In this post we want to explain an important concept in security systems designs with CCTV, such as the study of the scope of cameras in the security project. The scope of a security camera allows us to know the distance at which we can count on an adequate capture of the images of the cameras provided in the design. But when we talk about video surveillance, we cannot only refer to the meters we can see, as an example it is not the same to want to discern a hill on the horizon, a tree on the hill or the bird that is perched on a branch of that tree.
We must take into account other factors, in addition to distance, to establish the scope of a surveillance camera. These factors are defined by the use and objective that is intended to be carried out with the video surveillance system, thus appearing the definition of requirements of whether the objective of the system is to detect, recognize or identify a certain type of object or person.
Detection
The detection objective refers to the capacity of a camera, whatever the type, to detect a change in the captured image. It can be a car, a person or an animal. There are cameras that detect movements at 20 meters and others that detect them at 200 meters depending on the type of camera or the focal length of the lens being used. Detection is a basic feature of the video surveillance system that in many cases must be reinforced with additional capabilities that allow adequate decision making by the user or operator of the video surveillance system.
Recognition
In the face of detection, when we indicate that an image allows recognition we want to indicate that it is possible to discern whether it is a person, a vehicle or an animal in a reliable way.
The concept of recognition is conditioned to the specific needs of what is required to recognize. In some cases it may be necessary to move beyond the recognition of a person and it may be necessary to discern that it also carries a weapon or in the case of a vehicle to be able to discern whether the vehicle is a utility or a vehicle of the specific mobile park in a vehicle. Barracks for two examples.
In video surveillance tasks based on video analysis that transmit alarms to an alarm receiving center, it is usual that this threshold is required that allows ARC operators to discern whether the alarm that has arrived has been caused by an animal or there is a possible input of intruders in the protected area and the Security Corps should be called immediately.
Identification
In video surveillance of public enclosures it is common that for an adequate control and surveillance it is required that at least at the entrances and exits or at certain critical points the levels of image definition allow to establish the level called identification.
We can say that an image allows identification when the detected form (person, animal or vehicle) can be visualized with a level of sharpness and resolution that allows to identify a specific face or a license plate.
Normally this identification does not imply that the camera is more precise or of a better scope since normally the possibility of identification on an image does not allow the visualization and surveillance of wide environments that are sometimes necessary for tracking suspicious behaviors .
This last aspect can be compensated with the use of megapixel cameras in which the level of digital information allows simply by zooming digitally from an image based on the recognition that allows the tracking of suspicious behaviors or the surveillance of large areas at an identification level simply by zooming in on a certain area of the image.
How to choose the right security camera?
Depending on what our video surveillance needs are, it will be convenient to select the use of one type of camera or another: thermal, conventional or PTZ dome. The selection of the type of camera and the distance to the plane of vision that it is intended to have will condition the type of camera and lens that is required to be used.
For example, a thermal camera may have a wide range, but depending on the distance to the target we may be limited to detection and it will be practically impossible to use it for identification purposes regardless of distance due to its own technology. A thermal camera, when capturing the heat emission of the different objects in the field of vision, the image that is displayed, loses great capacity for definition. We can distinguish the forms (recognition) but we cannot identify a subject or read an enrollment (identification). The main advantage of this type of cameras is that at great distances they allow in many cases a more immediate recognition than a visible camera in a similar field of vision.
With a conventional camera, we will have a smaller range, but nevertheless we will have great capacity for recognition and identification. Especially if we use cameras with powerful and high-definition sensors or lenses that allow the field of vision to be adapted to the appropriate distance to the lens.
PTZ dome cameras offer a greater viewing capacity because they have a greater opening angle since they can rotate on their axis vertically and horizontally, but in general they are prepared for an overall view or for more precise identification in case of use of fixed cameras for an overview of an area that do not support digital zoom and a detail of a specific area is required.
The range and night vision
Another issue different from what we have discussed above would be the relationship between range and night vision capability. Thermal cameras can have a wide range and also be very practical for detection in low light conditions, since it takes advantage of the heat emitted by the bodies for the image capture by the sensor.
Conventional cameras will need lighting support by infrared systems or white light exterior lighting so that the camera’s sensor can capture images at night. Without this support lighting they would be completely useless, their range would be zero.
The same goes for PTZ dome cameras, which need exterior lighting, infrared or laser light to be operational at night.
Parameter to consider to know the scope of a surveillance camera
Surveillance cameras do not usually include this complete information that we need to know the scope of a camera, understanding that for us it is not only important the range in meters, but to know what is its capacity for detection, recognition and identification according to the needs Real video surveillance of each project.
When studying a design for a security system project, it is necessary to verify, by calculations of certain complexity, the requirements of the type of camera, lens and optimal focal length that should be used in each location to know exactly what detection capacity we will have. Each camera has different lenses and different viewing angle capabilities, which will determine its detection capacity.
Security cameras are an important part of the installation of security systems. Perhaps they are the most complex part of studying and analyzing, since there are many brands and solutions in the market and not all of them will give the same results.
The type of camera, the capacity of the sensor and the camera lens will tell us, making the appropriate calculations, what will be the detection capacity of the camera. We will know the range in meters and the degree of identification that will allow us.
Thus, with these calculations we can know by way of example what the specific capacity of a type of camera is.
If we opt for a camera like the Megapixel Dome that has: 3 megapixels; a 30X optics; a lens range 4.3 to 129 mm; sensor 1 / 2.8 ”), we can identify faces at 80 meters and identify them even in complex situations. With this camera we can achieve recognition at 300 meters and 1500 meters to know if there is a person or not.
The importance of the horizontal field of vision
Cameras should not only be chosen for the ability to detect, recognize or identify. We also have to take into account other important parameters such as the horizontal field of view of the camera. Depending on the size of the lens, the camera will cover a larger or smaller viewing surface. When choosing the camera, we have to know what degree of aperture we need to visualize around the central point of the image to lean towards one lens or another.
The focal length of the lens, which is given in millimeters, is what determines the horizontal viewing angle. Thus, for example, a lens with a focal length of 13 mm will have a horizontal viewing angle of 108 °.
To give us a more precise idea, an ultra-wide-angle lens, also known as fish eyes, can cover a 180-degree field of horizontal vision.
