Dedicated Micros ©2008
ANPR
Side Mounting
A mounting to the side of the road makes installation and servicing easier but presents the possibility
of vandalism or accidental damage from approaching vehicles. The camera angle on either the
vertical or horizontal should be no more than approximately 30°, as above this angle the license
plate image will become overly distorted for the ANPR software to recognise.
Note:
It is not advisable to try and capture the vehicle number plate from behind as rear number
plates are more commonly obscured by bicycle racks or tow bars. The only draw back with
this is that motorcycles only have number plates on the rear of the vehicle.
Other Considerations
Tailgating
Tailgating, the act of a vehicle driving close behind another will often cause the camera to miss the
second licence plate image. This is often a problem in locations that suffer from congestion resulting
in the vehicles bunching up. The common solution to which is to install a speed bump.
Network Infrastructure
Remember if the application is an upgrade to an existing site, power and data cabling needs to be
available. These aspects are easily overlooked or forgotten, until the installation is underway.
Software
Recognition accuracy is the most contentious issue with all ANPR systems. Manufactures claims
of 95% + accuracy will mean that at least 1 in 20 vehicle license plate details will be inaccurately
identified. This could lead to chaos at the entrance to a car park with an ANPR controlled barrier
each rush hour. Contingencies for such scenarios must be identified, developed and be made
available for use before the ANPR system becomes operational.
Picture Quality
Most initial teething troubles with ANPR systems are due to the camera not having a close enough
view of the vehicle and its number plate. A good rule of thumb is for the vehicle to take up at least
80% of the screen in its maximum exposure position.
If a second overview camera is being used to provide images of the vehicle and driver this will need
to be tested under night conditions and suitable illumination installed and camera settings (exposure
time, etc) adjusted.
Sun Rise / Sunset
It is also advisable not to align the camera so that it is pointing due East or West. The rising or
setting sun can often overexpose the IR camera receiver and distort the captured number plate
image. This problem is normally only associated with exposed green field sites.
Traffic Speed / Flow
It is important that the fastest traffic speed at your chosen location is known and how this speed
may fluctuate during the day. As vehicle speed increases the camera performance requirements and
ANPR processing engine requirements likewise increase. In access and exit control environments
the speed of an entering or exiting vehicle will be reduced by road restrictions to below 20 mph
(32 kph).
In order to control traffic speed at the entrance to the site it may be advisable to employ direction
control kerbing, speed bumps or traffic flow control plates.
