METHOD AND APPARATUS FOR TRANSMITTING POSITION INFORMATION ON A DIGISTAL MAP

[0001] This patent application is a continuation of U.S. Ser. No. 10/652,257 filed Aug. 29, 2003, which is a continuation of U.S. Ser. No. 10/169,639 filed Jul. 3, 2002.

[0002] The present invention relates to a method for transmitting position information on a digital map and apparatus for implementing the method, and in particular to a method and apparatus for accurately transmitting position information on a digital map by using only a small amount of data.

[0003] In recent years, the number of vehicles that have on-board navigation apparatus has been increasing rapidly. The on-board navigation apparatus maintains a digital map database and is capable of displaying traffic congestion and traffic accident positions on the map based on traffic congestion information and traffic accident information provided by a traffic information center as well as performing a route search using conditions including the aforementioned information.

[0004] In Japan, digital map databases are prepared by several companies. The problem is that map data contains errors due to the different base maps and digitizing technologies. The error depends on the digital map from each publisher.

[0005] In the traffic information, for example, in case latitude/longitude data of the position is presented alone in order to report for example a traffic accident position, on-board navigation apparatus may identify a different point on the road as a traffic accident position depending on the type of the digital database maintained by the apparatus.

[0006] In order to offset such incorrect transmission of information, in the related art, node numbers are defined for nodes such as intersections in a road network and link numbers are defined for links representing roads connecting nodes. A digital map database from each publisher stores intersections and roads in correspondence to node numbers and link numbers. For traffic information, a road number is identified by a link number and a point on the road is displayed in a representation that the road is XX meters away from the start of the link.

[0007] However, node numbers and link numbers defined on a road network must be changed to new numbers in case a road is constructed or modified. When a node number or link number is changed, the digital map database from each publisher must be updated. Thus, the method for transmitting position information on a digital map requires a huge cost of maintenance.

[0008] In order to solve such problems, the inventor of the invention proposed, in the Japanese Patent Application No. 214068/1999, a system where an information providing side transmits “road shape data” including a coordinate string showing the road shape in the road section of a predetermined length including the on-road position and “relative position data” showing the on-road position in the road section represented by the road shape data in order to report the on-road position, and a receiving side uses the road shape data to perform map matching, identifies the road section on a digital map, and uses the relative position data to identify the on-road position in the road section. The inventor proposed, in the Japanese Patent Application No. 242166/1999, a system where “supplementary information” is also transmitted including the road type, road number, number of crossing links in the road section, crossing link angles and intersection names, and a system where the transmission data amount of “road shape data” is reduced without causing erroneous matching at the receiving side.

[0009] In this case, map matching at the receiving side is made for example as follows:

[0010] As shown in FIG. 21, when the longitude/latitude data of the point P₀(x₀, y₀) , P₁(x₁, y₁), . . . , p_k(x_k, y_k) is transmitted as (x₀, y₀) (x₁, y₁) , . . . , (x_k, y_k) the receiving side uses the map data read from its digital map database to select roads included in the error range about the point P₀(x₀, y₀) as candidates, and narrows down the candidates by using the transmitted “supplementary information.” When a single candidate is finally selected, a position closest to the point P₀(x₀, y₀) and the point P_k (x_k, y_k) on the road is obtained, and the section is assumed as a road section represented by the “road shape data.”

[0011] When the final candidate is not selected but the roads Q, R are selected as candidates, the points Q₀, R₀ on the candidate roads closest to the point P₀(x₀, y₀) are obtained to calculate distance between P₀ and Q₀ and the distance between P₀ and R₀. This operation is repeated for each point P₁ (x₁, y₁) , . . . , P_k (x_k, y_k) and a road section where the sum of the root mean square of the distances from each point P₀, P₁, . . . , P_k is smallest is obtained. This section is assumed as a road section represented by “road shape data” to identify the road section.

[0012] The traffic congestion section A-B is identified based on “relative data” transmitted from the start point of the road section obtained from “road shape data.”

[0013] In the system where road shape data is transmitted, however, how to reduce the transmission data amount without degrading the information accuracy is a major problem. The inventor, in order to reduce the data amount, proposed a system whereby the shape data of the linear road sections is reduced and a system where the curve shape of a road is represented by Fourier coefficients, approximated by arcs, or represented by spline function to compress the data amount. In case, as shown in FIG. 23, the road density is low but the road shape is complicated and an interval between nodes is longer, as on the roads in the mountains, using such a system still requires a large amount of data to represent the road shape.

[0014] The invention solves such related art problems and aims at providing a position information transmission method for accurately transmitting a position and a shape on a digital map using a small amount of data and apparatus for implementing the method.

[0015] According to the invention, a position information transmission method wherein the transmitting side transmits road shape information to specify the target road section on a digital map and event information to specify an event position by using a relative position in the target road section and the receiving side performs map matching based on the road shape information to identify the target road section and identifies the event position in the target road section based on the event information is characterized in that the transmitting side intermittently selects nodes included in the target road section to include the coordinate data of the nodes in the road shape information for transmission, and that the receiving side performs map matching to determine the positions of the nodes included in the road shape information and obtains the road connecting the nodes by way of a route search to identify the target road section.

[0016] The transmitting side evaluates the potential for erroneous matching of the nodes in the target road section at the receiving side, and determines the length of the target road section or the number of nodes to be included in the road shape information.

[0017] The present invention also provide a position information transmission apparatus for transmitting road shape information to specify the target road section on a digital map and event information to specify an event position by using a relative position in the target road section. The transmission apparatus is characterized in that the apparatus includes position information converting means for selecting a target road section having the event position and transmit node extracting means for intermittently selecting nodes to be included in the road shape information out of the nodes arranged on the target road section.

[0018] The present invention further provide a position information receiving apparatus for receiving road shape information to specify the target road section on a digital map and event information to specify an event position by using a relative position in the target road section is characterized in that the apparatus comprises map matching means for performing map matching to determine the positions of the nodes included in the road shape information and route search means for obtaining the road connecting the nodes determined to reproduce the target road section.

[0019] This makes it possible to transmit event positions on a digital map efficiently and accurately with a small data amount thus enhancing the data transmission efficiency.

[0043] In the figures, numerals 10, 20 represent position information transmission/receiving apparatus, 11, 22 a position information receiver, 12 a map matching section, 13 a route search section, 14 a digital map database, 15 a digital map display section, 16 an event information input section, 17 a position information converter, 18 a transmit node group/supplementary information extracting section, and 19, 21 a position information transmitter.

[0044] According to a position information transmission method of the invention, a transmitting side selects a small number of nodes (which may be two points, start point and end point) out of the nodes included in a road section to be transmitted, and transmits the node information. A receiving side performs a map matching to determine the positions of the received nodes and sequentially searches for the shortest routes connecting the nodes, then links the shortest routes to identify the road section.

[0045] FIG. 2 shows the configuration of the position information transmission/receiving apparatus 10 that exchanges event information occurring in the jurisdiction with other apparatus 20.

[0046] The apparatus 10 includes a position information receiver 11 for receiving position information sent from the position information transmitter 21 of the other apparatus 20, a digital map database 14 for accumulating digital map data, a map matching section 12 for identifying the corresponding node position from the node information included in the received information by using a map matching, a route search section for searching for the shortest routes connecting nodes, a digital map display section 15 for displaying the event position on a map, an event information input section 16 for inputting event information, a position information converter 17 for displaying the event position by using the relative position of the target road section represented by road shape data, a transmit node group/supplementary information extracting section 18 for selecting nodes in the target road section whose node information is to be transmitted and supplementary information to be transmitted, and a position information transmitter 19 for sending the position information on the selected nodes together with the selected supplementary information to the position information receiver 22 of the other apparatus 20.

[0047] The digital map database 14 includes node data and link data on a digital map. The node data includes the latitude/longitude coordinate data of nodes, data of node type (identification information such as intersections, entrance and exit of a tunnel, interchange tollgates, road attribute change points, boundaries of prefectures, boundaries of secondary mesh, and landmarks), names, number of connection links to connect to nodes, and connection link angle representing the angle of the connection link. The link data includes data such as the road number, the road type (identification information on national highway, prefectural roads, and municipal roads), the link type (identification information on the main line, interchange entrance/exit, links in an intersection, by roads, connection roads and interlinking roads), presence/absence of traffic prohibition and direction of traffic prohibition, various costs of each link represented by distance or travel time, as well as interpolation point coordinate data representing a link shape. The interpolation points are points set to represent an inter-node road shape. Here, unless otherwise specified, nodes and interpolation points where coordinate data is maintained are called nodes. Node data and link data on a digital map includes rivers, administrative boundaries, contour lines and houses. Node data and link data other than node data of roads has inherent type and attribute code although the configuration is the same as that on roads. Thus the system can be applied to node data and link data other than road data. The coordinate data includes data represented by latitude and longitude, relative latitude/longitude representation with respect to the preceding/subsequent node, normalized coordinate representation in a predetermined section number and curvature function representation (relative polar coordinate representation with respect to the preceding/subsequent node).

[0048] FIG. 3 individually shows the processing procedure on the transmitting side and receiving side. FIGS. 1(1), (2), (3), (4), and (5) are schematic views of the individual processing details on a map.

[0049] Step 1: When the information to report an event such as a traffic congestion and traffic accident is input from the event information input section 16, the position information converter 17 selects a road section including the event position as a target road section based on the data in the digital map database 14 and generates traffic information displaying the event position by using the relative distance from the reference point of the target road section. FIG. 1(1) shows the selected target road section. Solid filled circles on the target embodiment show the nodes whose coordinate data is maintained in the digital map database 14.

[0050] Step 2: The transmit node group/supplementary information extracting section 18 selects nodes whose node information is to be transmitted out of the nodes in the target road section. As shown in FIG. 1(2), the nodes at the start point (p₁) and the end point (p₃) of the target road section must be selected. The nodes selected may be these two, but may include those selected intermittently, that is, in intervals of several hundreds of meters to several kilometers. In this example, an intermediate node P2 is additionally selected.

[0051] Step 3: Information that enhances the accuracy of map matching and a route search is extracted as required as supplementary information out of the node data of the selected nodes and link data of the target road section.

[0052] Step 4: The position information transmitter sends shape vector data string information comprising coordinate data of the selected nodes and selected supplementary information to represent the target road section and traffic information to represent the event position by the relative distance from the reference point of the target road section.

[0053] FIGS. 4(a), (b), (c) and (d) shows shape vector data string information without supplementary information. FIG. 4(b) shows traffic information including event position information represented by the relative distance from the reference point of the target road section and event detail information. The shape vector data string information may be represented by various coordinate data as mentioned earlier, but may be any data as long as it attains the present application. In the curvature function representation in FIG. 4(e), a deflection angle shown in FIG. 4(f) is used. The following description uses the example of FIG. 4(a). In the relative coordinate representation in FIG. 4(a), the coordinates of the start node is represented by absolute coordinates (longitude/latitude) and the coordinates of the remaining nodes by relative coordinates with respect to the start node (or preceding node in the line of nodes) in order to reduce the data amount. A reference point of the target road section in the traffic information may be the node p₂ halfway in the target road section instead of the start point (p₁) and end point (p₃).

[0054] FIG. 5(a) shows shape vector data string information as supplementary information including the link data such as the road type, road number and link type. FIG. 5(b) shows shape vector data string information as supplementary information including the node data such as the node type, node name, number of connecting links of the node, and angle between connecting links. The angle between connecting links is displayed by the angle θ1 to θ4 with respect to the absolute azimuth of the true north (dotted line) at the node (node type=intersection, name=4 cho-me, Tsunashima)

[0055] At the receiving side,

[0056] Step 5: The position information receiver 11 receives the shape vector data string information and the traffic information.

[0057] Step 6: The map matching section 12 uses the data in the digital map database 14 to perform map matching and determines the position of the nodes included in the shape vector data string information. In case the shape vector data string information includes supplementary information, the map matching section 12 uses the supplementary information to execute map matching.

[0058] FIG. 1(3) shows the plotting result of the received nodes p₁, p₂ and p₃ on the map of the receiving side. In case the publisher of the digital map data owned by the transmitting side differs from the publisher of the digital map data owned by the receiving side, such a “disposition” occurs frequently.

[0059] FIG. 1(4) shows a state where the position of the nodes p₁′, p₂′ and p₃′ corresponding to the nodes p₁, p₂ and p₃ on the map of the receiving side are determined. Even in case a nearby intersection exists that may be cause erroneous matching with p₁ around the node p₁ as shown in FIG. 7, matching with a correct node position is made possible by referencing supplementary information such as node name.

[0060] Step 7: The route search section 13 uses the link cost represented by the distance of the link data in the digital map database 14 to sequentially searches for the shortest route between nodes determined in step 6. In case the shape vector data string information includes the supplementary information on link data, the route search section 13 uses the supplementary information to execute a route search.

[0061] Step 8: The shortest routes obtained in step 7 are sequentially linked to reproduce the target road section.

[0062] FIG. 1(5) shows a state where the shortest route between the nodes p₁′ and p₂′ is searched for, and the shortest route between the nodes p₂′ and p₃′ is searched for, then these routes are linked to determine the target road section from the node p₁′ to the node p₃′. In case the Prefectural Road 123 (dotted line) bypassing the National Highway 256 (thick solid line) exists as shown in FIG. 7 thus easily causing an error in a search for the shortest routes, it is possible to reproduce the correct target road section by referencing supplementary information such as the road type and road number.

[0063] When the target road section is reproduced, the event position is calculated from the reference point of the target road section based on the received traffic information. The event position on the map is then displayed by the digital map display section 15.

[0064] When nodes are intermittently selected from the target road section, nodes must be selected so that the positions of the nodes will not cause an error in identifying the node positions or calculation of routes at the receiving side. For example, in FIG. 7, a point where the road type changes from the national highway to the main local road is selected as the node P2. This makes it possible to separately incorporate supplementary information between the nodes p₁ and p₂ (road type, road number=national highway, 256) and supplementary information between the nodes p₂ and p₃ (road type, road number=main local road, 923) into the shape vector data string information, thus facilitating reproduction of the target road section at the receiving side.

[0065] In this way, only transmission of the information on the nodes intermittently selected from the target road section is required as road shape data to identify the target road section in this position information transmission method. This considerably reduces the transmit data amount compared with the case where coordinate line information on each node in the target road section is transmitted.

[0066] By including supplementary information to facilitate node identification and supplementary information to facilitate route identification into the road shape data, the receiving side can perform map matching to accurately determine the node positions and accurately calculate the shortest routes between the nodes, thereby faithfully reproducing the transmitted target road section on the digital map of its own.

[0067] This position information transmission method is especially advantageous in transmitting a road shape such as mountain roads with low road density, less intersections and winding in a complicated way.

[0068] While an example of position information transmission/receiving apparatus constituting a traffic information provision system is shown as apparatus for implementing the position information transmission method, the receiving arrangement of this apparatus may be implemented in car navigation apparatus so as to provide the car navigation apparatus with the position information receiving feature by this method.

[0069] The second embodiment explains a method for including as supplementary information the intercept azimuth information in the node position in the shape vector data string information in order to enhance the matching accuracy at the receiving side in implementing a position information transmission method of the first embodiment.

[0070] The intercept azimuth in the node position is the azimuth of a tangent to the road curve at the node p_x as shown by the arrow of a dotted line in FIG. 8, and displayed clockwise within the range of 0 to 360 degrees, assuming the absolute azimuth of the true north as 0 degrees. The intercept azimuth of the node p_x is obtained by averaging the azimuth θ_x−1 of a line connecting the node p_x−1 and the node p_x−1 and the azimuth θ_x of a straight line connecting the node p_x and the node p_x+1 where p_x−1 is an upstream node adjacent to the node p_x and p_x+1 is a downstream node adjacent to the node p_x as shown in FIG. 10:

(θ_x−1+θ_x)/2   (Formula 1)

[0071] FIG. 11 shows the procedure for the transmitting side to obtain the intercept azimuth of a node selected from the target road section.

[0072] Step 11: The transmitting side obtains the coordinate data of a selected node and its upstream and downstream adjacent nodes from the digital map database.

[0073] Step 12: The transmitting side calculates the azimuths of straight lines connecting the nodes and uses (Formula 1) to obtain the intercept azimuth of the selected node.

[0074] FIG. 13 shows shape vector data string information including the information on the intercept azimuths of the nodes selected from the target road section as supplementary information. Here, the intercept azimuth of the start node (p₁) is displayed in absolute azimuth and the intercept azimuths of the remaining nodes in relative azimuth with respect to the immediately preceding nodes included in the shape vector data string information, in order to reduce the data amount.

[0075] The receiving side receives the shape vector data string information and uses the information on the intercept azimuth to perform map matching. FIG. 12 shows the map matching procedure.

[0076] Step 13: The receiving side uses the data in the receiving side digital map database to extract positions on the road close to the longitude/latitude data of the node p_x as candidates for matching in the increasing order of the distance to the node p_x.

[0077] Step 14: The receiving side obtains the coordinates of the adjacent node of the candidate position from the digital map database to calculate the intercept azimuth of the candidate position. Then the receiving side obtains the difference between the calculated intercept azimuth and the intercept azimuth of the node p_x sent in the supplementary information. In case the difference is smaller than the regulated value, the receiving side determines the candidate position as a selected node.

[0078] In case the difference is larger than the regulated value, the receiving side excludes the candidate position from candidates for matching. Execution returns to step 13 and the receiving side extracts the next closest position as a candidate for matching and follows step 14.

[0079] In this way, it is possible to prevent erroneous matching by referencing the azimuth information on the node position.

[0080] In FIG. 8, the node p_x on the road 1 is likely to be erroneously matched with the road 1 passing near the point p_x and crossing the road 1. In matching, as shown in FIG. 9, the receiving side could set the point on the road 2 closest to the point p_x as a candidate point 1 for matching and the point on the road 2 next closest to the point p_x as a candidate point 2 for matching. The candidate point 1 is excluded from candidates matching because the difference between the intercept azimuth of the candidate point 1 and that of the node p_x exceeds the regulated value. The candidate point 2 is determined as a selected node because the difference between the intercept azimuth of the candidate point 2 and that of the node p_x is below the regulated value.

[0081] In this practice, erroneous matching of the candidate point 1 on a different road as a selected node results in an error in the calculation of routes in the subsequent route search, thus making it impossible to reproduce the target road section.

[0082] A position information transmission method of this embodiment includes as supplementary information the information on the intercept azimuth at the node position into the shape vector data string information. This prevents inadvertent setting of a node point on a road crossing the target road thus enhancing the matching accuracy.

[0083] The third embodiment explains a method for increasing the number of transmit nodes at road points where the receiving side is likely to commit erroneous matching thus enhancing the matching accuracy at the receiving side in implementing a position information transmission method of the first embodiment.

[0084] FIGS. 14(1), (2), (3), (4), and (5) are schematic views of the processing details in the position information transmission method on the map.

[0085] The transmitting side, as shown in FIG. 14(1), selects a target road section, then the nodes to be transmitted out of the nodes in the target road section. In this practice, the transmitting side selects a plurality of nodes (node group) for easy identification of the different shape of the adjacent road at sections, where the receiving side is likely to commit erroneous matching due to presence of an adjacent road, which is parallel to the target road.

[0086] The transmitting side transmits shape vector data string information comprising the coordinate data of selected nodes and supplementary information together with traffic information.

[0087] FIG. 15 illustrates the shape vector data string information. In this example, a transmit node includes n node groups, the node group 1 has m nodes, . . . , the node group n has s nodes. While the coordinate data of nodes included in each node group is arranged in order in this shape vector data string information, the road shape represented by a plurality of nodes in individual node groups may be represented by Fourier coefficients, approximated by arcs and straight lines, or represented by spline function to compress the data amount.

[0088] Meanwhile, the receiving side that has received plots the node positions of the nodes in each node group included in the shape vector data string information on the map of the receiving side as shown in FIG. 14(3), then performs a map matching in order to calculate the position of each node on the map of the receiving side as shown in FIG. 14(4).

[0089] In this practice, by providing matching between the shape represented by the arrangement of a plurality of nodes in a node group and the road shape on the map of the receiving side, it is possible to accurately obtain the position of each node on the map of the receiving side.

[0090] When the node position is determined, the receiving side sequentially searches for the shortest routes connecting the nodes intermittently located, then links the shortest routes to reproduce the target road section, as shown in FIG. 14(5).

[0091] In this position information transmission method, the transmitting side selects nodes to be included in a node group based on the following criteria:

[0092] (1) As shown in FIG. 16, when the distance L_j from the node p_j to the closest position p_j′ is short and the difference (Δθ_j=θ_j−θ_j′) between the intercept azimuth angle θ_j at the node p_j and the intercept azimuth angle θ_j′ at the node p_j′ is small, the node p_j is determined as a node likely to be erroneously matched at the receiving side.

[0093] For example, the decision value ε_j is defined as

ε_j=α×L_j+β×|Δθ_j|  (Formula 2)

• • [0094] (where α and β are predetermined coefficients.)
    and when ε_j is smaller than the regulated value ε₀, the node p_j is determined as a node likely to be erroneously matched at the receiving side.

[0095] (2) When the node p_j is a node likely to be erroneously matched, it is determined whether the nodes before and after the node p_j are nodes likely to be erroneously matched at the receiving side based on the criterion under (1) and the range of nodes to be determined is sequentially expanded until a node unlikely to be erroneously matched at the receiving side is found. When a node unlikely to be erroneously matched at the receiving side, that is, a node satisfying ε_j≧ε₀ is found, it is assumed that a shape that identifies itself from the adjacent road shape is obtained and the node as well as the nodes satisfying ε_j<ε₀ are employed as members of a node group.

[0096] FIG. 17 shows an example of a procedure for selecting nodes to be included in a node group.

[0097] Step 21: The target road section is selected.

[0098] Step 22: The node p_j to be transmitted is selected.

[0099] Step 23: Assume m=0.

[0100] Step 24: The distance L_j±m to the adjacent road and the difference of intercept azimuth angle Δθ_j±m are calculated.

[0101] Step 25: The decision values ε_j±m is calculated by using (Formula 2).

[0102] Step 26: When both ε_j−m and ε_j+m are smaller than the regulated value ε₀,

[0103] Step 28: Procedure from step 24 is repeated as assuming m=m+1.

[0104] When either ε_j−m or ε_j+m is larger than the regulated value

[0105] Step 27: P_j−m, . . . , P_j, . . . , P_j+m are employed as members of a node group around P_j.

[0106] In this way, this procedure evaluates the potential for erroneous matching of nodes at the receiving side based on the distance from a node to an adjacent road and the difference between the intercept azimuth at the node and the intercept azimuth at the closest point on the adjacent road, and selects the nodes to be included in a node group depending on the evaluation value.

[0107] The transmitting side evaluates the potential for erroneous matching of nodes at the receiving side. The transmitting side transmits more nodes at road points where the receiving side is likely to commit erroneous matching thus enhancing the matching accuracy at the receiving side and faithfully reproducing the target road section.

[0108] The approach for evaluating the potential for erroneous matching of nodes at the receiving side based on the distance from a node to an adjacent road and the difference of the intercept azimuth can be applied to a method for transmitting “road shape data” comprising shape vector data strings as mentioned under “Background of the Invention.” It is possible to determine the length of the road shape specified by shape vector data strings and the number of nodes to be included into the shape vector data strings depending on the evaluation value.

[0109] The fourth embodiment explains a method for supporting a case where the digital map data maintained by the receiving side is of an earlier version.

[0110] In a position information transmission method according to the first through third embodiments, the receiving side obtains the shortest routes between nodes by way of a route search in order to reproduce the target road section. Thus the roads not included in the digital map database at the receiving side cannot be reproduced. For example, in case the digital map data at the receiving side is of an earlier version and does not include the data of a road recently opened for traffic, it is impossible to connect intermittent nodes specified by the transmitting side by using this road. As a result, the target road section intended by the transmitting side is different from that reproduced by the receiving side. This will cause the receiving side to assume by mistake that an event is present on another road.

[0111] In fact, such a trouble occurs frequently in case the transmitting side is information provision means of a traffic information provision system and the receiving side is car navigation apparatus provided with traffic information.

[0112] The fourth embodiment explains a position information transmission method for avoiding such a situation.

[0113] In this method, the transmitting side identifies the date when the digital map data of the target road was set, and selects the type of the position information transmission method used depending on the setting date. Setting date to a digital map database for the road substantially overlaps the opening period of the road. For example, when the target road has just been opened for traffic, the car navigation apparatus having the digital map database including the data of the new road is very small in number. In this case, the transmitting side employs a position information transmission method that will avoid misunderstanding that an event is present on a road other than the target road, not to mention identify the target road, even when the car navigation apparatus has a digital map database not including the data of the new road, in order to deliver traffic information.

[0114] In case the data setting date for the road is defined in each road link in the digital map database, the transmitting side employs the date. Otherwise, the transmitting side compares the versions of the digital map data and calculates the setting date from the revision date of the version that first carries the road link.

[0115] The transmitting side includes the information representing the setting date of data of the target road and the information on the distance between nodes in the shape vector data string information.

[0116] The receiving side references the setting date of data of the target road in the shape vector data string information received. When the receiving side has determined that the data of the target road is not included in the digital map database of its own, it stops reproducing the target road section.

[0117] In case the distance of the shortest route between nodes is extremely different from the distance between nodes included in the shape vector data string information, the receiving side determines that the data of the target road is not included in the digital map database of its own, and stops reproducing the target road section.

[0118] The flowchart of FIG. 18 shows the procedure at the transmitting side.

[0119] Step 30: The transmitting side selects the target road section.

[0120] Step 31: The transmitting side selects nodes to be transmitted.

[0121] Step 32: When the data setting date of the data of the road connecting the selected nodes is equal to or earlier than the reference date (regulated value),

[0122] Step 33: The transmitting side employs a position information transmission method according to the first through third embodiments.

[0123] In case the data setting date of the data of the road connecting the selected nodes is later than the reference date.

[0124] Step 35: The transmitting side employs a position information transmission method for transmitting data that directly represents the road shape of the target road section (such as coordinate data string on each node to identify the road shape)

[0125] Step 36: The transmitting side transmits the position information based on the selected method.

[0126] FIG. 20 illustrates shape vector data string information to be transmitted using a method of the invention.

[0127] This information includes the setting date of data of the roads connecting nodes and search distance data.

[0128] The flowchart of FIG. 19 shows the procedure at the receiving side that has received the shape vector data string information.

[0129] Step 40: The receiving side receives the information.

[0130] Step 41: The receiving side references the supplementary information to determine the coordinates of each node by way of map matching.

[0131] Step 42: The receiving side identifies whether the data setting date of the data between nodes included in the received data is earlier than the creation date of map data of the local apparatus, and in case it is earlier,

[0132] Step 43: The receiving side references the supplementary information to perform a route search between nodes and determine the target road section.

[0133] Step 44: The receiving side identifies whether the difference between the distance of the determined target road section and the search distance between nodes included in the received data is within the regulated error, and

[0134] in case it is within the regulated error,

[0135] Step 45: The receiving side reproduces the entire shape of the target road section.

[0136] In case the data setting date is not earlier than the creation date of map data of the local apparatus in Step 42, or in case the difference between the distance of the determined target road section and the search distance between nodes included in the received data is not within the regulated error, the receiving side discards the information between the nodes.

[0137] By following this procedure, it is possible to avoid transmission of erroneous position information caused by different versions of the digital map data maintained by the transmitting side and the receiving side when a position information transmission method according to the invention is applied.

[0138] While both the setting date of data of roads connecting nodes and data of the search distance are included in the shape vector data string information in the foregoing description, either data may be included.

[0139] While the invention has been described in detail referring to particular embodiments, those skilled in the art will appreciate that the invention may be modified or corrected in various forms without departing from the spirit and the scope of the invention.

[0140] This application is based on the Japanese Patent Application No. 020082/2001 filed Jan. 29, 2001, which is incorporated herein by reference.

[0141] As understood from the foregoing description, according to a method for transmitting position information on a digital map and apparatus for implementing the method, it is possible to efficiently and accurately transmit the information on the shape and position on a digital map using a small amount of data, thereby enhancing the data transmission efficiency.