Using web grammar to recognize dimensions in engineering drawings

摘要

A web grammar based on arrowhead-match is described in detail and used to recognize dimensions in machine engineering drawings. According to the national standard GB4458-84 of People's Republic of China, the dimensions are classified into 27 patterns and 48 subpatterns whose mathematical descriptions are given. The concept of arrowhead-match is presented and 9 arrowhead-match patterns are summarized. Based on this web grammar, an algorithm for recognizing dimensions is implemented in C on a HP workstation, which can recognize 27 dimension patterns and 48 dimension subpatterns mentioned above.