Study on the Real time Navigation Data Model for Dynamic Navigation
LIU Yuefeng，ZHENG Jianghua，YAN Lei and XU Yiqin
（Institute of RS&GIS, Peking University，Beijing 100871, China, Key Lab. of Spatial Information Integration and Its Applications, Beijing 100871, China, zjh73@126.com）
Abstract — Dynamic navigation is the advanced level of
navigation service. The construction for an efficient and effective navigation data model to meet the requirements of dynamic navigation is the key point of the study. It first introduces the system requirements of dynamic navigation for navigation data. Then it briefly discusses several current navigation data models, such as KIWI, SDAL and ISO-GDF. The study found that current navigation data models have limits in their design for dynamic navigation and more work should be done in the research of real time navigation data models. In the paper, it discusses the content of real time navigation data and gets that the content mainly contains data of traffic events and data of traffic flow. Both of them are different feature classes of real-time navigation data based on ISO-GDF model. The descriptions of them include definition, properties and relations. In the model construction, the relations among events, the executants of events and target statuses are given consideration. The model which is got by the study can be used with a certain physical data models in dynamic navigation applications.
Keywords-dynamic navigation; real time; GDF; traffic event; traffic flow
more practicable. Navigation data is the base to realize dynamic navigation. The data pay more attention to represent the information of road networks and their attributes, also including some other related information needed by ITS (Intelligent Transportation systems) and LBS applications, such as the information of background display and POI (Points of Interest). The content of navigation data can be divided into two parts, static traffic information (e.g. the information of infrastructure of road networks) and real-time traffic information. Compared to the data in general GIS applications, navigation data not only describes the location of road networks and their related spatial elements, but also represents the spatial-temporal relations and traffic relations in the traffic networks [5]. Dynamic navigation relies on the real-time traffic data. In this paper, the study focuses on model construction of real-time navigation data for dynamic navigation. And it describes the model from aspects of features, attributes and relations. Ⅱ. NAVIGATION DATA MODEL Navigation data model is a concept to describe navigation related entities and the relation among them. It provides basic methods to describe navigation data management and to design navigation database. Navigation data model contains concept model, logic model and physical model, the same as the content of data model of GIS [Jun CHEN, 1995]. This paper pays more attention to the former two. To concept model and logic model of a certain field, the realization of its physical model can be various. Most navigation data models are developed based on general data models of GIS, which mainly refers to three types of models, region model, discrete entity model and network model [Goodchild, 1992]. Traditional navigation data models are mainly the latter two. Nowadays, the traffic phenomena become increasingly complex and diverse. It is difficult for traditional navigation data models to deal with several important problems in applications, such as process of dynamic attributes [Goodchild，1998], highly effective data storage, non-planar feature representation[12], complex feature representation and consistent representation of multi-scale topological relations. A lot of work has been done on the problems by scholars and organizations over the world. And some technologies (e.g. Liner Reference Systems, LRS; Dynamic segmentation) have been adopted in data model
Ⅰ. INTRODUCTION The development of technologies, such as communication and positioning, together with the emergence of new algorithms and the increasing abundance of real-time traffic information, has made dynamic navigation a focus of research and application. The requirements of real-time, more accuracy and individuation for dynamic navigation can be met in the situation. The connotation of dynamic navigation is not only the real-time traffic information services for the public. More important meaning is the ability to provide predictive traffic information services for a certain future period based on the processing of real-time traffic information. There are at least two elements to realize dynamic navigation. One is the data that reflects the real-time traffic information. The other is effective and highly precise algorithms of short time traffic prediction. As to the latter one, there are some research fruits. The algorithms from linear ones to nonlinear ones, such as KARIMA and WDR (Wavelets Decomposition and Reconstruction) [16], have their own application characters and improve the dynamic navigation
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construction. Some new data models emerge, such as the network data model of ARCGIS, hypergraph data model and feature-based data model. These models promote the research and application of navigation data model. However, none of them completely solves the problems of traditional navigation data models. And from the application view, we see navigation services are not far away from SP (Service Provider), CP (Content Provider), transportation administrators and public. The trend is to improve navigation data models in applications by steps. More data models or standards that can be used for navigation services come forth. Here lists some of them: KIWI of Japan[4], ISO-GDF(Geographical Data Files)[19], SDAL(Shared Data Access Library) of NavTech Co.[20], NHCRP(National Cooperative Highway Research Program) 20-27(2), GIS-T Enterprise, and lane-based data model[Fohl, 1996; Xiaoqing ZUO,et.al.,2004]. The differences of emphasis and start points between the models make the models display different application effectiveness. Qingquan LI [2004] selected six navigation data models, including KIWI, ISO-GDF, GIS-T Enterprise, for general analysis and summarized some shortage of current models: 1) Variance in standards and definition of terms; 2) Lack practicable linear data model in application level; 3) Lack the ability to manage spatial-temporal data; 4) Lack linear user-oriented location reference methods (LRM); 5) Lack the ability to support traffic analysis; 6) Lack the tools for the process of storage and complex paths; The shortage of the abilities to cognize and represent complex traffic phenomena is the nature of the problems in current data models. To improve current data models and construct new data models/standards, studying the concept and logic model is the base. GDF, which became an ISO standard in early 2004, is more a common concept and logic model of road networks and road related information for navigation service. And its physical model can act as exchangeable format for navigation data. However, KIWI and SDAL are more physical data models. The concept and logic data model study based on GDF is meaningful. In the rest of the paper, data model mainly refers to concept and logic data model. There is a little research based on GDF has been done. Yanhui WANG and Jun CHEN [2003] carry out extensive E-R analysis from multi-scale data model construction based on GDF. In general, current data models for navigation are mainly focus on static navigation application. The situation can not meet the increasing intensive needs for dynamic navigation. Several factors, such as the emergence of new algorithms for dynamic navigation, more abundant measures to obtain real-time traffic information and etc., push the study of data model for dynamic navigation be a research focus. In this paper, we studied real-time navigation data model for dynamic navigation based on ISO-GDF.
Ⅲ. THE CONSTRUCTION OF REAL-TIME NAVIGATION DATA
MODEL FOR DYNAMIC NAVIGATION
1) Analysis of Real-Time Navigation Data Model Real-time navigation data model for dynamic navigation is a kind of spatial-temporal data models. Current spatial-temporal data models mainly focus on the changes of spatial-temporal entities, and ignore the events leading to the changes and executants of the event. They do not describe and represent the relations among the events, target statuses and the decision makers either [Jun CHEN, 2002]. In the study of real-time navigation data model for dynamic navigation, we consider the shortages. There are twelve feature themes and sixty-one feature classes in ISO-GDF4.0. However, the real-time traffic information is not mentioned in it. The features are divided into feature classes and feature classes are divided into themes. A feature class is the child class of a certain feature theme and it is also the parent class of all the features included in it. After systemic analysis and practical investigation, the research group thinks the real-time navigation data model should include a new feature theme that is real-time traffic information, besides original feature themes in GDF. The new feature theme is comprised of two event classes, traffic event and traffic flow. There are three basic elements makes up concept model of the real-time navigation data. They are feature, attribute, and relation. The methods for feature, attribute and relation classification, abstract level of feature are included in the concept model of real-time navigation data based on ISO-GDF. They are similar to those of ISO-GDF [19]. Fig.1 to Fig.4 shows some of them.
Fig.1 hierarchy classification of features Fig.2 abstract level of feature data
Fig.3 methods of attribute classification Fig.4 relation classification in concept model
The overall concept model for real-time navigation data based on GDF can refer to that of ISO-GDF4.0. The information of traffic event and traffic flow is the characteristic components of real-time navigation data. There are no such content in ISO-GDF. Here studies the feature theme of real-time navigation data from three elements, feature, attribute and relation, as the component and extension of feature theme of real-time navigation data. 2) Feature Classes Of Real-Time Navigation Data Theme (1) Traffic event Definition: Traffic event is event which happens along the road contingently or periodically, and the event will affect traffic behavior. The structure of traffic event: Shown as Fig.5
Type code of traffic event geometry type of traffic event Location of traffic event
Description: The real-time traffic information, which reflects network statues, is the base of dynamic navigation service. The content mainly includes ID of data collection equipment, value of parameters of traffic flow, and the units of the parameters, etc. 3) The Attribute Of The Feature Class For Real-Time Navigation Data Model
tab.1
items extenal ID event type impedance coefficient start time prediction terminating time real terminating time description attri 1 of TEM attri 2 of TEM …… attri n of TEM field descri type length name ption
tab.2 items extenal ID velocity unit of velocity flux unit of flux density unit of density time ID of data collection equipment data owner field descri type length name ption
Types of traffic event and Information of traffic event coding: There are several management views to code the types of Description of traffic event traffic event and codes take part in the real-time navigation service. Here we divide traffic events into four kinds based on their sources. They are POI (Points of Interests), accident, construction and transportation. Different kinds of traffic events may relate to different items. Take the type of POI as an example. The items of a gas station may include name, alias, the oil standards, administrative department, etc. While to the type of construction, its items may include type of construction, the road under construction, construction organization, begin and end time of construction, etc. The item of traffic event types is related to the information of traffic events management. The geometry types of traffic events: A geometry type is the spatial type of location where traffic event occurred. We divide the geometry types into point event, linear event, region event and topological event. In fact, topological event includes the former three. We put them on one level mainly to emphasize topological event. Location: It is a pair of coordination or coordination chain or location ID of location where the event occurred. The information of traffic event management (TEM): It mainly includes the time items of events, such as happening time, prediction time of terminating, real terminating time, event producer, and the supervisory department. Some of the items are related to data management. (2) Traffic flow Definition: It refers to the related information of the parameters of traffic flow that reflect the real-time network statues.
(!) Tab.1 attribute data structure of feature class of traffic event (2) Tab.2 attribute data structure of feature class of traffic flow 4) Relations Between A Feature Class Of Real-Time Traffic-Info Theme And Features Of Other Themes The two feature classes of traffic event and traffic flow are mainly related to road elements (1) Tab.3 relation between traffic event and road elements
tab.3 items ID of traffic event ID chain of road elements the start of reference location the start of reference location field descri type length name ption
tab.4 items ID of traffic flow ID of row elements descri field type length ption name
(2) Tab.4 relation between traffic flow and road elements
The feature class of traffic flow mainly reflects the real-time information of the traffic flow in some road elements. 5) Logical Model For The Real-Time Navigational Data The data model rises to the logical model when considering geometry data entities based on the conceptual data model [3]. The attributes of feature-oriented transportation entities are taken into account in ISO-GDF. The logical model of the real-time navigational data is shown as Fig.6.
information for dynamic navigation service. The research studies and improves the dynamic navigation oriented data content and data model based on ISO-GDF 4.0. We partition real-time traffic-info into two components: traffic events and traffic flow, and study the construction of the model from three aspects: feature, attribute and relation. The ignored relations among events, events executants and various relationships are considered in the construction of modeling. The results provide basic support for dynamic navigation-oriented data organization and application service. REFERENCES
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Fig.6 logic model for real-time navigation data（modified that of Dueker&Bulter,1998） Ⅳ. APPLICATION DISCUSSION GoodChild [1999] believes that the development of the digital navigational map goes through three stages: map view, navigational view and behavior view. There are a lot of related things to study. It not only promotes GIS to settle the problems of transportation, but also facilitates development of GIS. The real-time navigational service is closely related to the user’s behavior, and boosts digital navigation map from the navigation view to the behavior view. The dynamic navigation oriented real-time navigation data model presented here is a generic conceptual and logical data model of road network and road-related information. It is an extension model of ISO-GDF. Various physical models that meet the practical needs can be built based on this model. Thus it ensures the data support for implementing dynamic navigation. The data here includes static and real-time traffic-info data. Ⅴ. CONCLUSION This paper indicates there are two fundamental elements to meet the increasingly strong needs for dynamic navigation. One is real-time traffic-info; the other is highly effective and precise short-time traffic prediction algorithms. It systemically analyses the shortages of most currently navigation data models and their characters in applications. And points out that current navigation data models should first improve their conceptual and logical model to provide real-time navigation
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