moving vehicle, the synchronisation accuracy has to be within a few hundred microseconds,’ explains Philips. ‘Therefore, having the different components in the system electrically connected together at the camera head and not having a PC as an intermediary between the signal from the camera to the strobe, for instance, is a real benefit.’
Ring of steel One of the advantages with designing ANPR systems for European roads is the reflective qualities of the number plates. Adrian Cadd, head of sales and marketing at UK-based manufacturer of ANPR systems, NDI Recognition Systems (NDI-RS), explains that, due to their reflective nature, there is an excellent retro-returned signal from number plates under infrared illumination, irrespective of ambient lighting and weather conditions. Infrared illumination is invisible to the naked eye, meaning drivers are not dazzled by the cameras firing. NDI-RS has installed both the London and Manchester rings of steel – networks of cameras with ANPR capability surrounding both city centres that monitor vehicles entering the cities. The London network has in excess of 350 cameras, while the Manchester system has around 50 cameras. The ANPR results are fed into the local police database and the National ANPR Data Centre (NADC) for analysis. Both networks of cameras use NDI-RS’s C3
cameras providing infrared ANPR capture using SpecBright IR spotlights from ProPhotonix, a producer of LED arrays and other illumination solutions. Number plates are read and cross- matched against a police database. If a vehicle is
flagged, then operators in real time will be alerted to the fact that that vehicle has passed through. ‘That’s the benefit of ANPR,’ states Cadd. ‘It
enables the police and security services to have a real-time monitoring system of all vehicles travelling in and out of city centres at any time and, crucially, it will give them an alarm if a vehicle of interest passes through one of those check points.’ Cadd says the main challenge with setting up
any ANPR system is positioning the cameras in optimum locations for number plate capture. ‘Where the camera is positioned, the height of the camera, and the angle of the camera in relation to the road – the so-called skew and rotation angles – all have to be taken into consideration,’ he says.
‘The main challenge is positioning the cameras in optimum locations’
‘We have to minimise these angles to reduce the amount of image distortion, while, at the same time, using existing roadside furniture, such as lighting columns or gantries. In some locations where it’s difficult to do that, the ANPR software has an inbuilt algorithm that de-skews and de- rotates the number plate. Another challenge Cadd identifies is ensuring the infrared illuminators are powerful enough to get an accurate read over the working distance. ‘Ideally, we want to capture ANPR at distances between 15 and 25m, although distances further away are possible,’ he says.
NDI-RS is governed on the accuracy of its ANPR systems – in the UK, the NAAS guidelines specify that ANPR systems have to be able to read in excess of 93 per cent of number plates accurately on all vehicles that pass fixed cameras. According to Cadd, high quality components like ProPhotonix’s SpecBright spotlights were incorporated into the C3 system so that the cameras achieve an accurate read and meet these guidelines. Lighting manufacturer Gardasoft Vision also
provides high intensity strobe lights designed for ANPR and ITS applications with its VTR range of LED light sources.
Freeflow tolling applications are going to be- come more prevalent in most EU countries by the end of 2013. Image courtesy of Survision
Dangerous goods Survision has also developed systems for identifying vehicles carrying dangerous goods, based on recognition of the labels on the outside of the vehicle. The systems contain the same Sony head as in the tolling application; it’s only the algorithms loaded on the digital signal processor (DSP) module that differ – all the
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