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How to set up License Plate Recognition (ANPR, LPR, NPR, ALPR) in FLOW
How to set up License Plate Recognition (ANPR, LPR, NPR, ALPR) in FLOW

Learn what is possible with FLOW LPR and how it works and how to set up camera for license plate reading.

DataFromSky avatar
Written by DataFromSky
Updated over a week ago

Automated license plate reading (ALPR or also called LPR or ANPR) in FLOW can allow you to identify which vehicles, when, and where violated traffic rules and communicate this information further. This makes it a lot easier to spot some more specific violations like u-turns and identify the specific car to be fined.

Thanks to trajectory data FLOW is uniquely equipped with wrong-way driving detection, illegal lane change, and u-turn detection that are impossible to detect with most systems. If a license plate is detected at any point in the trajectory journey it is assigned to it and its respective object. FLOW is also quite flexible in terms of the angle at which it is able to read the license plate. As you can see in the GIF below the LP is detected even with the license plate being only a few pixels and the LP detection stays on the car even when it is no longer readable!

Inbuilt FLOW LPR is able to read LP once and then remembers it for the whole duration the object is present in the area and you can trace the trajectory of the object before the object was detected as well. You can see an example of this in the GIF above.

License plate filter for white and/or black list

As of FLOW 1.11, there is a special License plate operator that can be used to include/exclude specific License Plates from the dataset and respond adaptively based on the detected License plates. This can for example be used for parking management. For instance, if you have company-managed parking you can add all the license plates of your company vehicles into the exclusion and then be notified when a vehicle with an unfamiliar license plate uses the parking lot. Below you can see how to set up your analytics for such use-case by using a license plate list of allowed vehicles and notifying you of any unauthorized vehicles in your parking lot.

Available for all FLOW devices

TrafficEmbedded and TrafficEnterprise and all other devices except the TrafficCamera have built-in License plate reading (LPR). TrafficCamera needs to have the special FLOW ALPR application installed to be able to read license plates. The currently supported license plates include all of the European countries. Support for more LP formats will be added over time.

How to set up the camera for perfect LP reading

FLOW ALPR video analytics engine is very robust and built on neural networks trained for reading license plates even in poor light conditions and at various angles. Thanks to trajectory design, FLOW needs only one frame where the License Plate is legible and:

  • individual license plate characters must be bigger than 18px

  • all the characters are legible

  • vertical and horizontal angle does not exceed 30 degrees

  • maximum tilt is +/- 15 degrees

FLOW ALPR VA engine is also capable of reading license plates from streams from special cameras designed for license plate reading that significantly reduce exposition time and use IR illumination. For such scenes, however car contour still needs to be well distinguishable.

Read more about LPR in general

Read more about LPR with TrafficSurvey

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