Strict constraints on 2D primitive pairs for engineering symbol recognition: Theory and application

Geometric constraints on the line-line pair, line-arc pair and arc-arc pair are proposed. The constraints are able to encode the geometric relations between lines, arcs and circles. A geometric proof is presented to demonstrate that the constraints are stable under translation, rotation, uniform scaling or reflection of the primitive pairs. Based on the constraints, an algorithm for recognizing symbols in drawings is developed. Experimental results show that, compared with three other methods, our method can distinguish more primitive pairs and has higher accuracy in engineering symbol recognition.