A friend recently asked me about the ideal height to place a security camera. The truth is that there is no calculation or parameter to respond correctly to that question.
By Germán Alexis Cortés Hernández
- I remembered several videos (especially outdoors), where people can not be identified, simply because we are not looking at their faces, due to the very pronounced angle due to the height of the camera. Finally, at short distances, only heads are seen.
- I also remember 4 cameras that I once saw installed, on the terrace of a building of 20 flats and the image of one of them, that could detect a possible threat, more than 500 meters away.
- Finally I have in my memory, all the cameras on posts that are placed for citizen surveillance.
If we place the cameras at very low altitude, several problems occur:
1 It can easily obstruct the scene with other people, therefore, we can not have a clear image and without obstructions.
2 The camera is very vulnerable, being within reach of the hand of most people.
3 It hinders its volume and can be easily moved (Accidentally or intentionally).
However, set at a height of 1,20 mts. The image that could offer us would be directly pointing to the face of most people.
In general, to avoid that most people interfere with the image, the minimum height of the camera must be 1,90 mts. But he's still very vulnerable. So to avoid that a person of tall stature can touch it, the minimum height must be of 2,60 mts.
As many ceilings are lower than 2,40 mts; the cameras are accustomed to place at the height of the ceiling.
If minidomo type cameras are used, it is customary to install them better on roof than on wall, because many of them do not have the third axis that allows to straighten the image.
If we place the cameras at a great height, several problems also occur:
1 We must tilt them more than usual and then we end up cutting their reach.
2 We see heads and not faces.
3 Maintenance and service are difficult.
4 The vertical distance influences a lot and the objects look small in those scenes.
5 The camera can gain vision and reach by height, however, it requires great resolution to take advantage of this.
Calculations and assumptions
Inclination to safe minimum heights
Using a bit of basic geometry and applying Pythagoras, we can calculate that, at this height, the angle of inclination (downward) of the camera on the scene, less than 3 meters away should be approximately 20 degrees; Minor tilt, which allows you to really see the faces of passersby without much trouble. If we assume a lens with a low focal length, less than 3mm, in a traditional camera of 1 / 3 format, "we can see that only when they get too close to the camera (less than 1 meter), the scene is lost, because the image it does not reach the face of the people (they are very low and leave the field of vision).
This detail is very important, because we are located a camera at 2,6 meters high, to see front, with a tilt of 20 degrees. This allows you to see the faces of passers-by with relative ease in a range of 1 to 10 meters. Its clarity and sharpness will depend on many other factors, such as the resolution of the camera, its dynamic range and the incidence of light in the scene, to mention 3 of many more.
But the problem is that repeatedly the installer tilts the camera more than normal (I have seen many at 30 - 40 degrees and some at higher inclination level). In this case the same camera as in the previous example, will not have more range, because it will end up seeing the floor approximately 3 meters. The installer is forced to tilt it over, with the sole purpose of appearing on the scene the person who is very close.
Then we limited the scope and coverage of the camera and the worst thing is that everything was done to be able to observe the person nearby, but precisely to it we are going to see it a little distorted, sometimes out of focus and with a very strong Angle that perhaps does not allow Your ID.
Maximum height with maximum inclination, to be able to identify
Again doing the corresponding calculations:
1 According to some software manufacturers for video analytics, they request that a facial image is not seen above the 50 degrees, in order to identify important features.
2 Then calculating, we see that the maximum height at which we can locate a camera, to be able to see easily identifiable faces, less than 3 meters away, is 2,90 meters. And at 5 meters away is 4,80 meters.
3 However, the camera at 4,80 meters high would no longer be appropriate to see faces that are 3 meters away.
Use that will be given to the image
As we have always said, the first thing we must ask ourselves is why we want the image of that camera. The answer to this, guide on the use that is going to be given and how close or far the scenes can be seen.
In case it is to monitor in a generalized way, without requiring more detail, the height can be increased by offering security to the camera (4 to 5 meters in external areas). When it is internally, a maximum of 3 meters should be placed.
If identification or recognition of people is required, they should be placed at a lower height.
Another important aspect is the aesthetics associated with the installation. Many times the installer laziness or finish quickly, decides to place the camera always against the ceiling (regardless of height), to "hide" drivers and other accessory devices such as: Balums, sources, adapters, splices.
Externally and / or in large double-height accesses, it is important to make use of the walls in order to locate the cameras at a low height, without compromising the safety of the unit.
Cameras for citizen surveillance
This type of cameras, today of very high resolution, with long-range zoom lenses, take full advantage of the height on posts from 9 to 18 meters. However, it must be understood that at this point, what you can see in the vicinity of your post is minimal and with a high angle that does not allow you to identify almost anyone.
Some brands use a fourth engine that lowers the dome by the pole, up to heights close to the 4 meters, earning much at close range. What has been chosen lately is to place a dome on the tip of the pole to see in the distance and place a second camera (there can be several or one of 360 degrees), which allows better identification and angles of vision less inclined to less than 5 meter post.
Extremely high cameras
Sometimes, due to the needs of some sites, cameras are required that can see the possible threats or alert situations at a greater distance. This is the case of government entities, military forces and / or institutions critical mission in security as prison centers. They are located at the highest possible height of the property and the only recommendation is that they must be equipped with high resolution and large focal length zoom, to be able to clearly observe the monitored areas. It is obvious to think that these units do not serve to identify vehicles or people in short distances, due to their pronounced angle.
Then all this leaves us an important lesson and that is that it would be preferable to place the cameras as low as possible to have great coverage and distance observing the faces in front. But, on the other hand, they can not be placed so low, because the same integrity and security of each camera is compromised. It is recommended that the heights then not be exceeded much, in such a way that the maximum angle on the face of the people to observe, is not greater than 50 degrees.
* Germán Alexis Cortés Hernández. He is a Colombian Electronic Engineer, with a postgraduate degree in Engineering Management Systems. Consultant of the National Institute of Standards and Technology - NIST, in Electronic security and building automation. ASIS CCP, and ISC2 CISSP. He has more than 25 years of experience in the electronic security industry. Renowned lecturer and university professor on high-tech issues at the Latin level. He has been a director of several companies in the sector and is currently president of the consulting company Insetron - Electronic Networks Consulting, engineering and technical consulting company in projects of electronic networks for security, communications and automation. WINGS instructor and the ALFIL academy. He has participated in numerous Building Automation projects in Latin America. If you wish to contact him, write to the emails firstname.lastname@example.org - email@example.com