[Xastir] FGD files and Re: bounding boxes

[Tom Russo]

On Tue, Oct 07, 2003 at 12:00:03PM -0400, a Mr. Richard Feyler of Fort Lee, New Jersey <tyler at allisonhouse.com> writes 'Dear Rosanne Rosannadanna':
>
> Tom Russo wrote:
> [re picking average east/west/north/south values] 
> > I wouldn't.   [yadda yadda map collar yadda FGD yadda yadda]
> 
> Ahh..I understand..I think.
> 
> In the case of the Ohio and Kentucky geotiff files they have no collar (if
> I understand the term collar).  The ENTIRE image is the topographic data.
> So in theory there is no need to 'remove' any of the pixals.

If there's no map collar, there's no need for an FGD file --- Xastir only
uses the FGD file to get the bounding box so it can strip the collar away.

I'm  still very curious about that --- the UTM grid and the Lat/lon grid 
aren't aligned, and since the USGS file's pixel coordinate system is 
aligned with the UGM grid there should be *some* pixels that'd have to be 
chopped off if you put a rectangular lat/long box in there.  Unless you're
very, very close to the central meridian where there's hardly any distortion
in the projection.

> >
> > But I'm concerned about the actual values in Tyler's examples --- 
> 
> What can I say? ;)  Im using the geotiff fille: f48120a1.tif that was
> obtained from one of the URL's in the README.MAPS file. It works on my
> system yet the listgeo data that was posted here by me is exactly as you
> read.

Hmmmmm.  I'm curious about that.  Gonna have to look at that file myself.

I'm using maps from http://sar.lanl.gov/ which has a huge collection of
USGS files for New Mexico (complete with metadata both FGD and TFW, if you dig 
around the FTP server instead of the web interface), originally named with 
all the map collar info.  Pity they're all outdated by at least a decade or 
two :-( --- at least the topographic info is right.

-- 
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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