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Unformatted text preview: EUROGRAPHICS Workshop on Sketch-Based Interfaces and Modeling (2008) C. Alvarado and M.- P. Cani (Editors) ShortStraw: A Simple and Effective Corner Finder for Polylines A. Wolin † , B. Eoff ‡ , and T. Hammond § Texas A&M University Dept. of Computer Science College Station, TX 77843-3112 Abstract In this paper we introduce ShortStraw, a simple and highly accurate polyline corner finder. ShortStraw uses a bottom-up approach to find corners by: (1) resampling the points of the stroke, (2) calculating the “straw” distance between the endpoints of a window around each resampled point, and (3) taking the points with the minimum straw distance to be corners. Using an all-or-nothing accuracy measure, ShortStraw achieves an accuracy more than twice that of the current best benchmark. Categories and Subject Descriptors (according to ACM CCS): I.4.6 [Segmentation]: Edge and feature detection 1. Introduction Sketch recognition involves understanding user-drawn strokes to allow for new human-computer interface tech- niques besides the standard mouse and keyboard. In an at- tempt to make human-computer interaction as natural as human-human interaction, we would like to build sketch sys- tems that allow people to draw as they would naturally with- out placing drawing constraints on the user such as drawing strokes in a certain order, drawing each primitive in a sep- arate stroke, or requiring the user to learn a set of prespeci- fied gestures (e.g. [ Rub91 ]). Researchers have begun to build free-sketch recognition systems in domains such as circuit diagrams [ AD04 ] or UML diagrams [ HD02 ]. A fundamental step in providing free-hand sketch recog- nition is allowing users to draw multiple primitives (such as a square drawn out of four lines) with a single stroke. Once a stroke is broken down into primitives, the primitives can be recognized with high accuracy [ PH08 ], and then recombined using geometrical rules [ AD04 , HD05 ] to allow for recogni- tion of naturally sketched shapes. Corner finding is the technique that involves splitting up † e-mail: [email protected] ‡ email: [email protected] § e-mail: [email protected] a stroke into primitives, such as lines and arcs. In polyline corner finders, such as the one presented in this paper, the corner finder finds the minimum set of points such that, if the polyline is split at those points, the resulting primitives would consist of only lines. Other uses for polyline corner finding abound, including node traversal - identifying which nodes a user purposefully selected. For instance, ShapeWriter, previously known as SHARK [ SZ05 ], allows a user to stroke out words on a vir- tual keyboard by drawing a stroke that connects each letter of the word in sequence; a corner finder could be used as a first pass to identify the letters (effectively, the corners) of the word....
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- Spring '09
- Distance, Metric space, Euclidean space, The Corner, Interest point detection