Reading 15: Revisiting ShortStraw: improving corner finding in sketch-based interfaces

Citation

Xiong, Yiyan, and Joseph J. LaViola Jr. "Revisiting ShortStraw: improving corner finding in sketch-based interfaces." Proceedings of the 6th Eurographics Symposium on Sketch-Based Interfaces and Modeling. ACM, 2009.

PDF

Summary

This paper introduces a new method for corner finding called IStraw. This method tries to improve the existing method called ShortStraw. The two major shortcomings that the authors discussed in ShortStraw are not using direction information which is already present to enhance the corner finding algorithm and ShortStraw cannot handle curves and works only for polylines. The authors also argue that there is no straw length for the first w and last w points where w is the window used to find the straw lengths.

Discussion

The authors introduces formulas for finding the straw lengths for the first w and last w points. The idea is that missing straw lengths for these points could lead to some missed corners. Instead of the fixed empirical threshold in ShortStraw, IStraw uses a dynamic threshold. The paper also introduces a novel way to differentiate between a polyline intersection and a curve. The idea is to take equidistant points on either side of the detected corner. In a polyline intersection as these points come closer to the corner the angle doesn't change. Whereas in curves as these points come closer to the detected corner the angle increase. This finding is used to classify an earlier detected corner to be false. Overall IStraw improves all or nothing accuracy over ShortStraw and previous methods.