Patent Publication Number: US-2005143906-A1

Title: Systems, methods, and data structures for smoothing navigation data

Description:
INCORPORATION BY REFERENCE  
      The disclosure of Japanese Patent Application Nos. 2004-266759 filed on Sep. 14, 2004 and 2003-434756 filed Dec. 26, 2003 including the specifications, drawings, and abstracts are incorporated herein by reference in their entirety.  
     BACKGROUND  
      1. Related Technical Fields  
      Related fields include methods of smoothing navigation data, apparatus for smoothing navigation data, and navigation data structures.  
      2. Description of the Related Art  
      Japanese Patent Application Laid-Open No. 2002-148067, discloses a navigation method including accumulating received traffic information, date and time, and day of the week, and finding a shortest route or calculating a required period with the aid of the accumulated data.  
      In the aforementioned navigation method, however, the received traffic information is not always provided for all the links. For example, for some links only a congestion degree may be provided. The congestion degree may be classified into four stages, namely, “congested,” “crowded,” “not congested,” and “uncertain.” Although a vehicle speed range is defined for each of the stages, this defined speed is rather sweeping. Thus, the speed values derived from the congestion degree may be unreliable.  
     SUMMARY  
      Thus, it is beneficial to provide a method of smoothing navigation data, an apparatus for smoothing navigation data, and a smoothing navigation data structure wherein a link travel time calculated from a received congestion degree is smoothed.  
      Accordingly, various implementations provide a method of smoothing navigation data including accumulating traffic information including, for each link, a congestion degree at a plurality of trip times, calculating a link travel time on the basis of the congestion degree for each trip time, and smoothing the calculated link travel time.  
      Various implementations provide a system for smoothing navigation data including a memory that may accumulate traffic information including, for each link, a congestion degree at a plurality of trip times, and a controller. The controller may calculate a link travel time on the basis of the congestion degree for each trip time and smooth the calculated link travel time.  
      Various implementations provide a smoothing navigation data structure that may be produced by smoothing a link travel time calculated on the basis of traffic information that is made up of a congestion degree for each piece of time information. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Examples will now be described with reference to the accompanying drawings, wherein:  
       FIG. 1  is a block diagram showing an exemplary system for smoothing navigation data; and  
       FIG. 2  is a flowchart showing an exemplary method of smoothing navigation data. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       FIG. 1  is a block diagram showing an exemplary system for smoothing navigation data. This navigation system may be physically, conceptually, or functionally divided into, for example, a navigation apparatus N and an information communication system C, for example, installed in an information center. Navigation system N may be mounted in a vehicle. Further,  FIG. 1  shows a road traffic information communication system T (hereinafter also referred to as VICS®) that may be provided in a road traffic information center.  
      The navigation system N may be provided with a current position detector  10  (such as, for example, a GPS receiver). The current position detector  10  may receive radio waves sent from an artificial satellite of a satellite navigation system (also known as GPS) to detect a current position of a vehicle as well as a present day and time.  
      In addition, the navigation system N may be provided with an input unit  20 . The input unit  20  may be, for example, a portable remote controller that may send required information to a controller  30  (described later). The input unit  20  may also be, for example, a touch panel provided on a display screen of a display device. Such a display device may be part of an output unit  60  (described later).  
      Furthermore, the navigation system N may be provided with, for example, a controller  30 , a memory  40 , a communication unit  50 , and/or an output unit  60 . The controller  30  may include, for example, a CPU, a RAM, and/or a ROM and may be connected by, for example, bus lines.  
      The controller  30  may control, for example, map display, route search, and/or route guidance of the vehicle based upon, for example, a current position that is obtained by, for example, the current position detector  10 , operation of the input unit  20 , information in the memory  40 , communication from communication unit  50 , and/or information from the information communication system C.  
      The memory  40  may be, for example, a hard disk. Map data and/or traffic information data may be accumulated in the memory  40 , for example, in a database or other data structure. The communication unit  50  may receive, for example, road traffic information from the information communication system C to output to the controller  30 .  
      The information communication system C may include, for example, a controller  70 , a communication unit  80 , and/or the memory  90 . The communication unit  80  may execute wireless communication between the communication unit  50  and VICS T. The controller  70  may execute, for example, the exemplary methods shown in the flowcharts in FIGS.  2  to  6 . The controller  70  may also control the transfer of information between, for example, the communication unit  50  and VICS T via, for example, the communication unit  80 . Note that, control programs may be stored in advance in, for example, a ROM of the controller  70 .  
      Link travel times TT, vehicle speeds, congestion degrees D, and/or traffic information data (such as, for example, roads closed to traffic and traffic regulations) may be sent from VICS T and stored in the memory  90 , for example, in a database or other data structure. A congestion degree D is a degree of traffic congestion determined by a vehicle speed and the congestion degree may include, for example, four-stage data, that is, for example, “congested,” “crowded,” “not congested,” and “uncertain.” According to this example, the degree of congestion decreases in the order of “congested,” “crowded,” and “not congested.” The congestion degree is not limited to four stages and may include a plurality of stages.  
      Further, a VICS link length may be stored in the memory  90  as map data. The VICS link length is an actual length of a target link.  
      As used herein, the term link refers to, for example, a road or portion of a road. For example, according to one type of road data, each road may include a plurality of componential units called links. Each link may be separated and defined by, for example, an intersection, an intersection having more than three roads, a curve, and/or a point at which the road type changes.  
      The output unit  60  may be, for example, a display unit. Under the control of the controller  30 , the output unit  60  may display data. A display panel, such as, for example, a liquid crystal panel of the output unit  60  may be disposed in an instrument panel that is provided in a front wall in a cabin of the vehicle.  
      In the exemplary system described above, the controller  70  of the information communication system C, for example, may execute the exemplary method shown in  FIG. 2 . As shown in  FIG. 2 , in step S 100 , a target link is extracted from the map data stored in, for example, the memory  90 . As used herein a “target link” represents a first or next link in a predetermined group of links. The predetermined group may be, for example, a group necessary for a route search, a group within a predetermined area of the map data, or a whole of the map data (such as all of Japan).  
      Then in step  110 , a vehicle speed is set. Specifically, a vehicle speed corresponding to the congestion degree is set on the basis of, for example, the exemplary data in Table 1. Thus, on the basis of a congestion degree corresponding to the target link and included in the traffic information data, a vehicle speed corresponding to the congestion degree is set.  
                               TABLE 1                                   Congested   Crowded   Not congested                                                            General road    5 km/h   15 km/h   40 km/h           Urban highway   10 km/h   30 km/h   60 km/h           Intercity highway   20 km/h   50 km/h   80 km/h                      
 
      Table 1 shows exemplary data indicating a relationship among, for example, vehicle speed, road type, and congestion degree. The road type mentioned herein may refer to, for example, a general road, an urban highway, an intercity highway, or any other type of road. Based on Table 1, for example, if the target link is a general road, and the congestion degree is “congested,” “crowded,” or “not congested,” the vehicle speed may be set to 5 km/h, 15 km/h, or 40 km/h, respectively. The data such as that shown in exemplary Table 1 may be stored in the memory  90  in advance. Operation proceeds to step  120 .  
      In step  120 , a link travel time of the target link is calculated by dividing a link length of the target link by the set vehicle speed. Then, in step  130 , it is determined whether a link travel time of every link in the predetermined group has been calculated. If a link travel time of every link in the predetermined group has not been calculated operation returns to step  100 .  
      If a link travel time of every link in the predetermined group has been calculated, operation continues to step  140 . In step  140 , an average or “smoothed” link time is calculated. Specifically, for example, the calculated link travel time may be denoted by T. An averaged link travel time {overscore (T)} may be calculated using equation (1) shown below, on the basis of the one or more travel times T i  for trip times previous to the calculated link travel time T, where i is the number of travel times for trip times previous to the calculated link travel time that will be used for the average.  
               T   _     =         ∑     i   =   1     n     ⁢     T   i       n             (   1   )             
 
 Thus, if two travel times for previous trip times are used the averaged link travel time {overscore (T)} may be determined as (T 1 +T 2 )/2. Operation continues to step S 150 . 
 
      As used herein, the term “smoothing” refers to bringing extreme or abnormal values in a data set closer to the remaining values-in the data set. For example, when the data set is plotted, the extreme or normal values may create spikes in the data. Thus, by bringing the extreme or abnormal values closer to the remaining values the spikes may be “smoothed” out. It should be appreciated that smoothing may be accomplished by using, for example, means, medians, statistical interpolation, standard deviation, and/or any other method or means by which extreme values may be moved closer to remaining values in a data set.  
      As used herein, the term “trip time” refers to the time at which a link may be traveled. This is because a travel time for a particular link may vary depending on the time of day, day, and/or time of year. For example, trip times may be set as predefined intervals such as, for example, 12 PM-2 PM. Accordingly, a trip time previous to the 12 PM-2 PM trip time may be 10 AM-12 PM or 6 AM-8 AM. The trip times may be defined by large or small intervals and may also be defined by or grouped into events, such as “morning rush hour,” “evening rush hour,” or “weekend.” 
      In step  150 , a vehicle speed is set. Specifically, a vehicle speed of the target link is calculated by dividing a link length of the target link by the averaged link travel time T. Then in step  160 , the set vehicle speed is converted into a congestion level. Specifically, for example, the set vehicle speed of each link is converted into a congestion degree based on, for example, the exemplary data in Table 2.  
                                       TABLE 2                                       Slightly       Slightly               Congested   congested   Crowded   crowded   Not congested                                                            General   V ≦ 8 km/h    8 km/h &lt; V ≦ 12 km/h   12 km/h &lt; V ≦ 20 km/h   20 km/h &lt; V ≦ 32 km/h   32 km/h &lt; V       road       Urban   V ≦ 15 km/h   15 km/h &lt; V ≦ 25 km/h   25 km/h &lt; V ≦ 40 km/h   40 km/h &lt; V ≦ 55 km/h   55 km/h &lt; V       highway       Intercity   V ≦ 25 km/h   25 km/h &lt; V ≦ 40 km/h   40 km/h &lt; V ≦ 60 km/h   60 km/h &lt; V ≦ 75 km/h   75 km/h &lt; V       highway                  
 
      In Table 2, as is the case with Table 1, the road type may refer to, for example, a general road, an urban highway, an intercity highway, or any other road type. For example, if the road type of a target link is a general road, a set vehicle speed, which is expressed as Vkm/h, may be converted into a congestion degree such as, for example, “congested,” “slightly congested,” “crowded,” “slightly crowded,” or “not congested,” on the basis of, for example, V≦8 km/h, 8 km/h&lt;V≦12 km/h, 12 km/h&lt;V≦20 km/h, 20 km/h&lt;V≦32 km/h or 32 km/h&lt;V, respectively. Operation continues to step  170 .  
      In step  170 , the smoothed link travel time (e.g., step  140 ) and congestion degree (e.g., step  160 ) may be output to, for example, the memory  90  and/or the communication unit  80 . The data may then, for example, be transmitted to the communication unit  50  by the communication unit  80 . After being received by the communication unit  50 , the controller  30  may store the smoothed link travel time in, for example, the memory  40 .  
      According to the above-described exemplary method, a vehicle speed corresponding to a congestion degree may be set for each target link in the predetermined group, and a link travel time may be calculated from a link length and the set vehicle speed. Then, for each extracted target link, a smoothed link travel time is calculated.  
      This smoothed link travel time may be set as a link travel time in, for example, the traffic information for each extracted target link. Accordingly, if a particular link travel time is abnormally large or small compared to one or more previous travel times for the same link, the abnormal value of the link travel time may be counterbalanced in the average link travel time. If the average link travel time is set as a link travel time in the traffic information for each extracted target link, the traffic information may be more reliable by “smoothing out” any extreme or abnormal values. Further, in predicting traffic information by statistically processing an average link travel time, the quality of statistically processed data may be enhanced.  
      Furthermore, because the more reliable traffic information may be stored in the memory  40  of the navigation system N, a route search may be conducted using the reliable data stored in the memory  40 . In addition, the output unit  60  may correctly recognize a congestion degree of a searched route to be followed by the vehicle.  
      Further, because the average link travel time for each extracted target link and the congestion degree corresponding thereto may be stored in the memory  90  of the information communication system C, the reliable traffic information may be accessed from the information communication system C from, for example, a home terminal.  
      It should be appreciated that the above-described exemplary system and method are not limiting, various modifications may be made without departing from the broad scope and spirit of the underlying principles.  
      For example, a smoothed link travel time at a predetermined trip time (when traveling will occur) may be calculated by accumulating traffic information including a congestion degree at various trip times (calculated on the basis of the congestion degree) may be calculated by statistically processing link travel times at the plurality of trip times including a link travel time at the predetermined trip time.  
      Thus, even if abnormal traffic information is included in the accumulated traffic information, the link travel time calculated from traffic information may be smoothed by statistically processing the link travel times at the plurality of trip times including the link travel time at the predetermined trip time. Thereby, the link travel time may be smoothed and may be prevented from becoming abnormal and can be made more realistic and highly reliable.  
      An average link travel time for each extracted target link may be an average of a plurality of link travel times, for example, two or four link travel times or the like including a current link travel time to be targeted. Further, the plurality of link travel times may be the current link travel time and link travel times following it.  
      An average link travel time may be calculated by smoothing three link travel times, for example, through a processing of making an abnormal link travel time close to a normal period or the like, instead of averaging the link travel times. Furthermore, a statistically processed value such as a median and the respective calculated link travel times or the like may be adopted.  
      The navigation system N may directly receive traffic information from the vehicle information communication system T and may perform at least part of the aforementioned exemplary methods for smoothing navigation data.  
      Again, while various features have been described in conjunction with the examples outlined above, various alternatives, modifications, variations, and/or improvements of those features may be possible. Accordingly, the various examples, as set forth above, are intended to be illustrative. Various changes may be made without departing from the broad spirit and scope of underling principles.