Complex transform for extracting circular arcs and straight line segments in engineering drawings

It has been shown that the Hough transform is effective in extracting straight lines and circles from an engineering drawing. However, this requires a 3-D parameter space and considerable computation time. It also requires repeated scanning to extract both the straight lines and circles by using separate algorithms. To overcome these difficulties, this paper proposes a new method which requires no space for accumulators and both the straight lines and circular arcs are extracted by using a single scanning and transform with the same algorithm. In this method, the straight lines and circular arcs on an x-y plane are extracted by transforming them into straight lines on a u-v complex plane and by detecting them. This paper describes the proposed algorithm and some applications of the method to architecture drawings. This method can be applied to drawings which contain no region where the same color is painted.