There is an improved version of this algorithm called $Q Super-Quick Recognizer [0] which allows multi-stroke gesture and drawing stroke in different direction, a demo I implemented before [1]
The $1 algorithm could be used to implement gesture typing keyboard like SwiftKey/Swype, where direction matters, eg another project of mine [2]
[0] http://depts.washington.edu/acelab/proj/dollar/qdollar.html