Rich provided a link to the Zerox PARC map viewer.This may be a bit off topic, but while digital charts are not really accessible to most paddlers today, they will be much more widely used in the future. GIS has been around for a while, and the technology to provide interactive access to digital maps over the web is pretty much in its infancy, but developing really fast. This discussion started asking questions about storage space for scans of paper maps, but the future lies with geographic information systems that store the individual features on the map digitally. A scan of a paper map yields only a degraded raster image of the original map at the scale it was originally drawn, and on the projection it was originally drawn - the real power comes when the features on the map are stored as a collection of vectors. In the vector model features that you see on a map are represented by a series of lines, points or polygons stored as a string of coordinates. If you imagine that you have say a paper chart showing an island coastline, most of the map is redundant white space, but you still have to store the whole chart when it is scanned. This is obviously a simple case, and compression software would also do a good job here, but in the vector model you only store the features you want (if our hypothetical island was square, this would require a polygon consisting of four pairs of co-ordinates, and a label identifying the polygon as the island). In general if your maps represent contiunously changing surfaces then raster scans offer good storage/access efficiency, but if you are interested in a collection of discrete features (such as islands, depth soundings, coastlines, roads) then vector systems win in effeciency and have the major benefits that you can select the features that you want to display, scale, project, and symbolise the map as you wish, and perform spatial analysis (accurately measuring area, distance, proximity, plot waypoints, create 3D terrain models etc etc etc). I'll stop rambling about this on this list ... but if anyone is interested in digital mapping, they could do worse than download the free web client/lightweight GIS from ESRI at: http://www.esri.com/base/products/arcexplorer/arcexplorer.html and have a play with some of ESRI's online map data. HTH Cheers Colin *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Fri May 15 1998 - 02:43:28 PDT
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