[Proj] large difference while projecting utm to utm back and forth

Christoph Dohmen ChDohmen at gmx.de
Thu Feb 17 02:21:33 EST 2011

Dear list,
first of all I am happy that I did not do anything wrong :-)
And as I mentioned in the first mail, I know, that utm is not
the best way to transform coordinates in that way.
But I am working on a map scale of 1:50000 and have to use
utm coordinates. Those are the rules :-(
I am using proj for while and I do not want to miss it anyway.
But I'm not sure how to proceed. From my point of view there
could be a chance to extend proj with some "wide field tmerc
implementations". And afterwards it would be possible to do
the transformation in the very northern area with a higher
Can anyone tell me how this work will be done? May I help in

P.S. There seems to be a problem with the gmx-mailservice which
is rejected by lists.maptools.org.

-------- Original-Nachricht --------
> Datum: Wed, 16 Feb 2011 13:03:38 -0500
> Von: Frank Warmerdam <warmerdam at pobox.com>
> An: proj at lists.maptools.org
> Betreff: Re: [Proj] large difference while projecting utm to utm back and forth

> On 11-02-16 12:54 PM, Thomas Knudsen wrote:
> > 2011/2/16 Noel Zinn (cc) <ndzinn at comcast.net
> <mailto:ndzinn at comcast.net>>
> >
> >     I agree for what may be the "basic" TM in Proj.4, however Proj.4
> does have
> >     more than one of the Scandinavian implementations of TM that are
> robust far
> >     from the TM.  Search for and use one of those and you'll get better
> >     round-trip closure.  -Noel
> >
> >
> > Noel:
> > I assume you are talking about the "Engsager Extended Transverse
> Mercator"
> > (etmerc) implementation, written by my colleague Karsten Engsager. With
> > Karsten's approval, I submitted that implementation to Gerald Evenden a
> few
> > years ago. This was followed by one or two other similar "wide
> > field"-transverse mercator implementations, which were all integrated
> into
> > Gerald's original proj library, but I do not think it ever made its way
> into
> > Frank's version.
> >
> > Christoph:
> > I could dig out the Engsager source code with my modifications for
> > proj-compatibility, if you are interested. Integrating it into Frank's
> proj
> > version should be fairly straightforward, and you are most welcome to do
> it. I
> > just haven't had spare time to do it and submit a patch yet.
> Thomas,
> I agree - I don't see that any of the wide field tmerc implementation
> made it into my PROJ.4.  If someone (ideally Gerald) could identify a
> preferred implementation I'd be willing to port it over or apply a
> patch if someone else wants to file a ticket with a proposed change.
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent
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