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

Thu Feb 17 04:38:28 PST 2011

Dear Noel, Janne, and all other,

I am working on a map which must be in UTM coordinatesystem.
And while constructing the utm-grid over the area I don't have
any problems - in the resolution used - to transform between
positions from zone 34 to zone 30 and back.
Only if i extend the area so the zone 35 is also covered, I
get this large delta while projeting from zone 35 to 30 and
back.

@Janne I'm contructing the grid. And while doing so I have to
project several points from the _real_ zone to the 'base' zone.

Christoph

-------- Original-Nachricht --------
> Datum: Thu, 17 Feb 2011 05:15:33 -0600
> Von: "Noel Zinn \\(cc\\)" <ndzinn at comcast.net>
> An: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>
> Betreff: Re: [Proj] large difference while projecting utm to utm back	andforth

> Christoph,
> 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
> 
> 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 
> andforth
> 
> 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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