What you need to know when choosing an ANPR system

Many of the ANPR solutions up until recently have been based on closed systems with a specially designed camera and a box that outputs number plates to a screen or ticket. Right now many of the VMS manufacturers have found it easy to incorporate number plate recognition software into their recording platforms and offer it as an add-on.  With Windows PC application based VMS removing the closed nature of the old black box solution, a whole world of new solutions are open to end users to meet a variety of new business requirements.

Here are some guidelines to make the most of this open approach for the development of efficient number plate recognition hardware and software solutions.

  1. Choose an appropriate software package – You may already have a preferred VMS, if so they probably have an ANPR plug-in and it probably works. But ask around for feedback from colleagues and peers before you commit.  Read the trade press for testing information and comparisons.  Consider the manufacturer’s support. How do they plan on assisting you with this particular installation? Do they offer training and how much will it cost? What kind of documentation is available and how detailed is it? Also what is the total cost of installation, maintenance and ownership? Will this be a long term investment?
  1. Understand features and settings issues – Do I need to be a programmer or is there a simple interface to change parameters and settings to improve performance? What does the end user get – can they manage the plates database easily, can they differentiate between lists of wanted and unwanted? Can they control vehicle access rights? Can they match clear video with actual text number plate data and can they use the number plate to find the right piece of footage? And can they do all this without hours of training and endless support calls?
  1. Choose the right hardware – The best option is using a dedicated ANPR camera. However any camera that fulfils the required recognition rate can be suitable.

    The following rules should always apply but, as with software, each manufacturer has their own way of implementing them:

  • Choose camera drivers supported by VMS
  • Strong and focused infrared
  • High contrast, high shutter speed
  • There is really very little need for high definition
  • Compatible encoders if using analogue cameras (no interlacing issues)
  • Trying to use one camera to perform both an overview and recognition to save money is going to cost money in the long run.

When choosing a I/O device always keep in mind the following recommendations:

  • Choose devices that are compatible with the designed network environment
  • Ideally choose devices that are supported by the VMS manufacturer
  • HTTP-interface option recommended to allow applications to integrate translation functionality
  1. Camera installation and settings – A well installed ANPR system can read the plates in different conditions. However if you want to achieve 95-98% recognition rate you have to calculate the position of the camera accurately. For the best position the angle between the camera axis and the direction of the vehicle should be minimal.

anpr-camera-position

The distance between the camera and the plate is also important. If the camera is too far from the plate, the characters may not appear large enough or camera infrared might not be strong enough to illuminate the number plate during night time. If the distance is too short part of the plate could be out of the camera’suyhu8i999999999999999j field of view. The ideal distance should be between 2 – 4 metres.
The camera height should be as low as possible but still over headlight beams to avoid glare. When planning camera heights consider also other factors like sunlight direction and camera infrared reflection from number plate during night time. Typically the preferred mounting height is about 1.25 meters but might change based on environment requirements.

  1. Define what the system is being used for – Once you have captured the image and you have the system performing good recognition, you need to think about what the system is actually being used for. Is it going to send a message to the Police database? Will it open a barrier? Will it trigger an alert at an alarm monitoring centre or will it need to log how long the vehicle stays in the car park? There are many uses for ANPR and this is where a flexible VMS is important.  How can it be used to interact with third party systems?  Can an email be sent?  Is there an integration with alarm monitoring software?  Can it trigger a digital output?  Can the system be integrated with vehicle counting for car park management?  Can the system accept data from other systems such as POS or weigh bridges? Is the system flexible enough that with some consulting support it can be developed to meet a more unusual business requirement?
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