Co-authors Radu-Daniel Vatavu and Jacob O. Wobbrock and I have had a paper accepted to ICMI 2012, titled “Gestures as Point Clouds: A $P Recognizer for User Interface Prototypes,” in which we introduce $P, the latest member of the $-family of gesture recognizers. $P can handle multistroke and unistroke gestures alike with high accuracy, and remedies the main limitations of $N in terms of cost to store and match against all possible multistroke permutations.
Here is the abstract:
Rapid prototyping of gesture interaction for emerging touch platforms requires that developers have access to fast, simple, and accurate gesture recognition approaches. The $-family of recognizers ($1, $N) addresses this need, but the current most advanced of these, $N-Protractor, has significant memory and execution costs due to its combinatoric gesture representation approach. We present $P, a new member of the $-family, that remedies this limitation by considering gestures as clouds of points. $P performs similarly to $1 on unistrokes and is superior to $N on multistrokes. Specifically, $P delivers >99% accuracy in user-dependent testing with 5+ training samples per gesture type and stays above 99% for user-independent tests when using data from 10 participants. We provide a pseudocode listing of $P to assist developers in porting it to their specific platform and a “cheat sheet” to aid developers in selecting the best member of the $-family for their specific application needs.
You can find the camera-ready version of the paper here. Try out $P online in your browser here!