>I suppose you really mean transverse Mercator (e.g. Gauss-Krueger) as
>opposed to Universal TM. We simply use UTM and pretend it's GK, but then
>we don't have to do conversions from GK to UTM or v.v. ...
>Martin Ameskamp, Inst. f. Informatik I (Computing Dept.)
Whoa! Stop! Transverse Mercator, Universal Transverse Mercator (UTM)
and GK (USSR definition) are three different animals. Transverse
Mercator is the general case where the user is free to determine
ellipsoid-sphere, central merdian, central scale factor and false
easting-northings. UTM is restricted to specific central meridians,
latitude range, ellipsoids only (type dependent upon local tradition),
scale factor of 0.9996, and fixed false eastings and northings. GK
follows UTM except for scale factor of 1.0 and different zone
nomenclature and false easting may have a zone-based offset.Thus one CANNOT "pretend" that UTM and GK are equivalent.
I am sorry, but I get apoplectic when people get loose with their
definitions and usage of these systems.
I am sorry if I caused apoplectic fits and the like (may you recover
speedily...). Thanks for the clarifications.
However, I did not say anything about pretending that GK and UTM
are equivalent (see quote above). Maps in Germany use both systems
(e.g. GK for 1:5000, UTM for 1:100000) which can be a bit of
a nuisance if you have to use both scales.
Now GRASS doesn't offer GK as an option when you create a location,
so what we do is create a UTM region and enter GK coordinates as
UTM coordinates.
It's fairly obvious that things like conversions to latitude/
longitude coordinates would give spurious results and the scale
factor you mention seems to indicate that area/distance measurements
can be slightly inaccurate (negligible in our (mainly ecological)
applications).
Are there any other reasons why this 'method' should not be used?
I'll admit that it's not a very clean way of doing things, but
in applications that don't require great accuracy it seems a
sensible thing to do.
Martin
--
Martin Ameskamp, Inst. f. Informatik I (Computing Dept.)
Kiel University, Olshausenstr. 40, 24118 Kiel, Germany
Fax: ++49 431 8804054, Voice: ++49 431 8804474,
email: ma@informatik.uni-kiel.d400.de