The Global Positioning System (GPS) is a global, versatile (land, ocean, aerospace, and all-weather) navigation and positioning, timing, and speed measurement developed by the US military in the early 1970s on the "Mid Meridian Satellite Navigation and Positioning" technology. The system consists of three major subsystems: space satellite system, ground monitoring system and user receiving system. It has been widely used in many fields such as military and civilian. In developed countries, GPS technology has begun to be used in transportation and road engineering. At present, China's application in this area is still in its infancy.
The application of GPS in road engineering In the road engineering, GPS is mainly used to establish various road engineering control networks and to measure the external control points of aerial surveys. The rapid development of high-grade highways puts higher requirements on survey technology. Because of the long length of the line and the few known points, it is difficult to meet the requirements of high precision by conventional measurement methods. At present, China has gradually adopted GPS technology to establish a high-precision control network for the first-level line. For example, the Shanghai section of Shanghai-Nanjing and Shanghai-Hangzhou Expressway has established a first-level control network using GPS, and then wired the wire by conventional methods. Practice has proved that the point error within a few tens of kilometers is only about 2cm, which is difficult to achieve with conventional methods, and greatly advances the construction period. The Zhejiang Provincial Bureau of Surveying and Mapping used the fast static positioning function of the Wild 200 GPS receiver to measure all the initial conductors of the line, and established hundreds of kilometers of highway control network quickly and accurately, and achieved good results.
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GPS technology is also used in the control measurement of extra large bridges. Since it does not need to be viewed, it can form a strong mesh shape, improve the accuracy of the point, and is also very effective for detecting the fulcrum of the conventional measurement. For example, in the construction of the Jiangyin Yangtze River Bridge, a high-precision corner network was first established by conventional methods, and then the network was detected by GPS. The GPS detection network achieved millimeter-level accuracy, which is in good agreement with the conventional precision network. GPS technology also has broad application prospects in tunnel measurement. Its measurement does not need to be viewed, which reduces the intermediate links of conventional methods. Therefore, it has high speed and high precision, and has obvious economic and social benefits.
Differential dynamic GPS is mainly used in road surveying for data acquisition of digital ground models, encryption of control points, mid-line stakeout, longitudinal section measurement, and airborne GPS aerial survey without external control points. In June 1994, the KART real-time phase differential satellite positioning system was tested at Tongji University, achieving an accuracy of better than 2 cm in a range of 1 km. Therefore, it can be used for encryption of the line control network. GPS measurements contain three-dimensional information that can be used for data acquisition, midline stakeout, and profile measurement of digital ground models. At the same time as the center line plane is staked out, the profile can be obtained. In the center line stakeout, the data of the base station needs to be transmitted from the data link to the mobile station in real time, thereby providing the real-time position of the mobile station. Since the GPS instrument does not indicate direction like the theodolite, it needs to be combined with the CAD system so that the difference between the current position and the design coordinates can be seen on the computer screen. The airborne dynamic differential GPS is applied to aerial survey. It has achieved success in Germany and Canada. The three-dimensional coordinates of each camera center are measured by carrier phase difference, and the external control point measurement is no longer needed, and good results are obtained.
Application of GPS in Car Navigation and Traffic Management
3D navigation is the primary function of GPS, and aircraft, ships, ground vehicles, and pedestrians can use GPS navigation receivers for navigation. Car navigation system is a new technology developed on the basis of GPS. It consists of GPS navigation, autonomous navigation, microprocessor, vehicle speed sensor, gyro sensor, CD-ROM drive, LCD display.
GPS navigation is to receive GPS satellite signals (three or more) by the GPS receiver, and obtain the latitude and longitude coordinates, speed, time and other information of the point. In order to improve the accuracy of car navigation positioning, differential GPS technology is usually adopted. When the car travels to underground tunnels, high-rise buildings, highways, etc. to capture GPS satellite signals, the system can automatically import the autonomous navigation system. At this time, the speed of the car is detected by the vehicle speed sensor, and the micro-processing unit is used. Data processing, directly calculating the distance from the speed and time, the gyro sensor directly detects the direction of advancement, and the gyroscope can automatically store various data, even if the tire is temporarily stopped, the system can be reset.
The position coordinates and the forward direction of the car measured by GPS satellite navigation and autonomous navigation have certain errors with the actual route trajectory. In order to correct the error between the two and make it consistent with the route on the map, a map is needed. Matching technology, plus a map matching circuit, real-time correlation matching between the route of the car and the road on the electronic map, and automatic correction, at this time, the map matching circuit is quickly processed by the finishing process of the micro processing unit to obtain the car The correct location on the electronic map to indicate the correct route. The CD-ROM is used to store information such as road data, and the LCD display is used to display information related to navigation.
The combination of GPS navigation systems with electronic maps, radio communication networks, and computer vehicle management information systems enables many functions such as vehicle tracking and traffic management, such as:
1. Vehicle tracking Using GPS and electronic maps, you can display the actual position of the vehicle in real time, and zoom in, zoom out, restore, and change the map at will; you can move with the target to keep the target on the screen; you can also realize multi-window and multi-vehicle Multi-screen simultaneous tracking, this function can be used to track and transport important vehicles and goods.
2. Providing travel route planning and navigation planning Travel routes are an important auxiliary function of car navigation systems, including:
Automatic route planning The driver determines the starting point and the ending point. The computer software automatically designs the optimal driving route according to the requirements, including the fastest route, the simplest route, and the route with the fewest number of highway sections.
· Manual line design The line library is automatically created by the driver according to his destination design start point, end point and way point. After the route is planned, the display can display the design route on the electronic map, and simultaneously display the running path and operation method of the car.
3. Information inquiry provides users with main objects, such as tourist attractions, hotels, hospitals and other databases, users can query on the electronic map as needed. The query data can be displayed in the form of text, language and images, and its location is displayed on the electronic map. At the same time, the monitoring center can use the monitoring console to query the location of any target in the area, and the vehicle information will be displayed in digital form on the electronic map of the control center.
4. The traffic command and command center can monitor the running status of the vehicles in the area and make reasonable dispatch of the monitored vehicles. The command center can also talk to the tracked target at any time to implement management.
5. Emergency Assistance The GPS positioning and monitoring management system can provide emergency assistance to vehicles in danger or accidents. The electronic map of the monitoring station can display the help information and alarm targets, plan the optimal assistance plan, and alert the on-duty personnel to the emergency treatment with alarm sound and light.
The research and application of GPS technology in car navigation and traffic management engineering has just started in China, and foreign research in this area has already begun and has achieved certain results. The University of Calgary in Canada has designed a dynamic positioning system that includes a strapdown inertial system, two GPS receivers, and a microcomputer to measure the linear parameters of existing roads and serve the road management system. The United States has developed a road traffic management system for urban use. The system uses GPS and GIS to build a road database containing various current data such as the exact location of the road, road conditions, and facilities along the way. The system was in 1995. It officially operated in the year and played an important role in urban road traffic management.
In recent years, various systems for vehicle induction have been developed abroad, in which real-time determination of vehicle position mainly relies on an inertial measurement system and a wheel sensor. With the development of technology, GPS has a tendency to replace the first two methods. GPS positioning for urban vehicle induction is generally to set up a base station in the city. The vehicle GPS receives the information transmitted by the base station in real time. After differential processing, the real-time position can be calculated, and the current location and the target to be reached are on the road. Optimized calculations in the network can display the optimal route to the target on the road electronic map, serving the public security, fire fighting, emergency repair, first aid and other vehicles.
GPS is one of the most pioneering high-tech developments developed in recent years, and it will inevitably become more and more widely used in many fields. It is believed that with the development of China's economy and the rapid construction of high-grade highways and the application of GPS technology, its application in road engineering and transportation will be more extensive and deeper, and will play a greater role.
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