tmerc-coordinate system

[Gerald I. Evenden]

>From: Martin Ameskamp <ma at informatik.uni-kiel.d400.de>
>To: grassu-list at max.cecer.army.mil
>Subject:  Re: tmerc-coordinate system
>
>> >Hello!
>> >
>> >I like to know if or how it is possible to define
>> >a new location with transverse-Mercator coordinate system.
>> >
>> >Rolf Krell
>> 
>> Your question is unclear.  Do you mean define a "new" Transverse
>> Mercator system?  Simply defining a new location is as easily done
>> as it is written---just do it.
>> Gerald (Jerry) I. Evenden   Internet: gie at charon.er.usgs.gov
>
>Rolf, 
>
>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. ...
>
>If you find out anything else, please let us know.
>
>Martin
>--
>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.

To further confuse matters, GK may also refer to a different formulary
developed by Kruger (circa 1919).  And there is also the Lee formulas
applicable to world-wide elliptical computation (why bother?).  But UTM
and most Transverse Mercator use the series approximation of Thomas
(1952) which will adequately cover a 10 degree wide zone.

I am sorry, but I get apoplectic when people get loose with their
definitions and usage of these systems.

Gerald (Jerry) I. Evenden   Internet: gie at charon.er.usgs.gov
voice: (508)563-6766          Postal: P.O. Box 1027
  fax: (508)457-2310                  N.Falmouth, MA 02556-1027