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

support.mn at elisanet.fi support.mn at elisanet.fi
Fri Feb 18 08:35:09 EST 2011 

Christoph ,

why do you have to go all the way back to zone 30?

Why not first convert the base zone to zone 33
example? And do it from there? That way it
would stay within reach. Or even better, why
not convert the whole base zone to LCC and
stay accurate all the time?

I hope this helps?

Regards: Janne.

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

I hope this helps.

Regards: Janne.

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

Christoph Dohmen [ChDohmen at gmx.de] kirjoitti: 
> 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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