JPH09133540A - Method for acquiring a plurality of routes and car navigation system employing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for selecting a plurality of different routes without detouring significantly by determining a candidate route, having a link cost within a specified times that of an optimal route and lowest link cost at the part overlapping the optimal route, as a quasi-optimal route. SOLUTION: Links a, c being branched from the starting point O of a first link on an optimal route (links b, i, p) between a start and a goal is specified and then the entire route is searched from the link a, c to a goal link D. In this regard, all routes may be searched simultaneously from the links g, f, k branched from the starting points 4, 6 of links i, p to the link D. Routing cost is then calculated for each candidate route and a candidate route, having a routing cost lower than (1+a) times that of an optimal route (a>0) and the sum of link cost at the part common to the optimal route (e.g. links b, c) is minimum, is determined as a quasi-optimal route. Route information related to an optimal route tree or quasi-optimal route tree is transmitted to each vehicle as required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention obtains an optimum route from any link constituting route network data of a route providing area to any other link in the same area, and is different from the optimum route. The present invention relates to a multiple route acquisition method for obtaining one or more slightly detoured routes (hereinafter referred to as “suboptimal route”).

The present invention relates to a vehicle-mounted navigation device capable of obtaining route information about an optimum route and route information about a sub-optimal route in a vehicle.

[0003]

2. Description of the Related Art Conventionally, a vehicle-mounted navigation device that has been developed to display the position and orientation of a vehicle on a screen to facilitate traveling of the vehicle has been widely used. The vehicle-mounted navigation device is equipped with a display, a GPS receiver, a road map memory, a computer, etc. in a vehicle, and displays the vehicle position based on the position data input from the GPS receiver and the road pattern stored in the road map memory. The detected vehicle position is displayed on the display together with the road map.

In this case, in order to select a traveling route from the departure place to the destination, the route from the vehicle's current position (which is considered to be the departure place) to the destination is determined by the computer in response to the setting input of the destination by the driver. Has proposed a method for automatic calculation (see Japanese Patent Laid-Open No. 53504/1993). In this method, the roads or lanes to be calculated are expressed as a series of vectors (this vector is called a "link"), a link close to the starting point (or destination) may be used as the calculation start link, and the destination (or starting point may be Links that are close to each other) are used as calculation end links, the road map data stored in the road map memory between them is read and moved to the work area, and all tree trees of links starting from the calculation start link in the work area are searched, This is a method in which a tree with the lowest cost is obtained, the link costs (the running time and the running distance of the link) of the routes forming the tree are sequentially added, and the route reaching the calculation end link is selected.

This method is convenient for a driver who does not know the route because the route can be reliably calculated by calculating the route and traveling along the route.

[0006]

However, when the in-vehicle navigation devices of a plurality of vehicles each calculate the optimum route, the link cost of each vehicle does not differ greatly from vehicle to vehicle. It is expected that a plurality of vehicles going will calculate the same route, only a specific route will be congested, and the destination cannot be reached in the shortest time.

Therefore, it is desirable for the vehicle-mounted navigation device to calculate a plurality of routes that are as different as possible in order to reach the same destination, and show the user a plurality of routes to be selected. On the other hand, the link cost of each link fluctuates from moment to moment due to traffic congestion on the road, traffic restrictions due to road construction, the presence of accidents, etc. A ground system for transmitting the latest information for guiding the vehicle to a destination via a telephone line) is currently under consideration. According to this ground system, the ground system side prepares route information using the latest link costs including traffic congestion status, traffic restrictions, and accident information, and in the case of a road beacon via a road beacon or car phone, When the destination information is obtained from the vehicle, and the destination information and the departure point information are obtained from the vehicle in the case of a car phone, immediately after that, the route information is transmitted to the car through the same road beacon or the car phone. This can assist the vehicle in obtaining an optimal route.

[0008] When the route is calculated by the ground system and the result is distributed to each vehicle, if only the same route is shown to reach the same destination, only the specific route is congested.
On the contrary, it is expected that the phenomenon that the destination cannot be reached in the shortest time will occur. Therefore, in the ground system, for each vehicle, calculate a plurality of routes that are as different as possible and let the vehicles select and select a plurality of routes, or
It is desirable to select one of the routes and show it to the vehicle so that the deviation of traffic does not occur in the ground system.

In order to solve such a problem, the shortest cost between an arbitrary point on the network and the end point is calculated, and the partial route from the start point is divided into the cumulative cost from the start point and the shortest cost of the remaining route. Based on the sum, a method of expanding a plurality of routes according to an analysis condition has been proposed (Japanese Patent Laid-Open No. Hei 5).
-46590). According to this proposal, routes that largely detour can be eliminated, but it is difficult to obtain a plurality of routes that differ as much as possible because only a large number of routes that are almost the same as the shortest route are obtained.

An object of the present invention is to provide a multi-route acquisition method which does not cause a large detour and is capable of obtaining a plurality of routes that differ as much as possible. Another object of the present invention is to provide a vehicle-mounted navigation device that does not cause a large detour and can acquire a plurality of routes that differ as much as possible.

[0011]

According to the method for acquiring a plurality of routes of the present invention, (a) any two links constituting a route network of a route providing area are used as a calculation start link and a calculation end link, and calculation is performed from the calculation start link. A procedure for obtaining an optimal route having the minimum link cost to reach the end link and obtaining a route other than the optimal route from the calculation start link to the calculation end link as a candidate route in the route network of the same route providing area , (B) For a candidate route, the link cost of the candidate route is less than or equal to (1 + a) times the link cost C of the optimal route (0 <a), or the link cost C of the optimal route is a predetermined number. And (d) the link cost of the overlapping portion of the candidate route and the optimal route is b times or less the link cost C of the optimal route (0 <b 1 to) a is a candidate path,
Alternatively, it is a method of determining a candidate route selected as a sub-optimal route by adopting a procedure of selecting a candidate route whose link cost of the overlapping portion is a predetermined value or less (claim 1).

The procedure of (b) above is adopted. If the route cost of the candidate route is much larger than the route cost of the optimum route, a large detour is made, and there is no point in determining it as a sub-optimal route. It is due to being lost. Here, the numerical value a is set to a value such as 0.1 or 0.2. If a = 0.2, routes up to 20% more than the route cost of the optimal route are candidates for the sub-optimal route. Also, the link cost C of the optimum route
When the predetermined number is added to the “predetermined number”, the “predetermined number” is determined on the basis of the judgment as to how much the route cost can be increased from the route cost of the optimal route regardless of the length of the optimal route.

The procedure of (d) is adopted because if there are too many portions where the candidate route overlaps with the optimal route, it becomes almost the same as the optimal route, and it is determined as a sub-optimal route. It is because there is no. Here, the numerical value b is set to a value such as 0.3 or 0.4. If b = 0.4, routes that are 40% or more in common with the optimal route are excluded from the candidates for the sub-optimal route. If the link cost of the overlapping part is less than or equal to a predetermined value, the value "predetermined value" is used for the route that overlaps the optimum route and the distance or time of the optimum route regardless of the length of the optimum route. It is decided by the judgment whether to exclude.

According to the present invention, before the step (d) or (b), (c) the number of times that the candidate route joins and separates from the optimum route or the number of times of intersection is n or less (n ≧ 0). It may further include a procedure for selecting one (claim 2). This procedure (c) is adopted because the number of times that a candidate route joins and leaves the optimal route is large or the number of times it intersects is too large, the number of times of entering and leaving the optimal route is large, This is because it does not meet the purpose of the present invention to provide a plurality of routes that differ as much as possible without being driven along the routes.

In the present invention, instead of the procedure of (d) above, (d-
1) The candidate route may be determined as a sub-optimal route by selecting the one that has the lowest link cost in the overlapping portion of the candidate route and the optimal route. According to this, the suboptimal route can be finally narrowed down to one. If there are many sub-optimal routes, the user will be confused about the selection. Therefore, it is easier for the user to select one if it is narrowed down.

In the method for acquiring a plurality of routes according to the present invention, (a) any two links constituting the route network in the route providing area are used as a calculation start link and a calculation end link, and a link from the calculation start link to the calculation end link A procedure for acquiring an optimal route with the lowest cost and acquiring a route other than the optimal route from the calculation start link to the calculation end link as a candidate route in the route network of the same route providing area, (e) Candidate route On the other hand, the link cost of the overlapping portion of the candidate route and the optimum route is b times or less (0 <b <1) of the link cost C of the optimum route, or a predetermined number is set to the link cost C of the optimum route. The procedure for selecting a value that is less than or equal to the added value, and (g) the link cost of the candidate route is (1 + a) times or less (0 <a) the link cost C of the optimum route. Things, or employs a procedure to choose not more than a value obtained by adding a predetermined number to the link cost C of the optimum path, a method for determining the selected candidate route as the sub-optimal paths (claim 4).

Comparing with the invention of claim 1, the invention of claim 1
Only the steps (b) and (d) are interchanged,
The inventions are substantially the same. The present invention includes the above (g) or (e)
Before the procedure of (4), the method may further include (f) a procedure of selecting a candidate path that joins or separates into an optimum path or has a number of times of intersection of n times or less (n ≧ 0) (claim 5). ).

The reason for adopting the procedure (f) is the same as that of the invention described in claim 2. Instead of the procedure of (g) above,
(g-1) A candidate route having a minimum link cost may be selected and this candidate route may be determined as a sub-optimal route (claim 6). According to this, the suboptimal route can be finally narrowed down to one. This is because it is easier for the user to select the number of suboptimal routes rather than the number of suboptimal routes.

The navigation apparatus of the present invention acquires routes other than the optimum route as candidate routes, and the link cost of the candidate route is (1 + a) times or less than the link cost C of the optimum route (0 < a)),
Alternatively, a first determination unit that selects a link cost C of the optimum route that is less than or equal to a value obtained by adding a predetermined number, and the link cost C of the optimum route is the link cost of the overlapping portion of the candidate route and the optimum route
B times or less (assuming 0 <b <1) or a link cost of the overlapping part is less than or equal to a predetermined value.
The candidate route that has cleared the determination by the determination means is determined as the sub-optimal route (claim 7).

In the navigation device of the present invention, the number of times a candidate route joins and separates from the optimum route or the number of times it intersects is n.
You may further have the 3rd determination means which selects the thing which is less than the number of times (n> = 0) (Claim 8), and instead of the 2nd determination means, the determination by the 1st determination means was cleared. You may have a 4th determination means which selects the link cost of the overlap part of a candidate route and an optimal route from a candidate route, and it replaces with a 1st determination means. A fifth determination unit may be provided that selects a candidate route having the smallest link cost from the candidate routes that have cleared the determination by the second determination unit (claim 10).

The invention according to claim 7 is the same invention as the invention according to claim 1 or 4, the invention according to claim 8 is the same invention as the invention according to claim 2 or 5, and The invention described is the same as the invention described in claim 3, and the invention described in claim 10 is the same invention as the invention described in claim 6.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

I. First Embodiment First, a first embodiment of the present invention in which optimum route information and sub-optimal route information are calculated by a ground system and transmitted to a vehicle will be described in detail with reference to the accompanying drawings. FIG.
1 is a schematic diagram of a route information transmission system, in which a bidirectional optical beacon B is installed at a main intersection or the like in a route providing area for providing route information, and each optical beacon B is an information center through a communication line (public line or dedicated line). It is tied with A.

The information center A connects the installation point of the optical beacon B, the installation point of the vehicle detector or a main intersection (hereinafter collectively referred to as "main intersection") in consideration of the road traffic information which changes every moment. This route is calculated at any time, and this route data is transmitted to the optical beacon B. The information center A will be described in detail. The information center A has a map dedicated memory 13, a controller 11 and a communication line modem 12.

The map dedicated memory 13 provides route information.
Each major exchange installed in the route provision area
Various data related to links that connect difference points (route
Network data). Information center
-Specify the route network data format that A has
It is as shown below. For example, a road map is shown in Figure 2 (a).
If the link is
As shown in 2 (b), point N₁To N_TwoPhosphorus connecting
L ₁₂, Point N_TwoTo N₁Link L connecting up to_{twenty one},…When
It is shown as said. B₁, B_Two, B_ThreeThe light beeco
The installation point of the

The route network data is stored in the form of a route network table as shown in Table 1. In the route network table, the identification number (link number) of each link, link length (link distance), road type such as highway general road, coordinates of start and end points of the link, intersection shape, and connection to the end point of the link The arc cost (to be described later) to one or a plurality of exit links and a pointer to the exit links are included.

[0026]

[Table 1]

This route network data is not fixed to one value, but differs for each day, day of the week, and time zone. This is because the degree of traffic congestion and traffic regulations may change depending on the day, the day of the week, and the time of day. In addition, the arc cost and the pointer to the exit link correspond to the case where the conditions for route calculation (for example, whether to use a highway, whether to minimize the number of right turns, etc .; these are called "selection options") are specified. In order to have different values for each selection option.

If the terms are defined here, this next link when the next link connected to this link is seen from the end point of this link is the "exit link", from this link's start point to this link. When looking at the link before connecting to, the previous link is called the "entry link". It should be noted that the terms exit and approach are merely focused on the traveling direction of the link and have no relation to the direction in which the route is searched. For example,
When searching for a route from the departure point, the exit links of the links are followed one after another, and when searching for the route from the destination in reverse, the entry links of the links are followed one after another. “Connection cost” means the cost of turning left or right or going straight to exit from the link to the exit link. For example, when entry is prohibited, the connection cost is infinite, and when there is a traffic light, the cost takes into account the average signal waiting time when turning right or left or going straight. "Arc cost" means the link cost, which is the travel time when passing through the link, plus the connection cost for exiting the link (Fig. 3 (b)).
reference). Here, the arc is from immediately after the start node of a link to immediately after the start node of the next link, as shown in FIG. 3 (a).

As the arc cost, the cost at the time of traveling at the legal speed is usually used, but if the information center A contains traffic congestion information and the like, the arc cost is changed in consideration thereof. For example, when a certain link is cut off due to an accident, the arc cost of the link becomes infinite until the passage is restarted. Further, if the up lane of a certain road is congested, the arc cost of the up is increased according to the congested traffic.

The information center A calculates optimum routes and quasi-optimum routes from links corresponding to each main intersection to links corresponding to other main intersections in the route providing area, and stores the route information in the guidance table. Then, it is transmitted to the optical beacon B. When the control device 24 of the optical beacon B acquires the route information from the information center A, the control device 24 stores it in the route memory 21 in the form of a guide table.

This guidance table is, as shown in Table 2,
It consists of link attributes, links that make up the optimal route tree (including route costs and pointers to ingress links), and links that make up the sub-optimal route tree (including route costs and pointers to ingress links). There
It is created for each departure link.

[0032]

[Table 2]

In order to obtain the optimum route or the sub-optimal route using this guidance table, one target link may be specified and a series of approach links may be followed. The internal structure of the controller 11 is as shown in FIG. The controller 11 is a memory control unit for obtaining necessary data from the map dedicated memory 13, the Dijkstra method or the potential method (Shibata, Tenmoku, Shimoura “Development of Stochastic Route Search Algorithm” Sumitomo Electric No. 143, p. 16).
5, See September 1993), route calculation processing unit for calculating the optimum route from the destination to the departure point, SRAM and D
It is composed of a RAM.

Based on the route network data read from the map dedicated memory 13, the route calculation processing section D
Optimal route calculation and sub-optimal route calculation are performed using a pivot table (described later) provided in the RAM, and the result of the route calculation is recorded in the SRAM in the form of a result table (described later). The "pivot table" is a place for temporarily storing the link under route search when the route is calculated by the Dijkstra method or the potential method, and is one of the many links stored in the route network table. , A first-in first-out table that stores the links currently required for calculations.
As shown in Table 3, the pivot table is provided with a column of a pivot valid flag indicating whether or not a link to be searched for a route is included in the pivot table, and a column of a pointer to a route network table for specifying a link. There is.

[0035]

[Table 3]

As shown in Table 4, the "result table" has a link number and a link distance (these are copied from the route network table), a pivot registration flag, a pivot pointer, a route cost, and an approach link. Has each column of pointers.

[0037]

[Table 4]

The pivot registration flag is a flag indicating whether or not the link is registered in the pivot table. The pivot pointer is a pointer indicating where in the pivot table the link is registered. The route cost is the cost of reaching the link from the departure point link. More precisely, the route cost of a certain link is the sum of the arc costs of the links on the route connecting the starting value to the link (see FIG. 3 (b)).

Next, a route search method using the route network table, the result table and the pivot table will be described. In the calculation below, we will explain how to create a tree from the starting point to the destination and calculate the route.However, conversely, make a tree from the destination to the starting point and calculate the route. deep. In the former case, the departure point link becomes the calculation start link, but in the latter case, the destination link becomes the calculation start link.

The route search method of this embodiment is, in short,
One of the links forming the route network data of the route providing area is used as a calculation start link, and the optimum route tree reaching all other links in the same area is acquired from the calculation start link, and this optimum route tree is calculated. The route from the calculation start link to the calculation start link is acquired by using the route network, and the route cost of the route other than the optimum route in the route network of the same route providing area is the link cost of the optimum route ( 1 + a) times or less (0 <
a) (may be less than or equal to the value obtained by adding a predetermined number to the link cost C of the optimum route) as a candidate route, and the link cost of the overlapping portion of the candidate route and the optimum route is the minimum. The procedure is to determine this candidate route as a sub-optimal route.

The outline of the optimum route calculation procedure performed by the controller 11 is as follows. The procedure for calculating the optimum route is well known and will be briefly described below. First, the route network table corresponding to the day, the day of the week, and the time zone for which the route is desired is acquired from the map-dedicated memory 13. Then, the departure place links are set one by one. This is because, as the information center A, the purpose is to calculate the optimum routes from all the departure point links and record the results in the respective guidance tables. Further, reference is made to the part of the route network table corresponding to one selection option. This is to calculate the optimum route corresponding to each selection option so as to meet various demands of the driver.

Next, the arc cost is corrected based on the road traffic information currently obtained. This correction is made based on traffic jam information, accident information, construction information, etc., which are obtained from time to time. With this modification, the arc cost will consider static costs such as link costs when traveling at average speed, and dynamic costs that change depending on the time of day, day of the week, congestion, construction, accident, etc. . The driver can always obtain the optimum route that matches the latest road condition.

Next, the result table is initialized. That is, the pivot registration flag is cleared to 0, and the path cost is set to infinity (actually, the maximum value determined by the number of bits of the memory). It also initializes the pivot table.
Specifically, the pivot valid flag is cleared to 0. Next, the departure point link S is registered in the pivot table, the pivot valid flag of that row is set to 1, and the route cost of the departure point link S is set to a finite value on the result table, for example, the link cost of the departure point link S. change. This is for starting the route calculation from the departure point link S.

Thereafter, the route search is started. First, refer to the pivot table to see if there is a registered link. If there is a link, the link (link L
) Is taken out, the link L is deleted from the pivot table, and the pivot valid flag is set to 0. Next, referring to the route network table, the exit link P of the link L
To explore. When one exit link P is specified, the route cost of the link L (previously set as a finite value) is referred to on the result table, and the route cost obtained by adding the arc cost to the link P to the route cost A is referred to. And the route cost of the link P on the result table (the initial value is infinite). If the route cost A is smaller, the route cost of the link P on the result table is A
Replace with And link P on the result table
The link is connected by setting the link L as the incoming link of the link.

Then, the pivot table registration flag of the link P is referred to on the result table to register the link P in the pivot table. This is because the next link is searched based on the link P. Furthermore, for links registered in the pivot table, if there are other exit links, route search is continued for those links. In this process, if the route cost A is larger, further route search is terminated.

When the search for the link registered in the pivot table is completed, the route search is continued for the other links registered in the pivot table. In this way, when the links registered in the pivot table disappear, the tree of the optimum route is determined. On the result table, each link is traced in reverse, and the route cost and entry link of each route are registered in the optimum route tree column of the guidance table (Table 2).

The above procedure is performed for other selection options, other departure point links, and the day, the day of the week, and the time zone are changed. Therefore, finally, a plurality of optimum route trees will be obtained for each day, day of the week, time zone, departure link, and selection option. When the process for finding the optimum path tree is completed, the process for creating a sub-optimal path tree, which is a feature of the present invention, starts.

When a sub-optimal route tree is created, the departure point link that constitutes the route network data of the route provision area and any other link in this area (this is called a "destination link") are specified. Then, calculate the sub-optimal route from the origin link to the destination link, and in the same procedure as this, calculate the sub-optimal route to all destination links in the area and Create a suboptimal route tree that is a set of optimal routes.

It should be noted that one quasi-optimal route is obtained for one optimal route, but it is not always necessary to obtain one, and a plurality of routes having different differences are obtained according to the present invention. Considering from the purpose, it may be plural. When a plurality of trees are obtained, a plurality of sub-optimal route trees will be obtained accordingly. The reason why there are three columns of sub-optimal route trees in Table 2 is that a maximum of three sub-optimal route trees can be registered.

Further, the sub-optimal route tree is obtained for each day, day of the week, time zone, departure link, and selection option, like the optimal route tree. In order to obtain the sub-optimal route, in the route network of the route providing area, among routes other than the optimal route, the route cost is (1 + a) times or less (0 <a) times the route cost of the optimal route. The candidate route is selected, and when the route cost of the overlapping portion of the candidate route and the optimum route is the minimum, this candidate route is determined as the sub-optimal route.

To obtain the sub-optimal route, a result table for searching the sub-optimal route, which is similar to the result table shown in Table 4, is required. The result table of Table 4 was used to search the exit link of the specific link, but the result table for the sub-optimal route search reversely searches the entry link of the specific link. Therefore, the entry link is described instead of the exit link in the arc data column.

Table 5 shows an example of the result table for this sub-optimal route search. The difference from the result table in Table 4 is that even if the route cost is equal to or higher than the route cost of the link on the result table, the search is continued without being aborted, and thus the number of incoming links is not limited to one. For this reason, there are multiple pointers to the approach link (corresponding to the normally assumed maximum value of the number of branches at the intersection). Further, since the search is not aborted depending on the magnitude of the route cost, when the link is registered in the pivot table, it is necessary to newly register the link in the pivot table even if the link has already been registered in the pivot table. Therefore, the pivot registration flag is unnecessary.

[0053]

[Table 5]

In the following, description will be made assuming the route network shown in FIG. In the same route network, the number 0-
Reference numeral 10 represents a node, and symbols aq represent links. The thick line links represent the departure point link S and the destination link D, respectively. As shown by the double line, the optimum route is determined as link b → link i → link p, and the route cost of the optimum route is C.

Next, the route cost C is multiplied by (1 + a) to obtain (1 + a) C. a is a value set to about 0.1 or 0.2, for example. (I) First, the links a and c separated from the starting point 0 of the first link j (excluding the departure point link S) on the optimum route are specified, and all the routes going from the link a to the destination link D are searched. , Search all routes from link c to destination link D. In addition, at the time of this search, a link g separating from the starting point 4 of the next link i on the optimum route is specified, all the routes from the link g to the destination link D are searched, and the next route on the optimum route is searched. You may specify the link k separated from the starting point 6 of the link p, and may search all the routes from the link k to the destination link D.

In this search, specifically, the result table and the pivot table are initialized, the destination link D is registered in the pivot table, and the route cost of the destination link D is a finite value, for example, on the result table. This is performed by setting the link cost of the destination link D and starting reverse route search from the destination link D. First, refer to the pivot table to see if there is a registered link. If there is a link, the link (referred to as link L) is taken out, the link L is deleted from the pivot table, and the entry link P of the link L is searched by referring to the result table for searching the suboptimal route. When one ingress link P is specified, the route cost of the link L is referred to on the result table, and the route cost A plus the arc cost to the link P is set as the route cost A, which is the link P on the result table. Compare with the route cost of. If the route cost A is smaller, the route cost of the link P on the result table is replaced with A. Then, the link L is additionally set as the exit link of the link P on the result table to connect the links. At this time, the route cost A is not the route cost of the route R from the currently searched link P to the destination link D but the lower limit value of the route cost of the route R.

Then, the link P is registered in the pivot table. This is because the next link is searched based on the link P. That is, if there is another incoming link for the link registered in the pivot table, the route search is continued for that link. In this process, if the route cost A is larger than (1 + a) C, further route search is terminated. This is because the route cost of the candidate route that is larger than (1 + a) times the route cost of the optimal route is inappropriate as the sub-optimal route. For example, in the example of FIG. 4, link q ← link m ←
Link j ← link e ← link c is link e
The link q ← link m ← link j ← link g ← link f ← link d ← link a is discontinued at the stage when the route cost of link d is calculated. It is assumed that In this way, if the lower limit value of the route cost of the candidate route becomes larger than (1 + a) times the route cost of the optimum route, the search is aborted, so that it is more wasteful than the case of performing the search for all links without aborting the search. Calculation time can be saved. When searching all the routes from the link g to the destination link D, the route cost A of the intermediate route is [(1+
a) C- (link cost of link b)], the route search is further terminated, and when searching all routes from the link k to the destination link D, the route of the intermediate route is used. The cost A is [(1 + a) C-
(Link cost of link b + link cost of link i)], the further route search is terminated (described later).

However, in the present invention, all the candidate routes are obtained without evaluating the route cost of the candidate route during the calculation, and the route cost of the candidate route is evaluated in the subsequent stage, and the route cost of (1 + a) of the optimum route is calculated. ) If it is more than double,
You may take the procedure of deleting a candidate course. When the search is completed for all links registered in the pivot table, if the links a and c are traced in reverse on the result table, all candidate routes from the link a to the destination link D and from the link c All the candidate routes to the destination link D are obtained.

On the result table, the route cost of each candidate route is calculated by adding the link cost of each link when tracing the links in reverse, and the route whose value is larger than (1 + a) C Is excluded from the candidate routes.
Assuming the route network of FIG. 4, the candidate route is link a → link d → link f → link i → link p link a → link d → link h → link n link a → link d → link f → link i → Link k
→ Link m → Link q 3 (Three routes are not included in the search.) (Ii) Next, the candidate route obtained as described above is on the optimum route. After joining the link, it is determined again whether or not the route is away from the optimum route.

In the above example, link a → link d →
Link f → Link i → Link k → Link m → Link q
However, after joining the link i on the optimum route, it is determined to be away from the optimum route. This candidate route is
Since it is not suitable for the suboptimal route, it is excluded. If the candidate routes join the optimal route and then split again, then
This is because it does not meet the purpose of the present invention of providing a plurality of routes that are as different as possible from traveling on an optimum route.

In the above example, it is determined that the number of times that the candidate route joins the link on the optimal route and is separated from the optimal route is once or more. You may judge. In the present embodiment, whether or not the candidate route joins the link on the optimum route, in other words, whether or not the links overlap, the question is whether or not the candidate route intersects the optimum route. It doesn't matter. However, it may be possible to count whether or not the candidate route intersects with the optimum route, and determine whether or not the number of times is a predetermined number or more. (Iii) Next, for the remaining candidate routes, the sum of the link costs of the shared portion with the optimum route is obtained.

In the above example, two candidate routes of and remain, and among these, the shared part with the optimum route is as follows. Link i → link p No shared portion Therefore, the candidate route having the lowest shared portion cost (0) remains.

In this case, instead of selecting the one having the lowest cost of the shared part, the cost of the shared part is not more than b times the cost of the optimum route (0 <b <1), or an overlapping route. You may make it select all the candidate routes whose link cost of a part is below a predetermined value. In this case, it is highly possible that a plurality of candidate routes will eventually remain. (Iv) Next, the link g separated from the starting point 4 of the next link i on the optimum route is specified, and the link g is determined to the destination link D.
Search all the routes that go up to. This search is not necessary if it has been completed in step (i).

This search procedure can be performed in almost the same manner as described in (i) above. However, the difference is that the route cost A of the intermediate route is [(1 + a) C- (link b
Link cost))], the further route search is terminated. because,
This is because in this procedure, link b is omitted and a route from link g to destination link D is searched.

When the route is searched, the link b is matched with it. The route cost of the route thus obtained is obtained, and the route having a value larger than (1 + a) C is deleted from the candidate routes. The route thus obtained becomes the candidate route.
In the example of FIG. 4, link b → link g → link j → link m → link q is a candidate route. (V) Next, as in (ii), after the candidate route joins the link on the optimal route, it is determined again whether or not the candidate route is separated from the optimal route.

In the above example, is separated from the link b on the optimum route, but is not joined to the link b from the middle, so it is determined to be not applicable. (Vi) Next, for the candidate routes, the sum of the link costs of the shared portion with the optimum route is obtained. In the above example, since the shared part of the candidate route and the optimum route is the link b, the link cost of the link b is obtained. (Vii) Next, the link k separated from the starting point 6 of the next link p on the optimum route is specified, and the link k is determined to the destination link D.
Search all the routes that go up to. This search is not necessary if it has been completed in step (i).

This search procedure can be performed in almost the same manner as described in (i) above. However, the difference is that the route cost A of the intermediate route is [(1 + a) C- (link b
(Link cost of link + link cost of link i)]], the further route search is terminated. This is because in this procedure, a route from the link k to the destination link D is searched.

When a route is searched for, links b, i are added to it.
To match. The route cost of the route thus obtained is obtained, and the route having a value larger than (1 + a) C is deleted from the candidate routes. The route thus obtained becomes the candidate route. In the example of FIG. 4, link b → link i → link k → link m → link q is a candidate route. (Viii) Next, as in (ii), after the candidate route joins the link on the optimal route, it is determined again whether or not the candidate route is away from the optimal route.

In the above example, is passing through the link b → link i on the optimum route, but it is determined that it does not correspond because it does not join from the middle. (Ix) Next, for the candidate routes, the sum of the link costs of the shared portion with the optimum route is obtained. In the above example, the shared part of the candidate route and the optimal route of is link b → link i
Therefore, the sum of the link cost of the link b and the link cost of the link i is obtained. (X) As a result, the surviving candidate routes are ,, but the smallest sum of the link costs of the shared part is.

Therefore, the candidate route link a → link d → link h → link n is determined as a sub-optimal route. However, as described above, instead of selecting the one with the lowest cost of the shared part, the cost of the shared part is b times or less (0 <b <1) the cost of the optimum route, or an overlapping route. You may make it select all the candidate routes whose link cost of a part is below a predetermined value.

In the above embodiment, in the route network of the route providing area, among the routes other than the optimum route, the route cost is (1+
a) A route that is less than or equal to twice (0 <a) is selected as a candidate route, and when the route cost of the overlapping portion of the candidate route and the optimal route is the minimum, this candidate route is determined as the sub-optimal route. However, by replacing this procedure, in the route network of the route providing area, all candidate routes other than the optimal route are obtained, and the route cost of the overlapping part of the candidate route and the optimal route is b times the route cost of the optimal route. A candidate route that is the following (0 <b <1) or a candidate route in which the link cost of the overlapping portion is a predetermined value or less is selected, and the route cost of the minimum route cost or the route cost of the optimum route ( 1 + a) times or less (0 <a),
Alternatively, a link cost C of the optimum route, which is equal to or less than a value obtained by adding a predetermined number, may be selected.

As described above, when the sub-optimal routes are obtained, the sub-optimal routes reaching all the destination links in the same area are calculated by the same procedure, and the set of these sub-optimal routes is calculated. Create a suboptimal path tree that is Further, similar to the optimum route tree, the sub-optimal route tree is obtained by day, day of the week, time zone, departure link, and selection option.

The contents of the optimum route tree and the sub-optimal route tree thus obtained are registered in the guidance table,
When the registration in the guide table is completed, the contents of the guide table are transmitted to the optical beacon B. The control device 24 (see FIG. 1) of the optical beacon B selects the optimal route tree and the sub-optimal route tree from the “departure point link” near the point where the optical beacon B is installed, and then its own route memory 21
It is stored in the form of a guidance table inside.

Next, when the vehicle transmits a route provision request and destination data to the optical beacon B, the optical beacon B
The route information regarding the optimal route tree or the route information regarding the sub-optimal route tree acquired by the above method is transmitted to the vehicle through the transceiver 22. The configuration of the vehicle-mounted navigation device 30 will be briefly described with reference to FIG. The vehicle-mounted navigation device 30 has a function of acquiring route information from the optical beacon B, displaying it, and guiding it.

The vehicle-mounted navigation device 30 has a GPS receiver 32 as a direction sensor, and an engine control unit (ECU) 34 as a vehicle speed sensor.
The vehicle speed signal is obtained, and the direction information detected by the GPS receiver 32 and the position information based on the vehicle speed signal are compared with a road pattern stored in a vehicle-mounted map memory (not shown). It has a function of detecting the vehicle position based on a so-called map matching method (see Japanese Patent Laid-Open No. 64-53112).

The vehicle-mounted navigation device 30 further includes information on links (identification number of each link, start point and end point of each link) held by the information center A in the route providing area to which route information from the information center A is provided. Information such as coordinates of the vehicle), and when the destination to which the vehicle wants to go is entered on the screen using the remote control key 33, the link closest to this destination is specified from the links, and the transceiver The destination link and the position data of the own vehicle can be sent to the optical beacon B through 31.

Further, it is also possible to transmit the information indicating whether the vehicle has previously received the route information regarding the optimum route tree or the route information regarding the sub-optimal route tree from the optical beacon B. FIG. 5 is a flowchart showing a control procedure in the case of performing route guidance from the current position to the destination in the vehicle-mounted navigation device 30 of this embodiment.

First, the driver inputs the destination using the remote control key 33 (step T1). After that, when the vehicle reaches a predetermined point for route guidance, such as a main intersection on the route, during traveling (step T2; it is determined that such a predetermined point is reached based on the vehicle position detection information). And a guide route (this "guide route" is a route used for route display and route guidance, and is either the optimum route or the sub-optimal route obtained from the optical beacon B). Condition (step T
3) Instruct the driver of the shape of the intersection and the guidance direction on the screen or by voice (step T4). If it is determined that it is time to receive the route providing service of the optical beacon B while the vehicle is traveling while performing such route guidance (step T5), the vehicle-mounted navigation device 30 sets the destination link D. The transmitter / receiver 31 transmits to the optical beacon B the information for specifying and the information indicating which of the route information regarding the optimum route tree or the route information regarding the sub-optimal route tree has been received from another optical beacon B in the past (step T6). ). At this time, information indicating the selection option may be transmitted together with the driver's preference. The destination data or the like transmitted in this manner is the optical beacon B.
Received by

Upon receiving the destination data and the like, the control device 24 of the optical beacon B specifies the calculation end link which is the link closest to the destination, accesses the guidance table in the route memory, and ends the calculation. Information such as a series of links reaching a link and route costs is acquired and transmitted. In this case, the control device 24 of the optical beacon B selects either the optimum route information or the quasi-optimal route information from the "departure point link" near the point where the optical beacon B is installed, and transmits the selected information. However, this selection criterion is
If the vehicle has acquired route information regarding the sub-optimal route tree in the past, the route information regarding the optimal route tree is transmitted to the vehicle, and the vehicle has acquired route information regarding the sub-optimal route tree in the past. If there is no such case, a random number is generated for the vehicle to generate route information regarding the optimal route tree or route information regarding the sub-optimal route tree, and either one is selected and transmitted.

In the above embodiment, the control device 24 of the optical beacon B selects either the optimum route information or the sub-optimal route information and transmits it to the vehicle. May transmit both the optimum route information and the sub-optimal route information to the vehicle, and the vehicle may select the information. Thus, in the embodiment of FIG. 5, each vehicle
Since the optical beacon B gives either the route information about the optimum route tree or the route information about the sub-optimal route tree, if a guidance instruction is given based on the given route, deviation of traffic can be prevented. , Can avoid congestion.

The optimum route information and / or the sub-optimal route information obtained from the optical beacon B is updated to the latest one by the road traffic information coming from the information center A through the communication line as described above. Therefore, there is also an advantage that you can get a route that can avoid accidents and traffic congestion at the present moment. II. Second Embodiment Next, a second embodiment of the present invention in which an in-vehicle navigation device calculates optimal route information and quasi-optimal route information and uses the obtained route, based on the attached drawings. The details will be described.

FIG. 6 is a block diagram showing the configuration of the navigation device according to this embodiment. This navigation device is mounted on a vehicle and used to support the traveling of the vehicle. This navigation device
Gyro 3 as direction sensor, GPS as position sensor
The receiver 4 is provided, and the vehicle speed signal of the magnetic sensor 2 for detecting the rotation of the rotor of the wheel is acquired as the vehicle speed sensor. The detection outputs of these sensors are given to the vehicle position detection unit 1a in the navigation device body 1. The vehicle position detection unit 1a also reads the road map data stored in the map-dedicated memory D that functions as a road map memory via the CD driver 1c.

The vehicle position detector 1a compares the azimuth information detected by the azimuth sensor, the position information based on the vehicle speed sensor, and the road pattern stored in the map dedicated memory D (so-called map matching method, The vehicle position is calculated based on Japanese Patent Laid-Open No. 64-53112). Since this calculation is performed every fixed period (for example, 1.2 seconds), the vehicle position information is updated in this period as the vehicle travels.

The data representing the current position of the vehicle detected by the vehicle position detecting section 1a is given to the controller 1b in the navigation apparatus main body 1. Controller 1b
Is the control center of this navigation device, the current position data detected by the vehicle position detection unit 1a, the destination data and route calculation condition data input from the remote control key 5 while looking at the screen, and the map dedicated memory D. The optimum route and the sub-optimal route from the current position to the destination are calculated based on the road map data given from. Then, the road map, the current vehicle position mark on the map, and the lines along the optimum route and the sub-optimal route are generated and displayed on the liquid crystal display 6.

The controller 1b has VRAM 1f and SR
It has AM1d, DRAM1e and the like. VRAM 1f
Holds image data to be displayed on the liquid crystal display 6. SRAM1d memorize | stores the link row | line which comprises an optimal route and a semi-optimal route. Remote control key 5
Input the destination, set the route calculation conditions (whether to prioritize the use of toll roads or whether to prioritize the use of ferries, is the current location on an open road or toll road?), And calculate the route The request is made.

The map dedicated memory D stores vehicle position detecting road map data, display road map data, route network data, a link correspondence table and a wide area map correspondence table. The route network data is obtained by dividing a road map (including highway national roads, motorways, national roads, prefectural roads, city roads of designated cities, and other living roads) into a mesh shape, and each mesh node as a node. The route data, which is a combination of links, is divided into a highway national road map, a general road map, and a detailed map and stored. Highway National Highway Map (hereinafter “3rd
The "layers" mainly include highways and national roads (highway national roads, motorways, national roads), and general road correspondence maps (hereinafter referred to as "second layer") together with highways and national roads (general width 5. 5 m or more) is also included. The detailed map (hereinafter referred to as “first layer”) includes highways, national roads, general roads, and even living roads (road width 3.3 m or more). Due to the characteristics of the road map database, a closed route network is formed nationwide for roads above national roads.

The mesh is a Japanese road map with a longitude difference of 1
The upper mesh corresponding to the third layer, which is divided by 40 degrees in latitude and longitude and has a vertical and horizontal distance of about 80Km x 80Km, and this upper mesh is divided into 8 vertical and horizontal parts, and the vertical and horizontal distances are set to about 10Km x 10Km. It has a triple structure of a middle mesh corresponding to a layer and a lower mesh corresponding to the first layer in which the middle mesh is divided into 10 equal parts in length and width and the distance in length and width is about 1 km × 1 km.

A node is generally a coordinate position for identifying an intersection or a turning point of a road. A node indicating the intersection is an intersection node, and a node indicating a turning point of the road (excluding the intersection). It is called an interpolation point node. The link connects the start point node and the end point node, and can be understood as a polygonal line with a direction along the shape of the road (see Fig. 7 (a)).

Ignoring the shape of this polygonal line, link cost (passage time and running distance) information when passing through one or more links and information indicating the connection state with other compressed links are compressed. The link stored as such is referred to as a "compressed link" (see FIG. 7 (b)). This compressed link is
Since the number is small, it is useful for shortening the calculation time when performing the route calculation. Therefore, when the route calculation is performed below, the term “link” means a compressed link.
A link that takes into consideration the degree of curve of the road (see Fig. 7 (a)) is called a "shape link".

The link cost is the time required to travel the link, for example, expressed in seconds. Actually, the link cost changes due to traffic congestion and the like, but here, the cost when the vehicle runs at the legal speed is used. The cost to turn right or left or go straight to enter the next link after leaving the link is called the connection cost. For example, when entry is prohibited, the connection cost is infinite, and when there is a traffic light, the cost takes into account the average signal waiting time when turning right or left or going straight.

The link cost and the connection cost can be changed in consideration of the fact that a beacon receiver or a facsimile receiver is mounted on the vehicle and road congestion information is entered through these. A data file that stores the coordinates of the nodes that form each shape link is called a link shape file, and a data file that stores compressed links is called a link compression file.

The link shape file has, for each shape link, a link number, each coordinate of a start point node, an end point node, and an interpolation point node, a pointer to a compression link corresponding to the link, and one-way distinction. There is. The link compression file stores link numbers of compressed links, road types, link costs, link lengths, pointers to other links connected to the links, connection costs, and the like. This file format is similar to the "route network table" shown in Table 1 above.

The link correspondence table is a table for checking the one-to-one or one-to-many correspondence between the compressed links and the display link sequence, and the wide area map correspondence table includes the compressed links and the wide area map display coordinate sequence. It is a table for checking the correspondence of 1 to 1 or 1 to many. The road map data for display stores a link sequence for display of the second layer or the first layer and a coordinate sequence for second layer wide area map display together with topographical information of roads, famous facilities, bridges, rivers, lakes, etc. There is. The display link string and the wide area map display coordinate string are link strings for displaying the optimum route on the screen, and the compression link and the one-to-one or many pairs are set by the link correspondence table and the wide area map correspondence table, respectively. It is associated with 1.

The controller 1b has a vehicle position detecting section 1a.
The link closest to the current position of the vehicle input from is the calculation start link, the link closest to the destination is the calculation end link, and the tree with the lowest link cost from the calculation start link to all links is created. , Compute the optimal route using the Dijkstra method or the potential method of selecting the route reaching the end link.

As a work area for executing the Dijkstra method or the potential method, the controller 1b of the navigation device 1 prepares a buffer area for storing a pivot table on the DRAM 1e. An outline of the optimum route calculation procedure performed by the controller 1b is as follows. When the current position data of the vehicle is input from the vehicle position detection unit 1a, the controller 1b reads the link shape data of the medium mesh including the current position (for four medium meshes around the vehicle), and the predetermined area of the DRAM 1e. The link shape data is stored in. Furthermore, near the current position,
Attempt to acquire link compression data for the medium mesh (9 medium meshes around the vehicle). However, if the selected link compressed data does not fit in the DRAM 1e,
Reduce the number of meshes of link compressed data to be acquired. The acquired link compression data is stored in a predetermined area of the DRAM 1e.

Next, if the driver sets a destination with the remote control key 5, the link shape data (for four medium meshes around the vehicle) near the destination is read and DR
The link shape data is stored in a predetermined area of AM1e. Further, the link compressed data of the medium mesh near the current position is obtained in the same manner as described above and stored in a predetermined area of the DRAM 1e.

While acquiring the link shape data and the like near the destination, the driver gives priority to the calculation condition for requesting the route calculation by the remote control key 5, for example, the use of the expressway or the ferry. It is possible to set conditions such as whether to set a waypoint. Next, if there is a route calculation request from the driver using the remote control key 5, the link shape data including the current position is used to specify the link closest to the current position as the calculation start link, and the link shape data including the destination is calculated. Using the link compressed data and, if necessary, the third layer link compressed data between the calculation start link and the calculation end link as the calculation end link by specifying the link closest to the destination set using (The judgment as to whether or not the third layer link compressed data is necessary is “necessary”, for example, when the current position and the destination are far from each other and the route cannot be calculated by the link of the second layer only. If the route to the destination is close and the route can be calculated by the link of the second layer only, it is not necessary.) Calculate the route by the Dijkstra method or the potential method.

When the optimum route is obtained, a process for obtaining a sub-optimal route is started. When obtaining a sub-optimal route, I. The quasi-optimal route is obtained by the same procedure as in the "first embodiment of the present invention in which the ground system obtains the optimal route information and the quasi-optimal route information and transmits it to the vehicle". That is,
In order to obtain the sub-optimal route, among the routes other than the optimal route, the route cost is (1 + a) times or less (0 <a) times the route cost of the optimal route, based on the link compression data. The candidate route is selected as a route, and when the route cost of the overlapping portion of the candidate route and the optimal route is the minimum, this candidate route is determined as the sub-optimal route.

At this time, it is also possible to exclude the candidate routes whose number of times of joining and separating to the optimum route or number of times of crossing is 1 or more than n times. The procedure is the same. When the optimum route and the sub-optimal route are obtained, the link compression data forming the optimum route and the sub-optimal route and the intersection guidance data (data such as arrows for guiding the intersection) created based on the link compression data are stored in the result table of the SRAM 1d. The image memory VRA is stored in the image memory VRA and is converted into a display link sequence for displaying the optimum route or a coordinate sequence for wide area map display.
It is drawn on M1f and displayed on the road map.

When both the optimum route and the sub-optimal route are displayed as described above, the vehicle can travel along either route.

[0101]

As described above, according to the multiple route acquisition method of the present invention as set forth in any one of claims 1 to 6, routes other than the optimum route from the calculation start link to the calculation end link are set as candidate routes. It is possible to select a sub-optimal route for this candidate route, in which the link cost of the candidate route is not much larger than the link cost of the optimal route, and the overlap between the candidate route and the optimal route is not too long. Therefore, it is possible to acquire and show a plurality of routes that are not a large detour but have some differences.

In particular, according to the method for acquiring a plurality of routes according to the second or fourth aspect, in selecting the sub-optimal route, it is possible to exclude candidate routes that go in and out of the optimal route. It is possible to exclude candidate routes that do not change, and obtain and show multiple routes with differences. In particular, according to the method for acquiring a plurality of routes according to the third or sixth aspect, since one suboptimal route can be selected, the user can easily select it.

According to the navigation device of the present invention as set forth in any one of claims 7 to 10, a route other than the optimum route from the calculation start link to the calculation end link is acquired as a candidate route, and this candidate route is acquired. On the other hand, it is possible to select a sub-optimal route in which the link cost of the candidate route does not become much larger than the link cost of the optimal route and the overlapping portion of the candidate route and the optimal route does not become too long. However, it is possible to display to the driver a plurality of routes that differ as much as possible without causing a large detour, and it is possible to prevent traffic from being cut off.

In particular, according to the navigation device of the eighth aspect, when selecting the sub-optimal route, it is possible to exclude candidate routes that go in and out of the optimal route, so that it is different from the optimal route. It is possible to exclude candidate routes that do not exist, and it is possible to acquire and show multiple routes with differences.
In particular, according to the method for acquiring a plurality of routes according to the ninth or tenth aspect, since one suboptimal route can be selected, the driver can be easily selected.

[Brief description of the drawings]

1 is a schematic diagram of a route information transmission system, and FIG.
(a) is an information center, Fig. 1 (b) is an optical beacon, and Fig. 1 (c)
Indicates an in-vehicle navigation device.

FIG. 2 (a) is a road map including optical beacons B ₁ , B ₂ , and B ₃ , and FIG. 2 (b) is a corresponding link diagram.

FIG. 3 (a) is a diagram showing a series of links to be connected, and FIG. 3 (b) is a diagram explaining the concept of arc costs and route costs.

FIG. 4 is a link diagram showing an example of a route network for explaining a method of obtaining a sub-optimal route.

FIG. 5 is a flowchart showing a control procedure in the case where the vehicle-mounted navigation device indicated by the optimum route or the sub-optimal route guides the route from the current position to the destination.

FIG. 6 is a block diagram showing a configuration of an in-vehicle navigation device having a function of calculating an optimum route and a sub-optimal route.

7A and 7B are diagrams illustrating the shapes of links, FIG. 7A shows a shape link, and FIG. 7B shows a compression link.

[Explanation of symbols]

 1 Navigation Device Main Body 1a Vehicle Position Detecting Unit 1b Controller 1c CD Driver 1d SRAM 1e DRAM 1f VRAM 2 Magnetic Sensor 3 Gyro 4 GPS Receiver 5 Remote Control Key 6 Liquid Crystal Display D Map Memory A Information Center 11 Controller 12 Communication Line Modem 13 Map dedicated memory B Optical beacon 21 Route memory 24 Control device 30 In-vehicle navigation device 31 Transceiver 32 GPS receiver 32 33 Remote control key 34 Engine control unit (ECU)

Front page continuation (72) Kenji Tenme, 1-3 1-3 Shimaya, Konohana-ku, Osaka City, Sumitomo Electric Industries, Ltd. (72) Inventor, Hiroshi Imai 7-3-1 Hongo, Bunkyo-ku, Tokyo (72) Inventor Tetsuro Shibuya 7-3-1 Hongo, Bunkyo-ku, Tokyo Inside the University of Tokyo

Claims (10)

[Claims] (A) An optimum route that minimizes the link cost from the calculation start link to the calculation end link by using any two links constituting the route network of the route providing area as a calculation start link and a calculation end link. And a procedure for acquiring a route other than the optimum route from the calculation start link to the calculation end link as a candidate route in the route network of the same route providing area, (b) A procedure for selecting a link cost that is (1 + a) times or less (0 <a) times the link cost C of the optimum route or a value that is less than or equal to a value obtained by adding a predetermined number to the link cost C of the optimum route, and (d) A candidate route whose link cost of the overlapping portion of the candidate route and the optimal route is less than or equal to b times the link cost C of the optimal route (0 <b <1), or of the overlapping portion Multipath acquisition method characterized by Nkukosuto adopts a procedure to select a candidate path is less than a predetermined value, to determine the selected candidate path as a quasi-optimal route. 2. Before the step (d) or (b), (c) the number of times that the candidate route joins and separates to the optimum route or the number of times of intersection is n times or less (n ≧ 0). The method for acquiring multiple routes according to claim 1, further comprising the step of selecting. 3. The method according to claim 1, wherein instead of the procedure of (d), a procedure of (d-1) selecting a route having a minimum link cost in the overlapping portion of the candidate route and the optimum route is adopted. 2. The method for acquiring multiple routes described in 2. 4. (a) An optimal route that minimizes the link cost from the calculation start link to the calculation end link, with any two links constituting the route network of the route providing area being the calculation start link and the calculation end link. And a route network of the same route providing area, a procedure for obtaining a route other than the optimum route from the calculation start link to the calculation end link as a candidate route, (e) A procedure for selecting a link cost of the overlapping portion of the optimum route which is b times or less (0 <b <1) of the link cost C of the optimum route, or a link cost of the overlapping portion of which is a predetermined value or less; (g) The link cost of the candidate route is not more than (1 + a) times the link cost C of the optimal route (assuming 0 <a),
Alternatively, a procedure for selecting a link cost C of the optimum route that is equal to or less than a value obtained by adding a predetermined number to the selected route and determining the selected candidate route as a sub-optimal route. 5. Before the step (g) or (e), (f) the number of times that the candidate route joins and separates into the optimum route or the number of times of intersection is n times or less (n ≧ 0) The method for acquiring a plurality of routes according to claim 4, characterized in that a selecting procedure is further adopted. 6. The multi-route acquisition according to claim 4 or 5, characterized in that, instead of the procedure of (g), a procedure of (g-1) selecting a candidate route having a minimum link cost is adopted. Method. 7. A route calculation means for calculating an optimum route to a destination set by a user using a road map memory storing road map data, and a display means for displaying and guiding the calculated route. In the navigation device having the above, a route other than the optimum route is acquired as a candidate route, and a candidate route that has passed the determination by each of the following determination means is determined as a sub-optimal route. (i) For a candidate route, the link cost of the candidate route is (1 + a) times or less (0 <a) times the link cost C of the optimal route, or a predetermined number is set to the link cost C of the optimal route. First determining means for selecting a value that is less than or equal to the added value, and (ii) the link cost of the overlapping portion of the candidate route and the optimal route is b times or less (0 <b <1) of the link cost C of the optimal route. Second determining means for selecting a certain one or one in which the link cost of the overlapping portion is equal to or less than a predetermined value. 8. The third determination means for selecting a candidate route having a number of times of joining and separating an optimal route and a number of times of intersection or a number of times of intersection being n times or less (n ≧ 0). The described navigation device. 9. A fourth alternative to the second determining means, from among candidate routes that have cleared the determination by the first determining means, a route having a minimum link cost in the overlapping portion of the candidate route and the optimum route is selected. The navigation device according to claim 7, further comprising a determination unit. 10. In place of the first judging means, there is provided a fifth judging means for selecting a candidate route having a minimum link cost from among the candidate routes that have cleared the judgment by the second judging means. The navigation device according to claim 7, characterized in that: