LPR Events

Overview

LPR events are generated when a Viewtron camera detects a license plate. The event includes the plate number and, depending on the source (IPC or NVR), additional vehicle attributes.

Two classes handle LPR events:

• LPR — IPC v1.x format (direct from camera)
• VehicleLPR — NVR v2.0 format (via NVR, richer data)

Both have category == "lpr".

Common Properties

Available on both IPC and NVR LPR events:

Method	Returns	Description
get_plate_number()	str	Detected plate text (e.g., "ABC1234")
get_plate_group()	str	Plate list/group name (see IPC vs NVR below)

Plus all common properties from ViewtronEvent (timestamp, camera name, images, etc.):

Method	Returns	Description
get_ip_cam()	str	Camera device name
get_alarm_type()	str	Raw alarm type code ("VEHICE" for IPC, "vehicle" for NVR)
get_alarm_description()	str	"License Plate Detection"
get_time_stamp_formatted()	str	Timestamp like "2026-04-09 15:30:45"
get_time_stamp()	str	Unix timestamp string (for filenames)
source_image_exists()	bool	True if an overview/scene image is available
target_image_exists()	bool	True if a cropped plate image is available
get_source_image_bytes()	bytes or None	Overview image as JPEG bytes
get_target_image_bytes()	bytes or None	Cropped plate image as JPEG bytes

IPC vs NVR Comparison

Feature	IPC (LPR class)	NVR (VehicleLPR class)
Plate number	Yes	Yes
Plate group	Fixed: "whiteList", "blackList", "temporaryList"	User-defined group names from NVR database
Plate color	No	Yes
Vehicle type	No	Yes (sedan, SUV, truck, etc.)
Vehicle color	No	Yes
Vehicle brand	No	Yes (Toyota, Ford, etc.)
Vehicle model	No	Yes
Car owner	No	Yes (from NVR database)
Channel ID	No	Yes

NVR Vehicle Attributes

These methods are only available on VehicleLPR (NVR v2.0) events:

Method	Returns	Example
get_plate_number()	str	"ABC1234"
get_plate_color()	str	"blue", "yellow", "white"
get_plate_group()	str	User-defined group name
get_car_type()	str	"sedan", "SUV", "truck"
get_car_color()	str	"white", "black", "red"
get_car_brand()	str	"Toyota", "Ford", "Honda"
get_car_model()	str	Model name
get_car_owner()	str	Owner name from NVR plate database

All vehicle attribute methods return an empty string if the value is not detected or not available.

Code Examples

Basic Plate Logging

def handle_event(event, client_ip):
    if event.category == "lpr":
        plate = event.get_plate_number()
        group = event.get_plate_group()
        print(f"Plate: {plate} | Group: {group} | Camera: {event.get_ip_cam()}")

Full Vehicle Details (NVR)

from viewtron.events import VehicleLPR

def handle_event(event, client_ip):
    if event.category == "lpr":
        print(f"Plate: {event.get_plate_number()}")

        # NVR provides vehicle attributes
        if isinstance(event, VehicleLPR):
            print(f"  Vehicle: {event.get_car_color()} {event.get_car_brand()} {event.get_car_type()}")
            print(f"  Owner: {event.get_car_owner()}")
            print(f"  Plate color: {event.get_plate_color()}")

Saving Plate Images

def handle_event(event, client_ip):
    if event.category == "lpr":
        plate = event.get_plate_number()

        # Save the overview image
        if event.source_image_exists():
            with open(f"{plate}_overview.jpg", "wb") as f:
                f.write(event.get_source_image_bytes())

        # Save the cropped plate image
        if event.target_image_exists():
            with open(f"{plate}_plate.jpg", "wb") as f:
                f.write(event.get_target_image_bytes())

IPC Plate Groups

IPC cameras use three fixed plate groups:

• "whiteList" — Allow list
• "blackList" — Block list
• "temporaryList" — Temporary/visitor list

These are hardcoded in the camera firmware. The group is determined by which list the plate was added to via the camera's web interface or the ViewtronCamera API.

If the plate is not in the camera's database, get_plate_group() returns an empty string.

NVR Plate Groups

NVR plate groups are user-defined — you create custom group names in the NVR interface (e.g., "Residents", "Staff", "Visitors"). The get_plate_group() method returns whatever group name was assigned in the NVR database.

If the plate is not in the NVR database, get_plate_group() returns an empty string.

Related Pages

• ViewtronEvent — common properties and methods
• Images — working with plate and overview images
• ViewtronCamera — managing the plate database (add, delete, modify plates)
• API Reference: License Plate Recognition — raw XML endpoint documentation