[Proj] Re: Global Gauss-Kruger and libproj4---the final story

strebe strebe at aol.com
Wed Aug 27 13:40:43 EDT 2008

Not knowing anything about libproj4, I am surprised by this note. All projections of the complete globe are "multivariate". What does libproj4 do for other projections? Why would it not do something similar for ellipsoidal transverse Mercator?

-- daan Strebe

On Aug 27, 2008, at 8:45:53 AM, "Gerald I. Evenden" <geraldi.evenden at gmail.com> wrote:
From:   "Gerald I. Evenden" <geraldi.evenden at gmail.com>
Subject:    [Proj] Global Gauss-Kruger and libproj4---the final story
Date:   August 27, 2008 8:45:53 AM PDT
To: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>
Thanks to a reader I have a copy of the Lee-Thompson material for the 
Transverse Mercator projection.

After perusing the material it is clear that no bivariate function operation 
such as libproj4 can handle the general case of the global extent of the 
Gauss-Kruger projection. This is because of the nature of the equator 
graticule line and the fact that it branches into two parts as it approaches 
90 degrees from the central meridian. That is, all points with 0 latitude 
and with a delta longitude near 90 degrees will have *two* resultant 
Cartesian coordinates---one for the northern hemisphere and one for the 
southern hemisphere. Proj_fwd returns only one Cartesian point.

I had a suspicion that this was the case from viewing the "tombstone" 
illustrations of TM referenced many weeks ago but had to wait to learn the 
details of what was tranpiring.

So case closed.

The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist
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