On Tue, 2008-06-24 at 16:56 +0200, Wouter Schaubroeck wrote: > Hey List, > > I have the following question: what kind of projection method does > geotools use, to create images of data? Especially if the data is in > wgs84, and the resulting image is also asked in wgs84. Or am i missing > something here?
Hey, Not knowing your level of knowledge, I'll answer at the risk of stating the obvious. WGS84 uses a geographic coordinate system, something necessarily defined in a 'globular' mathematical space (a closed, finite, unbounded manifold), therefore which cannot possibly be drawn on a flat screen without some kind of alteration, called a projection. So if you see WGS84 data on a flat surface, they have been projected and are no longer in 'WGS84'---the real question is what projection is used. If no specific projection has been defined, most modern tools unfortunately fall back on the mindless projection, often formally called "platte carré", where the long, lat values of WGS84 simply become X,Y on the surface. You can recognize the shape of the world in this projection since it is everywhere. Greenland, as is often the case, can serve as a visual check on the distortion of this projection. Google says: http://www.mapresources.com/results.asp?txtkeys=platte +carre&name=Platte%20Carre%20World Projections can be done with more care so as to preserve certain characteristics from the original data (while sacrificing others). Platte carré does not preserve any characteristics of interest, whereas other projections preserve shape locally, direction from a particular position of origin, OR relative areas, but not all at once. Hence, those who are projecting data rather than images generally use formal projections, area preserving, line preserving, or shape preserving according to their needs. Hope that helps, --adrian > I know that it's possible to ask the images in > cartographic projections (ex lambert 72), but what happens if this > isn't the case? > > thx!! > Wouter Schaubroeck > > Geo Solutions ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
