Segmentation and Recognition of Dimensioning Text from Engineering Drawings

Recognition of dimensioning text in engineering drawings is an essential part of the drawing understanding process, as this text provides the exact dimensions and tolerances of the object described in the drawing. We consider engineering drawings produced according to either ISO or ANSI drafting standards. Text segmentation and recognition are preceded by orthogonal zig-zag vectorization, arc segmentation, and arrowhead pair recognition. Initial textbox extraction is done by a region growing process, performed on text-wire candidates. On the basis of textbox context (neighboring annotation wires) the drafting standard is detected. Raw textboxes are divided into logical textboxes, which are further decomposed into basic textboxes. A neural network based OCR algorithm is applied to each basic textbox. Finally, the OCR recognition results are verified by using contextual information and comparing the results with the measurements made directly on the drawing.