License Plate Recognition User Guide

Owned by Anand Rajaraman
Last updated: May 23, 2019
6 min read

This document is intended as a supplemental guide for customers who have installed and configured the 3VR License Plate Recognition plug-in on their 3VR Appliance/User Manual. For more information on any general application features not discussed in this guide, please refer to the full 3VR User Manual.

Viewing License Plate Events

Monitoring Recent License Plate Events in the Monitor Panel

The OpCenter Monitor panel allows you to view events as they happen. You can specify which cameras to view, and what types of events are displayed.

Use the following steps to view recent events generated by the License Plate Recognition plug-in:



  1. In 3VR OpCenter, click the Monitor tab to go to the Monitor panel.
  2. Click camera numbers to select the cameras associated with the License Plate Recognition plug-in.
  3. Click the arrow below the camera selector to open the event type drop-down menu.
  4. Select [ ] License Plate to display events of that type and click OK.
  5. The Monitor panel will update to display only License Plate events
    from the selected cameras.

    To view an event, click the event card. The event card will turn blue,
    indicating it is currently selected.

About License Plate Events Cards

A License Plate event will be generated in OpCenter whenever a license plate is captured on a camera bound to the License Plate Recognition plug-in.

License Plate event cards contain pictures, video, and information about each license plate. They appear in the Monitor panel for recent events and in the Search panel for search results. Each License Plate event card contains the following information in storyboard view:



a. Thumbnail image

b. Camera number and name
c. Time of event
d. Event type
e. Length of the event video clip
f. Lane (if specified)
with additional information displayed on mouse-over:
g. Date of event

Viewing License Plate Events

When a License Plate event card is selected, details about the event may be viewed in the event editor, located below the video player.

In addition to the tabs available for all event types, such as Notes and Images, License Plate events include the following information in the Details tab:

  • Lane: The name of the lane the license plate was captured in.

  • If no lane(s) have been drawn for the camera, the Lane box will be blank.

Searching for License Plate Events

Setting up a License Plate Search

Use the Search panel to find License Plate events recorded days, weeks, or months ago.



  1. To go to the Search panel, click the Search tab.
  2. Define the dates, days of the week, and time ranges to search for events.
  3. Under Cameras, select one or more cameras bound to the
    License Plate Recognition plug-in.
  4. Under Events, select [ ]License Plate to search for events generated by the License Plate Recognition plug-in.

5. The following options are available when searching for License Plate events:

  • Click ( )All License Plate to search for all plates captured during the specified time range
  • To restrict the search further, click ( )Specify
  • To search for License Plate events by lane, type the lane to search for in the Lane box

When searching for a specific lane, only exact matches (case-insensitive) will be returned.

  • To search for License Plate events with certain plate characters, type a full or partial license plate string in the License Plate String box
  • To search for more than one plate string at once, type each search string separated by a comma
  • The Search Threshold option allows you to filter the results of a License Plate String search by similarity.

    Increasing the Search Threshold will return fewer plates, but each individual plate will be more similar to the target string. Decreasing the Search Threshold will return more plate results, but the results will include more false positives.



6. When you are finished defining the criteria for the search, click the Search button.
7. License Plate events matching your criteria will be displayed in the Search panel results screen.
8. Select an event card to view the video clip and details associated with the event.

Sorting Search Results

There are two ways to sort the results of a search: by Time and by Similarity. Although the default sort order for standard motion events is by time, when searching for License Plate events using the options under ( )Specify it is recommended to sort by similarity. This will place the License Plate events that best match your criteria at the top of the Search panel results screen.

Sort order is specified when setting up the criteria for a search. To change the sorting of License Plate events:



  1. Under Events, select [ ]License Plate to search for events generated by the License Plate Recognition plug-in.
  2. Click ( )Specify.
  3. Change the Sort Results By radio button to ( )Similarity.
  4. Modify the search options under ( )Specify as desired. The following options will produce meaningful results when sorting by similarity:
    • License Plate String: Sorts license plates by similarity to the given search string

Creating Alerts for License Plate Events

In the Alerts panel, you can instruct the 3VR appliance to perform a specified action when video is recorded that matches certain criteria. Use the following steps to set up an alert that will perform an action, such as sending an email, in response to an event generated by the License Plate Recognition plug-in.



  1. To go to the Alerts panel, click the Alerts tab.
  2. To create a new alert, click New.

In the alert editing screen, define the criteria for the alert:

3. Type a name for the new alert.
4. Select a color for the alert. The color will be displayed on event cards that trigger the alert.
5. Specify the day of the week and hours that the alert should be active.
6. Under Cameras, select a camera associated with the License Plate Recognition plug-in.
7. Check the boxes next to one or more alert Actions to carry out when the alert is triggered.
8. If desired, type an alert response procedure. This text will be included with the alert and posted on events that trigger the alert.
9. Under Events, select [ ]License Plate.

The following options are available when alerting for License Plate events:

10. Click ( )All License Plate to generate an alert for all plates captured during the specified time range.

  • To generate alert for specific plates, click ( )Specify. The options under ( )Specify are identical to the event selector in
    the Search panel. Please refer to the previous section for more information about creating alerts for specific plates.


11. When you are finished defining the criteria for the alert, click the Save button.

12. The alert will be added to the list of alerts displayed in the main view of the Alerts panel. Click the check box next to the alert to
enable it.