JP3573525B2 - Current position calculation device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a current position calculation device that is mounted on a moving body such as a vehicle and measures a traveling distance, a traveling direction, and the like of the moving body, and thereby calculates a current position of the moving body.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a current position calculation device that calculates a current position of a vehicle traveling on a road, the current position of the vehicle is measured by a traveling direction of the vehicle measured by a direction sensor such as a gyro and a vehicle speed sensor or a distance sensor. It is calculated based on the traveling distance of the vehicle.
[0003]
Generally, the travel distance of a vehicle is measured by measuring the output shaft of a transmission or the number of rotations of a tire, and multiplying the number of rotations by a distance coefficient which is a distance that the vehicle travels per rotation of the tire. Is required by
[0004]
Further, in order to correct the error of the current position obtained from the traveling direction and the traveling distance of the vehicle in this manner, as described in JP-A-63-148115, the vehicle determined to match the road is used. The technique of so-called map matching, which corrects the current position, is known, and the accuracy of current position calculation can be increased by this map matching technique.
[0005]
[Problems to be solved by the invention]
However, it is necessary to execute a process of searching for all roads located within a predetermined range with respect to the virtual current position of the vehicle, and the time required for the search is determined by the density of roads located within the predetermined range. In particular, if the road is located in an urban area, the processing time becomes significantly longer. Further, the processing time required to calculate the reliability of the current position candidate point also increases.
[0006]
Since the processing time for searching for a road and the processing time for calculating the reliability are significantly increased, other processing to be performed by the device, such as reading data of a direction sensor, reading of a vehicle speed sensor or a distance sensor, may be performed. There has been a problem that it may not be possible to appropriately read data or calculate a travel distance of a vehicle based on data from a vehicle speed sensor or a distance sensor.
[0007]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a current position calculation device capable of reducing the processing load without impairing the accuracy of map matching.
[0008]
[Means to solve the problem]
An object of the present invention is a current position calculating device mounted on a vehicle and calculating a current position of the vehicle,
Azimuth detecting means for detecting the traveling azimuth of the vehicle,
Distance calculating means for calculating the traveling distance of the vehicle,
Road data storage means for storing road data;
Based on the relative displacement obtained based on the traveling direction and the traveling distance, the current position of the vehicle is estimated as a virtual current position, and the virtual current position is compared with a road constituting road data of the road data storage unit. And a map matching means for calculating a candidate point at the current position together with a reliability indicating its credibility, and identifying the candidate point having the highest reliability as the current position,
The map matching unit estimates a next virtual current position and calculates a candidate point associated therewith also for candidate points other than the candidate point having the highest reliability, and under the predetermined condition, When no candidate point of the current position is found on the road corresponding to the current position, the virtual current position outside the road is set as a candidate point, and when there are n (predetermined number) or more candidate points outside the road, The present position calculating apparatus is characterized in that the candidate points outside the road are sorted in descending order of reliability, and the nth and subsequent candidate points are deleted.
[0009]
In this device, preferably, the map matching means obtains an error cost based on a distance from the virtual current position to a road around the virtual current position and an azimuth difference between the road azimuth and the vehicle azimuth. An accumulated error cost reflecting a past error cost is obtained, and the reliability of the candidate point is calculated based on the accumulated error cost.
[0010]
Preferably, when no candidate point of the current position is found on the road corresponding to the virtual current position under the predetermined condition, A constant error cost that is larger than the above candidate point is determined, an accumulated error cost that reflects the past error cost is determined for the error cost, and the reliability of the candidate point is determined based on the accumulated error cost. calculate.
[0011]
The predetermined condition is, for example, that a road exists within a predetermined search range from the virtual current position, and that the azimuth difference between the road azimuth and the vehicle azimuth is within a predetermined value.
[0012]
Preferably, when obtaining a new candidate point from the candidate points outside the road, the map matching means sets a candidate point on the road satisfying the predetermined condition as a new candidate point, and The virtual current position itself obtained from the point is also set as a new candidate point.
[0013]
[Action]
In the map matching processing, in principle, a virtual current position is calculated based on a relative traveling distance and a traveling direction newly obtained with respect to the current position of the vehicle, and the virtual current position is calculated based on road data in the vicinity thereof. Then, a position on the road determined to be most probable (the highest reliability) is obtained, and this is determined as the current position. However, in order to prevent erroneous recognition due to errors, data of candidate points other than the candidate point of the current position determined to be most probable are not immediately discarded, and a new candidate point based on it will be Then, the most probable candidate point among these candidate points is identified as the current position. On the other hand, in the map matching, there is a case where the matching with the road data does not succeed for a specific virtual current position (a road satisfying a predetermined condition is not found). In such a case, the virtual current position itself is Treat as a candidate point.
[0014]
If new candidate points are sequentially obtained by such a method, the number of candidate points may significantly increase as the vehicle travels. This may impose an excessive processing load on the processor in executing the map matching process to be performed in real time. In particular, this problem is remarkable in an area where the roads are dense, such as in an urban area.Therefore, in the present invention, the candidate points outside the road have relatively low credibility and a large load. In view of the above, if a candidate number of outside roads exceeding a predetermined number is obtained, candidate candidate points outside the road exceeding the predetermined number and having lower reliability are deleted.
[0015]
As a result, while maintaining the reliability of the map matching process, the number of processing targets in the process, that is, the processing load can be reduced, and the time required for executing the process can be reduced.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0017]
FIG. 1 is a block diagram showing the configuration of the current position calculating device according to the embodiment of the present invention. As shown in FIG. 1, the current position calculating device 10 includes an angular velocity sensor 11 that detects a change in a traveling direction by detecting a yaw rate of a vehicle, and a geomagnetic sensor 12 that detects a traveling direction of a vehicle by detecting geomagnetism. And a vehicle speed sensor 13 that outputs pulses at time intervals proportional to the rotation of the output shaft of the transmission of the vehicle.
[0018]
The display 17 displays a map around the current position, a mark indicating the current position, and the like; a switch 14 that receives a command to switch the scale of the map displayed on the display 17 from a user (driver); and stores digital map data. And a driver 16 for reading map data from the CD-ROM 15. Further, a controller 18 for controlling the operation of each peripheral device described above is provided. In the present embodiment, the digital map data described above includes road data composed of coordinates indicating the ends of a plurality of line segments, or road width data indicating the road width of the road, and whether the road is an expressway or a general road. It includes a highway flag indicating whether there is a vehicle.
[0019]
The controller 18 includes an A / D converter 19 that converts a signal (analog) of the angular velocity sensor 11 into a digital signal, an A / D converter 20 that converts a signal (analog) of the geomagnetic sensor 12 into a digital signal, and a vehicle speed sensor. A counter 26 that counts the number of pulses output from the switch 13 every 0.1 second, a parallel I / O 21 that inputs the presence or absence of pressing of the switch 14, and a DMA that transfers map data read from the CD-ROM 15 ( It has a Direct Memory Access controller 22 and a display processor 23 for displaying a map image on the display 17.
[0020]
The controller 18 further has a microprocessor 24 and a memory 25. The microprocessor 24 includes a signal of the angular velocity sensor 11 obtained through the A / D converter 19, a signal of the geomagnetic sensor 12 obtained through the A / D converter 20, and an output pulse of the vehicle speed sensor 13 counted by the counter 26. The number, the presence or absence of pressing of the switch 14 input through the parallel I / O 21, the map data from the CD-ROM 15 obtained through the DMA controller 22 are received, and the processing is performed based on these signals, and The current position is calculated and displayed on the display 17 via the display processor 23. The display of the vehicle position is performed by superimposing an arrow mark or the like on the map already displayed on the display 17 as shown in FIG. Thereby, the user can know the current position of the vehicle on the map. The memory 25 includes a ROM storing a program for defining the contents of processing (described later) for realizing such an operation, and a RAM used as a work area when the microprocessor 24 performs processing. I have.
[0021]
Hereinafter, the operation of the current position calculating device 10 configured as described above will be described.
[0022]
The operation of the device 10 generally includes a process of calculating the heading and traveling distance of the vehicle, a process of determining the current position of the vehicle from the calculated heading and distance, and displaying the obtained vehicle position and heading. Since these processes can be divided into three processes, these processes will be sequentially described.
[0023]
With reference to FIG. 3, a description will be given of a flow of processing for calculating the traveling direction and the traveling distance of the vehicle.
[0024]
This process is a routine of the microprocessor 24 that is started and executed at a fixed period, for example, every 100 ms.
[0025]
In this routine, first, the output value of the angular velocity sensor 11 is read from the A / D converter 19 (step 301). Since the azimuth change is output as the output value of the angular velocity sensor 11, only the relative value of the traveling direction of the vehicle can be detected. Therefore, next, the output value of the geomagnetic sensor 12 is read from the A / D converter 20 (step 302), and the absolute direction calculated from the output value of the geomagnetic sensor 12 and the azimuth change output from the angular velocity sensor 11 ( The estimated azimuth of the vehicle is determined using the angular velocity output (step 303).
[0026]
For example, when the vehicle speed is low for a long time, the error of the angular velocity sensor is large. Therefore, when the vehicle speed is low for a predetermined time or more, only the azimuth of the geomagnetic sensor is used.
[0027]
Next, the number of pulses output from the vehicle speed sensor 13 is counted by the counter 26 every 0.1 seconds, and the counted value is read (step 304). The read value is multiplied by a distance coefficient to obtain a distance advanced for 0.1 second (step 305).
[0028]
Next, the mileage value per 0.1 second obtained in this way is added to the value obtained last time to check whether or not the mileage of the vehicle has reached 20 m (step 306). If not (No in Step 306), the current process is terminated, and a new process is started.
[0029]
As a result of the travel distance calculation processing, when the integrated travel distance becomes a fixed distance, for example, 20 m (Yes in step 306), the traveling direction and the travel distance (20 m) at that time are output (step S306). 307). In step 307, the integrated distance is further initialized, and the integration of the traveling distance is newly started.
[0030]
Next, a description will be given of a process of calculating a virtual current position of a vehicle based on the calculated heading and traveling distance, and obtaining a candidate point of the vehicle based on the calculated virtual current position.
[0031]
FIG. 4 shows the flow of this processing.
[0032]
This processing is a routine of the microprocessor 24 that is started and executed in response to the output of the traveling direction and the traveling distance from FIG. That is, this process is started every time the vehicle travels 20 m.
[0033]
In this processing, first, the sensor data output in the previous step 307, that is, the traveling direction and the traveling distance are read (step 401).
[0034]
Next, among the candidate points obtained in the previous process of FIG. 4, a map matching process is performed on a candidate point in a matching state described later, that is, a candidate point on a road (step 402). The reliability of the obtained candidate points is calculated (step 403). This will be described later in detail.
[0035]
Next, among the previous candidate points, a free state candidate point (also referred to as a free candidate point) described later, that is, the number cnt of candidate points outside the road is calculated (step 404). Whether or not the candidate point is a free candidate point is determined by a state flag attached to the candidate point stored in the memory.
[0036]
Therefore, the number cnt is compared with a predetermined constant number cnt_th (step 405). In the present embodiment, “4” is used as the fixed number cnt_th. If the number cnt of free candidate points is smaller than the certain number, the process proceeds to step 408.
[0037]
If the number cnt of free candidate points is equal to or larger than the certain value, the free candidate points are sorted in descending order of their reliability (step 406). As a result of this sorting, the free candidate points (and various types of information described later) after the cnt_th (in this case, the fourth and subsequent) from the order of higher reliability are deleted from the memory (step 407). In other words, a maximum of cnt_th−1 (here, three) free candidate points are left. By this deletion, the process of finding a new candidate point from this candidate point in the map matching process of the next step 408 is omitted, and the processing load can be reduced.
[0038]
That is, map matching processing is performed on the remaining free candidate points (step 408). Further, the reliability of the new candidate point thus obtained is obtained (step 409).
[0039]
Finally, a candidate point having the highest reliability is selected as a display candidate point from among the candidate points for which the degrees of reliability have been obtained in steps 403 and 409, and the display candidate point data is output (step 410). More specifically, the candidate point C having the highest reliability value is set as the display candidate point CD, that is, the candidate point to be displayed on the display 17, and its position, accumulated error cost, reliability, which will be described later. A state flag indicating whether the state is the matching state or the free state is stored in a predetermined area of the RAM of the memory 25, and the positions of the candidate points other than the display candidate points, the accumulated error cost, the reliability, The status flag and the like are also stored in a predetermined area of the RAM.
[0040]
FIG. 5 shows details of the map matching process.
[0041]
In the map matching process, first, the movement amount of the vehicle is separately obtained in the latitude and longitude directions. Further, the amount of movement in each of these directions is added to the position of the candidate point of the vehicle obtained in the process of obtaining the candidate point of the previous vehicle, and the virtual current position (the position where the current vehicle is estimated to exist) is added. A) is obtained (step 421). Details of this candidate point will be described later. If there is no candidate point obtained in the previous process for obtaining a candidate point for the vehicle, for example, immediately after the start of the apparatus, the position set separately is used as the position of the candidate point obtained last time, and the virtual current Find the position (A).
[0042]
Next, the obtained road data of the map around the virtual current position (A) is read from the CD-ROM 15 via the driver 16 and the DMA controller 23 (step 422). At this time, if the candidate point used to obtain the virtual current position (A) is a candidate point on the road (a candidate point in a matching state), the candidate point is a road within the distance search range D, and the candidate point is Select the line segment representing the road to be connected or the line segment connected to it. In the case of a candidate point that is not a candidate point on the road (a free state candidate point), a line segment within the distance search range D from the virtual current position (A) is selected. At this time, the search range D of the road may be variable based on the reliability (previously corrected) regarding the candidate point used to obtain the virtual current position. That is, for a virtual current position obtained from a candidate point with high reliability, a line segment included in a narrower range is selected, and conversely, for a virtual current position obtained from a candidate point with low reliability, a wider range is selected. Select the line segment included in. The reason for making the search range variable based on the reliability is that if the reliability is low, it is considered that the credibility of the accuracy of the current position obtained last time is low. This is because it is more appropriate for finding the correct current position.
[0043]
As described above, in the present embodiment, as shown in FIG. 6, as the road data, a plurality of line segments 51 to 55 connecting between two points are approximated, and these line segments are defined as a start point and an end point thereof. Those represented by coordinates are used. For example, the line segment 53 is represented by its start point (x3, y3) and end point (x4, y4).
[0044]
Next, from the line segments extracted in step 422, only the line segments whose azimuths are within the predetermined direction and the determined traveling direction are selected (step 423). With respect to all the n line segments, a perpendicular line is lowered from the virtual current position (A), and the length of the perpendicular line L (n) is obtained (step 424).
[0045]
In Steps 422 and 423, if there is no line segment that satisfies the above condition, matching is not established, and the virtual current position (A) itself becomes a candidate point (free state candidate point).
[0046]
Next, based on the lengths of these perpendiculars, an error cost value ec (n) defined by the following equation is calculated for all the line segments selected in step 423 (step 425).
[0047]
ec (n) = α × | θcar−θ (n) | + β | L (n) |
Here, θcar is the vehicle direction at the virtual current position (A), θ (n) is the direction of the line segment, and L (n) is the distance from the virtual current position (A) to the line segment, that is, the length of the perpendicular. , Α and β are weighting factors. The values of these weighting factors may be changed depending on which of the deviation between the traveling direction and the direction of the road and the deviation between the current position and the road is more important in selecting the road to which the current position belongs. For example, when importance is attached to a road whose direction is close to the traveling direction, α is increased.
[0048]
For the candidate points in the free state, a fixed value larger than the value of the error cost obtained in the matching state is given to the error cost ec (n) to be calculated in step 425.
[0049]
When a new candidate point is determined based on the free state candidate point, the virtual current position itself with respect to the free state candidate point is also unconditionally set as a new candidate point.
[0050]
Here, a more specific description of the candidate points will be added. In an initial state such as immediately after the start-up of the device, the virtual current position (A) is uniquely determined by the user (driver) inputting predetermined information using the switch 14, and the like. Is located on the line segment corresponding to the road. However, after the vehicle has traveled, the virtual current position (A) may not exist in the line segment corresponding to the road due to an error of a sensor such as a gyro. As a result, for example, as shown in FIG. 7, when the road is branched, that is, when two line segments 64 and 65 appear from the node 68 of the line segment 61 corresponding to the road, In many cases, it is not possible to clarify whether or not a vehicle exists on a road corresponding to.
[0051]
Therefore, in such a case, in this embodiment, predetermined points existing on two conceivable line segments are set as candidate points, and their current position, error cost, accumulated error cost described later, and the like are set. Are respectively stored in a predetermined area of the RAM of the memory 25. For the sake of simplicity, in the following description, one or more new candidate points will be generated from a single candidate point, unless otherwise specified.
[0052]
Next, a point advanced from a certain candidate point by a length corresponding to the distance R traveled by the vehicle along a corresponding line segment is set as a new candidate point C (n) (step 426). Therefore, if the number of line segments at which a candidate point is located or a line segment connected thereto and the difference between the azimuth and the vehicle azimuth is equal to or smaller than a predetermined value is n, n new candidate points C (n) will be generated. If there is a candidate point in the free state, which will be described later, there is no line segment on which the candidate point is located. Therefore, when calculating the next candidate point for this candidate point (steps 422 to 426), a predetermined value is calculated from the corresponding virtual current position. Since all the line segments within the range D are extracted, the number of candidate points may increase.
[0053]
The calculation of the reliability in steps 403 and 409 of FIG. 4 will be described. According to the previously calculated error cost ec (n) and the accumulated error cost es related to the candidate point obtained in the previous process, the accumulated error cost in the current process defined by the following equation: es (n) is calculated.
[0054]
es (n) = (1−k) × es + k × ec (n)
Here, k is a weight coefficient larger than 0 and smaller than 1. The accumulated error cost es (n) indicates how much the error cost calculated in the previous process is reflected in the error cost calculated in the current process.
[0055]
Further, based on the calculated accumulated error cost es (n), a reliability trst (n) defined by the following equation is calculated.
[0056]
trst (n) = 100 / (1 + es (n))
As is clear from this equation, as the accumulated error cost ec (n) increases, the reliability trst (n) decreases and approaches 0 (zero). On the other hand, as this becomes smaller, the reliability trst (n) increases, and its value approaches 100.
[0057]
By performing such processing, the reliability trst (n) relating to n line segments existing within a predetermined range from the current position A for a certain candidate point is obtained. Although the reliability is calculated for each selected line segment in this way, in this specification, it is also treated as the reliability for a candidate point obtained on the line segment.
[0058]
Here, the operation of map matching will be considered by taking a specific road as an example. For example, as shown in FIG. 7, it is assumed that a current position A is represented at a position indicated by a point 63 with respect to a certain candidate point 62 existing on a line segment 61. In such a case, a line segment 64 connected from the current position A to the line segment 61 at which the candidate point 62 is located, wherein the difference between the azimuth and the vehicle azimuth is equal to or less than a predetermined value, 65, the distances L (1) and L (2) from the current position A to the line segments 64 and 65 are calculated, and the calculated distances and angles θ (1) and θ ( Based on 2) and the vehicle direction θcar, the related error cost, accumulated error cost, and reliability are calculated. Further, based on the travel distance R of the vehicle obtained in step 307 of FIG. 3, a length corresponding to the travel distance R from a certain candidate point 62 along the line segments 61 and 64 or the line segments 61 and 65. Is calculated, and points corresponding to this position are set as candidate points 66 and 67, respectively.
[0059]
Further, as shown in FIG. 8, for the candidate point 66 on the line segment 64, a new current position A is represented at the position indicated by the point 71, while the candidate point 67 on the line segment 65 On the other hand, it is assumed that the new current position A ′ is represented at the position indicated by the point 72. In this case, from the current position A, the line segments 73 and 74 that are connected to the line segment 64 and whose difference between the azimuth and the vehicle azimuth is equal to or smaller than a predetermined value are extracted, and a new one is extracted. From the current position A ′, a line segment 75 that is connected to the line segment 65 and whose difference between the azimuth and the vehicle azimuth is equal to or smaller than a predetermined value is extracted. Next, the distances L1 (1) and L1 (2) from the current position A to the line segments 73 and 74 are calculated, and the distance L2 (1) from the current position A 'to the line segment 75 is calculated. . Further, based on the distance calculated in relation to the current position A, the angles θ1 (1) and θ1 (2) of the line segments 73 and 74, the vehicle direction θcar, and the like, the related error cost, accumulated error cost, and reliability And the associated error cost, accumulated error cost, and reliability are calculated based on the distance calculated in relation to the current position A ′, the angle θ2 (1) of the line segment 75, the vehicle direction θcar, and the like. .
[0060]
Further, based on the traveling distance R of the vehicle obtained in step 307 in FIG. 3, the line segment 64 and 73 from the candidate point 66, or the line segment 64 and 74, or from the candidate point 67, A position advanced by a length corresponding to the traveling distance R of the vehicle is calculated along 65 and 75, and a point corresponding to this position is set as a new candidate point. FIG. 9 shows candidate points 81 to 83 thus newly obtained.
[0061]
As can be easily predicted from the above description, the processing time for executing the map matching process depends on the density of the road corresponding to the road data, and in particular, the map corresponding to the read map data is When the density of roads is large, such as in an urban area, the processing time becomes very long. Therefore, in the present embodiment, as described above with reference to FIG. 4, by deleting a predetermined number or more of free candidate points, it is possible to reduce the processing load and prevent an increase in processing time. As for the free candidate points having the lower reliability than the predetermined number or more, it is unlikely that the candidate points are the true current position, and therefore, it is considered that the accuracy of the map matching is not reduced by the deletion.
[0062]
The display candidate points obtained in step 410 of FIG. 4 are displayed on the screen of the display 17 by processing based on the flowchart shown in FIG.
[0063]
This process is a routine of the microprocessor 24 which is started and executed every second.
[0064]
First, it is determined whether or not the switch 14 has been pressed to change the scale of the map by looking at the contents of the parallel I / O 21 (step 1301). If the button is pressed (Yes in step 1301), a predetermined scale flag is set accordingly (step 1302).
[0065]
Next, data indicating the position and orientation of the display candidate point is read from a predetermined area of the RAM of the memory 25 (step 1303), and a map of a scale corresponding to the contents of the scale flag switched in step 1302 is displayed on the display 17. For example, it is displayed in a state as shown in FIG. 2 (step 1304).
[0066]
Then, the position and the direction of the display candidate point are displayed on the map by using an arrow symbol “図”, for example, as shown in FIG. 2 described above (step 1305). Finally, a north mark indicating north and a distance mark corresponding to the scale are superimposed on them and displayed as shown in FIG. 2 (step 1306).
[0067]
In the present embodiment, the vehicle position and the direction are indicated using the arrow symbols as described above. However, the display form of the vehicle position and the direction is such that the position and the traveling direction are clearly displayed. If so, the form may be arbitrary. The same applies to the north mark and the like.
[0068]
By the way, according to the present embodiment, since a predetermined number or more of the free state candidate points are deleted, it is possible to reduce the processing requiring a long processing time while maintaining the reliability of the map matching processing. This is for the following reason.
[0069]
As described above, when generating the next candidate point from the candidate point in the previous matching state, the line segment where the candidate point in the previous matching state is located and the line segment directly or indirectly connected to the line segment Only the candidate points on these line segments and the error cost ec, the accumulated error cost es, and the reliability trst of the candidate points need to be obtained. Therefore, when the next candidate point is generated, the road on which the vehicle is traveling cannot be specified, so that the same processing must be performed on all the line segments around the virtual current position (A). For this reason, the load of the map matching process on the candidate points in the free state obtained last time is much larger than the load of the map matching process on the candidate points in the matching state obtained last time. In particular, in an area where the road density is high, the difference in the load becomes remarkable.
[0070]
Accordingly, by preferentially deleting candidate points in the free state, it can be expected that the processing time required for calculating the current position will be significantly reduced.
[0071]
The free state candidate point is a point where the vehicle travels in the first place, that is, a position that does not match the road on which the normal vehicle can be located, and its reliability as the current position is low. Accordingly, even if the number of free state candidate points is limited to some extent, the reliability of the current position calculation does not decrease so much.
[0072]
In this specification, means does not necessarily mean physical means, but also includes a case where the function of each means is realized by software. Further, the function of one unit may be realized by two or more physical units, or the function of two or more units may be realized by one physical unit.
[0073]
【The invention's effect】
According to the present invention, it is possible to provide a current position calculation device capable of reducing the processing load without impairing the accuracy of map matching.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a current position calculating device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a display example of a map and a current position according to the embodiment;
FIG. 3 is a flowchart illustrating a process of calculating a traveling direction and a traveling distance of a vehicle.
FIG. 4 is a flowchart illustrating a main process executed for each predetermined traveling distance according to the embodiment;
FIG. 5 is a flowchart showing a detailed process of one step (map matching process) shown in FIG. 4;
FIG. 6 is a schematic diagram illustrating an example of road data according to the embodiment;
FIG. 7 is a diagram for explaining a line segment corresponding to a road, a virtual current position, and a candidate point;
FIG. 8 is a diagram for explaining a line segment corresponding to a road, a virtual current position, and a candidate point;
FIG. 9 is a diagram for explaining a line segment corresponding to a road, a virtual current position, and a candidate point;
FIG. 10 is a flowchart illustrating a current position display process according to the embodiment;
[Explanation of symbols]
Reference Signs List 10 Current position calculating device 11 Angular velocity sensor 12 Geomagnetic sensor 13 Vehicle speed sensor 14 Switch 15 CD-ROM
16 CD-ROM read driver 17 display 18 controller

Claims (5)

A current position calculation device mounted on a vehicle and calculating a current position of the vehicle,
Azimuth detecting means for detecting the traveling azimuth of the vehicle,
Distance calculating means for calculating the traveling distance of the vehicle,
Road data storage means for storing road data;
Based on the relative displacement obtained based on the traveling direction and the traveling distance, the current position of the vehicle is estimated as a virtual current position, and the virtual current position is compared with a road constituting road data of the road data storage unit. And a map matching means for calculating a candidate point at the current position together with a reliability indicating its credibility, and identifying the candidate point having the highest reliability as the current position,
The map matching unit estimates a next virtual current position and calculates a candidate point associated therewith also for candidate points other than the candidate point having the highest reliability, and under the predetermined condition, When no candidate point of the current position is found on the road corresponding to the current position, the virtual current position outside the road is set as a candidate point, and when there are n (predetermined number) or more candidate points outside the road, A candidate position outside the road is sorted in descending order of reliability, and the nth and subsequent candidate points are deleted. The map matching means obtains an error cost based on a distance from the virtual current position to a road around the virtual current position and an azimuth difference between the road azimuth and the vehicle azimuth, and reflects a past error cost on the error cost. The current position calculation device according to claim 1, wherein the accumulated error cost is obtained, and the reliability of the candidate point is calculated based on the accumulated error cost. The map matching means, when the candidate point of the current position is not found on the road corresponding to the virtual current position under the predetermined condition, the candidate point on the road is compared with the candidate point on the road. In addition to obtaining a constant error cost that is larger than the error cost, obtaining an accumulated error cost that reflects a past error cost on the error cost, and calculating the reliability of the candidate point based on the accumulated error cost. The current position calculating device according to claim 2, wherein 4. The predetermined condition is that a road exists within a predetermined search range from the virtual current position, and that the azimuth difference between the road azimuth and the vehicle azimuth is within a predetermined value. 5. Current position calculation device. When finding a new candidate point from the candidate points outside the road, the map matching means sets a candidate point on the road that satisfies the predetermined condition as a new candidate point and obtains the candidate points from the candidate point outside the road. The current position calculation device according to claim 1, wherein the virtual current position itself is also set as a new candidate point.

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