System for automatically digitizing engineering drawings

Abstract

An electro-optical computer-controlled scanning system adapted to accurately and rapidly digitize an engineering or other line drawing and to store the digital data, making it possible to reassemble a stored drawing with virtually the same fidelity as the original document. Use is made of a laser beam scanner having a wide angle deflector to sweep the beam in the X and Y directions to a degree sufficient to traverse the X and Y dimensions of the drawing being digitized and a narrow angle deflector for sweeping the beam in the X and Y directions to a degree sufficient to examine any selected region of the drawing. Information is extracted from the drawing in a two-mode procedure, the first carrying out a low-resolution survey along a narrow stripe extending in the X direction across the drawing to determine whether any drawing information is contained therein. If none is found, the scanner skips one stripe width in the Y direction to carry out a survey of the next stripe, and if information is then found, only the X coordinate thereof is noted and stored in the memory. When a survey of a given stripe results in a finding, the system then switches over to operation in a high-resolution line follower mode in which the X coordinate stored during the survey mode serves to ensure that all information contained in an existing drawing line in the surveyed stripe is indicated in only one output vector. In this mode, the system examines each drawing line to determine its radius of curvature and singularities (nodes, branch points and termini), each line being defined as a vector. During such tracking, the coordinates and number of members of each node and branch points are determined and stored. The survey and line following procedures are repeated until the entire drawing is digitized.