The overall design idea of ​​the system 1, the realization process of the positioning function
After the vehicle obtains the code information used to mark the unique road position through the reader installed on the chassis, it passes it to the vehicle-side GIS data processing module. GIS uses this coded information in combination with the electronic map information database (part of the GIS module). Find out the specific geographic location on the electronic map corresponding to this coding information, and then display it on the electronic map through the display module. In this way, users can see their current geographical location and realize the vehicle's own positioning function.
2, the navigation function to achieve the process
The so-called vehicle navigation is to determine the line information of a vehicle's current location and destination location. If the vehicle is currently at point A and wants to reach point B, the information at point B (enter the name directly) can be entered into the on-board GIS module. After the on-board GIS module finds the destination location through the electronic map information database, it corresponds to a certain point on the electronic map display, and at the same time, one or more feasible routes are determined between the two points and displayed to the user. In this way, the user can decide which route to use to reach the destination according to the destination B point on the electronic map and the location A at the present location. It can be seen that the system does not need the assistance of external signals or the network, and it can use the on-board module to solve navigation problems directly and independently.
3, monitoring and scheduling functions to achieve the process
At the same time when completing the positioning function, the reader passes the acquired position encoding information and the vehicle's own unique identifier information to the back-end monitoring and dispatching center through the on-board communication module and uses the data transmission method (such as GPRS) of the mobile communication network. Based on the information received, the center combined with the center's GIS system can know the exact location of the vehicle now, thus realizing the real-time monitoring function of the vehicle. At the same time, if the dispatch center needs the vehicle to go to a certain destination to perform certain tasks (such as fire fighting, hospital rescue, etc.), the dispatch center transmits the location code information of the destination to a specific vehicle through the communication network, and the vehicle gets this coded information. , and correspond with the points on their own electronic maps, so as to achieve navigation, the fastest to reach the mission destination. So this is mainly for the special industries (bus, rental, hospital rescue, fire, etc.) applications need to use the function, because for the average private vehicle users, there is no need to tell their own location information to other parties, so This is an optional feature (dotted lines in the figure).
Detailed design description of various components of the system 1. Road labeling
Concept - an electronic tag used to uniquely identify a specific physical location, which corresponds to a point in the GIS electronic map information database, so that the physical location can be displayed and located.
The data encoding format in the tag--the data storage capacity of the electronic tag can reach a great extent, but here it does not need to be complicated, because the coded data can only make a certain point of actual geographical location and a certain point in the electronic map information database. Correspond to it one by one, so the encoding format can be very flexible, the number of digits does not need to design too complex (this also can speed up the speed of data reading). Therefore, some changes can be made based on the encoding format in the current GIS electronic map.
Road paste and maintenance of labels - this is the biggest difficulty of this system, not only to consider the situation of the road surface of the city (soft and hard, pavement material, deformation of the road surface), but also consider the external environment (temperature changes, Rain and snow weather conditions, in addition to the fact that some vehicles run irregularly on the labels. Considering the situation of the road surface, the system label first considers the ground that is ideally grounded on some road conditions (the so-called ideal, mainly refers to concrete roads and other relatively solid, will not change too much with external pressure and temperature, such as overpasses, viaducts and roads It is more ideal.) The impact on the external environmental conditions depends mainly on the improvement of the physical characteristics of the label (low temperature, high temperature resistance, deformation resistance and pressure and other qualities). Currently, the temperature range of RFID tag products can reach -40°C to 140°C. In addition, the anti-deformation and pressure can be handled through special packaging and road painting processes. As for the rolling phenomenon caused by irregular driving of vehicles, because the label itself is small in size and the tire contact area of ​​the vehicle is large, the average pressure does not cause direct physical damage to the label, and irregular driving conditions are Urban roads are not primarily common.
2. Vehicle terminal
The vehicle terminal is mainly composed of a reader module, a GIS information processing module, a communication module (optional), and a display module. Together, the vehicle terminal completes the processing and display of the entire positioning information.
Reader Module - This part of the module is responsible for accurately and quickly obtaining the position information in the electronic tag on the road. The data reading speed of the road tag and the speed of the vehicle directly determine the positioning accuracy of the system. At the same speed, the faster the reading speed of the reader, the smaller the distance between the tags on the road, and the higher the positioning accuracy. At present, readers generally can read an electronic tag in milliseconds. However, the speed of vehicles running on urban roads is generally limited to 60 km/h. According to such figures, the interval between tags can be calculated. At a distance of 5m, the tag data can still be read quickly and accurately. In other words, the accuracy of positioning can also be correspondingly within 5m of the accuracy, of course, in addition to the data processing and display speed of the GIS module, so to ensure that the positioning accuracy of 10m is theoretically feasible.
GIS information processing module - this part of the module is responsible for processing the coding information of the road label obtained by the reader, and is compared with the specific location point in the electronic map information base so as to realize the physical location and the display point on the electronic map. correspond. At the same time, in the navigation application, this part of the module must also be able to implement the query function, that is, to convert the input destination into a specific corresponding point on the electronic map, thereby providing the vehicle navigation route. In a sense, the design of this part of the module is the core and difficult point of the entire system, because all the positioning and navigation data are processed by it. When it is realized, it can use the existing GIS onboard modules. Make some necessary changes.
Communication module - mainly responsible for transmitting the coded information of the road tags read by the vehicle reader to the background control and dispatching center, or transferring the control and destination information of the background center to the onboard terminal to realize the monitoring of the vehicle And scheduling. Because the system can completely complete functions such as positioning and navigation without external network support, this part of the module itself is optional. Mainly for some special industrial applications, such as public transport systems, fire protection, hospital ambulances, traffic accident handling systems, etc., in these industries, it is required to know the exact position information of the vehicles in the system in real time so as to make the most effective in the event of an emergency and Fast response. As far as the current network situation is concerned, the GPRS network can be used. Because the GPRS network has a relatively high data transmission rate, on the other hand, it can achieve continuous on-line, flow-charging features that are suitable for bursty data transmission needs. .
Display module - that is to say, the information data after GIS processing is completely displayed on the electronic map, but it is not just a simple display, because when you want to complete the independent navigation, you need to input the relevant information of the destination, at this time you can use the current popular The touch screen display terminal integrates the operation and display interfaces, thereby reducing the operating complexity of the system.
Specific analysis of system solutions
This system must consider the following issues during the implementation phase of a specific project:
1. The pros and cons of road conditions. At present, the main urban roads still remain in the era of asphalt pavement. Such pavements pose a fatal threat to the layout of the labels, because at high temperatures, such roads undergo large deformation and direct Influencing the position and stability of the label, even directly causing the label to be lost or displaced;
2. The label rolling caused by violation of traffic regulations by vehicles is a problem that must be considered, but it can be avoided and minimized through a variety of ways. The road labels are basically arranged in the center of each lane of the road. In most cases, the passing of vehicles will not form a roller compaction; secondly, the process of label deployment can be improved and the force area of ​​the label can be increased. That is, a layer of hard and rigid waterproof material is packaged outside the label (a lot of labels currently on the market Already have a certain penetration ability, this will not cause too much influence on the reading range of the label), while at the same time through a special road painting process, can greatly increase the force limit of the label;
3. The impact of environmental conditions, because the label is located on the road surface, will inevitably encounter the impact of rain, snow, in order to reduce the impact of changes in external conditions, the label requires a strong corrosion resistance, high temperature, Low-temperature characteristics, this is a direct challenge to the labeling process, the current label has appeared in the temperature range of -40 °C ~ 140 °C;
4, the impact of the cost, the price of the label has now reached a few cents to several tens of cents within the range, but the price of the car terminal will bring greater problems, but according to the current GPS vehicle terminal to transform, add On the reader module, in fact, it will not bring too many problems; In addition, during the use of the label, for the label damage caused by some special accidents, but also to carry out timely updates, although the cost is not a lot, But it should also be considered.
System application ideas:
Based on the practical issues that must be considered in the above project implementation, the following areas are considered for the main areas and applications of the system's early application:
1. It is too early to lay and promote this system directly in large areas because of the road structure of urban roads, the physical characteristics of the labels, and the irregular driving of some drivers. At the same time, the road conditions of most cities (such as Beijing) are taken into account. The surrounding environment is not all high-rise areas, so you can use GPS, there is no need to be in place;
2. Positioning of system applications: As a useful supplement to existing GPS and other urban road traffic positioning systems that have been maturely applied, that is, GPS can be positioned on most road surfaces, and GPS positioning is used in some special areas. Such areas as high-rise buildings, overpasses, viaducts, and large underground parking lots use this RFID system to achieve positioning, that is, to carry out the construction of small-scale road labels in these areas; this requires certain modifications to the on-board terminals and the GPS The terminal and the reader are integrated together so as to achieve the goal of “no blind spots†for urban road positioning.
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