Constructing a Hierarchical Structure from Symbol Alphabets of Technical Line Drawings

This paper presents a method for analysing symbol alphabets of technical line drawings and finding their underlying structure, which is important for investigating (dis)similarity of different symbols. The proposed method constructs a hierarchical structure of a set of technical symbols. The method is based on agglomerative hierarchical clustering that uses either of two variants as a similarity measure: either geometric matching between symbols´ shapes, or an off-the-shelf shape descriptor. Identifying such a hierarchical structure of a set of symbols can improve symbol recognition / spotting systems, as it helps with scalability issues, and provides information on the degree of similarity among symbols, so that those systems can automatically adapt their parameter values for more accurate recognition. Our method has been tested on the symbol alphabet of the symbol recognition / spotting contest of GREC-2011, and achieved promising results.