An Automatic Recognition System for Piping and Instrument Diagrams

This paper describes an automatic diagram input system which reads the handwritten piping and instrument diagram and recognizes the symbol, character, and line drawn on the diagram. The object is a handwritten diagram which is easily understandable by the knowledge of the designer under a very mild constraint. The symbols which are the object of recognition are of more than 200 kinds of various sizes. In addition, a large symbol with unspecified shape may be drawn, and there can be various kinds of lines. To cope with such complex diagrams containing a large amount of handwriting distortions, various diagram processing techniques are proposed. Examples are vector representation with a high accuracy, shaping of various distortions, and the two-stage segmentation, where line, symbol and character are separated hierarchically from the vectorized figure. Other examples are the symbol recognition combining a decision tree and pattern matching, and recognition dictionary based on automatic generation of distorted patterns. The developed diagram input system is a flexible system, in which new symbols can be additionally registered, and complex handwritten diagrams can be recognized. A test was made for the system using the actually written design diagrams. The result indicated a practically satisfactory performance, where the processing time is 3 to 8 min for an A3 sized diagram by a large-scale computer and the recognition rate is above 95 percent.