Research On Map Tiles’ Indexing And Compression In Network

Internet GIS has been widely applied, its development process involves geography, mathematics, computer and other fields of knowledge, including multi-scale terrain data representation, organization and management of massive image data, data compression and transmission, terrain visualization and texture mapping, digital city modeling, three-dimensional analysis and inquiry. (This paper analyzes the characteristics of contemporary Internet GIS technology, including the main platform of electronic map in network (Mapabc, MapBar, city8, etc.) and 3D Virtual Earth platform (GoogleEarth, WorldWind, pTolemy3D, etc.). In particular, this paper analyzes the map tile technology which they used, and proposes a novel map tile indexing algorithm.The Virtual Earth platform of network environment has a very large number of map tiles. In addition to an efficient tile indexing mechanism, it also needs to the implement of high compression and rapid decompression of the map tiles. The paper combines the JPEG2000 standard of wavelet transform and EBCOT coding algorithm, reaearches the implementation process of compression and reconstruction of JJ2000-based image tile.)This paper analyzed and summarized a lot of literature, combined with the development process of www.vrwuhan.com and VREarth Demo, and then took the map tile index and data compression technology as the skeleton to organize the entire PhD thesis. This study main include:1. Map tiles technology of contemporary Internet GIS.This paper studied the tiles’ organization and management in contemporary Web map and Virtual Earth platform tile, and also analyzed their tiles’ indexing rules and cutting algorithms. Internet GIS adopted the map projection conversion formula and spatial indexing algorithms to index the map tiles, and the tile cutting algorithm and indexing algorithm usually keeps consistency.2. Correlation of Map projection and the tile indexing algorithm.This paper mainly studied the application of map projection in tile index, including Google Earth used the Web Mercator projection, World Wind and pTolemy3D adopted Platte Carree projection. Map projection distortion would affect the Web map which used this projection as index algorithm. This paper also compared the different map deformation caused by the indexing algorithm and showed that the Web map should adopt different indexing algorithm according to the regional difference.3. A novel map tile indexing algorithm.Based on the research of different map projection and tile indexing algorithm, the paper propose a novel map tile indexing algorithm, which have discontinuous standard wefts and non-fixed rate. This method meets the conformal properties at the standard weft and reduces the distortion through discontinuous change the standard weft in large area Web map. This paper give a comparison in angel distortion、area distortion and length/width distortion between this algorithm and others. The results show that this algorithm is simple and efficient which has the characteristics of small deformation and suitable to be applied in world or regional Web map.4. Security policies of GIS based on tile technologyToday’s mainstream platforms of Internet-based electronic map using the rich client framework, this paper puts forward to the use of confusion and encryption of client-side code, digital watermarking, vector data encryption to enhanc system security from the point of view of the security in client code, map tiles and vector data. It specifically includes the Ajax code encryption and confusion, URL’s Block TEA encryption method, the digital watermarking of map tiles and self-defined public key encryption of vector data.5. Image tile compression.This paper analyzes a variety of image compression method and adopted JPEG2000 which based on wavelet transform as the image tile compression method. This method can maintain good image quality in the case of high compression ratio. This paper realize the compression/decompression process of image tiles based on JJ2000 software in network environment, and also give a performance comparison by changing the block size and the compression ratio. This paper uses the peak signal to noise ratio (PSNR) to conduct an objective evaluation of image quality after different compression methods.6. Design and implementation of Virtual Earth based on tile technology.Based on these studies, A prototype platform of virtual earth named VREarth Demo is constructed and developed by using Java+JOGL, map tile technology, mipmap technology and point-to-point texture mapping algorithm. Combined with the development process of VREarth Demo, this paper studies the structure and organization of terrain data、image tiles texture mapping and dynamic data scheduling based on View frustum. Finally, these papers give the basic methods of three-dimensional query and analysis in Virtual Earth platform.