Digital map position information transfer method

[0001] The present invention relates to a method of transmitting position information of a digital map, and more particularly to a method in which date to be transmitted are devised to accurately transfer a position on a digital map to the receiving side.

[0002] In recent years, a vehicle mounting a navigation onboard machine has rapidly been increased. The navigation onboard machine holds a digital map data base and displays a traffic jam or an accident position on a map based on traffic jam information or accident information which is provided from a traffic information center, and furthermore, executes a path search by adding their information to conditions.

[0003] The data base of the digital map is created by several companies in our country, and the map data include an error because of a difference in a basic view and a digitization technique and the error differs depending on a digital map created by each company. For this reason, in the case in which an accident position is to be transmitted through traffic information, for example, there is a possibility that a position on a different road might be identified as the accident position depending on the type of the digital map data base held in the onboard machine if longitude and latitude data on the position are singly presented.

[0004] In order to improve the inaccuracy of the information transmission, conventionally, a node number is defined to a node such as an intersection present in a road system and a link number is defined to a link representing a road between nodes, each intersection and a road are stored corresponding to a node number and a link number in a digital map data base created by each company, a road is specified based on a link number in traffic information, and a point on a road is displayed by an expression method, for example, a distance from a head. However, the node number and the link number which are defined in the road system are to be newly changed according to the new construction or alteration of a road. Moreover, if the node number or the link number is changed, digital map data created by each company are to be updated. For this reason, a method of transmitting the position information of a digital map by using a node number and a link number requires a great social cost for maintenance.

[0005] In order to improve such a respect, the inventors of the invention have proposed the following method in JP-A-11-214068 and JP-A-11-242166.

[0006] In this method, when transmitting the position of a road on which an event such as a traffic jam or an accident occurs, the information providing side transmits, to the receiving side, road shape data comprising a coordinate string having a node in which the road shape of a road section having a predetermined length including the event position is arranged on the road and an interpolation point (the vertex of a polygonal line approximating the curved line of the road, which will be referred to as a node including the interpolation point if there is no notice in this specification) and event position data indicative of an event position based on a relative position in the road section represented by the road shape data, and the side receiving these information carries out map matching by using the road shape data, specifies a road section on a self-digital map, and specifies an event generation position in the road section by using the event position data.

[0007] Moreover, the inventors of the invention have also proposed a method in which a procedure for the map matching is executed efficiently. This method employs a sequential matching technique, and the receiving side calculates the coordinates of an event position by using the received road shape data and event position data and adds the event position as a node in the node string of the road shape data. Then, the map matching is executed in order from a node on the start edge of the node string and a point which is most greatly matched with a node indicative of the event position is specified as the event position on the road of a self-digital map.

[0008] In the case in which the position information of the digital map is to be transmitted by these methods, there is an important problem in that matching precision on the receiving side is to be enhanced. In the sequential matching method, particularly, when the start point of the map matching is wrong, the error tends to be taken over by the subsequent map matching so that mismatching is apt to be caused. Moreover, there is a problem in that the mismatching is easily generated in an intersection having a small intersecting angle.

[0009] The invention solves these problems and has an object to provide a method of transmitting the position information of a digital map which can enhance matching precision on the receiving side.

[0010] The invention provides a method of transmitting position information of a digital map in which a transmitting side transmits a vector shape on the digital map and a receiving side specifies the vector shape on a self-digital map by map matching, wherein the transmitting side selects a portion in which a plurality of candidate points are generated with difficulty during the map matching as an endpoint of the vector shape and transmits the vector shape having the endpoint in the portion to the receiving side.

[0011] Moreover, the transmitting side shifts an endpoing of the vector shape to a portion in which a plurality of candidate points are generated with difficulty during the map matching, and transmits, to the receiving side, the vector shape having an endpoint position deformed.

[0012] Furthermore, the transmitting side deforms an azimuth of the vector shape at an intersection in the middle of the vector shape in such a direction as to increase an angle formed by the vector shape and a connecting vector to be connected to the vector shape when the angle is small at the intersection, and transmits, to the receiving side, the vector shape having the azimuth deformed.

[0013] Consequently, mismatching on the receiving side can be prevented and the position information on the digital map can be transmitted accurately.

[0014] FIG. 1 is a view illustrating a processing on the transmitting side according to a first embodiment,

[0015] FIG. 2 is a flow chart showing a processing procedure on the transmitting side in a position information transmitting method according to the first embodiment,

[0016] FIG. 3 is a view illustrating a processing on the transmitting side according to a second embodiment,

[0017] FIG. 4 is a flow chart showing a processing procedure on the transmitting side in a position information transmitting method according to the second embodiment,

[0018] FIG. 5 is a view illustrating the deformation of shape vector data in the position information transmitting method according to the second embodiment,

[0019] FIG. 6 is a view illustrating a processing on the transmitting side according to a third embodiment,

[0020] FIG. 7 is a flow chart showing a processing procedure on the transmitting side in a position information transmitting method according to the third embodiment,

[0021] FIG. 8 is a block diagram showing the structure of a device for executing the position information transmitting method according to an embodiment,

[0022] FIGS. 9(a) and 9(b) are diagrams showing data to be transmitted in the position information transmitting method according to the embodiment, and

[0023] FIG. 10 is a flow chart showing a map matching procedure in the position information transmitting method according to the embodiment.

[0024] In the drawings, the reference numerals 10 and 20 denote a position information transmitting/receiving device, the reference numerals 11 and 21 denote a position information transmitting portion, the reference numerals 12 and 22 denote a position information receiving portion, the reference numeral 13 denotes a map matching portion, the reference numeral 14 denotes a digital map display portion, the reference numeral 15 denotes a digital map data base, the reference numeral 16 denotes an event information input portion, the reference numeral 17 denotes a position information converting portion, and the reference numeral 18 denotes a shape vector data deforming portion.

[0025] In a method of transmitting position information of a digital map according to the invention, the transmitting side selects the node of a start point and deforms the position of the node such that mismatching is not generated on the receiving side.

[0026] FIG. 8 shows a position information transmitting/receiving device 10 for exchanging event generation information on a road together with another device 20 as an example of a device for executing the position information transmitting method according to the invention.

[0027] The device 10 comprises a position information receiving portion 12 for receiving information including road shape data and event position data from a position information transmitting portion 21 of the device 20, a digital map data base 15 for storing digital map data, a map matching portion 13 for carrying out map matching by using the road shape data and the event position data to specify an event position on a digital map, a digital map display portion 14 for superposing and displaying the event position on the map, an event input portion 16 for inputting generated event information, a position information converting portion 17 for generating road shape data and event position data for transmitting the event information, a shape vector data deforming portion 18 for deforming the road shape data such that the mismatching is not generated on the receiving side, and a position information transmitting portion 11 for transmitting position information including the generated road shape data and event position data to a position information receiving portion 22 of the device 20.

[0028] FIGS. 9(a) and 9(b) show an example of the position information transmitted from the position information transmitting portion 11, and FIG. 9(a) shows shape vector data string information for specifying a road section which includes the road shape data and FIG. 9(b) shows traffic information including relative distance data from a reference point provided in the road section to the event position.

[0029] The position information converting portion 17 acquires coordinates (longitude/latitude) of nodes p1 to pn in the road section including the event generation position from the digital map data base 15 based on the event information input from the event input portion 16, generates road shape data (a shape vector data string), and furthermore, sets a reference point in the road section represented by the shape vector data string and generates traffic information including relative distance data from the reference point to the event generation position.

[0030] The position information converting portion 17 selects the node p1 to be the start point for the map matching on the receiving side such that mismatching is not caused when generating the shape vector data string. This processing will be described in a first embodiment.

[0031] (First Embodiment)

[0032] FIG. 2 shows a procedure for selecting the node p1 by the position information converting portion 17. This procedure is executed in accordance with a program by a computer for implementing the function of the position information converting portion 17 based on the program. With reference to a view of FIG. 1, the procedure will be described.

[0033] In FIG. 1, a solid line indicates a road on a digital map, and a white circle and a black circle indicate a node included in the shape of the road. In the case in which a traffic jam event is generated in a position on the road which is shown in an arrow, a node to be a start point for map matching on the outside of an event generation section (that is, a node to be the first node p1 in a shape vector data string) is shown in the black circle. The position information converting portion 17 selects a node in which mismatching is not generated on the receiving side from the black circle based on the procedure shown in FIG. 2.

[0034] Step 1: Select an object section included in the shape vector data string,

[0035] Step 2: Pick up some nodes positioned in the vicinity of the outside of an endpoint in the object section,

[0036] Step 3: Give a number (p1 to pm) to each node,

[0037] Step 4: In order from a first node pj with j1,

[0038] Step 5: Calculate a distance Lj between pj and an adjacent road and an intercept azimuth angle difference j, and

[0039] Step 6: Decide a decision value j of the node pj by the following (Equation 1). $\begin{array}{cc}j=\mathrm{Lj}+|j|=\mathrm{Lj}+\left|j-j\right|& \left(\mathrm{Equation}1\right)\end{array}$

[0040] and represent predetermined coefficients.

[0041] Step 7, Step 8: Carry out the processings of the Step 5 and the Step 6 for all the nodes p1 to pm,

[0042] Step 9: Select a node pr having the greatest decision value , and

[0043] Step 10: Select a path from the node pr to an endpoint in an original object section through a path search and add the path to the object section.

[0044] By the execution of such a processing, a point in which the receiving side makes an error with difficulty can be selected as the first node p1 in the shape vector data string to be the start point for the map matching.

[0045] (Second Embodiment)

[0046] In a second embodiment, description will be given to a method of deforming the endpoint position of an object section to prevent mismatching on the receiving side when a road running in parallel with an object road in the object section is present.

[0047] As shown in FIG. 3, in the case in which an object road in an object section is present between a parallel track 1 and a parallel track 2, the shape vector data deforming portion 18 shifts an endpoing P in the object section to the position of P, thereby preventing the endpoint P from being mismatched as a point on the parallel track 1. If P is too close to the parallel track 2, there is a possibility that the endpoint P might be mismatched as a point on the parallel track 2. The shape vector data deforming portion 18 selects the position of P such that there is not such a possibility.

[0048] FIG. 4 shows a processing procedure for the shape vector data deforming portion 18. This procedure is executed in accordance with a program by a computer for implementing the function of the shape vector data deforming portion 18 based on the program.

[0049] Step 11: Select the object section of an object road by the position information converting portion 17,

[0050] Step 12: Pick up the endpoint node P of the object section,

[0051] Step 13: Draw a perpendicular on each of peripheral adjacent roads from P and calculate the coordinates of m intersecting points Pj,

[0052] Step 14: Calculate a decision value j of each Pj from a distance Lj between P and Pj and an intercept azimuth j based on the (Equation 1),

[0053] Step 15: Select a node Pr taking a minimum decision value r in all j,

[0054] Step 16: Decide whether the node Pr is present on the left or right side in the direction of progress of a shape vector data string, and

[0055] Step 17: Put P on a point provided apart by LLr, L0 from the endpoint P in the direction of the perpendicular of the object road on the opposite side of the node Pr.

[0056] Herein, represents a predetermined coefficient of 0<<1 and L0 represents a predetermined decision value of approximately 120 m. LLr is obtained if Lr is equal to or smaller than L0, and LL0 is obtained if Lr is greater than L0.

[0057] Next, it is decided whether or not the endpoint is too close to another road by the shift of the endpoint P to P. If the endpoint is too close to another road, L is reduced every {fraction (1/10)}. The processing is repeated until the state of the endpoint is eliminated. More specifically,

[0058] Step 18: Set a reduction coefficient k10,

[0059] Step 19: Carry out the same processing as that of each of the Step 13 and the Step 14 from P to obtain a distance Lj between P and Pj and an intercept azimuth j, and calculate a decision value j of each Pj to select minimum s,

[0060] Step 20: Decide whether or not s>r is satisfied. represents a predetermined value of approximately 1.2 to 2,

[0061] At the Step 20, if s>r is not satisfied,

[0062] Step 21: Set the reduction coefficient k to kk1,

[0063] Step 22: Reduce L every {fraction (1/10)} based on L(k /10)L and repeat the procedure from the Step 19.

[0064] In the case in which L is reduced or s>r is satisfied even if the L is not reduced,

[0065] Step 23: Modify the coordinates of the start point P to P,

[0066] Step 24: Connect a point provided apart from P over the object section by a distance L1 (a predetermined distance) and P, thereby deforming a shape (a dotted line in FIG. 3),

[0067] Step 25: Set the position error of the node P to be the position error of transmitted data (FIG. 9(a)). In this case, P is shifted so that the shape itself of the object section is deformed and the direction does not always need to be changed as shown in FIG. 5.

[0068] By deforming the endpoint of the object section, thus, the mismatching on the receiving side can be prevented.

[0069] In the case in which the parallel tracks 1 and 2 running in parallel with the object section are present as shown in FIG. 3, there can also be proposed a method for displacing the whole object section in parallel. In this case, it is preferable that all the nodes should be shifted in the same direction by a distance L between P and P (a left and right offset distance).

[0070] (Third Embodiment)

[0071] In a third embodiment, description will be given to a method of deforming a node position in an object section to prevent mismatching on the receiving side in the case in which there is a branch path that an object road in the object section intersects at a small angle.

[0072] The entry and exit paths of an interchange intersect a main track at a small angle as shown in FIG. 6. Therefore, in the case in which sequential matching is carried out by using a shape vector data string representing an object section by the receiving side, mismatching is apt to be caused. The shape vector data deforming portion 18 shifts the position of a node in the object section to Pj1, thereby preventing the mismatching. Also in this case, if a point of Pj1 is too close to another connecting road, there is a possibility that the mismatching might be caused. Therefore, the shape vector data deforming portion 18 selects the position of Pj1 such that there is not such a possibility.

[0073] FIG. 7 shows the processing procedure of the shape vector data deforming portion 18 in this case. This procedure is executed in accordance with a program by a computer for implementing the function of the shape vector data deforming portion 18 based on the program.

[0074] Step 31: Select the object section of an object road by the position information converting portion 17,

[0075] Step 32: Extract an intersection node in the object section and give a number to each node (p1 to pm),

[0076] Step 33: In order from a first node pj with j1,

[0077] Step 34: Calculate jk for all connecting roads (intersecting roads) k on a vicinal intersection present in a range of L0 m (L0 represents a predetermined distance of approximately 120 m) around the intersection node pj. jk is obtained by jkjjk when

[0078] j: a turning angle at the node pj on the object road, and

[0079] jk: a turning angle for the object road of the intersecting road k as shown in FIG. 6.

[0080] Step 35: Calculate an evaluation value jk is for each connecting road by (Equation 2).

[0081] Herein, Lji represents a distance from the node pj to an intersection in which the object connecting road k is present.

[0082] Step 36: If all jk are equal to or greater than a specified value 0, the processing proceeds to Step 46. If no so, that is, a connecting road to intersect at a small angle is present,

[0083] Step 37: Extract kr with a minimum evaluation value .

[0084] Subsequently, the shape of the object road is deformed such that the connecting angle of the object road and the connecting road r is increased, and furthermore, a space with an intersection having the connecting road r is increased if the same intersection is shifted longitudinally. Moreover, the evaluation value is obtained after the deformation. If the object road is too close to another connecting road due to the deformation, the amount of deformation is decreased every {fraction (1/10)} and the decrease is repeated until such a state is eliminated. More specifically,

[0085] Step 38: m10 is set,

[0086] Step 39: the connecting angle is increased as follows: when jr0 is not satisfied, and:

[0087] represents a predetermined value of approximately 1.5 degrees.

[0088] Step 40: Increase the intersection space to LjiLjimL when Lji0 is satisfied. L represents a predetermined distance of approximately 10 m.

[0089] Step 41: Calculate an evaluation value jk of each connecting road after the deformation and decide whether or not all jk are greater than jr in order to obtain the result of the deformation. When jk are not greater than jr,

[0090] Step 42: mm1 is set and the procedure of the Steps 39 and 40 is repeated,

[0091] At the Step 41, in the case in which the amount of deformation is decreased or jk>jr is satisfied even if the same amount is not decreased,

[0092] Step 43: Modify the position of the node pj by Lji and set pj1 to a position placed apart by a distance L (a predetermined distance) in a j direction,

[0093] Step 44: Set pj2 to a place positioned at a distance 2L along the object road,

[0094] Step 45: Calculate the direction errors of the nodes pj to pj2 and the position errors of the nodes pj1 and pj and set them to the transmitted data (FIG. 9(a)), and

[0095] Step 46, Step 47: Repeat the procedure from the Step 34 for all the intersection nodes p1 to pm.

[0096] By deforming the object section, thus, it is possible to prevent mismatching on the receiving side.

[0097] While the positions of pj1 and pj2 are modified at the Steps 43 and 44 with the direction deformation of pj, this processing is not always required. In the case in which the modification of the position is not carried out, the direction error of the node pj and the position error of the node p are set at the Step 45.

[0098] At the Step 39, moreover, the direction deformation is not carried out if jr0 is satisfied. In the case of a lattice-shaped road system, there is a possibility that running might be carried out on the outside of the road if the angle is forcedly changed.

[0099] FIG. 10 shows a processing procedure to be carried out by the map matching portion 13 on the receiving side when receiving the position information shown in FIG. 9(a) in which the shape vector data are deformed.

[0100] Step 51: Receive the position information,

[0101] Step 52: Determine a candidate point for a map matching start point,

[0102] Step 53: Carry out map matching,

[0103] Step 54: Calculate a position error and a direction error between the coordinates of each node in the received shape vector data and the nearest point on the road section of a digital map which is defined by the map matching, respectively,

[0104] Step 55: Decide whether or not the position errors and direction errors of all the nodes are proper as compared with error information included in the received position information. If the errors are proper,

[0105] Step 56: Decide that the matching is successful and define the road section.

[0106] If the errors are not proper in the Step 55,

[0107] Step 57: Retrieve and determine a candidate point other than the matching starting candidate point in consideration of the position errors and the direction errors.

[0108] By such a processing, it is possible to accurately specify a position on a digital map which is transmitted. When the transmitting side selects the matching start point and deforms the shape vector data as described in each embodiment, the receiving side can prevent the generation of the mismatching even if a sequential matching method or a shape matching method is to be employed.

[0109] While the description has been given, as an example, to the case in which the position on the road of the digital map is transmitted, the invention can be applied to the case in which positions on various shape vectors represented on a digital map such as rivers or a contour line in addition to the road are to be transmitted.

[0110] While the invention has been described in detail with reference to the specific embodiments, it is apparent to the skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0111] The application is based on Japanese Patent Application (2001-132610) filed on Apr. 27, 2001 and the contents thereof are incorporated by reference.

[0112] As is apparent from the above description, in the position information transmitting method according to the invention, mismatching on the receiving side can be prevented so that matching precision can be enhanced. Accordingly, position information on a digital map can be transmitted accurately.