Abstract:
A method of selectively providing cartographic features on a video display of a navigation system for improved rendering is provided. The method includes the steps of determining an operational mode of the navigation system, selecting a desired cartographic entity for a cartographic feature based upon the operational mode, and displaying the desired cartographic entity on the video display. For example, less detailed cartographic entities are selected for display when the navigation system is in an operational mode that requires the video display to be updated frequently ore a mode in which it is desirable to focus the user&#39;s attention on a different cartographic entity. The less detailed cartographic entity may have a lower intensity than or contrast less with surrounding cartographic entities. In this manner, the user may be provided the desired level of map details with the video display regenerated rapidly.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to vehicle navigation systems and, more specifically, to map images appearing on a navigation system video screen of a display device. 
   Vehicle navigation systems typically include a display device with a video display that provides a graphical interface for the user. A main function of the video display is to depict the desired map area and route on which the user&#39;s vehicle is travelling. The map area shows various cartographic features, such as lakes and golf courses, to increase the utility to the user. These cartographic features are represented by cartographic entities that convey the nature of the cartographic feature so that the user may easily interpret it. For example, a solid green body may be used to represent a golf course and a solid blue body may be used to represent a lake. The map area shown on the video display may have numerous cartographic entities displayed making the vehicle route, which is typically the user&#39;s primary interest, more difficult to identify. That is, the shear number of cartographic entities displayed on the video display distracts the user and increases the amount of time it takes the user to locate the vehicle route on the video display. Additionally, displaying numerous cartographic entities increases the time it takes to regenerate or update the video display, which may cause an undesirable delay in displaying the updated information to the user as the vehicle moves across the map area. Furthermore, the intensity of the vehicle route and other roads in the map area are the same, making it difficult to quickly identify the vehicle route. 
   Depending upon the operational mode of the navigation system, it may be desirable to vary the intensity of certain roads and/or have fewer or less detailed cartographic entities displayed such as described above. However, in some operational modes it may desirable to display cartographic entities for all the cartographic features. Therefore, it is desirable to selectively display cartographic entities based upon the operational mode of the vehicle navigation system. In this manner, the user may be provided the desired level of map details and have the video display regenerated rapidly. 
   SUMMARY OF THE INVENTION AND ADVANTAGES 
   The present invention provides a method of selectively displaying cartographic features on a video display of a navigation system for improved rendering. The method includes the steps of determining an operational mode of the navigation system, selecting a desired cartographic entity for a cartographic feature based upon the operational mode, and displaying the desired cartographic entity on the video display. For example, less detailed cartographic entities are selected for display when the navigation system is in an operational mode that requires the video display to be updated frequently. 
   Accordingly, the above invention provides the desired level of map details and have the video display regenerated rapidly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is a schematic view of the vehicle navigation system of the present invention; 
       FIG. 2  is a front elevational view of the vehicle navigation system display unit having a video display; 
       FIG. 3  is the video display of the display unit in a first operational mode; 
       FIG. 4  is the video display of the display unit in a second operational mode; and 
       FIG. 5  is the video display of the display unit in a third operational mode. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The navigation system  20  of the present invention is shown schematically in  FIG. 1 . The navigation system  20  includes a CPU  22  (Central Processing Unit) connected to a display device  24  and a directional input device  26  attached to the vehicle interior by a bracket  27 , or the like. The navigation system  20  further includes a database  28  connected to the CPU  22 . The database  28  is a mass media storage device, such as a CD-ROM, hard drive, DVD, RAM, ROM or the like which includes a map of the road system in the area to be traveled by the user. Each road in the database is divided into road segments, each having an associated set of cost values, which indicate the “cost” of traveling that road segment. For example, the cost values may include the length of the road segment, the estimated time to travel the road segment, and the type of road (i.e., highway, secondary road, toll road, one way, etc.). The road segment may be part of the vehicle route or may be a road segment outside the vehicle route. 
   The database  28  also stores the type location and shape of the cartographic features and entities like: ocean or coastline, river, canal, water channel, lake, bay or harbor, golf course, railroad, island, city, Native American reservation, built up area, county, country, state, national park or monument, state park, city or county park, woodland, shopping center, university or college, cemetery, sports complex, hospital, airport, military base, pedestrian zone, aircraft road, industrial complex, or junction. Of course, the above list of cartographic features is only illustrative of the cartographic features that may be included on a map. 
   The navigation system  20  can, but need not, be installed in a vehicle  32 . The navigation system can be used in conjunction with position determining devices, such as a GPS receiver  34  and a multi-axis accelerometer  35 . Navigation system  20  could alternatively or additionally include a gyroscope  36 , a compass  38 , and a wheel speed sensor  40 , all connected to the CPU  22  (connections not shown for simplicity). Preferably, a combination of these position determining devices is utilized to assure accurate location. 
     FIG. 2  is a perspective view of one disclosed embodiment of the display device  24  and directional input device  26 , preferably designed as an integral unit attached to the CPU by connection  25 . The display device  24  includes a video display  50 , or screen, such as a high resolution LCD or flat panel display. The directional input device  26  includes a multiple of input buttons  78  including, preferably, an eight-way button shown generally at  80  and a selection key  86  such as an “Enter” key. Although an eight-way button is shown, it will be realized that other input devices, such as a joystick, mouse or roller ball can be employed. 
   The internal disk  82  is pivotally mounted in the eight-way button  80  and is capable of moving in the direction of any one of the directional arrows  84 . Movement of the internal disk  82  in the direction of one of the directional arrows  84  transmits a directional signal. 
     FIGS. 3–5  are video displays of the same map area in different operational modes using the present invention.  FIG. 3  depicts the video display  50  for a particular map area  51  when the navigation system is in an on-road guidance mode. In on-road guidance mode, the vehicle route  52  is highlighted in a bright color, such as magenta, and arrows  54  overlay the route for easy identification by the user. On-road guidance mode is typically used when the user selects a particular destination. The navigation system then selects and highlights the route  52  based upon certain user selected parameters, such as shortest distance or shortest time. Since the intended focal point of the map area is the vehicle route  50 , it is desirable that there be fewer and less detailed cartographic entities for the cartographic features in the map area. In this patent application cartographic feature means an aspect of the map area, such as a lake, golf course, forest, mountain, or sports arena. Cartographic entity means the icon used to represent the particular cartographic feature, such as a tree used to represent the location of a woodland in the map area. Road segments are the cartographic entities used to represent the cartographic feature of a road system. 
   In the on-road guidance mode shown in  FIG. 3 , a golf course  56  is represented by a cartographic entity defined by a perimeter having cross-hatching within the perimeter. The lines of the cartographic entity are green and are easily regenerated compared to a similarly shaped cartographic entity that is solid. A similar cartographic entity with blue lines is used to represent a lake  58 , with the cross-hatching oriented in a different direction so that a user may more easily distinguish the lake from the golf course. Not all the cartographic features may be displayed in on-road guidance mode. In the preferred embodiment, cartographic entities for the following cartographic features would be displayed: ocean or coastline, river, canal or water channel, lake, bay or harbor, golf course and railroad. 
   As mentioned above, the road system  44  includes road segments  46 . In on-road guidance mode, one of the road segments  46  is the vehicle route  52 . Although the vehicle route  52  may be a different color than the other road segments  46 , the vehicle route  52  may not stand out due to the number of cartographic entities being displayed or because of their similar entities. With the present invention, during on-road guidance mode the vehicle route  52  is displayed at full intensity while the other cartographic entities, including road segments, rivers, lakes, etc., are displayed at a lower intensity. Typically, the cartographic entities are displayed using a color palette having blue, green and red values. For cartographic entities displayed at a lower intensity, the blue, green, and red values may be decreased by an equal percentage, preferably, approximately twenty-five percent. The desired intensity is approximately twenty-five percent less than the vehicle route intensity wherein the first blue, green, and red values are approximately twenty-five percent less than the second blue, green, and red values, respectively. 
     FIG. 4  depicts the video display  50  for a particular map area  51  when the navigation system is in on-road mode. In on-road mode, no particular destination has been selected by the user. In this mode more detail may be desired than in on-road guidance mode because the user has not necessarily decided upon a particular route and knowledge of cartographic features may be more important to the user. Accordingly, it may be desirable to have the cartographic entities displayed more prominently so that they may be more quickly focused upon by the user. The golf course  56  and lake  58  are defined by the perimeter with solid shading so that the cartographic entity stands out. Not all the cartographic features may be displayed in on-road mode. In the preferred embodiment, cartographic entities for the following cartographic features would be displayed: ocean or coastline, river, canal or water channel, lake, bay or harbor, golf course and railroad. 
     FIG. 5  depicts the video display for a particular map area when the navigation system is in off-road mode. In off-road mode, the navigation system has determined that the vehicle is no longer on any known road and that the vehicle is travelling off the road. It is important that the user be aware of the surrounding cartographic features since the user is no longer utilizing known roads. To this end, preferably cartographic entities for all the cartographic features are displayed using the most detail. Cartographic features may now be seen by the user that could not be seen in on-road guidance and on-road modes. For example, mountain  60 , river  62 , and tree  64  cartographic entities are displayed representing the mountain, river, and woodland cartographic features. Other cartographic features for which cartographic entities are now displayed are: island, city, Native American reservation, built up area, county, country, state, national park or monument, state park, city or county park, woodland, shopping center, university or college, cemetery, sports complex, hospital, airport, military base, pedestrian zone, aircraft road, industrial complex, and junction. 
   Particular cartographic entities may be displayed to customers having specific interests. For example, a utility company may be interested in utility poles or easement being displayed in a particular mode. 
   The navigation system may include other operational modes in addition to the modes described above. One such operational mode may involve vehicle speed. If the vehicle is travelling rapidly compared to the map area displayed on the video screen, the map area may have to be regenerated frequently. As a result, it may be desirable to provide fewer and less detailed cartographic entities to minimize delay in displaying the updated information to the user. Therefore, the navigation system may enter into an operational mode when a predetermined vehicle speed is reached. Such an operational mode is relative to the operational mode from which the navigation system is changing. For example, if the navigation system is currently on-road guidance mode, which has few and less detailed cartographic entities, there may be no visible change in the display  50  when the predetermined speed is reached. However, if the current mode is off-road, then when the predetermined speed is reached fewer and less detailed cartographic entities will be displayed. 
   The navigation system may enter another operational mode displaying fewer and less detailed cartographic entities when the user pans the displayed map area using the arrow button  80 . Similar to the vehicle speed operational mode discussed above, the panning operational mode is relative to the operational mode from which the navigation system is changing. 
   The present invention provides a method of selectively displaying cartographic features on a video display of a navigation system. It is to be understood that any type of cartographic entity may be used for a cartographic feature in a particular operational mode. That is, the present invention may be accomplished by displaying different cartographic entities than described above. In operation, the navigation system determines an operational mode of the navigation system. The operational mode may be manually selected by the user or automatically determined by the navigation system, such as when entering off-road mode. The navigation system then selects a desired cartographic entity for a cartographic feature based upon the operational mode. If the navigation system is in a mode where fewer cartographic entities are desired, the navigation system may select no cartographic entity for a particular cartographic feature. An example of this is shown in  FIGS. 3 and 4  where no cartographic entity is selected for the river, woodland, and mountains. Finally, the navigation system displays the desired cartographic entity on the video display. Again, no cartographic entity may be selected for display. 
   The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.