Set-up guide - Installation
Journey time set up
Journey time is defined as the time passed between the sighting of the same vehicle across two or more camera streams. The identification of vehicles is based on number plates. Please refer to our detailed guide about ANPR for a general overview.
This guide focuses on specific details to be considered for journey times and area-wide traffic flow on public roads, focusing on camera placement, camera settings, and event trigger configuration.
Please be aware that the camera settings need to be adjusted according to the installed location as lightning conditions might differ.
Camera placement
Perfect camera placement is critical in order to get a clear image and readable number plates. While some parameters such as distance from the camera to the number plate can be fine-tuned by zooming after installation, mounting height and angle between the camera and travel direction of vehicles can only be adjusted by physical and cost-intensive re-arrangement. The camera 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 14 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 camera has to be set to.
| Mounting height [m] | Minimum capture distance [m] | Maximum capture distance [m] | Range of focal length [mm] |
|---|---|---|---|
3 | 5 | 19 | 4-12 |
4 | 7 | 18 | 5.4-12 |
5 | 9 | 18 | 6.6-12 |
6 | 10 | 18 | 10-12 |
7 | 12 | 18 | 11-12 |
8 | 14 | 17 | 12 |
Why between 3 and 8 meters of camera mounting height?
The lower bound of 3 meters is determined by rather practical reasons and not technical limitations. Cameras mounted lower than 3 meters are often prone to vandalism. Also, headlights from passing vehicles can lead to reflections on the camera. 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 Swarm Perception Box and cameras are mainly mounted on existing infrastructure such as traffic light poles, there are two general options to mount the cameras: side mounting or overhead mounting.
Overhead mounting
When positioning the camera above 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 camera and the travel direction of the vehicle. The distance between the center of the lane (4) and the camera determines the horizontal angle (5) between the camera and the travel direction of the vehicle.
Side mounting
When mounting the camera to the side of the road, two lanes can be covered, assuming the horizontal angle between the camera and the travel direction of the vehicles is not exceeding 20°.
Position the camera 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).
Night mode settings
While capturing sharp images during the day with good lighting conditions is relatively easy, low lightning and dark conditions make it a lot more difficult for cameras to deliver readable number plates from moving vehicles. The following section of this guide, therefore, provides an overview to fine-tune your camera to deliver readable number plates in such conditions.
However, the setting of the following parameters strongly depends on the specific camera mounting position and its environment. A light source such as a streetlamp or a vehicle passing on a different lane can send light to the camera sensors and influence the resulting image to a great extent. For this reason, this guide can only provide a general overview of relevant settings and their effect on image quality.
Day/Night Switch
We recommend that the Auto day/night switch mode from the cameras is used. As you can see in the examples below, it is crucial that the camera changes to night mode reliably.
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