矢量地图水印归一化相关检测的可行性分析与改进

为了使矢量地图水印检测算法具有鲁棒性和运算简单，首先分析了矢量地图归一化相关检测算法的可行性：鉴于矢量地图图形的可嵌入水印长度较短，而且其DFT系数的幅度不能较好地满足高斯分布等原因，对不同图形的水印，采用归一化相关检测方法无法确定检测阈值，因此是不可行的，同时还分析了图形简化对水印检测的影响。为使水印算法抗简化，对几何失真鲁棒及减小运算量，提出了以图形的特征点的DFT系数幅度和相位作为水印嵌人域的方法，并提出了一种以提取水印与原始水印的相关系数作为检测值的实用的检测算法。实验结果表明，该算法是鲁棒的和可行的。

The Feasibility Analysis of Normalized-correlation-based Vector Maps Watermarking Detection Algorithm and the Improved Watermarking Algorithm

Because the watermark lengths of many applied vector maps' polygonal lines are short,and the Gaussian distribution is not suited to describe magnitudes of discrete Fourier transform coefficients for vector maps' polygonal lines to difference polygonal lines in the vector maps,the uniform threshold of normalized-correlation-based watermarking detection is hardly confirmed.In this paper,to improve algorithm's efficiency and be invariant to simplification,the discrete Fourier transform is only used for the feature points of vector maps.The watermarking algorithm embeds the watermarks by changing both the magnitudes and the phases of discrete Fourier transform mid-frequency coefficients for vector maps' polygonal lines.The correlation coefficient of the detected watermarks and the embedded watermarks is regarded as the watermark detection value.Given applied map data,computing results show that watermarks generated by this technique are robust,and the algorithm is fairly good in efficiency and Feasibility.