[Xastir] Re: Bounding boxes

[Tom Russo]

On Tue, Oct 07, 2003 at 04:35:18PM -0400, a Mr. Richard Feyler of Fort Lee, New Jersey <tyler at allisonhouse.com> writes 'Dear Rosanne Rosannadanna':
[his "b40.tif" file contains the geotiff data:]
> 
> Corner Coordinates:
> Upper Left    (5205005.699,4299352.261)
> Lower Left    (5205005.699,4253418.698)
> Upper Right   (5241025.879,4299352.261)
> Lower Right   (5241025.879,4253418.698)
> Center        (5223015.789,4276385.479)
> ---------------
> 
> What would the FGD file need to be?

Unfortunately, the FGD file is the least of your worries.

I visited the Kentucky site you point to (http://kymartian.ky.gov/) and 
see that the maps you are downloading aren't USGS maps georeferenced to the
UTM system with the NAD83 datum, but rather processed versions of the USGS
maps georeferenced to the Kentucky Single Zone State Plane system.  

The description of the files in the "Images/metadata" link is very thorough --
the maps are scanned at a resolution of 6.66667 feet per pixel, and put through
a transformation process to get them referenced to the state plane system.

While you could probably cobble together a set of options to proj4 or cs2cs
to do a conversion of coordinate values from the KSZSPS to UTM/NAD83, you're
still SOL when it comes to the map -- the transformation of the file will not
be a simple linear one (as a world file (tfw) would provide).  The KSZSPS uses
the Lambert Conformal Conic projection, not the Universal Transverse Mercator.

I don't think that Xastir is set up to use the projection library in its most
general sense --- you'd basically have to read in each pixel in the image,
get its state plane coordinate via (coord1=5205005.699+6.6667*pixel x coord,
coord2=4299352.261-6.6667*pixel y coord), then transform that state plane
coordinate to lat/lon appropriately, then plot the pixel.  As far as I know,
Xastir's only set up to do that transformation for UTM.  Doable, but not a
matter of just setting up an FGD file or tweaking the geotiff metadata.

Details of the Kentucky Single Zone State Plane coordinate system can be had at
http://giac.state.ky.us/kyspcs.htm

Sorry to bear the bad news.

-- 
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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