The influence of thermal camera lens sizes on video analytics

February 15, 2015

 

 

Field of view, why is this important? The lower the mm (9mm) value of the lens, the wider the field of view will be, the SMALLER a person will be at a specific distance, which means that the amount of total pixels for a person will be lessor, than that of a lens with a higher (100mm) number.

Below is an indication of two different lens sizes, all cameras view the exact same 100m area and as important, the cameras are installed 5m above ground. The lower the lens number (9mm), the wider the angle of view, the smaller a person at the 100m mark and the opposite is true as well, the higher the lens number (100mm) the more narrow the field of view will be and the bigger the person will become.

Notice that the camera platform height is very important as well, as this do have a direct influence on the dead area underneath the camera. Good practice will be 4m above ground as to 5m above ground. Why is the dead spot area important? Best practice will be that all cameras are viewing in the same direction, to ensure that there is no dead area between sections. In short it means that the camera from the back covers the camera in front. Therefore, if the cameras are spaced around the perimeter in a circular fashion, each camera must cover and detect each space between camera platforms and the applicable dead area underneath the next camera, forming an overlap.

A 9mm lens vs 19mm lens

 

Thermal camera with 9mm Lens – Area View

 

 Thermal camera with 19mm Lens – Area View

 

 

 

The differences; the most important is the Pixels on a human target. The 9mm reads 11,8 pixels and the 19mm camera reads 52,7 pixels for a human target.

The real question is, will you be able to detect a human with 11,8 pixels and be able to determine if it is a human or an animal? No, you cannot as there is not enough information available. This is what you will see on a monitor. It is impossible for video analytics to distinguish between a human and animal successfully and to detect a human as a positive alarm.

 

9mm Lens – Monitor View

 

 

19mm Lens – Monitor View

 

 

 

Yes, you can detect with video motion detection as the principles between the two are vastly different. Video Motion detection algorithm analyse pixels and not the shape. What is the bottom line, plenty false alarms.

 

Video Analytics versus Video Motion Detection / Advanced Video Motion Detection

Video Motion Detection – looks at the change within a pixel on the screen, one pixel, two pixels or even 100 pixels, all are the same to the algorithm. The settings you do are directly "connected" to the pixels on the screen and the criteria set are compared within frames or fields of each image.

 

Video Content Analytics – Looks at shapes at various distances and the algorithm used is very different to that of video analytics. When used on perimeter detection systems, it is mainly used for accurate detection of humans entering an area.

 

False Alarms - This is the biggest enemy for surveillance monito-ring, especially when the weather is fowl and the rain and wind is heavy. Surprises came forth on various Estates where the Trustees and off-site monitoring companies received unexpected huge bills for data transmission, due to false alarms. The major triggers for false alarms are as follows:

 

Stormy winds – Video motion detection is more prone to false alarms as the algorithm is using pixel analyses and scene changes, and a moving platform will change the scene as it moves.

Video analytics is using picture analyses and it compares shapes in ensuring a real alarm. The scene change is not applicable in the movement of the platform as the background scene is not available for analyses, only when a human appears, will the shape be analysed. Non-Human movement – This can be animals, paper bags, small rats and mice, any heat signature moving across. It is important for the system to make that distinction between humans and the rest as Humans are the cause and reason for security systems. Hence the reason why you want to detect humans only.

 

The best Engineering Concepts to be used is: "To engineer for most conditions, within an affordable budget"

Camera Distances – ensure enough overlap to cover the dead zones underneath the next camera.

 

Object Size – ensure that the total amount of pixel count at the far end will be enough for climate changes.

Atmospheric Attenuation – ensure that the design allows for maximum probabilities and make sure that the customer is well aware of the shortfalls.

 

VMD versus Video Analytics – Familiarise yourself with the technology and what will be the nett effect on false alarms.

Camera Platform Height – ensure that all bends are considered, dead areas for each camera must be designed, minimize the dead zone underneath each camera.

Spares – Assure swop out stock.

 

Down Time – Assure minimal down time.

Technology advances – what is the difference in technology and why

Bandwidth – Edge recording is best, as you will have all recordings per camera at the camera, the video analytical processing happens at the edge and the bandwidth is minimized.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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