| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 104 === A group of characters are typically engraved on a computer aided design (CAD) model to represent a trademark, text notes, product model, etc. Such a group of characters are called lettering. Lettering recognition is a technique to recognize all kinds of characters on a CAD model. The objective of this study is to propose an automatic lettering recognition algorithm to recognize all characters from CAD models. The proposed lettering recognition algorithm is as follows. The virtual loops of a boundary representation (B-rep) model are recognized first; with the virtual loops, all extrusion features can be identified. Then, a series of rules are employed to separate “lettering” and “non-lettering” extrusion features. We propose a concept called “diversity” to classify and group extrusion features of similar geometry, and recognize all characters on the model. Once all characters are recognized, a character-removing algorithm can be implemented to remove all characters on the model. The feasibility of the proposed algorithm was tested by using 36 realistic CAD models, in which all characters on 34 models (94%) were successfully recognized, while some of the characters on 2 models were not completely recognized. A manual lettering recognition algorithm was also proposed to remove those characters which cannot be recognized by using the automatic letting recognition algorithm.
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