Citation:
Wolin, Aaron, Brian Eoff, and Tracy Hammond Proceeding SBM'08 Proceedings of the Fifth Eurographics conference on Sketch-Based Interfaces and Modeling
Link:http://dl.acm.org/citation.cfm?id=2386301.2386308&coll=DL&dl=GUIDE&CFID=550427120&CFTOKEN=14778671
Summary:
This algorithm is a very efficient algorithm for corner finding. The very first step is to re-sample the points. The re-sampling distance is calculated from the length of the bounding box diagonal divided by 40. The next steps involve two approaches- bottom up and top down. It also defines concept of straw which seems very intuitive.
The bottom up approach uses straws to calculate the distance between points pi-w and pi+w where w is a constant window defined. It is taken as 3 here. The median of all straw lengths is taken. A threshold value on straw distances is defined for classifying corners. It is empirically chosen to be as median*0.95.
Next step is Top down approach. It removes false positives and missing corners. A line test is performed to find missing corners. If the ratio of chord distance and total path distance lies below a threshold, then there exists a missed corner between them. If two vertices do not pass a line test, a new vertex is declared at the point where the mid point of two end points is. Also, a collinear test is performed between every three points. If the test passes, the center point is removed.
Discussion:
The best thing about this paper is its simplicity and the intuitive idea of using straws. I believe this idea comes straight from geometry and hence very easy to follow. The fixed window size if varied, I think can produce better results in case of corner finding as the space between the straws will increase when we move away from a corner much faster than when we move away from a line.
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