基于零水印和可逆水印的矢量地图多重水印算法

为实现对高保真矢量地图的版权保护，提出了一种基于零水印和可逆水印的矢量地图多重水印算法.该算法根据网格密度和属性熵值对矢量地图结点进行空间聚类，选取各集簇的密度中心点嵌入零水印，相对距离特征点嵌入可逆水印.其中，水印信息进行Arnold置乱以保障其安全性；零水印采用改进的零比特动态扩展方法，只对特征点的〖WTBX〗x〖WTBZ〗或〖WTBX〗y〖WTBZ〗坐标嵌入水印，在减少所需特征点数量的同时，提高对精度约减攻击的抵抗能力；可逆水印采用改进的差值扩展和平移算法，对不同差值区间的结点采用不同的水印嵌入方法，以提高水印容量，并通过〖WTBX〗x〖WTBZ〗或〖WTBX〗y〖WTBZ〗坐标独立嵌入水印信息，以降低水印对地图精度的影响.实验结果表明，基于零水印和可逆水印的多重水印方案能够较好地解决矢量地图精度和水印鲁棒性之间的矛盾，相对于单值水印算法具有更高的抗攻击能力，适用于矢量地图在高保真场合下的版权保护.

A Multiple Watermarking Algorithm for Vector Map Based on Zero-Watermark and Reversible Watermark

A multiple watermarking algorithm of vector map is proposed to achieve the copyright protection with the high-precision requirement. This algorithm uses two types of watermarks: zero-watermark and reversible watermark. First, the vertices are clustered according to the mesh density and the attribute entropy. The density center points are chosen to embed the zero-watermark bits, and the feature points within a relative distance to the center are applied to identify regions for the reversible watermark insertion. Then, the copyright watermark image is scrambled with Arnold transformation to improve security. And in the zero-watermarking scheme, the improved zero-bit dynamic extension algorithm is used to modify only the 〖WTBX〗x〖WTBZ〗 (or 〖WTBX〗y〖WTBZ〗) coordinate values of the center points, which will need less points to embed the copyright information and also can improve robustness against precision reduction. In the reversible watermarking scheme, the improved difference expansion and shifting algorithm is used. Different reversible watermarking formulas are applied to different interval points to embed a high capacity reversible watermark. Only the 〖WTBX〗x〖WTBZ〗 (or 〖WTBX〗y〖WTBZ〗) coordinate values of the feature points are hided copyright information to reduce the effect of the map on quality. The experimental results show that the proposed multiple watermarking algorithm can better solve the contradiction between vector map accuracy and watermark robustness.The multiple watermarking scheme based on zero-watermark and reversible watermark has better attack resistance than single watermarking scheme,which is eligible for copyright protection of vector map with high data precision requirement.