[Xastir] DRG's not cropping white space

[Tom Russo]

On Fri, Oct 09, 2009 at 09:43:41AM -0700, we recorded a bogon-computron collision of the <archer at eskimo.com> flavor, containing:
> On Fri, 9 Oct 2009, Kevin Ratcliff wrote:
> 
> > On Fri, Oct 9, 2009 at 12:08 PM, Tom Russo <russo at bogodyn.org> wrote:
> >> Hmmm. ?Well, then, recompiling proj.4 with correct datum shift grids would
> >> be required regardless, then.
> >
> > I've been meaning to modify the Ubuntu 9.04 wiki instructions to
> > address this, but haven't done so yet. I'll try to do it this weekend.
> 
> Nick was hoping to use these maps off-road this weekend.  Guess he's
> out of luck unless he finds that other package Tom mentioned that
> has it fixed.

*IF* the clipping is due to libgeotiff not being compiled against proj.4,
and the problem that Nick is having is related to proj.4 not being 
compiled correctly.  That has not been determined, it's just one possibility.
You brought it up, because that would be one explanation.

Lee almost certainly followed the wiki instructions for building Xastir
in the VM.  That would mean that libgeotiff was compiled after proj.4 was
installed from the repositories, meaning that border clipping should still
work.

We do NOT use proj.4 to do datum shifting in map_tif.c.  The only use of
proj.4 in map_tif.c is to convert coordinates in the geotiff file from their
native coordinate system (generally UTM) into lat/lon using GTIFProj4ToLatLong
--- no datum shift is applied in this step, and the lat/lon produced is
in the same datum as the original projected coordinate system.  Datum shifting 
is applied by the code you wrote in datum.c instead.  Since NAD27/NAD83 
conversion is not an analytic transformation (it requires an interpolation 
grid to be done correctly) this is at best an approximate shift that would 
actually be more correctly done by proj.4 (if it is compiled properly with
the interpolation grids), but that's another matter.  The point is, 
even if proj.4 is compiled incorrectly, it has no impact on Xastir because 
Xastir doesn't use proj.4 for exactly the thing that is wrong in the Ubuntu 
compilation of proj.4.

Even if it did, the error would show up as a few dozen pixels of incorrectly
cropped or uncropped white border around the map.  Most of the rest of the
border would be cropped.

Nick implied that no border was being trimmed, which would suggest something
much more serious, such as Xastir not finding the FGD files or being 
unable to read them.

I think it is much more likely that there is a problem with reading or
processing the FGD file than that the issue is related to libgeotiff and
proj.4.  Nick should try running with debug level set to 16 and see if
Xastir reports the various things that are printed out by the cropping
code (such as "Upper left <XXXXXX> <YYYYY>," "Lower Right <xxxxxx> <yyyyyy>,"
"Tiepoints:," "Datum:", "***** Attempting Datum Conversions",
"NW neat-line corner =" and so on and so forth, or errors such as 
"Failed GTIFProj4ToLatLong() call")

And now that I look, if the issue were libgeotiff not being compiled with
PROJ.4, there would also be error messages such as:

  draw_geotiff_image_map: Problem converting from lat/lon\n
  Did you follow the instructions for installing PROJ?\n

Nick should definitely try running Xastir from the command line and tell
us if he sees error messages such as these.  Read permissions of FGD files
would also be a good thing to check.  Also, if the files are called ".FGD"
instead of ".fgd", the function "read_fgd_file" will not find it.

-- 
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