Computer Aided Design (CAD) has greatly raised the efficiency of engineering design and can be taken full advantage in developing the following series or improved models. Before CAD found wide use, many companies had kept a large amount of paper-based drawings. There exists great difficulty in maintaining and indexing them. Meanwhile, they cannot be simply reused in the following designs, resulting in a large waste of resources. Raster to vector conversion refers to scanning the paper-based engi...