Watermarking Vector Maps Based on Minimum Encasing Rectangle

Vector maps are valuable asset of geographic data producers. In this paper, we propose a new watermarking algorithm for vector maps based on Minimum Encasing Rectangle of the map. Minimum Encasing Rectangle is employed to keep synchronization when watermarks are embedded and detected due to its geometry invariance property. After gridding the map into cells based on MER and constructing grid weight array, spatial data is converted into frequency domain with DCT. Watermarks are embedded in DCT coefficients with middle-frequency. By slightly modifying the distribution of vertices, a watermarked map is generated. Experiments show that our watermarking algorithm is robust against rotation, scaling, translation attacks. Furthermore, the robustness of the algorithm against geometry attacks stays invariant with the different magnitude of the translation offset, rotation angle and scaling factor.