How high should a CCTV camera be mounted?

Two things happen at once when you mount higher

The first is harmless and can be calculated. The camera moves further away from the target. Not on the site plan, but as the crow flies: put it at six metres, looking at a point ten metres away, and the real line of sight is around eleven metres. That slant distance is what the calculation uses, and it costs pixel density.

The second is the actual problem. The angle gets steeper. And a face shot from above shows mostly forehead, the bridge of a nose and shoulders. The pixels are all there. They are just in the wrong places.

Mounting higher makes the picture bigger and the detail smaller. You cannot have both at once.

What the numbers say

The table shows a camera with a 60° angle of view and Full HD looking at a point 15 metres away on the plan. Only the height changes.

The line of sight barely grows, from 15.0 to 17.2 metres. The pixel density falls just as little, from around 111 to around 97 px/m. Look at that column alone and ten metres of height seems like a good idea.

The third column tells the other story. 3.4° becomes 29.2°, and at that point the camera is looking down on the top of a head at almost thirty degrees.

The limit that is in the standard

DIN EN 62676-4 recommends limiting the vertical viewing angle. Two values are worth keeping in your head.

• Up to and including “Recognise” at 125 px/m: no more than around 22.5° of tilt.
• From “Identify” at 250 px/m: considerably flatter, around 15°.

Check that against the table. At eight metres of height and 15 metres of distance you are at 23.1°, so the recommendation for Recognise is already broken. For Identify you would be too steep at five metres.

Both are recommendations rather than limits. Anyone who exceeds them should be able to say why.

What works in practice

For faces at entrances, doors and tills the usable range is between 2.5 and 3.5 metres. High enough that nobody reaches the camera from the ground, flat enough that a face stays a face.

You go above four metres when there is a reason. Vandalism is such a reason, a forklift in the way is another. Then the rule is: pick a narrower angle of view, set the camera further from the target and let it look at the target more flatly. A camera on the opposite wall often sees a face better than one directly above it.

And if you have two tasks in one place, separate them. One camera mounted high for the overview, one mounted low for the face. Two cameras that each do one thing beat one that half does both.