Automatic number plate recognition
Automatic number plate recognition (ANPR), also known as Automatic Vehicle Identification (AVI), can be implemented using existing multi-purpose CCTV surveillance cameras or dedicated ANPR cameras. These systems use optical character recognition (OCR) software to isolate and identify vehicle registration details. This technology is typically utilised for automatic toll collection, or to detect speeding violations, but can also be used to monitor vehicle movement and for access control.
ANPR systems have been under development since the mid 1970s and have become increasingly reliable and cost effective. A typical ANPR system includes hardware and software components including roadside camera systems, control centre computer systems, software Applications to manage captured data, and a central database of vehicle registration details. There are two different approaches to data processing:
- Images are captured by camera equipment and sent directly to the control centre with time, date and location information without any pre-processing. The central computer system utilises OCR software which uses a set of algorithms to isolate vehicle registration details, and then compares this information with a database of known vehicle registration numbers to display driver and vehicle information.
- Images are captured by the camera equipment and processed immediately at the camera location by an embedded OCR processing unit on the camera. The isolated registration number is then transmitted to the control centre along with time, date and location data where it is compared with a database to provide driver and vehicle information.
In the source data processing method, the OCR process takes approximately a quarter of a second with modern equipment and transmission can be achieved wirelessly with different radio transmission systems depending on the type and quantity of data to be sent. Additionally, where multi-purpose camera systems are used, vehicle speed and trajectory information can also accompany registration data. Constant development of ANPR technologies has led to smaller processing computers with greater performance at a lower cost, and this has also allowed for the mobile application of ANPR equipment. While older systems may have had significant reliability issues, modern systems can accurately identify registration details of fast moving vehicles at very fast processing speeds. The introduction of infrared cameras for ANPR purposes has also further improved this technology, improving efficiency and all round usability.
- Operations management in terms of driving standards compliance.
- Traffic management in terms of access control, congestion detection and detection of unauthorised use of dedicated public transport lanes.
Benefits and cautions
In relation to data transmission from camera to control centre, there are Benefits and cautions for each method. Source processing allows for smaller quantities of data to be transmitted which require less bandwidth for improved transfer speed and reliability. However, for this method there is a requirement for OCR processing equipment at each location which may be too costly.
Weather conditions, lighting, dirt and obstructions by other vehicles, tow-bars or other vehicle parts, can prevent equipment from accurately reading registration details. As such the positioning of the camera is of the utmost importance. In addition to this, where there are no set regulations or standards in relation to registration number font style, size, spacing or colour, camera systems need to be more complex to recognise information, and this can increase processing speed and technology cost.
Relevant case studies
Not observed in the Case Studies
Used extensively in tolling and parking applications