[Xastir] Re: Bounding boxes [Re: USGS maps no longer free]

[Tom Russo]

On Mon, Oct 06, 2003 at 07:09:55PM -0600, a Mr. Richard Feyler of Fort Lee, New Jersey <russo at bogoflux.losalamos.nm.us> writes 'Dear Rosanne Rosannadanna':
> 
> But I'm concerned about the actual values in Tyler's examples --- USGS
> maps are usually defined by very simple lat/lons --- for example, the
> 7.5-minute quads are aligned so that they have west boundaries of,
> say, 106d-105d52m30s for one map, 105d52m30s-105d45m for the next one
> to the east, 105d45m-105d37m30s for the next, etc.  That the
> re-projected corner points don't map to neat values concerns me ---
> perhaps they were projected back using the wrong datum?  The
> difference seems too great for that, though.

And now that I think about it, the data listed by listgeo are probably the
corner coordinates of the entire image, not the data for the map collar --- 
therefore making their use in an FGD file pointless.

The best way to get the bounding data that allows stripping off the
map collar would be to look at the map itself and pick off the
lattitude of the top and bottom neatlines, and the longitude of the
left and right neatlines.  Those will, in all probability, be
multiples of 7.5m, 15m, etc., depending on whether they're 1:24000,
1:100000, etc.

-- 
Tom Russo   KM5VY    QRPL #1592   K2#398    http://www.swcp.com/~russo/
Tijeras, NM DM64ux   SOC #236     AHTB#1    http://www.qsl.net/~km5vy/
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