Hi, I have a set of digital paper maps. See this example for original jpeg maps [0]. Now the original maps are not really very nice anyway when rectified because of the polygon hatched styling.
I then combined all the maps using both VRT [1] and one big GTiff [2]. The rendering quality is just as bad especially when zooming to full extent. When I added external overviews using the Raster > Build Overview tool, the overviews are much worst when zoomed to full extent both in the VRT [3] and GTiff [4] Any idea why? I think the best option eventually is to digitize (by hand since its hard to automaticaly extract polygons due to the hatching) rather than using the images as underlay. I'm puzzled by the bad result of the overview rendering. Using QGIS 1.7, GDAL 1.8 [0] http://dl.dropbox.com/u/2096185/qgi_overview_degradation/original_jpg.png [1] http://dl.dropbox.com/u/2096185/qgi_overview_degradation/vrt.png [2] http://dl.dropbox.com/u/2096185/qgi_overview_degradation/tif.png [3] http://dl.dropbox.com/u/2096185/qgi_overview_degradation/vrt_ovrvw.png [4] http://dl.dropbox.com/u/2096185/qgi_overview_degradation/tif_ovrvw.png -- cheers, maning ------------------------------------------------------ "Freedom is still the most radical idea of all" -N.Branden wiki: http://esambale.wikispaces.com/ blog: http://epsg4253.wordpress.com/ ------------------------------------------------------ _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
