Reading 14: ShortStraw: A Simple and Effective Corner Finder for Polylines

Citation

Wolin, Aaron, Brian Eoff, and Tracy Hammond. "ShortStraw: A Simple and Effective Corner Finder for Polylines." SBM. 2008.

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Summary

This paper introduces a novel way to find corners in a sketch. This paper doesn't use any speed or direction information to find corners. The basic idea is to first re sample the sketch into points which are equidistant. Then take a window of points (w = 3) on left and right of a point. We calculate the length of the line segment joining the points n-w and n+w. The intuition is that this length will be smaller at the corners. All the lengths are calculated and 0.95 times the median length is taken as the threshold for the corners.

Discussion

This algorithm is a two step process, in  the bottom up step corners are found using the straw lengths. In the top-down step further calculations are done to find any missing corner or any special case. Each found corner is checked to be forming a line. If the corners don't pass the line test, then they may be removed. Then each three pair of corners are passed through co-linear test. If three corners are co-linear and each passed the line test then the middle corner is irrelevant. ShortStraw performed significantly better than previous algorithms from Sezgin and Kim and Kim.