Segmentation of Online Freehand Stroke Using Geometrical Feature

This paper describes a new method for segmenting non-single stroke to 2D geometric primitives based on geometrical features, which are further interpreted as 2D line drawings. This method can support rapid segmenting and fitting of non-single stroke based on the polygonal vertices each stroke during its preprocessing stage. A processing stroke method based on polygonal approximation is used for online stroke compression. According to the convexity-concavity of a polyline which can represent the stroke, the stroke is classified convex stroke and concave stroke. For the former, an extraction principle of geometric feature is presented that stroke should be divided into sections as little as possible. Meanwhile, a corresponding algorithm is proposed based on this principle. For the latter, stroke need to be split into several convex strokes, then their geometric features are extracted. A new segmenting principle that the polygonal vertices should be most in per unit length of the stroke for that the concave stroke is split several convex strokes. Finally, a combination method of primitives is also introduced to eliminate over-segmentation. The proposed method has been tested with our stroke segmentation sub-system of online freehand sketch recognition system(FSR_JS), which is robust and easier to use by removing some limitations embedded with most existing sketching systems which only accept single stroke drawing. The test results showed that the proposed method can support freehand sketching based conceptual design with no limitations on drawing sequence and directions while achieving a satisfactory segmentation rate.