On Sat, 2008-01-19 at 11:27 -0700, Tom Russo wrote: > On Sat, Jan 19, 2008 at 12:12:22PM -0600, we recorded a bogon-computron > collision of the <[EMAIL PROTECTED]> flavor, containing: > > I am collecting the USGS topographic maps for my area and I am fortunate > > in that all except one were on Libre Map. The one that was missing, The > > good folks at UW Madison Geography Library had the paper map and scanned it > > for me. So now I have a 454MB scanned image in tif format. > > Nice. > > > Setting aside the fact that for one map, I would probably be better off > > just buying the proper Geotiff map files............ How do I go from this > > scanned image to a georeferenced digital file? Can I get there from here? > > Yes, but you need a tool that you probably don't have yet. There are two > tools of choice, GRASS (http://grass.itc.it/) and QGIS > (http://www.qgis.org/). > GRASS can do more with your data, but QGIS has a simpler georeferencing tool. > > GRASS has a learning curve as steep that looks a lot like Everest, QGIS is > a bit of a PITA to install but is comparatively easy to use.
+1. My opinion is a bit partisan, being a GRASS developer. ;-) GDAL should be all you need to convert file formats and do basic warping. It is very comprehensive, but lacks any GUI for GCP selection. > The trick is to carefully select points of known coordinates (in the > coordinate system of the map, which in this case are probably UTM) and give > the georeferencer the locations of those points in the image (the USGS uses > the 16 lat/lon graticule points). It then computes the affine transformation > from image coordinates to geographic coordinates and puts in the > necessary TIFF tags. GRASS can help here (i.rectify) to select coordinate pairs for warping. > It is a fairly involved process. I might be willing to do it for you --- I've > done it for a few other people on the list. It just so happens that this > weekend I've chosen to set aside a lot of time to do GIS work, so if you > put your data somewhere where I could grab it today, I'd take a look. Learning GRASS is a fairly involved process. It is generally geared toward research as opposed to ease of use. I new wxPython GUI is actively been developed and should be mature by GRASS v7. One of these days, I really need to put together some tutorials geared towards Xastir. I'm usually too busy on other projects. :( [snip] > Yes, it does. Georeferencing scanned images is tricky and time consuming, so > it is expected that few will want to do it. I've done it many times, and I > try to avoid doing it if possible. But with the right tools and a little > care it can be done. This largely depends on your image size (cell count), resolution and GCPs. It can take anywhere from a few seconds to hours. -- 73, de Brad KB8UYR/6 <rez touchofmadness com> _______________________________________________ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir