In most security situations, you need to keep track of where objects and people travel within a facility. Object-based analysis first segments a particular object in a camera view and then tracks it as it moves around within that view or from one camera to another. This is particularly useful for monitoring ingress and egress to a building or flagging suspicious packages in high traffic areas.
â€¢ Exposing perimeter breaches - Whether you call it a digital fence, a tripwire or a virtual fence, an object-based IV system lets you designate a line or area in a facility where access control breaches may occur. If an object goes past that line in a particular direction or an object enters or leaves a certain area, the system can send an alert to security personnel.
â€¢ Spotting abandoned objects - With heightened concerns about explosives left behind in bags and packages, many public transportation facilities, government buildings and retail malls deploy object-based analysis as a critical component of their surveillance systems. The IV application watches an area, keeping track of all the objects in it. When a previously moving object becomes stationary and stays that way for a certain period of time, the system raises an alert and shows the security system operator the object of concern.
â€¢ Detecting loitering - A loitering function tracks the amount of time and the number of people who linger in a certain area, such as a parking lot or in front of an automatic teller machine, which could be an indication of malicious intent.
Techniques for tracking people and objects
There are a number of ways to track a particular person or object moving in a camera's view. An operator can select the person or object of interest or program the system to make the choice.
â€¢ Using a pan/tilt/zoom (PTZ) camera - A PTZ camera can automatically lock onto a person and keep that individual in sight, including zooming in to give security staff a better view. Once the person moves out of range, the camera finds another moving object to track. The application is useful in low-traffic environments like parking lots and hallways since it provides a view of the object without operator intervention. Some PTZ tracking systems, however, get confused as to what they should be tracking if more than one object appears in the camera view.
â€¢ Using multiple cameras - One of the most difficult IV applications to automate is multi-camera people tracking, also called camera hand-offs. This technique helps security personnel keep a particular suspect in constant view, even in a location or facility covered by a large number of cameras, by handing off the tracking of a particular object from one camera to another.
Pointers for real-world deployment
To ensure that your object-based intelligent video application works accurately, there are a couple of factors you should address:
â€¢ Camera placement. For people counting, you should place the camera immediately above the entrance. The height depends on the optic lens you choose and the width of the entrance. The size of the person passing under the camera must be larger than 6 percent of the camera's total horizontal field of view. It is important to choose a camera with sufficiently high resolution to enable surveillance operators to clearly distinguish the people passing under the camera.
â€¢ Field of view. For single-camera tracking applications, use a camera with a wide field of view. This allows a security operator to track a person of interest over a broader area. Network cameras with a 140o field of view will even allow an operator to zoom into a particular area without losing video quality. Cameras with a 360 o field of view many seem well-suited to this type of tracking, too. But generally they prove impractical because their resolution is often too low to provide sufficient image detail.
As was mentioned in last month's article on pixel-based intelligent video, no IV application is infallible. But with careful adherence to some best practices, your installation can achieve between 90 and 95 percent accuracy.
About the author: Fredrik Nilsson is general manager of Axis Communications, a provider of IP-based network video solutions that include network cameras and video encoders for remote monitoring and security surveillance. He can be reached via email at firstname.lastname@example.org.