Re: Geotiff with UTM from more than one zone?
- From: Murky <mercergeoinfo@xxxxxxxxx>
- Date: Wed, 26 Mar 2008 01:18:09 -0700 (PDT)
On Mar 24, 5:32 pm, Martin <martin.mmoel...@xxxxxxxxxxxxxx> wrote:
On 17 Mrz., 21:38, Paul Cooper <a.paul.r.coo...@xxxxxxxxxxxx> wrote:
On Mon, 17 Mar 2008 20:15:23 +0100, Luca Morandini
<lmorand...@xxxxxxxx> wrote:
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 Gauß-Krüger and geographic coordinates.
One option would be to add a shift in the eastings of the 32N and 33N
parts so that these abut in series. The coordinates wont be true UTM
but the projection for each part will be as good. The map will of
course be distorted and perhaps unfamiliar, but it is a map and that
is what maps are. If one were to use 32N as base then 31N would
require negative coordinates which is not to be recommended.
.
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