This flew under my radar for a while, and I figure some of you might care and not be aware: The USGS has been putting historic quads online for free download: http://store.usgs.gov
Lots more detail about the project that's doing this (it's being done on a state-by-state basis) here: http://nationalmap.gov/historical/ Of note, the maps seem to be generally available as GeoPDF rather than a more open format, however, there is support in GDAL (http://gdal.org/) for reading and converting these, in versions 1.8.0 and onward, and for using the (sometimes correct) embedded neatline data to crop them in versions 1.8.1 and onward. For you unix folks, assuming your map is $i, this usually works: gdalinfo $i|grep NEATLINE | awk -F= '{print "foo,WKT\nbla,\"" $2 "\""}' > $i.csv; gdalwarp -crop_to_cutline -cutline $i.csv -co "GDAL_PDF_DPI=250" -of GTiff $i $i.tiff (the FAQ says the maps were scanned at 250dpi, which is where the magic value above comes from) Xastir, the open source APRS system, now has courtesy of one of the developers a perl script which does a better job of converting to GeoTIFF, called geopdf2gtiff.pl Additionally, there's a free iOS app for viewing the GeoPDFs as-is, including georeferencing, called PDF Maps, if that's your thing. The only issue so far is the basic means of downloading, via a clickable, scrollable Google Map, provides little enough metadata that it's hard to know if you're getting an original from a date, or a photorevised, photoinspected, or otherwise not original. -- Derrick _______________________________________________ Geowanking mailing list [email protected] http://geowanking.org/mailman/listinfo/geowanking_geowanking.org
