[Proj] Switch utm from tmerc to etmerc

Roger Bivand roger.bivand at nhh.no
Sun Oct 25 18:09:10 EST 2015

Charles Karney <charles.karney <at> sri.com> writes:

> This change has now been made to the master branch of the source.  The
> "utm projection" now follows the NGA recommendation and uses etmerc
> instead of tmerc (which is less accurate).  You can expect small
> (typically < 1mm, except at high latitudes) changes in the results for
> the utm projection.

While correcting wrong parameterisations is good, here we are doing what the
mooted metacrs definitions were trying to avoid, that is altering in-place
code without user-facing versioning. Different versions (by commit hashes
now) of the underlying code will now give different answers, so re-running
an analysis with the same data and apparently the same code in software
linking to proj will give different answers, without the user necessarily
being able to re-instate the earlier relationship. It would be great to bear
in mind the fact that research does need to be reproducible (data from times
before this correction was known don't need to be obliged to use it). I
guess we have to assume that users really read commit logs and NEWS files.


>    --Charles
> On 10/06/2015 11:19 AM, Charles Karney wrote:
> > Reposted from
> >
> >    https://github.com/OSGeo/proj.4/issues/316
> >

More information about the Proj mailing list