在矢量地图中隐含水印信息,地图数据的质量往往由于水印的嵌入而受到影响。可逆水印技术(又称无损数据隐藏)具有完整恢复载体数据的能力,因而更加适用于矢量地图。基于差值扩大的思想,提出了一种应用于矢量地图的无损数据隐藏算法。算法根据矢量地图对数据精度的特殊要求提出了相应的水印嵌入条件,并通过修改地图中相邻顶点坐标间的差值来嵌入水印信息。水印的提取过程不仅能够得到隐藏信息,而且能够准确无误地恢复原始地图数据。采用两类地图进行实验,实验结果表明,算法在具有较强坐标相关性的地图中具有较高的嵌入容量,并且引入较低的扰动。算法的应用前景包括矢量地图数据的篡改鉴别、元数据格式兼容以及基于矢量地图的隐藏通信。

Embedding watermark in a digital vector map could generally degrade the quality of the map data.However,invertible watermarking(or lossless data hiding) is more appropriaue to vector maps for its ability to recover the original cover data.A lossless data hiding algorithm for digital vector maps based on difference expansion is proposed in this paper.According to the vector map's special requirement to data precision,an embedding condition is firstly presented.The watermark can be embedded by modifying the coordinate differences between the adjacent vertices and the original map can be recovered bit-by-bit after the watermark has been extracted.Two kinds of original maps are used in the experiments and the results indicate that higher payload and lower distortions could be achieved in the maps with higher correlated coordinates.The potential usages of the proposed scheme would include the map data authentication,meta data format compatibility,and secret communication based on vector maps.