Automatic drawing reader ‐ TOSGRAPH

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Abstract
A general‐purpose reader for circuit drawings (TOSGRAPH) has been developed. TOSGRAPH has the following features: (1) preprocessing is unified in a line segment tracking method and high speed and generality are realized by firmware control; (2) a drawing is described by a set of segments separated by feature points; (3) segments are grouped into candidate symbols by an estimation model; (4) symbols are recognized by matching with a model; (5) using hierarchical data (i.e., segment description ‐ thin line drawing ‐ original image), the feature measuring routines together with a blackboard system enhance the generality and processing speed; and (6) a flexible model is used to describe local geometric structure, connective relations and relative positional relations. A facsimile scanner is used for input and the image stored in the frame memory is processed. Experimental evaluation of symbol recognition results in a reject rate of 30/3972 (0.8%) and error rate of 22/3972 (0.6%). The processing time for the most common diagram of size A3 was approximately two minutes, confirming the pracical utility of the reader.

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