[Xastir-dev] Adding coordinate formats to Xastir

[Curt Mills]

On Sat, 1 Jan 2005, Tapio Sokura wrote:

> I was toying with the idea of adding support for the Finnish coordinate
> systems to Xastir. There are a few of them, some UTM-like with parameters
> differing from UTM and two datums (we are just beginning the change from a
> national system to the ETRS89/EUREF system that is close to WGS-84). I have
> all the formulas and transformation parameters needed for the translations
> to/from WGS-84, but I'm not sure what would be the best place to put them.
> 
> I see several ellipsoids and datums defined in datum.c/h, but they don't seem
> to be used that much. Is there some kind of a ready-thought "process" or
> something to go through if one wanted to add (display) support for some other
> coordinate system?
> 
> Maybe just adding these systems to the coordinate calculator would be a good
> start. Especially if there could be a coordinate calculator button in the
> station info-box, so when you pressed that button you would get the location
> of that particular station converted to other coordinate systems without
> having to type in the coordinates manually or without changing the Xastir
> coordinate system from file->configure.

Here's how it works now (to the best of my recollection):

*) The geotiff code uses the Proj.4 library in four places and four
places only.  It's only used to convert from NAD27 to WGS84 as I
recall.  No other uses.

*) The GDAL/OGR code uses the Proj.4 library.  For the OGR code this
allows us to read in all kinds of Shapefiles in different coordinate
systems.

*) In other places we use the datum.h/datum.c stuff, but that's a
relatively new part of the Xastir code.

So...  We have no overall scheme for doing coordinate conversions at
this point.  The datum.h/datum.c stuff was intended to eliminate our
dependence on Proj.4, but with the GDAL/OGR code using it as well,
we'll probably continue to need Proj.4 for that library.  Everything
else can probably be converted to use the datum.h/datum.c code
though, so that if one didn't have a need for GDAL/OGR, they
wouldn't need to install Proj.4 either.

If you wanted to add support for datum conversions into the
coordinate calculator, I wouldn't be at all hurt.  I think that'd be
great.

I've long thought it would also be good to allow use of the
coordinate calculator and free-form coordinate input anywhere in the
Xastir code where a coordinate is called for.  In fact that's on the
feature request list.

-- 
Curt, WE7U.				archer at eskimo dot com
http://www.eskimo.com/~archer
  Lotto:  A tax on people who are bad at math. - unknown
Windows:  Microsoft's tax on computer illiterates. - WE7U.
The world DOES revolve around me:  I picked the coordinate system!"