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Implementation of a GPS-based AVL System for Mazandaran Province
GPS menu of software has some options for monitoring of mobile vehicles. Connect option of GPS is used for connection of different mobile vehicles. A message error will be shown if connection to a mobile GPS encounters with any problem, and ask the user to modify setting. With successful connection, new mobile vehicle is added to mobile GPS list along with connection time. User can view classified status of a mobile GPS by choosing message103 option. Information such as date and time, coordinates, velocity, error factors and channel status can be viewed and modified on a window. Fig.5 shows different parts of message103 window.
 Fig.5. Different parts of message103 window Report menu has two options: Start auto save and Get report. By choosing Start auto save option, automatic saving of mobile vehicles status such as their position and velocity in user-determined intervals will be activated. Get report option is used for reporting saved data collected from mobile vehicles. Mobile position and velocity saved in data base at different times can be reviewed by user. All recorded data will be displayed by choosing show all record option. Moreover user can select special records by setting desired date and time intervals, geographical longitude or latitude, or velocity. Information related to maximum and minimum values of geographical longitude or latitude, velocity and average velocity is demonstrated for operator in report window. Records can be saved as QRP format, used by this software, or as html format. Fig.6 shows Get report form and reported information of a mobile vehicle.  Fig.6. Get report form and reported information of a mobile vehicle Tools menu has two options: Find path and Options. Fig.7 shows the Find path form. To find path between two nodes in a city, node list will be displayed for operator. By choosing source and destination nodes, path between two nodes along with intermediate nodes will be arranged. Fig.8 shows path finding between two nodes in Behshahr city.  Fig.7. Find path form  Fig.8. Path finding between two nodes in Behshahr city Options form helps to set serial ports of mobile vehicle transmitter along with reporting interval. Baud rate, data bits, stop bits, parity and flow control can be modified as shown in Fig.9. Refresh interval can be 5, 10, 20, or 30 seconds.  Fig.9. Options and Setup forms IV. Path finding Scanned or digital map file can not be used for precise tracking of a mobile vehicle. To be able to use SWF file obtained from scanned file for path finding, we should consider map as a graph. To extract a graph from scanned map, each fraction on the road was considered as a node. Therefore it is possible to have several nodes for a street and each street was divided to several lines. Each node was labeled and the distance between two nodes was considered as graph weight. The graph was saved as neighborhood matrix. A 2-D matrix , in which is the number of nodes, was generated. is the length of line between node and . It is obvious that is zero. If there is not any path between two nodes, a maximum value more than sum of all lines of the graph is considered as path length. To find the shortest path between two nodes the following problem should be solved [7]. Problem: Consider graph in which each line has a positive value and source node is obvious. Find the shortest path between source node and every other node in in such way that the total path length was summation of other length. Solution: To solve the problem Dijkstra's algorithm is used. This algorithm holds a set of nodes which have minimum distance from source node. For initial time, includes source node only. In each repeat a node of with minimum distance to source node is added to . Assuming that nodes of have positive cost, we can find the shortest path from source node to which pass from nodes of . This path is called "Special Path". In each repeat, array is used to record the shortest distance. When includes all nodes, all related paths will be "Special Path". Therefore contains the shortest distance from source node to each other nodes. An example of this algorithm is shown in Fig.10 and Table2. To find the shortest path between all couples of nodes, Floyd algorithm was used. Consider we have neighborhood matrix for all nodes with the name . Now repeats will be applied on . After repeats, has the shortest distance from node to which does not pass from other node with number larger than . In other words, nodes and can be every node but the number of each intermediate node should be equal or lower than . To calculate in repeat the following relation is used:  Fig.10. An example of graph for testing of Dijkstra's algorithm
An example of Floyd algorithm is shown in Fig.11 and Table3 and Table4.  Fig.11. An example of graph for testing of Floyd algorithm 
V. Conclusions In this paper, implementation of a GPS-based AVL system for Mazandaran province, a northern province of Iran, has been presented. A fuzzy map matching method was implemented for software, which uses a digital road map to correct the GPS position error. Software was developed with a GUI to report instantaneous position of mobile vehicle on the map and record contents of message103. Moreover, software has searching and path-finding capabilities. For experiments, a car navigation system was developed with a small number of sensors, such as a low cost GPS receiver and a microcontroller chip. The real road experiments demonstrate the effectiveness and applicability of the implemented algorithms for accurate navigation with low cost GPS receivers. The results show that real-time positioning error reduces from 25m to less than 1.5m using proposed fuzzy map matching algorithm. References:
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