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

Thomas Knudsen knudsen.thomas at gmail.com
Wed Feb 16 12:54:04 EST 2011

2011/2/16 Noel Zinn (cc) <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

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.

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.

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