JAI TS-9720EN, TS-1327EN manual Camera tilt considerations, Asynchronous triggering considerations

VIS-CAM System

Figure 4. Typical Over Lane Site Layout Plan.

2.1.1 (a) Camera tilt considerations

The requirement to freeze the motion of high-speed vehicles limits how steep or shallow the tilt angle of the camera may be. For example, it is important to prevent the horizon from appearing in the image, and thereby allowing the sun to blind the camera. For over lane installations, a camera tilt between 20° to 30° is recommended–with 25° being considered the optimal angle. This angle of tilt is the best compromise between minimizing visibility blockages caused by closely spaced vehicles and maximizing plate visibility for plate mounts that are slightly recessed or tilted downwards.

2.1.1 (b) Asynchronous triggering considerations

When the VIS is operated in trigger mode, a vehicle detector is employed to cause the camera to capture an image at the precise moment the vehicle is in the best position to image both the vehicle and its license plate. The delay between the time the vehicle passes the trigger position on the road and when the trigger signal actually reaches the VIS must be kept to a minimum to prevent high-speed vehicles from moving out of the area viewed by the camera before the image is snapped.

2.1.1 (c) Camera height versus trigger distance considerations

It is critically important, to select the correct distance between the camera and the location on the road where the camera is triggered to capture an image. Minimizing the cost of installation is usually also an important concern. This means that whenever possible, it is best to use existing structures or previously installed elements. The following charts (Figure 5 and Figure 6) provide a wide range of trade-offs between camera height and trigger distance to enable the installer to select convenient camera and light sensor locations relative to existing mounting structures and vehicle trigger locations. Adhering to the installation options provided in the installation charts, yields camera images that are generally suitable for automatic license plate readers (ALPR).

To use the charts correctly, please follow the steps below.

1.First measure the height above the road to convenient camera mounting locations.

2.Measure the distance along the road from directly beneath each candidate camera position to convenient trigger locations.

6 Preparing for Installation