ANPR questions & answers
Answers for the systems around number-plate recognition.
Practical, vendor-neutral guidance for cameras, NVRs, VMS platforms, access control and metadata integrations.
These are general industry answers, not product support. Setting up ANPR Edge? Read the camera connection guide.
15 answer
Why is my Milestone XProtect LPR server CPU usage hitting 100%?
High CPU usage on a Milestone XProtect LPR server is almost always caused by processing H.264 or H.265 compressed video streams. Milestone requires the LPR engine to decode these complex compression formats before analyzing the plates, which quickly overloads the server's processing capacity and causes dropped frames.
Milestone XProtect LPR Administrator Manual
Why does my Hikvision ANPR camera show video on a third-party NVR, but no license plates?
Video feeds and ANPR metadata are transmitted using completely different network protocols. While your third-party NVR can receive the standard video feed via ONVIF Profile S or RTSP, Hikvision transmits its license plate text and vehicle metadata using proprietary ISAPI or ISUP payloads that non-Hikvision NVRs cannot decode.
Hikvision ISAPI Event Notification Integration
Why does my ANPR camera capture plates perfectly during the day but fail completely at night?
Nighttime ANPR failures are overwhelmingly caused by "IR blooming" and slow shutter speeds. The camera's infrared light reflects too intensely off the retro-reflective coating of the license plate, turning it into a solid glowing white rectangle, while slow shutter speeds cause moving vehicles to severely blur in low light.
ANPR Watch: Minimising False Positives
Why is my Avigilon ACC/Unity LPR watch list CSV import failing?
Avigilon Unity and ACC require a very specific CSV formatting structure to successfully import a database of watch list plates. The most common cause of complete import failure is omitting the mandatory "Minimum Confidence" column, which tells the VMS how strict the OCR match must be before triggering a security rule.
Avigilon Unity Video Client User Guide - LPR Watch Lists
Can a Uniview (UNV) NVR perform Smart Plate Search with a third-party ANPR camera?
No. Uniview explicitly locks its advanced metadata analytics, including Plate Comparison and Smart Vehicle Search, to its own Uniview-branded LPR cameras. Third-party cameras can only provide basic, unsearchable video streams to the UNV NVR.
Uniview NVR516-64E Datasheet Specifications
How do I get Hikvision ANPR plate data via the HTTP API?
Many integrators discover that recent Hikvision firmware has deprecated traditional GET polling endpoints for plate data. Instead of polling the camera, you must configure the camera's HTTP Listening Server to actively push multipart XML payloads to a designated TCP server whenever a plate is detected.
Hikvision ISAPI Event Notification Integration
Why did my Dahua ANPR HTTP API stop working after a firmware update?
In recent firmware updates (late 2023 onward), Dahua intentionally deprecated and removed the local unencrypted HTTP/CGI endpoints that developers traditionally used to extract license plate events. This breaks custom third-party integrations that rely on these legacy scripts.
IP Cam Talk: Dahua Firmware Warning
Why does Avigilon LPR Performance Mode disable Face Recognition on AI NVRs?
Activating high-performance LPR heavily taxes the AI NVR's computational resources. To prevent frame dropping and maintain accurate plate reads on fast-moving vehicles, the system redirects all available processing power to the OCR engine, intentionally disabling conflicting analytics like Face Recognition.
Avigilon Unity Video - Setting up License Plate Recognition
Why are Wisenet WAVE LPR bookmarks playing back at the wrong time?
If clicking an LPR event bookmark in the Wisenet WAVE client jumps the video playback to a timestamp completely devoid of a vehicle, you are experiencing a severe clock synchronization mismatch. The VMS server and the edge cameras are operating on different clocks.
Hanwha Vision: Synch issue between playback time and camera time
Why does the Wisenet WAVE AI Plugin freeze or drop streams?
When utilizing the WAVE AI Plugin, adjusting the "AI Tracking Speed" too high exponentially increases the computational burden on the server. Setting the tracking speed to "Very Fast" for vehicles can severely reduce the number of AI streams the server can handle, leading to dropped frames and system freezing.
WAVE: How to Setup the AI Plugin
How do I configure Vaxtor VaxALPR events with Axis cameras?
To send license plate data from a Vaxtor on-edge application to third-party systems or local relays, you must utilize the Axis VAPIX/ONVIF event framework. This bridges the gap between the Vaxtor OCR engine and the Axis OS action rules.
VaxALPR On-Camera Axis Integration Guide
Why is my Nedap ANPR Lumo Wiegand output failing to open the barrier?
Wiegand communication relies heavily on perfect binary parity bit alignment. If a Nedap Lumo camera reads a plate perfectly but the access control panel rejects the credential, the Wiegand output format configured in the camera does not match the expectations of the control panel.
Nedap Wiegand format and Protocol for the Transit Ultimate
Why is the ZKTeco LPR camera relay not opening a boom barrier?
When a ZKTeco camera detects a whitelisted plate but the boom barrier fails to open, the issue often lies in the wiring architecture. If you are integrating via Wiegand to a ZKTeco Security Relay Box (SRB) instead of direct GPIO wiring, you must ensure the camera is outputting an encrypted signal.
ZKTeco Security Relay Box Specifications
How many pixels are required for accurate license plate recognition?
Installers frequently mount wide-angle cameras assuming 4K resolution guarantees readability, but OCR engines require a strict Pixels-Per-Meter (PPM) density. A standard 12-inch (0.5m) wide license plate must occupy an absolute minimum of 100 horizontal pixels across the image sensor to ensure reliable character segmentation.
Plate Recognizer: LPR Camera Resolution Guide
Can ONVIF Profile S send ANPR metadata?
No. There is a universal misunderstanding across the industry that ONVIF Profile S supports metadata. Profile S only standardizes the transmission of RTSP video pixels and simple binary motion alarms. It cannot transmit license plate text or structured XML metadata.
ONVIF Profile M Overview and Specifications
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