A ReversibleWatermakering Algrithm for Vector Map Based on Angle Modulating

Abstract

There is a decline in the quality of the original carrier when watermarking is embedded using the traditional technology.It can not meet the requirement of high-precision occasion and under the circumstance when original carrier data can not be tampered.Because the technology of reversible watermarking can completely recover the data of original vector map,it is highly suitable for the copyright protection with the high-precision requirement,for instance,military maps and maps provide evidence for the court.At present,the researches of reversible watermarking algorithm for image field become more mature,while the current reversible watermarking algorithm for vector map mainly refers to the relevant methods of the image field,having not fully considered the organization characteristic of the vector data,so the robustness is not strong.Aimed at the above issue,this paper carries out relevant researches on the algorithm of reversible watermarking of vector map.Based on the invariance of the basic spatial relationship of the points in vector map before and after conventional map operation,a robust reversible watermarking algorithm of vector map is introduced to resolve the problem.Firstly,Douglas-Poiker algorithm is used to classify the points of each feature into characteristic points and none characteristic points.Then the angle,constituted by the lines of each none characteristic point and two adjacent characteristic points,is computed by this algorithm.Finally,the watermarking bit is mapped by the angle and the water information is embedded into none characteristic point by modulating the angle mentioned above.The experiment shows that the watermarking using this paper's algorithm not only has the transparency and reversibility of the general reversible watermarking,but also has good robustness to normal attacks,for instance,rotating,zooming,translating,feature ordering,graphic carving,data compressing,and graphic simplification,etc.