1. Field of Invention
The present invention relates to a navigation apparatus capable of searching for an optimum route along which to drive a vehicle, and also to a navigation system including such a navigation apparatus.
2. Description of Related Art
A navigation apparatus is known which displays a route from a start point to a destination point and provides navigation information along the route making it possible for a user to easily navigate a vehicle.
In such a navigation apparatus, the current position of the vehicle is detected by using a GPS, or the like, and the detected current position is displayed together with a road map on a display. A route from a starting point to a destination is searched for, and navigation information resulting from the search is provided. The route search is performed, for example, by means of the Dijkstra method or a similar method. That is, in the navigation apparatus, the costs (scores) for routes from the start point to an arbitrary point are calculated on the basis of current road traffic information (at a time when searching is performed) and also on the basis of a distance from the current position to the arbitrary point. The distance from the current position to the arbitrary point is determined by using map data stored in the navigation apparatus or supplied from an external data storage device. After the calculation of the costs is completed for all possible routes to the destination, the route having the minimum cost is selected as an optimum route from the current position to the destination.
The above-described navigation apparatus is capable of acquiring road traffic information indicating the current status in terms of congestion and/or traffic restriction information, searching for a shortest route, and calculating a predicted time needed to reach a destination.
A navigation apparatus has been proposed that is capable of searching for road traffic information associated with a particular date/time at which to start driving a vehicle. The road traffic information is predicted using statistically predicted traffic information determined from past road traffic information indicating the congestion status or the like (Japanese Unexamined Patent Application Publication No. 2002-148067). This makes it possible to determine, in a more reliable fashion, a shortest route and a predicted time needed to reach a destination on a particular date/time at which to start driving.