Semi-Fragile Watermarking For Automatic Localization Of Engineering Drawing Modifications In Collaborative Design

The Internet technology solved regional problems in collaborative design, making it more and more practical. Collaborative design not only improves the design efficiency, but also reduces the cost effectively caused by different regions. However, the development of collaborative design leads to large amount of engineering drawings which bring management troubles in the process of product design. Designers need to spend a lot of time on checking different versions of engineering drawings, to find partial changes in a large number of primitives. This problem seriously decreases the collaborative design efficiency and increases cost of human resource and money.At present, the common solution is to compare every single primitive in engineering drawings, and find changes between two different versions to realize version management. This method needs the original engineering drawing for reference. The original drawing and the new drawing needs to be referred respectively so that we can find out the additions, deletions and modifications in these two drawings. This solution is not convenient for its low efficiency.After analyzing the characteristics of semi-fragile watermarking, it is introduced to locate the modifications in engineering drawings. The semi-fragile watermarking is either robust or fragile. In this paper, we use the vulnerability to locate the modification in engineering drawings, and use its robustness to protect the copyright of engineering drawings. At the same time, this paper proposes a kind of watermark embedding algorithm based on virtual point in the process of watermark embedding. The virtual point is calculated in the embedding process, but it does not really exist in engineering drawing, thus the algorithm has good concealment and higher efficiency, but the primitive attributes will not change, only the relative position of primitives is modified. First, obtain engineering drawing primitives one by one; then, calculate the virtual point according to different types of the primitives; the watermark embedding process is done through using these virtual points, and the primitives are marked with watermark. If the engineering drawing is modified, a modified the watermark sequence can be extracted from the drawing, the original watermark sequence is restored according to watermark occurrence frequency and its relative position. Then compare the modified watermark sequence with original watermark sequence and locate the different watermark. Finally, judge the kind of modification and locate the modification in engineering drawing.The approach was implemented, and the experimental results demonstrate that the method is reliable and can accurately detect entities that have been modified, deleted and added.