What is ANPR and how it works in a car park

ANPR stands for Automatic Number Plate Recognition. Some vendors call it LPR (License Plate Recognition). It is the same technology: a camera captures the vehicle, and an algorithm finds the plate and extracts the characters.

The result is text, for example RO123DEMO, that a parking management system can act on: open the barrier, start a tariff, log a pass.

A typical ANPR gate has four stages, which normally take a second or two:

• Detection: the car enters the camera's field of view or passes over an induction loop or sensor.
• Reading: the camera or server extracts the plate from the image and attaches a confidence score.
• Decision: the software checks whether the plate may use that gate at that time (resident, subscriber, authorised visitor) or enters the paid flow.
• Action and log: the barrier receives the open command and the pass is stored with time, gate, image and decision.

Camera makers usually quote very high read rates, but in practice accuracy comes down to installation. The most common causes of misreads are a steep angle to the plate, the wrong distance, backlight or headlights blinding the camera at night, and dirty or damaged plates.

That is why camera position and approach speed matter as much as the hardware model. A good camera, correct mounting and an area where cars slow down before the barrier give the best results.

• Keep the horizontal and vertical angle to the plate as small as possible.
• Use infrared lighting for night and settings that compensate for backlight.
• Read at a fixed distance, with the car almost stopped.
• Keep a single lane in the camera's view so cars do not overlap.

No ANPR system reads 100% of passes correctly, especially with dirty plates, trailers or unusual foreign formats. A good parking management system has a clear fallback for these cases.

Typical options are manual opening by an operator from a console that shows the gate image, phone-call entry from a registered number and, in paid car parks, issuing a code or ticket. What matters is that every manual action is logged with who did it and why.

For plate-based access you need, at minimum:

• One ANPR camera (or a good IP camera plus recognition software) for each direction of traffic.
• An automatic barrier or motorised gate that can be triggered electrically.
• A control module (relay) that receives the command from the software and opens the barrier.
• Management software that holds the access list, per-gate rules and the log.

ANPR makes sense wherever lost cards and remotes, visitors calling at all hours or the lack of records have become a real cost. In residential complexes it removes the need to hand out devices, in offices it simplifies staff and supplier access, and in paid car parks it enables ticketless entry and automatic exit after payment.

For a detailed comparison of the methods, read the guide on remotes, cards and license plates.