Sketch Based Interfaces: Early Processing for Sketch Understanding

Tevfik Metin Sezgin, Thomas Stahovich, and Randall Davis

Summary

Sezgin et al. present a corner finding algorithm based on calculated curvature and speed data of a stroke. The approach involves plotting a curvature graph and a speed graph. An average-based theshold is used on each the graphs to avoid problems of a fixed threshold. The algorithm generates a hybrid fit to determine which points of the stroke are corners. This process consists of three steps: computing vertex certainties, generating a set of hybrid fits, and selecting the best fit. The hybrid fit with the fewest vertices and error below a specific threshold is the selected best fit.

Discussion

The use of curvature and speed information seems critical to helping find corners, especially when extending a polyline approach to look at strokes with curves as well. While Sezgin reports high accuracy in this approach, his accuracy is based soley on whether or not the correct corners were found, and doesn't address additional found corners that are not correct. Others have reported that his accuracy decreases greatly when using an "all or nothing" accuracy. This is not to say that Sezgin's algorithm is in effective, but that further research needs to be done to address this issue.