201219748 六、發明說明： 【發明所屬之技術領域】 本發明大體而言係關於數位地圖’其為用於顯示道路或 路徑資訊之類型，且更特定言之，係關於—種用於偵測分 層交叉路口、地下道及隧道以便併入於一數位地圖中之方 法。 【先前技術】 如（例如）圖1中所示之個人導航裝置利用與來自GPS之準 確定位資料或其他資料流相結合的數位地圖。已針對許多 應用（諸如’汽車司機之導航輔助）開發出此等裝置。此等 裝置之效用本身取決於以數位地圖之形式提供給此等裝 置、儲存於此等裝置之記憶體中或經由合適的資料庫連接 (諸如，無線信號、纜線、電話線等）以其他方式存取的資 訊之準確度。 通常，導航裝置1〇(圖υ包括顯示幕丨2，其將一已儲存201219748 VI. OBJECTS OF THE INVENTION: TECHNICAL FIELD OF THE INVENTION The present invention generally relates to digital maps, which are types for displaying road or route information, and more specifically, for detecting points. A method of layer crossings, underpasses, and tunnels for incorporation into a digital map. [Prior Art] A personal navigation device such as that shown in Fig. 1 utilizes a digital map combined with a quasi-determined bit data or other data stream from GPS. Such devices have been developed for many applications, such as navigation aids for car drivers. The utility of such devices may themselves depend on the form of a digital map provided to such devices, stored in the memory of such devices, or connected via a suitable database (such as wireless signals, cables, telephone lines, etc.) to other The accuracy of the information accessed by the method. Usually, the navigation device 1 (the figure includes the display screen 2, which will have one stored
以產生探測器量 、、、彳間隔所記錄之離散地理編碼位 ，、他合適的農置可用以產 15I862.doc 201219748 測點’該等裝置包括(例如)手持型裝置、行動電話、pDA 及其類似者。因此’可將探測資料描述為關於運輸工具 (或攜帶探測裝置之人）之移動的資訊之一集合，其含有有 時間戳記之地理編碼（藉由緯度/經度座標識別之地理位置） 且亦可能含有中繼資料（運輸工具速度、接收器類型、運 輸工具類型、精度、來源、準確度等）。 已知為了漸進式地產生及/或更新數位地圖而收集探測 器量測結果。可經由無線（例如，蜂巢式）傳輸、經由網際 網路上載或藉由其他習知通信方法將該等探測器量測結果 以即時或後續監視方式傳輸至（諸如）收集服務或其他地圖 資料分析服務。網際網路上載可經同步而與數位地圖升級 —起發生，導航裝置使用者可能作為服務之部分而獲得該 等數位地圖升級。根據探測器量測結果之集合，可推斷道 路幾何形狀且可藉由適當分析方法導出其他特徵及屬性。 在一段時間内自穿越一數位地圖之一特定部分的複數個 探測器所收集之探測器量測結果之典型集合可含有上億個 離散資料點，每一資料點經地理編碼且有時間戳記。隨時 間流逝而收集之探測跡線可根據匹配於該數位地圖之一共 同區域之探測跡線而分組，且接著被覆疊以便由地圖資料 庫編輯器解譯。此等編輯器使用各種數學及統計技術判定 或推斷道路幾何形狀，計算速度分佈圖、加速度分佈圖、 行進方向、高度，偵測道路網之變化，以比較兩個道路網 及許多其他規格。 如上文所提出，個人導航裝置丨〇之效用取決於該數位地 151862.doc 201219748 ®中所3的貝訊之準確度。因而，數位地圖提供者繼續努 力以儘可μ有效且經濟之方式來改良及更新其地圖。然 而’為了有效且經濟’可能獲得不準確之資料。舉例而 5 ’不準確之資料可能損害導航裝置1G回應於導航查詢而 1*算最佳路線或將其他可靠資訊提供給行進者之能力。因 此，數位地圖中所含之不準確或不完整之資訊可導致不良 或錯誤的導航指令且導致不當的導航決策。舉例而言，一 一運輸工具（例如’特殊運輸王具，包括加油車、拖運揮 發!·生材料之運輸工具及超大型運輸工具）需要通過大體上 s障疑物（例如’低矮橋樑或隧道）的路線，及能夠承受 運輸工具負載之重量的橋樑。因此’對於一些行進者，數 位地圖必須準確地描綠道路及道路之特徵。因此，橋標或 随道之存在或不存在構成將記錄於數位地圖中之重要細 節。 攻7 ，用以準確地判定路線是否包括分層交又路口（亦 即合天橋/地下道）、地·Ρ道或㈣之方法需要使用跡 ^之南度資料獲得大量跡線，其中分析每—跡線點以使用 ”先。十方法獲得南度點之分佈，例如’高度點分佈上之高斯 分佈'然而，執行此詳細分析需要：第一，可獲得高度資 2 ;第二，高度資訊有足夠的解析度；第三，高度資訊可 靠，且最後，高度資訊需要精確地定位且歸因於GPS接收 :之平滑作用而不滞後於移動方向。因此，此項技術需要 一種用於以經濟的方式有效地獲得關於分層交又路口及隧 道之精確位置的準確資料之經改良方法。 151862.doc 201219748 【發明内容】 本發明係關於用於獲得關於分層交又路口及隧道之精確 位置的準確資料之方法及技術。該方法提供一系統，該系 統使探測資料能夠得到有效地收集及準確地評估，以判定 分層交又路口及隧道之存在及精確位置。該方法包括一數 位地圖’該數位地圖具有彼此交叉的兩個分層道路段或一 穿越一随道之道路段中之至少一者。該方法進一步包括自 穿越道路段之具備GPS功能之裝置經由複數條探測跡線 報告資料，其中該所報告資料包括精度稀釋（D〇p)值。接 著，該方法包括收集該等探測跡線且對其進行分析以判定 該等DOP值在何處相對強且在何處相對弱。接著，該方法 包括經由该專债測到的弱DOP值關聯一分層交叉路口或隨 道之位置。 根據本發明之另一態樣，提供一種用於藉由觀測探測資 料來判定一數位地圖中之一地下道存在之方法。該方法包 括以下步驟：提供一具有至少一道路段之數位地圖，及自 沿著該至少一道路段行進之複數條探測跡線報告資料。此 外’關於精度稀釋（DOP)值分析該所報告資料，且接著， 若該等DOP值突然自一實質上恆定之值減小至一減小之值 且接著突然返回該實質上恆定之值，則推斷沿著該至少一 道路段之一地下道之存在。 本發明之原理可用來有效地沿著一數位地圖定位分層叉 路及地下道，在該等分層叉路及地下道處存在相對低的 DOP值。該等低DOP值指示由於某種架空結構阻礙而對各 151862.doc -6- 201219748 别釔號之阻礙。此外，包含天橋之道路及包含地下道之道 路可易於藉由關於其D〇p值而分析各別跡線予以判定。此 外，右正在分析單一道路，則相對低的D0P值可以可靠地 歸因於地下道。因此，本發明使自社群輸入或其他探測器 量測結果收集技術所獲得的資訊能夠有一種新用途，用來 經濟且可靠地偵測分層交叉路口及地下道。 【實施方式】 鑒於以下對目前較佳實施例及最佳模式之詳細描述、附 加之申請專利範圍及隨附圖式’ A習此項技術者將容易瞭 解此等及其他態樣、特徵及優點。 更詳細地參看圖式，其中相同數字在若干視圖中始終指 示相同或對應的部分，本發明大體而言係關於由導航系統 及裝置10使用之數位地圖，以及其他地圖應用程式，其他 地圖應用程式可包括經由具備網際網路功能之電腦、 PDA、蜂巢式電話及其類似者看得見的地圖應用程式。 圖2以高度簡化形式描繪一呈複數條道路之形式（展示為 一對道路18、20)的分層交又路口 16。當然，分層交叉路 口可能有許多不同可能組態，且作為說明而非限制，僅論 述及展不一簡化實施例。因此，未詳細論述或展示的分層 交叉路口之不同可能組態意欲包括於分層交又路口16之定 義内，諸如至少部分地彼此重疊之多條道路、橋樑、鐵 路、隧道或其變體組合。 在圖2實例中，道路段18、20包含整個道路網14之包含 於數位地圖中之部分。通常，道路段丨8、2〇可為能夠支援 15I862.doc 201219748 諸如用汽車23、25展示的運輸工具交通流之類型，但本發 明之原理亦同樣可適用於其他運輸模式。 道路段18、20(在運輸工具在其上之行進意欲以實質上 不間斷之方式流動的情況下很典型）至少部分地沿著立體 交叉道組態，以使得一個道路段18位於另—路線2〇之下。 因此，該等道路段中之一者20以上覆關係在橋樑部分19之 上延伸以提供另一道路段18之下伏地下道部分之天橋。對 —些行進者而言，知道交叉路口是表示同層交又路口或是 分層交叉路口（諸如，天橋及地下道）报重要。在同層交叉 路口之情況下’運輸工具可能需要知道其是否可沿著同層 交叉路口進行必要的轉彎，或在分層交叉路口之情況下， 運輸工具可能需要知道（例如）任何道路負載容量要求、橋 襟高度要求、寬度要求或其類似者。因而，得到對同層交 叉路口或分層交叉路口（例如，橋樑或其他類型之分層交 又路口）之預先通知可經證明在為一些行進者繪製行進路 線時非常重要。 圖3為數位地圖之與圖2中所呈現之部分相同的部分之視 圖，但來自探測跡線之覆疊資料係自具有具備適當功能之 探測裝置（諸如，圖i之裝置1〇)之運輸工具收集到。可自來 自沿著道路段18、2G行進之運輸工具23、25之所報告資料 觀測到複數條探測跡線。此所報告資料包括D〇p值，其可 能為中繼資料’或其使得能夠藉由（例如）體現於每一探測 跡線中之有時間戮記之位置量測結果來導出速度資訊。根 據本心明，有可能自該等D〇p值偵測該等道路段之分層交 151862.doc 201219748 叉路口 16。在此特定實例中，（自穿越天橋之運輸工具25 傳輸之）所報告DOP值在該等道路段20中之—者上保持值 定或貫質上恆定’而（自穿越地下道之運輸工具23傳輸之） 所報告DOP值在另一道路段1 8之一構成地下道之小部分之 上自一實質上恆定之值顯著減小’且接著突然返回至該實 質上恆定之值（參見指示（x)及（0)相對信號強度之圖例）。因 此，可容易推斷，假設減小之D0p值在道路段18之同一所 偵測地理編碼位置中重複出現，則D〇p值之變化指示對自 運輸工具23傳輸之所報告信號之阻礙。 如呈線圖形式之圖4所示，沿著道路段所接收之D〇p值 可歸因於精確的地理編碼位置（緯度及經度）。因此，當 卿值隨時間流逝保持實質上值定（不論其指示強信號或 是弱信號）時，可以斷定··影響D〇p值的是固定障礙物而 非臨=阻礙。此外，在單獨道路段18、2〇彼此交又的情況 下，若DOP值沿著一個道路段2〇保持相對恆定且強則可 以斷定：沒有東西妨礙到正在接收的信號強度，且因此， 沒有東西上覆於道路段2〇或以其他方式對所接收信號呈現 章礙物然而，右DOP值沿著另一道路段i 8暫時不良（自 相對強之仏5虎變為相對弱之信號’且接著突然返回相對強 之U) ’則可容易斷定··道路段18有臨時架空阻礙，因 丁道路& 18在另-道路段2G之橋樑部分下方經過。 /應、瞭解’來自沿著在常規交叉路口處交叉之各條 „ — 丁進之運輪工具的探測跡線之DOP值分佈通常將具有 值同時刀層父又路口處之下層道路的D〇p值分 151862.doc 201219748 佈（亦即，來自在隨道内部、在橋樑下方等前進的運輸工 具之跡線之D0P值）通常將具有兩個可分辨的峰值❶因 此，且作為實例，可擬合關聯於交叉路口道路之D0P值分 =與高斯分佈’且比較此等分佈之各別平均值以判定道路 是否在常規或分層交又路口處彼此交又。 如圖4所不，接收到的DOP值可經地理編碼。因此，可 畫出藉由一跡線信號之特定緯度及經度識別之位置，且隨 時間机逝’建立—趨勢。因而，可監視所接收之強DOP值 及弱DOP值，以判斷是否存在異常，或相反地，是否存在 連續樣式。在所展示實例中，沿著道路段^ 8之一部分畫出 弱DOP值之一連續樣式，藉此可靠地指示在道路段之上 覆橋樑部分下方的地下道。 圖5所示，根據本發明之方法不僅可用來谓測分層交 叉路口之存在，而且可用來偵測隧道22之存在。使用上文 所論述之相同邏輯，可收集並分析可容易地自具備GPS功 能之導航系統或裝置10以及其他地圖應用程式獲得之標準 DOP值，以坪估道路丨8是否穿越一隧道（諸如，所描繪之 隧道22，其提供穿越河流24之地下道21)。如同橋樑之情 況一樣，當配備具備適當功能之探測裝置之運輸工具行進 穿過隧道22時，DOP值在進入隧道22後立即減小，且接著 立即返回至相對有所增加之值。 當然’雖然並不要求，但應認識到，可組合所接收之 DOP值與多種其他類型之資訊（諸如，標準高度資料）以進 一步增強表示準確數位地圖之能力且幫助數位地圖上之路 151862.doc •10· 201219748 線選擇操作》 已根據相關法律標準來描述 ^ 引迷發明，因此該描述本質 上為例不性的而非限制性 m ^ „ L 了所揭不貫施例之變化及修 改了4付對熟習此項技術者 範疇。 。‘·.、員而易見且屬於本發明之 【圖式簡單說明】 圖1為根據本發明之一眘祐点丨> _ 貫〜例之—攜帶型導航裝置㈣ 不性視圖，該導航裝置包括—用 用於呈現地圖資料資訊之顯 示幕； / 2為具有分層交叉路口（例如，兩條道路經由橋樑彼此 交又）之一數位地圖的高度簡化平面圖； 圖3為圖2中之數位地圖之視圖，其覆疊有經由沿著各別 道路行進的具備GPS功能之裝置經由探測資料所接收的一 般DOP信號強度； 圖4為來自經由沿著圖2之數位地圖之道路中之一者行進 的具備GPS功能之裝置所收集之探測資料的d〇p值之圖； 且 圖5為穿越地下道之道路的高度簡化平面圖，其覆疊有 、經由沿著各別道路行進的具備GPS功能之裝置經由探測資 料所接收的一般DOP信號強度。 【主要元件符號說明】 10 導航裝置 12 顯示幕 14 道路網 151862.doc 201219748 16 分層交叉路口 18 道路段 19 橋樑部分 20 道路段 21 地下道 22 隧道 23 汽車 24 河流 25 汽車 151862.doc -12In order to generate discrete geocoded bits recorded by the detector volume, and interval, his suitable farm can be used to produce 15I862.doc 201219748 points. These devices include, for example, handheld devices, mobile phones, pDA and Similar. Therefore, the probe data can be described as a collection of information about the movement of the vehicle (or the person carrying the detection device), which contains a time-stamped geocode (geographic location identified by latitude/longitude coordinates) and possibly Contains relay data (vehicle speed, receiver type, vehicle type, accuracy, source, accuracy, etc.). It is known to collect detector measurements in order to progressively generate and/or update digital maps. The detector measurements can be transmitted to the collection service or other map data analysis, such as by a wireless (eg, cellular) transmission, via the Internet, or by other conventional communication methods, in an immediate or subsequent monitoring manner. service. Internet uploads can be synchronized with digital map upgrades, and navigation device users may receive these digital map upgrades as part of the service. Based on the set of detector measurements, the path geometry can be inferred and other features and attributes can be derived by appropriate analysis methods. A typical collection of detector measurements collected over a period of time from a plurality of detectors traversing a particular portion of a digital map may contain hundreds of millions of discrete data points, each of which is geocoded and time stamped. The probe traces collected over time may be grouped according to probe traces that match a common area of the digital map and then overlaid for interpretation by the map database editor. These editors use a variety of mathematical and statistical techniques to determine or infer road geometry, calculate velocity profiles, acceleration profiles, direction of travel, altitude, and detect changes in the road network to compare two road networks and many other specifications. As suggested above, the effectiveness of the personal navigation device depends on the accuracy of the digital signal in the digital 151862.doc 201219748®. As a result, digital map providers continue to work to improve and update their maps in an efficient and economical manner. However, inaccurate information may be obtained in order to be effective and economical. For example, 5 'inaccurate data may impair the ability of the navigation device 1G to respond to a navigation query and to provide an optimal route or provide other reliable information to the traveler. As a result, inaccurate or incomplete information contained in digital maps can result in poor or incorrect navigation instructions and lead to improper navigation decisions. For example, one-to-one transport vehicles (such as 'special transport kings, including fuel trucks, hauling volatilizers! · raw materials transport vehicles and very large transport vehicles) need to pass through the general obstacles (such as 'low bridges' Or the route of the tunnel, and the bridge that can withstand the weight of the load of the vehicle. Therefore, for some travellers, digital maps must accurately characterize green roads and roads. Therefore, the presence or absence of a bridge or an accompanying track constitutes an important detail that will be recorded in a digital map. Attack 7 is used to accurately determine whether the route includes a stratified intersection (ie, Hetianqiao/Underpass), the Earth's raft, or (4). It is necessary to use the south data of the trace to obtain a large number of traces, where each of them is analyzed. The trace points are used "first. Ten methods to obtain the distribution of the southern points, such as the 'Gaussian distribution on the height point distribution'. However, to perform this detailed analysis, it is necessary to: first, obtain a high degree of capital; second, the height information has Sufficient resolution; third, the height information is reliable, and finally, the height information needs to be accurately positioned and attributed to the GPS reception: the smoothing effect does not lag behind the moving direction. Therefore, this technology requires an economy for economics. The improved method for efficiently obtaining accurate information on the precise location of the intersections and tunnels. 151862.doc 201219748 SUMMARY OF THE INVENTION The present invention relates to obtaining precise locations for stratified intersections and tunnels. Method and technique for accurate data. The method provides a system that enables the detection data to be efficiently collected and accurately evaluated to determine the hierarchical intersection The existence and precise location of the mouth and the tunnel. The method comprises a digital map having at least one of two layered road segments crossing each other or a road segment crossing a track. The method further comprises self-traversing The GPS-enabled device of the road segment reports data via a plurality of probe traces, wherein the reported data includes a precision dilution (D〇p) value. The method then includes collecting the probe traces and analyzing them to determine Where are the DOP values relatively strong and where they are relatively weak. Next, the method includes correlating a stratified intersection or a location of a trajectory via a weak DOP value measured by the special debt. Provided is a method for determining the presence of an underpass in a digital map by observing the detected data. The method comprises the steps of: providing a digital map having at least one road segment, and traveling from along the at least one road segment a plurality of probe trace report data. In addition, the data reported by the precision dilution (DOP) value is analyzed, and then, if the DOP values suddenly come from The substantially constant value is reduced to a reduced value and then abruptly returned to the substantially constant value, the presence of an underpass along one of the at least one road segment is inferred. The principles of the present invention can be used to effectively follow a digit The map locates the tiered forks and underpasses, and there is a relatively low DOP value at the tiered forks and underpasses. These low DOP values indicate that each of the 151862.doc -6-201219748 is not obstructed by some overhead structure. In addition, roads containing flyovers and roads containing underpasses can be easily determined by analyzing individual traces for their D〇p values. In addition, while a single road is being analyzed right, a relatively low DOP value can be reliably This is attributed to the underpass. Thus, the present invention enables information obtained from community input or other detector measurement collection techniques to be used for a new purpose to economically and reliably detect stratified intersections and underpasses. DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the preferred embodiments and the best mode, the appended claims, and the accompanying drawings . Referring to the drawings in detail, wherein like numerals refer to the same or corresponding parts throughout the several views, the present invention generally relates to digital maps used by navigation systems and devices 10, as well as other map applications, other map applications. This can include map applications that are visible via Internet-enabled computers, PDAs, cellular phones, and the like. Figure 2 depicts in a highly simplified form a layered intersection 16 in the form of a plurality of roads (shown as a pair of roads 18, 20). Of course, there may be many different configurations of the hierarchical intersections, and as a matter of illustration and not limitation, only a simplified embodiment will be discussed. Thus, different possible configurations of hierarchical intersections that are not discussed or illustrated in detail are intended to be included within the definition of hierarchical intersections, such as multiple roads, bridges, railways, tunnels, or variations thereof that at least partially overlap each other. combination. In the example of Fig. 2, road segments 18, 20 contain portions of the entire road network 14 that are included in the digital map. Typically, the road segments 、8, 2〇 can be of a type that can support the traffic flow of the vehicle, such as that exhibited by the cars 23, 25, but the principles of the present invention are equally applicable to other modes of transportation. The road segments 18, 20 (typically where the transport on which the transport is intended to flow in a substantially uninterrupted manner) are at least partially configured along the solid intersection such that one road segment 18 is located on another route 2〇. Thus, one of the road segments 20 overlaps over the bridge portion 19 to provide a flyover for the underpass portion of the other road segment 18. For some of the travellers, it is important to know that the intersection is a crossroads or a layered intersection (such as a flyover and an underpass). In the case of a cross-section intersection, the vehicle may need to know if it can make the necessary turns along the same-level intersection, or in the case of a tiered intersection, the vehicle may need to know, for example, any road load capacity. Requirements, bridge height requirements, width requirements or the like. Thus, obtaining advance notice of a cross-over intersection or a tiered intersection (e.g., a bridge or other type of tiered intersection) may prove to be important in drawing a route for some travellers. Figure 3 is a view of the same portion of the digital map as that presented in Figure 2, but the overlay data from the probe traces is transported from a probe device having a suitable function (such as the device of Figure i). The tools are collected. A plurality of probe traces can be observed from the reported data of the vehicles 23, 25 traveling along the road segments 18, 2G. The reported data includes a D〇p value, which may be a relay data' or it enables velocity information to be derived by, for example, a time-stamped position measurement embodied in each of the probe traces. According to Ben Xinming, it is possible to detect the layered intersection of these road segments from these D〇p values. 151862.doc 201219748 Fork junction 16. In this particular example, the reported DOP value (transmitted from the traversing flyover vehicle 25) remains constant or consistently constant in those road segments 20 (from the vehicle 23 that traverses the underpass) The reported DOP value is significantly reduced from a substantially constant value over one of the other road segments 18 forming a small portion of the underpass' and then suddenly returns to the substantially constant value (see indication (x) And (0) a legend of relative signal strength). Therefore, it can be easily inferred that, assuming that the reduced D0p value is repeated in the same detected geocoded position of the road segment 18, the change in the D〇p value indicates an obstruction to the reported signal transmitted from the vehicle 23. As shown in Figure 4 in the form of a line graph, the value of D〇p received along the road segment can be attributed to the exact geocoding position (latitude and longitude). Therefore, when the value of the value remains substantially constant over time (whether it indicates a strong signal or a weak signal), it can be concluded that the influence of the D〇p value is a fixed obstacle rather than a failure. In addition, in the case where the individual road segments 18, 2〇 intersect each other, if the DOP value remains relatively constant and strong along a road segment 2〇, it can be concluded that nothing interferes with the signal strength being received, and therefore, there is no Something overlies the road segment 2〇 or otherwise presents a blockage to the received signal. However, the right DOP value is temporarily bad along another road segment i 8 (from a relatively strong 仏5 tiger to a relatively weak signal' and Then suddenly return to the relatively strong U) 'It can be easily determined that the road section 18 has temporary overhead obstruction, and the Ding Road & 18 passes under the bridge section of the other-road section 2G. / should, understand 'from the intersections of the traces along the intersections at the regular intersections „ — Dingjin's wheel tools will usually have the value of the same level of the lower layer of the knife at the same level. p value 151862.doc 201219748 cloth (that is, the DOP value from the trace of the vehicle moving forward, under the bridge, etc.) will usually have two resolvable peaks. Therefore, as an example, Fitting the DOP value score associated with the road at the intersection = and the Gaussian distribution 'and comparing the individual averages of the distributions to determine whether the roads intersect each other at regular or stratified intersections. As shown in Figure 4, receive The resulting DOP value can be geocoded. Therefore, the position identified by a particular latitude and longitude of a trace signal can be drawn and 'established-trends over time. Thus, the received strong DOP value can be monitored and Weak DOP value to determine if there is an anomaly, or conversely, if there is a continuous pattern. In the example shown, a continuous pattern of weak DOP values is drawn along one of the road segments ^8, thereby reliably indicating on the road Overlying the underpass below the bridge portion. As shown in Figure 5, the method according to the present invention can be used not only to detect the presence of a stratified intersection, but also to detect the presence of the tunnel 22. Using the same logic discussed above, Standard DOP values that can be easily obtained from a GPS-enabled navigation system or device 10 and other map applications can be collected and analyzed to assess whether the road 丨 8 traverses a tunnel (such as the depicted tunnel 22, which provides traversal The underpass of the river 24 21). As in the case of a bridge, when a vehicle equipped with a suitably functioning detection device travels through the tunnel 22, the DOP value decreases immediately after entering the tunnel 22, and then immediately returns to the relative Increased value. Of course 'although not required, but it should be recognized that the received DOP value can be combined with a variety of other types of information (such as standard height data) to further enhance the ability to represent accurate digital maps and to assist on digital maps. Road 151862.doc •10· 201219748 Line Selection Operation 》 has been described according to relevant legal standards ^ 引 发明, because Not an example and not limiting description of the nature m ^ "L can not pull up the consistent variations and modifications of the embodiments 4 to pay for the person skilled in the art category. . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a portable navigation device (four) in accordance with one embodiment of the present invention. FIG. The device includes - a display screen for presenting map information information; / 2 is a highly simplified plan view of a digital map having a layered intersection (for example, two roads crossing each other via a bridge); FIG. 3 is a view of FIG. A view of a digital map overlaying the general DOP signal strength received via probe data via GPS-enabled devices traveling along respective roads; Figure 4 is from one of the roads via the digital map along Figure 2. A graph of the d〇p value of the detected data collected by the GPS-enabled device; and Figure 5 is a highly simplified plan view of the road passing through the underpass, which is overlaid with GPS functions traveling along the respective roads The general DOP signal strength received by the device via the probe data. [Description of main component symbols] 10 Navigation device 12 Display screen 14 Road network 151862.doc 201219748 16 Layered intersection 18 Road section 19 Bridge section 20 Road section 21 Underground road 22 Tunnel 23 Car 24 River 25 Car 151862.doc -12