Reading 13: A domain-independent system for sketch recognition

Citation

Yu, Bo, and Shijie Cai. "A domain-independent system for sketch recognition."Proceedings of the 1st international conference on Computer graphics and interactive techniques in Australasia and South East Asia. ACM, 2003.

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Summary

This paper introduces a domain independent system for sketch recognition. There are many sketch recognition systems that use domain knowledge to identify shapes. This paper introduces a more general recognizer which can be used as a first step before applying any domain knowledge. The paper introduces the concept of feature area to match given stroke with primitive shapes. A given stroke is matched with all of the primitive shapes with feature area. If a match is found the stroke is classified as that primitive. If no match is found the stroke is recursively broken down into smaller strokes and the smaller strokes are then used to match to primitives

Discussion

Feature are is an important metric which can be used in many other ways. This is an effective way to recognize corners as we can divide the stroke into line segments using feature area and take the intersection of those lines as corners. This paper also applies direction graph to distinguish between lines, circles and helix. The direction graph for a line segment will be a line segment. The direction graph for a circle will be a straight line with slope = 2*pie/n, where n is the number of the points in the circle. If the total direction change is more than 2*pie the shape is more likely to be a spiral or helix.