New method for GIS vector data protection based on the use of secondary watermark

The paper provides a study on the watermarking method for vector map data based on a cyclic shift of a polygon vertex list. We propose a method modification allowing to automate authentication procedure, as well as to increase robustness against map contents modification. The main idea of the improved method is to use a noise-like image as a secondary carrier for a watermark, represented in the form of a bit sequence. An algorithm for construction of a noise-like image carrying a watermark sequence, as well as an algorithm for extraction of such a sequence, are given. An experimental study explores the information capacity of the carrier image and its robustness against quantization and interpolation noise adding, i.e. distortions simulating the embedding into map objects. The efficiency of the method is also demonstrated on real cartographic data. Conclusions comprise recommendations for rational choice of embedding parameters depending on the number of polygons on the vector map.