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Posted by Martin on March 24, 2008, 12:32 pm
Please log in for more thread options > On Mon, 17 Mar 2008 20:15:23 +0100, Luca Morandini
>
>
>
> >Martin wrote:
> >> Hi,
>
> >> is it possible to create a world file with UTM, that covers more than
> >> one zone? In my example I would like to georeferenciate raster maps
> >> from whole Germany, covering the UTM zones 31 to 33 (well, the map
> >> images do...). So the upper left corner would be in the 31N zone.
>
> >You can cover as many zones as you like, though distortion will reach
> >levels not admitted in the UTM system (the further east or west you go
> >outside the zone's extent, the higher the distortion).
>
> >Regards,
>
> >--------------------
> > Luca Morandini
> >www.lucamorandini.it
> >--------------------
>
> Well, actually no. You can certainly create a map covering several UTM
> zones, but it won't be in UTM. UTM has the following properties which,
> I hope, will make it clear why what you ask is actually nonsensical.
>
> 1) UTM is a series of Transverse Mercator projections on central
> meridians at 6 degree intervals. UTM zones are 6 degrees wide, neither
> more nor less, and "extending" a zone is simply not UTM.
>
> 2) Each zone has its own coordinate system. The same coordinates can
> and do appear in each zone. If you simply plot UTM coordinates from
> several zones, they wil plot on top of each other.
>
> 3) The mathematics of the Transverse Mercator projection underlying
> UTM is such that it is difficult to provide an accurate transformation
> much beyond 10 degrees from the central meridian.
>
> The point is that UTM isn't a single projection, and can't be used as
> such. The way to do what you want is to decide a sensible projection
> for such a large area (and that won't be Transverse Mercator because
> of 3), project your data to it and the create your geotiff.
>
> UTM is a spectacularly nasty kludge created by the military; it is
> pretty much useless for serious small-scale (e.g. national scale)
> mapping. It was only ever meant for large-scale mapping, where it
> provides the illusion of ease of use and consistency (it is actually
> neither).
>
> Paul
Hi Paul,
thank you and the others for your answers.
I now decided to undo the German reunification and let the eastern
part have the zone of its own (UTM 33N) in
its own map set. Not very comfortable, but as I think the only way
(for me) to avoid any confusion as I also have to make
transformations from Gau=DF-Kr=FCger and geographic coordinates.
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