Reading 17: PaleoSketch: accurate primitive sketch recognition and beautification

Citation

Paulson, Brandon, and Tracy Hammond. "PaleoSketch: accurate primitive sketch recognition and beautification." Proceedings of the 13th international conference on Intelligent user interfaces. ACM, 2008.

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Summary

Paleosketch provides a a new low level primitive recognizer with ranking based system for providing different interpretations of the same sketch. The paper introduces two new features which very effectively distinguish between most primitive shapes. The primitive shapes considered in this paper are line, arc, circle, ellipse, polyline, helix, spiral, curve. A sketch could be recognized as combination or one or more primitives. The two new features are NDDE (Normalized distance between direction extremes) which is equal to the distance between the direction extreme points divided by the total stroke length. The other feature is DCR (Direction Change Ratio) which is maximum change in direction divided by average change in direction.

The paper also introduces a new ranking algorithm which provides ranking to different interpretations of the same sketch by adding the rankings of low level primitives. Line as rank 1, Arc 3, Helix, Spiral, Ellipse have rank 5.

Discussion

NDDE is usually close to 1 for highly curved shapes with direction changing in only one direction. For example circle, helix, spirals will have high NDDE. Whereas shapes like line, polyline where distance between direction extreme points is not the same as the length of the stroke the NDDE value is low. DCR is high for shapes where there is a sudden change in direction. So the maximum change in direction is high comparing it to average change in direction. So DCR will be high for polylines or shapes with sharp edges. DCR will be low for highly curved shapes as there is always slight change in direction and not a sharp one.