Activity Recognition using Visual Tracking and RFID (Krahnstoever, et al – 2005)

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Blogs I Commented On:

• Brandon Paulson
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Summary:
This paper discusses how RFID technology can augment a traditional vision system with very specific object information to significantly extend its capabilities. The system’s components consist of two modules: tracking and RFID tag tracking. For the former, human motion tracking estimates a person’s head and hand location in a 3D world coordinate reference frame using a camera system. The likelihood for a frame is estimated based on the summation of the image over the bounding box of either the head or hand in a specific view. The tracker continuously estimates proposal body part locations from the image data, which are used as initialization and recovery priors. The tracker also follows a sequential Monte Carlo filtering approach and performs partitioned sampling to reduce the number of particles needed for tracking. For the latter, the RFID tracking unit detects the presence, movements, and orientation of RFID tags in 3D space. An algorithm for articulated upper body tracking is given in the paper. Combining both trackers gives an articulated motion tracker, which outputs a time series of mean estimates of a subject’s head and hand locations in addition to visibility flags that express whether the respective body parts are currently visible in the optical field of view. By observing subsequent articulated movements, the authors claim that the tracker can estimate what the person is doing. These interactions were encoded as a set of scenarios using rules in an agent-based architecture. To test their system, a prototype system was created consisting of a shelf-type rack made to hold objects of varying sizes and shapes. When a person interacts with RFID-equipped objects, the system was able to detect which item the user was interacting with (difficult for a vision-only system) and the type of interaction the user was doing to the object (difficult for an RFID-only system).

Discussion:
I was familiar with RFID tags from other applications, but I didn't know or think that could be used for haptics. That's why I wasn't too sure at first about the relevance of this paper to our class. Josh P. fortunately enlightened our class that RFID tags can nicely supplement the existing devices we have in the labs. While the potential is definitely there for the type of things our class is doing, the paper itself was pretty poor in presenting that potential. Most of that can be attributed to a weak example application which, of course, happened to have no numerical results to speak of. But that's been like the norm in the paper's we've been reading.