[Geowanking] Historical USGS maps
nelson at crynwr.com
Thu Jan 20 22:25:45 PST 2005
Derrick Brashear writes:
> 2) When they're done, I'd like to georeference them as GeoTIFF.
I'd like to see them not only georeferenced, but split into 200x200
tiles like at Terraserver. Then I'll add support to mapview, and we
can get Jef Poskanzer to add support for them to mapper.acme.com.
> Tom Russo, one of the developers of Xastir, suggested a path involving
> GRASS, and even applied it to 2 maps for me to try. The georeferencing
> isn't quite accurate, sadly, but it may be "close enough".
Yeah, even with projection differences, those maps were not produced
from aerial photos. So when you try to get them to line up with
modern maps, they just don't. They did a damn good job given the
technology of the day, but there's no substitute for working off
> Anyway, I figure the fastest way to georeference these involves
> machine-recognizing the neatline corners, and where they exist, the
> grid, and then applying rubber-sheeting over the available points. I'm
> wondering if any of you have suggestions for corner detection, or for
> that matter, suggestions for detecting automatically how much I should
> be trimming from the bottom of 2 joined pieces to get map data the
> whole width of the map and not part of an edge which was not scanned
> straight with respect to the scanner, or a black area where the 2
> adjoining pieces did not get scanned starting at the same "center".
Well, one of the things I want to add to mapview is the ability to
click on the modern map, and then click on the historic map in the
same place. Do that to get a handful of reference points, and then
click in the four corners of the historic map to get the bounding box
Tedious, yes, but you'd only have to do it once.
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