The invention relates to a navigation system for making a route search to preset destinations, thereby providing route guidance.
Various navigation systems have been proposed to implement route guidance from departure or current position to any desired destination via transit points using screen displays and voice. As is well known in the art, a typical vehicular navigation system is made up of an information storage device in which there is stored map data, guidance data for achieving route guidance, provided to the operator, as to geometrical features of intersecting points and locations to be passed by, using screen displays and voice. By inputting the transit point(s) and destination, thereby providing route instructions, a route to the destination is identified (route search). For this reason, the vehicular navigation system includes an input/output device for inputting and outputting information about route guidance, a present-position sensing device for sensing the present position of the vehicle, an information storage device in which there is recorded the navigation data required for route calculation, and image and voice guidance data needed for route guidance, and a central processing unit for performing search processing and the image guidance processing needed for providing route guidance as well as for performing control of the overall system.
In general, the information storage device is a database which, as shown in FIG. 1 for example, comprises files such as an index, map data, search data, guidance data, map matching data, and destination data, with all the data needed for a navigation system recorded therein. CD-ROMs are often used as practical storage media. The device also has an application section including navigation programs, such as a map drawing subsection (a map drawing program), a route search subsection (a route search program), a route guidance subsection (a route guidance program), a present-position calculation subsection (a present-position calculation program) and a destination setting operation control subsection (a destination setting operation control program), and an operating system (OS) section. Given processing is performed using map data by the map drawing subsection, search data by the route search subsection, guidance data by the route guidance subsection, map matching data by the present-position calculation subsection, and destination data by the destination setting operation control subsection. It is here to be noted that at the present-position calculation subsection the calculation of the present position is performed using map data; that is, if the map data is used not only at the map drawing subsection but at the present position calculation subsection as well, it is then possible to dispense with the map matching data, thereby reducing the quantity of data required.
At the present-position calculation subsection, direction information and distance information obtained in the form of signals from a relative direction sensor, an absolute direction sensor and a distance sensor are collated with the map data or map matching data to detect the present position. Given instructions for input of the intended point, such as the destination and route search, the route search subsection uses the search data to make a search to find out the optimum route to the destination. Upon the startup of guidance following this, the route guidance subsection displays a map indicating in what direction the vehicle is to run from the present position, for instance. At the same time, the guidance data is used according to the identified route to output, in the form of screen displays and voice, a variety of information about intersecting points, geometrical features of locations to be passed by, distances to transit points, and in what direction the vehicle is to turn at an intersecting point.
A conventional vehicular navigation system is generally broken down into two types in terms of the manner of storing programs and data for performing the route search and developing the route guidance. In one type, as shown in FIG. 2B, only the data is stored in a CD-ROM while applications and OS programs are done in a central processing unit. In another type, as shown in FIG. 2A, programs and data are stored in the CD-ROM, and are then sequentially loaded into a program memory space located in the central processing unit.
However, the system of the type having both the navigation programs and map data stored in the CD-ROM, wherein, upon launching, the navigation programs are loaded into the program memory space for the purpose of running them, takes much more time to start up or launch, when compared with the system of the type having navigation programs stored in the central processing unit because, whenever the system is launched, the navigation programs must be loaded into the program memory space.
All these known navigation systems have programs and data of their own, and so are designed to perform a route search and route guidance of their own. For this reason, they are sophisticatedly different from each other not only in terms of the route search algorithm and its results, but also in terms of how to achieve the route guidance as well. For instance, differences are apparent in how maps are displayed and present positions are expressed, screen displays, voice information, and the timing of intersecting points and geographical features. It is, thus, always required for a supplier to provide a central processing unit and CD-ROM in a set-up form. Once a user has purchased a certain system, as set up by a certain maker, on the other hand, it is always required for the user to use CD-ROMs made to the specifications of that maker, i.e. compatible CD-ROMs. For example, in a system A, composed of a CD-ROM with program A and data A stored therein and a central processing unit, services rendered to the user are simply those of making use of the concepts behind a route search and route guidance in a specific system A. In other words, CD-ROM with program B and data B stored therein cannot be separated from a system B and the CD-ROM used with a central processing unit for running on the system A that is conceptually different from the system B even though the product, a specified route, is substantially the same. To update or complete maps, early users have to wait for software makers to develop appropriate applications, and if updated applications are not available to the users in the system they have, they must somehow replace their existing central processing unit and CD-ROM with a system having more current data and/or programs/applications.