation control means  22  generates command information that includes the target feature type of “white line” according to the feature extraction sequence table  223 T. 
       FIG.  11    is a diagram illustrating a second state of the central apparatus  2  after the first state. The map-information generation means  21  generates map information P 2  that includes the target feature types of “road” and “white line” based on the extraction information transmitted from the mobile terminal  1  that has received the command information. In  FIG.  11   , a mark line D 21 , a traffic-lane center line D 22 , and a pedestrian crossing D 23  correspond to the target feature type of “white line” included in the map information P 2 . The map generation control means  22  evaluates the map information P 2 , and when it is determined that the map information on the target feature type of “white line” is completed, the map generation control means  22  changes the completeness from “2” to “3.” Following this, the map generation control means  22  generates command information that includes the target feature type of “structure” according to the feature extraction sequence table  223 T. 
     Finally,  FIG.  12    is a diagram illustrating a third state of the central apparatus  2  after the second state. The map-information generation means  21  generates map information P 3  that includes the target feature types of “road,” “white line,” and “structure,” based on the extraction information transmitted from the mobile terminal  1  that has received the command information. In  FIG.  12   , a signal D 31 , a utility pole D 32 , and a pole D 33  correspond to the target feature type of structure” included in the map information P 3 . The map generation control means  22  evaluates the map information P 3 , and when it is determined that the map information on the target feature type of “structure” is completed, the map generation control means  22  determines that the map information is completed. 
     Operations of Mobile Terminal  1   
     Next, one example of the operations of a mobile terminal  1  in the map generation system A 1  according to Embodiment 1 of the present disclosure will be described with reference to the drawings.  FIG.  13    is a flowchart showing one example of the operations of a mobile terminal  1  in the map generation system A 1 . 
     First, in step S 101 , the mobile-terminal communication means  13  of the mobile terminal  1  receives command information transmitted from the central apparatus  2 . In step S 101 , the mobile-terminal communication means  13  also provides the command information to the command-information storage means  121 . When step S 101  is completed, the procedure proceeds to step S 102 . 
     In step S 102 , the positional-information acquisition means  10  acquires positional information on the mobile body and provides the acquired positional information to the command-information selection means  122 . When step S 102  is completed, the procedure proceeds to step S 103 . 
     In step S 103 , the measurement-information acquisition means  11  acquires measurement information on the surroundings of the mobile body and provides the acquired measurement information to the measurement-information extraction means  123 . When step S 103  is completed, the procedure proceeds to step S 104 . 
     In step S 104 , the command-information selection means  122  selects (retrieves) command information from the command-information storage means  121  based on the positional information acquired in step S 102 . When step S 104  is completed, the procedure proceeds to step S 105 . 
     In step S 105 , the measurement-information extraction means  123  performs feature estimation processing based on the measurement information acquired in step S 103  and associates and estimates feature types and feature regions. When step S 105  is completed, the procedure proceeds to step S 106 . 
     In step S 106 , the measurement-information extraction means  123  determines whether the feature type estimated in step S 105  corresponds to the target feature type included in the command information selected in step S 104 . When it is determined that the feature type does not correspond to the target feature type, the series of processing in  FIG.  13    is completed without transmission of the extraction information. When it is determined that the feature type corresponds to the target feature type, the procedure proceeds to step S 107  in order to transmit the extraction information. 
     In step S 107 , the measurement-information extraction means  123  extracts part of the measurement information based on the feature region corresponding to the future type that is determined as corresponding to the target feature type in step S 106 , and generates the result of the extraction as extraction information. Then, the measurement-information extraction means  123  provides the generated extraction information to the mobile-terminal communication means  13 . When step S 107  is completed, the procedure proceeds to step S 108 . 
     In step S 108 , the mobile-terminal communication means  13  transmits the extraction information generated in step S 107  to the central apparatus  2 . Since the extraction information according to Embodiment 1 of the present disclosure includes the positional information and the feature type, the positional information and the feature type are also transmitted to the central apparatus  2 , together with the extraction information. If the mobile terminal  1  is configured not to include the positional information and the feature type in the extraction information, the extraction information, the positional information, and the feature type may be transmitted separately to the central apparatus  2 . When step S 108  is completed, the series of processing in  FIG.  13    is completed. Although not shown in  FIG.  13   , the procedure may return to step S 101  after the completion of step S 108 . 
     In the above description, the sequence of the processing in steps S 101  to S 103  may be interchanged, or may be executed in parallel. The processing in step S 101  does not necessarily have to be executed in the initial state. Specifically, the processing in step S 101  may be executed only when the series of processing is completed and the central apparatus  2  has transmitted the command information. 
     Operations of Central Apparatus  2   
     Next, one example of the operations of the central apparatus  2  in the map generation system A 1  according to Embodiment 1 of the present disclosure will be described with reference to the drawings.  FIG.  14    is a flowchart showing one example of the operations of the central apparatus  2  in the map generation system A 1 . 
     First, in step S 201 , the central-apparatus communication means  20  of the central apparatus  2  receives extraction information transmitted from a mobile terminal  1 . In step S 201 , the central-apparatus communication means  20  also provides the extraction information to the map-information generation means  21  and the map generation control means  22 . Since the extraction information according to Embodiment 1 of the present disclosure includes the positional information and the feature type, the central-apparatus communication means  20  receives and provides the positional information and the feature type, together with the extraction information. In the case where the mobile terminal  1  is configured not to include the positional information and the feature type in the extraction information, the central-apparatus communication means  20  may separately receive and provide the extraction information, the positional information, and the feature type. When step S 201  is completed, the procedure proceeds to step S 202 . 
     In step S 202 , the estimation-method selection means  211  of the map-information generation means  21  selects a feature estimation method that is executed in the next step, based on the feature type included in the extraction information acquired in step S 201 . By way of example,  FIG.  14    illustrates feature estimation processes a to c that are respectively performed by the three feature estimation methods A to C illustrated in  FIG.  5   . In the case where the feature type included in the extraction information is a feature type aa, the procedure proceeds to step S 203 A. In the case where the feature type included in the extraction information is a feature type bb, the procedure proceeds to step S 203 B. In the case where the feature type included in the extraction information is a feature type cc, the procedure proceeds to step S 203 C. 
     In steps S 203 A to S 203 C, the feature estimation means  212  of the map-information generation means  21  generates map information by performing the feature estimation methods A to C based on the extraction information that includes the positional information acquired in step S 201 , and provides the generated map information to the map generation control means  22 . When any of steps S 203 A to S 203 C is completed, the procedure proceeds to step S 204 . 
     In step S 204 , the map-information evaluation means  221  of the map generation control means  22  calculates completeness by evaluating the map information generated in steps S 203 A to S 203 C and provides the calculated completeness to the command-information generation means  222  of the map generation control means  22 . When step S 204  is completed, the procedure proceeds to step S 205 . 
     In step S 205 , the command-information generation means  222  of the map generation control means  22  determines, based on the completeness obtained by the calculation in step S 204 , whether or not to switch the target feature type, i.e., the feature type to be extracted by the mobile terminal  1 , according to the feature extraction sequence table  223 . In the case of switching the target feature type, the procedure proceeds to step S 206 . In the case of not switching the target feature type, the procedure proceeds to step S 207 . 
     In step S 206 , the command-information generation means  222  of the map generation control means  22  generates command information that includes the target place and the target feature type, based on the map information generated in steps S 203 A to S 203 C and the target feature type determined in step S 205  and stores the generated command information in the command-information management means  224 . When step S 206  is completed, the procedure proceeds to step S 207 . 
     In step S 207 , the transmit-command selection means  225  of the map generation control means  22  predicts the accessible range based on the positional information included in the extraction information acquired in step S 201 . Then, the transmit-command selection means  225  selects (extracts) command information that includes the target place located in the accessible range, from the command information stored in step S 206  and provides the selected command information to the central-apparatus communication means  20 . When step S 207  is completed, the procedure proceeds to step S 208 . 
     In step S 208 , the central-apparatus communication means  20  transmits the command information selected in step S 207  to the mobile terminal  1 . When step S 208  is completed, the series of processing in  FIG.  14    is completed. Although not illustrated in  FIG.  14   , the procedure may return to step S 201  after completion of step S 208 . 
     In the above description, the sequence of the processing performed in steps S 201  and S 202  may be interchanged, or may be executed in parallel. In the case where only the positional information has been acquired in step S 201 , only the processing in steps S 207  and S 208  may be executed. 
     Summary of Embodiment 1 
     According to Embodiment 1 of the present disclosure as described above, the map generation control means  22  evaluates the completeness of the map information to generate command information that includes the target feature type corresponding to the completeness. The extraction-information generation means  12  generates extraction information based on the result of determination as to whether the feature type estimated from the measurement information corresponds to the target feature type included in the command information. This allows the map generation system A 1  to reduce the volume of information that is transmitted from the mobile terminal  1  to the central apparatus  2 , to the volume of information on the target feature type, i.e., the volume of information that is necessary for the central apparatus  2  to generate map information without using existing map information. Accordingly, it is possible to appropriately reduce communication data volume. 
     The map generation control means  22  further designates the target feature type that is included in the command information in order based on the feature extraction sequence table  223  that is set in advance. This allows the map generation system A 1  to preferentially generate map information that includes the target feature type of high importance. 
     Besides, the map generation control means  22  predicts the accessible range based on the positional information transmitted from the mobile terminal  1  to the central apparatus  2  and determines the command information that is to be transmitted from the central apparatus  2  to the mobile terminal  1 , based on the accessible range and the target place included in the command information. This allows the map generation system A 1  to improve the reliability of providing the command information to the mobile terminal  1  while reducing the number of times the command information is transmitted. 
     Moreover, the map-information generation means  21  selects a feature estimation method based on the feature type included in the extraction information. This eliminates the need for the map generation system A 1  to perform the estimation processing on every feature type assumed by the central apparatus  2  and accordingly results in a reduction in processing load on the central apparatus  2 . 
     Embodiment 2 
     Embodiment 2 of the present disclosure will now be described with reference to the drawings.  FIG.  15    is a block diagram illustrating a functional configuration of a map generation system A 2  according to Embodiment 2 of the present disclosure. Note that the basic configuration of the map generation system A 2  according to Embodiment 2 of the present disclosure is similar to the configuration of the map generation system A 1  according to Embodiment 1, and therefore the following description mainly focuses on points of difference. 
     The points of difference between the map generation system A 1  according to Embodiment 1 and the map generation system A 2  according to Embodiment 2 of the present disclosure are as follows. In the map generation system A 1  according to Embodiment 1, the central apparatus generates command information in advance, whereas the mobile terminals generate extraction information by sequential positioning and measurement. 
     In the map generation system A 2  according to Embodiment 2 of the present disclosure, on the other hand, each mobile terminal first generates provisional extraction information by pre-positioning and pre-measurement, the provisional extraction information being a candidate for the extraction information. The central apparatus generates and transmits command information with arbitrary timing. The mobile terminal selects extraction information that is to be transmitted to the central apparatus, from the provisional extraction information based on the command information. 
     As illustrated in  FIG.  15   , the map generation system A 2  includes one or more mobile terminals  1 B and a central apparatus  2 B, instead of the mobile terminals  1  and the central apparatus  2  in the map generation system A 1  according to Embodiment 1. 
     Each mobile terminal  1 B (i) generates provisional extraction information and estimation information from positional information and measurement information, (ii) stores the provisional extraction information, and (iii) selects extraction information that is to be transmitted to the central apparatus  2 B, from the stored provisional extraction information based on the command information transmitted from the central apparatus  2 B. 
     The central apparatus  2 B (i) generates map information based on the extraction information provided by a mobile terminal  1 B, (ii) evaluates completeness of the map information, (iii) generates command information based on the completeness, and (iv) selects, based on the command information and the estimation information transmitted from the mobile terminal  1 B, command information and transmits the selected command information to the mobile terminal  1 B that is the source of transmission. Hereinafter, the constituent elements of the mobile terminal  1 B and the central apparatus  2 B will be described in detail. 
     Mobile Terminal  1 B 
     The mobile terminal  1 B includes extraction-information generation means  12 B, instead of the extraction-information generation means  12  according to Embodiment 1. The extraction-information generation means  12 B is a processing unit similar to the extraction-information generation means  12  according to Embodiment 1. 
     Specifically, the extraction-information generation means  12 B is a processing unit that (i) associates and estimates feature types and feature regions from the measurement information acquired by the measurement-information acquisition means  11 , (ii) generates provisional extraction information based on the measurement information, the feature types, and the feature regions and stores the generated provisional extraction information, (iii) generates estimation information that includes the positional information acquired by the positional-information acquisition means  10  and a list of feature types and transmits the generated estimation information to the central apparatus  2 B, and (iv) selects extraction information from the stored provisional extraction information based on the command information transmitted from the central apparatus  2 B to the mobile terminal  1 B. 
     The extraction-information generation means  12 B includes measurement-information extraction means  123 B, provisional-extraction-information management means  124 , and extraction-information selection means  125 . Hereinafter, each constituent element of the extraction-information generation means  12 B will be described in detail. 
     The measurement-information extraction means  123 B is a processing unit that (i) associates and estimates feature types and feature regions from the measurement information, (ii) generates, as the provisional extraction information, partial measurement information by extraction from the measurement information on the feature region corresponding to each feature type, and (iii) generates estimation information that includes the positional information and the list of feature types that are included in the provisional extraction information and performs control to transmit the generated estimation information from the mobile terminal  1 B to the central apparatus  2 B. Note that the provisional extraction information according to Embodiment 2 of the present disclosure is similar to the extraction information ( FIG.  7   ) according to Embodiment 1. Specifically, the provisional extraction information includes positional information that is used as the reference position in the measurement information, data that represents a subset of distance data extracted from the measurement information on the feature region, and feature types of features that are expressed by the above data and used in the extraction of the provisional extraction information. 
     The measurement-information extraction means  123 B first combines multiple measurement information acquired by the measurement-information acquisition means  11 . The combining method may be similar to the combining method used by the measurement-information extraction means  123  according to Embodiment 1. Note that in the case of using one measurement information, the measurement-information extraction means  123 B may skip this combining processing. 
     Next, the measurement-information extraction means  123 B applies feature estimation processing on the measurement information combined by the combining processing and thereby associates and estimates feature types and feature regions from the measurement information. The feature estimation processing method may be similar to the feature estimation processing method used by the measurement-information extraction means  123  according to Embodiment 1. 
     Then, for each of all the feature types acquired by the aforementioned estimation, the measurement-information extraction means  123 B generates provisional extraction information by extraction from the measurement information on the feature region corresponding to the feature type. Then, the measurement-information extraction means  123 B stores the generated provisional extraction information in the provisional-extraction-information management means  124 . 
     Finally, the measurement-information extraction means  123 B generates estimation information that includes the positional information and a list of the feature types included in the provisional extraction information, and transmits the generated estimation information to the central apparatus  2 B via the mobile-terminal communication means  13 . 
     The estimation information according to Embodiment 2 of the present disclosure is information that includes the positional information, which represents the reference position in the measurement information, and a list of the feature types estimated by the feature estimation processing, and is also information that does not include data such as distance data, unlike the extraction information. In addition to the positional information and the list of feature types, the estimation information may further include, for example, a generation time that represents the time when the estimation information is generated, or an identifier for uniquely identifying a mobile body that has generated the estimation information. 
     The provisional-extraction-information management means  124  is a database that manages the provisional extraction information by registering, storing, or deleting the provisional extraction information. The provisional extraction information managed by the provisional-extraction-information management means  124  is registered by the measurement-information extraction means  123 B and referenced by the extraction-information selection means  125 . Since the provisional extraction information according to Embodiment 2 of the present disclosure includes the positional information and the feature types, the provisional-extraction-information management means  124  also stores the positional information and the feature types by storing the provisional extraction information. 
     The extraction-information selection means  125  determines whether the positional information and each feature type that are included in the provisional extraction information stored in the provisional-extraction-information management means  124  correspond respectively to the target place and the target feature type that are included in the command information transmitted from the central apparatus  2 B to the mobile terminal  1 B. The extraction-information selection means  125  selects, based on the result of the determination, extraction information that is to be transmitted to the central apparatus  2 B, from the provisional extraction information stored in the provisional-extraction-information management means  124  and transmits the selected extraction information to the central apparatus  2 B via the mobile-terminal communication means  13 . 
     In the method of selecting the extraction information, for example, when the positional information included in the provisional extraction information corresponds to the target place included in the command information and the feature type included in the provisional extraction information corresponds to the target feature type included in the command information, the extraction-information selection means  125  selects the provisional extraction information as the extraction information that is to be transmitted to the central apparatus  2 B. The determination of the target place and the determination of the target feature type may be respectively similar to the determination performed by the command-information selection means  122  and the determination performed by the measurement-information extraction means  123  according to Embodiment 1. 
     Next, one example of the operations of the measurement-information extraction means  123 B will be described with reference to the drawings.  FIGS.  16  to  18    are diagrams showing one example of the operations of the measurement-information extraction means  123 B. The example illustrated in  FIGS.  16  and  17    is similar to the example illustrated in  FIGS.  4  and  5    according to Embodiment 1. 
     First, the measurement-information extraction means  123 B acquires measurement information M 1  as illustrated in  FIG.  16   , as in the case illustrated in  FIG.  4   . Next, as in the case illustrated in  FIG.  5    according to Embodiment 1, the measurement-information extraction means  123 B performs feature estimation processing on the measurement information M 1  so as to obtain the result of estimation as illustrated in  FIG.  17   . 
     Then, the measurement-information extraction means  123 B generates provisional extraction information on features D 1  to D 4 .  FIG.  18 ( a )  is a diagram illustrating the generated provisional extraction information. As described above, the provisional extraction information includes positional information, feature types, and data extracted from the measurement information. As illustrated in  FIG.  18 ( a ) , the measurement-information extraction means  123 B does not necessarily have to generate provisional extraction information on the feature D 3  that has a dynamic feature type of “vehicle” that is unnecessary in the generation of the map information. 
     Finally, the measurement-information extraction means  123 B generates estimation information that includes the positional information and a list of the feature types included in the provisional extraction information. One example of generating estimation information that includes the positional information and a list of feature types of “building, “curb,” and “utility pole” that are included in the provisional extraction information is illustrated in  FIG.  18 ( b ) . 
     The description will now return to the mobile terminal  1 B illustrated in  FIG.  15   . The mobile-terminal communication means  13  of the mobile terminal  1 B is a communicator that carries out information communication with the central apparatus  2 B. The mobile-terminal communication means  13  not only carries out communication like the mobile-terminal communication means  13  according to Embodiment 1, but also transmits the estimation information generated by the extraction-information generation means  12 B to the central apparatus  2 B. 
     Central Apparatus  2 B 
     The central apparatus  2 B includes map generation control means  22 B, instead of the map generation control means  22  according to Embodiment 1. The map generation control means  22 B (i) evaluates completeness of the map information, (ii) generates command information based on the completeness, (iii) stores the estimation information transmitted from the mobile terminal  1 B to the central apparatus  2 B, and (iv) based on the command information and the stored estimation information, selects command information and transmits the selected command information to the mobile terminal  1 B that is the source of transmission. 
     As illustrated in  FIG.  15   , the configuration of the map generation control means  22 B is similar to a configuration obtained by deleting the command-information management means  224 , adding the estimation-information storage means  226 , and replacing the transmit-command selection means  225  by the transmit-command selection means  225 B in the configuration of the map generation control means  22  in  FIG.  8    according to Embodiment 1. 
     The estimation-information storage means  226  is a database that manages the estimation information transmitted from the mobile terminal  1 B to the central-apparatus communication means  20 , by registering, referencing, or deleting the estimation information. The estimation-information storage means  226  associates and manages terminal identifiers and the estimation information. 
     The terminal identifiers as used herein refer to information that is used by the central apparatus  2 B to uniquely identify each mobile terminal  1 B, and the terminal identifiers may be information that allows the transmit-command selection means  225 B to identify the mobile terminal  1 B that transmits the command information. The terminal identifiers may, for example, be unique numbers assigned to the mobile terminals  1 B, or may be communication addresses of the mobile terminals  1 B. 
     The transmit-command selection means  225 B is a processing unit that (i) determines whether the positional information and the list of feature types, both included in the estimation information stored in the estimation-information storage means  226 , correspond respectively to the target place and the target feature type that are included in the command information generated by the command-information generation means  222 , and (ii) selects, based on the result of the determination, command information that is to be transmitted from the central apparatus  2 B to the mobile terminal  1 B that is the source of transmission of the estimation information. 
     Specifically, the transmit-command selection means  225 B first determines whether the positional information included in the estimation information stored in the estimation-information storage means  226  corresponds to the target place included in the command information generated by the command-information generation means  222 . The determination as to whether the positional information corresponds to the target place may be similar to the determination made by the extraction-information selection means  125  according to Embodiment 2. 
     When it is determined that the positional information included in the estimation information corresponds to the target place included in the command information, the transmit-command selection means  225 B determines which feature type in the list of feature types corresponds to the target feature type included in the command information. 
     When it is determined that any feature type in the list of feature types included in the estimation information corresponds to the target feature type included in the command information, the transmit-command selection means  225 B identifies the terminal identifier of the mobile terminal  1 B that has transmitted the estimation information. Then, the transmit-command selection means  2258  transmits the command information via the central-apparatus communication means  20  to the mobile terminal  1 B that is identified by the terminal identifier and that is the source of transmission of the estimation information. 
     Note that, for example, the transmit-command selection means  225 B may be configured to store the number of times the command information is transmitted from the central apparatus  2 B to each mobile terminal  1 B and not to transmit the command information when the above number exceeds a preset threshold value. Alternatively, for example, the transmit-command selection means  225 B may be configured to store total data volume of the extraction information that can be transmitted from each mobile terminal  1 B to the central apparatus  2 B and not to transmit the command information when the total data volume exceeds a preset threshold value. 
     Next, one example of the operations of the transmit-command selection means  225 B will be described with reference to the drawings.  FIG.  19    is a diagram showing one example of the operations of the transmit-command selection means  225 B.  FIG.  19 ( a )  is a diagram illustrating a combination of the terminal identifiers stored in the estimation-information storage means  226  and estimation information F 1  to F 3  (the positional information and a list of feature types).  FIG.  19 ( b )  illustrates command information C 1  generated by the command-information generation means  222 .  FIG.  19 ( c )  is a diagram illustrating a positional relation between the estimation information F 1  to F 3  (positional information) and the position of the target place included in the command information C 1 . In  FIG.  19 ( c ) , the broken line indicating the command information C 1  represents the target place and indicates that the estimation information F 1  and F 3  exist in the target place included in the command information C 1 . In the example illustrated in  FIG.  19   , the feature type of “curb” is assumed to correspond to the target feature type of “road.” 
     First, the transmit-command selection means  225 B determines whether the estimation information F 1  corresponds to the command information C 1 . That is, the transmit-command selection means  225 B compares the positional information included in the estimation information F 1  with the target place included in the command information C 1  and compares the feature type included in the estimation information F 1  with the target feature type included in the command information C 1 . Since, in the example illustrated in  FIG.  19   , the estimation information F 1  exists in the target place included in the command information C 1  and the feature type of “curb” corresponds to the target feature type of “road,” the transmit-command selection means  225 B determines that the estimation information F 1  corresponds to the command information C 1 . Thus, the transmit-command selection means  225 B selects a terminal identifier of “V 1 ” as the destination of transmission of the command information C 1 . 
     Next, the transmit-command selection means  225 B determines, as in the case of the estimation information F 1 , whether the estimation information F 2  corresponds to the command information C 1 . The feature type of “curb” corresponds to the target feature type of “road,” but the estimation information F 2  does not exist in the target place included in the command information C 1 . Thus, the transmit-command selection means  225 B determines that the estimation information F 2  does not correspond to the command information C 1 . 
     Then, the transmit-command selection means  225 B determines, as in the case of the estimation information F 1  and F 2 , whether the estimation information F 3  corresponds to the command information C 1 . The estimation information F 3  exists in the target place included in the command information C 1 , but there is no feature type that corresponds to the target feature type of “road.” Thus, the transmit-command selection means  225 B determines that the estimation information F 3  does not correspond to the command information C 1 . 
     Finally, the transmit-command selection means  225 B transmits the command information C 1  to the mobile terminal  1 B identified by the terminal identifier of “V 1 .” 
     Summary of Embodiment 2 
     According to Embodiment 2 of the present disclosure as described above, in cases such as where the processing allows some leeway, the extraction-information generation means  12 B of each mobile terminal  1 B generates the provisional extraction information, irrespective of the presence or absence of the command information, and transmits the estimation information that includes the positional information and a list of feature types to the central apparatus  2 B. The map generation control means  22 B of the central apparatus  2 B selects the destination of transmission of the command information based on the positional information and the feature types that are both included in the estimation information. Accordingly, when the central apparatus  2 B transmits the command information, the provisional extraction information serving as a candidate for the extraction information has already been generated by a mobile terminal  1 B. This allows the central apparatus  2 B to quickly collect the extraction information. 
     Embodiment 3 
     Embodiment 3 of the present disclosure will be described with reference to the drawings.  FIG.  20    is a block diagram illustrating a functional configuration of a map generation system A 3  according to Embodiment 3 of the present disclosure. Note that the basic configuration of the map generation system A 3  according to Embodiment 3 of the present disclosure is similar to the configuration of the map generation system A 1  according to Embodiment 1, and therefore the following description mainly focuses on points of difference. 
     The points of difference between the map generation system A 1  according to Embodiment 1 and the map generation system A 3  according to Embodiment 3 of the present disclosure are as follows. The map generation system A 1  according to Embodiment 1 generates command information based on one feature extraction sequence table. On the other hand, the map generation system A 3  according to Embodiment 3 of the present disclosure includes a plurality of feature extraction sequence tables and changes, based on the map information, the feature extraction sequence table that is used in the generation of the command information. 
     The map generation system A 3  includes a central apparatus  2 C, instead of the central apparatus  2  of the map generation system A 1  according to Embodiment 1. The central apparatus  2 C not only has the function of the central apparatus  2  according to Embodiment 1, but also changes, based on the map information, the feature extraction sequence table that is used in the generation of the command information among the plurality of feature extraction sequence tables. 
     The central apparatus  2 C includes map generation control means  22 C, instead of the map generation control means  22  according to Embodiment 1. The map generation control means  22 C not only has the function of the map generation control means  22  according to Embodiment 1, but also changes, based on the map information in preparation, the feature extraction sequence table that is used to generate the command information among the plurality of feature extraction sequence tables. 
     The configuration of the map generation control means  22 C is similar to a configuration obtained by changing one feature extraction sequence table  223  into a plurality of feature extraction sequence tables  223 C and adding the extraction-sequence selection means  227  in the configuration of the map generation control means  22  according to Embodiment 1. The extraction-sequence selection means  227  selects a feature extraction sequence table that is used to generate command information from among the plurality of feature extraction sequence tables based on the map information in preparation. Hereinafter, each constituent element of the map generation control means  22 C will be described in detail. 
     The feature extraction sequence tables  223 C are each similar to the feature extraction sequence table  223  according to Embodiment 1, but differ from each other in the target feature type corresponding to each completeness. 
     The plurality of feature extraction sequence tables  223 C are respectively associated in advance with a plurality of space types, and each space type represents the type of space to be mapped, i.e., a class to which the target space belongs. 
     The space types are attribute values obtained by classifying each portion of the target space by similar spaces, and the number of feature extraction sequence tables is prepared advance to the same number as the number of space types. In the case of road map information, for example, the space types may include highway, trunk road, and service road for daily living. In the case of indoor map information, for example, the space types may include room, entrance hall, and passage. 
     In a map generation system for generating road map information, for example, the feature extraction sequence tables  223 C may include a feature extraction sequence table for highways, a feature extraction sequence table for trunk roads, and a feature extraction sequence table for service roads for daily living. In a map generation system for generating indoor map information, for example, the feature extraction sequence tables  223 C may include a feature extraction sequence table for rooms, a feature extraction sequence table for entrance halls, and a feature extraction sequence table for open passages. In a seamless map generation system of either indoor or outdoor type, for example, the feature extraction sequence tables  223 C may include all of the above feature extraction sequence tables. 
     The extraction-sequence selection means  227  is a processing unit that (i) estimates a space type based on the map information generated by the map-information generation means  21 , and (ii) switches the feature extraction sequence table by selecting a feature extraction sequence table  223 C that corresponds to the estimated space type from among the plurality of feature extraction sequence tables  223 C as the feature extraction sequence table that is used by the command-information generation means  222 . The extraction-sequence selection means  227  cuts the entire or part of the range indicated by the map information and selects a feature extraction sequence table that is applied to the cut range. 
     Alternately, for example, the extraction-sequence selection means  227  may estimate a space type by determining whether, in the map information generated by the map-information generation means  21 , the width or crossover spacing of a feature that represents the range of travel of a mobile body is included in a threshold range that is set in advance for each space type. As another alternative, for example, the extraction-sequence selection means  227  may estimate a space type by determining whether, in the map information generated by the map-information generation means  21 , the spacing of a feature that limits the travel of a mobile body is included in a threshold range that is set in advance for each space type. As yet another alternative, in the case where map information that includes a space type for each position is prepared in advance, for example, the extraction-sequence selection means  227  may estimate a space type based on the position of a feature included in the map information generated by the map-information generation means  21 . 
     Note that, in the case where the space type is not appropriately estimated, the extraction-sequence selection means  227  may use a preset standard feature extraction sequence table as the result of estimation. The map-information evaluation means  221  may further evaluate the completeness of the map information for each range that is cut by the extraction-sequence selection means  227 . 
     Next, one example of the operations of the extraction-sequence selection means  227  will be described with reference to the drawings.  FIGS.  21  to  23    are diagrams showing one example of the operations of the extraction-sequence selection means  227 . Here, the central apparatus  2 C is assumed to generate road map information as the map information. In the example illustrated in  FIGS.  21  to  23   , a case is assumed in which the extraction-sequence selection means  227  switches among the feature extraction sequence tables  223 C according to a table T 0  and based on a space type estimated from the width of a road and a threshold value for the width. Here, a case is also assumed in which the feature extraction sequence tables  223 C include a feature extraction sequence table  223 T 1  for trunk roads and a feature extraction sequence table  223 T 2  for service roads for daily living. 
       FIG.  21    is a diagram illustrating an input state of the extraction-sequence selection means  227 .  FIG.  21    illustrates map information P 4  that includes features D 13  and D 14 , the table T 0  that shows the correspondence between the threshold value for the width of each road and the feature extraction sequence tables  223 T 1  and  223 T 2 , and the feature extraction sequence tables  223 T 1  and  223 T 2 . The features D 13  and D 14  are road-related features, and in the map information P 4 , the solid lines indicate road shoulder edges, and the broken lines indicate road center lines. 
       FIG.  22    illustrates a state when the extraction-sequence selection means  227  switches the feature extraction sequence table for the surroundings of the feature D 13 . In  FIG.  22   , since the feature D 13  has a width of “20.0 m,” the extraction-sequence selection means  227  selects, for a region indicated by the dashed dotted lines around the feature D 13 , the feature extraction sequence table  223 T 1  from the table T 0  as a feature extraction sequence table that is used by the command-information generation means  222 . 
       FIG.  23    illustrates a state when the extraction-sequence selection means  227  switches the feature extraction sequence table for the surroundings of the feature D 14 . In  FIG.  23   , since the feature D 14  has a width of “4.0 m,” the extraction-sequence selection means  227  selects, for a region illustrated by the dashed dotted lines around the feature D 14 , the feature extraction sequence table  223 T 2  from the table T 0  as a feature extraction sequence table that is used by the command-information generation means  222 . 
     Summary of Embodiment 3 
     According to Embodiment 3 of the present disclosure as described above, the extraction-sequence selection means  227  estimates a space type based on the map information and switches, based on the estimated space type, the feature extraction sequence table that is used by the command-information generation means  222 . This allows the map generation system A 3  to switch the order of features that are collected according to the space type of the target space and to reduce unnecessary communication of information. Accordingly, it is possible to appropriately reduce communication data volume. 
     Embodiment 4 
     Embodiment 4 of the present disclosure will be described with reference to the drawings.  FIG.  24    is a block diagram illustrating a functional configuration of a map generation system A 4  according to Embodiment 4 of the present disclosure. Note that the basic configuration of the map generation system A 4  according to Embodiment 4 of the present disclosure is similar to the configuration of the map generation system A 1  according to Embodiment 1, and therefore the following description omits the same points and focuses on only the points of difference. 
     The points of difference between the map generation system A 1  according to Embodiment 1 and the map generation system A 4  according to Embodiment 4 of the present disclosure are as follows. The map generation system A 1  according to Embodiment 1 generates command information by designating the target feature type in the order of completeness according to the feature extraction sequence table. On the other hand, the map generation system A 4  according to Embodiment 4 of the present disclosure generates the ratio of acquisition for each target feature type. Note that the ratio of acquisition refers to the ratio of each target feature type to be extracted by a mobile terminal  1  and may correspond to, for example, the priority of extraction as will be described later. 
     The map generation system A 4  includes a central apparatus  2 D, instead of the central apparatus  2  of the map generation system A 1  according to Embodiment 1. The central apparatus  2 D not only has the function of the central apparatus  2  according to Embodiment 1, but also associates and generates the ratios of acquisition and the command information based on the completeness for each target feature type and selects, based on the ratio of acquisition, command information that is to be transmitted from the central apparatus  2 D to the mobile terminal  1 . 
     The central apparatus  2 D includes map generation control means  22 D, instated of the map generation control means  22  according to Embodiment 1. The map generation control means  22 D not only has the function of the map generation control means  22  according to Embodiment 1, but also (i) evaluates the completeness of the map information for each target feature type, (ii) associates and generates the ratios of acquisition and the command information based on the completeness for each target feature type, and (iii) selects command information that is to be transmitted from the central apparatus  2 D to the mobile terminal  1 , based on the positional information transmitted from a mobile terminal  1  to the central apparatus  2 D, the ratio of acquisition, and the target place included in the command information. 
     The configuration of the map generation control means  22 D is similar to a configuration obtained by deleting the feature extraction sequence table  223 , adding completeness management means  228  that manages (stores) the completeness for each target feature type, and replacing the command-information generation means  222 , the command-information management means  224 , and the transmit-command selection means  225  by command-information generation means  222 D, command-information management means  224 D, and transmit-command selection means  225 D in the configuration of the map generation control means  22  according to Embodiment 1. 
     The command-information generation means  222 D associates and generates the ratios of acquisition and the command information based on the completeness for each target feature type stored in the completeness management means  228 . The command-information management means  224 D manages (stores) the ratios of acquisition and the command information generated by the command-information generation means  222 D. The transmit-command selection means  225 D selects command information that is to be transmitted from the central apparatus  2 D to the mobile terminal  1  from the command-information management means  224 D based on the positional information transmitted from the mobile terminal  1  to the central apparatus  2 D, the ratio of acquisition, and the target place included in the command information. Hereinafter, the constituent elements of the map generation control means  22 D will be described in detail. 
     The completeness management means  228  is a database that manages the completeness for each target feature type by registering, updating, storing, or deleting the completeness for each target feature type, the completeness being evaluated (calculated) by the map-information evaluation means  221  for the map information generated by the map-information generation means  21 . The completeness management means  228  associates the target feature types, the completeness of the map information for each target feature type, and the regions to be evaluated with one another for the map information evaluated by the map-information evaluation means  221 , and stores the resultant information as completeness information. The completeness management means  228  provides this completeness information to the command-information generation means  222 D. 
     The command-information generation means  222 D is a processing unit that (i) calculates the ratio of features to be extracted by the mobile terminal  1  for each target feature type based on the completeness information managed by the completeness management means  228 , and generates the command information, and (ii) causes the command-information management means  224 D to manage the ratios of acquisition that is the result of calculation and the command information. 
     Specifically, the command-information generation means  222 D first acquires completeness information on the same sections from the completeness information managed by the completeness management means  228 . Next, the command-information generation means  222 D compares the completeness for each target feature type based on the completeness information so as to set the ratio of acquisition that represents, for each target feature type, the ratio of priority extraction of the extraction information by a mobile terminal  1 . At this time, the command-information generation means  222 D may set the ratios of acquisition such that a higher ratio of acquisition is set for the target feature type with lower completeness or such that, in consideration of the priority of each target feature type, a higher ratio of acquisition is set for a target feature type with higher priority. The command-information generation means  222 D associates and generates the command information and the ratios of acquisition from the completeness information. Finally, the command-information generation means  222 D registers the ratios of acquisition and the command information in the command-information management means  224 D. 
     The command information generated and managed by the central apparatus  2 D includes a target place and a plurality of target feature types. The command information may be generated by the command-information generation means  222 D, managed by the command-information management means  224 D, or may be processed by the transmit-command selection means  225 D into command information that is to be transmitted to a mobile terminal  1 . 
     The command-information management means  224 D is a database that manages the ratios of acquisition and the command information by registering, storing, or deleting one or more ratios of acquisition and one or more command information generated by the command-information generation means  222 D, and provides the ratio of acquisition and the command information in response to a request from the transmit-command selection means  225 D. 
     The transmit-command selection means  225 D is a processing unit that (i) predicts the accessible range of a mobile terminal  1  in the same manner as the transmit-command selection means  225  according to Embodiment 1, and (ii) selects (determines) command information that is to be transmitted from the central apparatus  2 D to the mobile terminal  1  from the command-information management means  224 D based on the accessible range, the ratio of acquisition, and the target place included in the command information. 
     Next, one example of the operations of the map generation control means  22 D will be described with reference to the drawings.  FIG.  25    is a diagram showing one example of the operations of the map generation control means  22 D. Here, a case is assumed in which the map generation system A 4  generates road map information and there are three target feature type including “road,” “white line,” and “structure.” 
       FIG.  25 ( a )  is a diagram illustrating completeness information H 0  that is evaluated by the map-information evaluation means  221  and managed by the completeness management means  228 . The completeness information H 0  indicates that the completeness for the target feature type of “road” is “75%,” the completeness for the target feature type of “white line” is “50%,” and the completeness for the target feature type of “structure” is “25%.” 
       FIG.  25 ( b )  is a diagram illustrating information H 1  that is generated by the command-information generation means  222 D and combines the ratios of acquisition and the command information managed by the command-information management means  224 D. This information H 1  indicates the ratios of acquisition for different target feature types when the ratio of acquisition for the target feature type of “road” is “1.0.” In this example, the command-information generation means  222 D determines the ratios of acquisition based on the ratio of the reciprocal of the completeness illustrated in  FIG.  25 ( a ) . 
       FIG.  25 ( c )  is a diagram illustrating command information H 2  to H 4  that are selected by the transmit-command selection means  225 D and transmitted from the central apparatus  2 D, and mobile bodies V 1  to V 3  that are the destinations of transmission of the command information H 2  to H 4 , respectively. The command information H 2  to H 4  include the same target place, and the accessible ranges of the mobile bodies V 1  to V 3  correspond to this target place. 
     The transmit-command selection means  225 D sets the target feature type to be extracted by a mobile terminal  1 , based on the ratios of acquisition illustrated in  FIG.  25 ( b ) . In this example, the transmit-command selection means  225 D makes the number of mobile terminals  1  for which the target feature type with a high ratio of acquisition is set, larger than the number of mobile terminals  1  for which the target feature type with a low ratio of acquisition is set. As a result, as illustrated in  FIG.  25 ( c ) , the transmit-command selection means  225 D sets the target feature type of “structure” for the mobile bodies V 1  and V 2  and sets the target feature type of “white line” for the mobile body V 3 . Accordingly, the command information H 2  and H 3  for extracting the target feature type of “structure” are transmitted respectively to the mobile terminals  1  of the mobile bodies V 1  and V 2 , and the command information H 4  for extracting the target feature type of “white line” is transmitted to the mobile terminal  1  of the mobile body V 3 . 
     Summary of Embodiment 4 
     According to Embodiment 4 of the present disclosure as described above, the map generation control means  22 D determines, based on the completeness of the map information for each target feature type, the ratio of acquisition that is the ratio of the target feature type to be extracted by the mobile terminal and selects command information that is to be transmitted to the mobile terminal, based on the ratio of acquisition. This allows the map generation system A 4  to generate the command information that includes a plurality of target feature types with the same timing while appropriately reducing communication data volume. 
     Other Variations 
     The map-information generation means  21  and the map generation control means  22  illustrated in  FIG.  8    described above are hereinafter referred to as the “map-information generation means  21  and so on.” The map-information generation means  21  and so on are achieved by a processing circuit  81  of the central apparatus  2  illustrated in  FIG.  26   . That is, the processing circuit  81  of the central apparatus  2  includes the map-information generation means  21  that generates the map information based on the extraction information transmitted from the mobile terminal  1  to the central apparatus  2 , and the map generation control means  22  that evaluates the completeness of the map information generated by the map-information generation means  21  and generates the command information based on the completeness. Dedicated hardware may be applied to the processing circuit  81 , or a processor that executes programs stored in a memory may be applied to the processing circuit  81 . Examples of the processor include a central processing unit, a processing unit, an arithmetic-logic unit, a microprocessor, a microcomputer, and a digital signal processor (DSP). 
     In the case where dedicated hardware is applied to the processing circuit  81 , for example, the processing circuit  81  may correspond to a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA), or may be any combination of the above. The function of each constituent element of the map-information generation means  21  and so on may be achieved as a circuit that includes distributed processing circuits, or may be achieved as one processing circuit that collectively has the functions of the constituent elements. 
     In the case where a processor is applied to the processing circuit  81 , the functions of the map-information generation means  21  and so on may be implemented by combining with software and so on. For example, the software and so on correspond to software, firmware, or a combination of software and firmware. The software and so on are described as programs and stored in the memory. As illustrated in  FIG.  27   , a processor  82  applied to the processing circuit  81  achieves the function of each constituent element by reading and executing programs stored in a memory  83 . That is, when the function of each constituent element is executed by the processing circuit  81 , the central apparatus  2  includes the memory  83  for storing a program that results in the execution of the step of generating map information based on the extraction information transmitted from the mobile terminal  1  to the central apparatus  2  and the step of evaluating the completeness of the generated map information and generating the command information based on the completeness. In other words, it can also be said that this program causes a computer to execute the procedure or method used in the map-information generation means  21  and so on. The memory  83  as used herein may, for example, be a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM), or a drive unit and so on for driving the above memory, such as a hard disk drive (HDD), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, or a digital versatile disc (DVD), or may be any other recording medium that may be used in the future. 
     The above has been a description of the configuration in which the function of each constituent element such as the map-information generation means  21  and so on is achieved by any of hardware and software and so on. The present disclosure is, however, not limited to the examples described above, and a configuration is also possible in which some of the constituent elements such as the map-information generation means  21  and so are realized as dedicated hardware, and other some of the constituent elements are realized as software and so on. For example, the function of the map-information generation means  21  may be achieved by the processing circuit  81  and the interface and so on that serve as dedicated hardware, and the functions of the other constituent elements may be achieved by the processing circuit  81 , which serves as the processor  82 , reading and executing programs stored in the memory  83 . 
     As described above, the processing circuit  81  can achieve each of the functions described above by hardware or software and so on or by any combination of the above. Although the above has been a description of the map-information generation means  21  and the map generation control means  22  of the central apparatus  2 , the same applies to the positional-information acquisition means  10 , the measurement-information acquisition means  11 , and the extraction-information generation means  12  of the mobile terminals  1 . The constituent elements of the map information generation system described above may be distributed and arranged in either of the mobile terminal  1  and the central apparatus  2 , or may be centrally arranged in any equipment. 
     It should be noted that the present disclosure can be implemented by freely combining the above embodiments or by making a modification or omission to the embodiments as appropriate without departing from the scope of the present disclosure. 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore to be understood that numerous modifications and variations can be devised without departing from the scope of the invention. 
     EXPLANATION OF REFERENCE SIGNS 
       1 ,  1 B mobile terminal 
       2 ,  2 B,  2 C,  2 D central apparatus 
       10  positional-information acquisition means 
       11  measurement-information acquisition means 
       12 ,  12 B extraction-information generation means 
       21  map-information generation means 
       22 ,  22 B,  22 C,  22 D map generation control means 
       121  command-information storage means 
       122  command-information selection means 
       123 ,  123 B measurement-information extraction means 
       124  provisional-extraction-information management means 
       125  extraction-information selection means 
       211  estimation-method selection means 
       212  feature estimation means 
       221  map-information evaluation means 
       222 ,  222 D command-information generation means 
       223 ,  223 C feature extraction sequence table 
       224 ,  224 D command-information management means 
       225 ,  225 B,  225 D transmit-command selection means 
       226  estimation-information storage means 
       227  extraction-sequence selection means 
       228  completeness management means 
     A 1 , A 2 , A 3 , A 4  map generation system 
     V 1  to V 3  mobile body