This guide focuses on specific details that need to be considered when capturing license plates. The focus is on the placement of the optical sensor, the camera settings themselves and the configuration of the event triggers.

Please note at this point that the camera settings must be adjusted according to the installation location, as lighting conditions may vary.

Sensor placement

Perfect sensor placement is critical in order to get a clear image and readable number plates. While some parameters such as distance from the sensor to the number plate can be fine-tuned by zooming after installation, mounting height and angle between the sensor and travel direction of vehicles can only be adjusted by physical and cost-intensive re-arrangement. The sensor position has to be chosen in a way that passing vehicles are fully visible and can be captured throughout several frames of the video stream while making sure the number plates are large enough for the ANPR system to identify every single character.

We recommend mounting heights between 3 and 8 meters, therefore the suitable minimum capture distance ranges from 5 to 20 meters. Besides the vertical angle constraint, number plates should be visible with at least 250 pixels-per-meter (PPM), this constraint determines the minimum focal length (zoom) the sensor has to be set to.

Why between 3 and 8 meters of mounting height?

The lower bound of 3 meters is determined by rather practical reasons and not technical limitations. Sensors mounted lower than 3 meters are often prone to vandalism. Also, headlights from passing vehicles can lead to reflections on the sensor. The upper bound of 8 meters is determined by the resulting minimum capture distance of at least 14 meters for the needed camera resolution of 1920x1080p. License plates need to be visible with 250 pixel-per-meter (PPM).

As the compute module and sensor are mainly mounted on existing infrastructure such as traffic light poles, there are two general options to mount the sensors: side mounting or overhead mounting.

Overhead mounting

When positioning the sensorabove the vehicles, two lanes can be covered with one sensor.

Consider mounting height (1) and capture distance (2) which determine the vertical angle (3) between the sensor and the travel direction of the vehicle. The distance between the center of the lane (4) and the senosr determines the horizontal angle (5) between the sensor and the travel direction of the vehicle.

Side mounting

When mounting the sensor to the side of the road, two lanes can be covered, assuming the horizontal angle between the sensor and the travel direction of the vehicles is not exceeding 20°.

Position the sensor as close as possible to the side of the road to avoid a horizontal angle larger than 20°. Larger angles can lead to lower accuracy because parts of the number plate can become unreadable. While traveling directions (1) and (2) are the same for both vehicles, horizontal angle (3) is much larger than (4).

1. Orientation

Good positioning and alignment of the optical sensor is crucial in order to guarantee optimum detection accuracy. Detailed instructions can be found in the section.

2. Mounting the sensor

The sensor is attached to the poles using clamps. These adapt to the diameter of the pole.

3. Mounting the compute module

The compute module is attached to the poles using clamps. These adapt to the diameter of the pole.

4. Connection the sensor with the compute module

The sensor is connected to the computer unit using the network cable supplied.

5. Power supply

Finally, the computer unit is connected to the respective power supply (12V, 24V or 230V) using the power cable. The BCA then starts up and can be configured in the Control Center.

*) for optimum alignment and calibration according to installation instructions

Function modes:

Parking Mode ANPR:

For parking space management, it is necessary to record license plates as well as images of vehicles entering and exiting in plain text so that evidence can be provided and penalties enforced. The data is only stored for this purpose and is limited in time, by default to 48 hours.

Parking Mode GDPR:

Statistical recording of the parking duration and countries/regions of the license plates is possible without storing the license plates. The license plates are pseudo-anonymized using a hashing process and thus form the data basis for determining the parking duration. A maximum parking duration of 72 hours can be recorded.

Data protection and security

The BCA processes personal data only vaguely, without storing it and only for the purpose of anonymization. This is done on the basis of Art. 6 para. 1 f) GDPR, namely in the legitimate interest of the operator. Only the anonymous data is then used to carry out traffic management. The BCAcomplies with the Low Voltage Directive 2014/35/EU and the Electromagnetic Compatibility Directive 2014/30/EU. This resulting CE certification is attached to the bottom of the device.

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