1 Overview
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With the expansion of urban construction in China, the increasing number of vehicles, the management and rational dispatch of transportation, the command and safety management of police vehicles has become an important issue in public security and transportation systems. In the past, the equipment used in the traffic management system was mainly a radio communication device. The dispatching center issued a dispatch command to the driver of the vehicle. The driver can only tell the approximate location of the vehicle according to his own judgment, but in the unfamiliar zone or at night. I can't confirm my position or even get lost. Therefore, its application is limited in terms of scheduling management and security management. The emergence of GPS positioning technology provides specific real-time positioning capability for navigation and positioning of vehicles, ships and other vehicles. The car GPS receiver allows the driver to know his or her specific location at any time. The GPS positioning information is sent to the dispatching command center through the vehicle radio station, and the dispatching command center can timely grasp the specific location of each vehicle and display it on the large-screen electronic map. At present, the main functions used in public security and transportation systems are: a command management system that combines GPS positioning and wireless communication systems; and a command management system that uses GPS differential technology. The working principle and equipment composition of the two management systems are described below.
2. Vehicle GPS positioning management system
The vehicle GPS positioning management system is mainly autonomously positioned by the vehicle GPS, and the vehicle is scheduled and managed in conjunction with the wireless communication system. Successfully developed such as vehicle global positioning alarm system, police GPS command system. It is used for urban bus dispatch management, vehicle and boat alarm and dispatch in scenic tourist areas, and dispatching and monitoring of vehicles and ships by customs, public security and coastal defense departments. The main functions of the monitoring center are:
· Data tracking capabilities. The real-time location of the moving vehicle is displayed as a list of 。. Such as car number, longitude, speed, heading, time, date, etc.
· Tracking function on the graph. The positioning information of the moving vehicle is compositely displayed on the corresponding electronic ground map. The electronic ground (sea) map can be arbitrarily enlarged, reduced, restored, and switched. There are two receiving modes: normal receiving and random point receiving. It is also possible to provide a selection function for whether or not the vehicle is to be traversed.
· Analog display function. Known target location information can be entered into the computer and displayed. Decision-making command function. The decision command command communicates with the mobile vehicle in a communication manner. Communication mode can be implemented by text, code or voice.
· The main functions of the car part are:
· The function of sending location information. The GPS receiver locates the real-time and sends the positioning information to the monitoring center through the radio.
· Data display function. The real-time position of the own vehicle is displayed on the display unit. Such as longitude, latitude, speed, heading.
· Receive function for scheduling commands. The receiving monitoring center sends a dispatch command command to display or send a voice on the display unit.
· Alarm function. In the event of an emergency, the driver activates the alarm device, and the monitoring center immediately displays information such as the vehicle situation, the location of the accident, and the personnel of the vehicle.
Vehicle GPS positioning is a single point dynamic navigation positioning. Its positioning accuracy is on the order of 100M. In order to improve positioning accuracy, differential GPS technology can be used.
3. Vehicle management system using differential GPS technology
If the general differential GPS technology is adopted, each vehicle should receive the differential correction number, which will make the system too complicated, so the centralized differential technology is often used in practical applications. Working principle: Each car is equipped with a GPS receiver and a communication station. The monitoring center is located at the base station and the coordinates are precisely known. A GPS receiver is placed at the reference point, and devices such as communication stations, computers, electronic maps, and large-screen displays are installed. At work, the GPS receiver on each vehicle sends its location, time and vehicle number to the monitoring center. The monitoring center differentiates the vehicle position from the base station GPS positioning result to obtain a differential correction number, corrects the vehicle position, calculates the precise coordinates, and displays the large screen after the coordinate conversion.
This centralized differential technology simplifies the equipment on the vehicle. The car part only receives GPS signals, regardless of the reception of differential signals. The monitoring center focuses on differential processing, display, recording and storage. Data communication can use the original vehicle communication equipment, as long as the communication conversion interface is added. Since the differential GPS device can provide accurate position, speed, heading and other information in real time, the onboard GPS differential device can also calibrate various sensors on the vehicle (such as a taxi, a speedometer, a magnetic compass, etc.).
4. Application prospects
Cars are the most closely related means of transportation in modern civilized society. According to statistics, only a few developed countries have tens of millions of cars. Therefore, vehicle navigation will be one of the largest potential markets for global satellite positioning system applications in the next 20 years. It is estimated that by the year 2000, one third of the total investment in vehicle navigation worldwide will be used.
In China, there are hundreds of thousands of special vehicles. The relevant departments require that the special monitoring, guidance and command of the special vehicles such as transport overtaking, ambulance, fire truck, patrol car and welcoming car should be realized. At present, there are few vehicles that use the car GPS receiver for autonomous positioning, and a large number of development and application hotspots are on the monitoring and dispatching system. The development direction of vehicle GPS navigation equipment should focus on several aspects such as multi-satellite system, remote monitoring and multi-function display.
The use of multi-satellite systems, such as the GNSS system (which will become an integrated navigation and positioning system after 2000), can ensure the accuracy and reliability of real-time positioning of vehicles due to the large number of satellites during navigation and positioning. For the monitoring system used for dispatching command, the distance between the monitoring center and the vehicle under its jurisdiction is limited to tens of kilometers due to the limited power of the communication station. To increase the monitoring distance, the long-distance communication problem should be solved. For example, the communication relay station is increased, the working distance is extended, and the monitoring range is covered by a broadcast or satellite communication method to cover a larger area. The function of the monitoring system should be multifaceted. For example, voice transmission, visual image transmission, and various commands and conditions of the surroundings of the vehicle are recorded and stored.
It can be said that the application prospect of GPS navigation and positioning in public transportation and transportation systems is very broad. While developing vehicle navigation applications, it will also drive the development of communication technology, information technology, control technology, multimedia technology and computer application technology.
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