Vehicle license plate recognition (VLPR) is a technology that can detect vehicles on the monitored road and automatically extract vehicle license plate information (including Chinese characters, English letters, Arabic numerals and license plate color) for processing. License plate recognition is an important part of modern intelligent transportation system, which is widely used. Based on digital image processing, pattern recognition, computer vision and other technologies, it analyzes the vehicle image or video sequence taken by the camera, and obtains the unique license plate number of each vehicle, so as to complete the recognition process.Through some follow-up processing means, the functions of parking lot charge management, traffic flow control index measurement, vehicle positioning, automobile anti-theft, expressway overspeed automatic supervision, red light running electronic police, highway toll station and so on can be realized. It has practical significance for maintaining traffic safety and urban public security, preventing traffic congestion and realizing traffic automation management.The vehicle license plate number is the only "identity" identification of the vehicle. The automatic license plate recognition technology can realize the automatic registration and verification of the vehicle "identity" without any change. This technology has been applied to various occasions, such as highway toll collection, parking management, weighing system, traffic guidance, traffic law enforcement, highway inspection, vehicle scheduling, vehicle detection and so on.

Installation process and precautions of license plate recognition systemA complete set of license plate recognition system includes license plate recognition integrated machine, parking lot toll display screen, intelligent gate, license plate recognition software, etc. Whether the installation of these equipment is standard or not greatly affects the working performance of the whole license plate recognition system.Before the installation of license plate recognition equipment, it is necessary to conduct a detailed survey of the project site, understand customer needs and formulate a perfect construction process. What factors should be emphasized in the survey site and installation process?

1. Installation of main equipment for license plate recognition1) First, determine the installation position of the integrated license plate recognition machine, which will directly affect the license plate recognition effect. It needs to be determined according to the site environment and conditions of each entrance and exit. Generally, one camera is installed in one lane. If the direction is not fixed when the vehicle drives into the lane, the recognition will be affected when the angle is too large, so it is necessary to consider installing an auxiliary camera, To ensure that the front of the vehicle can be identified no matter which side it is biased.

2) Secondly, if capture recognition is used, the installation position of the camera and coil shall be determined: the best distance between the camera and the side of the coil in the direction of vehicle coming is 4-4.5m. The position of the coil shall ensure that when the vehicle triggers the vehicle detector, the direction of the vehicle head shall be biased to the side of the camera as far as possible, so that the camera can take clear and complete pictures. If it is a single channel (the entrance and exit are in the same lane), a two-way vehicle detector needs to be used.

If the video recognition mode is used, the ground induction coil and vehicle detector do not need to be installed.3) Then determine the position of the gate and the anti smashing coil: the gate is generally installed on the same side of the camera and behind the camera (installed 30cm away from the camera pole to ensure that the gate can be opened easily). The position of the anti smashing coil is in the middle directly below the road brake rod. It is necessary to ensure that no part of the vehicle body is below the road brake rod when the front of the vehicle triggers the coil and when the rear of the vehicle leaves the coil.4) The camera and the gate shall be installed on a solid ground. If the ground is brick or asphalt, consider pouring cement piers on the broken pavement to increase stability. Before the installation of the above equipment, the wiring mode of the line shall be determined, and the threading pipe shall be reserved in advance according to the installation position of the equipment. In order to ensure that the recognition effect will not be affected by the vehicle speed, it is recommended to install a deceleration belt to control the vehicle speed.

2. License plate recognition accessory equipment1) Configure computer and server: the computer is generally placed in the exit sentry box or duty room for charging.The server can be placed in the customer's office or sentry box according to the customer's needs. If it is placed in the office, the optical fiber needs to be laid from the sentry box to the server. During site survey, the distance from the optical fiber to the nearest sentry box shall be estimated and allowance shall be made. If the customer does not need to set up the server separately, he will use the sentry box machine as the server and install the database and FTP service.

2) Switches are selected according to the number of devices that need to be networked. Generally, Gigabit 8-port or 5-port switches are selected. The switch should be placed in the guard box or distribution box nearby.3) Fabrication of safety island and sentry box: safety island shall be set according to the needs and site conditions. The safety island is generally poured with concrete. The size of the safety island shall ensure that there is enough installation space for equipment such as sentry box or road gate, and will not affect the passing of vehicles. The threading pipe shall be embedded during the pouring of the safety island. After the safety island is completed, it can be painted to increase the eye-catching effect.The sentry box is generally installed at the exit of the parking lot to facilitate charging. The size is determined according to the size of the safety island or installation location, but it must be ensured that there is enough space in the sentry box to accommodate computers and other equipment and the work of toll collectors.

4) The distribution box can be installed on the safety island or placed in the sentry box and duty room. If it is placed outdoors, it shall be rainproof and grounded.3. License plate recognition construction materials1) The power supply bus of the equipment shall use cables not lower than rvv3 * 1.5, and the integrated box, integrated machine and gateway shall be grounded. The air switch for bus power supply shall be selected according to the total power of all equipment to prevent overload tripping.

2) When transmitting network data, use category 6 network cable. When the transmission distance is greater than 100m, optical fibers need to be laid. Generally, single-mode optical fibers are used. At least 2 cores shall be reserved for standby at each optical fiber access point on site. The total number of cores shall be determined according to the access points and the number of fusion cores at each access point. When transmitting 485 signals, shielded cables shall be used. When threading, strong and weak current lines must be separated.3) The optical fiber transceiver can be Gigabit single-mode dual fiber type, and each pair of transceivers uses 2-core optical fibers. The specific model and quantity can be determined according to the needs of customers or projects.4) During outdoor wiring, the line shall be protected and fixed through JDG galvanized iron pipe, the buried line shall be laid through PVC pipe, and the indoor wiring shall also be protected and fixed through PVC pipe.