Route selection method and apparatus therefor

Abstract: A route between a starting point and a destination on a traffic network is derived by searching a first route from the starting point to a first route store point stored in an interpoint route memory (101) and a second route from the destination to a second route store point stored in the interpoint route memory (101), by retrieving a third route between the first and second route store points in the interpoint route memory (101), and by connecting the first, second and third routes to one route.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT 1. FIELD OF THE INVENTION The present invention relates to a route selection method and an apparatus to select an optimum route from a plurality of routes connecting between a starting point and a destination on a connection network such as a road network or a communication network. 2. DESCRIPTION OF THE RELATED ART An example of a route selection apparatus in the prior art is shown in the Japanese published unexamined patent application Sho 59-105113. In the prior art, a starting point and a destination are set in a guidance control apparatus installed on a vehicle. The guidance control apparatus is provided with a device for measuring a position and a course of the vehicle, and thereby a present position and the course of the vehicle which is running on a road are detected. The guidance control apparatus, furthermore, comprises a map stored in a memory including information of junctions of roads, setting points disposed at regular intervals along the roads and distances among the setting points. Then an optimum route from the starting point to destination is derived on the basis of the map. When the vehicle has arrived at a setting point, a direction to travel after then is indicated to a driver of the vehicle. The vehicle will arrive at the destination via the optimum route by driving it in compliance with the indication. In the prior art, the optimum route between the starting point and destination is derived by the known "Dijkstra method". According to the Dijkstra method, "directed routes" on which respective directions are given in advance are set among junction points of a plurality of roads connecting between the starting point and destination, and respective distances among the junction points are calculated along the directed routes from the starting point to destination. Then, a route having the shortest distance is selected between the starting point and destination as the optimum route. It is known that a search time in operation of the Dijkstra method increases in proportion to a square of the number of junction. Therefore, the more the number of the routes increases, the more the calculation operation to search an optimum route much more increases, and accordingly the search time increases very much. Another prior art is shown in the Japanese published unexamined patent application Hei 2-56591 (Tokkai 56591/1990). According to the prior art, data of a road network which is used in route selection operation is made to "hierarchy structure". In the hierarchy structure of the road network, a trunk line network of road is placed on an upper hierarchy, and a branch line network of road which is connected to the trunk line network is placed on a lower hierarchy, and thereby the road network is classified into plural hierarchies. Moreover, road network in each hierarchy is divided into a plurality of blocks, and information of junctions, connection information with respect to the roads among the junctions and connection information with respect to a junction in an upper hierarchy are stored as map data at every block of each hierarchy. In route selection operation of this prior art, when a block including a starting point and a block including a destination belong to an upper hierarchy, route selection operation is carried out between both the blocks of the hierarchy. On the other hand, when the starting point or the destination belongs to a block of a lower hierarchy, first, a route which is connected to a block of an upper hierarchy is selected, and the route selection operation is migrated to the block of the upper hierarchy. When a first block including the starting point is identical with a second block including the destination, or when the first block is placed adjacent to the second block on the same hierarchy, the route selection operation is completed. In this prior art, a block size representing a range of the block is determined so that information included in each block is uniform. Therefore, even if much information exists owing to a complicated road network, calculation operation is reduced in comparison with the Dijkstra method because information processing is carried out in each block. Still other prior art is shown in United States Patent No. 4,984,168. According to this prior art, in order to determine a route between a starting point and a destination within a short time, a digitally memorized road map is divided into at least two levels of different grid density and regional size. A plurality of smaller subregions of fine grid density are assigned to a lower level, and one or more larger subregions of coarser grid density are assigned to a higher level. Beginning with the lower level of the road map, a possible route is searched. If the result are negative, a transition is made to the next-higher level, until a positive result is attained. In determining an optimum route, favorable result are obtained for all possible relationship of starting point and destination. For instance, when the starting point and destination are in the same part (subregion) of a region, it is suitable for a route to be determined within the subregion. If that is not possible, then an attempt is made to reach the destination via an adjacent subregion. These operations are performed in the same level. If the starting point and destination are far apart, then the major transitions between these subregions are ascertained. In the road map, resistance values are assigned to the various roads and intersections. These resistors for instance define a route length, a required travel time, or a average traffic density. If the resistance of the resistor is low, the applicable road or connection is used preferentially for route determination. If the resistance of the resistor is high, it is not taken into account unless other routes are not favorable. Recently, constant development in the road network increases the numbers of trunk line and branch line connected thereto, consequently complicating the connections among them. Accordingly, information in the road network increases day by day, and thus information processing operation which is necessary to carry out route selection is increased. Therefore, a route selection apparatus for rapidly selecting an optimum route from the complicated road network has been sought. The FR-A-2 570 531 discloses a portable apparatus for indicating at least one route between two points comprising a microprocessor for storing a plurality of geographic points and indicating at least one route between two points, a control device for inputting a starting point and a destination point to the microprocessor and a display for displaying the route indicated by the microprocessor. A method for realizing "route finding", however, is not disclosed in this document. The FR-A-2 541 026 discloses a route retrieval scheme in which for each pair of stations of an underground network, the shortest connecting routes are stored as the sequence of connecting change-over stations. By inputting a departure and destination station the system outputs (in sequence) the change-over stations (and the connecting lines. From the AFIPS conference Proceedings, 1984 National conference, July '84, Las Vegas, USA, pp 695 to 706 it is known to divide a map into blocks which are provided along boundaries. From one block to the adjacent block, a shortest-path algorithm (Dijkstra's algorithm) is used successively for each block with connections across the boundary. From one block to the non-adjacent block, the problem is more difficult. One method could start with the source block and carry a directed search through adjacent blocks toward the destination block, using the directionality in the street map. Another method might be to store predetermined routes from each block to all other blocks. The second method requires much less computation than does the first one. However, if the predetermined routes are stored as sequences of intersections, much storage will be needed. A compromise was made by storing only the sequence of blocks containing the route and storing an entry point and an exit point on the boundaries for each block in the sequence (see Fig. 13 of this document). The route between the entry point and the exit point within each block is computed using the shortest-path algorithm. Since a route in a block is searched by the shortest-path algorithm, in the method disclosed in this document a longer time is required method disclosed in this document a longer time is required to select the route in the block. If the block is made small-scale in order to speed up searching operation in the block, the number of the blocks to be passed between a starting point and a destination inevitably increases. Consequently, a search time is prolonged and data amount to be stored in a memory is also increased. OBJECT AND SUMMARY OF THE INVENTION An object of the present invention is to provide a route selection method and an apparatus therefor in which information processing operation for selecting an optimum route between a starting point and a destination is reduced significantly in a connection network. This object is attained by the features of claim 1, concerning a method, respectively by the features of claim 2, concerning an apparatus. While to novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a block diagram of an embodiment of a route selection apparatus in accordance with the present invention; FIG.2 is a flow chart of an example of operation of the route selection apparatus; FIG.3 is an example of a road map in the rout selection apparatus; and FIG.4 is an example of a road map in the route selection apparatus in accordance with the method of the present invention. It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.1 is a block diagram of a route selection apparatus in accordance with a present invention. An "interpoint route memory 101" is a memory means such as a CD-ROM which stores data of entire routes among entire points on a road network in advance. "Point input means 102" is an input apparatus for designating two points (a starting point and a destination) to derive a route from among the points stored in the interpoint route memory 101. The point stored in the interpoint route memory 101 is named as "route store point". The data of the entire routes among the route store points are stored in the interpoint route memory 101. "Route retrieval means 103" comprising a CPU and a memory is to retrieve a route between the designated two points from among the data stored in the interpoint route memory 101. "Output means 104" is an output device such as a display device for displaying a route retrieved by the route retrieval means 103. The output means 104 may be a voice outputting device for indicating the route by voice. The output device can be constituted to indicate the route by image or voice by combining it with a present position detection apparatus representing a present position of a vehicle. The point input means 102 for designating the starting point and destination comprises a display device for displaying a map and the route store points in the map on the same display. An operator or a driver of the vehicle selects two points for the starting point and destination from among the route store points displayed on the display device. The designated starting point and destination are inputted to the route retrieval means 103, and a combination of the starting point and destination is retrieved from among combinations of two points on the network stored in the interpoint route memory 101, and thus a route corresponding to the combination is read out. The route data is output to the output means 104. An example of operation of a route selection method based on the above apparatus is shown in a flow chart of FIG.2. A starting point and a destination to derive a route are selected from among the route store points and are designated at step 201. At the step 201, the route between the designated two points is retrieved from among the data stored routes among entire points, and a retrieved route is output at step 203. Detailed operation of the above method is elucidated by using an example hereafter. FIG.3 is a diagram of a road network representing routes connecting among five points 1, 2, 3, 4 and 5. Entire routes which are produced by connecting among the five points are predetermined by designating one of five points as a starting point and the other thereof as a destination, and the data of the entire routes are stored in the interpoint route memory 101 as "interpoint route data". An example of the interpoint route data is shown in Table 1. Interpoint route data Combination of points Transit point Starting point Destination 1 2 - 1 3 - 1 4 2 1 5 3 2 1 - 2 3 - 2 4 - 2 5 4 3 1 - 3 2 - . . . . . . . . . 5 2 4 5 3 - 5 4 - In Table 1, combinations of two points selected from five points are shown in a comprehensive column of "combination of points", for example. Numerals in the left column thereof represent starting points and numerals in the right column represent destinations (the numerals in the right column are allowed to be the starting points and the numerals in the left column are allowed to be the destinations). Numerals in the column of "transit points" represent a transit point between two points shown on the same row in the comprehensive column of the combination of points. The combination of points having no transit point is represented by "-". The transit point is one of the route store point. As shown in the Table 1, a route which is formed by a combination between arbitrary two points is stored with respect to entire combinations of the points on the network and one point on the respective routes is also stored. When the point 1 is a starting point and a point 5 is a destination, for example, the combination of these two points 1 and 5 is retrieved in the column of the combination of the points, and a route transit point corresponding to the combination of these two points 1 and 5 is retrieved in the column of the transit point of the Table 1. In the above-mentioned example, a point 3 is retrieved in the column of the route transit point of the Table 1. Consequently, the route from the point 1 to the point 5 is determined as "point 1 → point 3 → point 5". In storing operation of the routes among entire points on the network, the routes which are predetermined by the Dijkstra method or the like using the road network can be stored therein. The road network data includes data of positions of points and connection relations among these points. Moreover the routes may be derived by hand on the basis of an ordinary human sense. In accordance with the above, the route between two points is obtained by combination of plural transit points. Combination of the route transit points with respect to combination of the two points is shown in Table 2. Combination of points Combination of route transit points 1 - 5 2 3 4 1 - 4 2 3 1 - 3 2 As shown in Table 2, for example, three route transit points 2, 3 and 4 need to be stored with respect to the route between the points 1 and 5. Therefore, the data of the transit points rapidly increase in accordance with increase of the number of point. In the above-mentioned reason, this route selection method is suitable for the road network having relatively small number of point. [Method according to the invention] The route selection method according to the invention is directed to greatly reduce data of route to be stored in the interpoint route memory 101 in comparison with the above method. In accordance with the invention at least one point on the way of a route is stored in the interpoint route memory 101, as a "transit point". The data of the transit point is included in the data of the routes among points on the road network. And when a route between designated two points is derived, the route is divided into plural sub-routes by putting the transit point on the way of the route as a boundary point. Then a further transit point is determined between the designated point and the boundary point. FIG.4 is an example of a road map of a route including five points 1, 2, 3, 4 and 5. A combination of points (the point 1 is a starting point) and transit point (corresponding) to the combination are predetermined as shown in Table 3. Combination of points Transit point 1 - 5 4 1 - 4 3 1 - 3 2 1 - 2 The data shown in the Table 3 are stored in the interpoint route memory 101. Retrieval operation of a route according to the invention is elucidated hereafter. After the two points (starting point and destination) to derive a route are designated, in the route retrieval means 103, the combination of the two points is retrieved from combinations among the entire points on the network stored in the interpoint route memory 101. Then a first transit point corresponding to the combination of the two points is read out. Subsequently, a combination of the starting point and the first transit point is retrieved, and hence a second transit point corresponding to the combination of the starting point and the first transit point is read out. In the same way, a third transit point corresponding to the combination of the starting point and the second transit point is read out. Furthermore, a fourth transit point is retrieved based on the combination of the destination and the first transit point, and a fifth transit point is also retrieved based on the combination of the first and second transit points. As mentioned above, the respective transit points corresponding to the combination of the starting point and a transit point, a combination of two transit points and the combination of the transit point and the destination are stored in the interpoint route memory 101. And points on the route between the starting point and the destination are determined by retrieving them in the interpoint route memory 101 by the route retrieval means 103. Consequently, the route between the starting point and the destination is determined by a chain of a plurality of transit points, the starting point → first transit point → a second transit point → a third transit point · · · the destination. The derived route is output from the output means 104. An example of route retrieval operation is shown in Table 4. In the Table 4, for the sake of simplicity, the point 1 of five points 1, 2, 3, 4 and 5 is designated as the starting point, and the point 5 is designated as the destination. In the example, a point located adjacent to the destination between the starting point and destination is selected for a transit point. Combination of points Transit point Chain of transit points Step 1 1 - 5 4 1 4 5 Step 2 1 - 4 3 1 3 4 5 Step 3 1 - 3 2 1 2 3 4 5 Step 4 1 - 2 - 1 2 3 4 5 In order to derive a route from the starting point to the destination, first, combination of the point 1 and the point 5 is retrieved (hereinafter, a route from the point 1 to the point 5 is represented by "combination 1 - 5"), and a transit point 4 corresponding to the combination 1 - 5 is derived at step 1 of the Table 4. Subsequently, at step 2, combination 1 - 4 is retrieved and a resultant transit point 3 is derived. In a similar manner at step 3, combination 1 - 3 is retrieved, and a resultant transit point 2 is derived. Finally at step 4, combination 1 - 2 is retrieved. If no transit point is stored with respect to the combination 1 - 2, the route between the points 1 and 5 is represented by a chain of the transit points 4, 3 and 2. "Chain of transit point" in the right column of Table 4 represents route derived in each step. According to the invention, in order to select a route between two points, only one point on the way of a route is stored in the interpoint route memory 101 in advance. Therefore, data for storing the route is greatly reduced in comparison with the above method (Fig. 2 and 3). In the example shown in the Table 3, a point located adjacent to the destination is selected for a transit point, but a point located adjacent to the starting point can be selected for a transit point. In this case, a chain of the transit points is derived in the order directed from the starting point to the destination.

Claims: A route retrieval method comprising the steps of: a) for each pair of points of a road network of points interconnected by roads storing in a data memory only one transit point, defined as a point of said road network which lies along a predetermined route connecting said pair of points and is adjacent to one of said pair of points, if a transit point exists, in association with each of said pair of points; b) designating a first pair of points in said road network as starting and destination points of a route to be retrieved; c) retrieving the transit point associated with said pair of points from said data memory; d) setting a new pair of points comprising said transit point and the other, non-adjacent one of said first pair of points; e) retrieving the transit point associated with said new pair of points from said data memory; f) repeating steps d) and e) until there is no transit point associated with the new pair of points; g) representing said route between said starting and destination points by the sequence of transit points and starting and destination points. A route retrieval apparatus comprising: a memory (101) storing for each of a pair of points of a road network of points interconnected by roads data representative of a predetermined route connecting the pair of points; input means (102) for designating a starting and a destination point of a route to be retrieved; route retrieval means (103) for retrieving a route from said memory (101) for a starting and destination point designated by said input means (102); output means (104) for outputting the route retrieved by said route retrieval means (103); characterized in that said memory (101) stores for each pair of points of said road network only one transit point, defined as a point of said road network which lies along a predetermined route connecting said pair of points and is adjacent to one of said pair of points, if such a transit point exists, in association with each of said pair of points; said retrieval means is adapted to retrieve the transit point associated with the input pair of starting and destination points; to designate a new pair of points comprising the transit point and the other, non-adjacent one of said input pair of points; to retrieve the transit point associated with said new pair of points; to repeat the preceding two steps until no transit point is found; and to constitute the retrieved route from the sequence of retrieved transit points and input pair of points.

Inventors: UEYAMA YOSHIKI, YAGYU TAKESHI, UEYAMA, YOSHIKI, YAGYU, TAKESHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1992
Main classification: G01C21
IPC codes: G01C21, G08G1, G09B29