The present invention relates to a car navigation system for displaying the present location and a heading direction of a car on a map displayed on a screen formed by a cathode ray tube or the like.
A car navigation system displays a map on a display, and points at the car""s position and a heading direction on the map. The map shows placenames and buildings with text or marks in addition to terrain and roads.
When items described with text or marks are closely located, the text and marks sometimes overlap each other. A prior art map has only shown the text closest to the car when such an overlap occurs.
FIGS. 1(A)-1(D) illustrate an example of the prior art map. In FIG. 1(A), a map (not shown) is displayed on screen 10, and a car position 11, place or point-of-interest names and buildings denoted with text 12, 13, 14, 15 and 16 are shown on the map. An arrow mark at car position 11 indicates that the car is heading upward. In FIG. 1(A), the heading direction is upward with respect to the paper.
In this case, a plurality of text such as 12, 13, 14, 15 and 16 are displayed and some of them overlap each other. This makes the map hard-to-read. Therefore, text 13 is deleted from the overlapping texts of text 12 and text 13, because text 13 is further away from car position 11, and text 15 is deleted from overlapping texts of text 14 and text 15, because text 15 is further away from car position 11. A resultant map thus drawn is shown in FIG. 1(B).
However, when the car moves, the text displayed varies accordingly, such as from FIG. 1(B), to FIG. 1(D) through FIG. FIG. 1(C), and the varied text thus blinks. This makes the screen hard-to-read.
The present invention addresses the problem discussed above, and aims to provide a car navigation system providing an easy-to-read display by avoiding a map hard-to-read due to a plurality of text, and free from text blinking.
The car navigation system of the present invention is defined in the appended claims and comprises the following elements:
a text memory for storing text data included in a map; and
a displayed data memory for storing displayed data.
This car navigation system determines an overlap of the text stored in the text memory with the displayed data stored in the displayed-data-memory, and displays a text free from overlap.