Criteria That Guide the Best Choice of the CCTV System

The concept of Projects with CCTV cameras only aimed at the coverage of environments with installation of cameras without any commitment to the final result is outdated and cameras with higher resolution require more planning of the location and the objective of the monitoring, that is, which the level of detail that is expected of the system.

In this sense, we must consider the criteria that should guide our choice, such as the field of vision, the horizontal resolution of the camera and concepts of pixel per square meter.

Who determines the field of vision is the focal length, and the smaller the “lens value” the greater the viewing angle.Consequently, a 2.8mm lens will provide a wider viewing angle than a 6mm lens.
During the design of the CCTV project the field of vision is one of the most important points that designers should be concerned about, because it is at this point that we will be deciding with the client what will be really “observed and recorded”.We should ask the client and make it clear which key monitoring points he wants best image definitions in his project.As an example the complete observation of the Cashier of an establishment.

To calculate how many cameras are needed in a particular area, simply carry out a very simple calculation.This calculation only requires 3 information: the field of view, the horizontal resolution of the camera and pixel per meter.

VISION FIELD – is determined primarily by the camera lens, is the measure (in meters) of the total length where the object of interest will be captured by the camera.

HORIZONTAL CAMERA RESOLUTION – Although the cameras have different descriptions in Megapixel, Full HD and VGA Cameras, etc., for this calculation the important thing is the number of pixels that the camera supports horizontally.A 2 Megapixel (1600 × 1200) camera has a horizontal resolution of 1600 pixels, while a Full HD (1920 × 1080) camera has 1920 pixels of horizontal resolution.

PIXEL PER METER (PPM) – is the result of dividing the horizontal resolution of a camera by the field of view of an area.

Thus, we must detail in each project what we really want to capture.

As an example the observation of vehicle license plates.

Depending on the resolution of the used camera and the employed lens (field of view), it may be possible to identify only the largest characters of a board or even of which city the vehicle belongs.

Therefore, when scaling the number of cameras in Shopareview, the first necessary information is the minimum PPM to achieve the monitoring goal.The minimum PPM is subjective and can vary greatly from one person to another, so it is only possible to know the minimum PPM of a project by performing tests with different lenses and cameras.

After knowing the minimum PPM for the project, it is sufficient to perform calculations to identify the number of cameras (the resolution of each one) and the appropriate lenses to ensure that the appropriate PPM is reached throughout the monitoring environment.

Although megapixel cameras are no longer new in the monitoring market, in Brazil, there is still a lack of knowledge of the benefits that increased resolution can bring to the end consumer, not only in equipment quality, but also financially.

The great advantage of megapixel cameras is that using the same lens, its equivalence over conventional cameras (720 × 480) can be 20 times or more.By making the number of cameras and all necessary infrastructure involved, such as cables, labor, power supplies, lenses, protective boxes, etc., for a single project, it is also 20 times smaller.

Another practical example that we cite to illustrate is the “monitoring of a toll road”.

In this lane with 14 tracks of 3 meters wide, it would take 14 VGA cameras with 640 pixels of horizontal resolution, since the minimum density in this case is defined as 145 pixels per meter (PPM).The minimum density calculation was done by dividing the horizontal pixel resolution by the horizontal field of view.If you used Full HD cameras with a resolution of 1920 pixels, you would only need 4 cameras to monitor the same area.

In this example, even though Full HD IP camera solutions are individually more expensive, they would be more interesting financially because of their technological reach.

There is a dilemma in the security industry: “Choose analog cameras because they have much lower costs or buy better quality IP cameras.”

We must emphasize that “every CCTV project requires a specific solution depending on its size”.