Author: Cheng, Wai-pun
Title: A geographic information system for dynamic path finding and route planning system
Degree: M.Sc.
Year: 1997
Subject: Motor vehicles -- Automatic location systems
Mobile communication systems
Geographic information systems
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Department of Computing
Pages: [x], 109, [22] leaves : ill. ; 30 cm
Language: English
Abstract: Finding the correct path from one place to another in any big city has never been an easy task, while being able to navigate the vehicle through the congested transportation network in the ever changing and rapidly developing city like Hong Kong has been the dream of every motor-car driver. With the advent of real-time position fixing, digital computing and communication technology, real-time car-navigation system has became a reality. The basic components of a car-navigation system are the position fixing system, geographic database system, a path finding and route planning system, a tele-communication system and a user interfacing system. The position fixing system was to locate the contemporary vehicle and destination position, the geographic database system was to store and maintain the road network and the associated traffic information, the route planning system was to search for the optimal path from the current vehicle location to the destination, the tele-communication system was to transmit the up-to-date information to the mobile system, and the user interfacing system was to generate the driving instruction at every decision point and monitor the vehicle's movement through the road network. ( H. Claussen and D. M. Mark 1991 ) In most countries, the benefits of having real-time road information and traffic data had been offset by the cost of building up the infrastructure to support and communicate such information, and the lack of up-to-date digital road map had led to the provision of a less user friendly textual interface to guide the driver. However, the infrastructure for capturing and broadcasting the real-time road and traffic information as well as an up-to- date digital road map of Hong Kong was readily available, which provided the basic requirements for the car-navigation system. Therefore the proposed solution in this study is intended to build a more user friendly graphical user interface system and a dynamic route planning system with the capability to handle dynamic road and traffic information. The prototype system developed for this project was broadly divided into two parts; the mobile system and the centralized system. The mobile system designed for uploading the digital road network, the generation of the optimal path and user instructions was developed on a geographic information system (Arc/Info); the centralized system designed for the updating and dissemination of the dynamic road and traffic information was developed on a relational database management system (Oracle); and the communication between the mobile and database system was simulated by the local area network (LAN). The advantage of using geographic information system is the improvement over the conventional dead reckoning system; on the user friendly graphical user interface for inputting destination location and outputting navigation instructions, the geo-referenced data model for location searching of the destination and map matching for the calibration of contemporary car position, the topological node-link data structure for path finding, and the capability of handling statistical and real time traffic data. The prototype system provided three tiers or route planning solutions to satisfy different user's requirement, namely, the local point to point route planning with exact address matching car navigation instruction and nearest facilities searching functions within an urban area; the district to district route planning using a higher degree of information abstraction on the road network information; and the even more high level region to region route planning in the territory context. The prototype system also handled two types of 'what if' situation, the first type is what if the vehicle did not or could not follow the navigation instruction and the second type is what if the broadcasted traffic information did not accurately reflected the road condition and the car get caught in a traffic jam. The system handled the first situation by a position trigger (comparing the current vehicle position with the suggested path; and the second situation by a time trigger (testing the car positions at two epochs of time). In both situation an alternative path would be suggested at the next decision point along the road network, while in the second case a road barrier would be added to the particular road segment ahead before the new route was computed. Through this study, it was found that the conventional single line road network topology cannot truly represent the road and traffic flow condition, in particular the U-turn restriction and the transport direction restriction at the starting point. In this project, a graphic link per traffic flow direction in the road network was developed to overcome these limitations. It was also found that an unique road code, road segment code and road junction code were necessary and essential for accurate and effective traffic information update. In each road segment an initial designed speed was assigned and subsequently updated by multiplying a factor depending on the current traffic condition. ( 0 for no through road ) to indicate the current traffic flow condition. In each road junction was assigned with the turn restriction for all possible turn direction, -1 for prohibited turn. The creation of additional graphic nodes and links to represent an actual traffic flow situation in order to complete the logical connectivity of the road network; and the use of predicted traffic flow estimated from periodic traffic survey information to complement the inadequacy of real-time traffic flow information were also essential to the success of the dynamic car navigation system. In the study, two implementation approaches for the dynamic car navigation was studied, namely the centralised and mobile approaches. I found that the centralized approach demanded the infrastructure support of an expensive full-duplex communication system and powerful centralized computing system, which is not practical business solution in Hong Kong. The mobile system approach is more flexible and expandable solution, which is satisfied the availability and quick response requirements of in Hong Kong. Therefore the prototype system in this study was developed based on the mobile system approach. The testing of the prototype system had been carried out in the Central and Wanchai district for detail car navigation, in the Hong Kong Island for district level path finding, and the whole territory of Hong Kong for regional route planning. An effective route was found in each case, as compared to the route suggested by professional drivers. However, there was a slight time difference between the computed and actual travelling time due to the different personal style. However, with the dynamic traffic information and daily traffic pattern a better route was planned. In general, the dynamic car navigation system with the capability of handling real-time traffic information was able to provide a technically feasible and effective solution for road navigation and route planning in Hong Kong, provided a real-time position tracking system and information broadcasting system were in installed. However, for a high precision automatic car navigation system, detailed lane information and vehicle motion control system were also required. The degree of automation relies on the availability of in-borne road surveillance and monitoring system and navigation instruction based vehicle control system. The beauty of integrating real time traffic information and road condition in the car navigation system is that the driver was informed about what lies ahead of his journey, such as traffic congestion, accident or road work, and system would suggested an alternative route for the driver to bypass such incidents. In reality even the driver might not follow the route suggested by the system, the user would found the real time traffic information and road condition as well as the facilities information very useful.
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