随着"天地图"等网站的建设与不断发展,地理信息资源的共建共享得到了积极推动。然而,网络环境下瓦片数据非法下载、违法使用等安全问题日益严重和突出,如何保护网络环境下瓦片数据版权是当前迫切需要解决的问题。为了节省存储空间,海量瓦片数据存储方式往往采用索引机制,这种存储机制与常见的图像、栅格地图等数据对水印技术的要求不同。本文首先着重分析了采用索引机制存储的瓦片数据特征及其对水印技术的要求;在水印信息生成方面,采用了m序列生成无意义水印信息,而在水印嵌入方面,提出了映射机制的瓦片数据数字水印嵌入算法,采用红色和绿色通道生成的映射函数,将水印信息嵌入到蓝色通道中,其中水印检测为水印嵌入的逆过程;最后,实现了水印技术的瓦片数据实时版权保护系统,并通过了实例验证。

With the construction and development of the sites such as the national "MapWorld" recently attracted a growing interest from the scientific and industrial communities, and mainly due to the large number of possible applications capable to provide map service, a crucial issue is arising when dealing with tile map web service publication in copyright protection. According to the need of having a confident and secure communication of tile map in the network environment, a novel mapping mechanism based on watermarking algorithm for tile map is presented here, in such a way that the invisible and robust watermark could be embedded effectively. In the network environment, the geographic data is usually stored in the form of tiles at service terminals, while indexing mechanism is often used as the storage method in order to save the huge amount of tile map. However, the tile map stored by indexing mechanism has different watermarking technology requirements with the common image and raster map data. So, the characteristics and requirements of watermarking technology of tile map stored by the indexing mechanism are firstly analyzed in this paper, which help to apply the watermark embedding and detecting. Then, the meaningless watermark information is generated by m sequence in the process of watermark generating. On this basis, the watermark algorithm based on mapping mechanism for tile map is presented. The watermark information is embedded into the blue channel using the mapping function generated by the red and green channels. The process of watermark detecting is the inverse process of watermark embedding. Finally, the real-time copyright protection system for tile map is implemented and verified experimentally. By experiments, it has been confirmed that the proposed watermark algorithm is robust to cutting, splicing, and additive noise. Besides, the embedding has little effect on the size of original tile map.