In the construction of intelligent transportation systems, road monitoring systems are an essential construction content. The road monitoring system focuses on the transmission of video images, including video capture, video transmission and video processing. In each construction link, it involves a number of construction demand units, a number of design and organization construction units and a number of related participating units. Combined with the characteristics of large bandwidth, multiple control links and high degree of sharing, the construction process of the system will be an extremely complex task.
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1. Video Surveillance System Overview
The intelligent transportation system integrates advanced information technology, data communication transmission technology, electronic control technology and computer processing technology into the entire transportation management system. The road monitoring system is an important part of the intelligent transportation system, providing the most intuitive reflection of the scene, and is the premise for implementing accurate traffic scheduling. The system deploys monitoring equipment at the front end of key places and monitoring points, and transmits the collected video images to the traffic command center through optical fiber and network dedicated lines. Through the background server and application software system for information storage, processing and release, the traffic command management personnel can make timely and accurate judgments on traffic violations, traffic jams, traffic accidents and other emergencies, and adjust the various traffic systems. Item control parameters and command scheduling strategy. The general road monitoring system architecture is shown in Figure 1:
Figure 1 Road monitoring system architecture
In order to meet the needs of higher applications and improve the intelligence and automation of traffic command, today's road monitoring systems not only provide video images, but also combine with peripheral systems such as GIS (Geographic Information System) and intelligent analysis and decision-making systems. The encoding and compression of video images provides monitoring, invocation and control functions for LAN and even WAN authorized users, enabling traffic command managers to more fully control real-time traffic information.
2. Video surveillance system difficult analysis
As an important part of intelligent transportation, road monitoring system is often designed and constructed with mature technology to ensure system stability and reliability. However, due to the particularity of the system, the front-end video capture equipment for road monitoring is mostly installed outdoors and has a relatively high altitude.
Figure 2 Outdoor surveillance camera lightning protection grounding
As shown in Figure 2, in the traditional construction technology, although the cameras erected on the poles have corresponding lightning protection and grounding protection measures, they are affected by factors such as precipitation weather, lightning, sand, sunshine, etc. The damage rate is generally relatively high. Due to the constraints of the erection and installation environment, the maintenance work of these equipments is often not resolved in time. Therefore, one of the difficulties in the road monitoring system for the protection of the front-end video capture equipment during the design and construction process.
On the other hand, with the technological innovation of informationization and intelligent systems, the application requirements of traffic management departments and personnel for intelligent transportation systems are also increasing. As part of intelligent transportation, the road monitoring system not only carries the most basic road traffic monitoring functions, but also the functional requirements such as automatic violation recording, interval speed measurement, night monitoring, license plate recognition, and event intelligent detection analysis are gradually inclined to the road monitoring system.
Figure 3 License plate recognition system in traffic monitoring
Compared with the traditional digital electronic police and coil vehicle detection, the video monitoring construction process is simple, does not need to destroy the cutting surface, and can provide more clear and effective images, and the evidence is high. However, the monitoring system is still not perfect for the identification technology of vehicles. Especially for the complicated road conditions with large traffic volume and mixed traffic of motor vehicles and non-motor vehicles in China, the daytime detection accuracy of video surveillance systems is generally about 60%. It is 30% to 50%. In the case of a faster speed, the recognition rate of the license plate is not high. This is a technical difficulty of the road monitoring system. For projects with such requirements, hardware devices with higher precision and better performance should be selected, and the background software application platform may be more optimized for pattern recognition algorithms.
In the actual construction process, the construction environment is complex, and electromagnetic interference in the vicinity of the front-end equipment is also a key concern of the project design and supervision personnel. Only considerate and comprehensive, in strict accordance with the relevant specifications design and construction to ensure the stability and clarity of the video signal, to meet system design requirements.
3. Monitoring system supervision process
The supervision work of the road monitoring system can be divided into three parts: supervision in the design phase, supervision in the construction phase and supervision in the acceptance phase according to the project construction stage. The design phase and construction phase are the focus of supervision work. These two parts of supervision work cover the project implementation for most of the time, providing guarantee for project quality control, schedule control and safety management. The supervision work in the acceptance stage is the summary and closing of the project, which ensures the integrity and smooth handover of the project.
1. Supervision points in the design stage
In the design stage of the road monitoring system, the project is based on the needs of the builder and the design of the design unit. Supervisors should respect the design plan without violating relevant regulations. The main duties of the supervisors are to provide supervisory opinions and suggestions based on the contract and bidding requirements, relevant norms, and their own knowledge, to assist in the design of the project. For the road monitoring system, the general supervisors can carry out supervision work for the aspects such as the transmission mode of the system and the distribution of monitoring points, which are difficult to be clearly defined by the constructor.
The choice of the way video images are transmitted depends primarily on system size and system function requirements. In the actual situation in most parts of China, it is better to use a transmission method based on wired transmission and supplemented by wireless transmission. The selected transmission mode must ensure the stability, accuracy and reliability of signal transmission to the greatest extent.
The distribution design of monitoring points is based on factors such as roads and traffic facilities, population distribution and other factors without special requirements. For the distribution of important military and political institutions, key commercial and commercial districts, large and medium-sized urban public transportation hubs, densely populated areas, and the distribution density of monitoring points around high-risk protection units should be appropriately increased. Conversely, for mountainous areas, rural areas, and sparsely populated areas, the distribution of monitoring points should be relatively small at design time.
Equipment selection is one of the important tasks in the construction of road monitoring system in the design stage. Unified equipment selection ensures uniform technical parameters and uniform application effects, laying a good foundation for future system expansion, maintenance management, and upgrading. Equipment selection mainly includes video acquisition, transmission, control, display, storage and so on. All selected products must meet the requirements of the contract and related specifications, and pass relevant tests by the national authorities.
2. Supervision points in the construction phase
(1) Supervision work flow
During the construction and acceptance phase, the supervision work is gradually carried out along with the construction progress of the project. The construction of general road monitoring system includes pre-construction preparation, construction materials and equipment access, front-end video acquisition equipment installation, transmission communication line laying, background application equipment installation, system commissioning detection, system acceptance and other stages. Figure 4 shows the main work content of the supervisors and contractors in each construction phase.
Figure 4 Road monitoring system workflow
(2) Key points of supervision work
This section mainly elaborates on the construction quality supervision work unique to the road monitoring system. It will not go into details for the construction of electronic computer room construction supervision and communication pipeline engineering supervision.
In the supervision work during the construction phase, the supervisors should focus on the supervision of the video capture equipment such as the front-end camera, the equipment installation of the monitoring center, and the electromagnetic compatibility in combination with the actual situation of the road monitoring project. The following describes the specific supervision requirements separately.
Front-end device installation
During the erection of the front-end video capture equipment, the supervisor should focus on the installation of the embedded parts of the pole, the installation of the camera, the installation of the cabinet, and the lightning protection grounding. At the same time, because the front-end equipment is installed outdoors, the safety protection during the construction process should also be given full attention.
Supervisors should require that the camera unit be installed securely and securely. The cable drawn from the camera should have a margin of 1m and must not affect the rotation of the camera. The cable and power cord of the camera should be fixed, and the plug cannot be used to bear the weight of the cable. When erecting a camera near a high-voltage live device, the safety distance should be determined according to the requirements of the live equipment.
During the installation of various types of cabinets (including power boxes, optical end cases), the height of the box can be positioned according to the on-site pole or the height of the pole used. The allowable deviation of the box verticality is 3 mm, and the horizontal direction inclination is allowed to be 3 mm. The installation of the cabinet should be selected in a place with sufficient light, good ventilation and convenient operation and maintenance. When the cabinet is installed in a place with vibration, vibration damping measures should be taken. The outdoor installation box should be waterproof, moisture-proof and dust-proof. The components between the cabinets should be tightly connected and the fasteners for installation should have a rust-proof layer.
Outdoor front-end equipment must be grounded in accordance with the specifications. When the construction interface takes up the road and occupies the land, a conspicuous safety sign should be set up, and a special person should be instructed to walk around the vehicle to avoid danger and corresponding disputes.
Monitoring center equipment installation
The installation of the monitoring station and the video wall of the monitoring center shall be completed after the video cables are laid, the power cables have been introduced into the room, the grounding wires have been laid, and the ground construction in the room is completed, and the painting and renovation works are completed. The construction quality control has the following requirements:
The TV wall should be installed indoors for monitoring, so that the monitor should not face the window, avoid the sun from entering, and should leave proper operation and maintenance space.
Cabinets, console installation and layout are strictly installed to control the layout of the control room. It should be ensured that the horizontal and horizontal are straight, beautiful and firm. After the console is installed, the center equipment such as the recorder, monitor, and matrix is ​​installed, and the focus is on fixing and being beautiful.
After all equipment is installed, the wiring should be marked accurately, neatly and reliably connected. At the same time, the wall and the platform are reliably grounded.
Electromagnetic Compatibility
Since the video image quality of the monitoring system is not only restricted by the performance of the monitored equipment, the main influencing factor is the transmission line problem. Therefore, electromagnetic problems in road monitoring systems are the key to signal transmission.
During the construction process, the supervisors shall require the contractor to lay the lines of the power system cable and the signal transmission system cable separately. The shielding capability, grounding requirements and construction process of the signal cable comply with the relevant standards. The device housing opening used in the system should be as small as possible and the number of openings should be as small as possible. If wireless transmission is used, the indicator parameters included in the wireless transceiver equipment comply with the relevant regulations and standards.
4. Conclusion
With the construction of new cities across the country, the investment in road infrastructure is getting bigger and bigger. Because the road construction period is generally long, its growth rate can not keep up with the rapid growth of vehicles, making traffic conditions worse and worse. This is almost all The common problem of the city. Therefore, establishing a functional traffic monitoring system in the urban traffic management department is an effective solution to improve the current traffic situation. Through the road monitoring system, traffic management can be enhanced, the capacity of existing roads can be improved, and sudden traffic incidents can be handled in coordination to alleviate traffic congestion, thereby improving traffic conditions. It is hoped that the analysis of the difficulties in the supervision of road monitoring system in this paper can help all parties to build an intelligent transportation system and provide a strong guarantee for the construction of urban traffic information.
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