A novel method for multiple object tracking

Prof. B. Seth and his students of Department of Mechanical Engineering have developed a method for tracking planar movement of multiple objects from sequence of digital images using markers. This invention is useful for videographic study of motion in machines. Tracking of objects from a sequence of images requires automatic identification of the objects of interest and accurate location and orientation information of the tracked objects in each frame. The approaches used to accomplish this include recognition based on the radiation characteristics and reflective properties of the object itself or of a tag or marker attached to the object. Use of markers, when permissible, assist in tracking by facilitating automatic recognition of the objects. Traditionally symmetric markers are used.

There are several drawbacks in the traditional marker system. In multiple marker system there is the problem of marker correspondence (i.e., identifying the corresponding markers in successive image frames). This problem can become unmanageable when markers get occluded or go out of the field of view. Also a traditional marker yields accurate position information; however, for obtaining accurate orientation multiple markers are needed on the same body.

In this tracking system, a number of parts move in parallel planes and it may be desirable to accurately track the motion of some parts. Markers are afixed on the different bodies of interest. During motion the markers can get occluded.

Advantages of the system
- Marker detection is robust
- There is no added difficulty when more markers are used
- A single mark yields both position and orientation information
- Correspondence problem of a marker is eliminated by a unique tag
- Re-tracking of an occluded markers starts immediately after the marker comes in the camera view again