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.