Best Practices for ANPR Setup
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Affected Roles: Owner, Administrator
Last Edit: August 2, 2024
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ANPR Setup Recommendations
The Automatic Number Plate Recognition (ANPR) camera uses the same technology as an LPR camera but with added analytic plugins for automatic numberplate detection. In addition to how the camera is physically installed and positioned, there may be certain settings that will need to be configured for your setup. This may vary depending on your situation, so this article will outline some general recommendations to consider when setting up your ANPR camera.
**NOTE: For guidelines on using LPR cameras, you can read the article MEGApix LPR - Best Practices and Setup Recommendations.
Supported/Affected Devices:
- DW MEGApix® Ai ANPR Camera (DWC-XSBA05MiL)
Placement and Position of Camera
When it comes to physically installing an ANPR camera, it is recommended to consider the distance and angle of the camera direction. When mounting the camera, consider that the camera is stationary and must be able to read a moving target. It is important that the camera is aligned as possible within the camera’s Region of Interest (ROI) so that the license plates will pass directly in front, however this may not always be possible due to camera environment limitations.
When mounting the ANPR camera, consider the following.
Vertical Angle
For vertical placement, define the camera installation height (H) and consider the distance between the camera’s position and the ROI. The maximum vertical angle to which the camera is positioned will affect the recognition ability of the ANPR camera, depending on the average speed that the target vehicles are moving.
|
Maximum Vertical Angle |
Speed of Target Vehicle |
|
30º |
25 MPH |
|
25º |
45 MPH |
|
15º |
75 MPH |
The forward distance (FD) can be determined with the equation:
- FD = cot 30º * H
|
Height (H) |
Min. Forward Distance (FD) |
|
1.5 m / 5 ft |
4 m / 13 ft |
|
2 m / 6.5 ft |
4 m / 13 ft |
|
3 m / 10 ft |
5 m / 17 ft |
|
3.5 m / 11.5 ft |
6 m / 20 ft |
|
4 m / 13 ft |
7m / 23 ft |
The Maximum Forward Distance (FD) depends on the zoom abilities of the lens, however it should not exceed the effective IR range.
|
Focal Length (Angle of View) |
Minimum Recognition Distance (ft) |
Maximum Recognition Distance (m) (At day/At night) |
|
2.7 - 13.5 mm |
Full wide: 9.84’ / 9.84’ Full Tele: 22.97’ / 22.97’ |
Full wide: 21.32’ / 21.32’ Full Tele: 45.93’ / 45.93’ |
|
2.7 - 13.5 mm |
Full wide: 9.84’ / 9.84’ Full Tele: 22.97’ / 22.97’ |
Full wide: 22.97’ /22.97’ Full Tele: 49.21’ / 49.21’ |
|
6 - 50 mm |
Full wide: 22.97’ / 22.97’ Full Tele: 101.71’ / 101.71’ |
Full wide: 45.93’ / 45.93’ Full Tele: 164.04’ / 131.23’ |
|
6 - 50 mm |
Full wide: 22.97’ / 22.97’ Full Tele: 101.71’ / 101.71’ |
Full wide: 45.93’ / 45.93’ Full Tele: 164.04’ / 131.23’ |
|
4 mm |
13.12’ / 13.12’ |
26.25’ / 26.25’ |
|
2.7 - 13.5 mm (98.3° to 31.6°) |
Full wide: 9.84’ / 9.84’ Full Tele: 22.97’ / 22.97’ |
Full wide: 22.97’ / 22.97’ Full Tele: 49.21’ / 49.21’ |
Horizontal Angle
The maximum horizontal angle to which the camera is positioned will also affect the recognition ability of the ANPR camera, depending on the average speed that the target vehicles are moving.
When determining the horizontal positioning, it can be beneficial to consider where the target point will be. For example, if the camera is positioned to overwatch a curve/turn in the road, the camera should be placed so that the cars will be forced to move through the ROI in such a way that the ANPR plugin can detect the plate information.
|
Maximum Vertical Angle |
Speed of Target Vehicle |
|
30º |
25 MPH |
|
25º |
45 MPH |
|
15º |
75 MPH |
Tilt Angle
For best results, check the angle of the horizontal angle of the camera compared to the angle of the plate. Rotate the camera to try and get license plates to appear with less than a 5° offset.
Recommended Settings
The ANPR camera is designed to detect license plates but here are some setting recommendations to improve the success rate.
Camera Settings
Using the camera’s Web Viewer, select Setup > Camera to configure the camera settings and consider the following:
- Enable Autofocus for the camera. If fine-tuning is needed to adjust the focus, Manual focus can be used before changing back to Autofocus.
- Disable Wide Dynamic Range (WDR); this setting may intermittently affect the appearance of contrast within the image.
- Use the Auto setting option for Day & Night mode; the camera will need to be able to change into Night mode when the light in the camera environment drops to a certain threshold.
- Set the maximum value of the Shutter Limit to 1/960 (approx. 1/1000).
- Set the maximum Gain Limit to 24 dB to optimize the blur and noise trade-off in most camera scenes. The maximum Gain Limit can be adjusted to 9 dB if license plates appear too overexposed.
- Set the Auto Exposure setting to ON.
ANPR Settings
Enable Setting
In the ANPR > Enable menu tab, the ANPR plugin activation toggle should be set to ON. Ensure that this setting is enabled for the ANPR feature to work.
Ensure that the correct region/country is selected for the camera installation.
Region of Interest (ROI)
In the ANPR > ROI menu tab, the camera’s Region of Interest (ROI) should be configured to help the camera detect license plate information.
To configure the ROI, right-click in the preview window and draw the desired detection area.
When setting the ROI, consider the following:
- Keep the drawn ROI as small as possible, but large enough as to what is necessary for license plates to pass through the detection area.
- Avoid drawing the ROI so that it covers the entirety of the camera’s field of vision (FoV).
Advanced Setting (License Plate Width Range)
License Plate Width Range
In the ANPR > Advanced menu tab, you can use an onscreen reference to gauge the approximate width of license plates as they pass through the camera’s Region of Interest (ROI).
It is important to ensure that the way that the license plate falls between the minimum and maximum points. The more level that the camera is with the target, the more accurate the detection will be.
In the image below, the camera is positioned so that license plates will be between the minimum and maximum size as they pass through the ROI.
While the human eye can read the text and see the details on a license plate from further away, the chances that the plate will be accurately read is greatly reduced if the plate appears smaller than the minimum size.
For example, in the images below, the ROI was set up so that license plates would barely be at the minimum size necessary for detection. The ANPR would inconsistently detect plates at an approximately 60 ft. distance. However, the success rate was low. However, when the ROI was reduced to a 24 ft. width (approximately) by zooming the camera in, license plates began to appear within the proper sizing range and the accuracy of detection increased.
Exposure Setting in Night Mode
The Exposure Setting in Night Mode configuration within the ANPR > Advanced menu tab will automatically adjust the camera exposure settings to fit ANPR when in Night mode. This will override the exposure settings found in Setup > Camera > Exposure Settings.
For More Information or Technical Support
DW Technical Support: 866.446.3595 (option 4)
https://www.digital-watchdog.com/contact-tech-support/
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DW Sales: 866.446.3595 [email protected] www.digital-watchdog.com
