Research On Recognition Of Dash-dotted Line, Roughness Degree Symbols And Tolerance Symbols In Shape And Relative Position In Engineering Drawings

Recognition of engineering drawings concerns the application of multi-disciplines such as image processing, pattern recognition, and artificial intelligence, etc. The research on recognition of engineering drawings is important both on theory and practical application and it is one of key issues in the field of CAD. Many progresses in the area have been made, raster images can be partly transformed into vector data that can be reused in a CAD system. However, the vectorization results made by the existed recognition systems are mainly some isolated graphic units, such as lines, arcs, circles and characters. Such recognition results lack of high-layer logic relations as position, topology and structure relations and engineering semantic information and are far away from the intelligence comprehending and reuse of engineering drawings. Based on the vectorization results, further work should be done to realize better comprehending and reuse for engineering drawings and transform it from 2D to 3D. In this paper, the recognition technology of dash-dotted line, roughness degree symbols and tolerance symbols in shape and relative position are studied.Based on the detailed analysis of the existed dash-dotted line recognition methods, this paper used structure characteristics and syntax rule of line or arc type of dash-dotted line, based on the vector, and presented a recognition algorithm based on key graphics characteristics. This algorithm consists of two main steps: firstly finding a line or an arc, and make them as the key components of dash-dotted line;secondly according to the specific graphic syntax of dash-dotted line, leading by key element, step by step to search other composing elements. This algorithm gets rid of anciently mode which only recognized the line type of dash-dotted line, and has a good result of arc type of dash-dotted line, improved the universal capability. Aim at the arcs or circles which have smaller radius, a recognition algorithm for circle's centre line is proposed. This algorithm can better adapt to the condition that dash-dotted line was only a straight line, and improved the recognition rate for circle's centre line.For the roughness degree symbols, this paper studied a new vector based recognition algorithm based on key graphics characteristics and label character according to the structure characteristics and syntax rule of roughness degree symbols, The algorithm consists of three main steps: firstly finding the key component, secondly extending it according to the specific graphic syntax and finally judging the validity by characters. This algorithm can recognize basic roughness and circle type roughness symbol besides line type roughness symbol, and improved the entire recognition rate. With the aide of the assistant judging by characters, powerful adaptability and fault-tolerance ability have been gotten. Experimental results indicate that this algorithm has such advantages as a higher recognition rate, a simpler processing process and a higher speed.Analyzing the characteristics of tolerance symbols in shape and relative position in engineering drawings, a vector-based recognition algorithm based on key graphics characteristics and label character is proposed and implemented. This algorithm consists of three main steps: firstly finding the key component, secondly extending it according to the specific graphic syntax, thirdly judging the validity by characters. If this symbol is very complicated, it can also get the good result by using this algorithm. Experimental results indicate that this algorithm can get a higher recognition rate.All above algorithms mentioned have been programmed by using C++ language in the VC++6.0 system by author. In the practice testing the recognition results are satisfactory.