COMPUTER VISION, GRAPHICS, AND IMAGE PROCESSING 49, 379-397 (1990) NOTE Engineering Drawing Processing and Vectorization System VIJAY NAGASAMY* AND NOSHIR A. LANGRANA Department of Mechanical and Aerospace Engineering, Rutgers, The State University of New Jersey, P. 0. Box 909, Piscataway, New Jersey 08855 Received October 27, 1987; revised April 12, 1989 This paper presents the methods for preprocessing and vectorking scan digitized images of engineering drawings for transferring the resulting data to commercially available CAD/CAM systems. The preprocessing steps include noise removal, void filling, image segmentation, line thinning, and contour extraction. Algorithms for raster-to-vector conversion capable of recog- nizing and fitting straight line segments, circles, arcs, and conic sections are presented along with results obtained from images of machine drawings. % 1990 Academic PESS. IX. I. INTRODUCTION One of the major components in any industrial design and production activity is proper technical documentation and in this context, engineering drawings play a very important role. Being graphical in nature, these drawings represent complex information in a concise manner. Surveys [l] have indicated that a typical project of reasonable magnitude could consist of well over 30,000 drawings as part of the documentation, with design lives ranging from about 10 to 40 years. In fact, recent studies [2] have shown that there are over 2 billion active drawings in the United States alone. Most companies file a large number of such drawings in their vaults, and roughly 20% of these are active each year. A large number of man hours are expended in creating updating and maintaining these drawings using conventional drafting techniques. Computerized design/drafting systems provide an efficient means for creating, storing and updating engineering drawings, yet these benefits are not available to the multitude of existing paper drawings due to the absence of a convenient bridge between the manual and the computerized world. Manual entry of drawings into a computer database is a slow, expensive, and tedious process, and hence one feels a need for an automated system that would scan the drawing and convert it into a format suitable for further processing by a computer. However, automated recognition and understanding of engineering drawings is by far a more complex task requiring the capacity for visual perception and intelligent interpretation. Some of the recent efforts aimed at understanding engineering drawings, include works by Haralick and Queeny [3], Fukada [4], Lin et al. [5], Sato [6], and others [7, 81. This paper presents the implementation of a system for processing scan-digitized engineering drawings, wherein the line structures are fitted with CAD primitives *Currently at LSI Logic Corporation, 1551 McCarthy Blvd., Milpitas, CA 95035. 379 0734-189X/90 $3.00 Copyright 0 1990 by Academic Press. Inc. All rights of reproduction in any form resewed.