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The overall design idea of the system
1. The realization process of positioning function
After the vehicle obtains the coding information used to mark the unique road position through the reader installed on the chassis, it passes it to the GIS data processing module on the vehicle side, and GIS combines this coding information with the electronic map information database (part of the GIS module) , Find out the specific geographic location point on the electronic map corresponding to this coded information, and then display it on the electronic map through the display module. In this way, the user can see where he is currently located, realizing the function of positioning the vehicle itself.
2. The realization process of navigation function
The so-called car navigation is to determine the route information of the current location of the vehicle and the destination location. If the vehicle is now at point A and wants to reach point B, enter the information of point B (input the name directly) into the on-board GIS module After the vehicle-mounted GIS module finds the corresponding destination location through the electronic map information database, it corresponds to a certain point on the electronic map display, and at the same time determines one or more feasible routes between the two points and displays them to the user. In this way, the user can decide which route to take to reach the destination based on the destination point B on the electronic map and the current location A point. It can be seen that this system does not need the assistance of external signals or the network, and can directly and independently solve the navigation problem by using the on-board module.
3. The realization process of monitoring and scheduling functions
While completing the positioning function, the reader transmits the acquired position code information and the unique identification information of the vehicle itself to the background monitoring and dispatching center through the on-board communication module using the mobile communication network data transmission method (such as GPRS, etc.). According to the information received, the center can know the exact location of the vehicle now in combination with the center’s GIS system, thus realizing the real-time monitoring function of the vehicle. At the same time, if the dispatch center needs a vehicle to go to a certain destination to perform a certain task (such as fire fighting, hospital ambulance, etc.), the dispatch center transmits the location code information of the destination to a specific vehicle through the communication network, and the vehicle obtains this code information , And correspond to the points on its own electronic map, so as to realize navigation and reach the mission destination at the fastest speed. So this is mainly for special industries (bus, rental, hospital ambulance, fire fighting, etc.) applications need to use functions, because for general private vehicle users, there is no need to tell their location information to other parties, so This is an optional feature (separated by a dashed line in the figure).
Detailed design description of each component of the system
1. Road label
Concept-an electronic label used to uniquely mark a specific physical location, which specifically corresponds to a certain point in the GIS electronic map information database, so as to realize the display and positioning of the physical location.
The data encoding format in the tag-the data storage capacity of the electronic tag can be very large, but it does not need to be so complicated here, because the encoded data only needs to make a certain point of the actual geographical location and a certain point in the electronic map information database. One point to one correspondence is enough, so the encoding format can be very flexible, and the number of bits does not need to be designed too complicated (this can also speed up the data reading speed). Therefore, certain changes can be made on the basis of the encoding format in the current GIS electronic map.
Labeling and maintenance of the road-this is the biggest difficulty of this system, not only the condition of the urban road pavement (soft and hard, pavement material, road deformation), but also the external environment (temperature change, Rain and snow weather conditions), in addition, we must also consider the situation that some vehicles are running irregularly on the label. Considering the pavement conditions, the system label is first considered to be pasted on some ground with ideal pavement conditions (the so-called ideal, mainly refers to the concrete pavement that is relatively solid, and will not change too much with external pressure and temperature, such as overpasses, viaducts and road surfaces. Ideally); the influence of the external environment mainly depends on the improvement of the physical properties of the label (resistance to low temperature, high temperature, resistance to deformation and pressure). At present, the temperature resistance range of existing RFID tag products can reach -40°C to 140°C. In addition, the deformation and pressure resistance can be dealt with through special outer packaging and road painting processes. As for the rolling phenomenon caused by the irregular driving of the vehicle, because the label itself is small and the tire contact area of the vehicle is large, the average pressure cannot cause direct physical damage to the label, and the irregular driving situation It is not mainly common on urban roads.
2. Vehicle terminal
The vehicle-mounted terminal is mainly composed of a reader module, a GIS information processing module, a communication module (optional), and a display module, which cooperate to complete 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 of the electronic tag on the road. The speed of reading the data of the road tag and the speed of the vehicle directly determines the positioning accuracy of the system. Under the same vehicle speed, the faster the reading speed of the reader, the smaller the interval between the tags on the road, and the higher the positioning accuracy. The existing readers generally take milliseconds to read an electronic tag, and the speed of vehicles running on urban roads is generally limited to 60km/h. According to this value, the interval between tags can be calculated approximately When the distance is 5m, fast and accurate reading of tag data can still be ensured. That is to say, the positioning accuracy can correspondingly reach the accuracy within 5m, of course, in addition to the data processing and display speed of the GIS module, it is theoretically feasible to ensure the positioning accuracy of 10m.
GIS information processing module-this part of the module is responsible for processing the coded information of the road label obtained by the reader, and comparing it with the specific location point in the electronic map information database, so as to realize the relationship between 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 realize the query function, that is, the input destination is converted into the information of a specific corresponding point on the electronic map, so as to provide 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 positioning and navigation data processing are all done by it. For specific implementation, the existing GIS vehicle-mounted module can be used. Just make the necessary changes.
Communication module-mainly responsible for transmitting the coded information of the road label read by the vehicle reader to the background control and dispatch center, or transmitting the control and destination information of the background center to the vehicle terminal, so as to realize the center’s monitoring of the vehicle And scheduling. Because the system can complete positioning and navigation functions independently without external network support, this part of the module itself is optional. Mainly for some special industry applications, such as public transportation system, fire fighting, hospital ambulance, traffic accident handling system, etc., in these industries, it is required to grasp the accurate position information of the vehicles in the system in real time in order to make the most effective response in an emergency. Quick response. As far as the current network situation is concerned, you can rely on the GPRS network, because on the one hand, the data transmission rate of the GPRS network is relatively high, on the other hand, it can achieve the characteristics of continuous online and traffic accounting, which is suitable for the transmission of sudden data volume. .
Display module-the information data processed by GIS is displayed on the electronic map completely, but it is by no means just a simple display, because when independent navigation is to be completed, the relevant information of the destination needs to be input, and the current popular ones can be used at this time. The touch screen display terminal integrates the operation and the display interface, thereby reducing the operating complexity of the system.
Specific analysis of the realization of the system scheme
The system must consider the following issues in the specific project implementation stage:
1. The pros and cons of road conditions. At present, the main urban roads are still on the asphalt pavement era. Such pavements will pose a fatal threat to the placement of labels, because under high temperatures, such pavements will be greatly deformed and directly Affect the position and stability of the label, and even directly cause the label to be lost or shifted;
2. Label rolling caused by vehicles violating traffic rules can be said to be a problem that must be considered, but it can be avoided and minimized in many ways. Among them, road labels are basically placed in the center of each traffic lane. In most cases, the vehicle will not be rolled; secondly, the label layout process can be improved to increase the force area of the label, that is, a layer of high-hardness waterproof hard material is packaged outside the label (there are many labels in the market. Already have a certain penetration ability, so that it will not cause too much impact on the label reading range), and at the same time through the special road flour brushing process, the force limit of the label can be greatly increased;
3. The impact of environmental conditions. Because the label is located on the road, it will inevitably be affected by rain and snow. In order to reduce the impact of changes in external conditions, the label is required to have strong corrosion resistance, high temperature resistance, and Low temperature characteristics, which are all direct challenges to the labeling process, the current labels have appeared in the temperature range of -40 ℃ ~ 140 ℃ products;
4. The impact of cost, the price of the label has now been within the range of a few cents to tens of cents, but the price of the vehicle terminal will bring greater problems, but according to the current GPS vehicle terminal, In fact, the reader module will not cause too many problems; in addition, in the process of label use, for the label damage caused by some special accidental reasons, it must be updated in time, although the cost is not too much. But the same should also be considered.
System application assumptions:
Based on the actual problems that must be considered in the implementation of the above project, the following assumptions are made on the main fields and occasions of the early application of this system:
1. Due to the structure of urban road conditions, the physical characteristics of labels, and the irregular driving of some drivers, it is too early to directly lay and promote this system on a large scale, taking into account the current road conditions in most cities (such as Beijing) The surrounding environment is not all high-rise dense areas, so GPS can be used, there is no need to be in place at one time;
2. System application positioning: as a useful supplement to the existing GPS and other mature urban road traffic positioning systems, that is, on most roads where GPS can be positioned, GPS positioning is used, in some special areas, Such as high-rise areas, overpasses, viaducts, large underground parking lots and other areas, use this RFID system to achieve positioning, that is, in these areas, a small-scale road label is laid; this requires a certain transformation of the on-board terminal, and the GPS The terminal and the reader are combined and integrated to achieve the goal of “no blind spots” in urban road positioning.
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