Map display apparatus

#This invention relates to a map display apparatus for use in a navigation system for measuring the position of a mobile body and reporting the present position to a user, and more specifically to a bird's-eye view map display apparatus which provides a map in a more comprehensible way to the user.

#A navigation apparatus mounted to a mobile body processes information from a variety of sensors to measure the position of the mobile body and reports the position to a user. This navigation apparatus comprises position measurement means for measuring the absolute position of a mobile body, memory means for storing map data constituted by two-dimensional vector data obtained by projecting points on the ground such as roads and buildings on a plane divided into meshes by universal transverse Mercator projection and character data accompanying the two-dimensional vector data, input means for receiving commands from the user, and display means for reading the necessary vector data from the map mesh stored in the memory means in accordance with the command inputted from the input means and conversion processing the data to display the map on a display. Here, data conversion processing includes movement conversion for changing the display position of the map, reduced scale conversion, such as enlargement and reduction, used for displaying the map in an arbitrary reduced scale and rotation conversion for changing the displaying direction of the map. By means of these processings, a plan view map depicting the ground surface directly overhead by normal projection is displayed on the display.

#In navigation apparatuses, according to the prior art, plan view map display which depicts a map by normal projection directly overhead has been employed to display the map. When two points spaced apart from each other are simultaneously displayed, therefore, a reduced scale becomes unavoidably great and detailed information cannot be displayed. One of the means for solving this problem is a bird's-eye view display system which displays a map when points having a certain height from the ground surface are looked down obliquely from afar on a plane. In order to apply this bird's-eye view display to the navigation apparatuses, the following problems must be solved.

#FIG. 1 shows a bird's-eye view map display according to an embodiment of the present invention;

#FIG. 2 is an explanatory view showing a perspective conversion processing of a map;

#FIGS. 3A, 3B, 3C and 3D are explanatory views showing a perspective conversion process of a map;

#FIG. 1 shows an example of the bird's-eye view map displayed by a bird's-eye view map display device mounted to a navigation system according to an embodiment of the invention. The bird's-eye view map display device according to this embodiment generates a bird's-eye view 102 showing a bird's-eye view from a specific position as a projection chart of two-dimensional map data (indicated by reference numeral 101 in FIG. 1), and displays it on a display screen of a display 2. Incidentally, in the bird's-eye view 102 shown in FIG. 1, a folded line 103 is provided with a thick line and is highlighted in order to represent a guiding route. An artificial background 104 represents the sky, a mark 105 represents the present position and an orbit mark 106 represents the orbit of a car so far driven. Further, arrows in FIG. 1 represent the relationship of projection from the two-dimensional map data 101 to the bird's-eye view 102.

#The outline of bird's-eye view map display as the characterizing feature of the present invention will be explained with reference to FIG. 2.

#In printed map charts or in the navigation systems according to the prior art, a map is represented by a plan map display obtained when a given area is viewed from an infinitely remote point above this area. Because this plan map display has the advantage that a reduced scale is constant irrespective of points inside the same display screen, the feel of distance is easy to grasp. When an area between certain two points is represented on the same screen, however, the operation for adjusting and optimizing the reduced scale of the map display becomes necessary, and if the distance between these two points is great, only limited information can be displayed because the quantity of information that can be displayed at one time is restricted by the size of the display used and the level of its precision. Bird's-eye view display is employed as means for solving this problem. When this bird's-eye view display is used, the information of those portions which are close to the viewpoint is enlarged while the information of those remote from the viewpoint is reduced, as is obvious from FIG. 2. Therefore, when the area between certain two points is displayed on the same screen, the point for which more detailed information is required is situated close to the viewpoint with the other being remote from the viewpoint, and their mutual positional relationship is represented in an easily comprehensible form by displaying the two points on the same screen. Further, a greater quantity of information can be provided to the user on the information near the viewpoint. This bird's-eye view display can be accomplished by effecting perspective conversion which projects two or three-dimensional map information of a plane A to a plane B describing a certain angle 0 with the plane A. Since two-dimensional map data can be used as the map information used, bird's-eye view display is feasible by adding the perspective conversion function to existing navigation systems without adding new map data, but various contrivances must be made when the bird's-eye view display is put into practical use.