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Originally Posted by tikku.dk Those type of cameras are installed in palayam, near to AKG centre, Thampanoor, Killippalam and atleast in 4 places in karamana balaramapuram widened road. By the way how will those cameras detect speed? |
Speed detection systems based on multiple principles. I'm listing down two of the most commonly used systems nowadays.
Type 1: Imaging Based
These cameras are capable of
High End Image Processing in real time wherein they detect speed using a simple principle. The steps seem to be comprehensive but take place in the backend with the blink of an eye.
A video in technical terms is simply a slideshow of multiple photos displayed at a high pace. Therefore, the video quality of a camera is determined with the pixel density it is sensitive to (resolution) and number of photos it can take within a second to make the video look high definition (fps).
So, when we talk of a single picture at an instant in a video, it has multiple pixels in it. The program analyses the very next picture to the one chosen and then picks up multiple frames from a video to compare the change in pixels w.r.t. the previous ones. There can be multiple objects possible:
- Some can be stationary (eg: the road, a sign board etc.)
- Some can be moving regularly (vehicles, people etc.)
- Some can show slight movement or not move in a longer period of time(eg: tree leaves, a parked car)
After analysing a few pictures in real time, the pixels which don't change are treated stationary along with the ones which have slight movement.
The pixels which have completely changed over the time are treated to be objects in motion. The image processors are able to draw a rough outline of all the changing pixels. (Including the car, its shadow etc.)
Once these changing pixels are highlighted, the first (x1) and last (x2) frame with the highest rate of change of pixels are marked by the system and treated as reference frames.
Usually speed is Distance per unit time but here, a camera (until its very advanced) can't measure the distance. So, the distance between the first changed pixel in x1 and the last change pixel in x2 (as per the camera resolution) is divided by time between x1 and x2 (as per the corresponding timestamp) ,thus treating it as the average speed of a vehicle.
Pros:
- Precise and can be used in any type of environment.
- Effective at night too.
- Can deliver an automatic challan by reading the HSRP.
- Can issue challans for 2 wheelers not wearing helmets and many other intelligent features
Cons:
Type 2: IR based IR based systems coupled with regular High-Res CCTVs act as two pairs of IR based transmitters and receivers placed at fixed distance.
When a moving object crosses the first IR sensor, the system is triggered to begin the lap timer and on crossing the second sensor, the lap timer stops. As the distance between the two points is fixed and the elapsed time has been recorded, the average speed can be calculated using distance/time. (based on drag race lap timers)
If this average speed is within the limits, the CCTV carries on to record regularly but if the average speed is out of the limits, then the loop recording mode is triggered wherein the DVR picks up the recording from those instants automatically and registers it to be the special
challan case.
Pros.:
- Low cost
- Can easily be bypassed (a boon for some, maybe
)
Cons:
- Placement of IR transmitters on the road: Can't be placed parallel to the vehicle and have to be placed somewhere high on the road to detect it using the car's top view.
- Placement of IR receivers: Generally in these kind of systems, the road tarmac/asphalt being black acts as a constant receiver thus absorbing IR all the time but if a car crosses, the rays would bounce off the car and trigger the system
- Type of road: Can't be used on light coloured, tiled or cemented roads because of the lack of a natural IR receiver
- Less reliable: At times turns out to be a boon for black coloured cars
- Can't work in low light conditions as they experience interference from automotive lighting
- Requires extra systems for reading HSRP thus being a semi-automatic system.
Drive safe
Vaibhav