A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Typically, the navigation system displays a map image on a monitor screen while superimposing thereon a mark representing the current location of the user. At an intersection, the navigation system notifies the user which direction to turn at the intersection.
When a destination is specified by a user, the navigation system determines a route to the destination based on, for example, the shortest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. After determining the calculated route, the navigation system starts the route guidance operation to guide the user along the calculated route to the destination. Typically, the navigation system shows the intersection to show the next turn and a direction of the turn. Such route guidance by the navigation system is also accompanied by voice instructions.
The navigation system displays a map image on a monitor screen on which various map elements such as streets including the calculated route to the destination, fields, rivers, mountains, buildings, etc., are illustrated. The user is able to scroll the illustrated image on the screen to change the map image to that of the desired location. The user can scroll the map image by placing a finger on the display screen and dragging a cursor on the screen or by operating a scroll key on a front panel or remote controller, etc. The scroll key may be configured by, for example, eight directional arrow keys, etc.
FIGS. 1A-1C are schematic diagrams showing display examples on the screen of a navigation system where the map image is being scrolled by moving a cursor 23 on the screen. Specifically, in FIG. 1A, the map image is scrolled by moving the cursor 23 to the right as shown by an arrow 25, which results in the map image shown in FIG. 1B. The map image of FIG. 1B is further scrolled by moving the cursor 23 to the upper left direction shown by an arrow 27, which results in the map image shown in FIG. 1C.
The schematic view of FIG. 2 shows a scroll direction involved in the above example of the map scroll operation shown FIGS. 1A-1C. In the scroll direction of FIG. 2, the first scroll path 51 (from point A to point B) is directed toward the right and the second scroll path 53 (point B to point C) is directed toward the upper left. Namely, the scroll direction is changed sharply between the first path 51 and the second path 53. Such a sharp change of the map scroll direction may confuse and/or dazzle the user watching the screen especially when the scroll speed is high because it is difficult to follow the abrupt change of the map image on the screen.
Namely, there is a drawback that the change of the map image is too abrupt as shown in FIG. 2 during the transition between the first scroll path 51 and the second scroll path 53. When the user changes the direction of the map scroll to another and the speed of the scroll operation is high, it may be difficult for the user to recognize what is actually illustrated on the screen is the one that the user wants. Moreover, the user may repeatedly overshoot the location on the screen in such a situation until reaching the actually desired location because it is difficult to accurately control the location on the map image. Thus, there is a need of a map scroll method and apparatus that overcomes the shortcomings described above.