Recognition of Mechanical Drawings. (2nd Report). Separation and Recognition Algorithm for Line Elements Based on their Geometrical and Topological Features.

This paper presents a method of bottom up processing for separating all drawing elements in a whole recognition system for mechanical drawings. This is the second report succeeding the first one which mainly dealt with a method of separating thick- and hair-lines using line width and the structural representations of thick-lines. However, this methed can be applicable only to the drawings which keep the JIS drawing rules vigorously, especially about line width. In this paper, we propose another approach which can be applicable to wider range of mechanical drawings. The method mainly utilizes geometrical and topological features and uses line width additionally. The whole algorithm is shown to separate all line elements, i. e., dimension lines, projection lines (temporarily separated), center lines, hidden outlines, leader lines, visible outlines, projection lines (finally separated) and characters, in this order. Some experimental results applied to sample drawings in a book of mechanical drawings are finally shown.