Managing License Plate Recognition (LPR)

Topics in this article:

• Overview
• Camera Positioning and Zooming
  • Offset Angles During Setup
• Night Adjustments
• Naming and Labeling
• Recent Sightings Tab
  • Search
  • Save a License Plate 
  • Adding a Label
  • Sighting Details
    • Details
    • All Sightings
    • Not a Plate
• Saved License Plates Tab
  • Search
  • Navigation
• License Plates Alert Policy
• Adding License Plates
• Adding Bulk License Plates
• Helpful Links
• Contact Support or Sales

Overview

License Plate Recognition (LPR) is not enabled by default. Ensure you have assigned an enterprise license to the camera that will be using LPR. Learn how to enable this feature by reading the Enabling Features section in this article. 

Camera Positioning and Zooming

Lighting, camera angles, and camera positioning all play critical roles in establishing an optimal license plate recognition environment. An inadequate setup in any one of these areas may result in missed or inaccurate detections.

• Mounting Position: Place the camera as close to license plate level as possible with an angle under 30° from all directions (up, down, left, right).
• Camera Distance: Mount at a distance that provides approximately 100 PPF (pixels per foot) on the license plate at the desired capture point. For maximum distance guidelines, refer to the article on Optics and Object Distances for Analytics. Using shorter distances than the maximum listed can help reduce bandwidth consumption.
• Lighting: Ensure the camera avoids back-lighting and is placed in a well-lit area. Minimize shadows and glare on the license plate. 
• Focus: Adjust the camera’s zoom to focus on the intended plate capture area.
• Framing: Framing of the vehicle is a key factor in accurate detection. Ideally, the vehicle should take up approximately 1/3 to 1/2 of the frame, and the license plate should have a minimum of a 100-pixel width. This can be accomplished with effective mounting or adjusted with digital and motor zooming. For more information on how to adjust the device zoom in the console, please see Digital Zoom and Pan article. 

Offset Angles During Setup

Figure 1.) The first angle offset to keep in mind during camera installation is the angle between the direction to the sky and the direction the car is facing from the camera's perspective. This "offset angle" should be between 5 and 30 degrees.

Figure 2.) The second angle offset is the angle between the imaginary line from the license plate to the camera and the imaginary line from the license plate parallel with the ground. This "offset angle" should be between 15 and 30 degrees.

Night Adjustments

When setting up the ideal environment for LPR, lighting must be taken into consideration.

To reduce blur and effectively detect readable license plates at night, faster shutter speeds are required. The specific shutter speed will vary depending on the environment, but we recommend setting the slowest speed to 1/60 of a second. If blur is still present, please contact support to make some custom image settings. This will help to reduce glare from headlights, therefore reducing missed sightings. 

When using higher shutter speeds, the camera captures less light. To compensate, we recommend adding extra lighting to the scene. This lighting should face the vehicle head-on to avoid potential complications with backlighting and should be bright enough to ensure the vehicle is visible, similar to daylight conditions.

Naming and Labeling

1. Navigate to the "Investigations" tab on the left-hand side. 
2. Click on the "License Plates" tab across the top. 
3. Navigate between "Recent Sightings" and "Saved License Plates" based on need.

Recent Sightings Tab

The Recent Sightings tab will display thumbnails of license plates that were recently captured. Here you can perform a variety of actions, such as naming thumbnails to be saved to your organization and adding label(s) to an LPR event.

Search

To search for a license plate number, use the search bar located in the top left area of the page. You can also type in a partial license plate and all relevant license plates will show up in the results area. 

For searching and matching license plates to saved vehicles for alerting, the software uses fuzzy searching which allows up to 3 characters to mismatch depending on length of the read plate. So even if the software can't identify all the the characters in the plate, it will still show and alert on the correct plates.

Other search filters are also available to narrow down or expand the time frame that you want your results to be.

• Select Labels - Labels that have been created for groupings, such as service trucks etc. 
• Select Cameras - Filter by vehicles picked up by a specific camera. 
• Select Locations - LPR events captured at a specific location. 
• Past 7 Days - Filter by LPR events that have occurred in a specific date range.

Save a License Plate

Save a license plate that has already been captured by the system. 

Adding a Label

Adding a label is crucial to setting up an alert for specific plates. Add multiple labels by clicking the "Add Label" button and entering a label of your choosing.

Sighting Details

When you hover over the thumbnail of a particular plate, more information about the sighting appears:

Details

This provides a more detailed snapshot of the LPR event, along with an option to view the footage.

If a plate is already saved, you can search for it in the "Saved License Plates" tab and click the thumbnail. You will see information such as the date and time, the name of the cameras that picked up the license plate, and the location where it was sighted.

All Sightings

This allows you to see all the events created for a specific plate. You can filter to a specific date range on this page, edit the name, and save the plate. 

Not a Plate

If an image is not of a license plate, selecting this will immediately remove this from the "Recent Sightings" tab and send the feedback to the system when looking for plate events in the future. 

Saved License Plates Tab

This tab shows all license plates that have been saved into the system. 

Search

To search for a license plate number, use the search bar located in the top left area of the page. You can also type in a partial license plate and all relevant license plates will show up in the results area. 

You can search by license plate number and/or label(s). 

Navigation

1. Hover over to click into "All Sightings" to be brought to a profile page for the saved plate. Here you can see all instances of the plate, edit its name, add/remove labels and unsave it if you wish. 

2. Click on the pencil icon to edit or add a name to a saved plate. 

3. Click "Add a Label" to add labels to a plate. If a plate already has a label, click on the label to add more or uncheck that label to remove it. 

License Plates Alert Policy

1. To set up License Plate Alerts, first create an Alert Policy. 
2. Select the License Plate Event to be added to the alert policy. Once it's been added with a time schedule, you will be presented with the following options:

• Alert if spotted: To generate alerts only for specific labels applied to vehicles, you can assign labels to saved plates and utilize the "Alert if Spotted" section of the above alert policy module. 
• Alert for license plates other than: To generate alerts for all vehicles except for specific labels, assign labels to these saved plates and then utilize the "Alert for license plates other than" section of the above alert policy module. 
• Alert for any unsaved license plates: To generate an alert every time a vehicle drives by with an unsaved license plate, you can toggle on the "Alert for any unsaved license plates" feature of the above alert policy module. 

Adding License Plates

Adding Bulk License Plates

You can bulk-add license plates on the Rhombus Web Console.

1. Create a CSV file where the data is in the following format:

name,plate,labels(optional) as the headers

Without labels:
name,plate
Example Name,RHOMBUS

With labels:
name,plate,labels

Example Name,RHOMBUS,[Trusted]

Note: License plates need to be 7 alphanumeric characters long (expanded functionality coming soon)

2. Once you have a CSV in the correct format, click the "Bulk Add License Plate" in the upper right corner.

3. A pop-up window will appear and you now you can upload the CSV file by clicking the Choose File button. Click "Upload." You may need to refresh the browser to see the uploaded data. 

Helpful Links

• Console Features & Licensing
• Enable AI Bounding Boxes

• Creating and Assigning Alert Policies

• Digital Zoom and Pan
• Optics and Object Distances for Analytics

Contact Support or Sales

Have more questions? Contact Rhombus Support at +1 (877) 746-6797 option 2 or support@rhombus.com.

Interested in learning more? Contact Rhombus Sales at +1 (877) 746-6797 option 1 or sales@rhombus.com.