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 correctly answer that question.
By Germán Alexis Cortés Hernández
Some Cases
- I remembered several videos (especially outdoors), where you can not identify people, simply because we are not observing their face, due to the very pronounced angle by 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 20-story building and the image of one of them, which was able to detect a possible threat, more than 500 meters away.
- Finally I have in my memory, all the cameras on poles that are placed for citizen surveillance.
Very low
If we place the cameras at a very low height, several problems occur:
1. You can easily obstruct the scene with other people, therefore, we will not be able to have a clear and unobstructed image.
2. The camera is very vulnerable, being within reach of most people.
3. It hinders its volume and can be easily moved (accidentally or intentionally).
However, set at a height of 1.20 meters. the image it could offer us would be directly pointing at the face of most people.
In general to prevent most people from interfering with the image, the minimum height of the camera should be 1.90 meters. But it's still very vulnerable. So to prevent a person of tall stature from touching it, the minimum height should be 2.60 meters.
As many roofs are at a height of less than 2.40 meters; cameras are accustomed to being placed at ceiling height.
If minidome cameras are used, it is customary to install them better on a ceiling than on a wall, because many of them do not have the third axis that allows the image to be straightened.
Very High
If we place the cameras at a high altitude, several problems also occur:
1. We must tilt them more than normal and then we end up cutting their reach.
2. We see heads and not faces.
3. Maintenance and service is difficult.
4. The vertical distance influences quite a bit and the objects look small in those scenes.
5. The camera can gain vision and range by height, however, high resolution is required to take advantage of this.
Calculations and assumptions
Inclination to minimum safe heights
Using a little 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 about 20 degrees; lower inclination, which allows you to really see the faces of passers-by without major problem. If we assume a lens with a low focal length, less than 3mm, in a traditional 1/3" format camera, we can see that only when they get very close to the camera (less than 1 meter), the scene is lost, because the image does not capture the face of people (they are very low and leave the field of vision).
This detail is very important, because we are locating a camera at 2.6 meters high, to see from the front, with an inclination of 20 degrees. This makes it possible to see the faces of passers-by with relative ease over 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 usual (I have seen many at 30 - 40 degrees and some at a higher level of inclination). In this case the same camera of the previous example, will not have greater range, because you will end up seeing the floor at approximately 3 meters. The installer is forced to tilt it too much, with the sole purpose of the person who is very close to it appearing on the scene.
Then we limit 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 her we are going to see her a little distorted, sometimes out of focus and with a very strong Angle that perhaps does not allow her identification.
Maximum Height with maximum Inclination, to be able to identify
Again doing the corresponding calculations:
1. According to some manufacturers of software for video analytics, they request that a facial image not be seen above 50 degrees, in order to be able to identify important features.
2. So 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 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 to 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, guides 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 offering security to the camera (4 to 5 meters in external areas). When it is internally, they must be placed at a maximum of 3 meters.
If identification or recognition of persons is required, they should be placed at a lower height.
Installation
Another important aspect is the aesthetics associated with the installation. Many times the installer by laziness or to finish quickly, decides to place the camera always against the ceiling (regardless of the height), to "hide" the drivers and other accessory devices such as: Balums, fountains, adapters, joints.
Externally and / or in large double-height accesses, it is important to make use of the walls to be able to locate the cameras at a low height, without compromising the security of the unit.
Cameras for citizen surveillance
This type of cameras, nowadays of very high resolution, with long-range zoom lenses, take full advantage of the height on poles of 9 to 18 meters. However, it should be understood that at this height, what you can see in the vicinity of your pole is minimal and with a high angle that does not allow you to identify almost anyone.
Some brands use a fourth motor that lowers the dome by the pole, to heights close to 4 meters, gaining a lot in short distance. What has been chosen lately is to place a dome at the tip of the pole to see in the distance and place a second camera (they can be several or one of 360 degrees), which allows better identification and less inclined viewing angles less than 5 meters from the post.
Extremely high cameras
Sometimes, due to the needs of some sites, cameras are required that can see possible threats or alert situations at a greater distance. This is the case of government entities, military forces and/or mission-critical security institutions such 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 zoom of great focal length, 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.
Conclusion
So 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 from the front. But, on the other hand, they cannot be placed so low, because the same integrity and security of each camera is compromised. It is recommended that the heights then are not exceeded much, so that the maximum angle on the face of the people to be observed, is not greater than 50 degrees.
* Germán Alexis Cortés Hernández. 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. CCP of ASIS, and CISSP of ISC2. He has over 25 years of experience in the electronic security industry. Renowned lecturer and university professor on high-tech issues at the Latino level. He has been a director of several companies in the sector and is currently president of the Insetrón Consulting company – Electronic Networks Consulting, an engineering and technical consulting company in electronic network projects for security, communications and automation. Instructor of WINGS and the ALFIL academy. He has participated in numerous Building Automation projects in Latin America. If you want to contact him write to the emails [email protected] - [email protected]
