Compression method

Abstract

The position information trajectory data is compressed.SOLUTION: The compression method includes a first acquisition step of acquiring a plurality of pieces of position information each indicating a position of a moving object at a different time, a second acquisition step of acquiring, based on one or more pieces of first position information indicating a position of the moving object in a predetermined range including a position indicated by the one or more pieces of first position information and map information, road information in a predetermined range including a position indicated by the one or more pieces of first position information, as first nearby road information, and a second acquisition step of acquiring, based on one or more pieces of second position information indicating a position of the moving object at a time later than the predetermined range in the plurality of pieces of position information and map information, the method includes a third acquisition step of acquiring road information within a predetermined range including a position indicated by the second position information as second neighborhood road information, a calculation step of calculating a change rate of information obtained by combining the first neighborhood road information and the second neighborhood road information from the first neighborhood road information, and a determination step of determining whether or not to store the second position information based on the change rate.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to the technical field of data compression methods. [Background technology]

[0002] This type of method may be used, for example, to compress position information trajectory data of a moving object, which may be used in the map matching technique described in Patent Document 1, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-187486 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, the position information trajectory data of a moving object may include multiple pieces of position information acquired periodically. For example, if the speed of the moving object is relatively high, the position information trajectory data will contain relatively few pieces of position information when the moving object moves through one section. On the other hand, if the speed of the moving object is relatively low, the position information trajectory data will contain relatively many pieces of position information when the moving object moves through one section. Here, from the perspective of storing the position information trajectory data, it is desirable to reduce the amount of data. For example, if the moving object's direction of travel does not change, the trajectory of the moving object can be represented by position information indicating the start point and position information indicating the end point. In other words, the trajectory of the moving object can be represented without using all of the multiple pieces of position information included in the position information trajectory data. Therefore, by appropriately thinning out some of the multiple pieces of position information included in the position information trajectory data, it is possible to achieve both data volume reduction (in other words, data compression) and reproduction of the trajectory of the moving object. Note that Patent Document 1 does not disclose a method for compressing the position information trajectory data.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a compression method capable of compressing position information trajectory data. [Means for solving the problem]

[0006] A compression method according to one embodiment of the present invention is a compression method for compressing position information trajectory data of a moving body, and includes: a first acquisition step of acquiring a plurality of position information each indicating the position of the moving body at a different time; a second acquisition step of acquiring, as first nearby road information, road information within a predetermined range including the position indicated by the one or more first position information from the plurality of position information, based on one or more first position information indicating the position of the moving body during a certain period of time and map information; a third acquisition step of acquiring, as second nearby road information, second position information from the plurality of position information, based on the map information, road information within a predetermined range including the position indicated by the second position information; a calculation step of calculating a rate of change from the first nearby road information of information combining the first nearby road information and the second nearby road information; and a determination step of determining whether to save the second position information based on the rate of change. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram illustrating an example of a configuration of an information processing apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of map information. [Figure 3] FIG. 10 is a diagram illustrating an example of position information trajectory data. [Figure 4] FIG. 10 is a diagram illustrating the concept of compression processing of position information trajectory data. [Figure 5] 1 is a flowchart illustrating a compression method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of a compression method will be described with reference to FIGS. 1 to 5. The compression method according to the embodiment is a compression method for compressing position information trajectory data of a moving object. Examples of moving objects include vehicles and robots. Note that vehicles may include four-wheeled motor vehicles, motorcycles, bicycles, etc. The position information trajectory data includes multiple pieces of position information each indicating the position of the moving object at a different time. An example of the position information is position information acquired using a GPS (Global Positioning System). The position information may be provided with a timestamp indicating the time of acquisition.

[0009] Here, the trajectory of the moving object can be represented by plotting the multiple positions indicated by the multiple pieces of position information in the order of time indicated by the timestamps. In this case, the trajectory of the moving object is represented by a set of points rather than a line. In this embodiment, data including multiple pieces of position information indicating the positions of the moving object at different times is referred to as position information trajectory data. Note that hereinafter, "position information trajectory data" will be referred to as "trajectory data" as appropriate.

[0010] An information processing device 10 that performs the compression method will be described with reference to Fig. 1. In Fig. 1, the information processing device 10 includes a calculation device 11, a storage device 12, and a communication device 13. The calculation device 11, the storage device 12, and the communication device 13 are connected via a data bus 14. Note that the information processing device 10 may include at least one of an input device and an output device in addition to the calculation device 11, the storage device 12, and the communication device 13. Note that the information processing device 10 may be mounted on a mobile object, or may be a server device (e.g., a cloud server) that can communicate with the mobile object.

[0011] The arithmetic device 11 may have, for example, at least one of a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit). That is, the arithmetic device 11 may have at least one processor. The storage device 12 may have, for example, at least one of a RAM (Random Access Memory), a ROM (Read Only Memory), a hard disk drive, and an SSD (Solid State Drive). The communication device 13 may perform wired communication or wireless communication.

[0012] The storage device 12 may store map information 121. Here, the map information 121 will be explained with reference to FIG. 2. The map information 121 includes a plurality of nodes (for example, nodes N1 to N5) and a plurality of links (for example, link L) connecting the nodes, as shown in FIG. a1 ~L a3 , L b1 ~L b3 , L c1 ~L c4 , L d1 ~L d3 and L e1 ) and a road model represented using the coordinates. Each of the plurality of nodes is set with latitude, longitude, and altitude. For example, each of the plurality of links may be set with attributes such as road type (e.g., expressway, main road, etc.), speed limit, direction of travel, etc. Note that various existing aspects can be applied to such a road model, and therefore detailed explanations thereof will be omitted.

[0013] Returning to FIG. 1, the calculation device 11 has an acquisition unit 111, an extraction unit 112, an evaluation unit 113, and a storage unit 114, which are logically realized functional blocks or physically realized processing circuits. The acquisition unit 111 acquires trajectory data of a moving object (in other words, multiple pieces of position information). If the information processing device 10 is not mounted on the moving object, the acquisition unit 111 may acquire the trajectory data from the moving object via the communication device 13. The acquisition unit 111 may also be referred to as a "trajectory data acquisition unit."

[0014] The operations of the extraction unit 112, evaluation unit 113, and storage unit 114 will be described with reference to Fig. 3 and Fig. 4. The acquisition unit 111 acquires trajectory data including a plurality of pieces of position information corresponding to positions P1 to P6, respectively, as shown in Fig. 3. The plurality of pieces of position information each include the latitude and longitude of positions P1 to P6.

[0015] Based on map information 121 and a plurality of pieces of position information included in the trajectory data, extraction unit 112 extracts road information within a predetermined range including the positions indicated by each of the plurality of pieces of position information (for example, positions P1 to P6) as nearby road information.

[0016] For example, for the position P1, the extraction unit 112 extracts road information within a predetermined range AR1 shown in FIG. 4 as nearby road information. Here, the road information may be identification information of links included in the map information 121. For example, the extraction unit 112 extracts road information within the predetermined range AR1 as nearby road information. a1 , L a2 , L b1 , L b2 and L c1 may be extracted as nearby road information. The shape of the predetermined range is not limited to a semicircle, and may be, for example, a circle, an ellipse, a polygon, etc. The extraction unit 112 may be referred to as a "trajectory data nearby road extraction unit."

[0017] For example, for the position P2, the extraction unit 112 extracts L b2 For example, for the position P3, the extraction unit 112 may extract L b2 , L d1 and L d2 For example, for the position P4, the extraction unit 112 may extract L c2 , L c3 , L d2 and L d3 For example, for the position P5, the extraction unit 112 may extract L within a predetermined range AR5. c3For example, for the position P6, the extraction unit 112 may extract L within a predetermined range AR6. c4 and L e1 may be extracted as nearby road information.

[0018] The evaluation unit 113 determines which pieces of position information are to be stored among the plurality of pieces of position information included in the trajectory data. In other words, the evaluation unit 113 determines which pieces of position information are not to be stored (i.e., thinned out) among the plurality of pieces of position information included in the trajectory data. Here, the description will be given assuming that the position information indicating position P1 is to be stored. In this case, the evaluation unit 113 evaluates the other pieces of position information based on the position information indicating position P1. The evaluation unit 113 may also be referred to as a "trajectory data evaluation unit."

[0019] For example, when the location information indicating the location P2 is evaluated, the evaluation unit 113 may obtain a set including the roads (e.g., links) indicated by the nearby road information for the location P1 and the roads (e.g., links) indicated by the nearby road information for the location P2 as the road set for the location P2. In this case, the road set for the location P2 is calculated as follows: (L a1 , L a2 , L b1 , L b2 , L c1 The evaluation unit 113 may obtain a road set for the position P1. In this case, the road set for the position P1 is equal to the roads (for example, links) indicated by the nearby road information for the position P1, so the road set for the position P1 is (L a1 , L a2 , L b1 , L b2 , L c1 )

[0020] Next, the evaluation unit 113 may calculate a change rate r between the road set for the position P2 and the road set for the position P1. In this case, the evaluation unit 113 may calculate the change rate r based on the number of elements in the road set for the position P2 and the number of elements in the road set for the position P1. As described above, if the road set for the position P2 is (L a1 , La2 , L b1 , L b2 , L c1 ), the number of elements is "5". Similarly, if the road set for the position P1 is (L a1 , L a2 , L b1 , L b2 , L c1 ), the number of elements is "5". The evaluation unit 113 may calculate the rate of change r as "rate of change r = (number of elements in the road set for position P2) / (number of elements in the road set for position P1)". In this case, the rate of change r is "1" (i.e., no change).

[0021] Next, the evaluation unit 113 may determine whether the calculated rate of change r is equal to or greater than a threshold value T. The threshold value T is a value greater than 1. As described above, the rate of change r is "1," so the evaluation unit 113 determines that the calculated rate of change r is not equal to or greater than the threshold value T. In this case, the evaluation unit 113 may determine not to store the position information indicating the position P2.

[0022] For example, when position information indicating position P3 is evaluated, the evaluation unit 113 may determine a set including roads indicated by the nearby road information for position P1, roads indicated by the nearby road information for position P2, and roads indicated by the nearby road information for position P3 as a road set for position P3. In other words, the evaluation unit 113 may determine a set combining the road set for position P2 and the roads indicated by the nearby road information for position P3 as a road set for position P3. In this case, the road set for position P3 is calculated as (L a1 , L a2 , L b1 , L b2 , L c1 , L d1 , L d2 )

[0023] Next, the evaluation unit 113 may calculate the rate of change r between the road set for the position P3 and the road set for the position P2. As described above, if the road set for the position P3 is (L a1 , La2 , L b1 , L b2 , L c1 , L d1 , L d2 ), the number of elements is "7". The evaluation unit 113 may calculate the rate of change r as "rate of change r = (number of elements in the road set for position P3) / (number of elements in the road set for position P2)". In this case, the rate of change r is "1.4". For example, if the calculated rate of change r (here, 1.4) is equal to or greater than the threshold T, the evaluation unit 113 may determine to save the position information indicating position P3. On the other hand, if the calculated rate of change r (here, 1.4) is smaller than the threshold T, the evaluation unit 113 may determine not to save the position information indicating position P3.

[0024] For example, when position information indicating position P4 is evaluated, the evaluation unit 113 may determine, as a road set for position P3, a set including roads indicated by the neighborhood road information for position P1, roads indicated by the neighborhood road information for position P2, roads indicated by the neighborhood road information for position P3, and roads indicated by the neighborhood road information for position P4. In other words, the evaluation unit 113 may determine, as a road set for position P4, a set combining the road set for position P3 and the roads indicated by the neighborhood road information for position P4. In this case, the road set for position P4 is calculated as (L a1 , L a2 , L b1 , L b2 , L c1 , L c2 , L c3 , L d1 , L d2 , L d3 )

[0025] Next, the evaluation unit 113 may calculate the change rate r between the road set for the position P3 and the road set for the position P2. As described above, if the road set for the position P4 is (L a1 , L a2 , L b1 , L b2 , L c1 , L c2 , Lc3 , L d1 , L d2 , L d3 ), the number of elements is "10". The evaluation unit 113 may calculate the rate of change r as "rate of change r = (number of elements in the road set for position P4) / (number of elements in the road set for position P3)". In this case, the rate of change r is "1.43". For example, if the calculated rate of change r (here, 1.43) is equal to or greater than the threshold T, the evaluation unit 113 may determine to save the position information indicating position P4. On the other hand, if the calculated rate of change r (here, 1.43) is smaller than the threshold T, the evaluation unit 113 may determine not to save the position information indicating position P4.

[0026] The evaluation unit 113 may perform the above-mentioned process on all of the multiple pieces of position information included in the trajectory data. Note that, for example, when other piece of position information is evaluated using the position information indicating P1 as a reference, if the evaluation unit 113 determines to save the position information indicating P3, the evaluation unit 113 may evaluate the other piece of position information using the position information indicating P3 as a reference. In other words, the evaluation unit 113 may change the reference piece of position information.

[0027] The saving unit 114 may save the position information that the evaluation unit 113 has determined to be saved in the storage device 12. As a result, the position information that the evaluation unit 113 has determined not to save is not saved, and therefore the number of pieces of position information saved becomes smaller than the number of pieces of position information included in the trajectory data acquired by the acquisition unit 111. In other words, the position information trajectory data is compressed.

[0028] The operation of the information processing device 10 will be further described with reference to the flowchart of Fig. 5. The flowchart of Fig. 5 shows the operation of the information processing device 10 after the acquisition unit 111 acquires position information trajectory data including n pieces of position information (n is an integer equal to or greater than 1).

[0029] 5, the extraction unit 112 of the information processing device 10 extracts road information in the vicinity of the position indicated by the ith position information among the n pieces of position information included in the trajectory data (step S101), where i is an integer equal to or greater than 1 and equal to or less than n.

[0030] Next, the evaluation unit 113 of the information processing device 10 calculates the rate of change r between the i-th road set and the (i-1)-th road set (step S102). Here, the i-th road set refers to a road set including roads indicated by the nearby road information for the 1st to i-th positions. The (i-1)-th road set refers to a road set including roads indicated by the nearby road information for the 1st to (i-1)th positions.

[0031] Here, it can be said that the multiple pieces of position information included in the trajectory data indicate changes in the position of the moving object over time. Therefore, the (i-1)th road set can be said to be a set of roads within a predetermined range including the 1st to (i-1)th positions during the period when the moving object moves from the 1st position to the (i-1)th position. Furthermore, it can be said that the i-th road set is a set of the roads indicated by the nearby road information extracted in the processing of step S101 and the (i-1)th road set.

[0032] After the process of step S102, the evaluation unit 113 determines whether the rate of change r is equal to or greater than a threshold value T (step S103). If it is determined in the process of step S103 that the rate of change r is smaller than the threshold value T (step S103: No), the process of step S105, which will be described later, is performed. On the other hand, if it is determined in the process of step S103 that the rate of change r is equal to or greater than the threshold value T (step S103: Yes), the storage unit 114 of the information processing unit 10 stores the position information indicating the i-th position (step S104).

[0033] In the process of step S105, "i" is incremented. The process of step S105 may be performed by the arithmetic device 11 of the information processing device 10. After the process of step S105, the arithmetic device 11 determines whether i is equal to or less than n (step S106). In the process of step S106, if it is determined that i is equal to or less than n (step S106: Yes), the process of step S101 is performed. On the other hand, in the process of step S106, if it is determined that i is greater than n (step S106: No), the operation shown in FIG. 5 is terminated.

[0034] (Technical Effects) In this embodiment, whether or not to save location information indicating the i-th location is determined based on the rate of change r between the i-th road set and the (i-1)-th road set (in other words, the rate of change r of the i-th road set from the (i-1)-th road set). Therefore, in this embodiment, location information indicating locations near points where links are relatively dense, such as intersections, tends to be saved. On the other hand, location information indicating locations near points where links are relatively sparse tends not to be saved. As a result, of the multiple location information included in the trajectory data, location information indicating locations that are important in representing the trajectory of a moving object can be retained, while other location information can be deleted. In other words, the compression method according to this embodiment can reduce (i.e., compress) the data volume of location information trajectory data while retaining the overall characteristics of the trajectory of a moving object.

[0035] The location information trajectory data may be used in traffic situation analysis techniques such as map matching. If uncompressed trajectory data is used in traffic situation analysis techniques, the time required for analysis will be relatively long. In contrast, if compressed trajectory data is used in traffic situation analysis techniques, the amount of data is relatively small, so the time required for analysis will be relatively short. In other words, compressing the trajectory data can shorten the time required for analysis. Research by the inventors of the present application has shown that the accuracy of traffic situation analysis using trajectory data compressed by the compression method of this embodiment is equivalent to the accuracy of traffic situation analysis using uncompressed trajectory data. In other words, the compression method of this embodiment can shorten the time required for analysis while suppressing a decrease in the accuracy of traffic situation analysis.

[0036] Aspects of the invention derived from the above-described embodiments will be described below.

[0037] A compression method according to one embodiment of the invention is a compression method for compressing position information trajectory data of a moving body, and includes: a first acquisition step of acquiring a plurality of position information each indicating the position of the moving body at a different time; a second acquisition step of acquiring, based on map information and one or more first position information among the plurality of position information, road information within a predetermined range including the position indicated by the one or more first position information as first nearby road information; a third acquisition step of acquiring, based on map information and second position information among the plurality of position information, road information within a predetermined range including the position indicated by the second position information as second nearby road information; a calculation step of calculating a rate of change from the first nearby road information of information combining the first nearby road information and the second nearby road information; and a determination step of determining whether to save the second position information based on the rate of change.

[0038] In the compression method, the second location information may be, among the plurality of location information, location information that chronologically immediately follows the one period. In the compression method, in the determining step, if the rate of change is greater than a predetermined threshold, it may be determined that the second location information is to be stored.

[0039] The present invention is not limited to the above-described embodiments, but may be modified as appropriate within the scope of the claims and the gist or concept of the invention as can be read from the entire specification, and compression methods involving such modifications are also included in the technical scope of the present invention. [Explanation of symbols]

[0040] 10...information processing device, 111...acquisition unit, 112...extraction unit, 113...evaluation unit, 114...storage unit

Claims

1. A compression method for compressing position information trajectory data of a moving object, comprising: a first acquisition step of acquiring a plurality of pieces of location information each indicating a location of the moving object at a different time; a second acquisition step of acquiring, as first nearby road information, road information within a predetermined range including the position indicated by one or more first position information among the plurality of position information, based on one or more first position information indicating the position of the moving object during a certain period and map information; a third acquisition step of acquiring, as second nearby road information, road information within a predetermined range including the position indicated by the second location information, based on second location information indicating the position of the moving object at a time after the one period of time and the map information, among the plurality of location information; a calculation step of calculating a rate of change of information obtained by combining the first nearby road information and the second nearby road information from the first nearby road information; a determination step of determining whether or not to store the second position information based on the rate of change; Compression methods including:

2. The second location information is, among the plurality of location information, location information immediately following the one period in time series. The compression method of claim 1 .

3. In the determining step, if the rate of change is greater than a predetermined threshold, it is determined that the second position information is to be stored. The compression method of claim 1 .

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