How wide should a people-counting zone be?
When using video to count people, you position a cctv camera above the counting area or zone. The system detects and counts people as they cross through the zone. Typically a zone will cover a doorway but it might instead be across a corridor, outside a shop window, above a turnstile or over a store display unit. For extra-wide counting-zones you simply connect several cameras together.
The size that a counting zone under a camera can be depends on two things:
- the focal length of the camera and
- the distance that the camera is from the floor.
This table shows the maximum counting width in meters for differing focal lengths and heights of camera. As the distance of the camera from the floor generally can’t be changed, you should choose the focal length of the camera accordingly. Remember, these are maximum widths – you can change these by up to 25% using our people counting software.
Maximum width of the people counting zone for different heights of camera and lens focal length
|Lens Focal Length||2.9 mm||3.6 mm||4.6 mm||6.0 mm||8.0 mm|
|Height of Camera above Floor||Maximum Width of Counting Zone|
|2 m||1.66 m|
|2.5 m||2.07 m||1.67 m|
|3 m||2.48 m||2.00 m||1.57 m|
|3.5 m||2.90 m||2.33 m||1.83 m|
|4 m||2.67 m||2.09 m||1.60 m|
|4.5 m||3.00 m||2.35 m||1.80 m|
|5 m||2.61 m||2.00 m||1.50 m|
|5.5 m||2.20 m||1.65 m|
|6 m||2.40 m||1.80 m|
|6.5 m||2.60 m||1.95 m|
|7 m||2.10 m|
|7.5 m||2.25 m|
|8 m||2.40 m|
The lens most often chosen has a 3.6 mm focal length. This is suitable when the distance between the floor and the camera is between 1.7 and 3 metres. As you can see from the above table though, by changing the focal length the camera can be as much as 8 m from the floor.
As the cameras only provide images, another component is required to analyse the images and allow people counting: the Video Turnstile units. The camera plugs into the VT unit which analyses the video and stores the people counts.