[Proj] Potentially (theoretically) dangerous changes in Proj4 internal routines that affect the end results..

Paul Kelly paul-grass at stjohnspoint.co.uk
Wed Nov 18 17:43:04 EST 2015

On 11/18/2015 10:27 PM, support at mnspoint.com wrote:
 > (so to say "keep the old version if you need
 > to be absolutely sure that the computations will be repeatable in the
 > future also..")

I seem to remember someone has already said this, but it shouldn't be 
necessary to keep an old version of PROJ.4 since all you have to do to 
keep the same formula is to reformulate the projection definition using 
+proj=tmerc instead of +proj=utm. The old +proj=tmerc formula will still 
be available in new versions of PROJ.4 in the future.

It would probably be a good idea for the release notes for the new 
version to make this clear, to avoid undue alarm, and to explain that 
projection definitions that use +proj=tmerc will give the same results 
in both previous and future releases.


More information about the Proj mailing list