Object Boundary Encoding — a new vectorisation algorithm for engineering drawings

Abstract

This paper presents a new engineering drawing recognition algorithm named Object Boundary Encoding (OBE). There are four steps in the algorithm: Object search, Boundary tracing encoding, Line approximation/arrowhead detection, and Arc construction. Drawing objects are searched by means of screen lines from the top-left corner of an image, in both left-to-right and top-to-bottom directions. During the tracing process, a set of pixels outlining part of the object’s boundary is analysed and a group of vector graphical elements is generated. Arrowheads can also be recognised. The Vector Perpendicular Bisector Tracing algorithm constructs arcs or circles based on the vectorised data. Definitions of Tracings and Tracing Series have been given in the eight-neighbourhood scenario. The algorithm significantly simplifies the vectorisation process — less than 50% of the object’s boundary is traced and more than 85% of the tracing time is saved. Java language is used to program, making the system platform independent and Internet accessible. The results from the sample tests demonstrate the capability of the system.