Research On Zero-watermarking Algorithm For Vector Buildings

GIS vector map data is an important part of the geographical spatial data, GIS vector map data is an important part of geospatial data, is an important national basic geographic information products, has been widely used in various sectors of society. However, the digital storage mode of vector map data is convenient to spread and copy, but also brings hidden trouble to the copyright problem of vector map data. However, the digital storage mode of vector map data is convenient to spread and copy, but also brings hidden trouble to the copyright problem of vector map data. Digital watermarking technology is a new technology of copyright judgment and pirate tracing. It has been successfully applied to the copyright protection of spatial data through a lot of research and experiments.Buildings is an important and indispensable element of map expression, which has important application value in the fields of urban planning, government decision-making analysis and academic research. The vector buildings in the dissemination of data, copying process will inevitably be stolen, pirated. Therefore, it is urgent to study a measure to protect the copyright of buildings.At present, researchs of watermarking algorithm for vector building data are fruitful, but if the existing algorithms are transplanted to the building data, it may damage the accuracy of the building data or cause the change of the topological relations among the elements.In view of this, this paper uses vector zero-watermark technology, combined with the characteristics of vector building data and the shortcomings of the existing watermarking algorithm, the vector data watermarking algorithm for buildings is studied systematically.A several of research results and innovations are as follows:(1) Taking into account the traditional embedded watermarking algorithm has the problem of the loss of original data precision or the change of the topological relation, the paper proposes a watermarking algorithm based on zero-watermark.(2) Based on the analysis of the vector building features, a zero-watermarking algorithm based on the vertex vector is proposed. The design idea is: the original image is pre-processed by Logistic chaotic scrambling encryption technology; Then, the vertex vectors of the building is calculated, and the vertex vectors of all buildings are mapped into a feature matrix; Finally,the zero-watermark is constructed by XOR operation between the feature matrix and the scrambled watermark image.(3) Aiming at the shortcomings of the method proposed in (2), this paper proposes a zero-watermarking algorithm based on invariant moments and Hilbert permutation code. The design idea is as follows: Multiple zero-watermarks were constructed by using the Hilbert permutation code to enhance the performance of resisting cropping. The construction method for each block of zero-watermark was to be as follows. First, the Arnold method was employed to shuffle the original watermark image. Then the vector invariant moments of buildings were calculated and mapped to a binary matrix. Finally, an XOR operation was done between the shuffled watermark image and the binary matrix mapped by invariant moments of buildings, and the zero-watermark image was obtained.In this paper,we test the robustness of the two algorithms above. The experiments show that The zero watermarking algorithm based on vertex vector can effectively resist geometric attacks and a certain degree of cropping attacks; The zero-watermarking algorithm based on invariant moments and hilbert codes for buildings has a good ability to resist geometric attacks,a certain degree of cropping attacks, and an increase of 10% or less.