A navigation system performs travel guidance for enabling a user to easily and quickly arrive at the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a user 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 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. When a destination is specified by the user, the navigation system calculates an appropriate route to the destination and starts a route guidance operation. At an intersection on the calculated route to the destination that requires a maneuvering action, the navigation system notifies the user which direction to turn.
Typically, recent navigation systems include a route simulation function to graphically display a simulated trip for reaching the destination through the calculated route. The purpose of the route simulation function is to allow the user preview the trip so that the user can become familiar with the basic route. The navigation system calculates a route from the starting point to the destination, and shows an image of travel along the calculated route on a monitor screen by moving a position indicator.
For example, on the map image on the monitor screen, the icon showing the vehicle position moves along the calculated route from the starting point to the destination. FIGS. 1A and 1B are schematic diagrams showing examples of image on the monitor screen of the navigation system when the route simulation is performed. In FIGS. 1A and 1B, a reference number 29 indicates the starting point, and a progression indicator 23 is a highlighted image on the calculated route which shows a simulated position of the vehicle. The head of the progression indicator 23 gradually moves toward the destination on the map image. Thus, the movement of the head of the progression indicator 23 illustrates the movement of the simulated vehicle during the route simulation operation.
FIG. 1A shows a case where a relatively short time has passed after the start of the route simulation operation. The progression indicator 23 moves on the calculated route in the direction as shown by the arrow with a constant speed. In FIG. 1B, the route simulation operation is further advanced toward the destination and the head of the progression indicator 23 is on a freeway 91. In the conventional route simulation operation, the simulation speed on the map image, i.e., the moving speed of the progression indicator 23, is constant regardless of the location on the route, the type of road on the route, or a scale factor of the map image.
Although the route simulation function is a useful feature, it can pose a problem when a distance of the route for the route simulation is very long. For example, in the case where a route from Los Angeles to New York is to be simulated on the navigation screen, it can take several hours to finish the route simulation operation. Thus, it is desired that the route simulation operation be completed within a relatively short period of time even when a distance between the starting point and the destination is very long while the route simulation can provide adequate information for the user to obtain a basic idea of the route before actually heading to the destination.