Abstract:
A map display method in a navigation system has a bird&#39;s-eye view display function of displaying a map image in conjunction with a background image. The map display method in a navigation system has a step of displaying a horizon that indicates a boundary between the map image and the background image, and is rounded at least in part. Besides the bird&#39;s-eye view display effect, the method can enhance a sense of realism of the bird&#39;s-eye view display. Thus, it can solve a problem of a conventional method in that the bird&#39;s-eye view display effect cannot be achieved satisfactorily because the conventional method displays a pseudo horizon in a straight line to indicate the boundary between the map image region and the background image region.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a map display method in a navigation system and a navigation apparatus having a bird&#39;s-eye view display function that provides visual effect as though its map image were seen from above obliquely. 
     2. Description of Related Art 
     For example, Japanese patent application laid-open No. 7-220055 discloses a navigation system with a bird&#39;s-eye view display function. It carries out calculations needed for the bird&#39;s-eye view display by processing the map data of each predetermined square block according to display parameters such as a display reference point (for example, the position of the vehicle itself) and a display angle, and draws a bird&#39;s-eye view as shown in FIG. 11 using the calculation result. The bird&#39;s-eye view display can provide an enlarged view of the information near the display reference point (the position of the vehicle itself) together with information about distant areas. Accordingly, it can reduce the frequency of map switching, thereby improving its operability. 
     In FIG. 11, the reference numeral  101  designates a map image region;  102  designates a background image region;  103  designates a horizon representing the boundary between the two regions;  104  designates a retrieved route displayed in the map image region  101 ; and  105  designates the position of the vehicle itself displayed on the retrieved route  104 . At the periphery of the map image region  101 , there are displayed a bearing display mark  106 , a display mark  107  of the distance to a destination and predicted arrival time, a map transfer switch  108 , a position registration switch  109 , an image mode switch  110 , a distance display mark  111  indicating the distance to the next corner and the like. Besides, current time  112  is displayed on the background image region  102 . 
     With the foregoing configuration, the conventional navigation system has the following problem with the bird&#39;s-eye view display. Although it sets a pseudo horizon  103  as a boundary between the map image region  101  and the background image region  102  that limits the display range of the map image, since the pseudo horizon is a straight line, it provides a viewer with little realism, presenting a problem of being unable to achieve enough effect of the bird&#39;s-eye view display. 
     SUMMARY OF THE INVENTION 
     The present invention is implemented to solve the foregoing problem. It is therefore an object of the present invention to provide a map display method in a navigation system and a navigation apparatus capable of enhancing a sense of realism by rounding the horizon. 
     According to a first aspect of the present invention, there is provided a map display method in a navigation system having a bird&#39;s-eye view display function of displaying a map image in conjunction with a background image, the map display method in a navigation system comprises a step of displaying a horizon that indicates a boundary between the map image and the background image, and is rounded at least in part. 
     Here, the map display method in a navigation system may further comprise the steps of: preparing a plurality of background data to be pasted with different degrees of roundness of the horizon; selecting one of the background data to be pasted in accordance with a display scaling; and displaying the background data with super imposing the background data upon the map data. 
     The map display method in a navigation system may further comprise the steps of: preparing a plurality of background data to be pasted with different degrees of roundness of the horizon; selecting one of the background data to be pasted in accordance with a vehicle speed; and displaying the background data with superimposing the background data upon the map data. 
     The horizon may be rounded within a display inhibition region which is adjacent to the background image, and in which display of a land mark or a destination mark of the map image is inhibited. 
     According to a second aspect of the present invention, there is provided a navigation apparatus comprising: a bird&#39;s-eye view generating section for generating a bird&#39;s-eye view from map data input in accordance with a display target area; a display section for displaying the bird&#39;s-eye view; and a horizontal background data generating section for generating background data including a rounded horizon as a background image to be superimposed upon a map image corresponding to the map data. 
     Here, the navigation apparatus may further comprise: a memory for storing a plurality of background data to be pasted with different degrees of roundness of the horizon; a display scaling decision section for deciding a display scaling; and a horizontal roundness decision section for deciding a degree of roundness of the horizon in accordance with the display scaling determined by the display scaling decision section, wherein the horizontal background data generating section may read from the memory the background data to be pasted with the degree of roundness determined by the horizontal roundness decision section. 
     The navigation apparatus may further comprise: a memory for storing a plurality of background data to be pasted with different degrees of roundness of the horizon; and a horizontal roundness decision section for deciding a degree of roundness of the horizon in response to a speed of a vehicle detected by a vehicle speed sensor, wherein the horizontal background data generating section may read from the memory the background data to be pasted with the degree of roundness determined by the horizontal roundness decision section. 
     The display target area may be decided in accordance with a display scaling, a display angle, a display position and a bearing of a vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a configuration of a navigation apparatus of an embodiment 1 in accordance with the present invention; 
     FIG. 2 is a functional block diagram of the navigation apparatus as shown in FIG. 1; 
     FIG. 3 is a flowchart illustrating the operation of the embodiment  1 ; 
     FIG. 4 is a diagram showing an example of the display on the monitor of the embodiment 1; 
     FIG. 5 is a functional block diagram of the navigation apparatus of an embodiment 2 in accordance with the present invention; 
     FIG. 6 is a flowchart illustrating the operation of the embodiment  2 ; 
     FIG. 7 is a diagram showing background patterns to be stored in a memory in advance, which are designed in accordance with a display scale and have different roundness; 
     FIG. 8 is an example of a detailed map viewed from a low angle; 
     FIG. 9 is an example of a general map viewed from a high angle; 
     FIG. 10 is a functional block diagram of the navigation apparatus of an embodiment 3 in accordance with the present invention; and 
     FIG. 11 is a diagram showing a display state on the monitor of a conventional navigation apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will now be described with reference to the accompanying drawings. 
     Embodiment 1 
     FIG. 1 is a block diagram showing a configuration of a navigation apparatus of an embodiment 1 in accordance with the present invention. In FIG. 1, the reference numeral  1  designates a navigation apparatus;  2  designates an operation keypad for inputting data to the navigation apparatus  1 ;  3  designates a vehicle speed sensor for detecting the vehicle speed; and  4  designates a CD-ROM or DVD-ROM that stores the map data. 
     The navigation apparatus  1  comprises a GPS receiver  6  with an antenna  5  for receiving satellite radio waves; a gyrocompass  7  for detecting the bearing of the vehicle; a CD/DVD drive  8  for reading map data from the CD-ROM or DVD-ROM; a main CPU  9  with a memory for executing various calculations; and a drawing IC  10  for generating a display image from the information fed from the main CPU  9 . The reference numeral  11  designates a monitor for displaying the image produced by the drawing IC  10 . 
     FIG. 2 is a functional block diagram of the navigation apparatus as shown in FIG.  1 . The correspondence between the components of the two figures are as follows. Map data  21  correspond to the CD-ROM  4  and CD/DVD drive  8  of FIG. 1. A vehicle-position/direction decision section  22  corresponds to a part of the main CPU  9  of FIG.  1 . It decides the position and direction of the vehicle itself from the data fed from the vehicle speed sensor  3 , gyrocompass  7  and GPS receiver  6  and the map data  21 . A horizontal background data generating section  23 , a bird&#39;s-eye view generating section  24 , a display scaling decision section  25 , and a display-position/bearing/angle decision section  26  are a part of the main CPU  9 , each. A display scaling input section  27  and a display-direction/angle/reference-point input section  28  corresponds to the operation keypad  2  of FIG. 1. A display section  29  corresponds to the monitor  11 . 
     Next, the operation of the present embodiment 1 will be described. 
     FIG. 3 is a flowchart illustrating the operation of the present embodiment 1. Upon the start of the operation, the following steps are taken: 
     (1) The display-position/bearing/angle decision section  26  decides the area to be displayed from the signals fed from the vehicle-position/direction decision section  22  and display-direction/angle/reference-point input section  28  in response to the vehicle speed signal from the vehicle speed sensor  3 , the vehicle bearing signal from the gyrocompass  7 , the received signal of the GPS receiver  6 , the map data read from the CD-ROM/DVD-ROM  4  via the CD/DVD drive  8 , and the display angle signal and display scaling signal input by a user via the operation keypad  2  (step ST 1 ). 
     (2) The display-position/bearing/angle decision section  26  reads the map data  21  corresponding to the decided area from the CD-ROM/DVD-ROM  4  via the CD/DVD drive  8  (step ST 2 ). 
     (3) The bird&#39;s-eye view generating section  24  (main CPU  9 ) transforms the map data  21  to the bird&#39;s-eye view data by computation (step ST 3 ). 
     (4) The horizontal background data generating section  23  generates the background data including a rounded horizon. Although the background data including the rounded horizon can be generated by processing data, the present embodiment 1 reads the background data including the rounded horizon from a memory  30  that stores the data in advance (step ST 4 ). 
     (5) The bird&#39;s-eye view generating section  24  superimposes the background data including the rounded horizon generated at step ST 4  upon the bird&#39;s-eye view data generated at step ST 3 , stores the resultant data into the drawing IC  10 , and displays the data on the display section  29  (monitor  11 ) as shown in FIG. 4 (step ST 5 ). 
     In FIG. 4, the reference numeral  103   a  designates rounded corners at the ends of the horizon  103  indicating the boundary between the map image region  101  and the background image region  102 . Since the remaining reference numerals designate the same items to those of FIG. 11, the description thereof is omitted here. 
     Although the present embodiment 1 employs, as its display reference point, the position of the vehicle itself that is estimated by the map-matching using the vehicle speed signal fed from the vehicle speed sensor  3 , the vehicle bearing signal obtained by the gyrocompass  7 , the received signal by the GPS receiver  6  and the map data read from the CD-ROM/DVD-ROM  4  by the CD/DVD drive  8 , this is not essential. For example, a position specified by a user in his or her map scrolling operation can be used as the display reference point. 
     As described above, the present embodiment 1 is configured such that the horizon is rounded which represents the boundary between the map image region and the background image region in the bird&#39;s-eye view display. Thus, it can achieve the bird&#39;s-eye view display with adding a sense of realism. In addition, superimposing the background data read from the memory upon the map data transformed into the bird&#39;s-eye view can facilitate the display of the horizon with rounded curves between the map image region and the background image region. 
     Embodiment 2 
     Although the roundness of the horizon is fixed in the foregoing embodiment 1, the present embodiment 2 varies the degree of roundness in accordance with the display scaling, thereby enhancing the sense of realism of the bird&#39;s-eye view display. FIG. 5 is a functional block diagram of the present embodiment 2, in which a horizontal roundness decision section  31  for deciding the degree of roundness in accordance with the display scaling is added to the functional block diagram of the foregoing embodiment 1. The horizontal roundness decision section  31  decides the roundness in accordance with the display scaling that is input from the display scaling decision section  25 . According to the decision result, the horizontal background data generating section  23  reads a horizontal pasted pattern from the memory  32 , and generates the horizontal background data. Thus, the roundness of the horizon of the bird&#39;s-eye view varies in accordance with the display scaling. 
     FIG. 6 is a flowchart illustrating the processing of the present embodiment 2, in which steps ST 11 -ST 13  are the same as the steps ST 1 -ST 3  of FIG. 3 of the foregoing embodiment 1. They differ only in the horizontal background data. 
     Specifically, although the foregoing embodiment 1 displays the horizon with the fixed roundness at the boundary between the map image region and the background image region regardless of the display scaling, the present embodiment 2 generates the horizontal background data with the roundness corresponding to the display scaling that is input by the user from the operation keypad  2 , and is decided by the display scaling decision section  25  (step ST 14 ). The horizontal background data is decided as follows. First, a plurality of horizontal background data  102   a - 102   c  differing their roundness are generated as shown in FIG. 7 in accordance with the display scaling. Second, these horizontal background data are stored in the memory  32  in advance, and one of them is read from the memory  32  in accordance with the display scaling. 
     Subsequently, the background data including the rounded horizon produced at step ST 14  is superimposed upon the bird&#39;s-eye view data generated at step ST 13  to be stored in the drawing IC  10 , and then displayed on the display section  29  (monitor  11 ) at step ST 15 . 
     FIG. 8 is an example of a detailed map of the present embodiment 2 viewed from a low angle, and FIG. 9 is an example of a general map viewed from a high angle. In these figures, the degree of roundness of the horizon  103  differs in accordance with the display scaling. 
     As described above, the present embodiment 2 is configured such that it varies the degree of roundness of the horizontal background data of the bird&#39;s-eye view in accordance with the display scaling. As a result, the present embodiment 2 can vary the horizon such that it becomes more linear in the detailed map viewed from a lower angle as shown in FIG. 8, and more round in the general map viewed from a higher angle, thereby further enhancing the sense of realism of the bird&#39;s-eye view display. 
     Embodiment 3 
     Although the foregoing embodiment 2 varies the degree of roundness in accordance with the display scaling, the present embodiment 3 varies it in accordance with the vehicle speed. Thus, the present embodiment 3 can offer a bird&#39;s-eye view display with a sense of realism similar to that of the foregoing embodiment 2. 
     FIG. 10 is a functional block diagram of the present embodiment 3, in which a horizontal roundness decision section  33  for deciding the degree of the roundness in accordance with the vehicle speed is added to the functional block diagram of the foregoing embodiment 1. The horizontal roundness decision section  33  decides the degree of roundness in accordance of the vehicle speed fed from the vehicle speed sensor  3 . According to the decision result, the horizontal background data generating section  23  reads appropriate pasted background data from the memory  32 , and generates the horizontal background data. Thus, it can display the bird&#39;s-eye view with varying the roundness of its-horizon in response to the vehicle speed. 
     As described above, the present embodiment 3 is configured such that the roundness of the horizontal background data of the bird&#39;s-eye view is varied in response to the vehicle speed. Thus, increasing the roundness with the vehicle speed can present a user such a feeling as though he or she were approaching the horizon more quickly, thereby enhancing the sense of realism of the bird&#39;s-eye view display. 
     Embodiment 4 
     As illustrated in FIG. 4, there is a display inhibition region  113  of the land mark and destination mark in a region close to the background image region  102  in the map image region  101 . In view of this, the present embodiment 4 prepares a plurality of horizontal background data to be pasted that are generated in such a manner that the horizontal roundness is fit to the display inhibition region  113 , and stores these data in the memory  32  in advance. Then, one of the horizontal background data to be pasted with the horizontal roundness decided according to the display scaling or vehicle speed is read from the memory  32 , and is superimposed upon the map data which is transformed to the bird&#39;s-eye view. 
     As described above, the present embodiment 4 can round the horizon within the display inhibition region  113  of the land mark and destination mark. Accordingly, it can maintain appropriate display conditions without eliminating the display of such items as the destination mark even if the degree of the roundness is varied. As a result, it can achieve the bird&#39;s-eye view display with a sense of realism. 
     The foregoing embodiments superimpose the background data upon the map data transformed into the bird&#39;s-eye view. As a result, the horizon of the background image can be displayed as it is even when the map image is scrolled, thereby allowing the scroll of the map image without any problem.