License Plate and MMC Recognition (Platerecognizer)

Recognize license plate numbers and make/model/color using Platerecognizer's Snapshot API for the license plates detected using the License Plate model.

Overview

This node uses Platerecognizer's Snapshot API to read license plates from vehicles that are detected using the Vehicle & License Plate models.

This node requires AI Model Node (Vehicle Detection model) -> Model Inference Node (License Plate model) -> Track Objects Node prior to it in order to function properly using the "LPR & Make/Model/Color" recognition mode.

Inputs & Outputs

  • Inputs : 1, Media Format : Raw Video
  • Outputs : 1, Media Format: Raw Video
  • Output Metadata : None

Properties

Property

Value

pr_api_key

Your Platerecognizer Snapshot API key from https://platerecognizer.com/snapshot/

geographies

Geographies that the license plates may belong to. Use this to optimize license plate recognition.

ex. us, us_ca

objects_to_track

Objects on which to perform License plate recognition. Unset means all.

ex. car, vehicle, truck

Accepted formats:
object_label: any object of this type, with or without a classifier attribute. Example: car

object_label.class_type: any object of this type that has a specific classifier attribute. Example: car.red

object_label.*: any object of this type that has at least one classifier attribute. Example: car.* (this will match car.red, car.yellow, etc)

display_info

Display License plate (+ MMC) information on the video stream itself.

ex. true / false

recognition_mode

Recognition mode

"LPR & Make/Model/Color" (lpr_mmc) => Requires a Model Inference Node for Vehicle Detection and another one for License Plate Detection. We will only perform recognition once we find a valid association between a Vehicle and a License Plate.

"LPR Only" (lpr_only) => Requires a Model Inference Node for License Plate Detection. Will perform recognition attempts using the detected License Plate image crop.

"Make/Model/Color Only" (mmc_only) => Requires a Model Inference Node for Vehicle Detection Performs recognition attempts using the detected Vehicle image crop.

requests_buffer

The interval (in seconds) before perform the initial LPR request and between subsequent retries

ex. 1.0

Metadata

Metadata Property

Description

nodes.<node_id>

License plate information as described in the JSON below.

<node_id> for License Plate Detection Nodes is of the form annotate_lprX (ex. annotate_lpr1)

"nodes":{
    "annotate_lpr*":{
        "type":"annotate_lpr",
        "license_plates_entered_delta":"<int>",
        "license_plates_exited_delta":"<int>",
        "license_plates_count":"<int>",
        "license_plates":{
            "<object_tracking_id>": {
                "plate":{
                    "type":"Plate",
                    "score":<float>,
                    "props":{
                        "plate":[
                            {
                            "value":"<license_plate_number>",
                            "score":<float>
                            }
                        ],
                        "region":[
                            {
                            "value":"<region>",
                            "score":<float>
                            }
                        ]
                    }
                },
                "vehicle":{
                    "type":"<vehicle_type>",
                    "score":<float>,
                    "props":{
                        "make_model":[
                            {
                            "make":"<make>",
                            "model":"<model>",
                            "score":<float>
                            }
                        ],
                        "orientation":[
                            {
                            "value":"<orientation>",
                            "score":<float>
                            }
                        ],
                        "color":[
                            {
                            "value":"<color>",
                            "score":<float>
                            }
                        ]
                    }
                }
            }
        }
    }
}

Format

Key

Type

Description

license_plates_entered_delta

Integer

Number of new license plates detected since last frame

license_plates_exited_delta

Integer

Number of license plates that left since last frame

license_plates_count

Integer

Total number of license plates in the view right now

license_plates

List of object IDs

Information about the license plate, make, model & color of each vehicle.

object_tracking_id : Unique identifier for a specific object, as specified by object.id property (see Model Inference Node )

The "plate" and "recognition"` fields contents may not be present depending on the current recognition results.

Please check the json example for more details.


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