[Proj] large difference while projecting utm to utm back andforth

Noel Zinn (cc) ndzinn at comcast.net
Thu Feb 17 06:15:33 EST 2011

Why, if I may ask, do you HAVE to use UTM.  Whose rules?  If your work 
requires you to span 5 UTM zones, shouldn't you be questioning the "rules"? 
Lambert Conformal Conic (LCC) is a better choice of projection for east-west 
extents.  You may be lucky to eventually get access to etmerc to span these 
UTM zones without algorithmic error, but those with whom you share your maps 
or computations may not be so lucky.  There may be disagreements.  But 
everyone has access to an appropriate LCC.

Noel Zinn, Principal, Hydrometronics LLC
+1-832-539-1472 (office), +1-281-221-0051 (cell)
noel.zinn at hydrometronics.com (email)
http://www.hydrometronics.com (website)

-----Original Message----- 
From: Christoph Dohmen
Sent: Thursday, February 17, 2011 1:21 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] large difference while projecting utm to utm back 

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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> Proj at lists.maptools.org
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