[Xastir] data in .fgd file for geotiff map

[Curt, WE7U]

On Tue, 6 Apr 2004, Wendell Turner wrote:

> I'm using FAA sectionals from
>   http://aviationtoolbox.org/raw_data/FAA_sectionals/current/
> which are (rather large) GeoTiff files.  I have them as maps to
> xastir, and the longitude seems to be right on, but the latitude
> seems to be about 1.4 minutes off.
>
> The site these are from has a .tfw file (for each .tif file)
> that contains
>   63.753925000000002
>   0.0
>   0.0
>   -63.753925000000002
>   -378078.33973611565
>   -18298.274814258024
> (there are no .fgd files at the site).  Can this be converted to
> the .fgd file?

No.  Not directly anyway.


> It looks nothing like what mapfgd.pl produced for the map, which
> is
>   1.5.1.1   WEST BOUNDING COORDINATE:  0.000000
>   1.5.1.2   EAST BOUNDING COORDINATE:  0.125000
>   1.5.1.3   NORTH BOUNDING COORDINATE:  0.000000
>   1.5.1.4   SOUTH BOUNDING COORDINATE:  -0.125000
> so I suppose it is something in this file that is incorrect.

mapfgd.pl is only for USGS-named geoTIFF topo maps.  It doesn't work
on anything else.

Xastir was written with the USGS topo maps in mind originally.  The
.fgd files are used only for cropping off the borders.  All of the
other parameters that Xastir uses come from the geoTIFF tags that
are inside the graphics file.  If you set the corners in the 4-line
FGD file to the corners where you want to crop off the image, it
might just work for you.

What do the geotiff tags inside the file tell you?  Are they in
NAD27, NAD83, or WGS84 datum?  If the parameters don't match closely
to a USGS geotiff file, Xastir may not work perfectly with the file.

--
Curt, WE7U			    archer at eskimo dot com
Arlington, WA, USA		http://www.eskimo.com/~archer
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