Abstract:
A search method and apparatus for a navigation system finds accessible points of interest (POI) along the route to the destination in a flexible manner. The navigation system changes its search range when the geographic condition warrants expansion of the search range. The search method is comprised of the steps of: searching POIs specified by a user along a route to a destination within a predetermined search range relative to the route, detecting POIs located within the predetermined search range, determining if a geographic condition on a specific area on the route exists that enables easy accessibility to POIs, expanding the search range if the geographic condition enabling the easy accessibility to POIs exists for the specific area, and detecting POIs located within the expanded search range.

Description:
FIELD OF THE INVENTION 
   This invention relates to a method and apparatus for navigation system for searching easily accessible points of interest along a route, and more particularly, to a method and apparatus for navigation system that can change search criteria based on geographical conditions, thereby facilitating to search accessible points of interest. 
   BACKGROUND OF THE INVENTION 
   A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a user drives a car by the guidance produced by navigation system. Such a navigation system detects the position of the user or user&#39;s vehicle, reads out map data pertaining to an area at the current vehicle position from a data storage medium. Alternatively, such map data can be provided to the user from a remote server through a communication network such as Internet and the like. 
   When a destination is set, the navigation system starts a route guidance function for guiding a user along a calculated guided route from the start point to the destination. During the route guidance, the navigation system reads the nodes data from the data storage medium such as DVD and successively stores the nodes data of road segments constituting the guided route in a memory. In the actual traveling, the node series stored in the memory is searched for a portion of the guided route to be displayed in a map display area of the monitor screen, and the portion of the guided route is highlighted so as to be clearly discernible from other routes. When the vehicle is within a predetermined distance from an intersection it is approaching, a highlighted intersection diagram with an arrow indicating the direction to turn at the intersection is displayed to inform the user of the appropriate road and direction at the intersection. 
     FIGS. 1A-1H  show an example of overall procedure and screen display involved in the navigation system.  FIG. 1A  shows an example of locator map screen of the navigation system when the destination is not specified. Typically, the navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. When selecting a “Destination” menu on a main menu screen (not shown), the navigation system displays an “Find Destination By” screen as shown in  FIG. 1B  for specifying an input method for selecting the destination. 
   The “Find Destination By” screen of  FIG. 1B  lists various methods for selecting the destination. The methods include “Address” for specifying the city and address of the destination, “Intersection” for specifying the names of two streets which intersect with one another, and “Point of Interest” (POI) for selecting the programmed destination based on the name, category or telephone number. Other methods in the “Find Destination By” screen include “Recent Route” for specifying the destination based on the recent history of destinations saved in the system, “Address Book” for selecting the address of the destination out of the prescribed address list stored in the system, and “Today&#39;s Plan” for selecting two or more destinations. 
   When selecting, for example, the “Point of Interest” method, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in  FIG. 1C . The “Place Name” is to specify a name of POI, and the “Place Type” is to specify a category of POI. If the “Place Type” is selected, the navigation system shows an “Select Category” screen such as shown in  FIG. 1D . 
   Suppose the user selects “Restaurant”, the navigation system retrieves the POIs in the selected category, restaurant, in this case, as shown in  FIG. 1E . Typically, names of POIs (restaurants) will be listed in the order of distance from the user (ex. current vehicle position). If the user selects a particular restaurant from the list, the navigation system displays a “Confirm Route” screen such as shown in  FIG. 1F . In this example, the “Confirm Route” screen lists the name, address and phone number of the destination (POI specified by the user) . If this is the correct destination, the user enters an “Ok to Proceed” key to proceed to the next procedure. 
   In  FIG. 1G , the navigation system calculates and determines a route to the destination, i.e., the selected POI. The navigation system determines a route to the destination based on, for example, the shortest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. Then, the navigation system starts the route guidance as shown in  FIG. 1H  to guide the user along the calculated route to the destination. Typically, the navigation system shows the intersection which is highlighted to show the next turn and a direction of the turn. Such route guidance by the navigation system is also accompanied by voice instructions. 
   The foregoing is a typical example of using the “Point of Interest (POI)” input method of the navigation system. Because the recent storage medium provides a large volume of POI data, this input method can be used in various applications. For example, suppose a user is driving a car for a relatively long trip and the final destination is already specified, i.e., a calculated route to the destination is established. During the trip to the destination, the user wants to stop-by various places such as a gas station, restaurant, shopping mall, etc., along the calculated route. Alternatively, the user may simply want to enjoy seeing various places surrounding the calculated route to the destination by retrieving POIs along the route. 
   Such a situation is shown in  FIG. 2A . As the vehicle indicated by VP moves to the destination (“Dest”), the user may want to stop by at a restaurant. Several restaurants exist along the guided route to the destination. Some restaurants are located close to the guided (calculated) route while others require a detour. Thus, it is helpful for the user if the navigation system provides information whether such POIs are easily accessible. 
   When searching POIs along the calculated route, the navigation system searches for POIs within a predetermined distance from the calculated route.  FIG. 2B  is a schematic diagram showing such a method of detecting POIs along the route to the destination. POIs  75   a - 75   f  of selected category are located along the route. A reference numeral  111  indicates the current position of the vehicle. A reference numeral  101  indicates the route to the destination calculated by the navigation system. 
   In this example, the navigation system creates a search range  113  which is formed, for example, by moving a search circle  135  on the calculated route  101 . The navigation system will repeatedly check if POIs exist within the search range  113  by moving the search circle  135  on the calculated route and retrieves POIs within the search range  113 . The outer edges of the search range  113  are denoted by lines  65   a  and  65   b  each of which has a distance Dt, for example, 0.3 miles, from the calculated route  101 . 
   If POIs fall within the predetermined search range  113 , the navigation system regards those POIs as accessible POIs and displays the information on the POIs. On the other hand, for POIs which do not fall within the predetermined range  113 , the navigation system regards those POIs as non-accessible POIs and will not display the POIs. In this example, POIs  75   a ,  75   c ,  75   e , and  75   f  are located within the search range  113 , and thus retrieved by the navigation system. POIs  75   b ,  75   d ,  75   g , and  75   h  are outside of the search range  113 , and thus, not retrieved by the navigation system because they are not easily accessible. 
     FIG. 3  shows an example of method for searching POIs along the route as applied to an actual situation. The navigation system checks if the POIs exist within the search range  113  along the calculated route  101 . As noted above, the search range  113  is created by incrementally shifting the search circle  135  on the calculated route  101 . Among several POIs  123   a - 123   e , the navigation system will retrieve only POI  123   b  as it falls within the search range  113 . 
   When using the function of searching POIs along the route, the user is primarily interested in knowing about accessibility to the POIs, rather than mere distance from the calculated route. For example, there arises a case in which the geographical conditions allow the user to easily access a particular POI, even though its location is outside of the predetermined search range. Typically, when a POI is located on a street intersecting with the calculated route  101 , the user can easily maneuver to the POI. In  FIG. 3 , the user can easily reach the POI  123   a  by making a left turn at a cross street  105   a  although the POI  123   a  is outside of the search range  113 . Likewise, the user can easily access the POI  123   d  by making a right turn at the cross street  105   b.    
   Thus, there is a need of a new function of a navigation system for searching POIs along the calculated route based on accessibility to the POIs. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a search method that can identify and retrieve easily accessible points of interest (POIs) along the calculated route to the destination. 
   It is another object of the present invention to provide a navigation system that can vary its search range when it determines that the geographic condition warrants expansion of the search range when searching POIs along the calculated route to the destination. 
   It is a further object of the present invention to provide a POI search method for searching POIs along the calculated route to the destination which is capable of expanding search range by searching POIs along a street crossing with the calculated route to the destination. 
   One aspect of the preset invention is a POI search method for a navigation system for identifying and retrieving easily accessible POIs along the calculated route to the destination. The search method is comprised of the steps of: searching points of interest specified by a user along a route to a destination within a predetermined search range relative to the route, detecting points of interest located within the predetermined search range, determining if a geographic condition on a specific area on the route exists that enables easy accessibility to points of interest, expanding the search range if the geographic condition enabling the easy accessibility to points of interest exists for the specific area, and detecting points of interest located within the expanded search range. 
   In one example, the geographic condition is an intersection where the route to the destination intersects with a cross street. In another example, the geographic condition is a freeway exit where the route to the destination includes a freeway. 
   The predetermined search range is created by shifting a search circle on the route to the destination. The expanded search range has a circular shape that encompasses the specific area. Alternatively, the expanded search range has a belt like shape that encompasses the specific area. 
   In the present invention, the geographic condition is an intersection where the route to the destination intersects with a cross street, and where the expanded search range having a circular shape is applied to the intersection. The geographic condition is an intersection where the route to the destination intersects with a cross street, and where the expanded search range having a belt like shape is applied to the intersection along both directions of the cross street by shifting a search circle. 
   Another aspect of the present invention is a POI search apparatus for a navigation system for implementing the various steps defined in the search method of the present invention noted above. The search apparatus detects the POIs along the route to the destination where a search range is expanded at a specific area such as an intersection. 
   According to the present invention, the navigation system changes its search range when it determines that the geographic condition warrants expansion of the search range when searching points of interest (POIs) along the calculated route to the destination. An example of such geographic conditions is an intersection where the search range is expanded to search POIs along a street that intersects with the calculated route to the destination. Therefore, the navigation system of the present invention is able to identify and retrieve easily accessible POIs along the calculated route to the destination with high flexibility and high speed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A-1H  are schematic diagrams showing an example of operational process and screen display of a navigation system for implementing the method and apparatus of the present invention. 
       FIG. 2A  is a schematic diagram showing an example of a situation where several points of interest are located along a calculated route to a destination, and  FIG. 2B  is a schematic view showing an example of conventional method for finding points of interest along a calculated route. 
       FIG. 3  is a schematic view showing an example of a situation where several points of interest are located around a calculated route and the conventional method of  FIG. 2B  is applied thereto for finding points of interest along the calculated route. 
       FIG. 4  is a block diagram showing an example of structure of a vehicle navigation system which is suitable for implementing the present invention for searching accessible POIs along the route to the destination. 
       FIG. 5  is a schematic view showing the method of a first embodiment of the present invention for finding accessible points of interest along the calculated route to the destination. 
       FIG. 6  is a schematic view showing the method of a second embodiment of the present invention for finding accessible points of interest along the calculated route to the destination. 
       FIG. 7  is a flow chart showing an overall procedure for identifying accessible POIs along the route in the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will be described in detail with reference to the accompanying drawings. The navigation system of the present invention is designed to find accessible points of interest (POI) along the route to the destination. When the user specifies a function for retrieving POIs along the calculated (guided) route to the destination, the navigation system will detects POIs within a predetermined range from the calculated route. When the navigation system determines that there is a geographical condition on the calculated route that allow easy accessibility to POIs, the navigation system will increase the search range. 
     FIG. 4  shows an example of structure of a vehicle navigation system implementing the present invention. It should be noted that the present invention can also be applied to portable navigation devices such as a PDA (personal digital assistant) device, a lap-top computer, or other hand-held devices. 
   In the block diagram of  FIG. 4 , the navigation system includes a map storage medium  31  such as a CD-ROM, DVD, hard disc or other storage means (hereafter “DVD”) for storing map information, a DVD control unit  32  for a controlling an operation for reading the map information from the DVD, a position measuring device  33  for measuring the present vehicle position. The position measuring device  33  has a vehicle speed sensor for detecting a moving distance, a gyroscope for detecting a moving direction, a microprocessor for calculating a position, a GPS receiver, and etc. 
   The block diagram of  FIG. 4  further includes a map information (data) memory  34  for storing the map information which is read out from the DVD  31 , a database memory  35  for storing database information such as point of interest (POI) information which is read out from the DVD  31 , a remote controller  37  for executing a menu selection operation, an enlarge/reduce operation, a destination input operation, etc., and a remote controller interface  38 . 
   The navigation system further includes a bus  36  for interfacing the above units in the system, a processor (CPU)  39  for controlling an overall operation of the navigation system, a ROM  40  for storing various control programs such as a route search program and a map matching program necessary for navigation control, a RAM  41  for storing a processing result such as a guided (calculated) route, a display controller  43  for generating a map image (a map guide image and an arrow guide image) on the basis of the map information, a VRAM (Video RAM)  44  for storing images generated by the display controller, a menu/list generating unit  45  for generating menu image/various list images, a synthesizing unit  46 , a POI search and display controller  47 , a buffer memory  48 , a wireless receiver  49 , and a monitor (display)  50 . 
   A POI search and display controller  47  directly relates to the present invention. The POI search and display controller  47  has a function of controlling an overall procedure for searching POIs along the guided route to the destination. Upon examining the geographic conditions, the POI search and display controller  47  freely changes the search range so that the navigation system can identify and retrieve accessible points of interest. 
   The details of the method for identifying accessible POIs are explained with reference to  FIGS. 5 and 6 .  FIG. 5  is a schematic view showing a method for searching accessible POIs along the calculated route in the first embodiment of the present invention. The user sets the destination by, for example, using the procedure described in  FIG. 1A-1H . The vehicle (user)  111  moves along the calculated route  101  in the direction shown by its arrow. Suppose the user selects the function for searching POIs along the route. Typically, as shown in  FIGS. 1C and 1D , the user also specifies a specific category of POIs such as grocery store, shopping mall, restaurant, etc., that he wants to search. 
   The navigation system normally searches relevant POIs by repeatedly checking whether POIs exist along the calculated route to the destination within a search range. A search range is predetermined in a manner that the search range encompass both sides of the calculated route to the destination. In this preferred embodiment, the navigation system will check whether a POI exists within the search range  113  defined by search circles  135  described with reference to  FIG. 2B . 
   As the search circle continuously shifts on the route  101  to the direction of the destination, the search range  113  is formed by the outer periphery of the search circles  135 . In  FIGS. 5 and 6 , the search range  113  is indicated by broken lines. Namely, the broken lines show the width of the search range  113 , i.e., a diameter of the search circle  135 , which is for example, 0.4-1.0 mile. Thus, the navigation system in effect determines if a POI is located within the search range  113  along the route  101 . 
   When the navigation system determines that the vehicle will enter into such a geographical area that allows a user to easily reach a POI even though such a POI is outside of the current search range  113 . If such a condition is found, the navigation system will expand the search range on such a specific area on the route. Such a case occurs when the calculated route  101  intersects with a street such as a cross street  105   a . In  FIG. 5 , although outside of the search range  113 , there is a POI  123   a  located along the cross street  105   a . When the vehicle approaches the intersection formed by the calculated route  101  and the cross street  105   a , the user can easily access to the POI  123   a  since the user only needs to make a left turn at the intersection and advances on the cross street  105   a  for a short distance. 
   A similar situation occurs when the vehicle approaches the intersection formed by the calculated route  101  and the cross street  105   b . In this case, the user can easily access to a POI  123   d  since the user only needs to make a right turn at the cross street  105   b  and drives on the cross street  105   b  by a short distance. Even though the user has to depart from the calculated route  101  greater than the search range  113 , since the POIs  123   a  and  123   d  are located along the cross streets  105   a  and  105   b , respectively, it is not a burden for the user to reach the POI  123   a  or  123   d . In other words, the POIs  123   a  and  123   d  are easily accessible. 
   In the conventional navigation system shown in  FIG. 3 , the POI  123   a  and POI  123   d  are not detected as POIs along the route because the navigation system only detects POIs located within the search range  113 . In the present invention, as shown in  FIG. 5 , in order to detect the accessible POIs with higher flexibility, the navigation system will expand the search range at a specific area, for example, an intersection. The expanded search ranges  131   a  and  131   b  are shaded to show the covered areas. As shown, due to its increased size, the expanded search ranges (circles)  131   a  and  131   b  now cover the POI  123   a  and  123   d , respectively. The navigation system therefore retrieves the POIs  123   a  and  123   d  and displays the information on the POIs  123   a  and  123   d.    
   As noted above, the navigation system extends the scope of search only for a specific area, where there is a geographical condition that facilitates easy accessibility to POIs, such as an intersection. Thus, the navigation system will not detect the POI  123   c  because it is not easily accessible from the calculated route  101  to the destination. If the initial search range  113  is as large as the expanded search range  131  throughout the calculated route  101 , the navigation system would detect POI  123   c  and POI  123   e  as POIs along the route. However, this will mislead the user because, in order to reach POI  123   c  or  123   e , the user will have to take a roundabout route to reach there. 
   Further, if the large search range  131  is used throughout the process, the navigation system needs a long time to detect the POIs because of the increase of the area to be searched or the navigation system has to use a high speed processor which increases the cost. In the present invention, because the search range expands only at intersections, the navigation system can avoid such problems. Thus, the POIs  123   c  and  123   e  are not detected as POIs along the route, thereby maintaining reliability of POI detection. 
   Although the present invention is described for the case where the navigation system expands the search range at an intersection in the above-described embodiment example, the application of expanding the search range is not limited to an intersection. For instance, when the route to the destination includes a freeway, and if a POI is located close to a freeway exit but not within a predetermined search range from the freeway, the present invention can be advantageously implemented to identify such a POI by enlarging the search range at the freeway exits. Moreover, although only one cross street intersects the calculated route in the above example, the navigation system of the present invention is applicable even when the two or more cross streets intersect with the calculated route. Further, it is possible that the navigation system will increase the search range in a country area than that in the downtown area. 
     FIG. 6  is a schematic diagram showing a second embodiment of the present invention for searching accessible POIs along the calculated route to the destination. This example is similar to that of  FIG. 5  except for the method of increasing the search ranges at a specific area, for example, an intersection. In this embodiment, the navigation system maintains the similar or same search range but extends the search range in both directions of the cross street for a predetermined distance. Thus, the area for the expanded search has a belt like shape formed by traces of the search circle shifting along the cross street. 
   When the navigation system detects that there is an intersection formed by the calculated route  101  and a cross street  105   a , the navigation system will move the search circle  133  along the cross street  105   a . Thus, the search area is expanded toward both north and south directions (upper and lower directions of  FIG. 6 ) on the cross street  105   a  by a predetermined distance to search POIs. In other words, the navigation system will search the POIs not only along the calculated route  101  to the destination but also along the cross street  105   a.    
   The search operation along the cross street  105   a  is conducted in a manner similar to the ordinary POI search along the route method. That is, the navigation system will repeatedly check if any POI is located within a search range created by the search circles  133 . The detection operation is repeated by shifting the search circle  133  for a predetermined distance on the cross street  105   a . Such a predetermined distance should be short enough to maintain the easy accessibility to the detected POIs while long enough to expand the search range substantially larger than the search range  113  on the calculated route  101 . 
   Since the POI  123   a  is located within the extended search area, the navigation system will determine that the POI  123   a  is an accessible POI and retrieve the information on the POI  123   a  to display on the monitor. Likewise, the navigation system will find the POI  123   d  by extending the search direction on the cross street  105   b  at the intersection formed by the calculated route  101  and the cross street  105   b . Because the navigation system extends the search only for a certain geographical condition, such as an intersection in this example, it can accurately detect accessible POIs along the route while avoiding detection of POIs that are not easily accessible. Further, since the search range is expanded only for a certain condition, the search process can be completed within a short period of time without using an expensive high performance processor. 
     FIG. 7  is a flow chart showing an example of overall procedure of the present invention for identifying accessible POIs along the calculated route to the destination. At step  201 , the navigation system determines if the user will encounter a geographic area that allows easy accessibility to POIs, such as an intersection. If so, the navigation system performs an expanded search in step  202  as described with reference to  FIGS. 5 and 6 . After the extended search is completed, the navigation system will return to the normal search. On the other hand, if the navigation system determines that the user will not encounter a geographic area allowing easy accessibility, it will perform a normal search within the predetermined search range in step  203 . The procedure is repeated until the navigation system finds all POIs that are easily accessible along the route. The search may be conducted in real time as the vehicle moves along the calculated route, or it may be performed without regard to an actual current vehicle position. 
   In the flow chart of  FIG. 7 , the navigation system checks if geographic condition, such as an intersection, that allows easy accessibility to POIs exists, and if such a condition does exist, the navigation system will apply the expanded search range. However, it should be noted that the present invention need not strictly follow this procedure, and procedural variations are also possible. For example, the navigation system may perform the normal search operation for POIs along the route without checking the geographic conditions, and then determine if intersections exist for applying expanded search. In effect, this procedural arrangement first makes a sweeping search for the route, then makes a fine-tuned search for some geographic conditions such as intersections. 
   Thus, the navigation system of the present invention can find easily accessible POIs along the route more accurately than conventional navigation systems. Consequently, the navigation system is able to retrieve and display information on the accessible POIs along the route to the destination to help the user to effectively use the navigation system. 
   As has been described above, according to the present invention, the navigation system changes its search range when it determines that the geographic condition warrants expansion of the search range when searching points of interest (POIs) along the calculated route to the destination. An example of such geographic conditions is an intersection where the search range is expanded to search POIs along a street that intersects with the calculated route to the destination. Therefore, the navigation system of the present invention is able to identify and retrieve easily accessible POIs along the calculated route to the destination with high flexibility and high speed. 
   Although the invention is described herein with reference to the preferred embodiments, one skilled in the art will readily appreciate that various modifications and variations may be made without departing from the spirit and the scope of the present invention. Such modifications and variations are considered to be within the purview and scope of the appended claims and their equivalents.