PaleoSketch: accurate primitive sketch recognition and beautification

Paper
Paulson, Brandon, and Tracy Hammond. "PaleoSketch: accurate primitive sketch recognition and beautification." Proceedings of the 13th international conference on Intelligent user interfaces. ACM, 2008.
Publication Link:http://dl.acm.org/citation.cfm?id=1378775

Summary

The work presents a primitive sketch recognition and beautification system known as paleosketch. The idea behind paleosketch is to recognize sketches based on a bottom up approach of identifying low-level primitive shapes as components that combine to form a recognizable high-level shape. The second stage of this system is to return a beautified version of the recognized shape.
To achieve this, they develop two new features in the pre-recognition stage: the normalized distance between direction extremes (NDDE) and the direction change ratio (DCR). The former computes the the difference between the point of highest direction value (ie dy/dx) and the lowest value normalized by stroke length.This feature is able to identify curved shapes (high NDDE values) from poly-lines which have lower NDDE values. The latter DCR value is computed as the maximum change in direction divided by the average change. This value is higher for a poly-line, whereas curves have a much lower value in comparison.

Discussion

Pros

The work is very thorough in presenting the details involved in the implementation.
They introduce two novel features for sketch recognition.

Cons.

A lot of thresholds are used, which are based on training data. Which seems like a lot of tuning. I would like to see how their results change as these different parameters are adjusted.