期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2002
卷号：XXXIV-6/W6
出版社：Copernicus Publications
摘要：The Internet is awash with a wealth of maps and spatial imagery, some crude and basic, some refined and highly developed. The availability of maps and imagery of Africa over the Internet and the sophistication of the methods used to display such spatial images will almost certainly increase and so continue to revolutionise the way maps and remotely-sensed images are marketed and delivered worldwide. With increasing Internet access and faster bandwidths, Africa is well-placed to benefit from Internet Mapping technology. There are three possible options for delivering and viewing maps and imagery over the Internet static, animated and interactive. Static mapping and imagery Web sites allow the user to access fixed raster maps and remotely sensed images for viewing and downloading over the Internet. Static maps and images are usually generated by raster scanning or direct vector-to- raster conversion. Animated Web sites allow the user to view maps and imagery dynamically as the content changes, utilising animated Gif89a file format, delayed refresh and multi-media video technology. Interactive Web sites allow the user to zoom or pan high resolution raster or vector images and to make decisions on map content or design with the use of plug-ins, applets, scripts or specialist GIS Web servers. The display of large high resolution raster map files, aerial photographs and satellite images has until recently, proved to be an impractical option on desktop computers and Internet browsers, due mainly to the massive file sizes encountered. Image compression techniques used in gif and jpeg raster file formats are well established, however they do not match the impressive lossless compression ratios of 20:1-50:1 being offered by the latest Discrete Wavelet Transformations which are now revolutionising the way maps, aerial photographs and satellite images can be delivered over the Internet or on the desktop. The two main developers of wavelet compression technology for the mapping and remote sensing industries are LizardTech with their Mr SID (Multi-resolution Seamless Image Database) range of products and ERMapping with their ECW (Enhanced Compression Wavelet) products. Both Mr Sid and ECW offer a range of compression / decompression and viewing software options either as stand alone desktop applications or free plug-ins for Internet browsers and GIS / mapping software. This paper will review and illustrate current Internet Mapping technology utilising example maps and images of Africa and in particular Tanzania
