Topics in this article:
- Overview
- Camera Placement and Zoom
- Night Adjustments
- Naming and Labeling
- Recent Sightings Tab
- Saved License Plates Tab
- License Plates Alert Policy
- Adding License Plates
- Adding Bulk License Plates
- Helpful Links
- Contact Support or Sales
Overview
Rhombus License Plate Recognition (LPR) detects, indexes, and searches license plates captured by supported cameras, helping you investigate vehicle activity and receive alerts for vehicles of interest. Effective LPR relies on proper camera setup and organizing detected plates with names and labels for easy search and alerting. This article covers deployment best practices, managing sightings, creating alert policies, and adding license plates individually or in bulk.
Camera Placement and Zoom
Lighting, camera angle, and camera positioning all play critical roles in creating an optimal environment for license plate recognition. An inadequate setup in any 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 of less than 30° in all directions (up, down, left, and right).
Camera Distance: Mount the camera 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 our article on Optics and Object Distances for Analytics. Using shorter distances than the maximum recommended can help reduce bandwidth consumption.
Lighting: Position the camera to avoid backlighting and ensure the capture area is well lit. Minimize shadows and glare on the license plate.
Focus: Adjust the camera's zoom to focus on the intended license plate capture area.
Framing: Proper vehicle framing is essential for accurate detection. Ideally, the vehicle should occupy approximately one-third to one-half of the frame, and the license plate should be at least 100 pixels wide. This can be achieved through proper camera placement or by adjusting the digital or motorized zoom. For more information about adjusting the device zoom in the Console, see our article on Digital Zoom and Pan.
Offset Angles During Setup
Figure 1.) The first angle to consider during camera installation is the vertical offset between the direction to the sky and the direction the vehicle is facing from the camera's perspective. This offset angle should be between 5° and 30°.
Figure 2.) The second offset angle is the horizontal angle between the camera and the license plate. It is measured between the line extending from the license plate to the camera and an imaginary line extending straight out from the license plate parallel to the ground. This angle should be between 15° and 30°.
Night Adjustments
When creating an optimal environment for license plate recognition (LPR), lighting is an important consideration.
To reduce motion blur and improve license plate readability at night, faster shutter speeds are required. The ideal shutter speed will vary depending on the environment, but we recommend setting the slowest shutter speed to 1/60 second. If motion blur is still present, contact Support to request custom image settings. This can also help reduce headlight glare, minimizing missed license plate detections.
Higher shutter speeds reduce the amount of light captured by the camera. To compensate, we recommend adding supplemental lighting to the scene. Position the lighting so it illuminates the front of the vehicle to avoid backlighting, and ensure it is bright enough to provide daylight-like visibility.
Naming and Labeling
1. Navigate to the "Investigations" tab, then click "License Plates" in the upper-right corner.
2. Alternate between "Recent Sightings" and "Saved License Plates" as needed.
3. Click the icon to name the license plate. If the detected license plate is incorrect, click the characters to edit them.
4. To add a label to a detected license plate, click the icon, then add an existing label or create a new one.
Recent Sightings Tab
The "Recent Sightings" tab displays thumbnails of recently captured license plates. On this page, you can name and save license plates, add labels to LPR events, and perform other related actions.
Search
To search for a license plate, use the search bar in the upper-left corner of the page. You can enter a full or partial license plate number, and matching results will appear below.
The license plate search uses fuzzy matching to improve search accuracy. Depending on the length of the detected license plate, the system allows up to three mismatched characters when searching and matching saved vehicles for alerts. This helps identify the correct license plate even when some characters cannot be accurately read.
Additional filters are available to narrow or broaden your search results:
- Labels: Filter by labels that have been assigned to license plates or vehicles, such as service trucks.
- Cameras: Show only LPR events captured by a specific camera.
- Locations: Show only LPR events captured at a specific location.
- Date Range (Past 7 Days by default): Filter LPR events by a specific date range.
Save a License Plate
Save a license plate that has been captured by the system.
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Adding a Label
Labels are used to configure alerts for specific license plates. To add one or more labels, click the icon, then select an existing label or create a new one.
Sighting Details
Hover over a captured license plate thumbnail to view additional information about the sighting.
Details
Click "Details" to view additional information about the LPR event, including the option to view the associated footage.
If a license plate has already been saved, you can find it in the "Saved License Plates" tab and click its thumbnail. The details page displays information such as the date and time of the sighting, the camera(s) that captured the license plate, and the location where it was detected.
All Sightings
Click "All Sightings" to view every recorded sighting of a license plate. On this page, you can filter results by date range, edit the license plate name, and save or unsave the license plate.
Not a Plate
If an image does not contain a license plate, click "Not a Plate" to remove it from the "Recent Sightings" tab and provide feedback that helps improve future license plate detections.
Saved License Plates Tab
This tab displays all license plates saved to your organization. Hover over a saved license plate and click "All Sightings" to view every recorded sighting.
Search
To search for a license plate, use the search bar in the upper-left corner of the page. You can enter a full or partial license plate number, and matching results will appear below. You can also filter results by one or more labels.
License Plates Alert Policy
1. To set up License Plate Alerts you must first create an Alert Policy.
2. Add "License Plate Alerts" to the alert policy. Once added with an alert schedule, you will be presented with the following options:
Alert if spotted: Assign labels to saved license plates, then use the "Alert if Spotted" section of the alert policy module to generate alerts only for vehicles with those labels.
Alert for license plates other than: Assign labels to saved license plates, then use the "Alert for license plates other than" section of the alert policy module to generate alerts for all vehicles except those with the specified labels.
Alert for any unsaved license plates: Enable the "Alert for any unsaved license plates" option in the alert policy module to generate an alert whenever a vehicle with an unsaved license plate is detected.
Adding License Plates
| 1. On the "License Plates" tab of the "Investigations" page, click “Add License Plate” in the upper-right corner of the page. |
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| 2. A dialog box appears, allowing you to enter a name for the license plate, its alphanumeric characters, and an optional label. |
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| 3. Click "Submit" to save the license plate. Once saved, it will appear on the "Saved License Plates" page. |
Adding Bulk License Plates
License plates can be added in bulk through the Rhombus Web Console.
1. Create a CSV file with 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 must be 7 alphanumeric characters long (expanded functionality coming soon)
2. Once the CSV file is in the correct format, click "Bulk Add License Plate" in the upper-right corner.
3. Click "Browse" in the dialog box to select the CSV file, then click "Upload." You may need to refresh your browser to view the uploaded data.
Helpful Links
- Console Features & Licensing
- Enable AI Bounding Boxes
- 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.
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