Recognition of characteristic symbols in engineering drawings
Chan P. Lai, Rangachar Kasturi · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1992
An algorithm to recognize characteristic symbols in engineering drawings is presented. Characteristic symbols help in the classification of dimensioning text into one of the following four classes: linear, angular, diametric, and radial. Recognition of characteristic symbols is an important tool for the extraction of dimension-sets in a machine drawing understanding system. Text in drawings is used to provide dimensioning and tolerance information, and to describe part details such as material, finish, etc. A text/graphics separation algorithm followed by a post-processing step is used to separate potential dimensioning text from graphics. The characteristic symbol in each dimensioning text block is recognized by the algorithm described here. This algorithm includes extraction of end points and critical points for each character/symbol in the text block, and a rule-based recognition system based on simple heuristics. Experimental results are presented.