Towards a 2D vector map with a feature nodes based watermarking method

Abstract

With a wide use of vector maps, the copyright issue is educing an increasing importance and attracting focus on the transmission and the exchange of the vector maps through a network environment. This paper discusses a feature nodes based watermarking method (FNBW) towards keeping robustness and high accuracy of digital map based on SVG and GML format. The digital map treats as a set of curves in the embedding algorithm, and each curve was divided up into several shorter curves under two given thresholds. And then a watermark bit combined with user certificate was embedded into each segment around the feature nodes with the maximum curvature in the segment series nodes. To extract the watermark, all watermark nodes were calculated and searched for in the watermarked map with the Watermark node Searching Algorithm by using the original map. Finally the method calculates the similarity between the original watermark bits and the extracted ones, and determines whether the watermark exists or not. As the experiment result shown, the method not only guarantees the accuracy of vector map but also possesses the good robustness, such as it gives 1.00 similarity under no attack or only geometric transformation with the map; And the anticopping ability is also good enough to give a more than 0.87 similarity for the map cropped 80%. In addition, the method has the full ability of anti-compression lossless methods and good ability to the loss approaches. And an experiment curve of the similarity threshold was given in the paper, which helped to control the anti-attack ability of the watermark and set parameters for an automatic procedure of watermark detection. © 2008 SPIE.