Overview

This node parses the output of "License Plate Recognition" model to extract the license plate information.

This node requires AI Model Node (Vehicle Detection model) -> Model Inference Node (License Plate model) -> Track Objects Node -> Model Inference Node (License Plate Recognition) prior to it in order to function properly.

Inputs & Outputs

Inputs : 1, Media Format : Raw Video
Outputs : 1, Media Format: Raw Video
Output Metadata: license-plate counts and entered/exited deltas under nodes.<node_id>, plus parsed object attributes.

Properties

Property	Description	Type	Default	Required
`display_info`	Display LPR?	`bool`	`true`	No
`objects_to_associate`	ex. `car`, `vehicle`, `truck`. If specified, detected license plates within these object types will be associated with that object.	model-labels	`car,vehicle,truck`	No
`watchlist`	Comma separated list of license plates to watch for.	`string`	`null`	No
`trackables_lists_ids`	Watchlist IDs that contain vehicle license plates to watch for. Format: comma-separated trackable list UUIDs.	`string`	`null`	No
`trackables_items_ids`	Watchlist items IDs from the previously selected watchlists. Leave blank to watch for all items. Format: comma-separated trackable item UUIDs.	`string`	`null`	No
`watchlist_tolerance`	Allow license plates to differ by this number of characters for matches. Unit: characters.	`number`	`0`	No
`watchlist_fuzzy_match`	If enabled, matches only allow visually similar differing characters (e.g. 0 vs O, 1 vs I). The number of differences must still be within the tolerance limit.	`bool`	`false`	No
`min_license_plate_length`	Ignore recognized license plates shorter than this length and remove those short license plate attributes from object metadata. Unit: characters.	`number`	`0`	No
`detection_buffer`	Time that the license plate must be present before reporting results in metadata. Unit: seconds.	`float`	`0.1`	Yes
`rejection_buffer`	Time during which objects that leave and re-enter the scene will be ignored. Increase to reduce duplicate alerts for a given object. Unit: seconds.	`float`	`5.0`	Yes

Output Metadata

The fields below are declared by this node's metadata schema; the JSON values are representative examples.

Path	Type	Description
`nodes.<node_id>.license_plates_entered_delta`	`integer`	Number of new license plates detected since last frame
`nodes.<node_id>.license_plates_exited_delta`	`integer`	Number of license plates that left since last frame
`nodes.<node_id>.watchlist_match_delta`	`integer`	Number of new license plates that matched the watchlist since last frame
`nodes.<node_id>.license_plates_count`	`integer`	Total number of license plates in the view right now
`nodes.<node_id>.license_plates.<object_id>.plate.type`	`string`	Recognition result category for the plate.
`nodes.<node_id>.license_plates.<object_id>.plate.score`	`number`	Overall plate-recognition confidence.
`nodes.<node_id>.license_plates.<object_id>.plate.props.plate[].value`	`string`	Recognized plate text.
`nodes.<node_id>.license_plates.<object_id>.plate.props.plate[].score`	`number`	Confidence of this plate-text candidate.
`nodes.<node_id>.license_plates.<object_id>.plate.props.plate[].watchlist_match`	`string`	String containing the matched watchlist plate, or null when unmatched.
`nodes.<node_id>.license_plates.<object_id>.plate.props.region[].value`	`string`	Recognized plate region.
`nodes.<node_id>.license_plates.<object_id>.plate.props.region[].score`	`number`	Confidence of this region candidate.
`nodes.<node_id>.license_plates.<object_id>.trackables[].trackable_list_id`	`string`	Identifier of the matched trackable list.
`nodes.<node_id>.license_plates.<object_id>.trackables[].trackable_id`	`string`	Identifier of the matched trackable item.
`nodes.<node_id>.license_plates.<object_id>.trackables[].trackable_name`	`string`	Name of the matched trackable item.
`nodes.<node_id>.license_plates.<object_id>.trackables[].trackable_labels`	`array`	Array of labels stored on the matched trackable item.
`nodes.<node_id>.license_plates.<object_id>.trackables[].matched_plate`	`string`	Plate text that produced the trackable match.
`nodes.<node_id>.search_text`	`string`	Text prepared by the node for downstream search or indexing.
`nodes.<node_id>.event`	`string`	Current event name, or null when no event is active.
`nodes.<node_id>.type`	`string`	Identifies the node type that produced this metadata.

JSON example

{
  "nodes": {
    "annotate_lpr_edge1": {
      "event": "value",
      "license_plates": {
        "object_id": {
          "plate": {
            "props": {
              "plate": [
                {
                  "score": 0.0,
                  "value": "value",
                  "watchlist_match": "value"
                }
              ],
              "region": [
                {
                  "score": 0.0,
                  "value": "value"
                }
              ]
            },
            "score": 0.0,
            "type": "value"
          },
          "trackables": [
            {
              "matched_plate": "value",
              "trackable_id": "value",
              "trackable_labels": [],
              "trackable_list_id": "value",
              "trackable_name": "value"
            }
          ]
        }
      },
      "license_plates_count": 0,
      "license_plates_entered_delta": 0,
      "license_plates_exited_delta": 0,
      "search_text": "value",
      "type": "annotate_lpr_edge",
      "watchlist_match_delta": 0
    }
  }
}

Object labels and attributes

Object labels/classes added: None.
Object attribute labels/classes added: Recognized plate text (10400), watchlist for a match (10401), trackable-list UUID (10402), and trackable-item UUID (10403).

The following information is added to the detected object's "attributes" array:

"class_id" field	"label" field	"probability" field
10400	The recognized license plate (string)	LP recognition confidence
10401	`watchlist` when the plate matches	`1.0`
10402	Trackable-list UUID	`1.0`
10403	Trackable-item UUID	`1.0`

"objects": [{
    "id": 5750484150146564100,
    "label": "car",
    "class_id": 0,
    "probability": 0.98,
    "rect": {
        "width": 47,
        "top": 201,
        "left": 656,
        "height": 25.
    },
    "attributes": [{
        "label": "ABC1234",
        "class_id": 10400,
        "probability": 1.0,
    }]
}]