Short Straw

-Aaron Wolin, Tracy Hammond

COMMENTS

SUMMARY

ShortStraw is a simple and accurate polyline corner finder. The first step is to resample the points, with the interspacing distance of the resampled points being the diagonal length divided by a constant factor. The 'straw' at point i is then computed as the euclidean distance between points (i-3) and (i+3). Since straw lengths would decrease when the stroke bends around a corner, the point where minima is reached is returned as the corner. After this some higher level processing is done to remove false positives and find missed corners. First every consecutive set of corners goes through a line test. If two points fails line test, more corners are assumed to be lying between them. Threshold is then relaxed and minima of straw length is calculated from among all the points in the middle half of the stroke segment. Thus a new corner is found. This process is repeated until all the consecutive corners pass line tests. A collinear check is then run and if any three consecutive corners are found to be collinear, the middle corner is removed. The algorithm was tested and compared with other benchmark corner finding algorithms. It was by far the most accurate, having an 'all or nothing' accuracy of 74.1 percent.

DISCUSSION

Short Straw algorithms is a perfect example of how complexity doesn't necessarily correlate with accuracy. One limitation compared to other algorithms is that, it restricts itself to polyline strokes. I am just guessing, could we do a second derivative test, to differentiate curves from corners. If we could then we could use this algorithm to work for curved figures as well.