[Xastir] Xastir is running on OSX

[Tom Russo]

On Thu, Apr 16, 2009 at 07:18:27AM -0500, we recorded a bogon-computron collision of the <gerry.creager at tamu.edu> flavor, containing:
> At the risk of harassing the core developers, I do think we should read 
> a .tfw, AND the geotiff header natively.  That's a weak spot in native 
> image use.

Since the .tfw file contains only image->PCS coordinate conversion information,
without any information about what the PCS is, that could be a problem.  One
would have to rely on the user only presenting Xastir with Tiff+TFW that are
always in one specific coordinate system, or get some non-standard way of
defining the PCS of the image.  The odds of that condition being
met are slim, and therefore supporting such an option would merely be opening
the field up for infinite support requests for "why doesn't this tiff 
display in the right place even though I have a world file?"

Proper GeoTIFFs have both affine transformation information *and* PCS
definition in the header, so the .tfw is superfluous.  And by always 
relying on the GeoTIFF tags, we can then check that the file is in a PCS we 
can deal with and either do the semi-correct warping we do or tell the user 
it's not usable. 

And for the record, the .fgd file is used *ONLY* for collar stripping.  It
is not used for georeferencing.  This is often misunderstood by users.
So if one has a normal Tiff file with no geotiff tags and a worldfile, it
is not useful to create a .fgd file until the geotiff tags have been installed
into the tiff file.  That can be done with gdal_translate rather easily once
one knows the spatial reference system to which the .tfw file refers.  This
is described in README.MAPS in the section "Defective GeoTIFF files need
even more special processing."

Once the geotiff has the right tags so it can be placed properly in Xastir,
*then* making a .fgd file for collar stripping makes sense.

> Curt, WE7U wrote:
> > On Wed, 15 Apr 2009, Tom Hayward wrote:
> > 
> >> My selected geotiff map is still not plotted in xastir.
> >>
> >> I've never used a geotiff in Linux either...is there a trick? I've got
> >> the .tif and .tfw, both world readable. The .tif is selected in Map
> >> Chooser. Xasitr knows it's a 7.5'--when I click the 24k button the
> >> .tif toggles selected/unselected.
> > 
> > There's the problem.  Xastir doesn't read .tfw files.  It does read
> > .fgw files.  See the README.MAPS file for how to create your own
> > .fgd for each .tif if you don't have one.  You only need a few lines
> > that Xastir needs, not the entire normal contents of a .fgd.
> > 
> > Here are some examples that do work, so you can verify your
> > installation:
> > 
> >     http://wetnet.net/~we7u/xastir/maps/geotiff/

-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236        http://kevan.org/brain.cgi?DDTNM
  In some cultures what I do would be considered normal. 
                                  -- Ineffective daily affirmation