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

Frank Warmerdam warmerdam at pobox.com
Wed Feb 16 13:03:38 EST 2011

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.


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

More information about the Proj mailing list