Citation
Sezgin, Tevfik Metin, Thomas Stahovich, and Randall Davis. "Sketch based interfaces: early processing for sketch understanding." ACM SIGGRAPH 2006 Courses. ACM, 2006.Summary
The important contribution by this paper is the Vertex detection algorithm. The paper re-establishes an earlier proved concept that speed of the pen reduces when a corner is reached while drawing a freehand sketch. This paper uses this approach and some more heuristics to find possible points which are corners. Mainly direction, curvature and speed graphs are used to determine the corners. The algorithm is as follows:
All the points which exceed certain threshold in the curvature and speed graphs are taken in sorted order. Then at each point a point is added to the corner set taken from either the curvature sorted points or speed sorted points based on an error metric.
Discussion
The error metric used in the corner finding algorithm is the sum of orthogonal distance squared between the actual sketch and the proposed hybrid fit. This is referred to as OSDQ in the paper. Curves are handled separately from lines and poly lines in the paper. Once the basic primitive shapes are recognized the sketch is passed through a beautification stage where slopes of line segments are altered from mid-point to match the actual drawn curve.
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