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

[support.mn at elisanet.fi]

Hello,

why do you have to project to the other UTM zone?

Why not keep them in the first zone all the time and not
to loose accuracy? Or if you have to project to another
projectio can't you just choose a better one?

Regards: Janne.

----------------------------------------------

Christoph Dohmen [ChDohmen at gmx.de] kirjoitti: 
> 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
> accuracy.
> Can anyone tell me how this work will be done? May I help in
> anyway?
>  
> thanks
>  
> Christoph
> 
> 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
> > http://lists.maptools.org/mailman/listinfo/proj
> 
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